US20120280953A1

US20120280953A1 - Display device

Info

Publication number: US20120280953A1
Application number: US13/461,805
Authority: US
Inventors: Hui-Chuan Cheng; Jin Yan; Takahiro Ishinabe; Shin-Tson Wu; Ching-Huan Lin; Kang-Hung Liu
Original assignee: AU Optronics Corp; University of Central Florida Research Foundation Inc UCFRF
Current assignee: AU Optronics Corp; University of Central Florida Research Foundation Inc UCFRF
Priority date: 2011-05-02
Filing date: 2012-05-02
Publication date: 2012-11-08
Also published as: TWI465803B; US20120307178A1; TW201245815A; CN102759818B; US8804067B2; CN102759818A

Abstract

A display device including a display module, a light source module, a turning optical film, a first compensation film and a second compensation film is provided. The display module includes a first substrate, a second substrate and a display medium. The light source module generates directional light. The display module is disposed above the light source module. The second substrate is disposed opposite to the first substrate. The display medium is disposed between the first substrate and the second substrate and is optically isotropic. The turning optical film is disposed on the second substrate of the display module. The directional light enters the turning optical film and then exits the turning optical film to form an output light. The first compensation film is disposed on the first outer surface of the first substrate. The second compensation film is disposed between the second substrate and the turning optical film.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefits of U.S. provisional application Ser. No. 61/481,295, filed on May 2, 2011 and Taiwan application serial no. 101114566, filed on Apr. 24, 2012. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to a display device, and more particularly to a liquid crystal display device.
2. Description of Related Art
With vigorous development of display technologies, consumers' requirements for favorable performance of displays have been increasing. Specifically, consumers have high demands for the response time of the displays in addition to the requirements for resolution, contrast ratio, viewing angle, grey level inversion, and color saturation.
To satisfy said requirements, blue phase liquid crystal displays (LCDs) characterized by fast response speed have been developed in the industry pertinent to displays. For instance, when a positive blue phase liquid crystal material is applied, a transverse electric field is required for operation, such that the positive blue phase liquid crystal material can function as a light valve. At this current stage, positive blue phase liquid crystal molecules in the blue phase LCD are driven by adopting the electrode design of an in-plane switching (IPS) display module.
However, in the electrode design of a typical IPS display module, many regions above the electrodes do not have transverse electric fields. Consequently, a plurality of liquid crystal molecules in the blue phase LCD cannot be properly driven, such that the transmittance of the display module is low. Although the transmittance of the IPS display module can be enhanced by increasing the driving voltage, the resulting excess power consumption is unfavorable. Accordingly, improving the low transmittance and high driving voltage of the blue phase LCD demand attention from research and developers. Moreover, further enhancement of the contrast ratio and viewing angle of the blue phase LCD is needed.

SUMMARY OF THE INVENTION

The invention provides a display device capable of solving issues of low transmittance and high driving voltage when blue phase liquid crystals are applied in a conventional IPS display module.
The invention provides a display device including a light source module, a display module, a turning optical film, a first compensation film, and a second compensation film. The light source module generates a directional light. The display module is disposed above the light source module, and the display module includes a first substrate, a second substrate, and a display medium. The first substrate has a first inner surface and a first outer surface. The second substrate is disposed opposite to the first substrate and has a second inner surface and a second outer surface. The display medium is disposed between the first substrate and the second substrate and is optically isotropic. The display medium is optically anisotropic when driven with an electric field. The directional light is not perpendicular to the first outer surface when the directional light enters the display module, and the directional light is not perpendicular to the second outer surface when the directional light exits the display module. The turning optical film is disposed on the second outer surface of the second substrate of the display module. The turning optical film has an incident surface and an output surface. The directional light enters the turning optical film from the incident surface, and exits the turning optical film from the output surface so as to form an output light. Moreover, an included angle is between the output light and the output surface. The first compensation film is disposed on the first outer surface of the first substrate. The second compensation film is disposed between the second substrate and the turning optical film.
In the display device according to an exemplary embodiment of the invention, the compensation films are disposed between the top polarizer and bottom polarizer. The configuration of the compensation films can adjust the polarization state of the directional light entering the display module, such that the polarization state of the directional light matches the absorption axis direction of the top polarizer. Accordingly, light leakage can be minimized and the contrast ratio and viewing angle of the display device can be enhanced.
In order to make the aforementioned and other features and advantages of the invention more comprehensible, embodiments accompanying figures are described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments and, together with the description, serve to explain the principles of the invention.

FIG. 1 is a schematic cross-sectional view of a display device according to an embodiment of the invention.

FIG. 2A is a schematic view of an optically isotropic display medium without an electric field.

FIG. 2B is a schematic view of an optically anisotropic display medium in an electric field.

FIG. 3A and FIG. 3B are schematic cross-sectional views of a display device according to an embodiment of the invention.

FIG. 4A is a schematic cross-sectional view of a first optical film in a display device according to an embodiment of the invention.

FIG. 4B is a perspective view of the first optical film depicted in FIG. 4A.

FIG. 5A is a schematic cross-sectional view of a second optical film in a display device according to an embodiment of the invention.

FIG. 5B is a perspective view of the second optical film depicted in FIG. 5A.

FIG. 6A is schematic cross-sectional view of an optical film in a display device according to an embodiment of the invention.

FIG. 6B is a perspective view of the optical film depicted in FIG. 6A.

FIG. 7 is an optical path diagram of light passing through a first optical film, a second optical film, and a turning optical film according an embodiment of the invention.

FIG. 8A is schematic cross-sectional view of an optical film in a display device according to another embodiment of the invention.

FIG. 8B is a perspective view of the optical film depicted in FIG. 8A.

FIG. 9A is schematic cross-sectional view of an optical film in a display device according to another embodiment of the invention.

FIG. 9B is a perspective view of the optical film depicted in FIG. 9A.

FIG. 10A is schematic cross-sectional view of an optical film in a display device according to another embodiment of the invention.

FIG. 10B is a perspective view of the optical film depicted in FIG. 10A.

FIG. 11 and FIG. 12 are schematic cross-sectional views of a display device according to embodiments of the invention.

FIG. 13 is a relational diagram of a voltage of a transverse electric field driving blue phase liquid crystals of a conventional IPS display module and a transmittance.

FIGS. 14A and 14B are relational diagrams of a voltage of a perpendicular electric field of a display device according to an embodiment of the invention driving blue phase liquid crystals and a light angle.

FIG. 15 is a relational diagram of a voltage of a transverse electric field driving blue phase liquid crystals of a conventional IPS display module and a transmittance.

FIG. 16 is a relational diagram of a voltage of a perpendicular electric field of a display device according to an embodiment of the invention driving blue phase liquid crystals and a transmittance.

FIG. 17 depicts the measurement results of a hysteresis phenomenon from a transverse electric field driving blue phase liquid crystals of a conventional IPS display module.

FIG. 18 depicts the measurement results of a hysteresis phenomenon from a perpendicular electric field of a display device according to an embodiment of the invention driving blue phase liquid crystals.

FIG. 19 is a relational diagram between display medium thickness and voltage for a display device according to an embodiment of the invention.

FIG. 20 is a relational diagram between voltage and transmittance under different display thickness conditions for a display device according to an embodiment of the invention.

FIG. 21 is a schematic cross-sectional view of a display device according to a first embodiment of the invention.

FIG. 22 is a perspective view of a light source module and a display module in a display device according to an embodiment of the invention.

FIG. 23 is a schematic view of a Poincaré sphere of a compensation process during a dark state when a display device according to the first embodiment of the invention employs compensation films.

FIG. 24 is a contour map of the contrast ratios measured on the display device of FIG. 21 with the parameter setting of Table 1.

FIG. 25 is a contour map of the contrast ratios measured on the display device of FIG. 21 with the parameter setting of Table 2.

FIG. 26 is a contour map of the contrast ratios measured on the display device of FIG. 21 with the parameter setting of Table 3.

FIG. 27 is a contour map of the contrast ratios measured on the display device of FIG. 21 with the parameter setting of Table 4.

FIG. 28 is a contour map of the contrast ratios measured on the display device of FIG. 21 with the parameter setting of Table 5.

FIG. 29 is a contour map of the contrast ratios measured on the display device of FIG. 21 with the parameter setting of Table 6.

FIG. 30 is a schematic cross-sectional view of a display device according to a second embodiment of the invention.

FIG. 31 is a schematic view of a Poincaré sphere for a compensation process during a dark state when a display device according to the second embodiment of the invention employs compensation films.

FIG. 32 is a contour map of the contrast ratios measured on the display device of FIG. 30 with the parameter setting of Table 7.

FIG. 33 is a schematic cross-sectional view of a display device according to a third embodiment of the invention.

FIG. 34 is a schematic view of a Poincaré sphere for a compensation process during a dark state when a display device according to the third embodiment of the invention employs compensation films.

FIG. 35 is a contour map of the contrast ratios measured on the display device of FIG. 33 with the parameter setting of Table 8.

FIG. 36 is a contour map of the contrast ratios measured on the display device of FIG. 33 with the parameter setting of Table 9.

FIG. 37 is a schematic cross-sectional view of a display device according to a fourth embodiment of the invention.

FIG. 38 is a schematic view of a Poincaré sphere for a compensation process during a dark state when a display device according to the fourth embodiment of the invention employs compensation films.

FIG. 39 is a contour map of the contrast ratios measured on the display device of FIG. 37 with the parameter setting of Table 10.

FIG. 40 is a schematic cross-sectional view of a display device according to a fifth embodiment of the invention.

FIG. 41 is a schematic view of a Poincaré sphere for a compensation process during a dark state when a display device according to the fifth embodiment of the invention employs compensation films.

FIG. 42 is a contour map of the contrast ratios measured on the display device of FIG. 40 with the parameter setting of Table 11.

FIG. 43 is a contour map of the bright state measurements on the display device of FIG. 40 with the parameter setting of Table 11.

FIG. 44 is a schematic view of a Poincaré sphere for a compensation process during a dark state when a display device according to the fifth embodiment of the invention employs compensation films.

FIG. 45 is a contour map of the contrast ratios measured on the display device of FIG. 40 with the parameter setting of Table 12.

FIG. 46 is a contour map of the bright state measurements on the display device of FIG. 40 with the parameter setting of Table 12.

FIG. 47 is a schematic cross-sectional view of a display device according to a sixth embodiment of the invention.

FIG. 48 is a schematic view of a Poincaré sphere for a compensation process during a dark state when a display device according to the sixth embodiment of the invention employs compensation films.

FIG. 49 is a contour map of the contrast ratios measured on the display device of FIG. 47 with the parameter setting of Table 13.

FIG. 50 is a contour map of the bright state measurements on the display device of FIG. 47 with the parameter setting of Table 13.

FIG. 51 is a schematic cross-sectional view of a display device according to a seventh embodiment of the invention.

FIG. 52 is a schematic view of a Poincaré sphere for a compensation process during a dark state when a display device according to the seventh embodiment of the invention employs compensation films.

FIG. 53 is a contour map of the contrast ratios measured on the display device of FIG. 51 with the parameter setting of Table 14.

FIG. 54 is a contour map of the bright state measurements on the display device of FIG. 51 with the parameter setting of Table 14.

DESCRIPTION OF EMBODIMENTS

FIG. 1 is a schematic cross-sectional view of a display device according to an embodiment of the invention. With reference to FIG. 1, a display device 100 of the present embodiment includes a display module P, a light source module B, and a turning optical film 25.
The display module P includes a first substrate 21 b, a second substrate 21 a, and a display medium 20.
The first substrate 21 b has an inner surface S1 and an outer surface S2, and a pixel array 22 b is disposed on the inner surface S1 of the first substrate 21 b. The first substrate 21 b may be made of glass, quartz, an organic polymer, or other suitable materials. According to the present embodiment, the pixel array 22 b includes a plurality of scan lines, a plurality of data lines, and a plurality of pixel units. Each of the pixel units includes an active element and a pixel electrode electrically connected to the active element. Moreover, the active element of the pixel unit is electrically connected to a corresponding data line and a corresponding scan line. The active element may a bottom-gate thin film transistor (TFT) or a top-gate TFT.
The second substrate 21 a is disposed opposite to the first substrate 21 b, and the second substrate 21 a has an inner surface S3 and an outer surface S4. Moreover, an opposite electrode 22 a is disposed on the inner surface S3 of the second substrate 21 a. The second substrate 21 a may also be made of glass, quartz, an organic polymer, or other suitable materials. The opposite electrode 22 a completely covers the inner surface S3 of the second substrate 21 a. According to the present embodiment, the opposite electrode 22 a is a transparent electrode, and a material of the transparent electrode includes a metal oxide such as indium tin oxide (ITO), indium zinc oxide (IZO), aluminum tin oxide (ATO), aluminum zinc oxide (AZO), indium germanium zinc oxide, other suitable metal oxides, or a stacked layer having at least two of the above materials.
It should be noted that, a color filter array may be disposed on the first substrate 21 b or the second substrate 21 a, so that the display module P can display color images. However, the invention is not limited thereto.
The display medium 20 is disposed between the pixel array 22 b of the first substrate 21 b and the opposite electrode 22 a of the second substrate 21 a. Moreover, the display medium 20 is optically isotropic when no electric field is applied thereto, as shown in FIG. 2A. The display medium 20 is optically anisotropic when a perpendicular electric field 201 is applied thereto, as shown in FIG. 2B. In other words, when no electric field is generated between the pixel array 22 b and the opposite electrode 22 a, the display medium 20 displays properties of optical isotropy. When the perpendicular electric field 201 is generated between the pixel array 22 b and the opposite electrode 22 a, the display medium 20 displays properties of optical anisotropy. According to the present embodiment, the display medium 20 includes blue phase liquid crystals, such as polymer-stabilized blue phase liquid crystals or polymer-stabilized isotropic phase liquid crystals. Since the display medium 20 switches between optically isotropic and optically anisotropic by the generation of electric fields, such that the display medium 20 functions as a light valve, the response speed of this type of display medium 20 is preferably faster than the twisting response speed of the conventional twisted nematic liquid crystal molecules.
The light source module B is disposed below the outer surface S2 of the first substrate 21 b of the display module P. Moreover, the light source module B generates a directional light 281. In other words, the directional light 281 projects along a specific projected direction and distributes within a specific angle. In the present embodiment, the directional light 281 is concentrated within a specific range. That is, the directional light 281 has directionality and is not like the conventional scattered light source with light spreading in all directions without any directionality. The light source module B is, for example, a side incident type light source module, including a light guide plate 26 a and a light source 26 b. It should be appreciated that the light source module B may further include elements such as an optical film set and a frame. In the present embodiment, the side incident type light source module is used as an example for description, although the invention is not limited thereto. According to other embodiments, the light source module B may be a light source module having other forms, such as the direct type light source module, for example.
Since the display medium 20 is optically anisotropic when no electric field is applied thereto, therefore, when the pixel array 22 b of the display module P and the opposite electrode 22 a form the perpendicular electric field 201 therebetween, the display medium 20 not only display properties of optical anisotropy, but the display medium 20 is also vertically aligned along the perpendicular electric field 201, as shown in FIGS. 1 and 2B. In order for the vertically aligned optically anisotropic display medium 20 to be birefringent to the light from the light source module B, in the present embodiment, the propagating direction of the light from the light source module B has a specific design as illustrated below.
According to the present embodiment, the directional light 281 generated by the light source module B propagates along an incident direction D1 when the directional light 281 enters the display module P. Moreover, the incident direction D1 is not perpendicular to the outer surface S2 of the first substrate 21 b. In other words, the directional light 281 generated by the light source module B does not perpendicularly enter into the display module P, but the directional light 281 is incident at a specific inclination angle into the display module P. In order for the directional light 281 generated by the light source module B to exit the light source module B at a specific angle, special optical microstructures can be designed on the light guide plate 26 a. Alternatively, a layer of optical film having special optical microstructures may be disposed on the light guide plate 26 a. Accordingly, when the light generated by the light source 26 b passes the light guide plate 26 a (or optical film), the propagating direction of the light changes, such that the directional light 281 generated by the light source module B exits at the specific inclination angle. According to the present embodiment, since the directional light 281 generated by the light source module B exits at the specific inclination angle, therefore, an included angle θ1 between the incident direction D1 of the directional light 281 and the outer surface S2 of the first substrate 21 b is 5°˜45°, for example. In other words, an inclination angle θ1′ of the directional light 281 generated by the light source module B is 45°˜85°, for example. The inclination angle θ1′ refers to the included angle between the incident direction D1 of the directional light 281 and a perpendicular axial line V.
Accordingly, after the direction light 281 enters the display module P at the inclination angle θ1′, a directional light 282 is formed. The directional light 282 in the display module P maintains the same direction when passing through the display medium 20. In other words, the directional light 281 generated by the light source module B becomes the directional light 282 when entering the display medium 20. Moreover, the directional light 282 propagates along an incident direction D2 not perpendicular to the inner surface S1 of the first substrate 21 b. Therefore, the included angle θ between the incident direction D2 of the directional light 282 and the inner surface S1 of the first substrate 21 b is not equal to 90°. According to the present embodiment, the included angle θ between the incident direction D2 of the directional light 282 and the inner surface S1 of the first substrate 21 b is 5°˜45°, for example.
After the directional light 282 passes through the display medium 20 and the second substrate 21 a, the directional light 282 is guided by the turning optical film 25 to form an output light 283 propagating along a propagating direction D3. Moreover, an included angle between the propagating direction D3 and a surface (output surface) of the turning optical film 25 is substantially 60°˜120°. In the present embodiment, the output light 283 exits the turning optical film 25 perpendicularly. Therefore, the included angle between the propagating direction D3 and the surface (output surface) of the turning optical film is substantially 90°, such that the output light 283 received by a user's eye 29 is a light propagating along the normal direction. Accordingly, an included angle θ2 between the propagating direction D3 of the output light 283 and the surface (output surface) of the turning optical film 25 is substantially equal to 90°.
In the present embodiment, a first optical film 24 b may be further disposed on the outer surface S2 of the first substrate 21 b, such that the directional light 282 maintains the same propagating or transmitting direction as much as possible before entering the display medium 20. Moreover, in order for the directional light 282 to maintain the same propagating or transmitting direction as much as possible after exiting the display medium 20, a second optical film 24 a may be further disposed on the outer surface S4 of the second substrate 21 a.
With reference to FIGS. 1, 4A, and 4B, the first optical film 24 b is disposed on the outer surface S2 of the first substrate 21 b. To be specific, the first optical film 24 b has a plurality of first optical structures T1. Moreover, the first optical structures T1 allow the directional light 281 passing through the first optical structures T1 without generating total reflection. That is, the directional light 281 directly passes through the first optical structures T1 of the first optical film 24 b. If the directional light 281 is not being totally reflected or refracted when directly passing through the first optical structures T1 of the first optical film 24 b, optical loss of the directional light 281 caused by the first optical film 24 b can be minimized. In other words, optical loss of the directional light 281 at the interface of air and the first substrate 21 b due to reflection can be reduced. Accordingly, the directional light 281 can pass through the first optical film 24 b in the same propagating direction as much as possible.
According to the present embodiment, the first optical film 24 b has a first surface S5 and a second surface S6 opposite to the first surface S5. The first surface S5 faces the light source module B, the second surface S6 faces the outer surface S2 of the first substrate 21 b, and the first optical structures T1 are disposed on the first surface S5. That is, the second surface S6 of the first optical film 24 b is a smooth plane, although the invention is not limited thereto. Moreover, the first optical structures T1 on the first surface S5 of the first optical film 24B can cause the directional light 281 of the light source module B to pass through the first optical film 24 b as directly as possible.
According to the present embodiment, the first optical structures T1 are grooves having a first side wall W1 and a second side wall W2, as shown in FIG. 4A. The incident direction D1 is substantially perpendicular to the first side wall W1, and the incident direction D1 is substantially parallel to the second side wall W2. To be specific, in the first optical structures (grooves) T1 of the present embodiment, the first side wall W1 of the grooves T1 is a short side wall, and the second side wall W2 is a long side wall. Moreover, the short side wall W1 is substantially perpendicular to the incident direction D 1. Furthermore, a refractive index of the first optical film 24 b is close to a refractive index of the first substrate 21 b. Accordingly, when the directional light 281 passes through the first optical structures (grooves) T1, the directional light 281 can directly pass through the short side wall W1 without generating total reflection or refraction, such that the directional light 281 can pass through the first optical film 24 b as directly as possible. In the present embodiment, a width p1 of the first optical structures (grooves) T1 is approximately 5 μm˜100 μm. An included angle θ4 between the first side wall W1 of the first optical structures (grooves) T1 and the perpendicular axial line V is approximately 5°˜45°. An included angle θ3 between the second side wall W2 of the first optical structures (grooves) T1 and the perpendicular axial line V is approximately 45°˜85°.
With reference to FIGS. 1, 5A, and 5B, the second optical film 24 b is disposed on the outer surface S4 of the second substrate 21 a. To be specific, the second optical film 24 a has a plurality of second optical structures T2. Moreover, the second optical structures T2 allows the directional light 282 passing through the second optical structures T2 without generating total reflection. That is, the directional light 282 directly passes through the second optical structures T2 of the second optical film 24 a. If the directional light 282 is not being totally reflected or refracted when directly passing through the second optical structures T2 of the second optical film 24 a, optical loss of the directional light 282 caused by the second optical film 24 a can be minimized. In other words, optical loss of the directional light 282 at the interface of air and the second optical film 24 a due to reflection can be reduced. Accordingly, the directional light 282 can exit the second optical film 24 a in the same transmitting direction as much as possible.
According to the present embodiment, the second optical film 24 a has a first surface S7 and a second surface S8 opposite to the first surface S7. The first surface S7 faces the outer surface S4 of the second substrate 21 a, and the second optical structures T2 are disposed on the second surface S8. That is, the first surface S7 of the second optical film 24 a is a smooth plane, although the invention is not limited thereto. Moreover, the second optical structures T2 on the second surface S8 of the second optical film 24 a can cause the directional light 282 to pass through the second optical film 24 a as directly as possible.
According to the present embodiment, the second optical structures T2 are grooves having a first side wall W3 and a second side wall W4, as shown in FIG. 5A. The incident direction D2 of the directional light 282 when passing through the second optical film 24 a is perpendicular to the first side wall W3, and the incident direction D2 is parallel to the second side wall W4. To be specific, in the second optical structures (grooves) T2 of the present embodiment, the first side wall W3 is a short side wall, and the second side wall W4 is a long side wall. Moreover, the short side wall W3 is substantially perpendicular to the incident direction D2 of the directional light 282. Furthermore, a refractive index of the second optical film 24 a is close to a refractive index of the second substrate 21 a. Accordingly, when the directional light 282 passes through the second optical structures (grooves) T2, the directional light 282 can directly pass through the short side wall W3 without generating total reflection or refraction, such that the directional light 282 can pass through the second optical film 24 a as directly as possible. In the present embodiment, a width p2 of the second optical structures (grooves) T2 is approximately 5 μm˜100 μm. An included angle θ6 between the first side wall W3 of the second optical structures (grooves) T2 and the perpendicular axial line V is approximately 5°˜45°. An included angle θ5 between the second side wall W4 of the second optical structures (grooves) T2 and the perpendicular axial line V is approximately 45°˜85°.
With reference to FIGS. 1, 6A, and 6B, the turning optical film 25 is disposed on the second optical film 24 a. The turning optical film 25 has a plurality of tuning optical structures T3, such that the directional light 282 is totally reflected by the tuning optical structures T3 to form the output light 283. Moreover, an included angle between the propagating direction D3 after the output light 283 passes through the turning optical film 25 and a surface (output surface) S10 of the turning optical film 25 is 60°˜120°. In the present embodiment, the propagating direction D3 after the output light 283 passes through the turning optical film 25 is substantially perpendicular to the surface (output surface) S10 of the turning optical film 25. That is, the directional light 282 is totally reflected by the tuning optical structures T3 of the turning optical film 25 as much as possible to form the output light 283. In other words, the tuning optical structures T3 of the turning optical film 25 is designed mainly to redirect the propagating or transmitting direction of the directional light 281 and 282 emitted from the light source module B after passing through the turning optical film 25. Thereby, the output light 283 can exit the turning optical film 25 perpendicularly to be received by the user's eye 29.
According to the present embodiment, the turning optical film 25 has a first surface S9 (also referred to as the incident surface) and a second surface S10 (also referred to as the output surface) opposite to the first surface S9. The first surface S9 faces the outer surface S4 of the second substrate 21 a, and the tuning optical structures T3 are disposed on the first surface S9. That is, the second surface S10 of the turning optical film 25 is a smooth plane, although the invention is not limited thereto. The directional light 282 is totally reflected by the tuning optical structures T3 of the turning optical film 25 by the first surface S9, so as to form the output light 283.
According to the present embodiment, the tuning optical structures T3 are grooves having a first side wall W5 and a second side wall W6, as shown in FIG. 6A. In the present embodiment, the first side wall W5 and the second side wall W6 of the grooves T3 are planar side walls. To be specific, in the optical structures (grooves) T3 of the present embodiment, an included angle θ7 between the first side wall W5 and the perpendicular axial line V is approximately 5°˜60°, and an included angle θ8 between the second side wall W6 and the perpendicular axial line V is approximately 15°˜45°. Therefore, when the directional light 282 enters the optical film 25, the directional light 282 is totally reflected by the first side wall W5 of the tuning optical structures T3 so as to form the output light 283, such that the output light 283 can exit the turning optical film 25 perpendicularly. In the present embodiment, a width p3 of the optical structures (grooves) T3 is approximately 5 μm˜100 μm.
In FIG. 7, the optical paths of the directional light 281 and 282 passing through the first optical film 24 b, second optical film 24 a, and the turning optical film 25 are illustrated. In order to clearly depict the optical paths of the directional light 281, the directional light 282, and the output light 283 respectively passing through the first optical film 24 b, the second optical film 24 a, and the turning optical film 25, only the first optical film 24 b, the second optical film 24 a, and the turning optical film 25 are drawn in FIG. 7. That is, the display module P and other film layers are omitted in the drawing.
As shown in FIG. 7, the directional light 281 passes through the first optical film 24 b as directly as possible without generating total reflection or refraction. The directional light 282 then passes through the second optical film 24 a also as directly as possible without generating total reflection or refraction. The directional light 282 is then totally reflected as much as possible by the tuning optical structures T3 of the turning optical film 25, so as to form the output light 283. By using the afore-described configuration of the first optical film 24 b, the second optical film 24 a, and the turning optical film 25, light from the light source module B can obliquely enter into the display module P and then exit the turning optical film 25 along the normal direction.
With reference to FIG. 1, besides the display module P, the light source module B, and the turning optical film 25, the display device 100 of the present embodiment may further include a bottom polarizer 23 b and a top polarizer 23 a. The bottom polarizer 23 b is disposed between the first substrate 21 b and the first optical film 24 b, and the top polarizer 23 a is disposed between the second substrate 21 a and the second optical film 24 a. Dichroic polymer films, such as polyvinyl-alcohol-based films may be adopted for the bottom polarizer 23 b and the top polarizer 23 a. An included angle between a transmission axis of the bottom polarizer 23 b and a transmission axis of the top polarizer 23 a may be 5°˜175°.
Moreover, in order to achieve favorable display quality for the display module P, the display module P of the present embodiment further includes a compensation film 231 and a diffusion film 27. The compensation film 231 is disposed between the bottom polarizer 23 b and the top polarizer 23 a. In the present embodiment, the compensation film 231 is disposed between the bottom polarizer 23 b and the first substrate 21 b as an example for description. In other words, a compensation film (not drawn) may also be disposed between the top polarizer 23 a and the second substrate 21 a. Alternatively, the compensation film 231 may be disposed between the bottom polarizer 23 b and the first substrate 21 b, and the compensation film (not drawn) may be disposed between the top polarizer 23 a and the second substrate 21 a. The configuration of the compensation film 23 a can enhance the contrast ratio of the display module P as well as the viewing angle. Moreover, the diffusion film 27 is disposed above the top polarizer 23 a, so that a diffusion effect is generated when the output light 283 passes through the diffusion film 27, thereby achieving preferable display quality for the display module P. However, the use of the diffusion film 27 is not necessary in the invention.
Accordingly, since the display medium 20 of the display module P of the present embodiment is driven by the perpendicular electric field 201 between the pixel array 22 b and the opposite electrode 22 a, the low transmittance and high driving voltage issues of the conventional IPS display module can be resolved. Moreover, since the incident direction D2 of the directional light 281 and the directional light 282 generated by the light source module B in the present embodiment are not perpendicular to the surface of the first substrate 21 b when entering the display medium 20, the display medium 20 is still birefringent to the directional light 282 of the light source module B when the display medium 20 is driven and becomes optically anisotropic. Accordingly, the display module P can display images.
In the embodiment depicted in FIG. 1, the top polarizer 23 a is disposed between the second substrate 21 a and the second optical film 24 a. Thereby, the effect from the second optical film 24 a and the turning optical film 25 on the polarization state of the directional light 282 is minimized. However, the invention is not limited thereto. According to other embodiments, the top polarizer 23 a may also be disposed above the second optical film 24 a or the turning optical film 25, as shown in FIG. 3A.
Moreover, according to another embodiment, the second optical film 24 b may be omitted in the display module P, as shown in FIG. 3B. Accordingly, the effect from the second optical film 24 a on the polarization state of the directional light 282 is minimized. However, the invention is not limited thereto.
Furthermore, in the embodiment depicted in FIG. 1, the optical film 25 of the display module P are shown in FIGS. 6A and 6B, for example. However, the invention is not limited thereto. According to other embodiments, the optical film 25 of the display device 100 may also adopt other forms or structures, as further elaborated below.
FIG. 8A is a schematic cross-sectional view of an optical film in a display device according to another embodiment of the invention. FIG. 8B is a perspective view of the optical film depicted in FIG. 8A. With reference to FIGS. 8A and 8B, the tuning optical structures T3′ of the optical film 25 in the present embodiment are grooves, a first side wall W5′ of the optical structures (grooves) T3 is a curved side wall, and a second side wall W6′ of the optical structures (grooves) T3′ is a planar side wall. Therefore, when the directional light 282 enters the optical film 25, the directional light 282 is totally reflected by the first side wall (curved side wall) W5′ of the tuning optical structures T3′ so as to form the output light 283, such that the output light 283 can exit the turning optical film 25 perpendicularly. It should be noted that, since the first side wall W5′ is a curved side wall, besides the directional light 282 generating total reflection at the first side wall (curved side wall) W5′, a part of the output light 283 generated by total reflection has an incident angle that is less than a total reflection angle. Therefore, after the part of the output light 283 is reflected to the first side wall (curved side wall) W5′, the part of the output light 283 is refracted out of the optical film 25. Therefore, when the curved side wall is adopted for the first side wall W5′ of the optical structures (grooves) T3′, the included angle between the propagating direction of the output light 283 and the output surface can be 60°˜120°. That is, the output light 283 can be diffused when emitted, thereby enhancing the image quality. In the present embodiment, a width p4 of the optical structures (grooves) T3′ is approximately 5 μm˜100 μm.
In the embodiment depicted in FIGS. 8A and 8B, the radaii of curvature of the curved side walls W5′ of all the tuning optical structures T3′ in the turning optical film 25 are the same. Therefore, each tuning optical structure T3′ in the turning optical film 25 of the embodiment depicted in FIGS. 8A and 8B has the same pattern. However, the invention is not limited thereto. According to other embodiments, the optical structures of the turning optical film 25 may have different patterns, as shown in FIGS. 9A and 9B.
FIG. 9A is a schematic cross-sectional view of an optical film in a display device according to another embodiment of the invention. FIG. 9B is a perspective view of the optical film depicted in FIG. 9A. With reference to FIGS. 9A and 9B, in the present embodiment, each tuning optical structure T3′ of the turning optical film 25 has a planar side wall and a curved side wall, but the radii of curvature of the curved side walls of the tuning optical structures T3′ are not all the same. For example, a radius of curvature of the curved side wall W5′ of the tuning optical structure T3′ in the present embodiment is different than a radius of curvature of a curved side wall W5″. Moreover, the tuning optical structure T3′ having the curved side wall W5′ with the larger radius of curvature is alternatively arranged with the optical structure T3′ having the curved side wall W5′ with the smaller radius of curvature.
FIG. 10A is a schematic cross-sectional view of an optical film in a display device according to another embodiment of the invention. FIG. 10B is a perspective view of the optical film depicted in FIG. 10A. With reference to FIGS. 10A and 10B, in the present embodiment, each tuning optical structure T3′ of the turning optical film 25 has a planar side wall and a curved side wall, and the curved side wall of each tuning optical structure T3′ has a plurality of radii of curvature. The radii of curvature of the curved side wall progressively decrease as the bottom of the groove T3′ is approached. For example, the first side wall of the grooves T3′ in the turning optical film 25 is a curved side wall, including a curved side walls W5-1 and a curved side wall W5-2. Moreover, the radius of curvature of the curved side wall W5-1 is smaller than the radius of curvature of the curved side wall W5-2. In order to facilitate the description, the present embodiment uses two different curvatures for the curved side walls W5-1 and W5-2 as an illustrative example, although in actuality the first side wall of the grooves T3′ in the turning optical film 25 is a continuous curved surface.
Based on the above, when the directional light 282 enters the turning optical film 25, besides the directional light 282 generating total reflection at the curved side walls W5-1 and W5-2, a part of the output light 283 can be refracted out of the optical film 25 after being reflected to the curved side wall W5-1. Since the radius of curvature of the curved side wall W5-1 progressively decreases as the bottom of the grooves T3′ is approached, an included angle between a tangent of the curved side wall W5-1 and the transmission direction of the output light 283 also decreases gradually. Accordingly, the output light 283 can be easily refracted out of the optical film 25 after being reflected to this area. That is, the curved side wall W5-1 having the smaller radius of curvature can refract more output light 283 out the optical film 25 at this area. In other words, the divergence angle and distribution of light from the turning optical film 25 depicted in FIGS. 10A and 10B is wider and broader than those of the embodiment illustrated in FIGS. 8A and 8B.
FIG. 11 and FIG. 12 are schematic cross-sectional views of a display device according to embodiments of the invention. The embodiment shown in FIGS. 11 and 12 is similar to the embodiment shown in FIG. 1, and thus identical components denoted with the same numerals and will not be repeated herein. A difference between the embodiments in FIGS. 11 and 1 lies in that, a pixel array 221 b has a slit alignment pattern 60, and a protruding alignment pattern 70 is disposed on an opposite electrode 221 a. By configuring the slit alignment pattern 60 on the pixel array 221 b and the protruding alignment pattern 70 on the opposite electrode 221 a, the distribution of a perpendicular electric field 202 changes and multi-domain alignment is achieved for the display medium 20, accordingly. Similarly, a difference between the embodiments in FIGS. 12 and 1 lies in that, the pixel array 221 b has the slit alignment pattern 60, and the opposite electrode 221 a has a slit alignment pattern 80. The distribution of the perpendicular electric field 202 can also be changed by configuring the slit alignment pattern 60 on the pixel array 221 b and the slit alignment pattern 80 on the opposite electrode 221 a, thereby achieving multi-domain alignment for the display medium 20.
Although the embodiments depicted in FIGS. 11 and 12 configure alignment patterns (e.g. slit alignment patterns or protruding alignment patterns) on the pixel array 221 b and the opposite electrode 221 a, the invention is not limited thereto. According to other embodiments, alignment patterns (e.g. slit alignment patterns or protruding alignment patterns) may only be disposed on the pixel array 221 b, or alignment patterns (e.g. slit alignment patterns or protruding alignment patterns) may only be disposed in the opposite electrode 221 a. The combination of alignment patterns on the pixel array 221 b and the opposite electrode 221 a is also not limited to the embodiments depicted in FIGS. 11 and 12. In other words, the protruding alignment pattern may be disposed on the pixel array 221 b and the slit alignment pattern may be disposed on the opposite electrode 221 a, or the protruding alignment pattern may be disposed on the pixel array 221 b and the protruding alignment pattern may be disposed on the opposite electrode 221 a
In order to illustrate that the display device according to an exemplary embodiment has lower driving voltage and preferable transmittance compared to the conventional IPS display device, several examples with comparison to the conventional IPS display device are set forth below.

Driving Voltage Comparison I

FIG. 13 is a relational diagram of a voltage of a transverse electric field driving blue phase liquid crystals of a conventional IPS display module and a transmittance. With reference to FIG. 13, the horizontal axis of FIG. 13 represents voltage (V), while the vertical axis represents the transmittance of the display module. As shown in FIG. 13, when the conventional IPS display module drives the blue phase liquid crystals, the driving voltage needs to reach 52 V to achieve a preferable transmittance. That is, the driving voltage needs to reach 52 V in order for the display module to have a Kerr constant of 12.68 nm/V².
FIGS. 14A and 14B are relational diagrams of a voltage of a perpendicular electric field of a display device according to an embodiment of the invention driving blue phase liquid crystals and a light angle. The horizontal axis of FIGS. 14A and 14B represent an inclination angle of light from a light source module (e.g. the angle θ1′ depicted in FIG. 1), and the vertical axis represents voltage (V).
With reference to FIG. 14A, a display medium thickness (also referred to as the cell gap) of the display module in this display device is 3.5 μm, and the display module of FIG. 14A has a Kerr constant of 12.68 nm/V². As shown in FIG. 14A, the driving voltage (below 15 V) needed by the display module of FIG. 14A is far lower than the driving voltage (52 V) needed by the IPS display module of FIG. 13. Moreover, in the display device of FIG. 14A, when the inclination angle of light from the light source module increases, the driving voltage thereof decreases.
With reference to FIG. 14B, a display medium thickness (also referred to as the cell gap) of the display module in this display device is 5 μm, and the display module of FIG. 14B has the same Kerr constant of 12.68 nm/V². As shown in FIG. 14B, the driving voltage (below 18 V) needed by the display module of FIG. 14B is far lower than the driving voltage (52 V) needed by the IPS display module of FIG. 13. Similarly, in the display device of FIG. 14B, when the inclination angle of light from the light source module increases, the driving voltage thereof decreases.

Driving Voltage Comparison II

FIG. 15 is a relational diagram of a voltage of a transverse electric field driving blue phase liquid crystals of a conventional IPS display module and a transmittance. With reference to FIG. 15, the horizontal axis of FIG. 15 represents voltage (V), while the vertical axis represents the transmittance of the display module. In FIG. 15, a laser light of 633 nm serves as the light from the light source module, and the laser light enters the IPS display module perpendicularly. As shown in FIG. 15, the display module has the greatest transmittance when the driving voltage reaches 193 Vrms.
FIG. 16 is a relational diagram of a voltage of a perpendicular electric field of a display device according to an embodiment of the invention driving blue phase liquid crystals and a transmittance. With reference to FIG. 16, the horizontal axis of FIG. 16 represents voltage (V), while the vertical axis represents the transmittance of the display module. In FIG. 16, the 633 nm laser light serves as the light from the light source module, t represents the display medium thickness (also referred to as the cell gap), and θ represents the light inclination angle (angle θ1′ depicted in FIG. 1) of the light source module. As shown in FIG. 16, under combinations of different display medium thicknesses (also referred to as the cell gap) and different light inclination angles, four relational curves of voltage and transmittance can be obtained. However, in the four curves, the driving voltages required for the display module to achieve the highest transmittance condition are all far lower than the driving voltage (193 Vrms) needed by the conventional IPS display module.

Hysteresis Comparison

Blue phase liquid crystals typically exhibit the hysteresis phenomeon. When blue phase liquid crystals are applied in the display medium of the display device, hysteresis usually needs to be suppressed or reduced to prevent the hysteresis of the blue phase liquid crystals from affecting the gray level control accuracy of the display module.
FIG. 17 depicts the measurement results of a hysteresis phenomenon from a transverse electric field driving blue phase liquid crystals of a conventional IPS display module. FIG. 18 depicts the measurement results of a hysteresis phenomenon from a perpendicular electric field of a display device according to an embodiment of the invention driving blue phase liquid crystals. Generally speaking, the hysteresis phenomenon of blue phase liquid crystals can be measured by gradually increasing voltage to measure the voltage and transmittance curves M and M′, and by gradually decreasing voltage to measure the voltage and transmittance curves N and N′. The voltage difference between the two curves M and N (M′ and N′) under a half transmittance condition is then calculated. As the voltage difference between the two curves M and N (M′ and N′) increases, the hysteresis phenomenon is more apparent. On the other hand, as the voltage difference between the two curves M and N (M′ and N′) decreases, the hysteresis phenomenon is less apparent.
As shown in FIGS. 17 and 18, the voltage difference between the curves M and N (FIG. 17) under the half transmittance condition is significantly greater than the voltage difference between the curves M′ and N′ (FIG. 18) under the half transmittance condition. Therefore, the blue phase liquid crystals of the conventional IPS display module driven by the transverse electric field exhibit high hysteresis.

Effects of Display Medium Thickness on Driving Voltage

FIG. 19 is a relational diagram between display medium thickness and voltage for a display device according to an embodiment of the invention. The horizontal axis in FIG. 19 represents the display medium thickness (also referred to as the cell gap), and the vertical axis represents voltage (V). In FIG. 19, the 550 nm laser light serves as the light from the light source module, θ represents the light inclination angle (angle θ1′ depicted in FIG. 1) of the light source module, and the four curves in FIG. 19 can all allow the display module to have a Kerr constant of 10.2 nm/V². As shown in FIG. 19, as the display medium thickness (also referred to as the cell gap) decreases, the required driving voltage is also reduced.
FIG. 20 is a relational diagram between voltage and transmittance under different display medium thickness conditions for a display device according to an embodiment of the invention. The horizontal axis of FIG. 20 represents voltage (V), while the vertical axis represents the transmittance. In FIG. 20, the display medium thickness (also referred to as the cell gap) are respectively 1, 2, and 5 μm, the 550 nm laser light serves as the light from the light source module, and the light inclination angle (angle θ1′ depicted in FIG. 1) of the light source module is 70°. As shown in FIG. 20, the driving voltage of the display device according to an embodiment of the invention is related to the display medium thickness.
Based on the above, in the display device according to an embodiment of the invention, the display medium of the display module is driven by the perpendicular electric field generated between the pixel array and the electrode layer. In particular, since the incident direction of the light generated by the light source module when entering the display medium is not perpendicular to the inner surface of the first substrate, the display medium remains birefringent to the light from the light source module when the display medium is driven to be optically anisotropic. Accordingly, since the display device according to an exemplary embodiment can adopt the perpendicular electric field to drive the display medium, the issues of low transmittance and high driving voltage from conventionally using the transverse electric field to drive the blue phase liquid crystals can be resolved.
Moreover, the display device according to an exemplary embodiment can further include a plurality of compensation films, which can be configured to enhance the display quality of the display device. Embodiments 1-7 provided below to further illustrate the advantages of configuring the compensation films. It should be noted that, the embodiments provided below are similar to the embodiment shown in FIG. 1, and thus identical components denoted with the same numerals and will not be repeated herein. The omitted portions can be referenced to the earlier embodiments. The differences between the embodiments are further described below.

First Embodiment

FIG. 21 is a schematic cross-sectional view of a display device according to a first embodiment of the invention. With reference to FIG. 21, a difference between a display device 100 a and the embodiment of FIG. 1 lies in that, the display device 100 a includes a first compensation film 28 b and a second compensation film 28 a, and does not include the compensation film 231. To be specific, the first compensation film 28 b is disposed on the outer surface S2 of the first substrate 21 b, and the second compensation film 28 a is disposed between the second substrate 21 a and the turning optical film 25.
In the present embodiment, the bottom polarizer 23 b is disposed on the outer surface S2 of the first substrate 21 b, and the top polarizer 23 a is disposed on the outer surface S4 of the second substrate 21 a. According to the present embodiment, the bottom polarizer 23 b is disposed between the first compensation film 28 b and the first optical film 24 b. The top polarizer 23 a is disposed between the second compensation film 28 a and the second optical film 24 a, and the second optical film 24 a is disposed between the turning optical film 25 and the top polarizer 23 a. According to the present embodiment, the directional light 282 passes through the bottom polarizer 23 b, the first compensation film 28 b, the second compensation film 28 a, and the top polarizer 23 a in sequence.
According to the present embodiment, the first compensation film 28 b and the second compensation film 28 a may be used to adjust the polarization state of the directional light 282 located in the display module P, such that the polarization state of the directional light 282 after adjustment matches the absorption axis direction of the top polarizer 23 a. Thereby, the light leakage generated when the directional light 282 forms the output light 283 can be reduced, and the contrast ratio of the display device 100 a in the dark state can be further enhanced.
In order to further describe the effects of the first compensation film 28 b and the second compensation film 28 a, a Poincaré sphere is used to illustrate the compensation process of the first compensation film 28 b and the second compensation film 28 a. To clearly define the directions of the directional light 281 and the directional light 282, as well as the absorption axis angles of the top polarizer 23 a, the bottom polarizer 23 b, the first compensation film 28 b, and the second compensation film 28 a, a polar angle θ and an orientation angle Φ are used for the definitions below.
FIG. 22 is a perspective view of a light source module and a display module in the display device according to an embodiment of the invention. With reference to FIG. 22, with the center of the display module P as reference, the orientation angle Φ is an included angle between a projection line on the XY plane of an arbitrary direction D4 and the X direction. The polar angle θ is an included angle between the arbitrary direction D4 and the Z direction. For example, the polar angle θ of a direction D5 is 90° and the orientation angle Φ is 0°; the polar angle θ of a direction D6 is 90° and the orientation angle Φ is 90°; the polar angle θ of a direction D7 is 90° and the orientation angle Φ is 180°; and the polar angle θ of a direction D8 is 90° and the orientation angle Φ is 270°.
FIG. 23 is a schematic view of a Poincaré sphere for a compensation process during a dark state when a display device according to the first embodiment of the invention employs compensation films. With reference to FIG. 23, when the polar angle θ of the directional light 282 is 70° and the orientation angle Φ is 270°, an effective angle between the bottom polarizer 23 b and the top polarizer 23 a changes. Therefore, a transmissive state P₁of the directional light 282 and a state A₁of the absorption axis of the top polarizer 23 a are separated, thereby causing the light leakage. According to the present embodiment, the first compensation film 28 b can rotate the polarization state of the directional light 282 from the state P₁to a state P₀, and the second compensation film 28 a can rotate the polarization state of the directional light 282 from the state P₀to the state A₁. Accordingly, after the directional light 282 passes through the first compensation film 28 b and the second compensation film 28 a, the polarization state of the directional light 282 can be rotated from the state P₁to the state A₁, and thereby prevent light leakage.
Table 1 tabulates a parameter setting data of each component in the display device 100 a, in which Nz denotes the ratio of refractive index anisotropy, and Nz can be represented by the following equation:
Nz=(n _x −n _z)/(n _x −n _y)
in which is n_xthe x-axis refractive index, n_ythe y-axis refractive index, n_zthe z-axis refractive index, d(nx−ny) is the phase difference, and the incident light refers to the directional light 281. FIG. 24 is a contour map of the contrast ratios measured on the display device of FIG. 21 with the parameter setting of Table 1.

TABLE 1

Incident Light	θ = 70° Φ = 270° λ = 550 nm
Bottom Polarizer	Φ = 45°
First Compensation Film	Φ = 38.5° Nz = 0.54 d(n_x− n_y) = 256 nm
Second Compensation Film	Φ = −38.5° Nz = 0.54 d(n_x− n_y) = 256 nm
Top Polarizer	Φ = −45°

With reference to FIG. 24, the four contour lines from outside to inside respectively represents the contour lines of contrast ratios 100, 200, 500, and 1000. As shown in FIG. 24, the viewing cone of contrast ratio greater than 1000:1 is approximately 20°, and the 20° viewing cone is sufficient for the straight directional light 282 in the vertical field switching blue phase LCD. In order to widen the viewing angle, the front diffusion film 27 or the turning optical film 25 can be used to diffuse the straight backlight source, so as to achieve the wide viewing angle. However, the invention is not limited thereto. An example of other parameter settings is provided below to optimize the contrast ratio.
Table 2 tabulates a parameter setting data of each component in the display device 100 a. FIG. 25 is a contour map of the contrast ratios measured on the display device of FIG. 21 with the parameter setting of Table 2.

TABLE 2

Incident Light	θ = 60° Φ = 270° λ = 550 nm
Bottom Polarizer	Φ = 45°
First Compensation Film	Φ = 42° Nz = 0.63 d(n_x− n_y) = 260 nm
Second Compensation Film	Φ = −42° Nz = 0.63 d(n_x− n_y) = 260 nm
Top Polarizer	Φ = −45°

The contour line area of contrast ratio 1000:1 in FIG. 25 is greater than the contour line area of contrast ratio 1000:1 in FIG. 24. However, the smaller polar angle of the incident light results in higher driving voltage.
Table 3 tabulates a parameter setting data of each component in the display device 100 a. FIG. 26 is a contour map of the contrast ratios measured on the display device of FIG. 21 with the parameter setting of Table 3.

TABLE 3

Incident Light	θ = 70° Φ = 270° λ = 550 nm
Bottom Polarizer	Φ = 40°
First Compensation Film	Φ = 36° Nz = 0.506 d(n_x− n_y) = 259 nm
Second Compensation Film	Φ = −36° Nz = 0.506 d(n_x− n_y) = 259 nm
Top Polarizer	Φ = −40°

Table 4 tabulates a parameter setting data of each component in the display device 100 a. FIG. 27 is a contour map of the contrast ratios measured on the display device of FIG. 21 with the parameter setting of Table 4. FIG. 27 illustrates the contour lines of the optimized contrast ratio for an incident light with a polar angle θ of 70° and an orientation angle Φ of 270°.

TABLE 4

Incident Light	θ = 70° Φ = 270° λ = 550 nm
Bottom Polarizer	Φ = 30°
First Compensation Film	Φ = 29.75° Nz = 0.399 d(n_x− n_y) =
	272 nm
Second Compensation Film	Φ = −29.75° Nz = 0.399 d(n_x− n_y) =
	272 nm
Top Polarizer	Φ = −30°

Table 5 tabulates a parameter setting data of each component in the display device 100 a. FIG. 28 is a contour map of the contrast ratios measured on the display device of FIG. 21 with the parameter setting of Table 5. FIG. 28 illustrates the contour lines of the optimized contrast ratio for an incident light with a polar angle θ of 70° and an orientation angle Φ of 270°.

TABLE 5

Incident Light	θ = 70° Φ = 270° λ = 550 nm
Bottom Polarizer	Φ = 30°
First Compensation Film	Φ = 31° Nz = 0.44 d(n_x− n_y) = 264 nm
Second Compensation Film	Φ = −31° Nz = 0.44 d(n_x− n_y) = 264 nm
Top Polarizer	Φ = −30°

Table 6 tabulates a parameter setting data of each component in the display device 100 a. FIG. 29 is a contour map of the contrast ratios measured on the display device of FIG. 21 with the parameter setting of Table 6. FIG. 29 illustrates the contour lines of the optimized contrast ratio for an incident light with a polar angle θ of 60° and an orientation angle Φ of 270°.

TABLE 6

Incident Light	θ = 60° Φ = 270° λ = 550 nm
Bottom Polarizer	Φ = 30°
First Compensation Film	Φ = 32.5° Nz = 0.4775 d(n_x− n_y) =
	264.5 nm
Second Compensation Film	Φ = −32.5° Nz = 0.4775 d(n_x− n_y) =
	264.5 nm
Top Polarizer	Φ = −30°

Second Embodiment

FIG. 30 is a schematic cross-sectional view of a display device according to a second embodiment of the invention. With reference to FIG. 30, a display device 100 b of the present embodiment is similar to the display device 100 a of the first embodiment. A difference therebetween lies in that, the display device 100 b further includes a third compensation film 31 b and a fourth compensation film 31 a. The third compensation film 31 b is disposed between the first compensation film 28 b and the bottom polarizer 23 b, and the fourth compensation film 31 a is disposed between the second compensation film 28 a and the top polarizer 23 a.
According to the present embodiment, the third compensation film 31 b and the fourth compensation film 31 a are respectively a biaxial compensation film, for example. The third compensation film 31 b and the fourth compensation film 31 a may be designed in accordance with different orientation angle Φ, so as to compensate for an angular difference between the top polarizer 23 a and the bottom polarizer 23 b. According to the present embodiment, the directional light 282 passes through the bottom polarizer 23 b, the third compensation film 31 b, the first compensation film 28 b, the second compensation film 28 a, the fourth compensation film 31 a, and the top polarizer 23 a in sequence.
FIG. 31 is a schematic view of a Poincaré sphere for a compensation process during a dark state when a display device according to the second embodiment of the invention employs compensation films. With reference to FIG. 31, in the present embodiment, a P₂state is shifted from a P₁state. The P₂state represents a polarization state when the orientation angle Φ is 300°, and the P₁state represents a polarization state when the orientation angle Φ is 270°. In the present embodiment, the third compensation film 31 b can rotate the polarization state from the state P₂to the state P₁. The first compensation film 28 b and the second compensation film 28 a can then rotate the polarization state from the state P₁to a state A₁. The fourth compensation film 31 a can then rotate the polarization state from the state A₁to a state A₂matching the absorption axis of the top polarizer 23 a.
Table 7 tabulates a parameter setting data of each component in the display device 100 b. FIG. 32 is a contour map of the contrast ratios measured on the display device of FIG. 30 with the parameter setting of Table 7.

TABLE 7

Incident Light	θ = 70° Φ = 270° λ = 550 nm
Bottom Polarizer	Φ = 30°
Third Compensation Film	Φ = 25.75° Nz = 0.851 d(n_x− n_y) =
	281.5 nm
First Compensation Film	Φ = 29.72° Nz = 0.3984 d(n_x− n_y) =
	272 nm
Second Compensation Film	Φ = −29.72° Nz = 0.3984 d(n_x− n_y) =
	272 nm
Fourth Compensation Film	Φ = −25.75° Nz = 0.851 d(n_x− n_y) =
	281.5 nm
Top Polarizer	Φ = −30°

Third Embodiment

FIG. 33 is a schematic cross-sectional view of a display device according to a third embodiment of the invention. With reference to FIG. 33, a display device 100 c of the present embodiment is similar to the display device 100 b of the second embodiment. A difference therebetween lies in that, in the display device 100 c, the third compensation film 31 b is disposed between the first compensation film 28 b and the first substrate 21 b, and the fourth compensation film 31 a is disposed between and the second compensation film 28 a and the second substrate 21 a.
According to the present embodiment, the third compensation film 31 b and the fourth compensation film 31 a are respectively a biaxial compensation film, for example. The third compensation film 31 b and the fourth compensation film 31 a may be designed in accordance with different orientation angles Φ, so as to compensate for an angular difference between the top polarizer 23 a and the bottom polarizer 23 b. According to the present embodiment, the directional light 282 passes through the bottom polarizer 23 b, the first compensation film 28 b, the third compensation film 31 b, the fourth compensation film 31 a, the second compensation film 28 a, and the top polarizer 23 a in sequence.
FIG. 34 is a schematic view of a Poincaré sphere for a compensation process during a dark state when a display device according to the third embodiment of the invention employs compensation films. With reference to FIG. 34, in the present embodiment, the first compensation film 28 b can rotate a polarization state from a state P₁to a state P₀. The third compensation film 31 b then rotates the polarization state from a linear polarization state of the state P₀to a circular polarization state of a state C₁. The fourth compensation film 31 a then rotates the polarization state from the circular polarization state of the state C₁to the linear polarization state of the state P₀. The second compensation film 28 a then rotates the polarization state from the state P₀to a state A₁matching the absorption axis of the top polarizer 23 a. Since circularly polarized light is not affected by the orientation angles of the blue phase liquid crystal materials, circularly polarized light can improve the viewing angle of the VFS blue phase LCD.
Table 8 tabulates a parameter setting data of each component in the display device 100 c. FIG. 35 is a contour map of the contrast ratios measured on the display device of FIG. 33 with the parameter setting of Table 8.

TABLE 8

Incident Light	θ = 70° Φ = 270° λ = 550 nm
Bottom Polarizer	Φ = 45°
First Compensation Film	Φ = 40° Nz = 0.575 d(n_x− n_y) = 256 nm
Third Compensation Film	Φ = 90° Nz = 0.5 d(n_x− n_y) = 137 nm
Fourth Compensation Film	Φ = 0° Nz = 0.5 d(n_x− n_y) = 137 nm
Second Compensation Film	Φ = −40° Nz = 0.575 d(n_x− n_y) = 256 nm
Top Polarizer	Φ = −45°

Table 9 tabulates a parameter setting data of each component in the display device 100 c. FIG. 36 is a contour map of the contrast ratios measured on the display device of FIG. 33 with the parameter setting of Table 9. FIG. 36 illustrates the contour lines of the optimized contrast ratio for an incident light 281 with a polar angle θ of 60° and an orientation angle Φ of 270°.

TABLE 9

Incident Light	θ = 60° Φ = 270° λ = 550 nm
Bottom Polarizer	Φ = 45°
First Compensation Film	Φ = 42° Nz = 0.63 d(n_x− n_y) = 260 nm
Third Compensation Film	Φ = 90° Nz = 0.5 d(n_x− n_y) = 137 nm
Fourth Compensation Film	Φ = 0° Nz = 0.5 d(n_x− n_y) = 137 nm
Second Compensation Film	Φ = −42° Nz = 0.63 d(n_x− n_y) = 260 nm
Top Polarizer	Φ = −45°

Fourth Embodiment

FIG. 37 is a schematic cross-sectional view of a display device according to a fourth embodiment of the invention. With reference to FIG. 37, a display device 100 d of the present embodiment is similar to the display device 100 b of the second embodiment. A difference therebetween lies in that, in the display device 100 d, the bottom polarizer 23 b is a wire-grid polarizer, for example.
In the present embodiment, the first compensation film 28 b, the second compensation film 28 a, the third compensation film 31 b, and the fourth compensation film 31 a are all disposed between the top polarizer 23 a and the wire-grid bottom polarizer 23 b. According to the present embodiment, the directional light 282 passes through the wire-grid bottom polarizer 23 b, the third compensation film 31 b, the first compensation film 28 b, the second compensation film 28 a, the fourth compensation film 31 a, and the top polarizer 23 a in sequence.
FIG. 38 is a schematic view of a Poincaré sphere for a compensation process during a dark state when a display device according to the fourth embodiment of the invention employs compensation films. With reference to FIG. 38, in the present embodiment, an orientation angle Φ of the absorption axis of the wire-grid bottom polarizer 23 b is 90°, and an orientation angle Φ of the absorption axis of the top polarizer 23 a is 0°. After the directional light 282 passes through the wire-grid bottom polarizer 23 b, the directional light 282 rotates from a state P₁to a linear polarization state of a state P₀.
The third compensation film 31 b does not change the polarization state when the orientation angle Φ is 270°. The first compensation film 28 b rotates the linear polarization state of the state P₀to a circular polarization state of a state C₁. The second compensation film 28 a rotates the circularly polarized light from the state C₁to a state A₀matching the absorption axis of the top polarizer 23 a. Accordingly, a preferable dark state performance can be achieved.
However, when the orientation angle Φ of the directional light 282 is not the same (e.g. 300°), the polarization state P₁shifts from the polarization state P₀. Here, the third compensation film 31 b can employ different orientation angles Φ (e.g. from 225° to 315°) in order to rotate the state P₁back to the state P₀. The first compensation film 28 b and the second compensation film 28 a then rotate the polarization state from the state P₀to a state P₂through the state C₁. The fourth compensation film 31 a then polarizes the linearly polarized light from the state P₂to a state A₁matching the absorption axis of the top polarizer 23 a.
Table 10 tabulates a parameter setting data of each component in the display device 100 d. FIG. 39 is a contour map of the contrast ratios measured on the display device of FIG. 37 with the parameter setting of Table 10. FIG. 39 illustrates the contour lines of the optimized contrast ratio for an incident light 281 with a polar angle θ of 70° and an orientation angle Φ of 270°.

TABLE 10

Incident Light	θ = 70° Φ = 270° λ = 550 nm
Bottom Polarizer	Φ = 90°
Third Compensation Film	Φ = 90° Nz = 0.81 d(n_x− n_y) = 317.35 nm
First Compensation Film	Φ = 45° Nz = 0.5 d(n_x− n_y) = 137 nm
Second Compensation Film	Φ = −45° Nz = 0.5 d(n_x− n_y) = 137 nm
Fourth Compensation Film	Φ = 0° Nz = 0.81 d(n_x− n_y) = 317.35 nm
Top Polarizer	Φ = 0°

Since the wire-grid bottom polarizer 23 b has a favorable extinction ratio, preferably high and broad contour lines can be obtained. Moreover, the wire-grid bottom polarizer 23 b is not sensitive to the incident light 281 angle and has minimal diffusion effect. Therefore, the wire-grid bottom polarizer 23 b is suitable for the VFS blue phase LCD.

Fifth Embodiment

FIG. 40 is a schematic cross-sectional view of a display device according to a fifth embodiment of the invention. With reference to FIG. 40, a display device 100 e of the present embodiment is similar to the display device 100 b of the second embodiment. A difference therebetween lies in that, in the display device 100 e, the top polarizer 23 a is disposed between the turning optical film 25 and the diffusion film 27, and the fourth compensation film 31 a includes an A-plate compensation film 31 a-1 and a C-plate compensation film 31 a-2.
According to the present embodiment, the first compensation film 28 b, the second compensation film 28 a, and the third compensation film 31 b are biaxial compensation films. The third compensation film 31 b is disposed between the bottom polarizer 23 b and the first compensation film 28 b, and the first optical film 24 b is disposed between the third compensation film 31 b and the first compensation film 28 b. Moreover, the fourth compensation film 31 a is disposed between the second compensation film 28 a and the top polarizer 23 a, and the second optical film 24 a is disposed between the fourth compensation film 31 a and the top polarizer 23 a. Specifically, the A-plate compensation film 31 a-1 in the fourth compensation film 31 a is disposed between the C-plate compensation film 31 a-2 and the second optical film 24 a. According to the present embodiment, the directional light 282 passes through the bottom polarizer 23 b, the third compensation film 31 b, the first optical film 24 b, the first compensation film 28 b, the second compensation film 28 a, the C-plate compensation film 31 a-2, the A-plate compensation film 31 a-1, and the second optical film 24 a in sequence. The output light 283 is formed after the directional light 282 passes through the turning optical film 25, and then the output light 283 passes through the top polarizer 23 a.
FIG. 41 is a schematic view of a Poincaré sphere for a compensation process during a dark state when a display device according to the fifth embodiment of the invention employs compensation films. With reference to FIG. 41, in the present embodiment, the orientation angles Φ of the bottom polarizer 23 b and the top polarizer 23 a are respectively 0° and 90°. According to the present embodiment, for the directional light 281 having a polar angle θ of 70° and an orientation angle Φ of 270° as an incident angle, when the directional light 281 passes through the bottom polarizer 23 b, the polarization state of the directional light 281 is a state P₀. However, when the orientation angle Φ of the directional light 281 changes (e.g. 300°), the polarization state of the directional light 281 shifts from the state P₀to a state P₁.
In the present embodiment, the third compensation film 31 b does not change the polarization state P₀when the orientation angle Φ is 270°, but when the orientation angle Φ is 200°, the polarization state changes from the state P₁to the state P₀. The first compensation film 28 b rotates the linearly polarized light from the state P₀to a circularly polarized light of of a state C₁. The second compensation film 28 a rotates the circularly polarized light from the state C₁to the linearly polarized light of of the state P₀. Since the polarization state may change with the turning optical film 25 corresponding to the top polarizer 23 a, therefore, the C-plate compensation film 31 a-2 is designed to rotate the polarization state from the state P₀to a state P₂, and the A-plate compensation film 31 a-1 is used to rotate the polarization state from the state P₂to a state A₁matching the absorption axis of the top polarizer 23 a.
Table 11 tabulates a parameter setting data of each component in the display device 100 e, in which n_ois the fast axis refractive index, n_eis the slow axis refractive index, and d is the thickness. FIG. 42 is a contour map of the contrast ratios measured on the display device of FIG. 40 with the parameter setting of Table 11. FIG. 42 illustrates the contour lines of the optimized contrast ratio for an incident light 281 with a polar angle θ of 70° and an orientation angle Φ of 270°, in which the contour lines from outside to inside respectively represents the contour lines of contrast ratios 100, 200, 500, and 1000. FIG. 43 is a contour map for the bright state measurements on the display device of FIG. 40 with the parameter setting of Table 11, in which the contour lines from outside to inside respectively represents the contour lines of transmittances 0.2, 0.25, 0.3, 0.35, and 0.4.

TABLE 11

Incident Light	θ = 70° Φ = 270° λ = 550 nm
Bottom Polarizer	Φ = 0°
Third Compensation Film	Φ = 0° Nz = 0.756 d(n_x− n_y) = 254 nm
First Compensation Film	Φ = −45° Nz = 0.501 d(n_x− n_y) = 137.5 nm
Second Compensation Film	Φ = 45° Nz = 0.501 d(n_x− n_y) = 137.5 nm
C-Plate Compensation Film	n_o= 1.5095 n_e= 1.511 d = 48 μm
A-Plate Compensation Film	Φ = 0° n_o= 1.5095 n_e= 1.511 d = 70 μm
Top Polarizer	Φ = 90°

However, the invention is not limited thereto. Another type of compensation process described below may be adopted by using the framework of the present embodiment.
FIG. 44 is a schematic view of a Poincaré sphere for a compensation process during a dark state when a display device according to the fifth embodiment of the invention employs compensation films. With reference to FIG. 44, in the present embodiment, the third compensation film 31 b is used in different orientation angles to compensate the polarization state from the state P ₁to the state P₀. The first compensation film 28 b shifts the state P₀to the state P₂. The second compensation film 28 a shifts the state P₂back to the state P₀. The C-plate compensation film 31 a-2 shifts the state P₀to a state P₃, and the A-plate compensation film 31 a-1 shifts the state P₃to the state A₁matching the absorption axis of the top polarizer 23 a.
Table 12 tabulates a parameter setting data of each component in the display device 100 e. FIG. 45 is a contour map of the contrast ratios measured on the display device of FIG. 40 with the parameter setting of Table 12. FIG. 45 illustrates the contour lines of the optimized contrast ratio for an incident light 281 with a polar angle θ of 70° and an orientation angle Φ of 270°, in which the contour lines from outside to inside respectively represents the contour lines of contrast ratios 100, 200, 500, and 1000. FIG. 46 is a contour map for the bright state measurements on the display device of FIG. 40 with the parameter setting of Table 12, in which the contour lines from outside to inside respectively represents the contour lines of transmittances 0.2, 0.25, 0.3, 0.35, and 0.4.

TABLE 12

Incident Light	θ = 70° Φ = 270° λ = 550 nm
Bottom Polarizer	Φ = 0°
Third Compensation Film	Φ = 0° Nz = 0.756 d(n_x− n_y) = 254 nm
First Compensation Film	Φ = 112.5° Nz = 0.6738 d(n_x− n_y) =
	275 nm
Second Compensation Film	Φ = 22.5° Nz = 0.9328 d(n_x− n_y) = 275 nm
C-Plate Compensation Film	n_o= 1.5095 n_e= 1.511 d = 65 μm
A-Plate Compensation Film	Φ = 0° n_o= 1.5095 n_e= 1.511 d = 70 μm
Top Polarizer	Φ = 90°

As shown in FIGS. 43 and 46, the bright state area in FIG. 43 is larger than the bright state area in FIG. 46. The foregoing result is because during the compensation process of FIG. 41, the polarization state of the directional light 282 in the blue phase liquid crystal materials is circularly polarized. Since the circularly polarized light is not affected by the orientation angle, the contour lines of the contrast ratio can be improved.

Sixth Embodiment

FIG. 47 is a schematic cross-sectional view of a display device according to a sixth embodiment of the invention. With reference to FIG. 47, a display device 100 f of the present embodiment is similar to the display device 100 e of the fifth embodiment. A difference therebetween lies in that, in the display device 100 f, the third compensation film 31 b is disposed between the bottom polarizer 23 b and the first compensation film 28 b, and the bottom polarizer 23 b is disposed between the first optical film 24 b and the third compensation film 31 b.
According to the present embodiment, the fourth compensation film 31 a is disposed between the second compensation film 28 a and the top polarizer 23 a, and the second optical film 24 a is disposed between the fourth compensation film 31 a and the top polarizer 23 a. In the present embodiment, the first compensation film 28 b, the second compensation film 28 a, and the third compensation film 31 b are biaxial compensation films. Moreover, the fourth compensation film 31 a includes the A-plate compensation film 31 a-1 and the C-plate compensation film 31 a-2. According to the present embodiment, the directional light 282 passes through the bottom polarizer 23 b, the third compensation film 31 b, the first compensation film 28 b, the second compensation film 28 a, the C-plate compensation film 31 a-2, the A-plate compensation film 31 a-1, and the second optical film 24 a in sequence. The output light 283 is formed after the directional light 282 passes through the turning optical film 25, and then the output light 283 passes through the top polarizer 23 a.
FIG. 48 is a schematic view of a Poincaré sphere for a compensation process during a dark state when a display device according to the sixth embodiment of the invention employs compensation films. With reference to FIG. 48, in the present embodiment, a polar angle of the directional light 281 is 70° and an orientation angle Φ is 270°, for example. After the backlight passes through the bottom polarizer 23 b, the polarization state of the directional light 282 is a state P₀. When the orientation angle Φ of the directional light 282 changes, such as when the orientation angle Φ becomes 300°, the polarization state of the directional light 282 shifts from the state P₀to a state P₁. The third compensation film 31 b does not change the polarization state P₀when the orientation angle Φ is 270°, but when the orientation angle Φ is 300°, the polarization state of the polarized light can be changed from the state P₁to the state P₀. The first compensation film 28 b shifts a linearly polarized light of the state P₀to a circularly polarized light of a state C₁. The second compensation film 28 a shifts the circularly polarized light of the state C₁to the state P₀. By using the turning optical film 25 for depolarization, the absorption axis of the top polarizer 23 a is shifted to the state A₁. The C-plate compensation film 31 a-2 shifts the directional light 282 from the state P₀to a state P₂, and the A-plate compensation film 31 a-1 shifts from the state P₂to the state A₁matching the absorption axis of the top polarizer 23 a.
Table 13 tabulates a parameter setting data of each component in the display device 100 f. FIG. 49 is a contour map of the contrast ratios measured on the display device of FIG. 47 with the parameter setting of Table 13. FIG. 49 illustrates the contour lines of the optimized contrast ratio for an incident light 282 with a polar angle θ of 70° and an orientation angle Φ of 270°, in which the contour lines from outside to inside respectively represents the contour lines of contrast ratios 100, 200, 500, and 1000. FIG. 50 is a contour map for the bright state measurements on the display device of FIG. 47 with the parameter setting of Table 13, in which the contour lines from outside to inside respectively represents the contour lines of transmittances 0.2, 0.25, 0.3, 0.35, and 0.4. The ideal maximum transmittance after passing the bottom polarizer 23 b and the top polarizer 23 a is 0.5.

TABLE 13

Incident Light	θ = 70° Φ = 270° λ = 550 nm
Bottom Polarizer	Φ = 0°
Third Compensation Film	Φ = 0° Nz = 0.568 d(n_x− n_y) = 209.6 nm
First Compensation Film	Φ = −45° Nz = 0.501 d(n_x− n_y) =
	137.5 nm
Second Compensation Film	Φ = 45° Nz = 0.501 d(n_x− n_y) = 137.5 nm
C-Plate Compensation Film	n_o= 1.5095 n_e= 1.511 d = 40 μm
A-Plate Compensation Film	Φ = 0° n_o= 1.5095 n_e= 1.511 d = 60 μm
Top Polarizer	Φ = 90°

Seventh Embodiment

FIG. 51 is a schematic cross-sectional view of a display device according to a seventh embodiment of the invention. With reference to FIG. 51, a display device 100 g of the present embodiment is similar to the display device 100 a of the first embodiment. A difference therebetween lies in that, in the display device 100 g, the bottom polarizer 23 b is an O-type polarizer, and the top polarizer 23 a is an E-type polarizer, for example.
Typically speaking, the absorption axis of the O-type polarizer follows an orientation angle Φ of 0°. Moreover, the c-axis (i.e. transmission axis) of the E-type polarizer follows the orientation angle Φ of 0°. Compared to the bottom polarizer 23 b (O-type polarizer), the top polarizer 23 a (E-type polarizer) transmits the extraordinary ray and absorbs the ordinary ray. The top polarizer 23 a (E-type polarizer) weakens light which is not perpendicular to any transmission direction of the c-axis. According to the present embodiment, the first compensation film 28 b and the second compensation film 28 a are disposed between the top polarizer 23 a and the bottom polarizer 23 b.
FIG. 52 is a schematic view of a Poincaré sphere for a compensation process during a dark state when a display device according to the seventh embodiment of the invention employs compensation films. With reference to FIG. 52, in the present embodiment, the polarization state of the directional light 181 after passing through the bottom polarizer 23 b is a state P₁. The first compensation film 28 b rotates a linearly polarized light from the state P₁to a circularly polarized light of of a state C₁. Since circularly polarized light is not affected by the orientation angles, circularly polarized light is applied in the display medium 20 to improve the contrast ratio and bright state performance. After the directional light 282 passes through the display medium 20 materials, the second compensation film 28 a shifts the circularly polarized light of the state C₁to a state A₁matching the absorption axis of the top polarizer 23 a, in which the display medium 20 is optically isotropic and no voltage is applied.
Table 14 tabulates a parameter setting data of each component in the display device 100 g. FIG. 53 is a contour map of the contrast ratios measured on the display device of FIG. 51 with the parameter setting of Table 14. FIG. 53 illustrates the contour lines of the optimized contrast ratio for an incident light 281 with a polar angle θ of 70° and an orientation angle Φ of 270°, in which the contour lines from outside to inside respectively represents the contour lines of contrast ratios 500, 1000, 2000, and 5000. FIG. 54 is a contour map for the bright state measurements on the display device of FIG. 51 with the parameter setting of Table 14, in which the contour lines from outside to inside respectively represents the contour lines of transmittances 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, and 0.4.

TABLE 14

Incident Light	θ = 70° Φ = 270° λ = 550 nm
O-Type Polarizer	Φ = 0°
First Compensation Film	Φ = −45° Nz = 0.5 d(n_x− n_y) =
	137.5 nm
Second Compensation Film	Φ = 45° Nz = 0.5 d(n_x− n_y) =
	137.5 nm
C-Axis of the E-Type Polarizer	Φ = 0°

In view of the foregoing, compensation films are disposed between the top and bottom polarizers in the display device according to an exemplary embodiment of the invention. The configuration of the compensation films can adjust the polarization state of the directional light entering the display module, such that the polarization state of the directional light matches the absorption axis direction of the top polarizer. Accordingly, light leakage can be minimized and the contrast ratio of the display device can be enhanced. Moreover, the configuration of the compensation films can convert the polarization state of the directional light from the linear polarization state to the circular polarization state for transmission in the display medium. Since the circularly polarized light is not affected by the orientation angle, the viewing angle of the display device can be increased.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.

Claims

1. A display device, comprising:

a light source module generating a directional light;

a display module disposed above the light source module, the display module comprising:

a first substrate having a first inner surface and a first outer surface;

a second substrate disposed opposite to the first substrate and having a second inner surface and a second outer surface; and

a display medium disposed between the first substrate and the second substrate and is optically isotropic, wherein the display medium is optically anisotropic when driven with an electric field, the directional light is not perpendicular to the first outer surface when the directional light enters the display module, and the directional light is not perpendicular to the second outer surface when the directional light exits the display module;

a turning optical film disposed on the second outer surface of the second substrate of the display module, the turning optical film having an incident surface and an output surface, the directional light entering the turning optical film from the incident surface and exiting the turning optical film from the output surface so as to form an output light, wherein an included angle is between the output light and the output surface;

a first compensation film disposed on the first outer surface of the first substrate; and

a second compensation film disposed between the second substrate and the turning optical film.

2. The display device as claimed in claim 1, further comprising:

a first optical film disposed on the first outer surface of the first substrate, the first optical film having a plurality of first optical structures allowing the directional light passing through the first optical structures without generating total reflection; and

a second optical film disposed on the second outer surface of the second substrate, wherein the second optical film has a plurality of second optical structures substantially allowing the directional light passing through the first optical structures without generating total reflection.

3. The display device as claimed in claim 2, further comprising:

a bottom polarizer disposed on the first outer surface of the first substrate; and

a top polarizer disposed on the second outer surface of the second substrate.

4. The display device as claimed in claim 3, wherein the bottom polarizer is disposed between the first compensation film and the first optical film, the top polarizer is disposed between the second compensation film and the second optical film, and the second optical film is disposed between the turning optical film and the top polarizer.

5. The display device as claimed in claim 4, wherein an orientation angle of the first compensation film is 20°˜50° and Nz is 0.35˜0.75; and an orientation angle of the second compensation film is −20°˜−50° and Nz is 0.35˜0.75.

6. The display device as claimed in claim 3, further comprising:

a third compensation film disposed between the first compensation film and the bottom polarizer; and

a fourth compensation film disposed between the second compensation film and the top polarizer; and

7. The display device as claimed in claim 6, wherein the third compensation film and the fourth compensation film are respectively a biaxial compensation film.

8. The display device as claimed in claim 7, wherein an orientation angle of the first compensation film is 20°˜40° and Nz is 0.25˜0.55; an orientation angle of the second compensation film is −20°˜−40° and Nz is 0.25˜0.55; an orientation angle of the third compensation film is 15°˜35° and Nz is 0.75˜0.95; and an orientation angle of the fourth compensation film is −15°˜−35° and Nz is 0.75˜0.95.

9. The display device as claimed in claim 6, wherein the bottom polarizer is a wire-grid polarizer.

10. The display device as claimed in claim 9, wherein an orientation angle of the first compensation film is 30°˜60° and Nz is 0.35˜0.65; an orientation angle of the second compensation film is −30°˜−60° and Nz is 0.35˜0.65; an orientation angle of the third compensation film is −10°˜10° and Nz is 0.71˜0.91; and an orientation angle of the fourth compensation film is 80°˜100° and Nz is 0.71˜0.91.

11. The display device as claimed in claim 3, further comprising:

a third compensation film disposed between the first compensation film and the first substrate; and

a fourth compensation film disposed between the second compensation film and the second substrate.

12. The display device as claimed in claim 11, wherein the third compensation film and the fourth compensation film are respectively a biaxial compensation film.

13. The display device as claimed in claim 12, wherein an orientation angle of the first compensation film is 25°˜55° and Nz is 0.45˜0.75; an orientation angle of the second compensation film is −25°˜−55° and Nz is 0.47˜0.67; an orientation angle of the third compensation film is 80°˜100° and Nz is 0.4˜0.6; and an orientation angle of the fourth compensation film is −10°˜10° and Nz is 0.4˜0.6.

14. The display device as claimed in claim 3, wherein the first compensation film and the second compensation film are respectively a biaxial compensation film.

15. The display device as claimed in claim 14, further comprising:

a third compensation film disposed between the bottom polarizer and the first compensation film, and the first optical film is disposed between the third compensation film and the first compensation film; and

a fourth compensation film disposed between the second compensation film and the top polarizer, and the second optical film is disposed between the fourth compensation film and the top polarizer.

16. The display device as claimed in claim 15, wherein the turning optical film is disposed between the second optical film and the top polarizer.

17. The display device as claimed in claim 16, wherein the third compensation film is a biaxial compensation film, and the fourth compensation film comprises an A-plate compensation film and a C-plate compensation film.

18. The display device as claimed in claim 17, wherein an orientation angle of the first compensation film is 100°˜125° and Nz is 0.55˜0.8; an orientation angle of the second compensation film is 10°˜35° and Nz is 0.8˜1.0; an orientation angle of the third compensation film is −10°˜10° and Nz is 0.6˜0.8; an orientation angle of the A-plate compensation film is −10°˜10°, n_ois 1.4˜1.6, and n_eis 1.4˜1.6; and n_oof the C-plate compensation film is 1.4˜1.6 and n_eis 1.4˜1.6.

19. The display device as claimed in claim 14, further comprising:

a third compensation film disposed between the bottom polarizer and the first compensation film, and the bottom polarizer is disposed between the first optical film and the third compensation film; and

20. The display device as claimed in claim 19, wherein the turning optical film is disposed between the second optical film and the top polarizer.

21. The display device as claimed in claim 20, wherein the third compensation film is a biaxial compensation film, and the fourth compensation film comprises an A-plate compensation film and a C-plate compensation film.

22. The display device as claimed in claim 21, wherein an orientation angle of the first compensation film is −35°˜−55° and Nz is 0.4˜0.6; an orientation angle of the second compensation film is 35°˜55° and Nz is 0.4˜0.6; an orientation angle of the third compensation film is −10°˜10° and Nz is 0.45˜0.65; an orientation angle of the A-plate compensation film is −10°˜10°, n_ois 1.4˜1.6, and n_eis 1.4˜1.6; and n_oof the C-plate compensation film is 1.4˜1.6 and n_eis 1.4˜1.6.

23. The display device as claimed in claim 3, wherein the bottom polarizer comprises an O-type polarizer, and the top polarizer comprises an E-type polarizer.

24. The display device as claimed in claim 23, wherein an orientation angle of the first compensation film is −35°˜−55° and Nz is 0.4˜0.6; and an orientation angle of the second compensation film is 35°˜55° and Nz is 0.4˜0.6.

25. The display device as claimed in claim 1, wherein the included angle is 60°˜120°.

26. The display device as claimed in claim 25, wherein the included angle is 90°.

27. The display device as claimed in claim 1, further comprising a diffusion film disposed on the turning optical film.