WO1988000715A1

WO1988000715A1 - Large, high density display with segmented support

Info

Publication number: WO1988000715A1
Application number: PCT/US1987/001761
Authority: WO
Inventors: Philip Jones
Original assignee: Raychem Corporation
Priority date: 1986-07-22
Filing date: 1987-07-22
Publication date: 1988-01-28
Also published as: GB8617866D0; KR880701892A; EP0277973A1; EP0277973A4

Abstract

A display having electrically activable display medium (16 or 17) positioned between first and second support members (12 and 14 or 72 and 74) each of which carries electrode means (such as 19 or 54) has at least one of said support members (14) comprising a plurality of segments (such as 41-44 or 50 and 52 or 66) with adjacent segments being aligned edge-to-edge. Each segment preferably has a plurality of pixel electrodes (19 or 54) and the display preferably comprises a larger number of pixels.

Description

^π LARGE, HIGH DENSITY DISPLAY WITH SEGMENTED

SUPPORT "

This invention relates to an electrically activatable display, such as a liquid crystal display.

Liquid crystal displays are well known and are usefully employed so that individual picture elements i.e., pixels, may be provided on a viewing surface of the liquid crystal display. A high definition liquid crystal display aims to provide as high a pixel density per unit area of display as the state of the art can realize. A relatively large display e.g., 15 cm diagonal, may contain a large number of pixels at a lower density or a larger number of pixels at high pixel density per unit area.

One difficulty with providing such large or high density liquid crystal display arises from the following. The liquid crystal display typically operates with an array of pixel electrodes^• and associated active circuit devices, for example, thin film transistors, at least one one for each pixel electrode. The array of thin film transistors is usually produced by mass deposition on a support, together with suitable "column" and "row" conductors for addressing selected pixels. The manufacturing yield rate of satisfac¬ tory arrays of such transistors, (i.e., arrays with substan¬ tially no electrical failures) typically decreases as the number of pixels on the support is increased. In practice, the mass manufacture of, for example, more than 250,000 transistors per array is likely to provide an unacceptable yield rate for commercially viable production of liquid crystal displays. The present invention alleviates this difficulty and can advantageously provide displays of larger-than-usual viewing area and/or increased pixel density per unit area regardless of the total viewing surface area. The invention is espe¬ cially useful in displays where the individual pixel electrodes are not more than 4mm2, preferably not more than Imm^, in area; and/or where the pixel density is at least 25, preferably at least 50 or 100, more preferably at least 250, especially at least 500, per square centimetre.

In one aspect, the present invention provides a display comprising:

a) first and second electrode support members each of which carries electrode means and at least one of which is substantially overlapped by the other,- wherein at least one of the electrode support mem¬ bers is physically segmented -with adjacent segments being arranged edge-to-edge in close proximity such that a boundary line is formed at the adjacent edges and the electrode means of adjacent segments are physically separated from each other; and

b) an electrically activatable display medium between said first and second electrode support members, which display medium can provide an optically discernable effect in response to an electrical signal which can be applied by way of the electrode means in use; with the proviso that if both said electrode support members are segmented,

i) each segment of said first electrode support member is at least partially overlapped by a segment of said second electrode support member and at least some of the segments of said first electrode support member are not coincident with segments of said second electrode support member;

or

ii) the segments of said first electrode support member are coincident with segments of said second electrode support member and the electrically'activatable display medium extends across at least some of the boundary lines of the coincident segments.

The display of the present invention can be used in a transmissive, a reflective, a projective and/or a transflec- tive mode.

In another aspect, the invention provides a method for making a display, which method comprises the steps of:

a) providing at least first and second electrode sup¬ port members, each of which carries electrode means, wherein at least one of the electrode sup- port members is physically segmented with adjacent segments being arranged edge-to-edge in close proximity such that a boundary line is formed at the adjacent edges and the electrode means of adja¬ cent segments are physically separated from each other; and

b) adhering together at least one of the segmented electrode support members and an electrically acti¬ vatable display medium, which display medium can provide an optically discerable effect in response to an electrical signal which can be applied by way of the electrode support members in use; and

c) placing the electrode support members such that at least one of said electrode support members is substantially overlapped by the other with the display medium positioned therebetween so as to be capable of responding to the said signal in use;

with the proviso that if both said electrode support members are segmented,

i) each segment of said first electrode support member is at least partially overlapped by a segment of said second electrode support member and at least some of the segments of said first electrode support member are not coincident with segments of said second electrode support member; or

ii) the segments of said first electrode support member are coincident with segments of said second electrode support member and the electrically activatable display medium extends across at least some of the boundary lines of the coincident segments.

The electrode support members carry one or more electrode means. The electrode means is generally a transparent conductive material, e.g. indium tin oxide (ITO), coated onto the electrode support member inthe desired pattern. The pattern generally is the well-known "column" and "row" arrangement, but any other pattern may be used if desired.

In assembling the display, the display medium may be coated onto at-, least one of the electrode support members, e.g., by solvent or melt coating or any suitable deposition technique, or may be inserted as a free-standing (i.e. self- supporting) film between the first and second electrode sup¬ port members. Electrode members precoated with the display medium may be convenient.

An adhesive may be used in order to obtain commercially acceptable adhesion between the various layers in the display, very good adhesion being required for displays sub¬ jected to intense mechanical vibrations e.g., military display systems. The display medium of the present invention may be an electrochromic, an electrophoretic, or an electroluminescent display medium. The display medium preferably comprises a substantially non-flowable e.g., substantially solid, display medium and preferably comprises an encapsulated liquid crystal solid material. A particularly preferred encapsulated liquid crystal solid material for the present purposes is described and claimed in U.S. Patent No. 4,435,047, the disclosure of which is incorporated herein by reference. This document discloses the use of a liquid crystal material that is particularly responsive to an electric field. Reference may also be made to PCT applica¬ tion publication No. WO85/04262, and Japanese 61047427A; the disclosure of both of which is incorporated herein by reference.

Display media consisting o£ droplets or particles of liquid crystal materials in a continuous polymeric matrix are advantageous, since adequate resolution and switching speeds for high frame rate dynamic displays can be achieved with a majority, preferably at least 75%, more preferably at least 90%, and most preferably substantially all, of the droplets or particles being less than 10 micrometres, pre¬ ferably not more than 5 micrometres, in average thickness in the direction of the electrical field to be applied by way of the electrode members in use. Such small thicknesses are extremely difficult to achieve in cells where the liquid crystal material is merely confined between two plates, since accurate spacing of the plates is difficult to achieve, especially over large areas. Further, display media consisting of droplets or particles of liquid crystal materials in a continuous polymeric matrix can be formed as into a self-supporting film, if desired.

The segmented electrode support member is preferably a quod mosaic i.e., a mosaic made up of four segments. Other arrangements may also be suitably employed, for example, a hex (6 segment) mosaic, an octal (8 segment) mosaic, or a mosaic of "row" and/or "column" strips. We have found that the quod mosaic, for example, can provide a liquid crystal display of, for example, from 10 cm to 100 cm diagonal, con¬ taining at least 100,000, especially at l ast 250,000, for example 2,000,000, pixels.

We have found that for typical applications, it is desirable to provide electrode support members that have a substantially planar configuration. The electrode support members are positioned such that at least one of them is substantially overlapped by the other. Preferably both electrode support members are substantially overlapped by the other, i.e. are substantially superposed. The electrode support members are preferably stacked in parallel planes.

In those electrode support members which are physically segmented, the segments are preferably arranged so that the width of boundary lines formed at the edges of adjacent segments is substantially the same as the interpixel gap of the display. In a typical application, for example, with regular interpixel gaps of about 50 micrometres, the edge of each segment will be about 25 micrometres from the nearest pixel electrodes (i.e. electrode means) carried by that segment or, if the pixel electrode is contiguous with the edge of the segment, the edge of each segment is positioned so that it is about 50 micrometres from the pixel electrode of the adjacent segment. Thus, an important feature of this invention provides a display wherein at least two segments each carrying a plurality of electrodes are arranged with their edges so spaced that the distance between electrodes on adjacent segments is approximately equal to the inter¬ pixel gap and there is substantially no discernable irregu¬ larity in the display in operation. By this is meant that the ordinary viewer of the display in normal operation will discern substantially no irregularlity in interpixel gap. Suitable viewing distances and viewing angles will be readily determined by the usual criteria.

In preparing a display in accordance with this inven¬ tion, registration means may be provided to facilitate accurate alignment of adjacent segments. Such registration means may be, for example, one or more protrusions along the edge of one segment with corresponding recesses along the appropriate edge of the adjacent segment. Another illustra¬ tive example of registration means involves the use of a frame shaped to receive segments along the edge of the display. One electrode support member may be a larger size than the other with alignment means mounted thereon or integral therewith for positioning segments of the other electrode support member thereon.

In the display of this invention, at least one of the electrode support members is segmented. When both are segmented, at least some of the segments, in one embodiment, are aligned so as to be non-coincident. The term "non-coincident" or "not coincident" is used herein to mean that a boundary line between segments of one of the electrode support members is not superimposed over a boun¬ dary line between segments of the other electrode support member. In this embodiment each segment of the first electrode support member is at least partially overlapped by a segment of the second electrode support member. In another embodiment, the segments of the electrode support members are coincident, i.e. the boundary lines of the segments of one electrode support member are superimposed over the boundary lines of segments of the other. In this case the electrically a'ctivatable material (i.e. display medium) extends across the boundary lines. The electrically activatable material used in this embodiment is preferably in the form of a free standing (i.e. self-supporting) film. Such self-supporting film is preferably a liquid crystal material encapsulated in a polymer matrix as disclosed, for example, in above noted U.S. Patent No. 4,435,047.

In a preferred embodiment of the invention, only one of the electrode support members is segmented. The other electrode support member is continuous. The display medium may, and preferably is, co-continuous with the continuous electrode support member. The display medium is preferably coated onto the continuous electrode support member over the electrode means. The segmented electrode support member is then applied over the display medium. The segments may be applied individually or may be pre-assembled into the second electrode support member and positioned over the display medium.

In all embodiments of the invention at least one, and preferably two, of the first or second electrode support members, or the display medium extends across any boundary line of segments of the segmented electrode support members. Thus, there are at most two coincident boundary lines at any place on the display. This greatly reduces the apparent width of the boundary line between segments, as viewed at an angle other than perpendicular to the face of the display.

Selection control means may be provided to activate or deactivate a selected segment of an electrode support member, and one or more segments of a segmented electrode support member may carry a single electrode. Each pixel 'electrode is preferably controlled by an active device, which can be actuated to activate or deactivate the asso¬ ciated pixel electrode. The active device may be, for example, a transistor, especially a thin film field effect transistor (FET) for each electrode. Although transistors are preferred, it is noted that the generic class of non¬ linear devices e.g., diode circuits, varistors and diacs may be suitably employed as the selection control means.

As discussed above, a liquid crystal display medium typically operates with associated active circuit devices e.g., the transistors, in order to define picture elements i.e., pixels, on the viewing surface of the liquid crystal display. Any convenient assembly method may be used in com- bining the display medium with the active circuit devices in order to provide an optically discernable effect in response to an electrical signal applied by way of the electrode members.

The invention is illustrated by way of example in the accompanying drawings, in which:

Figure 1 shows a display of the present invention;

Figure 2A and 2B provide a schematic drawing of electro¬ nic circuits associated with the display of the present invention;

Figures 3 a to d provide schematic drawings of the pre¬ sent invention in use in various modes; and

Figure 4 illustrates an example of the of the invention.

Figure 5A, 5B and 5C illustrate registration (or aligning) means integral with the segments of electrode sup¬ port members.

Figure 6 illustrates registration (or aligning) means not integral with the segments.

Figure 7A and 7B illustrate an embodiment of the inven¬ tion in whic both electrode support members are segmented and the segments of the first electrode support member are not coincident with the segments of the second. Attention is now directed to Figure 1, which shows a display 10 of the present invention. The display 10 compri¬ ses electrode members 12 and 14 and an electrically activa¬ table solid encapsulated liquid crystal display medium 16 between the electrode members 12 and 13. The electrode member 14 is physically segmented into six parts arranged as a hex mosaic. Figures 2A and 2B focus attention on one por¬ tion 18 of a segmented electrode member derived from Figure 1. The portion 18 comprises segments coated with indium tin oxide 19 and a plurality of field effect transistors, FET's (20). Each FET 20 includes a source line 22, a gate line 24 and a drawing line 26. The FET is selectively addressed by column and line drivers 28 and 30 respectively. Figures 3 a, b, c, d are schematic drawings that show the display of Figure 1 when used in a transmissive, a reflective, a pro¬ jective and a transflective mode, respectively. In Figures 3, a light source 31 a lens 32, a screen 34, a reflector 36 and a viewer 38 are used. Light directions are indicated by arrows.

Figures 5A, 5B and 5C illustrate a method of aligning or registering adjacent segments. Segments 50 and 52 are pro¬ vided with "sawtooth" edges 51 and 53 respectively. To align the segments they are positioned close together as shown in Figure 5A and then positioned in abutting rela¬ tionship as shown in Figure 5B. The sawtooth edges accura¬ tely aligns the segments. Figure 5C is an enlarged view of the are shown within the dotted line area of Figure 5B. In Figure 5C edges 51 and 53 are aligned. Each segment is pro¬ vided with triangular pixel electrodes 54. Figure 6 shows another technique for aligning the segments. In Figure 6, frame 60 is provided with recesses 62 which mate with protrusions 64 on segments 66.

Example 1

A display as illustrated in Figure 4 was made as follows.

A 50 cm^ piece of glass 40 already coated with indium tin oxide (ITO) 19 by conventional techniques was cracked into four segments. Independently, a 5 cm x 11.5 cm piece of mylar 46 was coated with a 25 micrometres thick layer of encapsulated liquid crystal material comprising 40% black guest/host liquid crystal and 60% deionized PVA. The coated mylar was then laminated to the four glass segments using TRULOC SUPERSET 45 cyanoacrylate adhesive 48, the encap¬ sulated material being between the ITO faces. The ITO layer of the piece of mylar was connected to neutral and the terminal of a 60 V (50 Hz) rms power supply was connected in turn to the ITO layer on the segments 41, 42, 43 and 44. In consequence, all four segments independently switched their optical states from dark to light. The display was mechani¬ cally durable and self-supporting, and when two abutting segments were simultaneously in the light state, the boun¬ dary between them was difficult to discern at a viewing distance of about 50 cm at right angles to the display surface. Example 2

An emulsion of liquid crystal material ZLl 3499 (black guest-host liquid crystal available from E.M. Industries Inc.) dispersed in a polyurethane resin (Neorez 967 available from Polyvinyl Chemical Industries, Wilmington, Massachusetts) in a ratio of 1.6 liquid crystal to 1 polyurethane resin was coated onto a silicone release paper. The resulting coating was dried for about 15 minutes and then peeled off the release paper as a free standing film.

Strips (4" long by i " wide) of polyester film coated with indium tin oxide CITO) were prepared. The strips were positioned into a column and row configuration as shown in Figure 7A. Free standing film 70 was positioned between the "row" strips 72 and "column" strips 74 and the structure laminated together to produce the structure shown in Figure 7B.

By connecting any pair of horizontal or vertical ITO coated polyester strips to a 50 Hz power supply at 35 volts any pixel square of the nine could be independently turned on.

The joins were difficult to see from a distance, in par¬ ticular the joins between the ITO coated polyester strip behind the continuous film of encapsulated liquid material.

Claims

1. A display, comprising:

a) first and second electrode support members each of which carries electrode means and at least one of which is substantially overlapped by the other, wherein at least one of the electrode support mem¬ bers is physically segmented with adjacent segments being arranged edge-to-edge in close proximity such that a boundary line is formed at the adjacent edges and the electrode means of adjacent segments are physically separated from each other; and

b) an electrically activatable display medium between said first and second electrode support members, which display medium can provide an optically discernable effect in response to an electrical signal which can be applied by way of the electrode means in use;

with the proviso that if both said electrode support members are segmented,

2. A display according to any preceding claim, wherein the display medium comprises liquid crystal material.

3. A display according to Claim 2, wherein the display medium comprises an encapsulated liquid crystal material.

4. A display according to any of Claims 1 to 3, wherein only said first electrode support member is segmented.

5» A display according to any of Claims 1 to 3 wherein both said electrode support members are segmented.

6._. A display according to claim 1, wherein at least one segment of a segmented electrode support member carries a plurality of pixel electrodes.

7. A display according to claim 6, wherein the indivi¬ dual pixel electrodes are not more than 4mm2_r preferably not more than Im ^ in area.

8. A display according to any proceeding claim, which in total comprises more than 250,000 pixels.

9. A display according to claim 6, 7 or 8 wherein the pixel density is at least 25 per square centimetre.

^'

10. A display according to Claim 6, wherein at least one of the electrodes of each pixel is selectively addressable.

11. A display according to claim 6, wherein at least one of the electrodes of each pixel is controlled by a respective active device which can be activated to activate or deac¬ tivate the associated pixel electrode.

12. A display according to any preceding claim, further comprising selection control means which can be actuated to activate or deactivate a predetermined segment of a segmented electrode member.

13. A display according'to claim 12, wherein the selection control means comprises an active device.

14. A display according to claim 11 or 13', wherein the active device comprises a field effect transistor.

15. A method of making a display, which method comprises the steps of:

a) providing at least first and second electrode sup¬ port members, each of which carries electrode means,

wherein at least one of the electrode support members is physically segmented with adjacent segments being arranged edge-to-edge in close proximity such that a boundary line is formed at the adjacent edges and the electrode means of adjacent segments are physically separated from each other; and

b) adhering together at least one of the segmented electrode support members and an electrically acti¬ vatable display medium, which display medium can provide an optically discernable effect in response to an electrical signal which can be applied by way of the electrode support members in use; and

c) placing the electrical support members such that at least one of said electrode support members is substantially overlapped by the other with the display medium positioned therebetween so as to be capable of responsing to the said signal in use,

with the proviso that if both said electrode support members are segmented,

or ii) the segments of said first electrode support member are coincident with segments of said second electrode support member and the electrically activatable display medium extends across at least some of the boundary lines defined by the coincident segments.

16. A method according to claim 15, wherein the display medium is a substantially solid film.