DE102007010712B4 - Process for making an EPD screen with an OTFT control matrix - Google Patents

Abstract

A method of manufacturing an electrophoretic screen (EPD) with a control matrix of organic thin film transistors (OTFT), comprising the steps: (i) providing an EPD module (10) with a plurality of EPD units (14), which are on a common substrate (12) are arranged and each comprise a cell which can be switched capacitively in optical behavior; (ii) applying pixel electrodes (21) to the EPD module (10), each pixel electrode (21) being designed and arranged on the EPD module (10) in such a way that when a voltage is applied, the optical behavior of one or more cells the EPD units (14) can be influenced; and (iii) creating the OTFT control matrix (20) by directly applying OTFT functional layers on the side of the EPD module (10) carrying the pixel electrodes (21).

Description

The invention relates to a method for producing an electrophoretic display screen (EPD) with an OTFT control matrix.

Technological background and state of the art

Electrophoretic displays (EPDs) represent a new type of reflective screen whose imaging mechanism relies essentially on the alternating arrangement of charged colored particles or liquids in a dispersion or multi-phase system by applying an electric field. Commercial examples include particle systems from E-Ink and Sipix, "Liquid Powder" from Bridgestone, and "Electrowetting" from Liqua Vista. The EPDs are all capacitively driven, i. H. they contain a capacitive switchable in optical behavior cell. For capacitive switching, each of these cells is assigned a pixel electrode. When applying a voltage to the pixel electrode so the optical behavior of one or more cells can be influenced. To illustrate the mode of operation, an EPD with a particle system is described in more detail below. However, the invention generally relates to all capacitively switchable EPDs and is not limited to the embodiment explained below.

An EPD comprises a multiplicity of individual EPD units, which in the simplest form comprise at least one cell in each case, which is filled with the dispersion of the charged particles and a suitable solvent. For the purpose of the circuit, each cell is assigned at least one pixel electrode which is designed and arranged such that when the voltage is applied, the charged particles are aligned in the field direction. The switching mechanism is therefore capacitive and the particles migrate in the presence of an electromagnetic field in the direction of the pixel electrode and are deposited there. The layer formed is now such that it is no longer transparent to light, while the dispersion with freely distributed particles allows a transmission of light. The relatively robustly realizable technology allows the production of highly flexible screens, for example in the form of electronic newspapers, but is also suitable as an imaging component in a variety of electronic products, such as laptops or mobile devices.

In the EPD, a plurality of EPD units are arranged on a common substrate. This component of the EPD is also referred to below as the EPD module. The pixel electrodes are applied to the EPD module. Controlling the activity of the plurality of EPD units of the EPD module requires the provision of a complex control circuit.

In the case of small EPDs, the control can take place via a so-called passive matrix (PM): A specific pixel is activated by applying a voltage to a row and column, which requires two lines. However, this method is not sufficient for large displays; To control an active matrix (AM: Active Matrix) must be used, in which each pixel (pixel) is addressed individually via at least one own transistor. Each individual pixel therefore has an active amplifier, for example in the form of a thin-film transistor (TFT). The amplifier assigned to each pixel has two important functions. On the one hand, the control voltage of a pixel decreases as the number of rows and columns used in a pixel matrix increases. Therefore, passive matrices are limited in size. However, an amplifier can increase this voltage to the value needed to switch the cell. On the other hand, the continuous increase in the number of columns and lines and the reduction in pixel sizes lead to an increase in the parasitic capacitances of a pixel. However, in order to achieve the often required high frame rate, the capacitance must not cause a reduction in the switching speed. A local amplifier with separate power supply line can guarantee fast switching with short, strong current pulses.

Organic thin-film transistors (OTFT: OrganicThin Film Transistor) have increasingly become the focus of the development of miniaturized electronic devices since the discovery and development of organic semiconductor materials. In its simplest form, an OTFT comprises a conductive gate electrode which is covered with a thin dielectric film which is followed by a layer of the active organic semiconductor material. Smaller molecules and oligomers, such as pentacenes and polythiophenes, are generally used as semiconductor materials. The semiconductor layer has a thickness of a few 10 nm and is bounded laterally by the source and drain electrodes. In the longitudinal direction, the semiconductor layer measures a few 100 nm. The organic semiconductor material is ideally present in monocrystalline form, but also polycrystalline or amorphous films can be used due to their much cheaper production.

The production of OTFTs can be realized very inexpensively, for. B. based on the existing technologies for the production of plastic microstructures, such as in particular the inkjet printing process (inkjet printing). The one for the production of OTFTs in practice The most important approach for producing the organic semiconductor layer is believed to be inkjet printing, in which an ink consisting of or consisting of the organic semiconductor material is selectively deposited in a certain area of the substrate. The pixel electrodes and the further OTFT layers are applied to the EPD module according to the invention. In the prior art, an EPD module and the OTFT module including pixel electrodes are laminated. In US 6 312 304 B1 There is a separate circuit layer between the EPD module and the OTFT module.

EPD modules are now commercially available from several manufacturers. The EPD modules must be provided with pixel electrodes and with a suitable control matrix, in particular just an OTFT control matrix, to produce the ready-to-use EPD. For this purpose, an OTFT module is used in the prior art, which is connected to the EPD module with applied pixel electrodes via a lamination process. The OTFT module includes a plurality of OTFT units arranged on a common substrate. The two modules must be aligned in lamination so that the desired electrical connectivity between the pixel electrodes and thus the plurality of EPD units and the activity controlling OTFT units is created. This usually requires structures that support correct alignment of the modules to each other. The creation of such structures as well as the process of aligning the two modules incurs costs and presents a source of error that can increase rejects.

Further disadvantages arise in the production of the OTFT control matrix on a separate substrate film: 1) There are always a few temperature steps in the process which lead to an uncontrollable deformation and expansion of the substrate film. This slightly deformed film can then be inaccurately combined with the EPD module, d. H. The yield, quality and reproducibility of the manufacturing process are reduced. 2) When laminating the two modules (EPD module and OTFT module) additional pressure is required. This pressure can damage the sensitive transistors.

Furthermore, the lamination usually also includes the application of an adhesion promoter between the modules as well as a generally thermal treatment for curing the adhesion promoter. On the one hand, the measures are in turn associated with costs for materials and litigation, and another potential source of error that increases rejects. On the other hand, it is precisely the organic semiconductor layers of the OTFT that are temperature-sensitive and can be limited in their functionality by the thermal treatment.

US Pat. No. 6,778,312 B2 describes a manufacturing process in which applied to the substrate pixel electrodes and holes are etched. Subsequently, the thin film transistor is created directly on the circuit. Then, another transparent substrate is placed with a transparent electrode and filled in the resulting gap, the electrophoretic dispersion.

There is therefore a need for alternatives that overcome the disadvantages of the previous manufacturing process.

Summary of the invention

• (i) Bereitstellen eines EPD-Moduls mit einer Vielzahl von EPD-Einheiten, die auf einem gemeinsamen Substrat angeordnet sind und je eine kapazitiv im optischen Verhalten schaltbare Zelle umfassen;
• (ii) Auftragen von Pixelelektroden auf dem EPD-Modul, wobei jede Pixelelektrode so ausgelegt und auf dem EPD-Modul angeordnet ist, dass beim Anlegen einer Spannung das optische Verhalten ein oder mehrerer Zellen der EPD-Einheiten beeinflussbar ist; und
• (iii) Erstellen der OTFT-Steuermatrix durch direktes Auftragen von OTFT-Funktionsschichten auf der die Pixelelektroden tragenden Seite des EPD-Moduls.

The invention relates to a method for producing an electrophoretic display screen (EPD) with an OTFT control matrix. The method according to the invention comprises the steps:

• (I) providing an EPD module with a plurality of EPD units, which are arranged on a common substrate and each comprise a capacitive in the optical behavior switchable cell;
• (ii) applying pixel electrodes on the EPD module, each pixel electrode being arranged and arranged on the EPD module such that upon application of a voltage, the optical behavior of one or more cells of the EPD units can be influenced; and
• (iii) Create the OTFT control matrix by directly applying OTFT functional layers to the EPD module's side carrying the pixel electrodes.

The invention is based on the finding that with the mentioned process management a waiver of the conventional lamination of EPD module and OTFT module is possible and thus the disadvantages of the conventional method thus described can be avoided. The method initially starts with a conventional EPD module, which forms the substrate for the OTFT control matrix. On the commercially available EPD module, the pixel electrodes are applied in an intermediate step known per se. The OTFT control matrix is then created in a manner known per se step by step, ie layer by layer, directly on the EPD module. In doing so, the contacts necessary for the OTFT control matrix between the OTFT transistors and the pixel electrodes are produced. On the conventional orientation of the modules and the necessary means and the process of lamination with its thermal substeps and the application of a primer layer can be dispensed with according to the method of the invention. As a result, the production can be significantly simplified and the waste can be minimized.

Preferably, the step (iii) of creating the OTFT control matrix comprises applying OTFT functional layers such as a drain, source, gate or organic semiconductor layer by photolithography or inkjet coating. The use of these coating methods is particularly suitable for large area EPDs, where a large number of switching elements of the OTFT control matrix has to be created.

Another aspect of the invention is to provide an EPD having an OTFT control matrix obtained or obtainable by the method of the invention. The EPD already differs from those of the conventional design in that no separate substrate is necessary for the OTFT control matrix and, moreover, it is also possible to dispense with an adhesion promoter layer in the conventional double-modular structure. In other words, much smaller layer thicknesses can be realized, which as a rule also provide increased flexibility of the EPD.

Brief description of the drawings

The invention will be explained in more detail with reference to embodiments and the accompanying drawings. Show it:

1 a highly simplified sectional view illustrating the construction of an electrophoretic display (EPD) according to the invention;

2 and 3 two schematic sectional views through an EPD with top gate or bottom gate architecture.

Detailed description of the invention

Of the 1 is a highly simplified sectional view of the structure of an electrophoretic display panel (EPD) according to the invention for purposes of illustration. The EPD includes an EPD module 10 , which in turn is a substrate 12 , a counter electrode 13 , an EPD unit 14 and a protective layer 15 includes. Each EPD unit 14 contains a cell filled with a dispersion of charged particles in a solvent. The counter electrode 13 is needed to build an electric field at all and is usually grounded or at a constant potential. Furthermore, each cell is assigned at least one pixel electrode, which is designed and arranged such that, when a voltage is applied, the charged particles are aligned in the field direction. In general, the pixel electrode from the screen manufacturer on the protective layer 15 applied and, since it is interpreted differently depending on the desired screen resolution in the dimensions, not shown in detail for the sake of simplicity. All mentioned functional elements of the EPD unit 14 as well as all others, in such an EPD unit 14 Usually existing components are omitted for clarity in the graph. As well as the functioning of the EPD module 10 is known, is also dispensed with a detailed representation of the processes of image formation. For the purposes of the invention is remarkable only that each EPD unit 14 of the EPD module 10 associated with at least one switchable in the above-mentioned manner pixel electrode whose activity is to be controlled. For this purpose, on the side of the EPD module carrying the pixel electrodes 10 an OTFT control matrix 20 arranged.

The OTFT control matrix 20 consists of a plurality of OTFT units, each containing one or more OTFT transistors. As already explained above, an OTFT transistor has a layered structure which necessarily comprises functional elements such as a drain, source and gate electrode and an organic semiconductor layer. Each OTFT unit is now one or possibly several EPD units 14 associated, ie, one or more OTFT transistors of an OTFT unit are for the control of the activity of one or more EPD units 14 responsible. For this purpose, at least one source or drain electrode of an OTFT transistor of the OTFT unit is in electrical contact with a pixel electrode. This pixel electrode may well have multiple EPD units 14 or only part of an EPD unit 14 extend. The screen resolution determines the size of the pixel electrode. Also on the graphical representation of the OTFT control matrix 20 including components was omitted for reasons of clarity. The basic structure of an OTFT control matrix 20 is known, so that in addition to a detailed presentation of the functional elements, their production and a representation of the operation is omitted. The 2 and 3 show two schematic sectional views through an EPD with top gate or bottom gate architecture. Components having the same function are assigned the same reference numerals in the figures. The excerpts of the 2 and 3 show only one pixel of an EPD. Unlike the pixel electrode, the counter electrode is not structured and extends over the entire EPD module.

2 shows a schematic sectional view through an EPD with an OTFT control matrix 20 , where in the OTFT control matrix 20 existing OTFT transistors with respect to the EPD module 10 have top gate architecture. In the section shown, the EPD module 10 from a pixel electrode 21 covered. The pixel electrode 21 can be applied by photolithography, ink jet printing and other commercial printing technologies such as screen printing.

To create the OTFT control matrix 20 can proceed as follows: By means of inkjet printing is first an insulator layer 22 on the pixel electrode 21 applied. In a subsequent process step, selective etching causes a breakdown in the insulator layer 22 created by inkjet printing with an electrically conductive material to produce a the pixel electrode 21 contacting drain electrode 24 is filled. Parallel to this is a source electrode 26 formed between the source and drain electrodes 24 . 26 then becomes an organic semiconductor layer 28 introduced, preferably also with ink jet printing. The resulting structure is characterized by a further insulator layer 30 covered. Then a gate electrode 32 applied, again preferably by ink jet printing, and this finally with a suitable protective layer 34 encapsulated. The insulator layer 22 is preferably prepared by ink jet printing, so that can be dispensed with the etching. Alternatively, the insulator layer 22 structured by photolithography. The source-drain electrodes 24 . 26 as well as the via are preferably produced by means of ink jet printing and produced in a process run. Alternatively, they can be structured by photolithography.

3 shows a schematic sectional view through an EPD with an OTFT control matrix 20 , where in the OTFT control matrix 20 existing OTFT transistors with respect to the EPD module 10 have bottom gate architecture. All OTFT functional layers can be used in an analogous way as for 2 executed to be created.

Through the use of photolithography, a higher screen resolution can be achieved than with the use of inkjet technology. For high-resolution screens, it would be preferable to perform all processes by means of photolithography (as far as the EPD module allows) and then the semiconductor layer 28 to print. In the variant after 2 can then also the gate electrode 32 to be printed.

The substrate 12 of the EPD module 10 can be made of glass or plastic. In particular, the substrate may consist of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), aromatic polyesters and polyimides (PI).

The pixel electrode 21 as well as the electrodes 24 . 26 . 32 the OTFT control matrix 20 can be made from a material conventionally used for electrodes. For example, chromium, aluminum, tantalum, molybdenum, copper, silver, gold, palladium, iridium, nickel and cobalt and their alloys can be used. Preferably, a portion of the electrodes or all electrodes are formed of a transparent material, such as indium / tin oxide (ITO). The pixel electrode 21 should preferably be made of a reflective material, such as Al and Ag. Only the counter electrode 13 in the EPD module 10 must be transparent.

The organic semiconductor layer 28 may for example consist of polymers such as poly (3-alkylthiophene), poly (3-hexylthiophene) (P3HT), poly (3-octylthiophene), poly (2,5-thienylenevinylene) (PTV) or poly (paraphenylenevinylene) (PPV) , Likewise, the use of molecular organic semiconductor materials, such as anthracene, pentacene, hexacene or tetracene, conceivable. Furthermore, functionalized and soluble pentacene materials, such as triisopropylsilyl (TIPS) and trimethylsilyl (TMS) derivatives, are applicable.

For the insulator layers 22 . 30 For example, organic materials such as polyolefins, polyacrylates, polyimides, polystyrenes, and polyisobutylenes can be used. Also, inorganic materials such as silicon dioxide, silicon nitride, alumina, tantalum oxide and the like can be used.

Claims (2)

Method for producing an electrophoretic display screen (EPD) with a control matrix of organic thin-film transistors (OTFT), comprising the steps: (i) providing an EPD module ( 10 ) with a plurality of EPD units ( 14 ) on a common substrate ( 12 ) are arranged and each comprise a capacitive in the optical behavior switchable cell; (ii) applying pixel electrodes ( 21 ) on the EPD module ( 10 ), each pixel electrode ( 21 ) and designed on the EPD module ( 10 ) is arranged such that upon application of a voltage, the optical behavior of one or more cells of the EPD units ( 14 ) can be influenced; and (iii) creating the OTFT control matrix ( 20 ) by direct application of OTFT functional layers on which the pixel electrodes ( 21 ) supporting side of the EPD module ( 10 ). Method according to Claim 1, in which the step (iii) of creating the OTFT control matrix ( 20 ) the application of OTFT functional layers, such as a drain electrode ( 24 ), Source electrode ( 26 ), Gate electrode 32 or organic Semiconductor layer ( 28 ), by photolithography or ink jet printing.

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