JP5316701B2 - Electrochemical display element - Google Patents

Abstract

A substrate (20) on a non-viewing side of a display element (1) comprises: a metal wiring line (23) for supplying a current from a power bath (VDD) to a pixel electrode (25) through a thin film transistor (Q2); and an interlayer insulation film (24) which is so formed as to cover the thin film transistor (Q2) and the metal wiring line (23). The pixel electrode (25) is formed on the interlayer insulation film (24), and is connected to the metal wiring line (23) through a contact hole (24a). The substrate (20) additionally comprises an insulation film (26) which is formed on the pixel electrode (25) so as to cover the contact hole (24a).

Description

  The present invention relates to an electrochemical display element that performs display by enclosing an electrolyte solution between a pair of substrates and causing a redox material in the electrolyte solution to undergo an oxidation-reduction reaction.

  In recent years, display devices having excellent visibility and low power consumption have been demanded. At present, a self-luminous display element represented by CRT and PDP and a display element that modulates light from a light emitter (backlight) such as an LCD are generally used. The image is bright and easy to see, but it consumes more power.

  From the viewpoint of low power consumption, it is desirable that the display element has a memory characteristic that keeps an image once displayed even in a non-powered state, and further, a low driving voltage is desirable. In recent years, electrochemical display elements such as an electrochromic display element (hereinafter also referred to as ECD) and an electrodeposition display element (hereinafter also referred to as ED) have been actively developed as display elements having such characteristics. . Both ECD and ED display by changing the light absorption state of the reactant alone due to the oxidation-reduction reaction on the electrode. That is, in ECD, display is performed by a reversible change (color change) of the light absorption state of the electrochromic material due to an oxidation-reduction reaction. On the other hand, in the ED, for example, display is performed by using silver deposition on an electrode from an electrolyte containing silver or a compound having silver in a chemical structure, and dissolution of silver in the electrolyte. These electrochemical display elements do not require additional members such as polarizing plates and backlights compared to LCDs, and are extremely advantageous in terms of cost reduction and process saving (ease of manufacturing). It has become.

  By the way, in the configuration in which each pixel is arranged in a matrix form in the ED, it is provided corresponding to each pixel of the substrate arranged on the non-observation side among the pair of substrates sandwiching the electrolyte (electrolytic solution). A current from a power supply bus is supplied to a pixel electrode to be connected via a driving transistor (for example, TFT). In this configuration, for example, by forming the pixel electrode and the driving transistor in different layers, it is possible to secure a certain aperture ratio due to the pixel electrode. In other words, for example, the driving transistor and the metal wiring connected to the driving transistor are covered with an insulating film, a pixel electrode is provided on the insulating film, and the pixel electrode and the metal wiring are connected via a contact hole provided in the insulating film. A certain degree of aperture ratio can be secured by the connection. As described above, for example, Patent Document 1 discloses an example in which a pixel electrode and a metal wiring thereunder are connected via a contact hole.

Japanese Patent Laying-Open No. 2007-11225 (see paragraph [0022], FIG. 5)

  As described above, in the configuration in which the pixel electrode, the driving transistor, and the metal wiring are separated from each other through the insulating film, the contact hole provided in the insulating film is a hole. Unevenness occurs in the pixel electrode. When the pixel electrode is uneven as described above, there is a problem that the deposition material is abnormally deposited on the uneven portion of the pixel electrode when it is repeatedly driven, and the performance as a display element deteriorates. The abnormal precipitation is considered to be due to the following reason.

  That is, in the uneven portion of the pixel electrode, during black display, the deposition reaction of the deposition material on the observation side is less likely to occur than other portions (for example, the flat portion of the pixel electrode), and the pixel electrode on the non-observation side On the side, the deposited deposition material remains undissolved. On the other hand, during white display, an oxidation-reduction reaction is performed in which the deposition material deposited on the observation side is sufficiently dissolved and deposited on the non-observation side. For this reason, every time the black / white driving is repeated, the deposition material deposited on the non-observation side gradually increases, resulting in abnormal deposition. Note that the number of times that abnormal deposition occurs depends on the electrolyte used and the driving conditions, but abnormal deposition is likely to occur in the portion where the unevenness of the pixel electrode is large.

  The present invention has been made to solve the above-described problems, and its purpose is to avoid an abnormal deposition of deposition material on the uneven portion even when the unevenness occurs in the pixel electrode due to the contact hole. An object of the present invention is to provide an electrochemical display element capable of avoiding the performance deterioration of the element.

  In the electrochemical display element of the present invention, an electrolytic solution is sealed between an observation-side substrate having a common electrode and a non-observation-side substrate having a pixel electrode, and the electrolytic solution according to the potential between the electrodes. An electrochemical display element that performs display by oxidation-reduction reaction of the deposition material therein, the substrate on the non-observation side supplying current from a power supply bus to the pixel electrode through a driving transistor And a first insulating film formed so as to cover the driving transistor and the metal wiring, and the pixel electrode is formed on the first insulating film, The substrate is connected to the metal wiring through a contact hole provided in the first insulating film, and the non-observation side substrate is further formed on the pixel electrode so as to cover the contact hole. It is characterized by having an insulating film.

  According to the present invention, since the second insulating film is formed on the pixel electrode so as to cover the contact hole provided in the first insulating film, unevenness due to the contact hole occurs in the pixel electrode. Between the portion and the common electrode on the observation side, the current does not flow in the electrolyte due to the presence of the second insulating film, and the deposition / dissolution of the deposition material itself is not performed. Therefore, it is possible to avoid abnormal deposition of the deposition material at the uneven portions of the pixel electrode in repeated driving, and to avoid performance deterioration of the display element.

(A) is explanatory drawing which shows the pixel in a black display state while showing typically the schematic structure of 1 pixel of the display element of one Embodiment of this invention, (b) is in a white display state. It is explanatory drawing which shows this pixel. (A) is explanatory drawing which shows the equivalent circuit of 1 pixel of the said display element, (b) is a top view which shows the example of 1 structure of the pixel in the board | substrate of the non-observation side of the said display element. It is sectional drawing which shows the detailed structure of the said pixel. It is sectional drawing which shows the other structure of the said pixel. (A)-(c) is sectional drawing which shows the example of formation of the pixel electrode and 2nd insulating film in the said pixel. (A)-(c) is sectional drawing which shows the further example of formation of the said pixel electrode and said 2nd insulating film. (A)-(f) is a top view which shows each process until it forms a pixel electrode on the drive substrate of the said display element. 6 is a plan view showing a formation pattern of a second insulating film in Example 1. FIG. 6 is a plan view showing a formation pattern of a second insulating film in Example 2. FIG. (A) is a top view which shows the formation pattern of the 2nd insulating film of Example 3, (b) is a top view which shows the peripheral part of the pixel electrode of the display element of Example 3. FIG. It is a top view which shows the formation pattern of the 2nd insulating film of Example 4 and 5. FIG. It is explanatory drawing which shows the contact angle of two surfaces. (A) is a top view of the pixel in the board | substrate on the non-observation side of the display element of Example 6, Comprising: It is a top view in the state before forming a 2nd insulating film and a 2nd pixel electrode, (B) is a plan view in a state after forming the second insulating film and the second pixel electrode, and (c) is a cross-sectional view of the display element. (A) is a top view of the display element of Example 7, (b) is typical sectional drawing of the said display element. It is explanatory drawing which shows the effective pixel area of the display element of each Example and a comparative example. It is explanatory drawing which shows the generation | occurrence | production state of abnormal precipitation of Ag for every driving frequency of the display element of each Example and a comparative example. 3 is a plan view showing a region where Ag is abnormally precipitated in Example 1. FIG. 6 is a plan view showing a region where Ag is abnormally precipitated in Example 2. FIG. In Example 6, it is a top view which shows the area | region where Ag precipitates abnormally. 6 is a plan view showing a region where Ag is abnormally precipitated in Example 3. FIG. It is a top view which shows the area | region where Ag abnormally precipitates in Examples 4 and 5. It is a top view which shows the other structural example of the pixel in the board | substrate of the non-observation side.

  An embodiment of the present invention will be described below with reference to the drawings.

[Basic structure of display element]
FIGS. 1A and 1B are explanatory diagrams schematically showing a schematic configuration of one pixel of the display element 1 of the present embodiment. However, FIG. 1A shows a pixel in a black display state, and FIG. 1B shows a pixel in a white display state. The display element 1 is configured by an electrochemical display element called ED, and is configured by sealing an electrolytic solution 30 between an observation side substrate 10 and a non-observation side substrate 20. In the electrolytic solution 30, silver as a deposition material is dissolved, and silver ions 31 are present. The details of the electrolytic solution 30 will be described later.

  The observation-side substrate 10 includes a common substrate 11 made of, for example, a transparent glass substrate. A common electrode 12 (common electrode) common to the pixels 1a is formed on the common substrate 11. On the other hand, the non-observation side substrate 20 has a drive substrate 21 made of, for example, a transparent glass substrate. In addition, since the drive board | substrate 21 is arrange | positioned at the non-observation side, it does not need to be transparent. On the driving substrate 21, pixel electrodes 25 corresponding to the respective pixels 1a are formed. The substrates 10 and 20 are bonded to each other so that the common electrode 12 and the pixel electrode 25 are on the inner side (so as to face each other with the electrolytic solution 30 therebetween).

  Since the common electrode 12 is an observation side electrode, it is necessary to be transparent. For this reason, as the common electrode 12, a transparent electrode such as indium tin oxide (hereinafter referred to as ITO) is usually used. Here, in order to increase the etching resistance by the electrolytic solution 30, ITO is desirably crystalline. In the case of using amorphous ITO, it is necessary to anneal and crystallize at a temperature of 300 ° C. or higher. However, since no material that is damaged by heat is formed on the substrate 10 side on the observation side, the amorphous ITO is used. Thus, the common electrode 12 can be formed.

  On the other hand, the pixel electrode 25 is made of a material having a larger ionization tendency than the deposition material in the electrolytic solution 30. For example, when silver is used as the deposition material, the pixel electrode 25 is often made of amorphous ITO, which is a metal oxide. This is because the transistor (for example, TFT) formed on the non-observation side drive substrate 21 and the insulating film covering the transistor are damaged at a low temperature (usually sputtered) at about 200 ° C. on the insulating film. This is because patterning by photolithography is possible without damaging the transistor or the like. Thus, amorphous ITO is advantageous from the viewpoint of the film formation process of the pixel electrode 25, and the pixel electrode 25 can be easily formed by a general-purpose apparatus.

Next, the display principle of the display element 1 will be described.
In FIG. 1A, when the switch SW1 is closed, a negative voltage Vb equal to or higher than the threshold is applied to the pixel electrode 25 as the common voltage Vcom of the common electrode 12, and electrons are supplied from the common electrode 12 to the electrolyte 30. The common current Icom flows by being injected, and the silver ions 31 are reduced and the silver layer 32 is deposited at the position of the common electrode 12 facing the pixel electrode 25. When viewed from the common electrode 12 side, it looks black.

  On the other hand, in FIG. 1B, when the switch SW1 is similarly closed and a positive voltage Vw equal to or higher than the threshold is applied to the pixel electrode 25 as the common voltage Vcom of the common electrode 12, FIG. The silver layer 32 deposited in step 1 is oxidized into silver ions 31 and dispersed in the electrolyte 30. The state in which the silver layer 32 is changed to the silver ion 31 is transparent when viewed from the common electrode 12 side. Therefore, the electrolyte solution 30 is colored white, or a diffusion layer is provided on the pixel electrode 25. Looks white. In this way, it is possible to switch between white and black display.

  In FIGS. 1A and 1B, a voltage is applied to the pixel 1a of the display element 1 using the switch SW1, but if two thin film transistors (TFTs) are used per pixel as the switch SW1, each pixel 1a. Can be arranged in a matrix, and a so-called active matrix type display element 1 can be configured in which a voltage is applied to each pixel 1a to perform display.

[Detailed pixel configuration]
Next, a detailed configuration of one pixel of the display element 1 will be described.
2A is an explanatory diagram illustrating an equivalent circuit of the pixel 1a of the display element 1, and FIG. 2B is a plan view illustrating a configuration example of the pixel 1a on the non-observation side substrate 20 of the display element 1. FIG. FIG. In FIG. 2B, for the sake of convenience, illustration of a gate insulating film 22, an interlayer insulating film 24, and a pixel electrode 25 shown in FIG. 3 to be described later is omitted. For).

  In the pixel 1a, two thin film transistors Q1 and Q2 are formed. The thin film transistor Q1 is a selection transistor (switching transistor) for selecting the pixel 1a to be driven, and the thin film transistor Q2 is a drive transistor for driving the pixel 1a.

  The thin film transistor Q1 is driven by the signal of the gate bus Gm and applies the signal of the source bus Sn when turned on to the gate electrode of the thin film transistor Q2. The thin film transistor Q2 has a potential difference between the common potential Vcom and the drive potential Vdd by the power supply bus VDD when the gate potential is raised by the thin film transistor Q1, that is, the voltage Vb described with reference to FIGS. Vw is applied between the common electrode 12 and the pixel electrode 25 to pass a current through the electrolytic solution 30. Depending on the potential between the common electrode 12 and the pixel electrode 25, silver as a deposition material in the electrolytic solution 30 causes an oxidation-reduction reaction, and thereby the pixel 1a may be blackened or whitened. it can.

  Thus, since the display element 1 as the ED is a current-driven display element, a relatively large current instantaneously flows through each pixel 1a during driving. In order to prevent a voltage drop at this time, the power supply bus VDD needs to be thick. However, since the power supply bus VDD cannot be unnecessarily thickened in the width direction due to the balance with the pixel size, it is general that the power supply bus VDD is formed thicker.

  Next, the configuration of the non-observation side substrate 20 in the pixel 1a will be described in more detail. FIG. 3 is a cross-sectional view showing a detailed configuration of the pixel 1a. In FIG. 3, in order to facilitate the understanding of the description, a plurality of cut surfaces that are bent with respect to each other are schematically shown connected in one direction, and are not cross-sectional views when cut by a single surface. I refuse that first. This also applies to the sectional views appearing below.

  On the drive substrate 21, a scanning bus Gm and gate electrodes of the thin film transistors Q1 and Q2 are formed. The gate electrode of the thin film transistor Q1 is connected to the scanning bus Gm. A gate insulating film 22 is formed on the drive substrate 21 so as to cover the scanning bus Gm and each gate electrode.

  On the gate insulating film 22, the semiconductors of the thin film transistors Q1 and Q2 are formed by patterning, and the source bus Sn, the power supply bus VDD, the source / drain electrodes of the thin film transistors Q1 and Q2, and the metal wiring 23 are formed. One electrode of the source / drain electrodes of the thin film transistor Q1 is connected to the source bus Sn, and the other electrode is connected to the gate electrode of the thin film transistor Q2 through a contact hole 22a provided in the gate insulating film 22. Yes. One electrode of the source / drain electrodes of the thin film transistor Q2 is connected to the power supply bus VDD, and the other electrode is connected to the metal wiring 23. The other electrode may be formed integrally with the metal wiring 23.

  Then, an interlayer insulating film 24 (first insulating film) is formed so as to cover the semiconductors of the thin film transistors Q1 and Q2, the source bus Sn, the power supply bus VDD, the source / drain electrodes of the thin film transistors Q1 and Q2, and the metal wiring 23. A pixel electrode 25 (first pixel electrode) is formed on the interlayer insulating film 24. The pixel electrode 25 is connected to the metal wiring 23 through a contact hole 24 a provided in the interlayer insulating film 24. Therefore, when the thin film transistor Q2 is turned on, the current from the power supply bus VDD is supplied to the pixel electrode 25 via the thin film transistor Q2 and the metal wiring 23.

  An insulating film 26 (second insulating film) is formed on the pixel electrode 25 so as to cover the contact hole 24a (with a size larger than the contact hole 24a). A porous metal oxide electrode 27 (second pixel electrode) is formed so as to conduct in the pixel electrode 25 and the non-formation region 25a of the insulating film 26. Details (materials and formation method) of the insulating film 26 and the porous metal oxide electrode 27 will be described later. Instead of the porous metal oxide electrode 27, an electrode made of the same metal material (amorphous ITO) as the pixel electrode 25 may be formed as the second pixel electrode.

  Since the contact hole 24a provided in the interlayer insulating film 24 is a hole, the pixel electrode 25 has irregularities inside and outside the contact hole 24a. However, since the insulating film 26 is formed on at least the pixel electrode 25 so as to cover the contact hole 24a, the portion of the pixel electrode 25 where the irregularities due to the contact hole 24a are generated and the common electrode 12 on the observation side In the meantime, due to the presence of the insulating film 26, no current flows through the electrolytic solution 30, and silver deposition / dissolution itself is not performed. Therefore, it is possible to avoid abnormal precipitation of silver on the uneven portions of the pixel electrode 25 in repeated driving, and to avoid performance deterioration of the display element 1.

  In addition, since the insulating film 26 is formed so as to cover the contact hole 24a, the pixel electrode 25 is made of amorphous ITO having a higher ionization tendency than silver which is a deposition material in the electrolytic solution 30 as in the present embodiment. Even when configured, it is possible to prevent the pixel electrode 25 located in the contact hole 24 a and on the contact hole 24 a from being dissolved by the electrolytic solution 30. Therefore, by dissolving the pixel electrode 25 in the contact hole 24a, the current from the power supply bus VDD is not supplied to the pixel 1a, resulting in a defective pixel, which can reduce display defects.

[Other pixel configurations]
FIG. 4 is a cross-sectional view showing another configuration of the pixel 1a. As shown in the figure, the insulating film 26 may have an opening 26p and may be formed so as to cover a portion other than the region T having the same layer configuration in one pixel 1a. Note that the same layer structure means that the material, thickness, number of layers, and the like of each layer are the same. For example, in FIG. 4, each layer of the gate insulating film 22, the power supply bus VDD, the interlayer insulating film 24, and the pixel electrode 25 is laminated in this order with the same thickness inside the opening 26 p. Can be said to be the same.

  As shown in the figure, in the region T having the same layer structure, the pixel electrode 25 does not have irregularities, so that the insulating film covers the portion other than the region T in one pixel, that is, the portion where the irregularities occur. By forming 26, it is possible to avoid abnormal precipitation of silver in the uneven portion. Further, the region T is not covered with the insulating film 26 due to the presence of the opening 26p, and the pixel electrode 25 faces the common electrode 12 through the opening 26p. Therefore, the pixel electrode 25 is displayed by deposition / dissolution of silver. The aperture ratio can be ensured by contributing to the above.

  The porous metal oxide electrode 27 is formed by applying a porous ITO material on the pixel electrode 25 by, for example, an inkjet method, as in Example 5 described later. In the case of being formed with 26p, the insulating film 26 may also serve as a partition wall when the porous metal oxide electrode 27 is formed in the opening 26p. In this case, it is not necessary to separately provide a partition dedicated to the formation of the porous metal oxide electrode 27 when the display element 1 is manufactured, and patterning of the porous metal oxide electrode 27 for each pixel 1a is not necessary. The manufacturing process can be simplified.

  In the configuration of FIG. 4, the pixel electrode 25 is formed on the interlayer insulating film 24 so as to cover the thin film transistor Q2, which is a driving transistor, and the insulating film 26 is also formed on the pixel electrode 25 so as to cover the thin film transistor Q2. Is formed. The formation region of the thin film transistor Q2 has a structure in which the gate, source, and drain electrodes, the semiconductor, and the gate insulating film 22 are stacked. Therefore, the pixel electrode 25 in the upper layer of the thin film transistor Q2 is likely to be uneven. However, in addition to covering the contact hole 24a, the uneven portion of the pixel electrode 25 generated by the thin film transistor Q2 is covered with the insulating film 26, thereby avoiding abnormal precipitation of silver on the uneven portion in repeated driving, thereby preventing the display element. 1 performance degradation can be further avoided.

  Incidentally, FIGS. 5A to 5C are cross-sectional views showing examples of forming the pixel electrode 25 and the insulating film 26. 5A and 5C correspond to the configurations of FIGS. 3 and 4 described above, respectively. As shown in these drawings, the pixel electrode 25 is formed on a part of the surface of the interlayer insulating film 24 in one pixel 1a, and the insulating film 26 is formed on both the pixel electrode 25 and the interlayer insulating film 24. It may be. The insulating film 26 may be formed so as to cover only the portion where the contact hole 24a is formed, as shown in FIG. 5A, or the opening 26p may be formed as shown in FIG. It may be formed so as to cover only a relatively uneven region (for example, a region where the contact hole 24a and the thin film transistor Q1 are formed), or an opening 26p is formed as shown in FIG. The layer structure may be formed so as to cover a region other than the same region T (and may be formed so as to cover the thin film transistor Q2).

  FIGS. 6A to 6C are cross-sectional views showing further examples of forming the pixel electrode 25 and the insulating film 26. As shown in these drawings, the pixel electrode 25 may be formed on almost the entire surface of the interlayer insulating film 24 in one pixel 1a. Even in this case, the insulating film 26 formed on the pixel electrode 25 may be formed so as to cover only the portion where the contact hole 24a is formed, as shown in FIG. ), The opening 26p may be formed so as to cover a relatively large uneven area (for example, the formation area of the contact hole 24a and the thin film transistor Q1), as shown in FIG. As shown, the opening 26p may be formed so as to cover a region other than the region T having the same layer configuration (and may be formed so as to cover the thin film transistor Q2).

  That is, even when the pixel electrode 25 is formed smaller than one pixel as shown in FIGS. 5A to 5C, one pixel is used as shown in FIGS. 6A to 6C. On the other hand, even when the pixel electrode 25 is formed to be large, by adjusting the formation range of the insulating film 26 formed on the upper layer, a region that substantially functions as an electrode in the pixel electrode 25 (a region facing the common electrode 12). ) Can be reduced, and the flatness in that region can be improved.

[Electrolyte]
Next, the detail of the electrolyte solution 30 mentioned above is demonstrated.
The electrolytic solution 30 contains silver or a compound containing silver in the chemical structure, and silver ions are present in the electrolytic solution 30. Here, silver or a compound containing silver in the chemical structure is a general term for compounds such as silver oxide, silver sulfide, metallic silver, silver colloidal particles, silver halide, silver complex compounds, and silver ions. At this time, any state state species such as a solid state, a solubilized state in a liquid, or a gas state, and a charged state species such as neutral, anionic, and cationic are not particularly limited.

  The silver ion concentration contained in the electrolytic solution 30 is preferably 0.2 mol / kg ≦ [Ag] ≦ 2.0 mol / kg. When the silver ion concentration is less than 0.2 mol / kg, the driving speed is delayed due to a dilute silver solution. Conversely, when the silver ion concentration is greater than 2 mol / kg, the solubility deteriorates and precipitates during low-temperature storage. Tends to occur, which is disadvantageous.

  The electrolyte solution 30 preferably has a viscosity at 25 ° C. of 0.1 mPa · s or more and less than 100 mPa · s, and the amount of the polymer binder with respect to the solvent is preferably less than 10% by weight. Furthermore, the electrolytic solution 30 may be configured by selecting an organic solvent, an ionic liquid, a redox active substance, a supporting electrolyte, a complexing agent, a white scattering material, a polymer binder, and the like as necessary.

[Second insulating film]
Next, details of the insulating film 26 as the second insulating film will be described.
As the material of the insulating film 26, a material having good insulating properties and not deteriorating the semiconductor material of the switching elements (thin film transistors Q1 and Q2) at the time of film formation can be used. For example, as the insulating film 26, inorganic oxides such as silicon oxide, inorganic nitrides such as silicon nitride, or polyimide, polyamide, polyester, polyacrylate, photo radical polymerization type, photo cation polymerization type photo curable resin, An organic compound such as a copolymer containing an acrylonitrile component, polyvinylphenol, polyvinyl alcohol, a novolac resin, cyanoethyl pullulan, or parylene is applicable. Further, the insulating film 26 may be formed by superposing a plurality of layers of an organic material and an inorganic material.

  As a method of forming the insulating film 26, for example, there are a method of patterning into a predetermined shape after coating the entire surface, and a method of patterning and forming directly in a predetermined shape. In the case of the former method, it is desirable to form a spin coat film using the above-mentioned photocurable resin, leave the pattern slightly larger than the shape of the contact hole 24a through the steps of pattern exposure and development. If the formation pattern of the insulating film 26 is too large, the contact area between the porous metal oxide electrode 27 and the pixel electrode 25 is reduced and the resistance during conduction is increased. Conversely, if the formation pattern is too small, the contact hole 24 a The protective function and the function of preventing abnormal precipitation of silver are lost. Note that the coating method of the film forming material is not limited to the above-described spin coating, and may be spray coating, slit coating, dipping coating, or the like. Also, a dry film resist can be laminated and used. On the other hand, in the case of the latter method, it is possible to apply coating methods, such as an inkjet method, a dispenser method, and screen printing.

[Porous metal oxide electrode]
Next, details of the porous metal oxide electrode 27 will be described.
In general, as the main component of the fine particles constituting the electrode having a porous structure, metals such as Cu, Al, Ag and Pd, metal oxides such as ITO, SnO ₂ , TiO ₂ and ZnO, carbon nanotubes, glassy carbon, Examples of the carbon electrode include diamond-like carbon and nitrogen-containing carbon. From the viewpoint of durability of the pixel electrode 25, the porous metal oxide electrode 27 is particularly preferably a metal oxide such as ITO, SnO ₂ and ZnO. Is preferably selected from.

  Here, the “porous structure” has a structure in which ionic species contained in the electrolytic solution can move inside a so-called nanoporous structure in which an infinite number of nanometer-sized pores exist in the electrode. Say. Therefore, the average particle diameter of the fine particles constituting the porous metal oxide electrode 27 is preferably about 5 nm to 30 nm. As the fine particles, those having an arbitrary shape such as an indeterminate shape, a needle shape, a spherical shape and the like can be used.

  By providing the porous metal oxide electrode 27 having such a porous structure, silver as a deposition material is supported in the porous metal oxide electrode 27, and current from the power supply bus VDD is supplied to the pixel in this portion. Since it is supplied via the electrode 25, the oxidation-reduction reaction speed (driving speed) at the time of current supply can be increased.

  As the method for forming the porous metal oxide electrode 27, there are a method of patterning into a predetermined shape after coating the entire surface, and a method of patterning and forming directly in a predetermined shape, as in the case of the insulating film 26. In the embodiment, the latter method is particularly employed. As the latter method, a method of flying a material without contact with the substrate 20 such as an ink jet method or a dispenser method is desirable. In this case, the insulating film 26 serving as a bank is used as a separator, and the insulating film 26 is subjected to a liquid repellent treatment, whereby the porous metal oxide can be satisfactorily patterned for each pixel.

〔Example〕
Next, examples of the display element 1 of the present embodiment will be described as Examples 1 to 7 with reference to FIG. Moreover, Comparative Example 1 is also shown for comparison with Examples 1-7.

Example 1
<Preparation of electrolyte>
In 2.5 g of dimethyl sulfoxide (hereinafter referred to as DMSO), 90 mg of sodium iodide and 75 mg of silver iodide were added and completely dissolved. The solution was stirred for 1 hour to form a solution. To this solution, polyethylene glycol having an average molecular weight of about 100,000 (hereinafter referred to as PEG) and titanium oxide powder were added and mixed to prepare a gel-like white electrolytic solution 30. At this time, PEG was 5 wt% of the electrolytic solution 30, and the titanium oxide powder was 30 wt% of the electrolytic solution 30.

<Preparation of the substrate on the observation side>
A glass substrate was used as the common substrate 11. Then, on the common substrate 11, a crystalline ITO that is a transparent conductive film is formed to a thickness of 150 nm by a sputtering method, and a common electrode 12 (common to each pixel 1a) is formed on the entire surface. The substrate 10 on the observation side was produced.

<Preparation of non-observation side substrate>
[Step 1: Formation of base]
A glass substrate is used as the driving substrate 21, and a TFT array having two TFTs (thin film transistors Q 1 and Q 2) per pixel is formed on the driving substrate 21 in a two-dimensional matrix form so as to cover the TFT array. An interlayer insulating layer 24 was formed, and a thin pixel electrode 25 was formed on the interlayer insulating film 24 using amorphous ITO corresponding to each pixel 1a. The substrate formed up to the pixel electrode 25 on the drive substrate 21 is referred to as the base of the substrate 20 here.

  Note that the process up to the production of the base, that is, the formation of the pixel electrode 25 can be performed by a known technique. For example, it is possible to form up to the pixel electrode 25 by a technique widely known for ECD, which is the same current drive type element as the display element 1, an organic EL display element, and the like.

  Here, for the purpose of clarifying the positional relationship between an insulating film 26, which will be described later, and the electrode pattern and wiring pattern below it, the description up to the formation of the pixel electrode 25 will be supplemented with reference to the drawings. FIG. 7A to FIG. 7F are plan views showing each process until the pixel electrode 25 is formed on the drive substrate 21.

  First, the scanning bus Gm and the gate electrodes G1 and G2 of the thin film transistors Q1 and Q2 are formed on the driving substrate 21 (see FIG. 7A). Next, a gate insulating film 22 is formed on almost the entire surface of the drive substrate 21 so as to cover the scanning bus Gm and the gate electrodes G1 and G2, and a contact hole 22a is formed in the gate insulating film 22 (FIG. 7B). )reference). In FIG. 7B, when the gate insulating film 22 is illustrated, the vertical relationship between layers is complicated. For convenience, the gate insulating film 22 is not illustrated and only the outer edge of the contact hole 22a is indicated by a broken line. Is shown.

  Subsequently, the semiconductors A1 and A2 of the thin film transistors Q1 and Q2 are patterned and formed at predetermined positions on the gate insulating film 22 (see FIG. 7C), and further the source bus Sn and the source / drain electrodes of the thin film transistor Q1 are formed. The electrode E11 functioning as one and the electrode E12 functioning as the other, the electrode E21 functioning as one of the source / drain electrodes of the thin film transistor Q2, the electrode E22 functioning as the other, the metal wiring 23, and the power supply bus VDD are formed (FIG. 7 ( d)). At this time, the electrode E11 of the thin film transistor Q1 is formed connected to the source bus Sn, and the electrode E12 of the thin film transistor Q1 is formed connected to the gate electrode G2 of the thin film transistor Q2 through the contact hole 22a of the gate insulating film 22. Further, the electrode E21 of the thin film transistor Q2 is formed connected to the power supply bus VDD, and the electrode E22 of the thin film transistor Q2 is formed connected to the metal wiring 23. The electrode E22 and the metal wiring 23 may be integrally formed.

  Next, an interlayer insulating film 24 is formed so as to cover the electrode pattern and the wiring pattern formed in FIG. 7D, and a contact hole 24a is formed in the interlayer insulating film 24 (see FIG. 7E). In FIG. 7E, when the interlayer insulating film 24 is illustrated, the illustration of the vertical relationship of the layers is complicated. For convenience, the interlayer insulating film 24 is omitted and only the outer edge of the contact hole 24a is indicated by a broken line. Is shown.

  Then, the pixel electrode 25 is formed on the interlayer insulating film 24 and inside the contact hole 24a (see FIG. 7F). Thus, the pixel electrode 25 is connected to the metal wiring 23 through the contact hole 24a. At this time, the pixel electrode 25 is formed over the entire pixel so as to cover the thin film transistors Q1 and Q2 and the stepped portion C shown in FIG.

  Here, the stepped portion C is a portion where a step is formed when the power supply bus VDD and the gate electrode G2 of the thin film transistor Q2 intersect via the interlayer insulating film 24. Note that an auxiliary capacitor (also referred to as Cs) is formed at a portion where the power supply bus VDD and the gate electrode G2 intersect via the interlayer insulating film 24.

[Step 2: Formation of second insulating film]
Next, an insulating film 26 as a second insulating film was formed on the base pixel electrode 25 formed in Step 1 so as to cover only the contact hole 24a. More specifically, a coating type photosensitive acrylic resin (JSR, model number: PC403) was formed on the base at a spin coat of 3000 rpm. The thickness of the resin was 0.5 μm. Subsequently, using a predetermined photomask, exposure was performed with an irradiation light amount of 200 mJ / cm ² , and then development and baking were performed. The development was performed for 1 minute with a predetermined developer TMAH (tetramethylammonium hydroxide) 0.238 wt% aqueous solution. Firing was performed at 220 ° C. for 1 hour. FIG. 8 shows a formation pattern of the insulating film 26 (coating photosensitive acrylic resin) at this time. In FIG. 8, only the edge of the pixel electrode 25 is indicated by a two-dot chain line in order to clarify the positional relationship between the insulating film 26 and the lower layer. The same applies to the following drawings.

[Step 3: Application of porous metal oxide electrode material]
Next, porous ITO was applied to cover the pixel electrode 25 and the insulating film 26 on the pixel electrode 25 to form a porous ITO film having an average film thickness of 0.5 μm. For the application, a spray application apparatus (STS600 manufactured by YIDY MECATOR SOLUTIONS Co., Ltd.) was used. The coating conditions at this time are as follows.
・ Nozzle model number of spray gun: Atmax nozzle AM25 (manufactured by Atmax Co., Ltd.)
・ Atomization air: Nitrogen gas (N ₂ )
・ Flow rate of atomizing air: 8L / min
-Coating liquid (ITO ink) Model number: X806CN27S (manufactured by Sumitomo Metal Mining Co., Ltd.)
・ Coating liquid flow rate: 7mL / min
・ Nozzle discharge speed: 300 mm / second ・ Nozzle-drive substrate distance: 60 mm

[Step 4: Patterning of porous metal oxide electrode]
The porous ITO film formed in step 3 was patterned by an existing photolithography technique to form a porous metal oxide electrode 27. Details of patterning are as follows.

A resist material (model number: OFPR800LB) manufactured by Tokyo Ohka Kogyo Co., Ltd. was applied at a spin coating condition of 1000 rpm, and then dried at 80 ° C. for 5 minutes on a hot plate. Then, using a photomask of a predetermined size, pattern exposure was performed with an exposure amount of 120 mJ / cm ² , and then development was performed with a predetermined developer (TMAH (tetramethylammonium hydroxide) 2.38 wt% aqueous solution) for 120 seconds. Thereafter, etching was performed for 200 seconds using an etching ferric salt solution manufactured by Hayashi Pure Chemical Industries. The resist material was peeled off by using a NaOH 2 wt% aqueous solution, followed by drying in an oven at 80 ° C. for 1 hour after peeling.

<Application of sealant>
Next, a thermosetting olefin-based sealant was applied to the peripheral edge of the substrate 20 on which the porous metal oxide electrode 27 was formed, using a dispenser, except for the inlet for the electrolytic solution 30. Then, by arranging a 25 μm bead spacer in the sealant, the gap between the substrates 10 and 20 was set to 25 μm.

<Board bonding>
After the substrates 10 and 20 were bonded to each other through the above-described sealing agent, the sealing agent was cured by heating and pressing to produce an empty cell with an empty interior. At this time, in order to keep the distance between the substrates 10 and 20 constant, spherical spacers with a diameter of 25 μm were arranged on the common substrate 11 at about 50 pieces / mm ² . Subsequently, the electrolytic solution 30 is injected into the empty cell using a vacuum injection method used in the manufacture of a liquid crystal panel, and the injection port of the electrolytic solution 30 is sealed with an ultraviolet curable adhesive. The display element 1 of Example 1 was obtained.

(Example 2)
FIG. 9 is a plan view showing a formation pattern of the insulating film 26 of the second embodiment. In Example 2, in [Step 2: Formation of second insulating film] of Example 1, in addition to the contact hole 24a, the insulating film 26 is covered with the pixel electrode 25 so as to further cover the two thin film transistors Q1 and Q2. A display element 1 was produced in the same manner as in Example 1 except that it was formed above.

(Example 3)
FIG. 10A is a plan view showing a formation pattern of the insulating film 26 of Example 3, and FIG. 10B is a plan view showing a peripheral edge 25b of the pixel electrode 25. FIG. In Example 3, in [Step 2: Formation of second insulating film] of Example 1, in addition to the contact hole 24a, the two thin film transistors Q1 and Q2 and the peripheral portion 25b of the pixel electrode 25 are further covered. The display element 1 was produced in the same manner as in Example 1 except that the insulating film 26 was formed on the pixel electrode 25. In Example 3, the insulating film 26 has a shape covering at least the peripheral edge 25b of the pixel electrode 25. As a result, the insulating film 26 has the opening 26p, and the pixel electrode 25 is formed in a region other than the opening 26p. Will be covered.

Example 4
FIG. 11 is a plan view showing a formation pattern of the insulating film 26 of the fourth embodiment. In Example 4, in [Step 2: Formation of second insulating film] of Example 1, in addition to the contact hole 24a, two thin film transistors Q1 and Q2, a peripheral portion 25b of the pixel electrode 25, and a stepped portion C are used. The display element 1 was produced by the same method as in Example 1 except that the insulating film 26 was formed on the pixel electrode 25 so as to further cover the film.

  In the fourth embodiment, as in the third embodiment, since the insulating film 26 has a shape covering at least the peripheral edge portion 25b of the pixel electrode 25, the insulating film 26 has an opening 26p narrower than that in the third embodiment. Therefore, the pixel electrode 25 is covered with a portion other than the opening 26p.

(Example 5)
In Example 5, the display element 1 was produced in the same manner as in Example 4 except that part of the process of <production of the non-observation side substrate> in Example 4 was changed as follows. Example 5 is the same as Example 4 except that the formation method of the insulating film 26 and the formation method of the porous metal oxide electrode 27 are different. That is, the shape (formation range) of the insulating film 26 is the same as that of the fourth embodiment, and covers the contact hole 24a, the two thin film transistors Q1 and Q2, the peripheral portion 25b of the pixel electrode 25, and the step portion C. An insulating film 26 is formed on the pixel electrode 25 (see FIG. 11).

<Preparation of non-observation side substrate>
[Step 2: Formation of second insulating film]
A coating type photosensitive acrylic resin (JSR, model number: PC403) was formed on the base pixel electrode 25 formed in step 1 by spin coating at 700 rpm. The thickness of the resin was 2.0 μm. Subsequently, using a predetermined photomask, exposure was performed with an irradiation light amount of 200 mJ / cm ² , and then development and baking were performed. Development was performed for 2 minutes with a 0.238 wt% aqueous solution of a predetermined developer TMAH (tetramethylammonium hydroxide). Firing was performed at 220 ° C. for 1 hour.

  In Example 5, the degree of non-affinity (ease of repelling) of the liquid material (the porous ITO to be applied next) with respect to the surface of the insulating film 26 depends on the non-formation region (pixels) of the insulating film 26 on the substrate. Surface treatment is performed on at least one of the surface of the insulating film 26 and the non-forming region of the insulating film 26 so as to be higher than the non-forming region on the electrode 25 and the surface of the interlayer insulating film 24. preferable. Even if a large amount of liquid material is ejected compared to the thickness of the thin film layer (porous metal oxide electrode 27) to form the porous metal oxide electrode 27 next by such surface treatment, the liquid material The liquid material can be filled only in a predetermined region of each pixel 1a, that is, a region where the insulating film 26 is not formed. That is, the insulating film 26 can function as a bank.

Here, as the above-described surface treatment, for example, a gas containing fluorine or a fluorine compound is used as an introduction gas, and the plasma irradiation is performed in a reduced pressure atmosphere or an atmospheric pressure atmosphere containing a fluorine compound and oxygen or an atmospheric pressure. Plasma treatment is mentioned. Examples of the gas containing fluorine or a fluorine compound include CF ₄ , SF ₆ , and CHF ₃ . In Example 5, CF ₄ plasma treatment (pressure: 5 Pa, output: 5 W, CF ₄ flow rate: 7 sccm, time: 1 minute) is performed, and the contact angle between the insulating film 26 and the liquid material (porous ITO material) is about The angle was 60 °.

  The contact angle refers to an angle α (°) between the surface S and the surface L at the contact point between the solid surface S and the liquid surface L, as shown in FIG. The larger the contact angle α, the higher the non-affinity of the liquid with respect to the solid. In order to surely obtain the effect of the surface treatment described above, the contact angle of the liquid material (porous ITO material) with respect to the surface of the insulating film 26 is set to 50 ° or more, and the contact angle with respect to the non-formation region of the insulating film 26 is set to 20 °. The following is preferable.

[Step 3: Application of porous metal oxide electrode material]
Porous ITO, which is a liquid material, is dropped into the opening 26p of the insulating film 26 formed in step 2 by an inkjet method. The ejection amount in the ink jet method is set to an amount such that a desired thickness is obtained when the volume is reduced by the heat treatment after the application of porous ITO. In addition, you may make it become desired thickness by discharging porous ITO again after drying, and performing an overlay process.

  In Example 5, the thin film layer (porous metal oxide electrode 27) is defined by defining the size (height, width) of the insulating film 26 with respect to the size of the liquid material droplets to be discharged. Even when a large amount of liquid material is ejected compared to the thickness of the liquid material, the liquid material does not overflow over the insulating film 26, and the liquid material is filled in a predetermined region. In the case where the liquid material is a material containing a solvent, the volume of the liquid material is reduced by removing the solvent component by performing heat treatment and / or pressure reduction treatment after filling the liquid material, and the insulating film 26 is not formed. A thin film layer is formed in the region. At this time, the surface of the non-formation region of the insulating film 26, that is, the substrate surface is surface-treated so as to exhibit affinity (lyophilicity) as described above, and thus the thin film layer is suitably adhered.

  The ink jet method may be either a piezo jet method or a method of discharging by the generation of bubbles due to heat, but the piezo jet method is preferred because there is no change in the quality of the fluid due to heating. In Example 5, a porous ITO with a film thickness of 1.2 μm was formed using an inkjet apparatus having a piezo head KM512M manufactured by Konica Minolta IJ Co., Ltd.

  In Example 5, the insulating film 26 becomes a bank, and the porous metal oxide electrode 27 is separated by the insulating film 26 simultaneously with the formation of the porous metal oxide electrode 27. Therefore, [Step 4: [Pattern Formation of Porous Metal Oxide Electrode] is unnecessary.

(Example 6)
13A and 13B are plan views of the pixel 1a on the non-observation side substrate 20 of the display element 1 of Example 6, and FIG. 13A shows the insulating film 26 and the porous metal oxide. FIG. 13B shows a plan view of the state after forming the insulating film 26 and the porous metal oxide electrode 27. FIG. 13A and 13B, the gate insulating film 22 and the interlayer insulating film 24 are not shown for convenience. FIG. 13C is a cross-sectional view of the display element 1 of Example 6.

  In the display element 1 of Example 6, the material and thickness (height) of the insulating film 26 are changed, and the insulating film 26 has a function of a spacer for controlling the distance (gap) between the substrates. These are the same as in Example 1. Therefore, in Example 6, the display element 1 was manufactured by changing a part of the process of <Manufacturing the non-observation side substrate> in Example 1 as follows.

  In Example 6, as shown in FIG. 13A, the pixel electrode 25 is formed so as to cover the contact hole 24a and the power supply bus VDD that forms the auxiliary capacitance, and above the thin film transistors Q1 and Q2. Is not formed. Further, it is assumed that the porous metal oxide electrode 27 is formed on the pixel electrode 25 that covers the power supply bus VDD that forms the auxiliary capacitance.

<Preparation of non-observation side substrate>
[Step 2: Formation of second insulating film]
On the base pixel electrode 25 formed in the step 1, an epoxy negative photosensitive dry film resist having a thickness of 25 μm is used with a laminator at a temperature of 50 ° C., a pressure of 0.4 MPa, and a speed of 1 m / min. Laminated. Next, ultraviolet light of 400 mJ / cm ² was irradiated through a photomask on which a cylindrical pattern was formed with a parallel light exposure machine, followed by heat treatment on an 80 ° C. hot plate for 5 minutes. After heat treatment, develop with propylene glycol monomethyl ether acetate (PGMEA) solution, remove the resist material not irradiated with ultraviolet rays, rinse with isopropyl alcohol (IPA) solution, and then dry the solution As a result, a columnar structure having a height of 25 μm was obtained as the insulating film 26. The size of the columnar structure was larger than the contact hole size (10 μm square), and a 30 μm square column was formed.

<Board bonding>
After the substrates 10 and 20 were bonded together via a sealing agent, the sealing agent was cured by heating and pressing to produce an empty cell having an empty interior. At this time, a spherical spacer for keeping the distance between the substrates 10 and 20 constant was not arranged, and the distance between the substrates 10 and 20 was kept constant by the insulating film 26. Then, using the vacuum injection method, the electrolytic solution 30 was injected into the empty cell, and the injection port of the electrolytic solution 30 was sealed with an ultraviolet curable adhesive to obtain the display element 1 of Example 6. .

(Example 7)
FIG. 14A is a plan view of the display element 1 of the seventh embodiment, and FIG. 14B is a schematic cross-sectional view of the display element 1 of the seventh embodiment. In FIG. 14A, the gate insulating film 22, the interlayer insulating film 24, the pixel electrode 25, the common substrate 11 and the common electrode 12 of the observation-side substrate 10 are omitted for convenience. In FIG. 14B, the gate insulating film 22, the interlayer insulating film 24, the thin film transistors Q1 and Q2, etc. are not shown for the sake of convenience. The display element 1 of Example 7 is the same as Example 5 except that the partition wall 13 is provided on the substrate 10 side and the shape of the opening 26p of the insulating film 26 on the substrate 20 side is circular. Only the steps different from those in Example 5 are shown below.

<Preparation of the substrate on the observation side>
A glass substrate was used as the common substrate 11. Then, crystalline ITO, which is a transparent conductive film, was formed on the common substrate 11 to a thickness of 150 nm by a sputtering method, and the common electrode 12 was formed by photolithography. Further, a grid-like partition wall 13 was formed on the common electrode 12 with a line width of 5 μm and a height of 15 μm, and the substrate 10 on the observation side was manufactured.

  Here, as a material which comprises the partition part 13, materials, such as a thermoplastic resin, a thermosetting resin, and a photocurable resin, can be used. The partition wall 13 may be formed by, for example, (1) applying a photosensitive resin composition on a substrate by a spin coating method, a slit coating method, or the like, and forming a desired pattern through an exposure / development process. (2) A method in which a non-photosensitive resin composition is formed on a substrate, a resist pattern is formed by using a photo process or a printing process, and then the resin composition is removed by a sandblast etching method. 3) There is a method of printing the pattern of the partition wall 13 directly by a direct screen printing method. What is necessary is just to select the material to be used suitably according to the formation method of the partition part 13.

<Preparation of non-observation side substrate>
[Step 2: Formation of second insulating film]
The insulating film 26 was formed under the same conditions as in Example 5 except that the shape of the opening 26p was circular.

<Board bonding>
The substrates 10 and 20 are bonded together with a sealant so that the pixel electrode 25 faces the common electrode 12 at a position other than the partition wall 13 through the circular opening 26p of the insulating film 26, and then heated and pressed. Then, the sealing agent was cured, and an empty cell was produced. Then, using the vacuum injection method, the electrolytic solution 30 was injected into the empty cell, and the injection port of the electrolytic solution 30 was sealed with an ultraviolet curable adhesive to obtain the display element 1 of Example 7. .

(Comparative Example 1)
In Comparative Example 1, a part of the process of <Preparation of Non-Observing Side Substrate> described in Example 1, that is, [Step 2: Formation of second insulating film] is omitted, and a display element is manufactured. These are the same as in Example 1.

[Drive inspection]
Next, a driving test was performed using the display elements of Examples 1 to 7 and Comparative Example 1. The inspection procedure is as follows.

  In Examples 1 to 7 and Comparative Example 1, the pixel pitch of each display element was 0.2 mm, and the effective pixel area R was 70 mm × 50 mm as shown in FIG. Therefore, the number of pixels in the effective pixel area R is (70 / 0.2) × (50 / 0.2) = 350 × 250 = 87500. Further, here, the effective pixel area R is divided into eight and the following inspection is performed. Therefore, the number of inspection pixels per area is 87500 / 8≈10000.

  First, voltage application and non-application were repeated for all pixels in each area, and white / black display was alternately repeated. Note that black display by voltage application was performed so that the contrast was 10. Note that the contrast 10 indicates that the luminous reflectance (Y value) ratio between white and black is 10: 1. At this time, black display is performed by applying a voltage of +1.2 V to the pixel electrode 25 with respect to the common electrode 12 for 1200 msec, and white display is a voltage of −1.2 V to the pixel electrode 25 with respect to the common electrode 12. Was applied by applying 2000 msec. During continuous driving, a waiting time of 1000 msec was inserted between the black application pulse and the white application pulse.

  Next, when the number of driving times (the number of black display times) reached 1000 times, the display element was disassembled and the electrolytic solution 30 was removed. Then, 20 × 20 = 400 pixels were observed with a microscope on the non-observation side substrate 20 for each area, and the presence or absence of abnormal precipitation of Ag was examined. At this time, precipitation of Ag having a size of φ5 μm or more was regarded as abnormal precipitation. Such treatment was performed every time the number of driving times reached 5000 times, 10,000 times, 50,000 times, and 100,000 times until the abnormal precipitation of Ag was confirmed.

  FIG. 16 shows the occurrence of abnormal precipitation of Ag for each number of driving times of the display elements of Examples 1 to 7 and Comparative Example 1.

  In the comparative example, abnormal deposition of Ag was observed in the contact hole 24a of the interlayer insulating film 24 at the time of driving 1000 times. This is thought to be because, in the contact hole 24a in which the pixel electrode 25 is uneven, the reaction of depositing Ag when applying a voltage is less likely to occur compared to the surrounding flat portion. In other words, when the observation side is displayed in black, since the precipitation of Ag on the observation side is slow, the Ag that has precipitated on the non-observation side remains without being completely dissolved. Then, when the observation side is displayed in white, a sufficient reaction to completely dissolve the Ag precipitated on the observation side occurs, and therefore, precipitation of Ag occurs in addition to the remaining Ag on the non-observation side. By repeating such a process, Ag deposited on the non-observation side gradually increases and is considered to be observed as abnormal precipitation.

  On the other hand, in each of Examples 1 to 7, since the insulating film 26 covered at least the contact hole 24a, abnormal precipitation of Ag in the contact hole 24a was not confirmed at least when the driving was performed 1000 times. . Therefore, according to the display elements of Examples 1 to 7, it can be said that the abnormal precipitation of Ag in the contact hole 24a in the repeated driving can be avoided and the performance deterioration of the display element can be avoided.

  In Example 1, abnormal deposition of Ag was confirmed in the region X1 (see FIG. 17) of the pixel electrode 25 located above the thin film transistors Q1 and Q2 at the time of driving 5000 times. This is because the unevenness of the thin film transistors Q1 and Q2 causes unevenness in the pixel electrode 25 in the region X1, and the reaction for depositing Ag in the unevenness portion is relatively less likely to occur than in the surrounding flat portion. This is probably because of this.

  However, as in Examples 2 to 7, the insulating film 26 is formed on the pixel electrode 25 so as to further cover the thin film transistors Q1 and Q2, thereby avoiding abnormal precipitation of Ag in the region X1, and It can be seen that performance degradation can be further avoided.

  The interlayer insulating film 24 has a flattening function to reduce the unevenness of the thin film transistors Q1 and Q2 formed in the lower layer, but it is difficult to completely flatten, and some unevenness remains. As a result, the pixel electrode 25 is uneven. However, it can be said that by providing the insulating film 26 as in Examples 2 to 7, abnormal precipitation of Ag due to unevenness that cannot be removed by the interlayer insulating film 24 can be avoided, and performance deterioration of the display element can be avoided. it can.

  In Examples 2 and 6, abnormal deposition of Ag was observed in the regions X2 and X3 (refer to FIG. 18) and the region X4 (refer to FIG. 19) in the peripheral portion of the pixel electrode 25 after 10,000 times of continuous driving. It was done. This is because, in the regions X2 to X4, the pixel electrode 25 is uneven due to the step with the wiring electrode (power supply bus VDD, scanning bus Gm), and the reaction of depositing Ag in this uneven portion is more than that of other flat portions. This is thought to be relatively difficult to occur.

  However, the abnormal deposition of Ag in the regions X2 to X4 can be avoided by forming the insulating film 26 so as to cover the peripheral edge 25b of the pixel electrode 25 as in the third to fifth and seventh embodiments. It can be seen that the performance deterioration of the display element can be further avoided.

  In Example 3, after the continuous driving of 50,000 times, the region X5 (see FIG. 20, step), which is an uneven portion of the pixel electrode 25 due to the electrode for Cs formation (gate electrode G2) and wiring (power supply bus VDD) Abnormal precipitation of Ag was observed in part C). However, as shown in Examples 4, 5, and 7, by forming the insulating film 26 on the pixel electrode 25 so as to cover the stepped portion C, abnormal precipitation of Ag in the region X5 can be avoided, and the display element It can be seen that further performance degradation can be avoided.

  Furthermore, in Examples 4 and 5, abnormal Ag deposition occurred in the corner X6 (see FIG. 21) of the opening 26p of the insulating film 26 after 100,000 times of continuous driving. This is because the pixel electrode 25 is not uneven in the opening 26p of the insulating film 26, but the Ag precipitation reaction is slightly less likely to occur in the corner portion X6 of the opening 26p than in other portions of the opening 26p. This is probably because of this.

  In this regard, in Example 7 in which the opening 26p of the insulating film 26 was circular, there was a place where abnormal precipitation of Ag was locally observed even after continuous driving 100,000 times. This is presumably because Ag precipitation occurs in the same way at any position of the opening 26p. Therefore, it can be seen that by making the opening 26p circular, abnormal precipitation of Ag at the corner portion X6 can be avoided, and further performance deterioration of the display element can be avoided. Needless to say, after the opening 26p is formed in a quadrangular shape, the corner X6 is rounded by etching or the like, so that the same effect as described above can be obtained.

  The evaluation based on the number of times of continuous driving this time is an index for relatively evaluating the manufactured display element. Further, the number of times of continuous driving described above varies depending on the electrolytic solution 30 and other constituent materials, and does not determine practicality.

  In this embodiment, the power supply bus VDD and the source / drain electrode layers of the thin film transistors Q1 and Q2 are formed on the same surface. However, as shown in FIG. 22, the power supply bus VDD is connected to the thin film transistors Q1 and Q2. Even when it is formed on the same surface as the gate electrode layer, the same effect as that of the present embodiment can be obtained by covering the part where the pixel electrode is uneven by the insulating film 26.

  The electrochemical display element of the present invention can be expressed as follows, and has the following effects.

  In the electrochemical display element of the present invention, an electrolytic solution is sealed between an observation-side substrate having a common electrode and a non-observation-side substrate having a pixel electrode, and the electrolytic solution according to the potential between the electrodes. An electrochemical display element that performs display by oxidation-reduction reaction of the deposition material therein, the substrate on the non-observation side supplying current from a power supply bus to the pixel electrode through a driving transistor And a first insulating film formed so as to cover the driving transistor and the metal wiring, and the pixel electrode is formed on the first insulating film, The substrate is connected to the metal wiring through a contact hole provided in the first insulating film, and the non-observation side substrate is further formed on the pixel electrode so as to cover the contact hole. It is characterized by having an insulating film.

  According to the above configuration, in the non-observation side substrate, the current from the power supply bus is supplied to the pixel electrode via the drive transistor and the metal wiring. Therefore, a current corresponding to the potential between the common electrode on the observation side and the pixel electrode on the non-observation side flows through the electrolytic solution, and on the electrode side serving as the negative electrode, a deposition material (for example, silver) in the electrolytic solution by a reduction reaction The deposition material is dissolved by the oxidation reaction on the electrode side that becomes the positive electrode. By such deposition / dissolution of the deposition material, black / white display and switching thereof can be performed.

  The drive transistor and the metal wiring are covered with a first insulating film, and the pixel electrode is connected to the metal wiring through a contact hole provided in the first insulating film. The contact hole is a hole, and a level difference (unevenness) occurs at that portion. Therefore, unevenness occurs in the pixel electrode inside and outside the contact hole. However, since the second insulating film is formed on the pixel electrode so as to cover the contact hole, between the portion of the pixel electrode where unevenness due to the contact hole is generated and the common electrode on the observation side, Due to the presence of the second insulating film, no current flows through the electrolytic solution, and deposition / dissolution of the deposition material itself is not performed. Therefore, it is possible to avoid abnormal deposition of the deposition material at the uneven portions of the pixel electrode in repeated driving, and to avoid performance deterioration of the display element.

  In the electrochemical display element of the present invention, the pixel electrode is formed on the first insulating film so as to cover the driving transistor, and the second insulating film covers the driving transistor. It is desirable that it be formed on the pixel electrode.

  The formation region of the driving transistor has a structure in which the gate, source, and drain electrodes, the semiconductor, and the insulating film (gate insulating film) are stacked. Therefore, when the pixel electrode is formed so as to cover the driving transistor, the pixel electrode Concavities and convexities occur on the surface. Therefore, a second insulating film is also formed on the pixel electrode so as to cover the driving transistor, and the uneven portion of the pixel electrode due to the driving transistor is covered with the second insulating film, whereby the unevenness portion in the repeated driving is degenerated. It is possible to avoid the abnormal deposition of the position material and further avoid the performance deterioration of the display element.

  In the electrochemical display element of the present invention, the non-observation side substrate further includes a selection transistor for selecting a pixel driven by the driving transistor, and the pixel electrode covers the selection transistor. It is preferable that the second insulating film is formed on the pixel electrode so as to cover the selection transistor.

  Similarly to the drive transistor, the selection transistor formation region has a structure in which gate, source, and drain electrodes, a semiconductor, and an insulating film (gate insulating film) are stacked. Therefore, a pixel electrode is formed to cover the selection transistor. As a result, the pixel electrode is uneven. Therefore, a second insulating film is formed on the pixel electrode so as to cover the selection transistor, and the uneven portion due to the selection transistor of the pixel electrode is covered with the second insulating film, so that the deposition at the uneven portion in repeated driving is performed. Abnormal deposition of the material can be avoided, and the performance deterioration of the display element can be further avoided.

  In the electrochemical display element of the present invention, it is preferable that the second insulating film is formed so as to further cover a peripheral portion of the pixel electrode.

  The periphery of the pixel electrode (the region including the periphery) is uneven, for example, by intersecting with the power supply bus. Therefore, by covering the periphery of the pixel electrode with the second insulating film, it is possible to avoid abnormal deposition of deposition material at the periphery in repeated driving, and to further avoid performance degradation of the display element.

  In the electrochemical display element of the present invention, the pixel electrode is formed so as to cover a step portion formed by the power supply bus and the gate electrode of the driving transistor intersecting with each other through the first insulating film. The second insulating film is preferably formed on the pixel electrode so as to cover the stepped portion.

  Since the power supply bus and the gate electrode of the driving transistor intersect with each other through the first insulating film, a so-called auxiliary capacitor is formed. A pixel electrode is formed so as to cover the step portion of the auxiliary capacitor. Therefore, the pixel electrode is uneven. However, since the second insulating film is formed on the pixel electrode so as to cover the stepped portion, abnormal deposition of the deposition material at the stepped portion in the repeated driving can be avoided to further deteriorate the performance of the display element. It can be avoided.

  In the electrochemical display element of the present invention, it is desirable that the second insulating film has an opening and is formed so as to cover a portion other than the region having the same layer configuration in one pixel.

  In regions where the layer structure (material, thickness, and number of layers) is the same, unevenness does not occur. Therefore, the second insulation is provided so as to cover portions other than the above regions (portions where unevenness occurs) within one pixel. By forming the film, it is possible to avoid abnormal deposition of the deposition material in the uneven portion. In addition, a region having the same layer structure is not covered with the second insulating film (because there is an opening), and the pixel electrode located in this region faces the common electrode through the opening, so that the inside of the opening The aperture ratio can be ensured by making the pixel electrode contribute to display by deposition / dissolution of the deposition material.

  In the electrochemical display element of the present invention, when the pixel electrode is a first pixel electrode, the second insulating film forms a second pixel electrode that is electrically connected to the first pixel electrode in the opening. It may also serve as a partition wall.

  In this case, when the second pixel electrode is formed by, for example, an ink jet method, it is not necessary to provide a separate partition wall, and even when the second pixel electrode is formed, the manufacturing process can be prevented from becoming complicated.

  In the electrochemical display element of the present invention, the opening of the second insulating film is preferably circular.

  Unlike the case where the opening of the second insulating film is polygonal, when the opening is circular, the redox reaction of the deposition material occurs in the same way at any position of the opening. In this case, abnormal deposition of the deposition material is less likely to occur, and deterioration of display performance can be reliably avoided.

  In the electrochemical display element of the present invention, the second insulating film may be formed so as to fill a space between the pixel electrode and the common electrode.

  In this configuration, since the distance between the pixel electrode and the common electrode is made constant by the second insulating film, variation in the display state of the distribution state of the deposition material contained in the electrolytic solution can be suppressed. Display unevenness (display density and display speed unevenness) can be reduced.

  The present invention can be used for an electrochemical display element such as an ED constituting various display devices such as an electronic book.

1 Display element (electrochemical display element)
1a pixel 10 substrate 12 common electrode (common electrode)
20 Substrate 23 Metal wiring 24 Interlayer insulating film (first insulating film)
24a contact hole 25 pixel electrode (first pixel electrode)
25b peripheral edge 26 insulating film (second insulating film)
26p opening 27 porous metal oxide electrode (second pixel electrode)
30 Electrolytic solution C Stepped portion T region Q1 Thin film transistor (selection transistor)
Q2 Thin film transistor (drive transistor)
VDD power bus

Claims (9)

An electrolytic solution is sealed between an observation-side substrate having a common electrode and a non-observation-side substrate having a pixel electrode, and the deposition material in the electrolytic solution is subjected to an oxidation-reduction reaction according to the potential between the electrodes. An electrochemical display element that performs display,
The non-observation side substrate is:
Metal wiring for supplying current from the power supply bus to the pixel electrode via the driving transistor;
A first insulating film formed to cover the drive transistor and the metal wiring,
The pixel electrode is formed on the first insulating film and connected to the metal wiring through a contact hole provided in the first insulating film,
The non-observation side substrate further includes:
A second insulating film formed on the pixel electrode so as to cover the contact hole ;
The electrochemical display element , wherein the pixel electrode has a region where the second insulating film is not formed . The pixel electrode is formed on the first insulating film so as to cover the driving transistor,
The electrochemical display element according to claim 1, wherein the second insulating film is formed on the pixel electrode so as to cover the driving transistor. The non-observation side substrate further includes a selection transistor for selecting a pixel driven by the driving transistor,
The pixel electrode is formed on the first insulating film so as to cover the selection transistor,
The electrochemical display element according to claim 2, wherein the second insulating film is formed on the pixel electrode so as to cover the selection transistor.   The electrochemical display element according to claim 1, wherein the second insulating film is formed so as to further cover a peripheral portion of the pixel electrode. The pixel electrode is formed so as to cover a step portion formed by the power supply bus and the gate electrode of the driving transistor intersecting with each other via the first insulating film,
The electrochemical display element according to claim 4, wherein the second insulating film is formed on the pixel electrode so as to cover the stepped portion.   6. The second insulating film according to claim 4, wherein the second insulating film has an opening and is formed so as to cover a portion other than the region having the same layer configuration in one pixel. Electrochemical display element. When the pixel electrode is a first pixel electrode,
The electrochemical display according to claim 6, wherein the second insulating film also serves as a partition wall for forming a second pixel electrode that is electrically connected to the first pixel electrode in the opening. element.   The electrochemical display element according to claim 6, wherein the opening of the second insulating film is circular.   The electrochemical display element according to claim 1, wherein the second insulating film is formed so as to fill a space between the pixel electrode and the common electrode.