JPH0219443B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electrochromic display device (ECD) that exhibits color change through an electrochemical redox reaction.
More specifically, it relates to ECDs with improved characteristics.

[Prior Art] A solution-type electrochromic display element has a display electrode and a counter electrode, and has a salt such as lithium perchlorate dissolved in a non-aqueous solvent such as propylene carbonate as an electrolyte. In order to reduce the amount of noise or to improve the contrast, a reflective layer is usually provided between the display electrode and the counter electrode to be used as a reflective type. FIG. 1 shows a cross-sectional view of a typical example.

The counter electrode substrate 1 is usually made of glass, plastic,
A conductive thin film 2 is placed on an insulating substrate such as ceramics.
After forming a power supply electrode to the counter electrode 3 made of the above, the counter electrode 3 made of a depolarizer such as manganese dioxide, conductive fibers such as carbon, a binder, etc. is bonded.

The display electrode substrate 4 is produced by forming a transparent conductive film 5 such as ITO on glass, patterning it, and then forming an electrochromic material 6 such as amorphous tungsten oxide in required areas. Further, a protective layer 7 for protecting the exposed transparent electrode may be formed as necessary.

These counter electrode substrates 1 and display electrode substrates 4 are arranged to face each other, and a porous light reflecting layer 8 is provided between them and overlapped, and the periphery is coated with a sealant 9 such as epoxy resin.
Seal with. After vacuum injecting an electrolyte 10 such as propylene carbonate in which lithium perchlorate is dissolved, the injection port 11 is sealed to produce a reflective electrochromic display element.

In conventional ECDs, transparent electrodes such as tin-doped indium oxide (ITO), metal wires, etc. have been used as power supply electrodes to the counter electrode 3.

[Problems to be Solved by the Invention] The electrochromic display element thus produced develops color by applying a DC voltage of 1 to 2 volts between the counter electrode and the display electrode. The color is also erased by reversing the polarity of the voltage. Driving methods for developing and decoloring include the constant current method, constant voltage method, and constant potential method, but in actual devices, it is difficult to incorporate a reference electrode into the device, so the constant current method is usually used. A constant voltage method is used.

The constant current method is generally applied to relatively small devices due to the nature of the circuit. On the other hand, the constant voltage method has fewer circuit restrictions and is therefore widely used for devices ranging from small to large devices.

When an electrochromic display element is driven by a constant voltage method, uneven contrast between segments or dots becomes a problem. Furthermore, when a plurality of electrochromic display elements are used side by side, uneven contrast between the elements also becomes a problem.
This contrast unevenness is caused by the fact that electrochromic display elements are current-controlled elements.
This is because transparent electrodes such as ITO have a large sheet resistance value, so the response speed varies greatly depending on the operating area. In other words, the electrochromic display element has a fast response when the number of operating segments (area) is small, and the response becomes slower as the number of operating segments (area) increases. Furthermore, this tendency becomes more pronounced as the device becomes larger. Therefore, in the constant voltage method, it is necessary to devise ways to keep the contrast constant even depending on the displayed content. On the other hand, it is possible to keep the contrast constant by controlling the time period for which a constant voltage is applied depending on the display content, but this method increases circuit cost and is not practical.

For this reason, it was considered to use a metal wire as the feeding electrode of the counter electrode, but there were problems in fixing the counter electrode to the substrate and arranging it within the cell, and sufficient reliability could not be obtained.

[Means for Solving the Problems] The present invention has been made to solve these problems, and is a reflective electrolyte having a display electrode and a counter electrode, with an electrolyte layer and a light reflection layer sandwiched between them. The present invention provides an electrochromic display element characterized in that the inner surface of the counter electrode is coated with titanium as a power supply electrode to the counter electrode in the chromic display element.

The titanium film may be formed by any method such as a vacuum evaporation method, an ion plating method, or a sputtering method. However, such a thin film forming method using a vacuum system is preferable because it can easily be applied even when the counter electrode substrate has a complicated shape such as a concave shape. In order to lower the resistance value, it is preferable for the substrate temperature to be higher than room temperature, but if it is too high, the working time will be longer, so a range of 50°C to 350°C is appropriate. Also,
In order to suppress an increase in resistance value due to oxidation during film formation, it is necessary to minimize residual oxygen in the bell gear. In the case of vacuum evaporation, 10 ^-5 Torr or less is preferable. The deposition rate should also be as fast as possible in order to prevent oxidation during film formation, depending on the equipment, but for normal vacuum evaporation it is desirable to be at least 10 Å/sec or more.

When the counter electrode substrate is glass, depositing a chromium film of about 500 to 1500 Å on the titanium film is effective in increasing adhesion.

The chromium film may be formed by ordinary vacuum deposition, and titanium can be deposited continuously without breaking the vacuum. Therefore, it is advantageous in terms of work efficiency to keep the substrate temperature and other conditions the same as those for titanium.

[Function] The response of an electrochromic display element depends not only on the performance of the electrochromic layer and the counter electrode but also on the resistance of the electrolyte and the resistance of the display electrode and the power supply electrode to the counter electrode. The contribution of these components to the response speed varies depending on the structure, composition, material, size, etc. of the cell. Generally, as the cell size increases, the resistance of the power supply electrode to the display electrode and the counter electrode becomes a rate-limiting factor in response. Therefore, especially in large devices, lowering the resistance of the power supply electrode leads to improved response.

On the display electrode side, since it affects the display, it is basically necessary to use a transparent electrode, and at best, part of the lead portion is made of a low-resistance material such as metal to reduce the power supply resistance. On the other hand, on the counter electrode side, one counter electrode usually corresponds to all the display electrodes, so the current flowing as a single electrode is extremely large, so the effect of making it low resistance is large, and the counter electrode , since it is placed on the back side of the reflective layer, there is no adverse effect even if the entire surface is made of a metal electrode.

The contrast unevenness, that is, the variation in response speed due to the number of motion segments is caused by the common impedance. In other words, as the number of operating segments increases and the current flowing through the element increases accordingly, the voltage dropped across the common impedance becomes relatively large. Therefore, of the applied voltage, the effective voltage applied to the display electrodes becomes smaller, resulting in slower response.

The common impedance is made up of the counter electrode impedance and the resistance of the power supply electrode to the counter electrode.

The impedance of the counter electrode can be lowered by making it as thick as possible and having a porous structure. The power supply electrode serving as the counter electrode is required to have low resistance and be electrochemically stable. ITO has traditionally been mainly used as a material that satisfies these conditions. However, improvements have been desired in terms of resistance and cost.

In the present invention, by using titanium as the power supply electrode of the counter electrode, the resistance is reduced to a fraction of that of ITO, making it possible to improve response speed and suppress contrast unevenness due to differences in display content. Furthermore, since titanium is extremely stable in the electrolytic solution, it does not elute into the solution or redeposit on the display area when driven, unlike ordinary metals, and has excellent reliability.

In particular, it is preferable to form titanium by a thin film forming method using a vacuum system such as vacuum evaporation or sputtering, and even if the counter electrode substrate has a complicated shape such as a concave shape, conductive connection can be easily made and reliability can be achieved. Good too.
This is because there is only one power supply electrode for the counter electrode substrate, and it is sufficient to form it almost on the entire surface, and even if a part of the conductive film is cut off at a step or the like, it is hardly a problem because it can be covered with another part.

Furthermore, when the counter electrode substrate is a glass substrate, it is preferable to form a chromium layer between the titanium and the glass because it improves the adhesion between the titanium and the glass.
Productivity is improved by continuously forming layers in a vacuum state.

In the present invention, conventionally known materials and structures can be used for the display electrode, EC material, light reflection layer, counter electrode, electrolyte, etc., and the light reflection layer is not limited to the example shown in FIG. EC, which is laminated on top of the EC material of the display electrode, uses a flat counter electrode substrate, and seals it with a sealant by sandwiching a spacer between the sealant parts.
A color filter is used on the surface of the substrate to display different colors using two types of EC substances.
An opaque mask or the like may be provided.

[Example] Example 1 Glass substrate 4 with patterned transparent electrodes
Using a metal mask, approximately 5000 Å of tungsten oxide 6 was deposited on the segment by electron beam heating to form a display electrode substrate.

Glass substrate 1 with recesses formed by etching
Titanium 2 was applied to the surface by 6000 Å electron beam heating evaporation. Also, for comparison, ITO was used instead of titanium.
We also prepared one with 6000Å attached. A sheet-shaped counter electrode 3 was made from oxides of tungsten and vanadium, carbon, and a binder. In addition, a sheet-shaped light reflecting plate was similarly made from white pigment and binder. This light reflecting plate and the counter electrode sheet prepared earlier were stacked and integrated to create an integrated structure. This sheet was fixed to a prepared substrate having concave portions with a conductive adhesive to form a counter electrode substrate.

After these display electrode substrates and counter electrode substrates were overlapped and their surroundings sealed, electrolyte 10 in which 1 mol/l of lithium perchlorate was dissolved in propylene carbonate was injected under vacuum, and injection port 11 was sealed.

When 1.5V is applied to the electrochromic display element made in this way, the response is 600msec for the titanium one and the ITO one.
It was 700msec.

Next, we measured the charge density per unit area injected when a 1.5V, 700msec square wave was applied to the device. When the area increases by 35 times, the titanium element
The drop was 23% less than that of ITO.

When we conducted a coloring/decoloring cycle test, no abnormalities were observed in appearance even after 500,000 cycles, and the product was operating normally. Furthermore, no problems such as peeling occurred during heat shocks between 70°C and -25°C.

Example 2 An electrochromic display element was produced in the same manner as in Example 1, except that chromium was deposited to a thickness of 1000 Å before the titanium was deposited on the counter electrode.

This element also exhibited response performance and reliability similar to the titanium element produced in Example 1. A tape test was conducted to examine the adhesion of the chromium/titanium double layer film and the titanium film to glass. Although some parts of the titanium film peeled off during the tape test,
The chromium/titanium double layer film did not peel off at all.

Adhesion strength depends on the degree of cleaning of the substrate, deposition conditions, presence of slow cooling, etc., but for process control and high reliability, it is preferable to have a strong adhesive, such as a two-layer film of chromium and titanium.

[Effects of the Invention] In the case of a conventional electrochromic display element using ITO as the power supply electrode of the counter electrode, the response becomes extremely slow when the display element becomes large, although it is not so bad when the display element is small. In addition, the difference in response speed due to the operating area becomes large, which poses a problem when put into practical use. In order to improve this, there is a method of increasing the ITO film thickness, but this increases the required film thickness determined by the resistivity, increases the required vapor deposition time, and takes into account raw material costs, etc., which makes it unrealistic. Not.

There are noble metals such as gold and platinum that have low resistance and are stable even in electrolytes, but these cannot be used due to material cost.

There is also a method of lowering the resistance by embedding mesh-shaped titanium in the counter electrode material, but it is difficult to extract electricity to the outside and is not suitable for mass production.

The present invention was born from this background, and by using a titanium single-layer film or a chromium/titanium double-layer film as the power supply electrode of the counter electrode, it is possible to improve productivity without increasing manufacturing costs or material costs. This is an excellent product that can improve the above-mentioned problems such as response speed and color density unevenness without impairing reliability.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an electrochemical display element. DESCRIPTION OF SYMBOLS 1... Counter electrode substrate, 2... Conductive thin film, 3... Counter electrode, 4... Display electrode substrate, 5... Transparent conductive film, 6...
Electrochromic substance, 7... Protective layer, 8... Light reflective layer, 9... Sealing agent, 10... Electrolyte, 11... Inlet.

Claims (1)

[Claims] 1. In a reflective electrochromic display element having a display electrode and a counter electrode, with an electrolyte layer and a light reflective layer sandwiched between them, titanium is used as a power supply electrode for the counter electrode. An electrochromic display element characterized by coating the inner surface of a substrate. 2. The electrochromic display device according to claim 1, wherein the counter electrode substrate is a glass substrate, and a chromium layer is formed between the glass substrate and titanium.