JPH0219444B2 - - 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.

The counter electrode substrate 1 and the display electrode substrate 4 are disposed to face each other, a porous light reflecting layer 8 is provided between them, and the periphery of the stacked structure is sealed with a sealant 9 such as epoxy resin. 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 reflecting 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. Alternatively, 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 power supply electrode of the counter electrode, but there were problems with fixing the counter electrode to the substrate and placement within the cell, and sufficient reliability could not be obtained.

In order to solve this problem, the present inventors have proposed using titanium as a power supply electrode. However, even when this titanium is used as a power supply electrode, surface oxidation of the power supply electrode causes variations in contact resistance with the counter electrode, resulting in uneven contrast between segments when colored.

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

The titanium film may be formed by any method such as a vacuum evaporation method, an ion plating method, or a sputtering method. However, it is preferable to use such a thin film forming method using a vacuum system because even if the counter electrode substrate has a complicated shape such as a concave shape, it can be easily handled.

The thickness of this titanium film may be set as appropriate depending on the resistance value required of the power supply electrode depending on the electrode pattern, the capacitance required for the electrode, etc., but generally it should be about 3000 to 50000 Å. .

In order to lower the resistance value of this titanium film, it is preferable that the substrate temperature 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. Further, in order to suppress an increase in resistance value due to oxidation during film formation, it is necessary to reduce residual oxygen in the bell gear as much as possible. For this reason, in the case of vacuum evaporation, a value of 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.

In the present invention, a conductive film is formed on the titanium film, and this film prevents the surface of the titanium film from increasing in contact resistance due to oxidation, thereby producing an electrochromic display element with less variation in response. can be obtained stably.

This film only needs to have conductivity itself and not be oxidized or reduced by the electrolyte.
Since it is provided for the purpose of preventing an increase in contact resistance due to oxidation of the titanium film, it only needs to be thick enough to partially prevent contact between the electrolyte and the titanium film, and is usually about 100 to 5000 Å. good.

Specifically, conductive metal oxides, particularly In ₂ O ₃ , SnO _{2 ,} titanium nitride, titanium silicide, and gold are preferable as this conductive film, and they do not cause any problems in reactivity with the electrolyte and their It is also easy to form, and in particular, if the titanium coating is formed in a vacuum system, the formation of these films can be continued, which is preferable because of good productivity. titanium nitride,
In the case of titanium silicide, the productivity is particularly excellent because it is possible to form a film continuously by forming titanium by vapor deposition or sputtering, then introducing a gas and switching to reactive ion plating or reactive sputtering.

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 can be formed by ordinary vacuum deposition, and the titanium coating and titanium coating can be formed continuously without breaking the vacuum.
Deposition of a conductive film is then carried out. Therefore, the conditions such as substrate temperature are the same as those for titanium, which is advantageous in terms of work efficiency.

[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 counter electrode becomes rate-limiting for 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.

By using the titanium of the present invention 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 electrolyte, it does not elute into the liquid or redeposit on the display area when driven, unlike ordinary metals, and has excellent reliability. Since the conductive film is formed on the titanium film, the titanium film can be prevented from oxidizing, and the resistance value of the power supply electrode is unlikely to increase over time.

In particular, from the point of view of reliability and durability as an electrode, as well as past usage results, metal oxides such as indium oxide and tin oxide are suitable for this coating, while non-oxides such as titanium nitride and silicide are used as this coating. Preference is given to using titanium compounds such as titanium, and gold as the metal. By using ITO, which has traditionally been used as a power supply electrode, it is possible to significantly reduce its resistance value while maintaining the reliability of the conventional power supply electrode made only of ITO.

In particular, it is preferable to form the conductive film and titanium by a vacuum-based thin film forming method such as vacuum evaporation or sputtering, so that even if the counter electrode substrate has a complicated shape such as a concave shape, a conductive connection can be easily made. , reliability is also good. 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 the conductive film is partially cut off at a step or the like, it is hardly a problem because it can be covered by another part. In particular, it can be manufactured with high productivity by successively depositing the conductive film and titanium in the same vacuum system.

In addition, when a glass substrate is used as the counter electrode substrate, it is preferable to form a chromium layer between titanium and glass because it improves the adhesion between titanium and glass. Productivity is improved by continuously forming three layers of the adhesive film while maintaining the 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. Laminated on top of the EC material of the display electrode. The counter electrode substrate is a flat plate, a spacer is sandwiched between the sealing agent parts, and the sealing agent is applied. E.C.
Two types of EC substances are used as substances to display different colors. Color filter on the board surface,
An opaque mask or the like may be provided.

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

Glass substrate 1 with recesses formed by etching
Titanium is used as the conductive coating 2 as a power supply electrode.
6000 Å, followed by ITO 1000 Å by electron beam heating vapor deposition. For comparison, we also prepared a product with only titanium coated at 6000Å instead of titanium and ITO.
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 created 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.

In order to evaluate the density unevenness between the dots of the electrochromic display element thus produced, -1.5V was applied to the display electrode, and the response time for injecting a charge of 6 mC/ ^cm2 was measured individually. For elements made of titanium coated with ITO, this response time is 600 to 800 msec.
It was distributed in On the other hand, an element made only of titanium has a
It was distributed over ~1200msec, with large variations.

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 Three types of electrochromic display elements were produced in the same manner as in Example 1. The difference is that titanium nitride, titanium silicide, or gold is used instead of ITO as the titanium coating. Titanium nitride and titanium silicide were deposited to a thickness of 500 Å by reactive ion plating after forming a titanium film, and gold was deposited to a thickness of 500 Å by conventional vapor deposition.

Example 1 to evaluate density unevenness between dots
When similar measurements were carried out, it was found that, like those coated with ITO, there was little variation and the reliability was also good.

Example 3 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 ITO and titanium for the counter electrode were deposited.

This element also exhibited response performance and reliability similar to the ITO and titanium element produced in Example 1.

A tape test was conducted to examine the adhesion strength of the three-layer film of ITO, chromium, and titanium and the two-layer film of ITO and titanium to glass. The two-layer film of ITO and titanium sometimes peeled off in some cases during the tape test, but
The three-layer film of ITO, chromium, and titanium did not peel off at all.

Adhesion strength depends on the cleanliness of the substrate, deposition conditions, and whether slow cooling is used, but for process control and high reliability, it is preferable to use a strong three-layer film of chromium, titanium, and ITO.

[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.

In addition, titanium membranes have excellent performance in terms of stability and low resistance against electrolytes, but they have the problem of being easily oxidized, and when connecting titanium membranes with other conductive materials, it is difficult to It had the disadvantage that it was oxidized and its resistance value increased.

The present invention was born from this background, and by using a two-layer film of a conductive material such as ITO and titanium, or a three-layer film of a conductive material such as ITO, titanium and chromium, as the power supply electrode of the counter electrode. This is an excellent product that can improve production and improve the aforementioned problems such as response speed and color density unevenness without increasing manufacturing cost or material cost, and without impairing reliability. In particular, by forming a conductive film such as ITO on a titanium film, oxidation of the surface of the titanium film can be prevented and the connection resistance between this power supply electrode and other conductive materials can be reduced.

Thereby, the conductive connection between the power supply electrode and the counter electrode by the conductive adhesive and the conductive connection with the display substrate by the transfer of the power supply electrode are ensured and variations are reduced. Further, since this conductive connection is maintained stably even after long-term use, fluctuations in density unevenness between displayed segments can be prevented.

The present invention is not limited to these embodiments, and the number of types of films for the power supply electrode may be further increased by forming a film of a metal weak in electrolyte under the titanium film, and various applications may be realized in the future. It can be used mainly for large segment displays, dot matrix displays, etc.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an electromic display element. DESCRIPTION OF SYMBOLS 1... Counter electrode substrate, 2... Conductive 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)

[Scope of 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, a conductive material on the surface is used as a power supply electrode to the counter electrode. 1. An electrochromic display element characterized in that the inner surface of a counter electrode substrate is coated with a titanium film on which a transparent film is formed. 2. The electrochromic display element according to claim 1, wherein the counter electrode substrate is a glass substrate, and a chromium layer is formed between the glass substrate and the titanium coating. 3. The electrochromic display element according to claim 1 or 2, wherein the conductive film formed on the titanium film is a metal oxide. 4. The electrochromic display element according to claim 1 or 2, wherein the conductive film formed on the titanium film is titanium nitride. 5. The electrochromic display element according to claim 1 or 2, wherein the conductive film formed on the titanium film is titanium silicide. 6. The electrochromic display element according to claim 1 or 2, wherein the conductive film formed on the titanium film is gold.