JPS6355686B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a display element that applies an electrochemical coloring/decoloring phenomenon, that is, an electrochromic (hereinafter abbreviated as EC) phenomenon. Regarding EC display elements.

First, the conventional structure of an all-solid-state EC display element will be described below with reference to FIG. A transparent conductive film 2 is formed on a transparent substrate 1, and an EC material layer 3 is formed on it.
and dielectric layer 4 are sequentially laminated. EC material layer 3
Transition metal oxides such as tungsten trioxide (Wo ₃ ) and molybdenum trioxide (MoO ₃ ) are mainly used, and are usually controlled by controlling the substrate temperature, film formation rate, etc. by vacuum evaporation or sputtering.
It is formed using gas pressure such as O ₂ gas or N ₂ gas as a parameter. For the dielectric layer 4, oxides such as chromic oxide Cr ₂ O ₃ and tantalum pentoxide Ta ₂ O ₅ and fluorides such as lithium fluoride LiF and barium fluoride BaF ₂ are used. It is formed using a method similar to the material layer forming method. Finally, when the upper electrode 5 is a reflective type, a metal treated to have a background effect is formed, and when the upper electrode 5 is a transmissive type, a transparent conductive film is mainly formed. In the display element constructed as described above, when a voltage is applied between the lower transparent conductive film and the upper electrode, the EC material layer sandwiched between the two electrodes electrochemically colors and discolors, thereby providing information. can be provided.

Although there are still many unknowns about the coloring and fading mechanism of EC display elements with such a configuration, EC
When a negative voltage is applied to the material layer side, the cation species in the dielectric layer, here the main proton H ⁺
It is interpreted that a colored reaction is exhibited due to migration into the material layer and formation of bronze. In addition, the protons mentioned here usually exist in a dielectric layer with weak bonds, and must be able to move around quite freely when a coloring voltage is applied;
It is thought to exist in the layer in the form of H ₂ O. From this, in order to create a display element with a large change in optical density when voltage is applied, that is, a display element with good coloring efficiency, it is necessary to
A major issue is how to stably retain a large amount of H ₂ O in the layer. Conventional structure EC display elements are extremely unsatisfactory in terms of the above-mentioned problems, and it is impossible to stably contain a large amount of H ₂ O in the layer using normal forming methods, resulting in poor coloring efficiency. It had very large drawbacks as a display element, such as poor performance and a decrease in optical density change during aging.

The present invention solves these drawbacks of conventionally structured EC display elements and provides a long-term stable EC display element with good coloring efficiency by adopting a formation method that can stably contain a large amount of H ₂ O in the layer. The purpose is to The EC display element according to the present invention will be described below. Although the effects of the present invention are obvious in any layer constituting a display element, the dielectric layer, which is considered to have the greatest effect from the above interpretation of the EC coloring mechanism, will be described as an example. After forming a transparent conductive film and an EC material layer on a substrate, a dielectric layer of, for example, chromic oxide Cr ₂ O ₃ is formed using parameters such as substrate temperature, film formation rate, and film thickness. According to the present invention, at this time 1×
It is known that the amount of H ₂ O in the film increases by introducing H ₂ O saturated vapor up to about ^{10 -3} Torr and forming a film therein. _H2O near ^-1
Figure 2 shows the absorption peak. In the figure, A is a film formed by a normal vacuum evaporation method, B is a film formed by introducing H ₂ O saturated steam according to the present invention,
As is clear from the comparison between the two, a large amount of H ₂ O is present in the dielectric layer according to the present invention, and the same fact has been confirmed from the results of differential thermal analysis. The effect of introducing H ₂ O saturated steam during film formation is also observed in the EC material layer; for example, the IR of WO ₃ film
The absorption spectrum is shown in FIG. As before, in the figure, A is a film obtained by the usual vacuum deposition method, and B is a film obtained by the present invention. EC display elements created using EC material layers and dielectric layers with the above characteristics retain a large amount of H ₂ O, which is involved in deposition and decolorization, and therefore do not have conventional structures. The coloring efficiency is greatly improved compared to the display element shown in FIG. 4. The display element structure in this case is a stacked structure of a WO ₃ film as the EC material layer, a Cr ₂ O ₃ film as the dielectric layer, and an Au thin film as the upper electrode. are the characteristics for the EC display element according to the present invention. In the figure, I ₀ represents the incident light intensity, and I represents the transmitted light intensity, and a silicon detector with visibility correction is used for detection. As is clear from the figure, the EC display element according to the present invention has improved optical density change with respect to the amount of injected charge, that is, coloring efficiency, and can obtain a large optical density change with respect to the same amount of injected charge. Furthermore, in terms of aging characteristics, the deterioration in optical density change is sufficiently small compared to conventional EC display elements, indicating that H ₂ O retained in the display element effectively acts on the EC mechanism.

Into the membrane by introducing H ₂ O saturated steam according to the present invention
The increase in the amount of H ₂ O is considered to be due to the incorporation of H ₂ O into the film during film formation, but further increase in the amount of H ₂ O in the film is expected by considering the film structure. From this perspective, we investigated the ion plating (hereinafter abbreviated as IP) method and found a region that has fine crystal grains and grows close to a columnar structure under a certain range of conditions. This kind of film structure is difficult to obtain using ordinary vacuum evaporation methods;
This is the most preferable structure for EC display elements,
By combining this with the aforementioned introduction of H ₂ O saturated steam, it becomes possible to further increase the amount of H ₂ O present in the film. As an example, when a dielectric layer is formed under conditions that combine H ₂ O saturated vapor introduction and IP method,
The IR absorption spectrum is shown in Figure 5. By considering the membrane structure compared to the previous figure 2B,
It can be seen that the amount of H ₂ O increases further, and similarly
Effects have also been recognized for the EC material layer. Furthermore, by adopting the IP method and adopting the above structure, phenomena such as color bleeding outside the pattern and coloring residue during aging, which were problems with conventional EC display elements, can no longer be observed.
This is thought to be an effect of the IP film structure, and is a very large advantage in terms of appearance as a display element.
EC obtained by combining H ₂ O saturated steam introduction and IP method
Figure 6 shows the coloring efficiency of an EC display element created using a material layer and a dielectric layer. The figure shows the same curve as in FIG. 4, and is the display element characteristic obtained by the combined use of H ₂ O saturated vapor introduction and the IP method. As can be seen from the figure, by adopting the IP method, the proportional part between the amount of injected charge and the optical density change extends to the region of high optical density change, and further improvement in coloring efficiency can be seen. This is due to the fact that the IP method is used in thin films.
This indicates that the increased amount of H ₂ O is effectively involved in the EC coloring mechanism, indicating that the display element has sufficient durability for practical use.

As described above, according to the present invention, the poor coloring efficiency that the EC display element of the conventional structure had,
It is possible to solve the drawbacks such as low aging and aging properties, and provide a practical EC display element that has a large optical density change, no color bleeding, and is stable over a long period of time.

Although the above description has been made regarding the dielectric layer and the EC material layer, the transparent conductive film can also contain moisture by being deposited in an atmosphere containing water vapor, and the same effect can be obtained.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing the structure of a conventional all-solid-state EC display element, Figures 2A and B, and Figures 3A and B are Cr ₂ O ₃ films obtained under the introduction of H ₂ O saturated steam, respectively. ,
IR absorption spectrum diagram of WO ₃ film, Figure 4 is a characteristic diagram of the amount of charge injected into a display element obtained under the introduction of H ₂ O saturated vapor of a conventional display element, and changes in optical density.
Figure 5 is an IR absorption spectrum diagram of a Cr ₂ O ₃ film obtained by both the introduction of H ₂ O saturated steam and the IP method, and Figure 6 is
Display element and H ₂ O obtained under introduction of H ₂ O saturated steam
FIG. 2 is a characteristic diagram of the amount of charge injected into a display element and the change in optical density obtained by both the introduction of saturated steam and the IP method. 2...Transparent conductive film, 3...EC material layer, 4...
Dielectric layer, 5...upper electrode.

Claims (1)

[Scope of Claims] 1. An all-solid-state electrochromic display element formed by laminating films or layers such as a transparent conductive film 2, a tungsten trioxide-based electrochromic material layer 3, and a dielectric layer 4, wherein the above-mentioned 2. An all-solid-state electrochromic display element, characterized in that at least one of the films or layers described in items 3 and 4 is formed by a physical vapor deposition method in an atmosphere containing water vapor. 2. The all-solid-state electrochromic display element according to claim 1, wherein the physical vapor deposition method is an ion plating method.