JPS62156261A - Production of iridium oxide film by thermal oxidation - Google Patents

Abstract

PURPOSE:To obtain an Ir oxide film having homogeneity over a large area and showing electrochromism by forming a composite Ir-C film on a substrate and oxidizing the film under heating in the air. CONSTITUTION:A composite Ir-C film is formed by an electron-beam binary vapor deposition method by which Ir and C are evaporated from separate evaporating sources to form a composite film on the same substrate or by other method. The composite Ir-C film is oxidized under heating in the air to obtain an Ir oxide film.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing an iridium oxide film having "electrolytic oxidation color development" that develops color in an oxidized state.

(Prior art and its problems) The phenomenon in which a film-like substance changes color, develops, or disappears due to the implantation of positively or negatively charged ions is called electrochromism, and this phenomenon can be used, for example, in electrochromic devices. has been done.

Metal oxides such as iridium oxide, rhodium oxide, nickel oxide, and cobalt oxide are known as inorganic materials that exhibit in-electrolytic oxidation coloring properties. Among the nitrous oxides, iridium oxide is the most actively researched because it has advantages such as fast response speed and excellent chemical stability. Conventionally, the method for producing iridium oxide film is as follows:
The 5aii+2 method and the reactive sputtering method are known, but both have problems that need to be solved. In the anodic oxidation method, an iridium film formed on a substrate using a sputtering method or a vacuum evaporation method is anodized in a sulfuric acid solution to form an iridium oxide film. had the disadvantage that a homogeneous iridium oxide film could not be obtained over the entire display surface. A further serious drawback is that it cannot be laminated onto substrate materials exhibiting electronic 1ζ insulating properties, such as solid electrolytes.

In addition, since the optimum deposition rate for reactive sputtering to obtain an iridium oxide film is very slow at 10 people/minute, it is necessary to produce a thin film with a thickness necessary for a display element, for example, an iridium oxide film with a thickness of about 900 people/minute. The disadvantage was that it took more than one hour to obtain the desired results.

Furthermore, in addition to this method, it is theoretically possible to obtain an iridium oxide film by heating an iridium film. However, when an iridium oxide film is heated above 800°C, it crystallizes and loses its electrochromic properties, as reported by Hackwood in Solid State Ionics, No. 2, published in 1981.
, Beni and Gal lag
Her). Therefore, in the case of thermal dispersion, in order to obtain an iridium oxide film exhibiting electrochromism, the heat treatment temperature must be at least 8.
The temperature must be 00'C or less, but normally, the temperature of iridium alone is 8o.

Even if heated to ℃, an iridium oxide film cannot be obtained.

For example, if an iridium film obtained by sputtering is
Although heat treatment was performed at 00° C. for 1 hour, the surface remained metallically shiny and an iridium oxide film could not be obtained.

(Means for Solving the Problems) As a result of various studies in view of the current state of the technology as described above, the present inventors have discovered that a composite yt made of iridium and carbon formed on a substrate in advance is As a result of thermal oxidation, we have discovered the novel fact that an iridium oxide film can be obtained by a short-time treatment at a low temperature of 250° C. and a short thermal oxidation time of 10 to 20 minutes. That is, the present invention significantly shortens the time required for film production by thermally oxidizing a composite film made of iridium and carbon, and also enables the production of a homogeneous iridium oxide film over a large IMI time. This is what I did.

(Structure of the Invention) In the present invention, first, an iridium-carbon composite film is formed on a substrate. The substrate can be made of a conductive material such as metal or glass.

Non-electrical materials such as porcelain 1 and synthetic resin can also be used with resistances exceeding Ω.

The iridium-carbon composite film can be formed by a co-deposition method generally employed in known thin film production, such as a particle beam evaporation method or a sputtering method. More specifically, (1) evaporating iridium and carbon from separate evaporation sources using an electron beam,
An electron beam binary evaporation method for forming a composite film on the same substrate, (il) a method for placing iridium in a graphite crucible and using an electron beam to evaporate carbon together with the iridium to form a composite film on the substrate. ) A method of forming a composite film of nickel and oxide by sputtering in argon gas using iridium arranged on charcoal as a target. However, it goes without saying that the iridium-carbon composite film can be formed not only by these exemplified methods but also by other methods.

By controlling the evaporation source, an iridium-carbon composite film having an arbitrary composition ratio can be obtained, but when thermal oxidation is performed, the composition ratio of iridium to carbon in the composite film is in the range of 0.05 to 0.80. In this case, the oxide film was well formed. That is, when the composition ratio of iridium to carbon in the composite film is less than 0.05 and when the composition ratio of iridium to carbon is less than 0.80t-
When it exceeds the range, carbon is not sufficiently desorbed from the iridium-carbon composite film for the first time in thermal oxidation, and only a film with low transmittance can be obtained.

In addition, when using non-conductive glass, porcelain 9 synthetic resin, etc. as a substrate, a transparent conductive film or a conductive metal film is provided on the substrate in advance in order to improve the response as an electrochromic element, and then It is preferable to form an iridium-carbon composite film.

In the present invention, the desired iridium oxide film is then obtained by heating and oxidizing the iridium-carbon composite film formed on the substrate as described above in the atmosphere. There is no particular limitation as long as the atmosphere is formed; for example, an atmosphere enriched with oxygen or an atmosphere enriched with oxygen and aquatic gas may be used.

The iridium oxide film obtained by the method of the present invention exhibits remarkable 'F1-deactivated color development, and is therefore extremely useful as electrochromic devices, thin film batteries, and the like.

(Effect of the invention) According to the present invention, the following effects are achieved.

11> A homogeneous iridium oxide film can be formed over a wide area.

(2) It is also possible to form an iridium oxide film on an insulating substrate.

An iridium oxide film exhibiting f31 a-1f electrochromism can be formed in a short time.

(Example) Examples will be shown below to further clarify the characteristics of the present invention.

Put iridium powder into a graphite crucible, accelerate voltage 6KV,
Emission current 18l80-2O0, degree of vacuum 1~2X
An iridium-carbon composite film with metallic luster was formed on the substrate by electron beam evaporation under conditions of 10' Torr. The time required for electron beam evaporation was 60-180 seconds. The substrate used was a glass plate on which an indium oxide transparent conductive film was previously formed. Next, the iridium-carbon composite film was heated to 225 ~
An iridium oxide film was obtained by heating and oxidizing in a temperature range of 850° C. for 10 to 20 minutes.

The transmittance of the iridium oxide film obtained in the example at a wavelength of 6828λ is shown by curve a in FIG. No. 0 and No. 0 indicate thermal oxidation times of 10 minutes and 20 minutes, respectively.

The thickness of the exemplified iridium-carbon composite film was 1,850 mm, and the ratio of iridium to carbon in the film was in the range of 0.10 to 0.20 as a result of photoelectron spectroscopy and density measurement. As shown by curve a, an iridium oxide film with sufficiently high transmittance cannot be obtained at a thermal oxidation temperature of 225°C. However, by extending the hot oiling time to 1 hour, the transmittance is equivalent to that of the sample heated and oxidized at 250° C. or higher. When heating and fermentation was carried out at 250°C or higher, the transmittance showed a saturated value after about 20 minutes of thermal oxidation time, and the transmittance hardly changed even if heating was continued.

In FIG. 1, the curves indicate the transmittance after each carbon film was heated and oxidized at a predetermined temperature for 30 minutes. As shown in the curve, in the single carbon film, almost no change in transmittance was observed over the heat treatment temperature range of 200 to 800°C. Further, even in the case of the iridium single film produced by the sputtering method, under the heat treatment conditions of 300° C. for 1 hour, the surface of the film still exhibited metallic luster, and an oxide film could not be obtained. Therefore, it can be seen that in the iridium-carbon composite film, an iridium oxide film can be obtained for the first time by heat treatment at low temperature and for a short time.

As shown in Figure 1, the transmittance of the iridium oxide film that has been thermally oxidized is low at about 40%, but this is because the iridium oxide film that has been thermally oxidized is in a colored state, and cannot be electrolytically reduced. This results in an even higher transmittance state. For example, an iridium oxide film with a thickness of about 100 yen (300 yen) produced according to the present invention exhibits a transmittance of 80% or more in an embellished state.

The iridium oxide film obtained in the present invention was immersed in an aqueous solution, and a voltage of 1 to -0, 2 V was applied using a saturated electrode as a reference electrode.
When the potential was scanned in the range of , color development and fading of the thin film was observed. FIGS. 2A and 2B show changes in current density and transmittance when potential scanning is performed.

The potential scanning rate was 10 mV/sec. c, d.

0 curves respectively show changes in current density applied to iridium oxide films obtained under conditions of thermal oxidation temperatures of 250, 800, and 850° C. in the air with a constant heat treatment time of 20 minutes.

Further, the f, g, and h curves show transmittance changes corresponding to the c, d, and 0 curves, respectively.

When the thermal oxidation temperature was set to 250°C, there was a noticeable occurrence of
A discoloration change was observed, but even at a thermal oxidation temperature of up to 850°C, a discoloration change was observed.

If the thermal oxidation temperature is lower than 250℃, for example 225℃
At the thermal oxidation temperature of , a film exhibiting electrochromism was obtained, although it had the disadvantage that a treatment time of about 1 hour was required. That is, in the present invention, 225 to
An iridium oxide film exhibiting electrochromism over a wide heating temperature range of 850°C was obtained.

The iridium oxide film obtained in the present invention is extremely stable and has a
．． Deterioration and peeling of the film can be prevented by placing it in a 5M Na2SO4 solution and repeating 4x105 times or more of coloring and decoloring under an applied potential of -0.5 to 0.5V using a saturated plaster electrode as a reference electrode. was not recognized.

[Brief explanation of drawings]

The first factor shows the transmittance after thermal oxidation of the iridium-carbon composite film according to the example of the present invention, and for comparison, the transmittance after thermal oxidation of the single carbon film. FIGS. 2A and 2B show changes in °C flow density and transmittance of the malted iridium membranes obtained under predetermined thermal oxidation conditions according to examples of the present invention. The first cause is winter

Claims (1)

[Claims] (1) A method for producing an iridium oxide film, characterized by heating and oxidizing a composite film made of metallic iridium and carbon.