JPH04107263A - Thin film of stabilized zirconia solid electrolyte and its production - Google Patents

Abstract

PURPOSE:To produce a thin film of stabilized zirconia solid electrolyte having free and precise shape by forming a thin film of stabilized zirconia solid electrolyte on a separation layer capable of removal by etching and then separating the above thin film from a substrate by means of etching. CONSTITUTION:A thin film of aluminum, etc., is formed as a separation layer on a glass substrate by a vacuum deposition method. Because the aluminum layer has superior spreadability, it has superior characteristics that not stress is accumulated in it at the time of forming the thin film of stabilized zirconia solid electrolyte and that the thin film of stabilized zirconia solid electrolyte is free from deformation after separation from the substrate. Subsequently, the thin film of stabilized zirconia solid electrolyte of the desired film thickness is formed on the above by an ion plating method, etc. The resulting laminated body is cut into the desired size, immersed into an etchant, and heated, by which the separation layer is dissolved and the thin electrolyte film is peeled from the substrate. After the substrate is taken out, the etchant is discharged and the remaining thin film is washed with alcohol and dried, by which the independent thin film of stabilized zirconia solid electrolyte can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a stabilized zirconia solid electrolyte thin film particularly useful as a solid electrolyte material for gas sensing elements (gas sensors), and a method for producing the same.

[Technical background of the invention and prior art] A gas detection element (gas sensor) using a solid electrolyte is
For controlling the exhaust gas of industrial combustion equipment, controlling the oxygen concentration in chemical processes involving oxygen at high temperatures such as petrochemicals, steel, and metallurgy, and controlling the air-fuel ratio by detecting the oxygen concentration of the exhaust gas of θ vehicles. In recent years,
It is becoming more and more popular. Moreover, more recently, it has been used not only as a conventional oxygen gas detection sensor but also as a humidity sensor.

Among the solid electrolyte materials used in such gas sensing elements, stabilized zirconia is currently one of the most well-researched and practically used solid electrolyte materials.

For oxygen sensors and humidity sensors using stabilized zirconia, see, for example, new ceramic oxygen sensors and their applications 1 ("Electronic Materials J19B5 August issue, 115-1
20 pages), ``Microchip oxygen sensor using zirconia thin film'' (``Sensor Technology J March 1989 issue, 75~
78 pages), and thick film humidity sensor J using r-stabilized ZrO2 ultrafine powder (r sensor technology J19B6 November issue, 7
Detailed descriptions can be found in publications such as (pp. 3-79).

Zirconia (ZrOz) ceramics alone is 110
There is a transition between monoclinic system and tetragonal system at around 0°C, and at this time, a change in volume of several percent is accompanied by cracks. Therefore, it is known that by adding MgO1CaO1Y203 or CeO as a stabilizer to form a solid solution and making the crystal structure equiaxed, it is possible to make a ceramic that is stable from room temperature to high temperature. Such zirconia is called stabilized zirconia. Stabilized zirconia is not only free from cracks that cause volume changes. By adding stabilizers, Z in ZrO7 crystals
Stabilizing agent cation (Mg” C
a2◆ Y"Ce3◆ etc.) are substituted and dissolved, and as a result, there is a lack of positive charge, and in order to maintain the electrical neutrality of the entire crystal, a vacancy for the deficient charge is created at the 02- position, and as a result, the crystal As a whole, it becomes an oxygen ion conductor. Therefore, the difference in the oxygen partial pressure or water vapor partial pressure on both sides of the stabilized zirconia can be detected by examining the conductivity of the oxygen ions inside.

Ceramic sensors for gas detection using stabilized zirconia solid electrolytes have conventionally been manufactured by a sintering method.

That is, after forming the raw material of stabilized zirconia, it is fired to form a stabilized zirconia thick film (film thickness: approximately 0.1 to 2
．． This thick film is then sandwiched between electrodes such as platinum to form a sensor. This sintering method uses, for example, Zr
It is generally carried out by combining O2 powder and Y2O3 powder with a solvent at a certain ratio, forming the mixed material into a desired shape, size, thickness, etc., and firing it.

However, the actual implementation of the sintering method not only involves a large number of steps and is complicated, but also requires a wide range of techniques. In addition, the shape of the solid electrolyte layer is fixed to some extent during the forming stage before firing, so even though there are methods such as cutting and polishing, it is difficult to freely modify the shape after firing. be. In particular, in order to make the solid electrolyte membrane thin,
Although methods such as cutting and polishing can be used, there is a limit to how thin a film can be made, and a uniform thin film of about 100 μm can only be obtained at most. On the other hand, the stabilized zirconia solid electrolyte manufactured by the sintering method does not have a very high density, and if the film is made thinner, the permeability to gases such as oxygen becomes too high, making it impossible to obtain the characteristics as a gas sensor. There is also.

Another method is to apply a dispersion of stabilized zirconia solid electrolyte raw material for firing onto the surface of the substrate and then fire it, but with this method, it is difficult to produce a thin film with a uniform thickness, and the substrate is always left on one side. Since it is attached and its separation is virtually impossible, there are restrictions on its use.

In recent years, there has been a strong demand for miniaturization of various sensors, but it is difficult to reduce the thickness of stabilized zirconia solid electrolyte sensor materials using conventional sintering methods. Furthermore, it is not possible to manufacture a stabilized zirconia solid electrolyte thin film whose surfaces on both sides are exposed and on which electrodes of any material and form can be freely provided, using conventional methods.

[Object of the invention] The present invention enables the formation of a stabilized zirconia solid electrolyte thin film with any thickness from raw materials in one step without using a sintering method, and the resulting solid electrolyte thin film does not have to be restricted by the substrate. It is an object of the present invention to provide a stabilized zirconia thin film that is particularly useful as a material for a gas sensing element that is free from oxidation, and a method for producing such a stabilized zirconia thin film.

[Summary of the Invention] The present invention comprises: a) forming a processable separation layer on a substrate; b) forming a stabilized zirconia solid electrolyte thin film on the separation layer by an ion plating method; and C) a method for producing a stabilized zirconia solid electrolyte thin film, comprising the steps of removing the separation layer by etching and separating the stabilized zirconia solid electrolyte thin film from the substrate.

By using the above method, a stabilized zirconia solid electrolyte thin film having a thickness of 15 μm or less can be manufactured with high reliability.

In the present invention, the stabilized zirconia solid electrolyte thin film is formed on a separation layer that can be removed by etching, and is easily separated from the substrate by etching after formation.
The thickness and shape of the stabilized zirconia solid electrolyte thin film produced are not limited by the substrate. Furthermore, according to the present invention, a stabilized zirconia solid electrolyte thin film that does not require complicated processes such as the conventional sintering method and has a much more free and precise shape than the sintering method can be created. can.

[Description of the Invention] The present invention comprises a) a step of forming a separation layer on a substrate, b) a step of forming a stabilized zirconia solid electrolyte thin film on the separation layer by an ion plating method, and C) a step of forming the separation layer on the separation layer. The process consists of etching and separating the stabilized zirconia solid electrolyte thin film from the substrate.

First, an etchable separation layer is formed on the substrate [step a)]. Examples of the substrate include plates of glass, alumina, porous glass, and the like.

Furthermore, an aluminum metal layer is used as the etchable separation layer. Therefore, step a) is carried out, for example, by forming a thin aluminum film as the separation layer on a flat glass substrate by a conventional vacuum deposition method.

Since the aluminum layer is highly malleable, no stress is accumulated in it during the formation of the stabilized zirconia solid electrolyte thin film, and the stabilized zirconia solid electrolyte thin film does not deform after separation from the substrate. has.

Next, a stabilized zirconia solid electrolyte thin film having a desired thickness is formed thereon [step b)].

This stabilized zirconia solid electrolyte membrane is formed by an ion plating method, but in order to form a stabilized zirconia solid electrolyte thin film with excellent properties, a known ion bombardment device (Japanese Unexamined Patent Publication No. 6137962 or Kaisho 6
1-233957) is preferably used.

Fig. 1 shows an example of the above-mentioned ion bombardment device
37962). High frequency power is supplied from a power source 5 via an auxiliary electrode 3 and a matching box 4 to a substrate 1 held by a rotating substrate holding device in a vacuum chamber.

When using this device, for example, yttrium oxide stabilized zirconia (hereinafter referred to as YSz) is used as the evaporation material.
is used to evaporate it from the evaporation source 2 and deposit it on the substrate. The 02 gas introduced into the vacuum chamber is ionized in plasma by high frequency waves, and the ions are accelerated by a negative bias electric field generated for the plasma, and the ions are
It impinges on the surface of the thin film that is being deposited on the surface. The film quality of the gas sensor thin film produced by this ion bombardment has a high density, almost like a lumpy material, compared to the film quality of the thin film produced by the conventional vacuum evaporation method. It has the characteristic of becoming.

That is, the above-mentioned publication discloses that the ion bombardment device is used to form a multilayer film of TiO2 and SiO2 used in interference filters, etc. It has been found that it is preferable to use the device. That is, in the present invention, the stabilized zirconia solid electrolyte thin film must be self-supporting since it is peeled off from the substrate in step C). Therefore, in this film formation, it is preferable to use an ion bombardment device that can easily form a thin film with high density and excellent self-supporting properties.

Next, the separation layer is removed by etching, and the obtained stabilized zirconia solid electrolyte thin film is peeled off from the substrate [step e)]. This step C) may also be carried out by cutting the substrate on which the thin film is formed into a suitable size using the tip of the nail.

Next, the etching process of the separation layer will be explained using an example in which an aluminum thin film is used as the separation layer.

First, the substrate-separation layer-electrolyte thin film laminate produced as described above is cut into a desired size, immersed in a common aluminum etching solution, and heated. As the heating continues, the aluminum separation layer dissolves and the electrolyte thin film peels off from the substrate. After removing the substrate, the etching solution is drained, and the remaining thin film is washed with alcohol, and then dried to obtain an independent stabilized zirconia solid electrolyte thin film.

The stabilized zirconia solid electrolyte thin film produced in this way can obtain a film thickness of 10 μm or less (generally 2 to 10 μm), which cannot be achieved with the conventional method of polishing a fired stabilized zirconia solid electrolyte thick film. In addition, the stabilized zirconia solid electrolyte thin film is composed only of a thin film and does not have a substrate, and can be used in a variety of forms.

In order to use this as a gas sensor element, an electrode film is attached. In that case, the electrode M (e.g., a platinum film) can be made of a laminate of a substrate, a separation layer, and an electrolyte thin film, with an arbitrary film thickness. In the process of formation, it may be laminated on both sides of the solid electrolyte membrane using a normal vacuum evaporation method.

For example, a separation layer (aluminum), an electrode layer (platinum), a solid electrolyte M (stabilized zirconia), and an electrode layer (platinum) may be laminated in this order on a glass substrate. Further, the electrode layer can be pattern-deposited depending on the shape.

[Operations and Effects of the Invention] The stabilized zirconia solid electrolyte thin film produced by the ion plating of the present invention is a thin film having a dense internal structure, and when used for example in an oxygen gas detection sensor or a humidity sensor, It has excellent effects such as miniaturization of the sensor, higher sensitivity, and improved reliability.

Furthermore, according to the method for producing a stabilized zirconia solid electrolyte thin film of the present invention, arbitrary parts and materials can be attached to both sides of the thin film in an arbitrary form, and various functional parts using the stabilized zirconia solid electrolyte can be attached. It can be done.

Next, examples of the present invention will be shown.

[Example] A glass substrate on which aluminum had been vapor-deposited in advance was used as a substrate. Further, a platinum film for electrodes was formed on the aluminum crotch using a normal vacuum deposition method.

Next, using the ion bombardment apparatus shown in FIG. 1, a 75 μm thick yttrium oxide stabilized zirconia (YSZ) thin film was formed on the platinum film for electrodes. Finally, a platinum film for electrodes was formed on the above thin film using a normal vacuum evaporation method. At this time, a evaporation mask with many holes was used to maintain insulation between the platinum films on both sides. did.

FIG. 2 shows a cross-sectional view of the thin film for gas sensor manufactured in this manner. In the figure, 9 is a glass substrate, 8 is an aluminum film, 7 is a YSZ film, and 6 is a platinum film (electrode).

Next, as shown in FIG. 3, this gas sensor thin film was cut along with the substrate at a place where there was no platinum film on the upper side, the aluminum film was removed by etching, and the yttrium oxide stabilized zirconia thin film was separated from the substrate.

Removal of aluminum film H3P O4: HN O3:
The process was carried out at 80° C. using an aluminum etching solution with a composition of CH, .C00H:H20=16:1:2:1, and a damage-free yttrium oxide stabilized zirconia thin film could be obtained.

[Brief explanation of the drawing]

FIG. 1 shows a conceptual diagram of the structure of an example of an ion bombardment apparatus preferably used for producing the stabilized zirconia solid electrolyte thin film of the present invention. FIG. 2 is a cross-sectional view showing the structure of the thin film for a stabilized zirconia solid electrolyte of the present invention in the manufacturing process. FIG. 3 is a plan view showing an example of cutting a thin film in the manufacturing process of the stabilized zirconia solid electrolyte thin film of the present invention. 1: Substrate 2: Evaporation source: Auxiliary electrode 4: Matching box: Power supply 6: Platinum film: Stabilized zirconia thin film for solid electrolyte 8 Nialuminum film Niglass substrate

Claims (2)

[Claims] 1. Film thickness 15μ manufactured by ion plating method
Stabilized zirconia solid electrolyte thin film of less than m. 2. a) forming an etchable separation layer on the substrate; b) forming a stabilized zirconia solid electrolyte thin film on the separation layer by ion plating; and c) removing the separation layer by etching. A method for producing a stabilized zirconia solid electrolyte thin film, comprising the step of separating the stabilized zirconia solid electrolyte thin film from the substrate.