JPH06102235A - Limiting current type oxygen sensor - Google Patents

Abstract

PURPOSE:To obtain a thin film-made limiting current type oxygen sensor which enables the obtaining of excellent limiting current characteristic by preventing penetration of an oxygen gas. CONSTITUTION:A Pt cathode electrode 12 and an anode electrode 13 are arranged on a ZrO2-BN substrate 11 as opposed to each other at a fixed interval in a comb-shaped pattern with one inserted into the other. A ZrO2-Y2O3 14 is arranged as an oxide ion conducting film on the substrate where the cathode electrode 12 and the anode electrode 13 are formed. The ZrO2-Y2O3 film 14 is formed in a pattern having a window 15 to discharge an oxygen gas generated in the anode electrode 13 thereby enabling the checking of the oxygen gas from penetrating into the cathode electrode 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a limiting current type oxygen sensor, and more particularly to a thin film type limiting current type oxygen sensor in which an ionic conductor and electrodes are formed by a thin film technique.

[0002]

2. Description of the Related Art Conventionally, zirconium oxide stabilized with yttrium (Y), that is, zirconia-yttria (ZrO ₂ -Y ₂ O ₃ ) is used as an ion conductor (solid electrolyte).
A ceramic oxygen sensor used as is known. In the bulk type ceramic oxygen sensor, ZrO ₂ —Y ₂ O
₃ Ionic conductor bulk is obtained by press molding and firing,
A Pt electrode having a catalytic function is formed by printing and firing a Pt paste. Such a conventional bulk type limiting current type oxygen sensor is shown in FIGS. 4 (a) to 4 (c). Figure 4
In (a), a Pt cathode electrode 2 is formed on both surfaces of a ZrO ₂ —Y ₂ O ₃ sintered body substrate 1 having ionic conductivity by a printing method.
The element chip on which the anode electrode 3 is formed is the support base 4
It is supported by the glass material 5 at a predetermined interval. A small gas diffusion hole 6 for obtaining a limiting current characteristic is formed in the supporting substrate 4, and ZrO ₂ —Y ₂ is formed on the small gas diffusion hole 6.
A heater 7 for activating the O ₃ sintered body substrate 1 is provided. In FIG. 4B, the gas diffusion hole 6 is formed on the element chip side, contrary to FIG. 4A. Figure 4 (c) is
In this example, the supporting gas 4 and the glass material 5 in (b) are integrally molded.

For these bulk type ceramic oxygen sensors, in recent years, in order to miniaturize, miniaturize, mass-produce elements, etc., ZrO ₂ --Y ₂ O ₃ ion conductors and electrodes have been formed by vapor deposition or sputtering. A thin film type ceramic oxygen sensor formed by thin film technology has been proposed. FIG. 4 (d) shows such a thin film type limiting current type oxygen sensor. This is because a gas permeable insulating substrate 8 is used to obtain a limiting current characteristic by controlling the diffusion of oxygen molecules, and a gas permeable insulating substrate 8 is formed on the insulating substrate 8 by sputtering.
Pt cathode electrode _{2 ', ZrO 2 -Y 2 O} 3 film 1', P
It is obtained by sequentially stacking the t anode electrodes 3 '.

However, the thin-film oxygen sensor shown in FIG. 4 (d) is of a sandwich type in which electrodes are formed on both sides of the ionic conductor film, so that the ionic current characteristics greatly affect the thickness of the ionic conductor film. To be done. Therefore, strict thickness control is required. Therefore, as a thin film type oxygen sensor structure in which the influence of the thickness of the ion conductor film is small, as shown in FIG. 5, both the cathode electrode 2'and the anode electrode 3'are provided on the substrate 8 side of the ion conductor film 1 '. Planar structures formed as interdigitated comb patterns have been considered.

[0005]

However, when the planar structure as shown in FIG. 5 is adopted, when the element is downsized and the distance between the cathode electrode 2'and the anode electrode 3'is reduced,
The wraparound of oxygen gas becomes a problem. This is shown in FIG. The oxygen gas generated by the electrode reaction at the anode electrode 3'has to be discharged to the outside through the substrate 8, and a part of the oxygen gas diffuses laterally in the substrate 8 as shown by a broken line, and the cathode electrode 2 '. Wrap around. This is an obstacle to obtaining a flat current saturation characteristic with a small oxygen sensor. The present invention has been made in consideration of such circumstances, and a thin film type limiting current type oxygen sensor capable of obtaining an excellent limiting current characteristic by suppressing oxygen gas wraparound when miniaturized. The purpose is to provide.

[0006]

In a limiting current type oxygen sensor according to the present invention, first, at least a pair of a cathode electrode and an anode electrode are arranged on a gas permeable substrate so as to face each other at a predetermined interval, and above that. Characterized by having a planar structure in which an oxide ion conductor film is disposed on the cathode, and the oxide ion conductor film is selectively disposed so as to cover a part from the cathode electrode to the anode electrode. I am trying. Secondly, in the limiting current type oxygen sensor according to the present invention, a cathode electrode is formed in a comb pattern on a gas permeable substrate, and an oxide ion conductor film is formed on the entire surface of the substrate on which the cathode electrode is formed. The anode electrode is formed on the oxide ion conductor film in a comb pattern overlapping the cathode electrode.

[0007]

In the oxygen sensor structure according to the first aspect of the invention, since the upper surface of the anode electrode is open, the oxygen gas generated at the anode electrode is easily released from the upper surface. Therefore, the phenomenon that the oxygen gas generated at the anode electrode returns to the cathode electrode again is suppressed. As a result, excellent limiting current characteristics can be obtained. In the oxygen sensor structure according to the second aspect of the present invention, the cathode electrode, the oxide ion conductor film, and the anode electrode are of a thin film type laminated in this order, and the ionic current generated at the cathode electrode moves upwards through the oxide ion conductor film. Oxygen gas flowing to the anode electrode and being generated by the electrode reaction of the anode electrode is easily released to the upper portion because the upper surface of the anode electrode is exposed. Therefore, the wraparound phenomenon of oxygen gas generated at the anode electrode is suppressed, and excellent limiting current characteristics can be obtained.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. 1 (a) and 1 (b) are plan views of a planer type limiting current type oxygen sensor according to one embodiment of the present invention and its AA ′.
FIG. In this example as a gas permeable substrate,
A ZrO ₂ -BN (BN 10%) substrate 11 is used,
A Pt cathode electrode 12 and a Pt anode electrode 13 are arranged on the upper surface of the Pt cathode electrode 12 and the Pt anode electrode 13 so as to face each other at a predetermined interval in a comb pattern. Cathode electrode 12
The anode electrode 13 is formed by sputtering using a metal mask. These cathode electrodes 12
On the substrate on which the anode electrode 13 is formed, a ZrO ₂ -8 mol% Y ₂ O ₃ film 14 is formed as an oxide ion conductor film.
(Hereinafter simply referred to as ZrO ₂ —Y ₂ O ₃ film) is provided.

Here, ZrO ₂ −, which is an ion conductor film, is used.
The Y ₂ O ₃ film 14 is selectively formed so as to cover a part of the anode electrode 13 from above the cathode electrode 12, that is, with the window 15 opened on the upper surface of the anode electrode 14. Specifically, for the ZrO ₂ —Y ₂ O ₃ film 14 having such a pattern, for example, a metal mask having a window is arranged on the anode electrode 13, and a mixed gas of argon and oxygen using a Zr—Y alloy target is used as a carrier. It is formed by reactive sputtering using gas. It can also be formed by sputtering using a ZrO ₂ —Y ₂ O ₃ ceramic target.

In this limiting current type oxygen sensor, the substrate 11
Oxygen molecules are supplied to the cathode electrode 12 through diffusion control, oxygen ions are generated at the cathode electrode 12, and this is ZrO ₂ −.
An ion current flows in the Y ₂ O ₃ film 14. At this time, the oxygen gas generated by the electrode reaction at the anode electrode 13 is
Since the upper surface of the anode electrode 13 is opened by the window 15, it is emitted to the outside from here. Therefore, it is possible to suppress the phenomenon that the release of the oxygen gas is prevented and the oxygen gas circulates again to the cathode electrode 12 through the substrate as in the conventional case.

FIG. 3 shows a concrete limiting current characteristic of the sensor of this embodiment together with a comparative example. The ZrO ₂ -BN substrate 11 used has a size of 5 mm × 5 mm × 0.2 mm, the cathode electrode 12 and the anode electrode 13 have a thickness of 0.2 μm, a line width a = 75 μm, and a facing distance b of comb teeth b = 50 μm. Of 2
There were 0 pairs of patterns. In addition, the ZrO ₂ —Y ₂ O ₃ film 1
No. 4 has a film thickness of 0.5 μm, and the width c of the portion covering the cathode electrode 12 between the adjacent windows 15 is 180 μm.
Width d = 70 μm. In the comparative example, the ZrO ₂ —Y ₂ O ₃ film, which is an ion conductor film, covers the entire surface of the substrate so that the cathode electrode and the anode electrode are not exposed.
It is an element produced under the same conditions as in the example. As is clear from FIG. 3, in this example, very good limiting current characteristics were obtained. The measurement temperature is 450 ° C. The reproducibility of the characteristics was also good, and almost the same limiting current characteristics were obtained for the 30 prototype sensors.

With the same device structure as the above embodiment, the electrode width a
= 100 μm, electrode spacing b = 100 μm, adjacent window 1
The width c of the portion covering the cathode electrode 12 between 5 and c = 310 μ
A slightly larger oxygen sensor was manufactured with m 2, and therefore the width d of the window 15 = 90 μm. For this prototype sensor, the current rise characteristics were slightly degraded compared to the above-mentioned embodiment,
Regarding the limiting current characteristics, good characteristics with extremely excellent flatness were obtained.

FIGS. 2 (a) and 2 (b) are a plan view showing a limiting current type oxygen sensor of another embodiment of the present invention and a sectional view taken along the line AA 'thereof. Although this embodiment is a thin film type, it is not a planar type in which a cathode electrode and an anode electrode are on the same surface, but a sandwich type in which these are arranged with an ion conductor film sandwiched therebetween. A Pt cathode electrode 12 is formed in a comb pattern on a ZrO ₂ —BN substrate 11 similar to that in the previous embodiment, and a ZrO ₂ —Y ₂ O oxide film is formed on the entire surface so as to cover the cathode electrode 12. ₃ film 1
4 are arranged, and the Pt anode electrode 13 is further formed thereon in a comb pattern. Cathode electrode 12
And the anode electrode 13 is patterned by sputtering using a metal mask. ZrO ₂ -Y
_{The 2} O ₃ film 14 is formed by reactive sputtering using a mixed gas of argon and oxygen with a Zr—Y alloy target as a carrier gas. As is clear from the figure, the cathode electrode 12 and the anode electrode 13 are ZrO ₂ —Y ₂ O ₃
A pattern is formed so that the comb-tooth portions overlap with each other so as to face each other with the film 14 interposed therebetween.

The ZrO ₂ -BN substrate 11 used is 5 mm ×
5 mm × 0.2 mm, the cathode electrode 12 and the anode electrode 13 have an electrode width a = 75 μm and an electrode interval b = 50.
20 μm pattern of μm. The electrode film thickness is 0.5 μm for the cathode electrode 12 and 0.3 μm for the anode electrode 13. The ZrO ₂ —Y ₂ O ₃ film 14 has a film thickness of 0.8.
μm. In the sensor of this embodiment, the anode electrode 1
The oxygen gas generated here is effectively released to the outside because the portion other than the portion of the No. 3 contacting the ZrO ₂ —Y ₂ O ₃ film 14 is released. Therefore, the deterioration of the limiting current characteristic due to the wraparound of oxygen gas was prevented, and the same excellent limiting current characteristic as that of the previous example was obtained. Both electrode width and spacing are 10
In addition to 0 μm, excellent limit current characteristics were obtained for the sensor manufactured as a trial under the same conditions as in the above embodiment.

The present invention is not limited to the above embodiment. In the examples, ZrO ₂ —Y ₂ O ₃ was used as the oxide ion conductor, but the present invention can be similarly applied to a thin film oxygen sensor using another oxide ceramic thin film. The present invention is also effective when other materials are used for the gas permeable substrate or the electrode for obtaining the limiting current characteristic.

[0016]

As described above, according to the present invention, by ensuring the release portion of the oxygen gas generated by the electrode reaction at the anode electrode, it is possible to suppress the characteristic deterioration due to the wraparound of the oxygen gas and to achieve an excellent limit. It is possible to provide a thin film type limiting current type oxygen sensor capable of obtaining current characteristics.

[Brief description of drawings]

FIG. 1 is a plan view showing a limiting current type oxygen sensor according to an embodiment of the present invention and a sectional view taken along the line AA ′.

FIG. 2 is a plan view showing a limiting current type oxygen sensor according to an embodiment of the present invention and a sectional view taken along the line AA ′.

FIG. 3 is a characteristic diagram of the oxygen sensor of the oxygen sensor of the embodiment of FIG.

FIG. 4 is a configuration example of a conventional oxygen sensor.

FIG. 5 is a diagram showing how the conventional planar type oxygen sensor circulates oxygen gas.

[Explanation of symbols]

11 ... ZrO ₂ -BN substrate, 12 ... Pt cathode electrode,
13 ... Pt anode electrode, 14 ... ZrO ₂ —Y ₂ O ₃
Membrane, 15 ... window.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Issei Ishibashi 1-5-1, Kiba, Koto-ku, Tokyo Within Fujikura Electric Wire Co., Ltd. (72) Inventor Yoshinori Kato 1-5-1, Kiba, Koto-ku, Tokyo Fujikura Electric Wire Co., Ltd.

Claims (2)

[Claims] 1. A gas-permeable substrate, at least a pair of a cathode electrode and an anode electrode arranged on the substrate so as to face each other at a predetermined interval, and to cover a part of the anode electrode from above the cathode electrode. A limiting current type oxygen sensor, comprising: 2. A gas permeable substrate, a cathode electrode formed in a comb pattern on the substrate, an oxide ion conductor film formed on the entire surface of the substrate on which the cathode electrode is formed, A limiting current type oxygen sensor, comprising: an anode electrode formed in a comb-shaped pattern overlapping the cathode electrode on a material ion conductor film.