JPH0720085A - Limiting current type oxygen sensor - Google Patents

Abstract

(57) [Summary] [Purpose] A structure that is easy to manufacture assuming that the limiting current characteristics are uniform and that is suitable for mass production. A gas permeable substrate 1 made of porous alumina or the like, an anode electrode thin film 2 in a comb pattern uniformly formed on one surface of the substrate so as to have a porous property, and this anode An ion conductor thin film 3 of stabilized zirconia or the like formed on the electrode thin film 2, a comb-shaped cathode electrode thin film 4 formed on the ion conductor thin film 3, the cathode electrode thin film 4 and the ion conductor. The porous layer 5 formed on the thin film 3 and the diffusion-controlling layer 6 which is a part of the porous layer 5
Except for the above, the sealing layer 7 formed of crystallized glass or the like covers all of the above.

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 using an ionic conductor.

[0002]

2. Description of the Related Art A limiting current type oxygen sensor detects an oxygen concentration by utilizing the fact that the amount of oxygen introduced into an ionic conductor and the current using oxygen ions in the ionic conductor as carriers correspond to each other. Is. That is, when electrodes are provided on both sides of the ion conductor and a voltage is applied between the electrodes,
A current flows using oxygen ions in the ionic conductor as carriers. If the amount of oxygen introduced into the ionic conductor per unit time is narrowed, the current does not increase above a certain value even if the voltage applied between the electrodes is increased. This current value is called the limiting current and corresponds to the amount of oxygen introduced into the ionic conductor per unit time, and the oxygen concentration in the surrounding atmosphere can be known from this current value.

As a structure for reducing the amount of oxygen introduced into the ionic conductor per unit time, it is general to provide a cap that hermetically covers one surface of the ionic conductor and to provide a small hole in the cap. In order to reduce the sensor thickness and facilitate manufacturing, it has been considered to use a porous substrate and utilize the gas permeability of the substrate.

[0004]

However, in the conventional limiting current type oxygen sensor having a thinned structure,
There are problems such as gas permeability in the electrodes, and it is not easy to mass-produce electrodes with uniform limiting current characteristics.

In view of the above, it is an object of the present invention to provide a limiting current type oxygen sensor which is easy to manufacture with uniform limiting current characteristics and which is suitable for mass production.

[0006]

In order to achieve the above object, in the limiting current type oxygen sensor according to the present invention,
A porous substrate having gas permeability, an anode electrode thin film uniformly formed on one surface of the substrate so as to have a porous property, and an ion conductor thin film formed on the anode electrode thin film, Further, a comb-shaped cathode electrode thin film formed on the ion conductor thin film, a porous layer formed on the cathode electrode thin film and the ion conductor thin film, and further, the porous layer is covered except for a part thereof. It is characterized by having a sealing layer.

[0007]

[Function] The ion conductor thin film is sandwiched between the anode electrode thin film and the cathode electrode thin film, but the anode electrode thin film is formed on a porous substrate and reflects the surface state of the substrate. It is easy to make it porous and to have gas permeability. On the other hand, the cathode electrode thin film cannot be made porous because it is formed on the ion conductor thin film having a dense surface. Therefore, the cathode electrode thin film has a comb-shaped pattern to ensure the gas flow in the gap between the patterns. The porous layer formed on the cathode electrode thin film and the ion conductor thin film is covered with the sealing layer except for a part thereof, but oxygen is introduced from the uncovered part (that is, the exposed part) to form the porous layer. It diffuses throughout the layer and is guided into the ionic conductor. Therefore, the exposed portion functions as a diffusion-controlling layer, and the amount of oxygen introduced into the ionic conductor per unit time can be determined by the shape of the exposed portion. It is easy to control the porosity of the porous layer, that is, the air permeability, and the shape and the like of the exposed portion can be manufactured with high reproducibility. Therefore, it is easy to make the limiting current characteristics uniform.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a plan view of a chip of a limiting current type oxygen sensor according to the present invention, and FIG. 2 is a sectional view taken along the line AA of FIG. As shown in these figures, the anode electrode thin film 2 is uniformly formed on the gas permeable substrate 1 so as to have a porous property. An ion conductor thin film 3 is formed thereon, and a comb-shaped cathode electrode thin film 4 is further formed on the ion conductor thin film 3, similarly to the anode electrode thin film 2 described above. The ion conductor thin film 3 is formed by sputtering or vapor deposition, for example. Then, a porous layer 5 having gas permeability is formed so as to cover the cathode electrode thin film 4 and the ion conductor thin film 3. The porous layer 5 is formed in a pattern having a thin lead portion 6. The lead-out portion 6 functions as a diffusion rate controlling layer as described later. Further, a sealing layer 7 made of crystallized glass or the like is formed so as to cover the entire porous layer 5 except the tip of the diffusion controlling layer (lead-out portion) 6.

The limiting current type oxygen sensor having such a structure is specifically manufactured, for example, as follows. First, as the gas permeable substrate 1, for example, alumina (Al
The surface of a porous substrate made of ₂ O ₃ ) material or the like is machined to be flat. Then, an anode thin film 2 is formed by sputtering platinum as a target. Thus, a uniform anode electrode thin film 2 is formed so as to cover almost the entire surface of the substrate 1. Next, stabilized zirconia (ZrO ₂ -8 mol% Y ₂ O ₃ )
An ion conductor thin film 3 is provided by using the target of No. 2, and a cathode electrode thin film 4 having a comb pattern is formed on the ion conductor thin film 3 by sputtering similarly to the anode electrode thin film 2. The cathode electrode thin film 4 and the ion conductor thin film 3
The porous layer 5 on the top is made of steatite ceramic powder 5
Print (apply) crystallized glass paste with 0 wt% addition
It is formed by doing. At the time of printing, the drawer portion 6 is formed in the pattern as shown. Further, the sealing layer 7 which covers the porous layer 5 except for the lead-out portion 6 is formed by printing (applying) crystallized glass 10
It is formed by baking at a temperature of 00 ° C. for 10 minutes. Finally, although not shown, a heater is formed on the sealing layer 7 by printing a platinum paste to complete the process. Although this heater may be provided on the back surface side of the substrate 1, it is preferable to be on the sealing layer 7 from the viewpoint of being close to the ion conductor thin film 3 and having high heating efficiency.

When the limiting current type oxygen sensor thus obtained was actually measured, a voltage-current characteristic as shown in FIG. 3 could be obtained. This measurement was carried out in an air atmosphere at 200 ° C., but it was found that very good limiting current characteristics were obtained as shown in FIG.

Generally, when the electrode thin films 2 and 4 are formed by sputtering or the like as described above, the formed electrode thin films 2 and 4 tend to have a dense structure, and in terms of gas permeability for gas exchange. Although there is a drawback, the anode electrode thin film 2 can be made porous because it is formed on the surface of the porous substrate 1. That is, when the anode electrode thin film 2 is formed on the porous substrate 1 by sputtering, the electrode thin film 2 having a porous shape can be obtained by reflecting the surface state of the substrate 1, and is uniformly formed on the entire surface. The gas permeability can be assured even if the gas is changed.

On the other hand, the cathode electrode thin film 4 is provided on the ionic conductor thin film 3, and the ionic conductor thin film 3 is provided.
Since the surface of is very dense, the electrode thin film 4
Is a very dense film and does not have gas permeability. Therefore, the electrode thin film 4 has a comb-shaped pattern as described above, so that the surface area thereof is reduced and air is allowed to flow in and out of the ion conductor thin film 3.

Oxygen flows in from the end of the lead-out portion 6 of the porous layer 5 exposed from the sealing layer 7, spreads over the entire porous layer 5, is introduced to the surface of the ion conductor thin film 3, and is oxygen. Become an ion. The oxygen ions move to the side of the anode electrode thin film 2 and a current flows between the anode electrode thin film 2 and the cathode electrode thin film 4. Then, the oxygen generated on the back surface of the ion conductor thin film 3 permeates the porous substrate 1 and goes out to the back surface side.

Therefore, the amount of oxygen introduced into the ionic conductor thin film 3 is determined by the amount of permeated air per unit area of the porous layer 5, the cross-sectional area of the thin lead portion 6, and its length. That is, this drawer 6
Is made to function as a diffusion control layer. This porous layer 5
Since it is easy to control the degree of porosity, that is, the air permeability, a limiting current type oxygen sensor with uniform limiting current characteristics can be easily manufactured. On the other hand, when the gas permeability of the substrate 1 is used as the diffusion rate-controlling property, it is difficult to control the gas permeability and it is difficult to make the limiting current characteristics uniform. Therefore, it can be said that this limiting current type oxygen sensor has a structure suitable for mass production of products with uniform characteristics.

[0015]

As described above with reference to the embodiments, according to the limiting current type oxygen sensor of the present invention, it is possible to easily obtain the one having uniform limiting current characteristics even in mass production.

[Brief description of drawings]

FIG. 1 is a plan view of a limiting current type oxygen sensor according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a graph showing voltage-current characteristics of the example.

[Explanation of symbols]

 1 Gas Permeable Substrate 2 Uniform Anode Electrode Thin Film 3 Ion Conductor Thin Film 4 Cathode Electrode Thin Film with Comb Pattern 5 Porous Layer 6 Diffusion Controlling Layer 7 Sealing Layer

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

Claims (1)

[Claims] 1. A porous substrate having gas permeability, an anode electrode thin film uniformly formed on one surface of the substrate so as to have a porous property, and ions formed on the anode electrode thin film. The conductive thin film, the comb-shaped cathode electrode thin film formed on the ion conductive thin film, the porous layer formed on the cathode electrode thin film and the ion conductive thin film, and the porous layer, respectively. A limiting current type oxygen sensor having a sealing layer which covers except a portion.