JP2514567B2 - Limit current type oxygen sensor - Google Patents

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.

[0002]

2. Description of the Related Art Conventionally, zirconium oxide stabilized with yttrium (Y), that is, zirconia-yttria (ZrO2-Y2O3) has been used as an ion conductor (solid electrolyte).
A ceramic oxygen sensor used as is known. In bulk type ceramic oxygen sensor, ZrO2 -Y2 O
3 Ion conductor bulk is obtained by press molding and firing,
A porous Pt electrode having a catalytic action is formed by a thick film technique, that is, Pt paste printing and firing.

In such a ceramic oxygen sensor,
In order to obtain the limiting current characteristic, a gas diffusing means for supplying oxygen gas to the cathode electrode with diffusion rate control is required. Therefore, conventionally, a method has been used in which a cap having a small hole is provided on the cathode electrode side and the gas inflow is restricted by the small hole. On the other hand, the present inventors
Various methods have been proposed for using a porous solid film as a gas diffusion layer instead of a cap having small holes. One of them is to use the cathode electrode lead portion formed continuously with the cathode electrode, which is a porous Pt film, as it is as a gas diffusion layer.

[0004]

However, when the lead portion of the Pt cathode electrode is used as it is as a gas diffusion layer, the following problems occur in maintaining the characteristics and reliability of the sensor. The oxygen sensor is usually used in an atmosphere of a temperature of several 100 ° C., and an electric current is passed through the cathode electrode. Energy generated by these temperatures and currents causes grain growth of the porous Pt film, which is an electrode material, and the stability of the limiting current characteristics cannot be maintained. Further, since the ionic conductivity of the ionic conductor becomes higher as the temperature becomes higher, if an attempt is made to secure a lead width required for the gas diffusion layer, the leak current becomes large, and excellent limiting current characteristics cannot be obtained. On the contrary, when the thin electrode lead part is used as the gas diffusion layer, the pores of the gas diffusion layer are clogged with soot etc.,
Oxygen gas cannot be supplied to the cathode electrode while maintaining the necessary diffusion rate control.

The present invention has been made in consideration of such circumstances, and an object thereof is to provide a limiting current type oxygen sensor having excellent device characteristics and high reliability.

[0006]

A limiting current type oxygen sensor according to the present invention covers an ion conductor, a cathode and an anode electrode formed by a porous layer in contact with both surfaces of the ion conductor and facing each other, and a cathode electrode. And a dome glass layer formed as described above, and at least one gas diffusion layer integrally formed with the cathode electrode, in addition to the lead portion of the cathode electrode.

[0007]

In the present invention, since the gas diffusion layer is provided separately from the lead portion of the cathode electrode, no current flows in the gas diffusion layer. Therefore, there is no deterioration of device characteristics due to grain growth of the gas diffusion layer material, and there is no leakage current passing through the gas diffusion layer. Further, if a plurality of gas diffusion layers are provided, the influence of clogging etc. is reduced accordingly. As described above, a highly reliable oxygen sensor having excellent limiting current characteristics can be obtained.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. 1A and 1B show a main configuration of a limiting current type ceramic oxygen sensor according to an embodiment of the present invention. (A) is a top view (cathode side), (b) is AA 'of (a). Cross section,
(c) is a rear view (anode side). As the oxide ceramic ion conductor substrate 1, in this embodiment, 6.5 mm
φ, 0.14mm thick stabilized zirconia (ZrO2-8m
ol% Y2 O3). The cathode electrode 2 having a circular pattern is formed on the central portion of one surface of the ion conductor substrate 1 by printing and firing the Pt paste, and on the other surface, a circular pattern is formed by printing and firing the Pt paste on the central portion. A patterned anode 3 is formed. These cathode electrode 2 and anode electrode 3 have a size of 4 mm.
It is a Pt electrode having a diameter of φ and a thickness of 5 μm.

A lead portion 21 for connecting the cathode electrode 2 to the terminal portion is formed continuously with the cathode electrode 2. In addition to the lead portion 21, four gas diffusion layers 22 (221 to 22) for supplying oxygen gas to the cathode electrode 2 are provided.
4) is also made of the same material as the cathode electrode 2 and is patterned integrally with this. In the case of this embodiment, the four gas diffusion layers 22 are arranged at 90 ° intervals, and the lead portion 21 is arranged between the two. Also on the anode electrode 3 side, the anode electrode lead portion 31 is continuously formed with this.
Are patterned. Anode electrode lead portion 31
Are arranged in a direction orthogonal to the cathode electrode lead portion 21.

On the cathode electrode 2 side, the cathode electrodes 2,
Dome glass layer 4 in which crystallized glass and ceramic powder are blended so as to cover the lead portion 21 and the gas diffusion layer 22.
Has been applied. The ends of the lead portions 21 are exposed so as not to be covered with the dome glass layer 4 in order to connect to the terminals as described later. Similarly, the end of the gas diffusion layer 22 is not covered with the dome glass layer 4 and is used as a gas inlet. A sealing glass layer 5 is further formed on the dome glass layer 4 so as to cover the region of the cathode electrode lead portion 21. This is the lead part 2
1 is used only for electrical conduction, and the gas diffusion layer 22
Is to clearly separate the functions.

Although not shown in FIG. 1, an anode terminal 6, a cathode terminal 7, heater terminals 8 and 9 and a heater 10 are further disposed on the dome glass layer 4 on the cathode electrode side as shown in FIG. It The terminals 6, 7, 8, 9 and the heater 10 are also Pt films having a thickness of several μm formed by printing and firing Pt paste. The anode electrode lead 31 and the anode terminal 6 are connected using the side surface of the substrate.

According to this embodiment, the gas diffusion layer 22 and the cathode electrode lead portion 21 are separately provided and their functions are separated. That is, no current flows in the gas diffusion layer 22. Therefore, P of the gas diffusion layer 22 is changed by temperature and current.
Grain growth does not occur in the t layer and the device characteristics are not deteriorated. Further, since there is no leak current passing through the gas diffusion layer 22, excellent element characteristics having a flat limiting current value can be obtained. Further, since four gas diffusion layers 22 are provided, the influence of clogging and the like is reduced accordingly, and the reliability is improved.

FIG. 5 shows the characteristics of the limiting current type oxygen sensor according to this embodiment at an operating temperature of 400.degree. The solid line is the embodiment, and the broken line is the device characteristic of the structure in which one cathode electrode lead is used as it is as the gas diffusion layer. As is clear from the figure, excellent limiting current characteristics are obtained in this embodiment. As a result of a heat cycle test and an accelerated deterioration test, it was confirmed that excellent reliability was obtained.

FIG. 3 shows an anode side pattern of a limiting current type oxygen sensor according to another embodiment of the present invention, corresponding to FIG. 1 (c). The pattern on the cathode side is similar to that of the embodiment shown in FIG. FIG. 4 is a sectional view taken along the line BB ′ of FIG. In this embodiment, a flat end face 11 is provided by partially cutting out a region of the circular anode electrode 3 overlapping the cathode electrode lead portion 21. The dimensions of the notch are shown in Fig. 4.
It is about 2 mm as shown in.

According to this embodiment, as a result of effectively suppressing the leak current between the cathode electrode lead portion 21 and the anode electrode 3, it is possible to obtain an element exhibiting a more excellent flat limiting current value.

The present invention is not limited to the above embodiment. For example, in the embodiment, four gas diffusion layers functionally separated from the cathode electrode lead portion are provided, but at least one gas diffusion layer may be provided separately from the cathode electrode lead portion. The difficulty in using a gas diffusion layer as one unit is solved to some extent. In the embodiment, the cathode electrode lead portion is covered with the sealing glass and is used only for electrical conduction. However, even if the cathode electrode lead portion also serves as the gas diffusion layer, this If there is another gas diffusion layer, a certain effect can be obtained. Further, the anode electrode structure of the embodiment shown in FIG. 3 is effective even if it is adopted in a structure in which the cathode electrode lead and the gas diffusion layer are not functionally separated, that is, one cathode electrode lead is used as it is as a gas diffusion layer. is there.

[0017]

As described above, according to the present invention, a limiting current type oxygen sensor having excellent device characteristics and reliability is obtained by providing a gas diffusion layer continuous with the cathode electrode separately from the cathode electrode lead. be able to.

[Brief description of drawings]

FIG. 1 is a diagram showing a main part configuration of a limiting current type oxygen sensor according to an embodiment of the present invention.

FIG. 2 is a diagram showing a terminal portion pattern of the embodiment.

FIG. 3 is a diagram showing an anode side pattern of a limiting current type oxygen sensor according to another embodiment of the present invention.

FIG. 4 is a sectional view taken along line BB ′ of FIG.

5 is a diagram showing device characteristics of the embodiment of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Oxide ceramic ion conductor substrate, 2 ... Pt cathode electrode, 3 ... Pt anode electrode, 4 ... Dome glass layer, 5 ... Sealing glass layer, 21 ... Cathode electrode lead part, 221-224 ... Gas diffusion layer , 31 ... Anode electrode lead part.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shoji Sukuri 1-5-1 Kiba, Koto-ku, Tokyo Fujikura Ltd. (72) Inventor Isao Ishibashi 1-1-5 Kiba, Koto-ku, Tokyo Fujikura Co., Ltd. (72) Inventor Yoshinori Kato 1-5-1, Kiba, Koto-ku, Tokyo Co., Ltd. Fujikura Co., Ltd. (56) Reference JP-A-6-294768 (JP, A) , U) Special Table 3-500085 (JP, A) Special Table 63-501379 (JP, A)

Claims (1)

(57) [Claims] 1. A cathode electrode comprising an ionic conductor, a cathode and an anode electrode formed by porous films in contact with each other and facing each other, and a dome glass layer formed so as to cover the cathode electrode. A limiting current type oxygen sensor, characterized in that it has at least one gas diffusion layer integrally formed with the cathode electrode by the same material as the cathode electrode, separately from the lead part.