JPH05157726A - Oxygen sensor - Google Patents

Abstract

PURPOSE:To obtain an oxygen sensor which can be manufactured by a simple production process and can achieve improved ion current characteristics. CONSTITUTION:An insulation coating 21 consisting of silicon oxide is formed on a surface of a flat silicon wafer 20, thus enabling the insulation coating 21 on the silicon wafer 20 to be flat and a stable critical current to be generated for a sensor element which consists of a solid electrolyte layer 22 and electrode layers 23 and 24 which are provided on the insulation coating 21. Also, a sensor element which consists of the solid electrolyte layer 22 and the electrode layers 23 and 24 is provided on one insulation coating 21 of the silicon wafer 20 and a pair of electrode layers 23 and 24 are provided only at one side of the solid electrolyte 22, thus enabling a manufacturing process to be simplified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film type oxygen sensor having good limiting current characteristics.

[0002]

2. Description of the Related Art FIG.
The structure shown in FIG. 8 is conventionally known. Among these oxygen sensors A to D, the oxygen sensors A to C have a thick film type structure, and the oxygen sensor D has a thin film type structure. In addition,
In the following description of the oxygen sensors A to D, the same reference numerals are given to the portions having the same configuration, and the description will be simplified.

First, the oxygen sensor A shown in FIG. 5 will be described. This oxygen sensor A is an ionic conductor Zr-.
Solid electrolyte layer 1 such as 8Y (ZrO ₂ -8 mol% Y ₂ O ₃ ).
And a pair of electrode layers 2 and 3 laminated on both surfaces of the solid electrolyte layer 1 to which a predetermined voltage is applied, and these solid electrolyte layer 1
And a ceramic substrate 6 such as forsterite, which is joined to the sensor element 4 formed of the electrode layers 2 and 3 and forms a closed space 5 with the sensor element 4, and between the sensor element 4 and the ceramic substrate 6. A gas diffusion hole 7 for communicating the enclosed space 5 with the outside and a heater 8 for heating a sensor provided on the upper surface of the ceramic substrate 6, and in the solid electrolyte layer 1, the sensor is provided. When the heater 8 for heating is turned on and a constant sensor monitoring voltage is applied to the electrode layers 2 and 3, an ionic current with oxygen ions as carriers is caused to flow by the oxygen pumping action. There is. The oxygen pumping action that occurs here is limited by the gas diffusion holes 7, and even if the sensor monitoring voltage is increased, the ion current value does not increase and remains constant (plateau state). It is designed to generate a limiting current.

In the thick film type oxygen sensors A to C, the difference between the oxygen sensor A (see FIG. 5), the oxygen sensor B (see FIG. 6), and the oxygen sensor C (see FIG. 7) is the gas. It is at the position where the diffusion holes are formed. That is, the gas diffusion holes 7 of the oxygen sensor A are formed in the ceramic substrate 6, while the gas diffusion holes 9 of the oxygen sensors B and C are formed on the sensor element 4 side. Further, in the oxygen sensor C shown in FIG. 7, reference numerals 10 and 11 respectively indicate a ceramic cap and a sealing material for forming a closed space on the upper surface of the sensor element 4.

Next, the thin film type oxygen sensor D will be described. The oxygen sensor D is formed by laminating a sensor element 13 on a porous ceramic substrate 12 formed of a porous ceramic such as forsterite. Yes, this sensor element 13 is Zr- which is an ionic conductor.
Solid electrolyte layer 14 such as 8Y (ZrO ₂ -8 mol% Y ₂ O ₃ ).
And a pair of electrode layers 15 and 16 which are respectively laminated on both surfaces of the solid electrolyte layer 14 and to which a predetermined voltage is applied to the solid electrolyte layer 14. Then, in the solid electrolyte layer 14, when a constant sensor monitoring voltage is applied to the electrode layers 15 and 16, oxygen ions are used as carriers by the oxygen pumping action, like the oxygen sensors A to C. Ion current is flowing. The porous portion of the porous ceramic substrate 12 functions as a gas diffusion hole that is conventionally known in oxygen sensors.

[0006]

By the way, in the oxygen sensors A to C, the electrode layers 2 and 3 are laminated on the respective surfaces of the solid electrolyte layer 1, and in the oxygen sensor D, the solid electrolyte layer 14 is formed. The electrode layers 15 and 16 are laminated on each surface, which increases the number of processes for production as compared with the case of forming electrodes on only one surface, which causes a problem that it is unsuitable for mass production. On the other hand, the oxygen sensor A in which the electrode layers 2 and 3 are formed on both surfaces of the solid electrolyte layer 1
~ C, in the oxygen sensor D in which the electrode layers 15 and 16 are formed on both surfaces of the solid electrolyte layer 14, these ion current characteristics are affected by the thickness of each solid electrolyte layer 1/14. Therefore,
In order to maintain good ionic current characteristics, it is necessary to strictly set the thickness of the solid electrolyte layer 1/14, which also causes a problem that the production process becomes complicated.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an oxygen sensor which can be manufactured by a simple production process and can obtain good ion current characteristics. ..

[0008]

In order to achieve the above object, in the present invention, an insulating coating made of silicon oxide formed on the surface of a silicon wafer, and a solid electrolyte layer laminated on the insulating coating. , A pair of electrode layers laminated on the solid electrolyte layer, to which sensor monitoring voltages are respectively applied, and a gas diffusion function that is provided so as to cover the entire electrode layers and has a gas diffusion function of partially penetrating the outside air. A layer, and the electrode layers are arranged on the insulating coating at regular intervals.

[0009]

According to the present invention, since the insulating coating made of silicon oxide is formed on the surface of the silicon wafer which is the substrate, the insulating coating can be easily formed, and the insulating coating is extremely Since it is formed on a flat silicon wafer, the upper surface of the insulating coating formed on the silicon wafer also becomes flat, whereby a sensor element composed of a solid electrolyte layer and an electrode layer is formed on the insulating coating. On the other hand, the limiting current can be generated in a stable state. On the other hand, the solid electrolyte layer and the electrode layer are provided on one of the insulating coatings of the silicon wafer, and since it is sufficient to provide the pair of electrode layers only on one side of the solid electrolyte,
The production process is simplified compared to conventional oxygen sensors. On the other hand, in this oxygen sensor, the ionic current characteristics depend on, for example, the distance between the electrodes arranged on the solid electrolyte layer, the degree of porosity of the gas diffusion layer, etc. The troublesome work of setting the thickness strictly can be omitted.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. The oxygen sensor E shown in FIG. 1 has an insulating film 21 made of silicon oxide (SiO2) provided on the lapping surface of a silicon wafer 20 used as a substrate.
And Zr-8Y laminated on one side of the insulating coating 21.
And (ZrO ₂ over 8mol% Y ₂ O ₃₎ or the like of the solid electrolyte layer 22,
Electrode layers 23 and 24 made of platinum, which are laminated on the solid electrolyte layer 22 and to which sensor monitoring voltages are applied, respectively.
And a gas diffusion layer 25 that is provided so as to cover the entire electrode layers 23 and 24 and has a gas diffusion function that allows a part of outside air to pass therethrough. Are arranged on the insulating coating 21 at regular intervals.

Further, the solid electrolyte layer 22 and the electrode layer 23.
24 is applied by screen printing, and the gas diffusion layer 25 covering the entire electrode layers 23 and 24 is applied by mixing powder of crystallized glass and steatite in a weight ratio of 3: 2. There is. Then, the solid electrolyte layer 2 applied to the insulating coating 21 on the silicon wafer 20 in this way
2, the electrode layers 23 and 24, and the gas diffusion layer 25 are finally fired so that the oxygen sensor E is manufactured.

In the oxygen sensor E constructed as described above, when a constant sensor monitoring voltage is applied to the electrode layers 23 and 24, as shown in FIG.
The oxygen pumping action causes an ion current with oxygen ions as carriers to flow, and the oxygen pumping action is limited by the gas diffusion layer 25, and the ion current value does not increase and becomes constant even if the sensor monitoring voltage is increased ( A plateau state) was satisfactorily obtained. In particular,
When the sensor monitoring voltage applied to the electrode layers 23 and 24 is gradually and continuously increased from 0 [V] to around 2.0 [V] in the atmosphere of 450 ° C., 0.7 to 1.3 [V ], It was confirmed that a limit current (a limit current value of 60 μA) is generated in which the ion current value does not increase even if the sensor monitoring voltage is increased.

Next, a second embodiment of the present invention will be described with reference to FIGS.
Will be described. The oxygen sensor F shown in FIG. 3 is different from the oxygen sensor E shown in FIG. 1 in the manufacturing method. That is, the solid electrolyte layer 30, the electrode layers 31, 32, and the gas diffusion layer 33, which are laminated on the insulating coating film 21 of the silicon wafer 20, are all formed by sputtering. In this case, Zr-8Y (ZrO ₂ -8 mol% Y ₂ O ₃ ) is used as a target material when forming the solid electrolyte layer 30.
Platinum was used as the target material when forming the electrode layers 31 and 32, and steatite was used as the target material when forming the gas diffusion layer 33. On the other hand, the electrode layers 31 and 32 on the solid electrolyte layer 30 were integrally formed by sputtering. After that, an etching process was performed to separate the electrode layers 31 and 32. Then, at this time, the distance between the electrode layer 31 and the electrode layer 32 was adjusted by etching so as to be about 10 μA.

In the oxygen sensor F constructed as described above, when a constant sensor monitoring voltage is applied to the electrode layers 31 and 32, as shown in FIG.
The oxygen pumping action causes an ion current with oxygen ions as carriers to flow, and the oxygen pumping action is limited by the gas diffusion layer 33, and the ion current value does not increase and becomes constant even if the sensor monitoring voltage is increased ( A plateau state) was satisfactorily obtained. In particular,
When the sensor monitoring voltage applied to the electrode layers 31 and 32 is gradually and continuously increased from 0 [V] to around 2.0 [V] in the atmosphere of 350 ° C., 0.7 to 1.3 [V ], It was confirmed that a limit current (the limit current value is 20 μA) is generated in which the ion current value does not increase even if the sensor monitoring voltage is increased.

In the oxygen sensor E / F described above, the insulating coating 21 made of silicon oxide is formed on the surface of the silicon wafer 20 which is the substrate.
The insulating coating 21 is formed on the surface of the silicon wafer 20 that is extremely flat, so that the insulating coating 21 formed on the silicon wafer 20 is also flat. Insulation film 2
1. Solid electrolyte layer 22 and electrode layer 23.2 provided on 1
4 and a sensor element F (see FIG. 1) including the solid electrolyte layer 30 and the electrode layers 31 and 32.
A stable limiting current can be generated. On the other hand, a sensor element E including the solid electrolyte layer 22 and the electrode layers 23 and 24 (see FIG. 1) and a sensor element F including the solid electrolyte layer 30 and the electrode layers 31 and 32 (see FIG. 2).
Is provided on one of the insulating coatings 21 of the silicon wafer 20 and the pair of electrode layers 23/24/31/32 is provided only on one side of the solid electrolyte 22/30.
The production process is simplified as compared with the conventional oxygen sensors A to D, and as a result, the industrial production is facilitated and the cost can be reduced.

On the other hand, in the oxygen sensors E and F, the ionic current characteristics are, for example, the distance between the electrode layers 23 and 24 arranged on the solid electrolyte layer 22/30, the distance between the electrode layers 31 and 32, and the gas diffusion layer 25. Since it depends on the porosity of / 33, etc., it is possible to omit the troublesome work of setting the thickness of the solid electrolyte layer 1/14 exactly like the conventional oxygen sensors A to D. Also in this, the effect that the production process can be made efficient and the cost can be reduced can be obtained.

[0017]

As described in detail above, according to the oxygen sensor of the present invention, since the insulating coating made of silicon oxide is formed on the surface of the silicon wafer which is the substrate, the insulating coating can be easily formed. In addition, since the insulating coating is formed on a silicon wafer that is extremely flat, the upper surface of the insulating coating formed on the silicon wafer is also flat, thereby providing the insulating coating. Further, the limiting current can be generated in a stable state for the sensor element including the solid electrolyte layer and the electrode layer.

On the other hand, the solid electrolyte layer and the electrode layer are provided on one of the insulating coatings of the silicon wafer, and it is sufficient to provide the pair of electrode layers only on one side of the solid electrolyte. To simplify the production process,
As a result, industrial production is facilitated and cost reduction is possible. On the other hand, in this oxygen sensor, the ionic current characteristics depend on, for example, the distance between the electrodes arranged on the solid electrolyte layer, the degree of porosity of the gas diffusion layer, etc. It is possible to omit the troublesome work of setting the thickness strictly, and also in this respect, we aim to improve the efficiency of the production process,
The effect that the cost can be reduced can be obtained.

[Brief description of drawings]

FIG. 1 is a front sectional view of an oxygen sensor E showing a first embodiment of the present invention.

FIG. 2 is a graph showing a limiting current characteristic of the oxygen sensor E shown in FIG.

FIG. 3 is a front sectional view of an oxygen sensor F showing a second embodiment of the present invention.

FIG. 4 is a graph showing limiting current characteristics of the oxygen sensor F shown in FIG.

FIG. 5 is a front sectional view showing a conventional oxygen sensor A.

FIG. 6 is a front sectional view showing a conventional oxygen sensor B.

FIG. 7 is a front cross-sectional view showing a conventional oxygen sensor C.

FIG. 8 is a front sectional view showing a conventional oxygen sensor D.

[Explanation of symbols]

E ... Oxygen sensor, F ... Oxygen sensor, 20 ... Silicon wafer, 21 ... Insulating film, 22 ... Solid electrolyte layer,
23/24 electrode layer, 25 gas diffusion layer, 30
Solid electrolyte layer, 31/32 ... Electrode layer, 33 ... Gas diffusion layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshinori Kato 1-5-1, Kiba, Koto-ku, Tokyo Inside Fujikura Electric Wire Co., Ltd.

Claims (1)

[Claims] 1. A silicon oxide insulating coating formed on the surface of a silicon wafer, a solid electrolyte layer laminated on the insulating coating, and a solid electrolyte layer laminated on the solid electrolyte layer, to which sensor monitoring voltages are applied respectively. A pair of electrode layers, and a gas diffusion layer having a gas diffusion function that is provided so as to cover all of the electrode layers and has a gas diffusion function that partially transmits the outside air. An oxygen sensor characterized in that it is arranged at a constant interval on the top.