JPH07190987A - Limiting current-type oxygen sensor - Google Patents

Abstract

PURPOSE:To improve mechanical strength and thermal efficiency by providing a through hole penetrating to a rear surface on a sensor chip mounting member. CONSTITUTION:An electrode 2a for connecting a heater 2, a connection electrode 3a for a cathode, and a connection electrode 3b for an anode are provided on a cap of a sensor chip 1. On the other hand, a chip mounting member 4 is constituted of an angular cylindrical insulation member 5 formed by porous ceramic. Then, a through hole 6 penetrating from the upper surface to the rear surface along the center axis is provided. Therefore, the gas inside the hole 6 acts as a heat-insulating material, thus suppressing the heating of the mounting member 4, and increasing heat efficiency. The mounting member 4 is a cylindrical structure and the hole 6 is provided at a position matching the heater 2. Therefore, even if the sensor chip 1 is curved, the contact with the mounting member 4 can be avoided. The mounting member 4 is produced by extruding ceramic in a tube shape by injection molding, etc., in a mass production.

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 which is small and inexpensive and is used for an oil fan heater or the like, and more particularly to a limiting current sensor having a pair of electrodes arranged with a solid electrolyte substrate interposed therebetween. The present invention relates to a limiting current type oxygen sensor that detects oxygen concentration in gas by utilizing its characteristics.

[0002]

2. Description of the Related Art FIG. 6 is a sectional view showing an example of a sensor chip of a limiting current type oxygen sensor. In this type of limiting current type oxygen sensor chip, a cathode electrode 42 and an anode electrode 43 are formed with a solid electrolyte substrate 41 made of stabilized zirconia interposed therebetween. These electrodes 42,
43 is made of porous platinum,
Gas can flow through the inside. Further, a cap 44 having an open lower end is provided on the surface of the solid electrolyte substrate 41 on the cathode electrode 42 side with the lower end edge fixed to the substrate 41, whereby the cap 44 and the substrate 41 are surrounded. A closed internal space is formed. The cathode electrode 42 is in contact with this internal space, and the anode electrode 43 is in contact with the external atmosphere. The cap 44 is provided with one or a plurality of fine gas diffusion holes 44b, which allows the external atmosphere and the internal space to communicate with each other through the gas diffusion holes 44b. A heater 46 is provided on the cap 44, and the heater 4 is turned on by energizing the heater 46.
6 heats the oxygen sensor due to resistance heating. Further, a power source 49 is connected between the cathode electrode 42 and the anode electrode 43, and an ammeter 48 and a voltmeter 47 are connected to the power source 49 in series and in parallel, respectively.

Normally, four connecting electrodes electrically connected to the heater 46, the cathode electrode 42 and the anode electrode 43 are provided on the cap 44.
Then, the sensor chip is arranged in a suspended state between the four pins erected on the supporting member by the lead wires joined to these connecting electrodes.

In the limiting current type oxygen sensor having the above-mentioned structure, the heater 46 is supplied with electric power to generate resistance and heat the sensor chip to a high temperature, and at the same time, the power source 4 is used.
9 applies a predetermined voltage (V) between the cathode electrode 42 and the anode electrode 43. Then, due to the oxygen pumping action, oxygen molecules (O ₂ ) contained in the gas existing in the internal space surrounded by the solid electrolyte substrate 41 and the cap 44 acquire electrons via the cathode electrode 42 to obtain oxygen ions. And enters the solid electrolyte substrate 41. The oxygen ions move in the substrate 41 in the thickness direction through the oxygen ion holes in the substrate 41. Then, the oxygen ions reach the anode electrode 43 to emit electrons,
It becomes oxygen molecules again and is released to the outside. Due to the movement of the oxygen ions, the anode electrode 43 and the cathode electrode 42
A current (A) flows between and.

By the way, due to the movement of oxygen, the internal space of the sensor chip becomes a negative pressure, and the gas flows in from the outside through the gas diffusion hole 44b. At this time, the inflow amount of the gas is limited by the gas diffusion hole 44b, so that the current does not change even if the voltage applied between the cathode electrode 42 and the anode electrode 43 is increased in the current-voltage characteristic of the oxygen sensor, which is a so-called flat region. Is observed. This characteristic is called the limiting current characteristic, and the current at this time is called the limiting current.

The value of the limiting current of the limiting current type oxygen sensor is
If the shape of the gas diffusion hole, the temperature of the sensor during use, and the pressure of the atmosphere are constant, it depends on the oxygen concentration in the atmosphere. Therefore, if the relationship between the limiting current value and the oxygen concentration is obtained in advance, the oxygen concentration in the atmosphere of unknown oxygen concentration can be known by measuring the limiting current value.

[0007]

However, in the above-mentioned conventional limiting current type oxygen sensor, since the sensor chip is suspended by the lead wire, the heat generated by the heater is effectively used for heating the sensor chip. However, it has the advantage of good thermal efficiency, but has the disadvantage of insufficient mechanical strength.

In order to improve the mechanical strength, it can be considered to bond the limiting current type oxygen sensor chip on a heat resistant insulating member such as a ceramic plate. But,
In this case, since the heat generated by the heater is absorbed by the insulating member, the thermal efficiency is deteriorated and extra power is required.

The present invention has been made in view of such problems, and an object thereof is to provide a limiting current type oxygen sensor having high mechanical strength and high thermal efficiency.

[0010]

A limiting current type oxygen sensor according to the present invention is a sensor chip provided with a detecting section for detecting oxygen concentration by utilizing limiting current characteristics and a heater section for heating the detecting section. A chip mounting member provided with a through hole penetrating from the position where the sensor chip is mounted and aligned with the heater part to the back surface side thereof.

[0011]

In the present invention, the sensor chip is bonded to the chip mounting member. In this case, if the sensor chip is simply joined on a flat surface, the mechanical strength is improved compared with the conventional limiting current type oxygen sensor suspended by the lead wire between the pins, but it is generated by the heater part. Since the generated heat is also used for heating the chip mounting member, the thermal efficiency is poor. However, since the oxygen sensor chip mounting member according to the present invention is provided with a through hole penetrating from the position aligned with the heater portion to the back surface side, the gas in this hole acts as a heat insulating material, and the chip mounting member is mounted. The heating of the member can be suppressed and the thermal efficiency is high. Further, the sensor chip is bent by the heat generated in the heater part so that the central part of the surface on the heater part side is projected. Therefore, when the sensor chip is bonded onto a chip mounting member having a flat bonding surface, the sensor chip bends. As a result, the sensor chip and the chip mounting member may come into contact with each other and the joint may be damaged. However, in the present invention,
Since the chip mounting member has a cylindrical structure and the hole is provided at a position aligned with the heater portion of the sensor chip, it is possible to avoid contact with the chip mounting member even if the sensor chip is curved. Further, since the chip mounting member can be manufactured by extruding ceramics into a tube shape using a technique such as injection molding, mass production is easy and manufacturing cost can be reduced.

If only contact between the sensor chip and the chip mounting member is to be avoided, it is conceivable to increase the amount of conductive paste to increase the gap between the sensor chip and the chip mounting member. However, if so, the bonding strength between the two is significantly reduced. Therefore, it is necessary that the chip mounting member be provided with a hole at a position aligned with the heater portion of the sensor chip.

It is also conceivable to provide a groove at a position aligned with the heater portion of the sensor chip, instead of the through hole. However, in the case of the groove, the chip mounting member cannot be manufactured by injection molding because the groove has the bottom. Although it is conceivable to use a mold to form the groove, the groove must be deep to some extent in order to obtain good heat insulation. However, it is extremely difficult to form a small deep groove with a mold. Therefore, the chip mounting member needs to be provided with a through hole penetrating from the front surface side to the back surface side.

In the present invention, the chip mounting member is provided with a conductive portion formed by patterning with a conductive material, and an electrode led from the conductive portion is provided, so that the electrode of the sensor chip and the electrode of the chip mounting member are made of a conductive material (conductive material). Bonding with a paste or the like eliminates the step of bonding the lead wire to the sensor chip and improves productivity. For this reason, a conductive portion and an electrode are provided on the sensor chip mounting member,
It is preferable that the electrode of the sensor chip and the electrode of the chip mounting member are joined with a conductive material, and the both are electrically connected via this conductive material.

In the present invention, the heater portion may be provided on the surface opposite to the chip mounting member to bond the sensor chip to the chip mounting member. In this case, the cathode electrode and the heater electrode are connected to the anode electrode. To pull to the side
It is necessary to newly form an insulating layer on the anode electrode side.
Therefore, the sensor chip is preferably bonded with the surface on which the heater portion is provided facing the chip mounting member.

[0016]

Embodiments of the present invention will now be described with reference to the accompanying drawings.

FIG. 1 is a front view showing a limiting current type oxygen sensor according to a first embodiment of the present invention, and FIGS. 2 (a) and 2 (b) are a front view and a top view showing a chip mounting member 4, respectively. . Further, FIG. 3 is a plan view showing the sensor chip 1.

The limiting current type oxygen sensor according to this embodiment is
It is composed of a limiting current type oxygen sensor chip 1 and a chip mounting member 4. The sensor chip 1 is configured, for example, as shown in FIG. 6, and the connection electrode 2a of the heater 2, the connection electrode 3a for the cathode electrode, and the connection electrode 3b for the anode electrode are provided on the cap. On the other hand, the chip mounting member 4 is composed of a rectangular cylindrical insulating member 5 made of porous ceramics, and a through hole 6 penetrating from the upper surface side to the back surface side is provided along the central axis thereof. . Further, connection electrodes 7a are provided at the four corners of the upper surface of the chip mounting member 4. These connecting electrodes 7a are electrically connected to the side surface conducting portions 7 provided on the two side surfaces of the insulating member 5, two parallel to each other. The sensor chip 1 is joined to the chip mounting member 4 by the conductive connecting portion 8, and the connecting electrodes 2a, 3a, 3b of the sensor chip 1 are connected to the conductive connecting portion 8 respectively.
It is electrically connected to the connecting electrode 7a of the chip mounting member 4 via.

The conductive connecting portion 8 is formed by applying Pt (platinum) paste to the connecting electrode 7a, bonding the sensor chip 1 and then firing. As the conductive paste for forming the conductive connection portion 8, besides Pt-based paste, for example, Pt-Pd, Rh-Pd, and Pt are used.
-Ag-based paste or the like can be used, but when firing at a high temperature (about 900 to 1000 ° C), the electrode material may be oxidized. Therefore, in terms of the bonding strength of the electrode,
Pt-based paste, which is difficult to oxidize, is preferable. Further, when firing at a low temperature and the bonding strength is not so important, it is preferable to use a Pt-Ag paste.

Further, the material of the ceramic constituting the insulating member 5 is not particularly limited, but its thermal expansion coefficient is close to that of zirconia (90 × 10 ^-7 ) which is the substrate of the sensor chip. Those are preferable. For example, the material of the insulating member 5 is alumina (coefficient of thermal expansion: 7
0 × 10 ^-7 ), steatite (coefficient of thermal expansion: 75 × 10
^-7 ) and forsterite (95 × 10 ^-7 ) can be used. In particular, alumina is extremely suitable as a material for the insulating member because it is resistant to repeated heat. When the insulating member is made of porous alumina, the heat retention of the insulating member is further improved by the gas contained between the ceramic particles, and the apparent thermal expansion coefficient of the insulating member is increased to increase the zirconia content. Since the coefficient of thermal expansion is approached, damage to the insulating member due to the difference in coefficient of thermal expansion can be reliably avoided. Further, when the insulating member 5 is made of porous ceramics, there is an advantage that the contact area with the conductive connecting portion 8 is increased and the bonding strength is improved as compared with the case where it is made of dense ceramics which is usually used.

In this embodiment, as described above, since the through hole 6 is provided in the chip mounting member 4 at a position aligned with the heater 2 of the sensor chip 1, the gas inside the through hole 6 is a heat insulating material. As a result, the heat generated by the heater 2 is hardly absorbed by the chip mounting member 4, and the thermal efficiency is good. Further, even if the sensor chip 1 is bent by the heat of the heater 2, there is no possibility that the sensor chip 1 and the chip mounting member 4 will come into contact with each other. Therefore, it is not necessary to excessively use the Pt paste to form a large gap between the sensor chip and the chip mounting member 4, and the sensor chip 1 and the chip mounting member 4 are not necessary.
High joint strength with. Further, there is also an advantage that it is not necessary to join a lead wire to the sensor chip 1 and the manufacturing is easy.

The cross-sectional shape of the through-hole 6 does not necessarily have to be rectangular, and may be circular or any other shape as long as it facilitates injection molding. Further, the shapes of the connecting electrodes of the sensor chip 1 and the connecting electrodes of the chip mounting portion are not particularly limited, and may be circular, rectangular or other shapes. Further, in the above-described embodiment, the case where the conducting portion is provided on the outer surface of the chip mounting member 5 has been described, but the conducting portion may be provided on the inner surface of the chip mounting member. For example, if the conductive portion for the heater is formed in a large area on the inner surface of the chip mounting member, the resistance value of the conductive portion can be reduced and power loss can be reduced.

FIG. 4 is a plan view showing a sensor chip of a limiting current type oxygen sensor according to a second embodiment of the present invention, and FIG. 5 is a sectional view taken along line AA of the same. This sensor chip has a solid electrolyte substrate 11 made of stabilized zirconia.
A porous cathode electrode 12 and an anode electrode 13 respectively formed on both sides of the solid electrolyte substrate 11, and electrode lead portions 12b extending from the cathode electrode 12 and the anode electrode 13 toward the corners of the substrate, 13b,
A glass dome layer 14 that hermetically seals the base ends of the cathode electrode 12 and the electrode lead portion 12b, a heater 15 and a heater electrode 1 formed on the glass dome layer 14.
5a and 15b. Further, the electrode lead-out portion 12b of the cathode electrode 12 is electrically connected to the connecting electrode 12a provided at the corner portion of the substrate, and the electrode lead-out portion 13b of the anode electrode 13 is provided at the corner portion of the heater side surface. It is electrically connected to the connected connection electrode 13a.

In the sensor chip constructed as described above, when a voltage is applied between the heater electrodes 15a and 15b, the heater 15 heats resistance to heat the sensor to a high temperature. When a predetermined voltage is applied between the cathode electrode 12 and the anode electrode 13 in this state, the oxygen molecules contained in the gas inside the cathode electrode 12 obtain electrons through the cathode electrode 12 and become oxygen ions, Solid electrolyte substrate 1
1 is moved in the thickness direction. Then, when the oxygen ions reach the anode electrode 13, they emit electrons and become oxygen atoms again, and are released into the atmosphere. Due to the movement of oxygen, the inside of the cathode electrode 12 has a negative pressure, and new gas flows into the cathode electrode 12 through the electrode lead-out portion 12b. At this time, the gas inflow amount is determined by the electrode lead-out portion 12
It is limited by the base end portion of b, and the limiting current characteristic can be obtained.

In the present embodiment, the limiting current type oxygen sensor chip thus constructed is joined to the chip mounting member 4 shown in FIGS. 2 (a) and 2 (b) with the heater side surface facing the chip mounting member side. To do. Also in this embodiment, the same effect as that of the first embodiment can be obtained. In addition, in this embodiment, since the glass dome layer 14 can be formed by screen printing, for example, a mechanization step for forming the cap and the diffusion hole is unnecessary, and the limiting current type oxygen sensor can be easily manufactured. There is also an advantage.

In the above embodiments, the heater-side surface of the sensor chip is the chip mounting member side, but the anode electrode side may be the chip mounting member side. In this case also, the gas in the holes of the chip mounting member acts as a heat insulating material, so that the heating of the chip mounting member can be suppressed, and the thermal efficiency is improved as compared with the case where the chip bonding surface is flat.

Next, the results of actually manufacturing the limiting current type oxygen sensor according to the present invention and examining the power consumption and the joint strength of the conductive connecting portion will be described in comparison with a comparative example. As an example, a limiting current type oxygen sensor having the shape shown in FIG. 1 was manufactured. However, the size of the chip mounting member 4 is 3 m in the vertical direction.
m, width 3 mm, height 15 mm, wall thickness 100-20
It is 0 μm. In addition, as a comparative example, an oxygen sensor similar to the above-described example was manufactured except that no hole was provided. In addition, in this comparative example, P serving as a conductive connection portion is used.
By increasing the amount of t paste, the gap between the sensor chip and the chip mounting member was increased so that the sensor chip and the chip mounting member would not come into contact with each other.

The heaters of the oxygen sensors of these Examples and Comparative Examples were energized and heated, and the power consumption at that time was examined. As a result, the power consumption of the oxygen sensor of the comparative example was twice that of the oxygen sensor of the example. In addition, the bonding strength of the conductive connection portion of each oxygen sensor of the example and the comparative example was examined. As a result, the bonding strength of the oxygen sensor of the comparative example is about 0.
It was 7 times. Furthermore, when the manufacturing costs of the oxygen sensors of the example and the comparative example were compared, the material cost was lower in the example because the chip mounting member was hollow, and the other costs were substantially the same.

[0029]

As described above, according to the present invention, the limiting current type oxygen sensor chip is joined to the chip mounting member, and the chip mounting member is arranged from the position aligned with the heater portion of the sensor chip. Since the through hole is provided on the back side, the mechanical strength is high and the thermal efficiency is high.

[Brief description of drawings]

FIG. 1 is a front view showing a limiting current type oxygen sensor according to a first embodiment of the present invention.

2A and 2B are respectively a front view and a top view showing a chip mounting member.

FIG. 3 is a plan view showing a sensor chip.

FIG. 4 is a plan view showing a sensor chip of a limiting current type sensor according to a second embodiment of the present invention.

5 is a cross-sectional view taken along the line AA of FIG.

FIG. 6 is a cross-sectional view showing an example of a sensor chip of a limiting current type oxygen sensor.

[Explanation of symbols]

 1; Sensor chip 2,15,46; Heater 2a, 3a, 3b; Connection electrode 4; Chip mounting member 5; Insulating member 6; Through hole 7; Side conduction part 7a; Connection electrode 8; Conduction connection part 11 , 41; solid electrolyte substrate 12, 42; cathode electrode 13, 43; anode electrode 14; glass dome layer 44; cap 44b; gas diffusion hole 47; voltmeter 48; ammeter 49; power supply

 ─────────────────────────────────────────────────── ─── Continuation of 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 Shares Inside Fujikura

Claims (2)

[Claims] 1. A sensor chip provided with a detection part for detecting oxygen concentration by utilizing a limiting current characteristic and a heater part for heating the detection part, and from a position where the sensor chip is mounted and aligned with the heater part. A limiting current type oxygen sensor, comprising: a chip mounting member having a through hole penetrating the back surface thereof. 2. The electrode of the sensor chip and the electrode of the chip mounting member are bonded by a conductive material, and the electrode of the chip mounting member is formed by a conductive portion patterned on the chip mounting member with a conductive material. The limiting current type oxygen sensor according to claim 1, which is derived.