JPH01232246A - Semiconductor exhaust gas sensor - Google Patents

Abstract

PURPOSE:to improve the temp. characteristics of semiconductor elements of each of sensors by constituting a print heater (HT) in a manner as to prevent the oxidation reaction thereof and disposing the same near the semiconductor elements. CONSTITUTION:The HT 3 which heats the semiconductor element 2 is disposed on the surface of a substrate 1 around the element 2. Both the element 2 and the HT 3 are held on the substrate 1 surface by dense thermally sprayed layers 5, 6, thermally sprayed from above. Since the element 2 is heated by the HT 3 disposed on the same substrate 1 surface as the surface of the element 2 and around the element 2, an adhesive agent does not exist between the HT 3 and the element 2 and the element 2 can be heated nearly at the same temp. under the same heat generating conditions of the HT 3. The fluctuations among the semiconductor exhaust gas sensors are eliminated. In addition, the HT 3 is held on the substrate 1 surface together with the element 2 by the dense thermally sprayed layers 5, 6 and, therefore, the HT 3 is shut off from the exhaust gas. The oxidation reaction is thereby suppressed and prevented and the heat transmission on the semiconductors are improved, by which the output characteristics of the elements 2 are uniformized among the sensors and the temp. characteristics of the elements 2 are improved.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention includes an n-type or p-type semiconductor element, and detects the oxygen concentration in exhaust gas based on the change in resistance value due to oxygen adsorption of the semiconductor element. This invention relates to improvements in semiconductor exhaust gas sensors.

(Prior Art) Conventionally, this type of semiconductor exhaust gas sensor has been disclosed, for example, in the specification and drawings of Japanese Patent Application No. 1984-1981. As shown in FIG. 9, after a semiconductor element a made of an n-type semiconductor or a p-type semiconductor is buried in the surface of a substrate, the semiconductor element a is made to absorb oxygen in exhaust gas. , except for the central part, a ceramic material or the like is thermally sprayed on the surrounding area surrounded by the dotted chain line in the figure to form a thermally sprayed layer, and the semiconductor element a is held on the surface of the substrate by the thermally sprayed layer, In order to prevent the semiconductor element a from falling when removed from the substrate, a heater d is printed and provided on the surface of another substrate C, and the printed heater d on the surface of the other substrate C is attached to the back side of the former substrate. Both substrates (A) and (C) are bonded together with an adhesive such as cement material while the two substrates are placed in the same position. The print heater d is provided to heat the semiconductor element a so that the semiconductor element a can be used within a set temperature range, since the resistance value change characteristic of the semiconductor element a changes depending on its temperature. It is something.

By disposing this semiconductor exhaust gas sensor in the exhaust passage of the engine, and forming a series circuit to which a predetermined voltage is electrically applied by the semiconductor element a and the additional resistor, the semiconductor exhaust gas sensor is When a absorbs oxygen in the exhaust gas and its resistance value changes, the partial pressure (output voltage) generated at the additional resistance in the series circuit is measured and the oxygen concentration in the exhaust gas (air-fuel ratio of the mixture) is detected. It was designed to do so.

(Problem to be Solved by the Invention) By the way, in the semiconductor exhaust gas sensor as described above, the reason why the printed heater d is located between the side substrates and c is that when the printed heater d comes into contact with exhaust gas, it is affected by the heat. This is for the purpose of suppressing the deterioration of the heat generating function caused by the oxidation reaction.

However, since the side substrates (S, C) are bonded with a cement material, etc., the above-mentioned cement layer is interposed between the substrate (S) having the semiconductor element (A) and the print heater (D), and the thickness of this cement layer is equal to or greater than the thickness of the semiconductor exhaust gas. Since each sensor is different, the state of heat transfer from the print heater d to the semiconductor element a is different for each sensor, and the semiconductor element a cannot be heated to the same temperature range even under the same heat generation conditions, and the output characteristics of each sensor are different. However, different disadvantages arise.

The present invention has been made in view of the above, and an object thereof is to arrange the printed heater near the semiconductor element while preventing the oxidation reaction of the semiconductor exhaust gas sensor as described above. This prevents contact with the exhaust gas of the print heater and ensures its heat generation function, while effectively demonstrating the heating performance of the semiconductor element by the print heater and making it uniform among each sensor. The objective is to improve the temperature characteristics of semiconductor elements.

(Means for Solving the Problems) In order to achieve the above object, the solving means of the present invention is a semiconductor exhaust gas sensor that includes a semiconductor element housed in a recess provided on the surface of a substrate, The premise is that the oxygen concentration in exhaust gas is detected based on changes in resistance due to adsorption. A printed heater for heating the semiconductor element is arranged on the substrate surface around the semiconductor element, and both the semiconductor element and the printed heater are held on the substrate surface by a dense sprayed layer sprayed from above. It is structured as follows.

(Function) With the above configuration, in the semiconductor exhaust gas sensor according to the present invention, the semiconductor element is heated by the printed heater placed on the surface of the same substrate as the semiconductor element and around the semiconductor element. There is no adhesive layer such as a cement layer between the print heater and the semiconductor element, and the semiconductor element can be heated to almost the same temperature under the same heat generation conditions of the print heater, eliminating variations between semiconductor exhaust gas sensors. .

Moreover, the printed heater is held on the surface of the substrate together with the semiconductor element by a thermally sprayed layer that holds the semiconductor element on the substrate surface, and this thermally sprayed layer is a dense thermally sprayed layer. The layer reliably isolates it from the exhaust gas, prevents it from coming into contact with the exhaust gas, and effectively suppresses and prevents the oxidation reaction. As a result, the heating performance of the semiconductor element by the print heater is ensured well, and the temperature of the semiconductor element is reliably maintained within the set temperature range, making it possible to improve its temperature characteristics.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a semiconductor exhaust gas sensor A according to the present invention, in which 1 is a substrate made of alumina, and on the surface near the side of the substrate 1, as shown in FIGS. 2 and 3, A recess 1a having a rectangular cross section for accommodating a semiconductor element is formed, and a semiconductor element 2 having approximately the same shape as the recess 1a and made of, for example, an n-type semiconductor (chemical symbol: Ba Sn 03 ) is placed in the recess 1a. It is embedded with the surface exposed to the outside.

The semiconductor element 2 has a resistance characteristic in which the resistance value changes when oxygen is adsorbed.

Further, a printed heater 3 made of W/MO<tungsten/molybdenum) is arranged around the semiconductor element 2 on the surface of the substrate 1 to surround the semiconductor element 2 from the outside. The semiconductor element 2 is heated through.

In addition, directly above the surface of the semiconductor element 2, as shown in FIGS.
Alumina fibers 4 having elasticity are arranged so as to cover only the periphery of the semiconductor element 2.

Two thermally sprayed layers are formed on the surface of the substrate 1 by thermally spraying MgAC 20a from above the substrate 1, except for the central portion of the semiconductor element 2, in the area shown by the broken line in FIG. 5.6 is provided, and the double sprayed layer 5.6 covers the entire surface of the printed heater 3 and alumina fiber 4, as well as the peripheral edge of the semiconductor element 2, and holds them on the surface of the substrate 1. are doing.

In the two thermal sprayed layers 5 and 6, the lower thermal sprayed layer 5 is made of porous MgAUzo4 with a large particle size (for example, 30 μm or less), and the upper thermal sprayed layer 6 is made of porous MgAUzo4 with a small particle size (for example, 1 μm or less). It consists of dense MgA crystals 204 (about 10 μm in diameter).

Thus, in the semiconductor exhaust gas sensor A as described above, the semiconductor element 2 is electrically connected in series with a separately provided additional resistor (not shown) to form a series circuit to which a predetermined voltage is applied. For example, when the semiconductor element 2 is disposed in the exhaust gas passage of an engine and adsorbs oxygen in the exhaust gas, and its resistance value changes, the voltage (partial pressure) generated across the additional resistance of the series circuit changes. However, by detecting this partial pressure signal (output voltage), the oxygen concentration in the exhaust gas, that is, the air-fuel ratio of the air-fuel mixture supplied to the engine is detected.

Next, a specific configuration in which the semiconductor exhaust gas sensor A as described above is disposed in the exhaust passage of an engine is shown in FIGS. 6 to 8. In FIG. 6, at the rear end of the substrate 1, a pair of lead wires 8 connected to the semiconductor element 2 to form a series circuit are arranged in the axial direction of the substrate 1, and each of the lead wires 8 A pair of copper wires 9 are connected to the rear end of the wire on an extension line thereof. Similarly, a pair of lead wires 10 are connected to the rear end of the print heater 3 in order to energize the print heater 3, and a pair of lead wires 10 are connected to the rear end of each lead wire 10. A pair of copper wires 11 are connected.

In addition, as shown in FIG. 7, the rear part of the board 1 is
It is protected by a ceramic protection tube 12 that covers it, and each lead wire 8, 10 and conductor wire 9, 11 is protected by a spacer 13, 14 for preventing contact.

In addition, as shown in FIG. 8, the outside of the semiconductor exhaust gas sensor is surrounded by a holder 15, except for the front part of the center of the substrate 1 (the part where the semiconductor element 2 is located), and the holder 15 surrounds the semiconductor exhaust gas sensor. At the tip of the head portion 15a of 15, a double protector 16, 17, which is an inner and outer layer that covers the semiconductor element 2, is arranged to prevent unburned components in the exhaust gas from adhering to the semiconductor element 2. .

Therefore, in the above embodiment, in the semiconductor exhaust gas sensor A, the printed heater 3 is arranged on the substrate 1 in which the semiconductor element 2 is embedded, around the semiconductor element 2, so that Since there is no cement layer for bonding the substrate, heat transfer from the print heater 3 to the semiconductor element 2 is improved, and the temperature characteristics of the semiconductor element 2 can be improved. Furthermore, when mass-producing such exhaust gas sensor A, the heat transfer properties between each sensor are made uniform and variations thereof are prevented, and the output characteristics of the semiconductor element 2 can be made almost the same between each sensor. .

Further, the printed heater 3 is connected to the substrate 1 of the semiconductor element 2.
It is held on the surface of the substrate 1 together with the semiconductor element 2 by a thermal sprayed layer 5.6 for preventing extraction from the substrate.Since this upper thermal sprayed layer 6 is a dense thermal sprayed layer, this thermal sprayed layer 6 is used as a print heater. 3 and the exhaust gas, effectively suppressing or preventing the exhaust gas from coming into contact with the print heater 3, sufficiently suppressing or preventing the oxidation reaction of the print heater 3, and improving its heat generation performance. will be effectively retained. Therefore, the print heater 3 is placed near the semiconductor element 2 on the surface of the substrate 1 while reliably preventing the oxidation reaction of the print heater 3, thereby making the temperature characteristics of the semiconductor element 2 uniform among the sensors and improving it. be able to.

Moreover, since the thermal sprayed layers 5 and 6 have a two-layer structure, and the lower thermal sprayed layer 5 is porous, its buffering effect increases the adhesion force, and the semiconductor element 2 and printed heater 3 are attached to the surface of the substrate 1. Can be held securely. In addition, the semiconductor element 2
Even if the semiconductor 2 thermally expands due to the temperature influence of the exhaust gas, the alumina fibers 4 on the outside of the surface have elasticity, so the thermal expansion of the semiconductor 2 is absorbed by the alumina fibers 4 and the sprayed layer 5 .6 peeling does not occur.

In the above embodiment, an n-type semiconductor was used as the semiconductor element 2, but it may also be applied to a semiconductor exhaust gas sensor that linearly detects the oxygen concentration in exhaust gas using a p-type semiconductor or both. Of course, the thermal spray material is MgA.
It is not limited to QzO4, and other thermal spraying materials may be used.

(Effects of the Invention) As explained above, according to the semiconductor exhaust gas sensor of the present invention, a printed heater is arranged on the surface of a substrate housing a semiconductor element and around the semiconductor element, and the printed heater is used to hold the semiconductor element. The semiconductor element is held on the surface of the substrate together with a thermal sprayed layer, and this thermal sprayed layer is made of a dense thermal sprayed layer that effectively suppresses and prevents oxidation reactions caused by contact with the exhaust gas of the print heater. It is possible to improve the heat transfer to the element, make the output characteristics of the semiconductor element uniform among the sensors, and improve the temperature characteristics of the semiconductor element.

[Brief explanation of the drawing]

1 to 8 show embodiments of the present invention, FIG. 1 is a perspective view showing the main parts of a semiconductor exhaust gas sensor, FIG. 2 is an enlarged view of the main parts, and FIG. 3 is a longitudinal sectional side view of the same. , FIG. 4 is a plan view of the same essential part, and FIG. 5 is a longitudinal sectional plan view of the same. In addition, Figures 6 to 8 show the specific configuration of a semiconductor exhaust gas sensor when placed in the exhaust passage of an engine, with Figure 6 being a side view of the main part, and Figure 7 being the main part with spacers etc. added. The side view and FIG. 8 are principal part plan views with a holder added. Also, the 9th
The figure is a perspective view of essential parts of a conventional semiconductor exhaust gas sensor. DESCRIPTION OF SYMBOLS 1...Substrate, 2...Semiconductor element, 3...Printed heater, 5...Inner sprayed layer, 6...Outer sprayed layer. Patent applicant Mazda Co., Ltd. Patent applicant Figaro Giken Co., Ltd. Agent Patent attorney
Previous 1) Hiroshi 1゜Patent attorney Nami Nami
Chimei, 1'-1' Figure 1A, (?qFffi';)-7,"C'/'7-)9th
Figure 5 Figure 4 (makukari)

Claims (1)

[Claims] (1) A semiconductor exhaust gas sensor that includes a semiconductor element housed in a recess provided on the surface of a substrate and detects the oxygen concentration in exhaust gas based on a change in resistance value due to oxygen adsorption of the semiconductor element, the semiconductor exhaust gas sensor comprising: On the substrate surface around the element,
A semiconductor exhaust gas sensor characterized in that a printed heater for heating the semiconductor element is disposed, and both the semiconductor element and the printed heater are held on a substrate surface by a dense thermal sprayed layer sprayed from above.