JP2897471B2 - Oxide semiconductor oxygen concentration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a structure of an oxygen concentration sensor using an oxide semiconductor.

[0002]

2. Description of the Related Art An oxygen concentration sensor is mounted on, for example, an exhaust pipe of an internal combustion engine and detects an oxygen concentration in exhaust gas which is closely related to an air-fuel ratio of an air-fuel mixture supplied to the engine. It is used for providing a feedback signal in feedback control. It is widely known that zirconia is used as a detection element material of this oxygen sensor.This zirconia oxygen sensor generates an electromotive force corresponding to a difference between an oxygen concentration in a gas to be detected and an oxygen concentration in a reference gas. Oxygen concentration is detected. However, in this detection method, since a reference gas introduction part is required, there are limitations on miniaturization and weight reduction, and there are inconveniences such as a large number of parts. Therefore, as disclosed in, for example, Japanese Patent Application Laid-Open No. Sho 62-174644, an oxide semiconductor oxygen concentration sensor using titania whose electric resistance value directly changes in accordance with the oxygen concentration is used as a detection element. This oxide semiconductor oxygen sensor (titania oxygen concentration sensor) has a pair of electrodes 2a and 2b on an insulating substrate 1 as shown in FIG. 6, and is covered with titania so that a gap between the electrodes is conducted. ing. In this oxygen sensor, the resistance of titania present between the electrodes changes according to the oxygen concentration, and the change in resistance is detected as a change in oxygen concentration using a pair of electrodes. As described above, the oxide semiconductor oxygen sensor does not require the reference gas introduction section, and thus can solve the above-described inconvenience. In the oxide semiconductor oxygen sensor disclosed in the above publication, electrodes 2a and 2b are applied at a predetermined interval to a pre-sintered body 1 of alumina used as an insulating substrate, and then a porous substrate is applied to the substrate on which the electrodes are applied. Of the oxide semiconductor layer 4 of a predetermined thickness.

[0003]

However, in the prior art, as shown in FIG. 7 which is a detailed view of FIG. 6, since there is a step between the substrate 1 and the electrodes 2a and 2b, the electrodes 2a and 2b
When the oxide semiconductor is applied so as to cover b, a gap 7 is formed between the oxide semiconductor 4 and the electrodes 2a and 2b and the substrate 1. This gap 7 is present in the oxide semiconductor portion between the electrodes, which is the oxygen detecting portion, and cannot be measured accurately due to the contact resistance near this gap 7, resulting in a problem that the output value decreases and the response is adversely affected. is there. Furthermore, the gap 7 makes it easy for the oxide semiconductor layer to peel off 10 or crack 8 due to vibration or the like during operation of the engine. If the peeling 10 or the crack 8 occurs, the resistance value output further decreases and the responsiveness deteriorates, and the oxygen concentration may not be able to be measured. Therefore, the present invention eliminates the gap between the oxide semiconductor, the electrode, and the substrate by eliminating the step between the electrode surface covered with the oxide semiconductor and the substrate surface located at the predetermined gap, and solves the above problem. The purpose is to solve.

[0004]

As shown in FIG. 1, an electronic control unit for an internal combustion engine according to the present invention comprises an insulating substrate and a pair of first and second substrates arranged on the insulating substrate at predetermined intervals. An oxide semiconductor formed so as to cover a second electrode and an electrode surface of the first and second electrodes and a semiconductor support surface on the insulating substrate sandwiched between the first and second electrodes; An oxide semiconductor oxygen concentration sensor comprising:
The electrode surface of the second electrode and the semiconductor support surface on the insulating substrate are arranged on the same plane.

[0005]

Since the surface of the electrode covered with the oxide semiconductor and the surface of the substrate located at a predetermined gap coincide with each other, there is no step between the substrate and the electrode. Therefore, there is no gap between the substrate and the electrode and the oxide semiconductor. As a result, peeling or cracking of the oxide semiconductor located in the electrode gap is prevented, the output value is not reduced, and the response is not adversely affected, so that the oxygen concentration can be accurately measured.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An oxide semiconductor oxygen sensor according to one embodiment of the present invention will be described. As shown in FIG. 1, 1 is an insulating substrate, 2a is an electrode on the outer cylinder surface (platinum plating), 2b is an electrode on the inner cylinder surface (platinum plating), 4 is an oxide semiconductor (titania), and 5 is a coating layer. , 6 indicate heaters, respectively. Since the electrode (platinum plating) is not formed on the cross section (cut portion) of the distal end of the cylindrical insulating substrate 1, the electrode 2b on the inner cylindrical surface and the electrode 2a on the outer cylindrical surface are not electrically connected. Also, the end 13 of the substrate and the end 14 of the electrode
a and 14b are on the same plane. That is, the surface of the electrode located at a predetermined gap from the electrode surface covered with the oxide semiconductor is flat without any step. The oxide semiconductor 4 is formed on this flat surface, and the electrodes 2 on the inner and outer cylindrical surfaces are formed.
a, 2b are conducted by the oxide semiconductor 4. In forming the oxide semiconductor 4, no gap is generated between the insulating substrate 1, the electrodes (platinum plating) 2 a and 2 b, and the oxide semiconductor 4 because there is no step in the above structure. Next, a method of manufacturing the above-described cylindrical oxygen sensor will be described. First, an insulating substrate 1 made of an insulating ceramic such as alumina is formed in a cup shape as shown in FIG. 2, and platinum is plated on the entire outer cylindrical surface and inner cylindrical surface to form electrodes 2a and 2b. Thereafter, the portion 9 corresponding to the bottom of the cup mold is cut by a cutting machine to form a tubular element. In this case, since the cut surface is not plated with platinum, there is no conduction between the electrodes 2a and 2b on the outer cylinder surface and the inner cylinder surface, and the electrodes 2a and 2b on the outer cylinder surface and the inner cylinder surface are insulated. The substrate 1 has the same cut surface, and there is no step between the semiconductor support surface on the insulating substrate 1 sandwiched between the two electrodes and the boundary between the electrodes 2a and 2b.
Thereafter, the cylindrical element is immersed (dipped) in a solution or a slurry containing a catalyst, and an oxide semiconductor 4 is formed at a tip portion having a predetermined height or less as shown in FIG. The immersion area varies depending on the type, porosity, thickness, and the like of the oxide semiconductor to be used, and thus may be experimentally determined. by this,
The electrodes 2a and 2b of the outer cylinder and the inner cylinder can be electrically connected by the oxide semiconductor 4. Since the resistance value of the oxide semiconductor 4 changes depending on the oxygen concentration, the oxygen concentration can be measured. Here, a dip layer (coating) of alumina or the like may be provided on the surface of the oxide semiconductor layer or the electrode to protect the electrode. Further, the heater 6 may be provided inside the insulating substrate 1 or in a hollow cylinder in order to keep the temperature at the time of measurement for detecting the oxygen concentration by the oxygen concentration sensor constant. FIG.
As shown in (1), a cover 11 having a large number of small holes for protecting it from mechanical damage while being exposed to exhaust gas at the time of measurement is attached, and this cover 11 is fixed to a flange 12.
Then, the flange 12 is bolted to an exhaust pipe (not shown) of an engine, whereby the oxygen concentration sensor is attached as an oxygen concentration detector. Finally, in order to immediately stabilize even when measuring the oxygen concentration by the oxygen concentration sensor manufactured as described above, a running-in operation (aging) is performed at a temperature of about 700 ° C. for a predetermined time. The point of this embodiment is as follows. The electrodes 2a and 2b and the insulating substrate 1
There is no step since the boundary is the same plane as the cut surface of the tubular element. Therefore, when the cylindrical element is immersed (dipped) by a predetermined amount in a solution or a slurry containing a catalyst, there is no step at the boundary between the insulating substrate 1 and the electrodes 2a and 2b.
The gap 7 between the electrode 2a, 2b and the insulating substrate 1 does not occur.

Next, the oxygen concentration sensor of this embodiment and the oxygen concentration sensor of the prior art (FIG. 1) are mounted on the exhaust pipe of the engine as described above, and when the oxygen concentration is lean in a certain engine operating state. The result of measuring the oxygen concentration with the output being 0 and the output being 1 when the oxygen concentration is rich will be described. In this engine operation state, it is assumed that whether the fuel is lean or rich is constantly changing as shown in FIG. At this time, the output values of the two oxygen concentration sensors after performing the aging operation for a predetermined time are shown in FIG.
(B). Referring to FIG. 4B, even if an attempt is made to output a rectangular wave, the output value (dotted line) of the oxygen concentration sensor having the gap 7 according to the prior art is the gap 7, the crack 8 and the peeling 10.
However, the output value (solid line) of the oxygen concentration sensor having no gap 7 according to the present invention has good responsiveness and can output a square wave accurately. further,
In this embodiment, since the electrodes are provided by plating,
Compared to the case of applying and printing an electrode, the adhesiveness to the alumina element is better, the amount of platinum in the electrode can be reduced, and the cost is reduced. Further, since the oxygen concentration sensor is a cylindrical element, the strength and the assembling property are better than a flat plate, and the circular shape can eliminate variations in characteristics due to directionality. As a second embodiment, as shown in FIG. 5, a structure in which no gap is formed even on a flat plate can be provided.
That is, the electrodes 2a and 2b are applied to both sides of the strip-shaped insulating substrate 1 made of alumina green sheet by a printing method. At this time, the electrodes 2a and 2b and the insulating substrate 1 are made to be on the same surface on the F-plane (the surface made to conduct by the oxide) so that no step is formed, and then the oxide semiconductor 4 is made to conduct on this surface. cover. In this way, by making the end surface between the electrodes 2a and 2b, which are the two oxygen concentration sensor detecting portions, the end surface of the insulating substrate 1 the same as the end surface, the step at the boundary between the electrodes 2a and 2b and the insulating substrate 1 is formed. To eliminate As a result, the gap between the electrodes 2a and 2b, the insulating substrate 1, and the oxide semiconductor 4, which is a point of the present invention, can be eliminated. As described above, the gap 7 between the two electrodes 2a and 2b is eliminated by the structure as in the first and second embodiments,
It is possible to eliminate a decrease in responsiveness and output due to the gap 7,
Further, if the measurement is continued while the gap 7 is present, the problem that the crack 8 and the peeling 10 occur from the gap 7 to further reduce the above-described responsiveness and output deterioration can be solved.

[0008]

As described above, the step between the substrate and the electrode is eliminated by matching the pair of electrode surfaces covered with the oxide semiconductor with the substrate surface located at a predetermined gap between the electrode surfaces, and the substrate and the electrode are connected to each other. A gap between oxide semiconductors can be eliminated. As a result, peeling and cracking of the oxide semiconductor are prevented, and a decrease in output value and an adverse effect on responsiveness are prevented,
The oxygen concentration can be measured accurately.

[Brief description of the drawings]

FIG. 1 is a diagram of an embodiment of an oxygen concentration sensor of the present invention.

FIG. 2 is a diagram illustrating a process of manufacturing an oxygen concentration sensor according to the present invention.

FIG. 3 is an installation diagram of an oxygen concentration sensor.

FIG. 4 is an output value of an oxygen concentration sensor output according to the related art and the present invention.

FIG. 5 is a view of a second embodiment.

FIG. 6 is a detailed view of a conventional oxygen concentration sensor.

FIG. 7 is a detailed view of a part S in FIG. 1;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Insulating substrate 2a ... Electrode 2b ... Electrode 3a ... Lead wire 3b ... Lead wire 4 ... Titania 5 ... Coating layer 6 ... H -Ta 7… Gap 8… Crack 9… Bottom part of cup type 10… Peel off 11… Cover 12… Flange 13… End of substrate 14a End of the electrode 14b

Claims (1)

(57) [Claims] An insulating substrate; a pair of first and second electrodes disposed on the insulating substrate at a predetermined interval; an electrode surface of the first and second electrodes; An oxide semiconductor oxygen concentration sensor comprising: an oxide semiconductor formed so as to cover a semiconductor support surface on the insulating substrate sandwiched between second electrodes; and an electrode surface of the first and second electrodes. And an oxide semiconductor oxygen concentration sensor, wherein a semiconductor support surface on the insulating substrate is arranged on the same plane.