JPH0894559A - Gas sensor and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent resistance variation between lots in thick-film gas sensors. A pair of electrodes connected to the metal oxide semiconductor film 8 are branched into a plurality of branches 10 to 15 inside the film 8, and are led out to the outside of the film 8 by a lead-out portion 18 and connected to a joint portion 16. . The lead-out portion 18 is cut according to the resistance value of the film 8 to adjust the resistance value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas sensor for detecting a gas such as a flammable gas or a toxic gas, or water vapor generated during a cooking process in a microwave oven, and a method for manufacturing the same. The invention particularly relates to adjusting the output of a gas sensor.

[0002]

[Terminology] In this specification, gases include not only ordinary gases such as flammable gases and toxic gases but also water vapor. Further, in this specification, "on a substrate" does not mean that the object is directly supported on the surface of the substrate but means that the object is supported by the substrate.

[0003]

2. Description of the Related Art The applicant provides a metal oxide semiconductor film and a heater film on an insulating substrate, and detects gases such as methane, CO, hydrogen, and water vapor from the change in the resistance value of the metal oxide semiconductor film. Have been developed (for example, JP-A-5-87,762 and JP-A-5-340,910).
Issue). The metal oxide semiconductor film may be a thin film or a thick film, and the heater film and the metal oxide semiconductor film may be provided on the front and back sides of the substrate, or a layer of heat insulating glass may be provided on the substrate to form the heater film on the heat insulating glass. You may laminate | stack an interlayer insulation film and a metal oxide semiconductor film in order (for example, Unexamined-Japanese-Patent No. 5-34.
0,910). The structure of such a gas sensor is well known and can be variously modified. For example, if a thin layer of silica is provided on the surface of a silicon substrate and the substrate is etched from the back side, a thin layer of silica remains on the cavities created by the etching. When a heater film and a metal oxide semiconductor film are provided on this thin layer, a gas sensor with small heat capacity and low power consumption can be obtained.

However, the inventor has found that in such a gas sensor, the resistance value of the sensor (the resistance value of the metal oxide semiconductor film) significantly varies from lot to lot. The variation in the resistance value for each lot reaches about 10 times at the maximum, whereas the variation in the resistance value in the lot is small. The reason why the variation of the resistance value within the lot is small is that the manufacturing process itself of the gas sensor, whether it is a thin film or a thick film, is uniform with respect to the position in the base substrate, and the variation from sensor to sensor is small. Therefore, the problem is the fluctuation of the sensor output from lot to lot.

The cause of the change in the resistance value of the metal oxide semiconductor film depending on the lot has not been fully clarified, but in the case of a thick film, the water content of the metal oxide semiconductor paste before printing may change depending on the season. it is conceivable that. In the case of a thin film, it is considered that this is due to a change in the state of the vacuum apparatus or a change in the state of the target after each film formation.

[0006]

An object of the present invention is to prevent the lot-to-lot variation in the output of the metal oxide semiconductor gas sensor (claims 1 to 3).

[0007]

A gas sensor according to the present invention comprises a metal oxide semiconductor film whose resistance value is changed by gas on an insulating substrate, a pair of electrodes connected to the metal oxide semiconductor film, and the metal oxide semiconductor film. And a heater for heating, the metal oxide semiconductor film covers only a part of the substrate surface, and at least one of the pair of electrodes is provided with a plurality of branches inside the metal oxide semiconductor film. Branch off into
Moreover, the branch is drawn out of the metal oxide semiconductor film, and the branch is connected outside the metal oxide semiconductor film (claim 1).

The gas sensor detects gas or humidity. Further, the metal oxide semiconductor film does not cover the entire surface of the substrate so that the branch can be drawn out.
In addition, the branched electrode is directly drawn out of the metal oxide semiconductor film and bonded there. Apart from these points,
The structure and manufacturing method of the gas sensor of the present invention are arbitrary. For example, the type of metal oxide semiconductor used may be a thick film or a thin film as long as its resistance value changes with gas such as SnO2 or In2O3. Although the heater is provided on the back surface of the substrate in the embodiment, the heater and the metal oxide semiconductor film may be laminated on the substrate. The electrode was placed under the metal oxide semiconductor film,
The electrodes may be arranged on the metal oxide semiconductor film by changing the arrangement.

Preferably, the contribution of each branch to the combined resistance value between the electrodes is made different depending on the branch, and gradation is provided for the contribution to the resistance value for each branch. In manufacturing such a gas sensor, a part of the branch is cut outside the metal oxide semiconductor film to adjust the output of the gas sensor (claim 3). The resistance value of the metal oxide semiconductor film, which is a prerequisite for cutting, may be measured by selecting a representative sample for each lot, and the resistance value of each individual sensor may not be measured. Further, the resistance value to be measured may be a resistance value in air at room temperature or the like, for convenience, in addition to the resistance value in gas at the intended use temperature.

[0010]

According to the present invention, the electrode is branched into a plurality of branches inside the metal oxide semiconductor film, and the electrode is led out to the outside of the film while being branched and bonded. As a result, the resistance value of the metal oxide semiconductor film can be adjusted by cutting the branch outside the film. Since the cutting is performed outside the metal oxide semiconductor film, the metal oxide semiconductor film is not deteriorated by overheating, thermal shock, or the like at the time of cutting. Preferably, the contribution of the film to the combined resistance value is made different for each branch, and the resistance value of the film is adjusted in a large range and in fine steps.

[0011]

EXAMPLE An example is shown in FIGS. FIG. 1 shows an electrode pattern before the metal oxide semiconductor film is formed, FIG. 2 shows a gas sensor after the metal oxide semiconductor film is formed, and FIG. 3 shows a heater arrangement on the back surface of the substrate. In these figures, 2 is Al
A heat resistant insulating substrate such as 2O3 or SiO2, 4 and 6 are a pair of pads, and 8 is a metal oxide semiconductor film such as SnO2 or In2O3. A pair of electrodes is connected to the metal oxide semiconductor film 8, and these electrodes are branched into three electrodes each of which has a total of six electrodes. , Branches 10, 11, 12, 13, 14, 15
And The branches 10 to 15 are connected to the connecting portion 16 outside the membrane 8 in groups of three.
And a lead-out portion 18 is provided between the branches 10 to 15 and the connecting portions 16 and 16. 20 is a position of a cutting line for adjusting the resistance value, and the resistance value is adjusted by cutting the lead portion 18 at a position outside the film 8 and before connecting each branch to the connecting portion 16.

The contribution of the membrane 8 to the combined resistance value is largest in the branch 10 and smallest in the branch 15. Between the branches 14 and 15 that have the smallest contribution to the resistance value, the lengths of the branches facing each other are small, and the intervals between the branches are large. Between the branches 13 and 14, the lengths of the branches facing each other are increased and the distance between them is made smaller. Between the branches 12 and 13, protrusions are provided on the branches 12 and 13 to further increase the length of the branches facing each other.
The distance between the branches 12 and 10 is further reduced, and the lengths of the branches facing each other are further increased. Last branch 1
The distance between the branches is very small between 0 and 11, and 1
Numerals 0 and 11 are comb-like teeth, and the lengths of the branches facing each other are extremely long. In the embodiment, the branches 10 to 15 are formed, for example, by a rule of 20 μm, the line width of each of the branches 10 to 15 is set to 20 μm, and the distance between the branches is set to 20 μm at the minimum.

As shown in FIG. 3, the heater 24 is used in the embodiment.
Was provided on the opposite surface of the metal oxide semiconductor film 8, and a heater 24 such as a RuO2 film, pads 22, 22 connected to these, and heater electrodes 26, 26 were provided on the back surface of the substrate 2.
Then, the pads 4, 6 and 22 are connected to an external terminal (not shown) by welding, wire bonding or the like.

The method of manufacturing the gas sensor will be described. The substrate 2 is a quadrangle having a side length of about 1 to 2 mm, and a film is formed by using a mother substrate such as Al 2 O 3 or SiO 2 having a diameter of 2 inches or 5 inches. For example, first, the pad 22 and the heater electrode 26 are printed, and then the RuO2 film 24 is printed and baked. Then substrate 2
The branches 10 to 15, the lead-out portion 18, the connecting portion 16, and the pads 4 and 6 are printed on the opposite surface by screen printing or the like. After that, while monitoring the resistance value between the pads 22 and 22, the heater 24 is trimmed with a laser or the like to make the heater resistance uniform. Next, a paste such as SnO2-Pd-Al2O3 is prepared, screen-printed to form the metal oxide semiconductor film 8 and baked.

After that, the composite electric conductivity of the metal oxide semiconductor film 8 is measured and recorded for each sensor using the pads 4 and 6. The measurement is performed at the stage of the mother substrate before dividing into the individual sensors. Since the variation of the conductivity of the film 8 in the mother substrate is small, the representative sample is selected at several places for one mother substrate and the representative sample is selected. The electrical conductivity may be measured only for that. Also, the measurement atmosphere is 3,000 ppm of methane at 400 ° C. in the gas to be detected at the planned temperature of use.
It may be medium or in air at room temperature for convenience. The conductivity at room temperature in air is almost correlated with the conductivity in methane gas at 400 ° C.

When the conductivity of the metal oxide semiconductor film 8 is measured, the conductivity is adjusted to a constant value by trimming with a YAG laser or the like accordingly. Trimming is done with 6 drawers 1
This is done by cutting the selected drawing portion 18 for 8. When the metal oxide semiconductor film 8 is directly trimmed with a laser, the film 8 may deteriorate due to overheating during trimming, or the film 8 may be peeled off from the substrate 2 due to a thermal shock. However, since the lead portion 18 outside the film 8 is cut, the metal oxide semiconductor film 8 is not deteriorated, and the film 8
The thermal shock to is also small.

FIG. 4 shows the conductivity adjustment level by trimming. The area between the branches 14 and 15 is the area A, and the branch 13 is
Area 14 is defined as area B, and areas A to E are defined in this order. For example, here, the contribution of each region to the total electric conductivity of the film 8 is 5% in the region A, 8% in the region B, 20% in the region C, 27% in the region D, and 40% in the region E. , Branches 10
Define 15 shapes. This electrical conductivity distribution is an example,
The contribution of electrical conductivity is changed for each branch to increase the control range of conductivity and enable fine adjustment. When the branch 15 is cut, the electric conductivity of the region A is lost, and when the branch 11 is cut, the electric conductivity of the region E is lost. Middle branch 1
When 0, 12, 13, and 14 are cut, the electrical conductivity on both sides of each is lost. As a result, branch 11 or branch 15
When cut, the electrical conductivity of 4 areas remains, and branches 10,1
If 2, 13, 14 are cut, the electric conductivity of 3 regions remains. Next, when the two branches 12 and 13 are cut, the electric conductivity of the regions A and E remains. However, in this case, the branch 12,
Since a small electric conductivity is generated between the branches 10 and 14 when the branch 13 is cut, the change in the electric conductivity shown in the figure is qualitative. Similarly, when the branches 10 and 12 and the branches 11 and 12 are cut, the areas A and B remain, and when the branches 11 and 13 are cut, the areas A and D remain. Also, the electrical conductivity of only one region can be left. For example, when the branches 12 to 15 or the branches 12 and 14 are cut, only the electrical conductivity between the branches 10 and 11 remains. As a result, the electric conductivity of the membrane 8 is 6 in the case where only one branch is cut, 4 in the case of maintaining two regions, and 5 in the case of maintaining only one region. At least 16 gradations can be changed by combining the gradation and one gradation when trimming is not performed.

When the contribution to the electric conductivity of each region is determined as described above and the branches 10 to 15 are cut and trimmed,
The electric conductivity can be adjusted as shown in FIG. The vertical axis of the figure shows the conductivity before trimming σ0 and the conductivity after trimming σS.
Was displayed as a relative value. The trimming range is σ0 of 5
Since it is 20 times as large as 100% and there are 15 gradations between them, the conductivity can be adjusted in steps of 20%, and the electric conductivity of the film 8 can be adjusted with an accuracy of ± 10%.

[0019]

[Modification] FIG. 5 shows a modification in which only one of the pair of electrodes is branched into a plurality. The other points are the same as those of the embodiment shown in FIGS. In FIG. 5, 30 is one electrode,
Reference numerals 31 to 34 are branches, and 18 is a lead-out portion of each branch. The contribution of the membrane 8 to the combined conductivity is greatest because the distance between the branch 31 and the electrode 30 is small and the facing distance is large. In the branch 32, the distance facing the electrode 30 is about 1/2, and the contribution to the conductivity is about 1/2 that of the branch 31. The distance between the branch 33 and the electrode 30 is twice that of the branch 32, and the contribution to the conductivity is 1/2 that of the branch 32. In the branch 34, the direction of the branch is the electrode 30.
At right angles to, the contribution to the combined conductivity is about 1/2 that of the branch 33. Therefore, the contribution of the branches 31 to 34 to the conductivity is reduced to 1/2 for each increase in the branch number. Branches 31,3
The contribution of 2,33,34 to the electrical conductivity is 8: 4: 2: 1
Then, assuming that the composite electric conductivity is 15, the conductivity can be adjusted in 15 steps of 1 to 15 in 1 step by trimming. That is, if only the branch 34 is cut, the conductivity becomes 14 and the branch 3
The number 3 is 13, the number 32 is 11, the number 31 is 7, and the branches 33 and 34 are cut to be 12, the branches 32 and 34 are cut, and the branches 32 and 33 are cut to be 9. Next, if only the branch 31 is left, the conductivity becomes 8, and the branch 3
When leaving 2, 33, it becomes 6, when leaving branches 32 and 34, it becomes 5, and when leaving only branch 32, it becomes 4. Further, when only the branch 34 is left, it becomes 1. In this way, the combined electrical conductivity of the membrane 8 can be adjusted to 15 gradations of 1 to 15 by combining the cuts of the four branches 31 to 34.

[0020]

According to the present invention, the resistance value of the metal oxide semiconductor gas sensor can be trimmed. Moreover, since the trimming is performed outside the metal oxide semiconductor film, the gas sensor is not deteriorated.

[Brief description of drawings]

FIG. 1 is a plan view showing an electrode pattern of a gas sensor according to an embodiment.

FIG. 2 is a plan view of a gas sensor according to an embodiment.

FIG. 3 is a bottom view of the gas sensor according to the embodiment.

FIG. 4 is a characteristic diagram showing a trimming range of resistance values of the gas sensor of the embodiment.

FIG. 5 is a plan view showing an electrode pattern of a gas sensor of a modified example.

[Explanation of symbols]

 2 Substrate 4,6 Pad 8 Metal Oxide Semiconductor Film 10-15 Branch 16 Bonding Part 18 Leading Part 20 Cutting Line 22 Pad 24 Heater 26 Heater Electrode 30 Electrode 31-35 Branch

Claims (3)

[Claims] 1. A metal oxide semiconductor film, the resistance value of which changes with gas on an insulating substrate, a pair of electrodes connected to the metal oxide semiconductor film, and a heater for heating the metal oxide semiconductor film. In the gas sensor provided with, the metal oxide semiconductor film covers only a part of the substrate surface, at least one of the pair of electrodes is branched into a plurality of branches inside the metal oxide semiconductor film, and Is drawn out of the metal oxide semiconductor film and a branch is bonded outside the metal oxide semiconductor film. 2. The gas sensor according to claim 1, wherein each branch contributes differently to a combined resistance value of the metal oxide semiconductor film between the pair of electrodes. 3. A metal oxide semiconductor film whose resistance value is changed by gas on an insulating substrate, a pair of electrodes connected to the metal oxide semiconductor film, and a heater for heating the metal oxide semiconductor film. In the method for producing a gas sensor, the metal oxide semiconductor film covers only a part of the substrate surface, and at least one of the pair of electrodes is formed into a plurality of branches inside the metal oxide semiconductor film. The branch is branched, the branch is drawn out of the metal oxide semiconductor film, the branch is bonded outside the metal oxide semiconductor film, a part of the branch is cut outside the metal oxide semiconductor film, and the gas sensor A method of manufacturing a gas sensor, comprising a step of adjusting an output.