JP3219253B2 - Gas sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pulse-driven gas sensor.

[0002]

2. Description of the Related Art The present inventors have proposed a gas sensor in which a heater film and a metal oxide semiconductor film for gas detection are formed on an insulating substrate via a glass heat insulating film so that the heater generates heat in a pulsed manner. (Japanese Patent Laid-Open No. 1-206,252). Japanese Patent Publication Nos. 4-1301 and 219 disclose that a thin silica bridge is provided on a cavity obtained by undercut etching a silicon substrate, and a heater film and a metal oxide semiconductor film for gas detection are provided on the bridge. Is shown. Also in these publications, the heater generates heat in a pulsed manner. In these gas sensors, the heater is pulsed to generate heat, and the pulse driving of the sensor significantly reduces power consumption.

If the power consumption is reduced by pulsing the sensor, the next problem is to pattern the heating portion of the heater to a small size. For this purpose, a high-resistance heater material is used, and a low-resistance electrode such as Pt or Au is connected to the heater. FIG. 4 shows a possible electrode arrangement. When the electrodes 01 and 01 are arranged as shown in the figure, the heater current flows as shown by the broken line in the figure, and the heat-generating portion spreads out of the originally intended range. This increases power consumption.

[0004]

The object of the present invention is as follows. (1) To suppress the spread of the heat generating portion and suppress the power consumption. (2) When a heater film or a gas detection film is provided, the heater film and the gas detection film are etched on the outside of the opposing portion, so that excess heat generation and power consumption due to heat transfer are reduced. (3) Overlap the electrode pattern of the heater film with the electrode pattern of the gas detection film to minimize heat radiation from the electrodes, and to prevent short-circuit between the heater film and the gas detection film due to the adhesion of dust (claim) Item 5).

[0005]

According to the present invention, there is provided a gas sensor in which a heater film to which a pair of electrodes are connected is provided on an insulating substrate so that the heater film generates heat in a pulsed manner. Part, a connection part with the outside, and an electrode body connecting the facing part and the connection part, and the facing part of each electrode overlaps the heater film, and the facing parts are parallel to each other. The area of the heater film between the opposing portions is a heat generating portion, and the electrode body is disposed at a right angle or obliquely to the opposite portion from the heat generating portion as viewed from the opposing portion. It is characterized by the following.

Here, for example, the base is provided with a heat insulating glass film on the surface of an insulating substrate. A bridge-like silica film or the like is provided on a cavity formed by undercut etching of a substrate such as silicon. May be used as a substrate. When a heater film or a gas detection film is provided, the heater film and the gas detection film have, for example, a rectangular shape, and are provided on the electrode portion but are not provided outside the facing portion. This means that the etching of the heater film or the metal oxide semiconductor film is more difficult than the etching of the electrode film, and the heater film or the metal oxide semiconductor film is etched outside the facing portion, and the lead portion of the electrode is left. . In the case of using a metal oxide semiconductor film whose resistance value changes by contact with a gas, the metal oxide semiconductor film is stacked on a heater film, and the combined resistance value of the heater film and the metal oxide semiconductor film is formed by the pair of electrodes. May be detected, or an insulating film may be provided in the middle, a metal oxide semiconductor film whose resistance value changes by contact with a gas is laminated on the insulating film, and a pair of electrodes is formed on the metal oxide semiconductor film. And a pair of these electrodes connected to the heater film,
The patterns may be overlapped at the portion drawn from the heater film. The heater film and the gas detection film to be used are, in principle, a thin film which is easily patterned and has a small heat capacity, but may be a thick film.

[0007]

The operation of the present invention will be described. A linear opposing portion is provided at the tip of the electrode, and a heater region between the opposing portions is a heating portion. The opposing portion is linear and is disposed obliquely or at right angles to the electrode body, and since the electrode body is masked by the opposing portion of the electrode and the opposing portion, heat is generated only between the opposing portions, and the heat generating portion is generated. It is determined to be clear, and an increase in power consumption due to the spread of the heat generating portion can be prevented.

[0008]

1 to 3 show a first embodiment. In FIG. 1, reference numeral 2 denotes a substrate made of alumina or the like, and reference numeral 4 denotes a heat insulating glass film provided on the entire surface of the substrate, which may be partially provided, and preferably has a thickness of about 20 to 100 μm. Reference numerals 6 and 8 denote electrode pads, and reference numerals 10 and 12 denote a pair of electrodes, made of, for example, Au or Pt. Reference numeral 14 denotes a thin film heater made of iridium oxide, ruthenium oxide, tantalum nitride, or the like.
The thickness is about μm. The thin film heater 14 is preferably made of an iridium oxide film having high durability. Reference numeral 16 denotes a gas detection film such as a SnO2 thin film, an ITO thin film (In2O3-SnO2 thin film), a tungsten oxide thin film, or a proton conductor thin film such as Nafion. The thickness of the gas detection film 16 is, for example, 0.1 to 1 μm. When a contact combustion type gas sensor is used and a temperature change of the heater 14 is used as a gas detection signal, the gas detection film 16 is unnecessary. 18 and 18 are etching parts.

FIG. 2 shows the arrangement of the electrode bodies 10 and 12. In the drawing, reference numerals 20 and 20 denote constricted portions, and 22 and 22 denote opposing portions of the electrodes, which are disposed substantially at right angles to the electrode main bodies 10 and 12 so that the opposing portions 22 and 22 face in parallel. The facing portions 22, 22 have a simple linear shape as shown in FIG. This is to clearly define a portion of the heater film 14 that generates heat with a simple shape. For example, in the case of a comb tooth-shaped electrode, the resistance value of the sensor can be reduced, but patterning is difficult, and the size of the heat generating portion is increased, and power consumption is increased. The etching portions 18 and 18 are formed by removing the heater thin film 14 and the gas detection film 16 by ion milling (reverse sputtering) in parallel with the lines at both ends of the facing portion 22. Reference numeral 24 denotes a heat-generating portion of the heater 14 between the facing portions 22. The shape accuracy of the sensor is determined by the electrode bodies 10 and 12 that are easy to etch.
To the electrode bodies 10 and 12
The original line width W1 is 40 μm, the line width W2 at the constricted portions 20 is 20 μm, and the length of the constricted portions 20 is 20 μm, for example. The facing portions 22 have a line width of 30 μm.
m, the length L of the facing portions 22 and 22 is 100 μm, and the facing portion 2
It is assumed that the interval D between the two 22 is 60 μm. As a result, the size of the heating section 24 is 100 μm × 60 μm.

FIG. 3 shows a cross section of a main part of the gas sensor. The electrode bodies 10 and 12 are arranged on the heater thin film 14, for example,
Also serves as an electrode of the gas detection film 16 and is a two-terminal sensor as a whole.

FIG. 5 shows a modified electrode arrangement. In the modification, the opposing portions 34, 34 connected to the electrodes 30, 32 are inclined obliquely, and the electrodes 30, 32 and the opposing portion 34 are arranged obliquely. Even in this case, similarly to the electrode arrangement of FIG.
There is almost no spread of the heater current outside the region between 34.

FIG. 6 shows a manufacturing process of the embodiment. First, a heat insulating glass film 4 is printed on the entire surface of the substrate 2 and fired. Next, for example, an iridium oxide film is formed by printing or the like and fired to complete the heater 14. Thereafter, the electrode material is largely printed, and is etched by ion milling, wet etching, or the like so as to leave the electrode main bodies 10, 12, the pads 6, 8, and the opposing portions 22, 22. Etching of an electrode material such as Au or Pt is easy. Instead of etching after film formation, a pattern may be defined by lift-off using a mask from the beginning. After the electrode bodies 10 and 12 are formed, the gas detection film 16 is formed. Film formation is performed by sputtering, vacuum evaporation, printing of a raw material solution, or the like. After these, a resist is printed and exposed to form a mask, and the etching unit 18 and the
At 18, the heater thin film 14 and the gas detection film 16 are etched. Since wet etching of SnO2 is difficult,
Ion milling (reverse sputter etching) was used. However, in the case of the ITO film, wet etching was possible.
As shown in FIG.
Etching is performed on the outside of the electrode body 22 so that the base sides of the electrode bodies 10 and 12 are left. This is because the electrode material is easily susceptible to etching, so that if the electrode bodies 10 and 12 are etched, the electrode bodies 10 and 12 are also etched, and the heater film 14 and the metal oxide semiconductor film 16 are formed on the electrode bodies 10 and 12. Even if it remains, it does not affect the power consumption.
As a result, the heater thin film 14 and the gas detection film 16 in the vicinity of the facing portions 22 and 22 have a rectangular shape.

In the gas sensor of the embodiment, 8 mSec / S
pulse driving under the condition of ec, and the maximum temperature of the heat generating portion 24 is set to 4
When the temperature is slightly higher than 00 ° C., the power consumption can be reduced to about 0.5 mWatt. This is 100 × 60 μm and the heating part 2
4, the opposed portions 22, 22 are arranged in parallel to suppress the spread of the heat generating portion 24, and the etching portions 18, 18
Is provided to suppress heat transfer to the unnecessary portion and heat generation in the unnecessary portion.

[0014]

[Embodiment 2] FIGS. 7 to 11 show three to four terminal gas sensors. In FIG. 7, reference numeral 40 denotes an insulating film such as a silica or alumina film having a thickness of about 1 μm. As shown in FIG. 8, the gas detecting film 16 is
When the insulating film 40 and the heater film 14 are etched on the same line, the heater film 14 and the gas detection film 16 are short-circuited due to adhesion of dust particles 44 and the like. Therefore, as shown in FIG. 7, the heater film 14 is etched before the insulating film 40 is formed so that the end of the heater film 14 and the end of the gas detection film 16 are not exposed on the same line.

FIG. 9 shows the electrode arrangement of this sensor. In the figure, 42 and 42 are gas-sensitive electrodes, 46 and 46 are constricted portions, and 48 and 48 are opposing portions. The distance between opposing portions 48 and 48 is, for example, 20 μm, and the length of opposing portions 48 and 48 is 10
0 μm, and the electrode bodies 10 and 12 on the heater side indicated by broken lines in the figure.
Layer on top. As a result, the facing portion 48,
48, the influence of the temperature distribution can be reduced by using the gas detection film 16 at the center of the heat generating portion 24. Also 50
Denotes an etched portion of the gas detection film 16. The gas-sensitive electrodes 42, 42 overlap the heater-side electrode bodies 10, 12 to minimize heat radiation from the electrodes. That is, the patterns of the electrode main bodies 10 and 12 and the gas-sensitive electrodes 42 and 42 are overlapped to prevent an increase in a heat radiation area from the electrodes. The sensor may have four terminals as a whole, or may have three terminals by using any of the pads 6 and 8.

FIG. 10 shows a disassembled state of the sensor according to the second embodiment. FIG. 11 shows the manufacturing process.

[0017]

According to the present invention, the following effects can be obtained. (1) The spread of the heat generating portion can be suppressed, and the power consumption can be suppressed. (2) When a heater film or a gas detection film is provided, the heater film and the gas detection film are etched outside the facing portion, so that excess heat generation and power consumption due to heat transfer can be reduced. (3) The electrode pattern of the heater film and the electrode pattern of the gas detection film are overlapped to minimize heat radiation from the electrodes, and it is possible to prevent short-circuit between the heater film and the gas detection film due to dust or the like. 5).

[Brief description of the drawings]

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

FIG. 2 is a main part plan view showing an electrode arrangement of the gas sensor of the embodiment.

FIG. 3 is an end view of a main part of the gas sensor according to the embodiment.

FIG. 4 is a plan view of a main part showing an electrode arrangement of a conventional gas sensor.

FIG. 5 is a main part plan view showing an electrode arrangement of a gas sensor according to a modification.

FIG. 6 is a process chart showing a manufacturing process of the gas sensor of the embodiment.

FIG. 7 is a sectional view of a main part of a gas sensor according to a second embodiment.

FIG. 8 is a sectional view of a main part showing a short circuit due to dust in a conventional gas sensor.

FIG. 9 is a plan view of a main part showing an electrode arrangement of the gas sensor according to the second embodiment.

FIG. 10 is a perspective view showing a disassembled state of the gas sensor according to the second embodiment.

FIG. 11 is a process diagram showing a manufacturing process of the gas sensor according to the second embodiment.

[Description of Signs] 2 Substrate 4 Glass film for heat insulation 6, 8 Electrode pad 10, 12 Electrode main body 14 Thin film heater 16 Gas detection film 18, 18 Etching unit 20, 20 Constriction unit 22, 22 Electrode facing unit 24 Heat generation unit 30, 32 electrode 34, 34 facing part 40 insulating film 42, 42 gas-sensitive electrode 44 dust 46, 46 constricted part 48, 48 facing part 50, 50 etching part

Claims (5)

(57) [Claims] 1. A gas sensor in which a heater film to which a pair of electrodes are connected is provided on an insulating substrate, and the heater film generates heat in a pulsed manner. And an electrode body that connects between the opposing portion and the connecting portion. The opposing portions of the respective electrodes overlap with the heater film, and the opposing portions face each other in parallel. It is characterized in that the region of the heater film between the opposed parts is arranged as a heat generating part, and the electrode body is arranged at a right angle or obliquely to the opposed part from the heat generating part to the opposite side when viewed from the opposed part. A gas sensor. 2. The substrate according to claim 1, wherein the base is provided with a heat insulating glass film on a surface of an insulating substrate.
Gas sensor. 3. The gas sensor according to claim 2, wherein the heater film is removed outside the opposing portion of the electrode, and the heater film on the electrode body side is left without being removed. 4. A metal oxide semiconductor film having a resistance value changed by contact with a gas is laminated on the heater film, and a combined resistance value of the heater film and the metal oxide semiconductor film is detected by the pair of electrodes. The gas sensor according to claim 3, wherein: 5. An insulating film is laminated on a heater film, a metal oxide semiconductor film whose resistance value changes by contact with a gas is laminated on the insulating film, and a pair of electrodes is connected to the metal oxide semiconductor film. 4. The gas sensor according to claim 3, wherein the electrodes overlap with a pair of electrodes connected to the heater film, and a pattern is drawn out at a portion drawn from the heater film.