JPH0627070A - Gas sensor - Google Patents

Abstract

PURPOSE:To obtain a pulse driven gas sensor, whose power consumption is small. CONSTITUTION:Gold electrodes 10 and 12 are connected to a thin film heater 14 of iridium oxide. Opposing parts 22 and 22 are provided and heated with a heating part 24 therebetween. An SnO2 film 16 is laminated in the heater 14, and a gas sensor having two terminals is formed. Etching parts 18 and 18 formed by ion milling are provided in parallel with the lines at both ends of the opposing parts 22 and 22. The thin film heater 14 and the gas detecting film 16 are removed, and power consumption is further reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse drive type gas sensor.

[0002]

2. Description of the Related Art The 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, and the heater is caused to generate heat in a pulsed manner. (JP-A-1-206,252). Japanese Patent Publication Nos. 4-1301 and 219 disclose that a thin bridge of silica 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. Shows. 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 sensor is pulse-driven to significantly reduce the power consumption.

When the sensor is pulse-driven to reduce power consumption, the next problem is to pattern the heating portion of the heater in a small size. For this purpose, a high resistance material is used for the heater, and a low resistance electrode such as Pt or Au is connected to the heater. FIG. 4 shows an electrode arrangement that can be easily considered. When the electrodes 01, 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 beyond the originally intended range. This increases power consumption.

[0004]

The problems of the present invention are as follows. (1) The expansion of the heat generating part is suppressed and the power consumption is suppressed (claims 1 and 2). (2) When the heater film and the gas detection film are provided, the heater film and the gas detection film are etched outside the facing portion to reduce power consumption due to extra heat generation and heat transfer (claim 3). (3) Overlapping the electrode pattern of the heater film and the electrode pattern of the gas detection film to minimize the heat radiation from the electrode and prevent the heater film and the gas detection film from being short-circuited due to dust adhesion (claim Item 5).

[0005]

According to the present invention, in a gas sensor in which a heater film is provided on an insulating substrate and the heater film is made to generate heat in a pulsed manner, a pair of electrodes are connected to the heater film and the tips of these electrodes are connected. Each of them is characterized in that a linear opposing portion disposed obliquely or at a right angle to the electrode body is provided at a contact portion with the heater film, and the pair of opposing portions are disposed in parallel to face each other.

Here, for example, the substrate is assumed to have an insulating glass film provided on the surface of an insulating substrate, but a bridge-like silica film is provided on a cavity formed by undercut etching of a substrate made of silicon or the like. May be used as the base. Further, when the heater film or the 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 part, but not provided on the outside of the facing part. This is because etching of the heater film and the metal oxide semiconductor film is more difficult than etching of the electrode film, and the heater film and the metal oxide semiconductor film are etched outside the facing portion, and the electrode lead-out side is left. . When a metal oxide semiconductor film whose resistance value changes in contact with gas is used, the metal oxide semiconductor film is laminated on the heater film, and the combined resistance value of the heater film and the metal oxide semiconductor film is formed by the pair of electrodes. Alternatively, an insulating film may be provided in the middle, and a metal oxide semiconductor film whose resistance value changes due to contact with gas is laminated on the insulating film, and a pair of electrodes may be formed on the metal oxide semiconductor film. And a pair of electrodes in which these electrodes are connected to the heater film,
The patterns may be overlapped at the drawn-out portion from the heater film. The heater film and the gas detection film to be used are, in principle, thin films having a small heat capacity because they are easy to pattern and may be thick films.

[0007]

The operation of the invention will be described. The electrode is provided with a linear facing portion at the tip, and the heater region between them is used as a heat generating portion. The facing portion is linear and is arranged obliquely or at a right angle to the electrode body, and since the electrode body is masked by the opposing electrode or the facing portion at the facing portion, heat is generated only between the facing portions, and the heat generating portion is It is clear and can prevent the increase of power consumption due to the expansion of the heat generating part.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment is shown in FIGS. In FIG. 1, 2 is a substrate of alumina or the like, 4 is a glass film for heat insulation provided on the entire surface thereof, which may be partially provided, and the thickness is preferably about 20 to 100 μm. Reference numerals 6 and 8 are electrode pads, and 10 and 12 are a pair of electrodes, for example, Au or Pt is used. Reference numeral 14 is a thin film heater of iridium oxide, ruthenium oxide, tantalum nitride, etc., for example, 0.1-2.
The film thickness is about μm. For the thin film heater 14, an iridium oxide film having high durability is preferable. Reference numeral 16 is a gas detection film such as a SnO2 thin film, an ITO thin film (In2O3-SnO2 thin film), a tungsten oxide thin film, and a proton conductor thin film such as Nafion. The film thickness of the gas detection film 16 is, eg, 0.1-1 μm. When the contact combustion type gas sensor is used and the temperature change of the heater 14 is used as the gas detection signal, the gas detection film 16 is not necessary. Reference numerals 18 and 18 are etching portions.

FIG. 2 shows the arrangement of the electrodes 10 and 12. In the figure, 20 and 20 are constricted portions, and 22 and 22 are facing portions of the electrodes, which are arranged substantially at right angles to the electrodes 10 and 12 so that the facing portions 22 and 22 face each other in parallel. Facing part 22,
22 has a simple linear shape as shown in FIG. This is because the shape of the heater film 14 having a simple shape is clearly defined. For example, with a comb tooth-shaped electrode, the resistance value of the sensor can be reduced, but patterning is difficult,
The heat generating part becomes large and power consumption increases. Etching part 1
Reference numerals 8 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 on both ends of the facing portion 22. 24 is the facing portion 22,
It is a heat generating part of the heater 14 between 22. The shape accuracy of the sensor is 20μ for electrodes 10 and 12 which are easy to etch.
Applying the m rule, the original line width W1 of the electrodes 10 and 12 is 40 μm, and the line width W2 at the constricted portions 20 and 20 is 20 μm.
m, and the length of the constricted portions 20, 20 is, for example, 80 μm. The line width of the facing portions 22, 22 is 30 μm, and the facing portions 22,
The length L of 22 is 100 μm, and the distance D between the facing portions 22 and 22 is 60 μm. As a result, the heat generating portion 24 is 100
It becomes μm × 60 μm.

FIG. 3 shows a cross section of the main part of the gas sensor. The electrodes 10 and 12 are arranged, for example, on the heater thin film 14 and also serve as the electrodes of the gas detection film 16 to form a two-terminal sensor as a whole.

FIG. 5 shows a modified electrode arrangement. In the modification, the facing portions 34 and 34 connected to the electrodes 30 and 32 are tilted obliquely, and the electrodes 30 and 32 and the facing portion 34 are arranged diagonally. Even in this case, as in 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, the heat insulating glass film 4 is printed on the entire surface of the substrate 2 and baked. Next, for example, an iridium oxide film is formed by printing or the like and baked to complete the heater 14. After that, the electrode material is printed large, and the electrodes 10 and 12, the pads 6 and 8, the facing portion 2 are printed.
Etching is performed by ion milling, wet etching or the like so as to leave 2, 22. Etching of electrode materials such as Au and Pt is easy. Instead of etching after film formation, a mask may be used from the beginning to define the pattern by lift-off. After forming the electrodes 10 and 12, the gas detection film 16 is formed. The film is formed by sputtering, vacuum evaporation, printing of raw material solution, or the like. After these, a resist is printed and exposed to form a mask.
Then, the heater thin film 14 and the gas detection film 16 are etched. Wet etching of SnO2 is difficult, so ion milling (reverse sputter etching) was used. But IT
In the case of the O film, wet etching was possible. As shown in FIG. 2, the etching portions 18 and 18 are opposed portions 22 and 22.
The outer sides of the electrodes are etched so that the base sides of the electrodes 10 and 12 are left. This is because the electrode material is susceptible to etching, so if the electrodes 10 and 12 are etched,
2 is also etched, and even if the heater film 14 and the metal oxide semiconductor film 16 remain on the electrodes 10 and 12, the power consumption is not affected. As a result, the facing portion 2
In the vicinity of 2 and 22, the heater thin film 14 and the gas detection film 16 have a rectangular shape.

In the gas sensor of the embodiment, 8 mSec / S
Pulse drive under the condition of ec, and set the maximum temperature of the heat generating part 24 to 4
When the temperature is slightly higher than 00 ° C, the power consumption can be about 0.5 mWatt. This is a heating unit 2 with a size of 100 × 60 μm.
4, the opposing portions 22 and 22 are arranged in parallel to suppress the spread of the heat generating portion 24, and the etching portions 18 and 18 are
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 a gas sensor having three terminals or four terminals. In FIG. 7, 40 is an insulating film such as a silica or alumina film having a film thickness of about 1 μm. As shown in FIG. 8, the gas detection film 16 is formed in the etching portion 18.
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 portions of the heater film 14 and 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 thereof, and 48 and 48 are facing portions, and the spacing between the facing portions 48 and 48 is, for example, 20 μm, and the length of the facing portions 48 and 48 is 10 μm.
The thickness is set to 0 μm, and they are overlapped on the electrodes 10 and 12 on the heater side indicated by the broken line in the figure. As a result, in the heat generating part 24, the facing parts 48, 48
And 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 is
It is an etching part of the gas detection film 16. Sensitive gas electrode 4
Reference numerals 2 and 42 overlap the electrodes 10 and 12 on the heater side to minimize heat radiation from the electrodes. That is, the patterns of the electrodes 10 and 12 and the gas-sensitive electrodes 42 and 42 are overlapped with each other to prevent an increase in heat radiation area from the electrodes. Note that the sensor may have four terminals as a whole, or may have three terminals by using either of the pads 6 and 8.

FIG. 10 shows a disassembled state of the sensor of the second embodiment. Further, FIG. 11 shows the manufacturing process.

[0017]

According to the present invention, the following effects can be obtained. (1) It is possible to suppress the spread of the heat generating portion and suppress power consumption (claims 1 and 2). (2) When the heater film and the gas detection film are provided, the heater film and the gas detection film can be etched outside the facing portion to reduce power consumption due to extra heat generation and heat transfer (claim 3). (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 electrode, and it is possible to prevent the heater film and the gas detection film from being short-circuited due to dust adhesion or the like. 5).

[Brief description of drawings]

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

FIG. 2 is a plan view of the essential parts showing the electrode arrangement of the gas sensor of the embodiment.

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

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

FIG. 5 is a plan view of a main part showing an electrode arrangement of a gas sensor of a modified example.

FIG. 6 is a process drawing showing the 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 cross-sectional view of essential parts showing a short circuit due to dust in a conventional gas sensor.

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

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

FIG. 11 is a process drawing showing the manufacturing process of the gas sensor of the second embodiment.

[Explanation of symbols]

 2 Substrate 4 Glass film for heat insulation 6,8 Electrode pad 10,12 Electrode 14 Thin film heater 16 Gas detection film 18,18 Etching part 20,20 Constriction part 22,22 Electrode facing part 24 Heating part 30,32 Electrode 34, 34 Opposing part 40 Insulating film 42,42 Gas sensitive electrode 44 Dust 46,46 Constricted part 48,48 Opposing part 50,50 Etching part

Claims (5)

[Claims] 1. A gas sensor in which a heater film is provided on an insulating substrate, and the heater film is made to generate heat in a pulsed manner. A pair of electrodes is connected to the heater film, and the heater film is respectively attached to the tips of these electrodes. A gas sensor, characterized in that a straight-line facing portion is provided obliquely or at a right angle to the electrode body at a contact position with the electrode body, and the pair of facing portions are placed in parallel while facing each other. 2. The substrate according to claim 1, wherein an insulating glass film is provided 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 facing portion of the electrode, and the heater film on the electrode body side is left without being removed. 4. The heater film is laminated with a metal oxide semiconductor film whose resistance value changes in contact with gas, and the 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, characterized in that. 5. An insulating film is laminated on the heater film, a metal oxide semiconductor film whose resistance value is changed by contact with 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 have a pattern overlapping with a pair of electrodes connected to the heater film at a lead-out portion from the heater film.