JP3085749B2 - Gas sensor - Google Patents

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 the presence of a gas in an atmosphere and a gas sensor heater used for the same.

[0002]

2. Description of the Related Art In a conventional electric heater for a gas sensor shown in FIGS. 1 and 2, a heat generating portion 20 is supported in the air to perform thermal insulation with a substrate by minute heat conduction of air.
It is characterized by minimizing heat diffusion to the substrate. Therefore, the heat generating portion 20 is processed so as to prevent contact with the wall surface 13. For this purpose, the heat generating portion 2 shown in the sectional view of FIG.
0 has a planar structure without warping or sagging. However, since the heat generating portion 20 is softened at a high temperature due to the operation at 200 to 600 ° C., a slack is generated particularly in the vicinity of the center, and the heat generating portion 20 expands and bends due to thermal expansion. There is. In addition, a stress acts on the film at the time of high-temperature operation, causing a decrease in the adhesive force between the layers and causing film peeling. Further, as is apparent from FIG. 3, there is no room for escape when the heat-generating portion expands thermally, so that the stress of the displacement is concentrated on the support portion 16 supporting the heat-generating portion and a crack is generated at the base of the overhang portion. There is.

[0003]

An object of the present invention is to increase the temperature of a heat generating portion 20 of a detecting device provided on a double-supported or cantilever provided on a substrate shown in FIGS. An object is to reduce a load acting on a double-supported (air bridge-shaped) or cantilevered (cantilever-shaped) beam.

[0004]

The present invention relates to a gas sensor having a substrate having an air conditioner, an overhang portion made of an electrically insulating material provided overhanging the air on the air conditioner portion of the substrate, and a gas sensing layer provided on the overhang portion. The present invention relates to a gas sensor, wherein the overhanging portion has a continuous flat plate shape with no step, and is bent upward as it moves away from a joint portion with the substrate. When the gas sensing layer is a gas sensing material made of a metal oxide semiconductor, the gas sensor functions as a sensor for detecting the presence or absence of a gas and the type of the gas. Further, when the gas sensing layer is a gas flow rate detecting member including a heating element and a heat receiving element, it functions as a gas flow rate sensor.

According to the present invention, the overhanging portion has a continuous flat plate shape with no steps, and is bent upward as it moves away from the joint with the substrate. The degree of stress is different, and the adverse effects caused by the stress can be avoided. FIG. 4 shows an example in which the displacement due to the thermal expansion in the horizontal direction is escaped up and down, and the bridge portion is curved to prevent the film from peeling. In this case, the displacement due to the thermal expansion in the plane direction only displaces up and down, and does not increase the load on the support portion. Further, even if the material is softened at high temperature, the material is hardly sagged because it is supported by the arch-shaped structure, and the load in the vertical direction is dispersed in the horizontal direction as shown in FIG. In the example of the gas sensor shown in FIGS. 8 to 11, when the sensor material is further laminated on the overhang portion, the load is increased. Therefore, in the case where the sensor is provided in addition to the electric heater, the effect is further enhanced by having the warpage. large. It is particularly preferable that the bend angle of the overhanging portion be maintained at an angle of 60 degrees or less with respect to the horizontal (triangular type).
Further, as shown in FIG. 6, the thickness of the layer on the support portion side is increased, for example, the thickness of t 'may be increased by at most 30% as compared with the conventional example. or,
The overhang dimension d 'is preferably at most about 30% of the total length d. FIG.
Up to this point, the shape of the air bridge has been described, but the same applies to the cantilever as shown in FIG. The heating section 20 is supported by the support section 16.
To have a bend along the tip.

A method of manufacturing a beam portion (an air bridge shape and a cantilever shape) will be described with reference to FIG. For example,
Heat resistant substrate 14 of Si, Al, Cu, Ni, Cr, stainless steel, Kovar, Mo, W, Al ₂ O ₃ , SiO ₂ , glass, ceramic, epoxy resin, polyimide resin, etc.
First, SiO ₂ , MgO, Al ₂ O is used as the lower layer 21.
_3, Ta ₂ O _5, an electrically insulating material such as TiO ₂ 0.3-3
It is formed using a film forming method such as vapor deposition, sputtering, or CVD with a thickness of about μm. At the time of this film formation, the degree of vacuum is 10 ^−6.
It is preferable to set the pressure to 10 ^-3 Torr or less, and it is necessary to form the film in a high vacuum atmosphere and reduce the porosity as much as possible to increase the density so that the density does not increase and does not shrink in the baking treatment described later. There is. Next, NiCr, Ir, P constituting the heating element layer and the extraction electrode 1 etc. as the upper layer 22.
A conductive resistance heating material such as t, Ir-Pt alloy, SiC, TaN, and Kanthal alloy is formed to a thickness of about 0.1 to 3 μm by vapor deposition, sputtering, or the like. The upper layer 22 is photo-etched into a predetermined shape to form a pattern. When the protective coating layer 18 is further laminated, the lower layer 21
The film may be formed using the same electrically insulating material as described above and under the same conditions. Here, since the upper layer 22 and the protective coating layer 18 are successively formed from the lower layer 21, the roughness and the level difference of the surface state increase, and the larger the film thickness, the larger the grain size, and many pores and defects. After the baking treatment, the lower layer can be further contracted, and the beam can be bent. In addition, the upper layer 22 and the protective coating layer 1
At the time of film formation of No. 8, if the degree of vacuum is lowered to about 10 ⁻⁴ to 10 ⁻² Torr as compared with the case of film formation of the lower layer, a film quality containing a large number of pores can be obtained. It can be shrunk after processing. Next, when the cavity 15 is formed in the substrate 14 by etching, the lower layer 21 is formed.
Beam or lower layer 21, upper layer 2 composed of upper layer 22
2. A beam portion made of the protective coating layer 18 is formed. Further, if this is sintered at 350 to 800 ° C., a predetermined warped shape can be obtained. In addition, even if baking is performed before forming the cavity 15, even after forming the cavity, the upper layer 22 and the protective coating layer 1 are formed.
Since the force constrained from the substrate 14 is eliminated by the force of the contraction 8, a warped shape is obtained. Therefore, it is possible to specify the order of the baking process and the formation of the hollow portion 15 without specifying the order.

[0007]

【Example】

Embodiment 1 FIG. 6 shows the case of an electric heater, and the protective coating layer 18 may or may not be included. As an electric heater, the electric resistance value of the heating element layer itself of the upper layer 22 changes according to a change in the surrounding temperature, so if this is detected, it can be used as a temperature detection sensor. Also, when the humidity is high, the temperature of the heat-generating portion falls due to heat dissipation due to the humidity, so that it can be used as a humidity detection sensor.

Embodiment 2 FIGS. 12 and 13 show a case where the present invention is applied to a flow sensor as an electric heater. Two or more electric heaters are provided side by side on a series of common cavities 45, one of which is used as a heating element 42a and the other as a heat receiving element 42b, and each element has a lower layer 41, a heating element layer 42, and a protective coating layer 48. When a laminated structure is formed and the material, forming conditions, and baking conditions are the same as those in FIG. 6, a beam portion having a bent shape is formed as is clear from FIG. 13, and the strength can be maintained. In FIG. 12, when the fluid flows in the direction of the fluid flow 40, the heating element 42
When the fluid comes into contact with a, the temperature of the fluid rises, and when the flow further proceeds and the high temperature fluid reaches the heat receiving element 42b, the temperature of the heat receiving element 42b rises, and the resistance value of the heating element layer 42 of the heat receiving element becomes the flow rate. Therefore, it can be used as a flow sensor. Here, the electrode portion 43 is composed of wiring connection bonding pads 43a, 43b, 43c, and 43d. By applying a constant power between the 43a and 43b, the temperature of the heating element 42a is increased by Joule heat generated, and the temperature of the fluid is reduced. The electric resistance value received at the heat receiving element 42b at that time can be detected between 43c and 43d.

Embodiment 3 FIGS. 8 and 9 show a gas sensor 1 according to an embodiment of the present invention.
0 is a plan view and a cross-sectional view, and is integrally formed on a substrate 1 having a substantially square shape. As shown, pedestals 1b, 1b are provided at the upper left corner and the lower right corner of the substrate 1, respectively.
b is formed, and a recess 1a is formed in another portion of the substrate 1. A lower layer 4a made of an electrically insulating material is formed bridging between these pedestals 1b, 1b, and forms a cross-linked structure projecting in the air. On the lower layer 4a, a pair of detection leads 5a, 5b are arranged with their ends facing each other and separated by a predetermined distance, and a gas detection layer 7 made of a predetermined semiconductor material is provided in the facing region. Formed to define a gas detection region. The gas detection layer 7 is provided in contact with the opposite ends of the detection leads 5a and 5b, and the resistance value changes due to the adsorption of the gas. The gas is detected by detecting the change. The detection leads 5a and 5b extend on the bridge 3 in opposite directions and are connected to detection electrodes 9a and 9b provided on the respective pedestals 1b and 1b via an insulating layer. Heater leads 8c are provided on the lower layer 4a so as to extend in parallel with the detection leads 5a and 5b corresponding to the upper layers, respectively, and the heater electrodes provided on the pedestals 1b and 1b, respectively. 8a and 8b. A current is applied to the heater lead 8c to heat the semiconductor layer 7 for detection to detect gas. In this embodiment, the detection leads 5a, 5a,
b and the heater lead 8c are completely covered with a coating layer made of an electrically insulating material. On the bridge 3, the detection leads 5a and 5b and the heater lead 8c are electrically separated by the coating layer. I have. FIG.
FIG. 3 is an X-ray cross-sectional view, which simply shows a doubly supported beam portion, that is, a bridge structure (air bridge type) of the “warped structure” of the present invention. The lower layer 4a is an insulating heat-resistant layer for supporting the gas detection layer 7, the detection leads 5a and 5b, and the heater lead 8c and for insulating the electrodes. A material that has heat resistance, high insulation, and a linear expansion coefficient close to that of the heater material, for example, Si
_{O 2, Al 2 O 3,} MgO, using a _{Si 3 N 4, Ta 2 O} 5 or the like. In this embodiment, SiO ₂ is formed to a thickness of 0.3 to ₂ μm by sputtering. At this time, Ar
The pressure is set to 10 ⁻³ Torr or less to increase the density of the film. Further, it may be formed by a vacuum evaporation method. NiCr, Ir, Pt, Ir may be used as the electrically conductive material composed of the patterns of the detection leads 5a, 5b and the heater leads 8c.
-Pt alloy, SiC, TaN, Kanthal or the like is deposited to a thickness of 0.2 to 2 [mu] m by vapor deposition, sputtering or the like, and a pattern is formed by photoetching. Reference numeral 4b denotes a protective coating layer. In this embodiment, SiO ₂ , Al ₂ O ₃ , MgO,
After film formation of Si ₃ N ₄ , Ta ₂ O ₅ or the like by vapor deposition, CVD, sputtering, or the like, photolithography is performed after forming a film of 0.2 to 3 μm. Thus, the detection lead and the heater lead are separately surrounded by the insulating layer, and are electrically separated from each other. Next, in order to operate as a gas sensor, a detection unit 7 made of a metal oxide semiconductor material or a catalyst material is additionally provided.
８００800 ° C., preferably at 450 ° C., for 0.5 to 10 hours
By performing the heat treatment to a certain degree, a warped shape that can withstand the load of lamination of the detection unit 7 can be obtained. As metal oxide semiconductor materials, Sn, Zn, Fe, Ti, In, Ni, W,
An oxide such as Cd or V is formed by a method such as sputtering, vapor deposition, or CVD, and is photoetched into a predetermined shape.
In the case of a gas sensor using a catalyst material, in the electric heater shown in FIG. 6, metal oxide is obtained by mixing Pd, Pt fine particles, or a Pt-Pd alloy alone or with a silica-alumina binder instead of the protective coating layer 18. What is necessary is just to form by the same method as the case of a semiconductor material. That is, after depositing and sputtering Pd, silica and alumina are deposited,
A method of alternately repeating the sputtering process or forming a film of Pd after forming a film of silica / alumina is used.

Embodiment 4 FIG. 10 shows still another embodiment of the present invention, which has a cantilever structure in contrast to the bridge structure in the above-described embodiment. is there. That is, the gas sensor 30 of the present embodiment has the bridge 33 as a portion projecting into the air, but this bridge 33 has a cantilever structure instead of a bridge structure. Therefore, the pedestal portion 31b is formed only at the lower right corner of the substrate 31, and the cantilever-like bridge 33 extends from the base 31b into the air. On the bridge 33, a heater lead 38c and detection leads 35a and 35b are provided side by side.
The detection leads 35a and 35b are juxtaposed and spaced apart from each other.
Are formed. In this embodiment, the heater leads 38c
Are provided so as to surround the detection leads 35a and 35b. FIG. 11 shows a cross section along the longitudinal direction of the cantilever bridge 33 of the apparatus of FIG. FIG.
Numeral 1 simply shows a cantilever portion (cantilever shape) of the "warp structure" of the present invention. In the figure, 34
a indicates an insulating heat-resistant layer for supporting the heater lead 38c and performing insulation between electrodes; 34e indicates an insulating layer;
Indicates a detection lead, and 39 indicates an electrode.

[0011]

According to the present invention, since the overhanging portion is formed by bending upward, stress is not applied to the base of the overhanging portion, no crack is generated at the root, and the film of the overhanging portion peels off. Nor. In addition, since it is bent upward, the drawback that the overhang portion falls down to the hollow portion as in the conventional type and the reliability is reduced is eliminated.

[Brief description of the drawings]

FIG. 1 is a plan view of a conventionally known gas sensor having a detection unit on a beam projecting over a substrate.

FIG. 2 is a sectional view taken along line XX of the gas sensor of FIG.

FIG. 3 is an explanatory view showing a state where stress is applied to a beam portion.

FIG. 4 is an explanatory view of a state where stress is applied to a beam portion.

FIG. 5 is an explanatory view showing a state where stress is applied to a beam portion.

FIG. 6 is a schematic view of an air bridge type gas sensor of the present invention for describing a method of manufacturing a beam portion of the present invention.

FIG. 7 is a schematic view of a cantilever type gas sensor of the present invention for describing a method of manufacturing a beam portion of the present invention.

FIG. 8 is a schematic plan view showing one embodiment when a beam portion of the gas sensor of the present invention has a bridge structure.

FIG. 9 is a sectional view taken along line XX of FIG. 8;

FIG. 10 is a schematic plan view showing an embodiment in which a beam portion of the gas sensor of the present invention has a cantilever structure.

FIG. 11 is a sectional view taken along line XX of FIG. 10;

FIG. 12 is a plan view showing one example of a flow sensor according to the present invention.

FIG. 13 is a sectional view taken along line BB of FIG. 12;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 1a Depression 1b Pedestal 3 Bridge 4a Lower layer 4b Protective coating layer 5a Detection lead 5b Detection lead 7 Gas detection layer 8a Heater electrode 8b Heater electrode 8c Heater lead 9a Electrode 9b Electrode 10 Gas sensor 11 Substrate 13 Wall surface Reference Signs List 15 cavity portion 16 support portion 17 support portion 18 protective coating layer 20 heating portion 21 lower layer 22 upper layer (heating element) 23 extraction electrode 30 gas sensor 31 substrate 31b pedestal portion 33 bridge 34a insulating heat-resistant layer 34e insulating layer 35a detection lead 35b Detection lead 37 Gas detection layer 38a Heater electrode 38b Heater electrode 38c Heater lead 39 Electrode 39a Electrode 39b Electrode 40 Fluid 41 Lower layer 42 Heating element layer 42a Heating element 42b Heat receiving element 43 Electrode part 43a Bonding pad for wiring connection 43b Wiring connection bonding pad 43c Wiring connection bonding pad 43d Wiring connection bonding pad 45 Cavity 46 Substrate 48 Protective coating layer

Continued on the front page (72) Inventor Takayuki Yamaguchi 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Wasaburo Ota 1-3-6 Nakamagome, Ota-ku, Tokyo Co., Ltd. Inside Ricoh (72) Inventor Junji Manaka 1-9-17 Omori Nishi, Ota-ku, Tokyo Ricoh Seiki Co., Ltd. (72) Inventor Shigeki Takano 1-9-17-1 Omori Nishi, Ota-ku, Tokyo (56) References JP-A-3-293553 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27/12 G01F 1/68 G01P 5/12

Claims (3)

(57) [Claims] 1. A gas sensor having a substrate having an air conditioner, an overhang portion made of an electrically insulating material provided overhanging the air on the air conditioning portion of the substrate, and a gas sensing layer provided on the overhang portion. A gas sensor, wherein the overhanging portion has a continuous flat plate shape with no step, and is bent upward as it goes away from a joint portion with the substrate. 2. The gas sensor according to claim 1, wherein the gas sensing layer is a gas sensing material made of a metal oxide semiconductor. 3. The gas sensor according to claim 1, wherein the gas sensing layer is a gas flow detecting member including a heating element and a heat receiving element.