JP3077428B2 - Electrode structure of gas sensor and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode structure of a gas sensor utilizing a change in resistance value due to adsorption and desorption of a gas to and from a metal oxide semiconductor and having a heating element and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a semiconductor gas sensor has a sheet shape,
A linear or coil-shaped heating element is formed on a support such as a substrate, and a gas-sensitive film (semiconductor film) as a sensitive part and an electrode for measuring the resistance of the sensitive film are provided on another substrate facing the heating element. It has a three-layer structure in which it is placed on a surface or is placed on a heating element with an insulator interposed therebetween.

Further, the conventional product has a structure in which an alumina substrate or the like is interposed between a sensing part and a heating body, or a structure in which an insulating layer and a sensing part are laminated on a heating body. It is difficult to install the sensor in contact with the temperature sensor, and the temperature is not measured or the temperature measuring unit is placed at a position away from the sensitive unit.

[0004]

Due to the above structure, a method of heating the entire support substrate to heat the sensitive portion has been considered, but the energy loss is large. There is also a mechanism that heats only the sensitive part, but because the contact area between the heating resistor and the substrate is large, heat escapes to the substrate side, and eventually wastes energy.

Conventionally, the sensitive portion and the heating resistor are formed in separate steps, so that it is difficult to align the two when they are laminated, and because of such a laminated structure, the entire sensor is formed. There was a disadvantage that it was difficult to reduce the size.

Further, regarding the temperature control of the sensitive part, it is necessary to keep the temperature of the sensitive part constant because the resistance of the sensitive part changes depending on the temperature. Or, even if it is installed, it is difficult to keep the temperature of the sensitive part constant because there is a distance from the sensitive part, so that the accuracy of the gas sensor has not been improved. As for the heating method, since the sensitive part and the temperature measuring part are separated from each other as described above, it is difficult to perform pulse-like (intermittent) heating due to poor thermal response.

Further, in the above-mentioned laminated structure, since the insulating layer having a low thermal conductivity is provided between the sensitive part and the heating resistor, the heat of the heating resistor is not transmitted uniformly, and the temperature of the sensitive part becomes uneven.
As a result, the accuracy of the gas sensor was adversely affected.

[0008]

As a first means for solving the above problem, a heating resistor and a sensitive film electrode are insulated so that at least a part of the both overlaps in the thickness direction. Preferably, the gas sensor electrode structure is arranged via a body, and preferably, the heating resistor and the sensitive film electrode are alternately arranged in a comb-like manner via an insulator.

The gas sensor electrode structure of the first means is manufactured by the following method. That is, a first step of forming a metal resistor film on an insulating substrate and processing it into a heating resistor, and forming an insulating layer covering both the insulating substrate and the heating resistor, A second step of coating the surface with a material for forming a sensitive film electrode, a third step of coating the surface with a resin or a liquid glass component-containing material, and flattening the multilayer-coated substrate by etching. ,
A fourth step of arranging the heating resistor and the sensitive film electrode via an insulator so that at least a part thereof overlaps in the thickness direction, and forming a sensitive film on the flattened substrate. It is manufactured by a fifth step of coating with a material for use.

As a second means for solving the problem, a gas sensor electrode structure in which a temperature sensing film is disposed between a heating resistor and a semiconductor sensing film, preferably a temperature sensing film The temperature-sensitive film electrode for measuring the temperature of the heating resistor, the heating resistor, a gas sensor electrode structure disposed via an insulator so that at least a part of both overlap in the thickness direction, more preferably heating A gas sensor electrode structure in which resistors for temperature sensing and electrodes for a temperature-sensitive film were alternately arranged in a comb-like manner with an insulator interposed therebetween.

The gas sensor electrode structure of the second means is manufactured by the following method. That is, a first step of forming a metal resistor film on an insulating substrate and processing it into a heating resistor, and forming an insulating layer covering both the insulating substrate and the heating resistor, A second step of coating the surface with a material for forming a temperature-sensitive film electrode, a third step of coating the surface with a resin or a liquid glass component-containing material, and flattening the multilayer-coated substrate by etching. A fourth step of arranging the heating resistor and the temperature-sensitive film electrode via an insulator such that at least a part of the heating resistor and the electrode for the temperature-sensitive film are overlapped with each other in the thickness direction; A fifth step of coating with a warm film forming material and further forming an insulating layer thereon, a sixth step of coating the surface of the insulating layer with a sensitive film forming material, and connecting to the sensitive film Manufactured by Seventh installing electrodes for sensitive membranes It is.

[0012]

In the first means, since the sensitive portion electrode is formed in a self-aligned manner, it is easy to overlap with the heating resistor, and the size of the entire device can be reduced. Here, the self-alignment means that the adjusting operation is unnecessary because the positional relationship between the heating resistor and the sensitive part electrode is automatically determined by a series of steps. In addition, since the heating element and the sensitive section are in direct contact with each other with the thin insulating layer interposed therebetween, the heating efficiency of the sensitive section is improved and power consumption can be reduced. Further, since the surface on which the sensitive portion is formed is flattened, it is possible to prevent the sensitive film from being cut due to a step, which has conventionally been a problem.

In the second means, since the temperature sensing portion electrodes are formed in a self-aligned manner, the positioning with the heating resistor is facilitated, and the size of the entire device can be reduced. Further, since there is a temperature measuring section between the heating element and the sensitive section, the temperature of the heating element and the sensitive section can be directly measured. Further, by using a material having good thermal conductivity for the temperature measuring section, power consumption can be reduced.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, FIGS. 1 to 5 sequentially explain each step of the gas sensor electrode structure manufacturing process according to the first means, and FIGS. 1 (a) to 5 (a) are plan views of each process. FIGS. 1 (b) to 5 (b) are AA in FIGS. 1 (a) to 5 (a).
It is sectional drawing in a line. FIGS. 6 to 12 are diagrams for sequentially explaining each step of the gas sensor electrode structure manufacturing process according to the second means, and FIGS. 6A to 12A are plan views of each process. FIGS. 6 (b) to 12 (b) show FIGS. 6 (a) to
It is sectional drawing in the BB line of FIG.12 (a). FIG. 13 shows a response time until the temperature-sensing thermistor is stabilized.

First, an embodiment according to the first means will be described with reference to FIGS. FIG. 1 illustrates the formation of the heating resistor 2. A tungsten metal resistor film is formed on an insulating substrate 1 made of glass, and is processed into a heating resistor 2. As the insulating substrate 1, any substrate having an insulating property can be used, and in addition to the above glass substrate, an alumina substrate, a substrate obtained by oxidizing silicon, or the like can be used. Examples of the material of the heating resistor 2 include Ti, Cu, Al, Si, Pt, and Au, in addition to W described above. The width of the heating resistor 2 is preferably 2 to 100 μm.

FIG. 2 shows a SiO ₂ insulating layer 3 covering both the insulating substrate 1 and the heating resistor 2, and the insulating layer 3.
The material 4 for forming an electrode for a sensitive film made of tungsten which further covers the surface of FIG. The insulating layer 3 is made of Si ₃ N ₄ , Ta ₂ O ₅ or the like, and has a specific resistance of 10 ⁶ Ω · cm.
It is preferable to use the above. The thickness of the insulating layer 3 is preferably 0.1 μm to 5 μm. The insulating layer 3 can be formed by a sputtering method, a CVD method, a spin coating method, or another method. In this example, the sputtering method was used. Although the material 4 for forming the electrode for the sensitive film is formed by the vapor deposition method in this example, a sputtering method, a CVD method, or the like can be used instead. As the material 4 for forming the sensitive film electrode, in addition to W, for example, Ti, Al, N
i, Cu, Pt, and Au can be used.

FIG. 3 shows a step of forming a temporary coating 6 in preparation for later flattening. The temporary coating 6 is formed by forming a coating such as a resin or a liquid glass component-containing material by a coating method such as spin coating. By forming the temporary coating 6, flattening later can be performed as intended.

FIG. 4 shows a process of flattening the surface of the insulating substrate 1 and forming the sensitive film electrodes 4a and 4b. In order to planarize the insulating substrate 1 covered with the temporary coating 6, the temporary coating 6 and the material 4 for forming an electrode for a sensitive film are etched in a plasma atmosphere. At this time, by adjusting the etching rate ratio, the material 4 for forming a sensitive film electrode on the heating resistor 2 is completely removed, and the portion overlapping the heating resistor 2 in the thickness direction, that is, the heating resistor 2 is removed. The electrode forming material 4 for the sensitive film in the sandwiched region is left. As a result, as shown in FIG. 4 (a), the sensitive film electrode is divided into 4a and 4b.
These are alternately arranged in a comb shape with the heating resistor 2 via the insulating layer 3 (self-alignment). That is, since the positional relationship between the heating resistor 2 and the sensitive film electrodes 4a and 4b is automatically determined, the step of performing the adjustment is unnecessary, and there is no fear of the occurrence of positional displacement. Further, the heating resistor 2 and the sensitive film electrodes 4a, 4
b is arranged on the insulating substrate 1 so that at least a part thereof overlaps in the thickness direction, so that the entire device can be made thinner.

FIG. 5 shows a process for forming the sensitive film 5. In this example, a Zn film is formed by a sputtering method. This coating was not formed on the terminal portion by the metal mask treatment. Suitable materials for forming the sensitive film 5 include Ni, Co, Fe, Ti, Zr, Sn, W, L
Metal oxides such as a or composite films thereof, or those obtained by adding an additive such as Pt to these metal oxides. Examples of the method for forming the sensitive film 5 include a vapor deposition method and a sol-gel method in addition to the above-described sputtering method.
The sensitive film 5 is in contact with the heating resistor 2 with the insulating layer 3 interposed therebetween.
Since the thickness of the insulating layer is as thin as 0.1 to 5 μm, there is no change in heat conduction when substantially in direct contact, and waste of power consumption for heating can be prevented. Further, since the sensitive film 5 is formed on the flattened surface, there is no risk of cutting due to a step.

Next, an embodiment according to the second means will be described with reference to FIGS. FIG. 6 illustrates a step of forming the heating resistor 8. A tungsten metal resistor film is formed by vapor deposition on a glass insulating substrate 7, and is processed to form a heating resistor 8. I do. Any material can be used as the insulating substrate 7 as long as it has an insulating property. In addition to the above glass, an alumina substrate,
Examples of the substrate include a silicon wafer whose surface is oxidized and a substrate made of a resin that can withstand the temperature of the heating resistor 8. It is preferable that the substrate has a flat surface and low thermal conductivity. As the material of the heating resistor 8, in addition to W described above, Si, Ti, Al, Pt, Ni, Cr, Sn,
Au, Ag, Pd, Cu and alloys thereof can be used, but a high resistance material having excellent migration resistance is preferable from the viewpoint of miniaturization of equipment. The width of the heating resistor 8 is preferably 2 to 100 μm, and the thickness thereof is 0.2 to 10 μm.
μm is preferred.

FIG. 7 shows a SiO ₂ insulating layer 9a covering both the insulating substrate 7 and the heating resistor 8 and a tungsten temperature-sensitive film electrode for further covering the surface of the insulating layer 9a. 4 illustrates a step of forming the material 10. As the insulating layer 9a, in addition to the above, Si ₃ N ₄ , Ta ₂ O ₅ ,
It is preferable to use TiO ₂ or a resin or the like that can withstand the temperature of the heating resistor 8 and has a specific resistance of 10 ⁶ Ω · cm or more. The thickness of the insulating layer 9a is 0.1 μm or more.
5 μm is preferred. The insulating layer 9a is formed by sputtering, C
It can be formed by a VD method, a spin coating method, an evaporation method, a sol-gel method, a dipping method, a method of oxidizing the surface of the heating resistor 8 to form an insulating layer, and the like. In this example, the CVD method was used. The material 10 for forming the temperature-sensitive film electrode is formed by a vapor deposition method in this example, but a sputtering method, a CVD method, or the like can be used instead. The material 10 for forming the temperature-sensitive film electrode may be, for example, Ti, Al, N in addition to W.
i, Cr, Sn, Ag, Cu, and Si can be used.

FIG. 8 shows a step of forming a temporary coating 11 in preparation for later flattening. The temporary coating 11 is formed by forming a coating such as a resin or a liquid glass component-containing material by a coating method such as spin coating. The thickness of the temporary coating 11 is 1.1 to 1.3 times the height difference (step) on the insulating substrate 7 caused by the formation of the heating resistor 8, and further 1.15.
The minimum film thickness at which the step is flattened by 1.25 times is preferable. By forming the temporary coating 11, flattening later can be performed as intended.

FIG. 9 shows a process of flattening the surface of the insulating substrate 7 and forming the electrodes 10a and 10b for the temperature-sensitive film. To perform planarization, the temporary coating 11 is etched in an oxygen plasma atmosphere. The etching is terminated when the temporary coating 11 on the upper surface of the heating resistor 8 is completely removed and the temporary coating 11 between the heating resistors 8 remains. Next, the temperature-sensitive film electrode forming material 10 exposed on the upper surface of the heating resistor 8 is etched with a chemical or the like, and the remaining temporary film 11 is removed with oxygen plasma or the like. The formation of the temperature-sensitive film electrode can also be realized by the following method. That is, the temporary film 11 and the heating resistor 8 are simultaneously etched. However, by adjusting the etching rate ratio, the temperature-sensitive film electrode forming material 10 on the upper surface of the heating resistor 8 is completely removed. The material 10 for forming an electrode for a temperature-sensitive film in a place overlapping with the heating resistor 8 in the thickness direction, that is, in a region sandwiching the heating resistor 8 is left. As a result, as shown in FIG.
0a and 10b, which are alternately arranged in a comb-tooth shape with the heating resistor 8 via the insulating layer 9a (self-alignment). That is, since the positional relationship between the heating resistor 8 and the temperature-sensitive film electrodes 10a and 10b is automatically determined, a step of performing adjustment is unnecessary, and there is no fear of occurrence of positional displacement. Further, since the heating resistor 8 and the sensitive film electrodes 10a and 10b are arranged on the insulating substrate 7 so that at least a part thereof overlaps in the thickness direction, it is possible to make the whole element thinner and smaller.

FIG. 10 shows a process for forming the temperature-sensitive film 12 and the insulating layer 9b. In this example, a film was formed as the temperature-sensitive film 12 by a sputtering method. Materials suitable for forming the temperature-sensitive film 12 include Mn, Co, Ni, F
e, Cu or other two- or four-component transition metal oxide or Si
Non-oxides such as C, Sn, and Se can be used. Examples of the method for forming the temperature-sensitive film 12 include a vapor deposition method and a sol-gel method in addition to the above-described sputtering method. The insulating layer 9b formed on the surface of the temperature sensitive film 12 was made of SiO _2, Si ₃ N
₄ , Ta ₂ O ₅ or the like having a specific resistance of 10 ⁶ Ω · cm or more is preferably used. In addition, the thickness of the insulating layer 9b is 0.1.
1 μm to 5 μm is preferred. The insulating layer 9b can be formed by a CVD method, a spin coating method, or the like in addition to the sputtering method.

FIG. 11 shows a process of forming the sensitive film 13. In this example, a Zn film is formed by a sputtering method. This coating was not formed on the terminal portion by the metal mask treatment. Materials suitable for forming the sensitive film 11 include Ni, Co, Fe, Ti, Zr, Sn,
Examples thereof include metal oxides such as W and La, composite films thereof, and those obtained by adding an additive such as Pt to these metal films. In addition, as a forming method, an evaporation method, a sol-gel method, or the like can be given in addition to the above-described sputtering method. As a result of the above steps, the temperature-sensitive film 12 is placed between the heating resistor 8 and the sensitive film 13.
Is sandwiched, so that the temperatures of the heating resistor 8 and the sensitive film 13 can be substantially directly measured,
The temperature sensing time difference (response time) of the temperature measuring object to the temperature measuring object is reduced.

FIG. 12 shows a state in which a sensitive film electrode 14 made of tungsten is formed on the sensitive film 13. In this example, as shown in FIG. 12A, the sensitive film electrodes 14a and 14b are arranged so as to mesh with each other at a distance. Although the sensitive film electrode 14 is formed by a vapor deposition method, a sputtering method, a CVD method, a thick film printing method, or the like can be used in addition thereto. As a material for forming the sensitive film electrode 14, in addition to W, for example, Ti, Al, Ni, Cr, Sn, Ag, Cu,
Au, Pt, and Pd can be used.

A gas sensor having an electrode structure manufactured by the second means and a gas sensor having a conventional structure provided with a temperature-sensitive thermistor are used to detect the temperature after starting to supply a current to the heating resistor. The time (response time) until the warming thermistor was stabilized was measured, and the result is shown in FIG. Curve I shows the result of the gas sensor according to this example, and curve II shows the result of the conventional product. As is apparent from FIG. 13, the temperature-sensing thermistor is stable in only 2 seconds in this example, whereas it takes 13 seconds for the conventional product to be stable.

[0028]

As described above, in the invention relating to the first means, since the electrode for the sensitive film is formed by self-alignment, the alignment with the heating resistor becomes easy, and the whole element can be miniaturized. it can. Further, since the heating resistor and the sensitive part are close to each other, the heating efficiency of the sensitive part is improved, and the power consumption can be reduced. Further, since the surface on which the sensitive portion is formed is flattened, it is possible to prevent the sensitive film from being cut due to a step.

In the invention relating to the second means, since the temperature-sensitive film electrode is formed in a self-alignment manner, the alignment with the heating resistor becomes easy, and the entire device can be miniaturized. In addition, since the temperature-sensitive film is sandwiched between the heating resistor and the sensitive film, the temperature of the heating resistor and the sensitive film can be substantially directly measured. The temperature sensing time difference (response time) of the thermometer is shortened.

[Brief description of the drawings]

FIG. 1A is a plan view showing a step of forming a heating resistor of a gas sensor electrode structure according to the present invention, and FIG. 1B is an enlarged sectional view taken along line AA of FIG.

FIG. 2 is a plan view (a) showing a process of forming an insulating layer and an electrode for a sensitive film, and an enlarged cross-sectional view taken along line AA of FIG. 2 (a).

FIG. 3 is a plan view (a) showing a process of forming a temporary coating, and
(a) AA line enlarged sectional view (b)

FIG. 4 is a plan view (a) showing a process of flattening and a self-alignment of the electrode for a sensitive film accompanying the planarization, and an enlarged cross-sectional view taken along line AA of FIG. 4 (a).

FIG. 5 is a plan view (a) showing a step of forming a sensitive film, and
(a) AA line enlarged sectional view (b)

FIG. 6 is a plan view (a) showing a step of forming a heating resistor of a gas sensor electrode structure (containing a temperature-sensitive film) according to the present invention, and
(a) B-B line enlarged sectional view (b)

FIG. 7 is a plan view (a) showing a process of forming an insulating layer and an electrode for a temperature-sensitive film, and an enlarged cross-sectional view taken along line BB of FIG. 7 (a).

FIG. 8 is a plan view (a) showing a step of forming a temporary coating, and
(a) B-B line enlarged sectional view (b)

FIG. 9 is a plan view (a) showing the process of flattening and the accompanying self-alignment of the electrode for a temperature-sensitive film, and an enlarged sectional view taken along the line BB of FIG. 9 (a).

10A and 10B are a plan view showing a process of forming a temperature-sensitive film and an insulating layer, and an enlarged cross-sectional view taken along line BB of FIG. 10A.

FIG. 11 is a plan view showing a step of forming a sensitive film, and
(a) B-B line enlarged sectional view (b)

FIG. 12 is a plan view showing a step of forming an electrode for a sensitive film.
And (a) is an enlarged cross-sectional view taken along the line BB (b)

FIG. 13 is a graph showing the response time of a gas sensor electrode structure (with a thermosensitive film) according to the present invention and a conventional product.

[Explanation of symbols]

1,7 ... insulating substrate, 2,8 ... heating resistor, 3,9a,
9b: an insulator; 4, 14: a material for forming a sensitive film electrode;
4a, 4b, 14a, 14b ... sensitive film electrodes, 5, 13
... Sensitive film, 6,11 ... Temporary coating, 10 ... Material for forming electrode for temperature-sensitive film, 10a, 10b ... Electrode for temperature-sensitive film, 12 ... Temperature-sensitive film.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-145802 (JP, A) JP-A-61-145803 (JP, A) JP-A-62-44250 (JP, A) JP-A-6-44250 160324 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 27/12 G01K 7/16 G01K 7/18

Claims (7)

(57) [Claims] 1. A gas sensor electrode structure in which a heating resistor, a metal oxide semiconductor sensitive film, and an electrode for a sensitive film are formed on an insulating substrate, and a change in resistance value due to adsorption and desorption of a gas to and from the semiconductor sensitive film is used. , The heating resistor,
The gas sensor electrode structure, wherein the electrode for a sensitive film is disposed via an insulator so that at least a part of the electrode for the sensitive film overlaps at least a part thereof. 2. The gas sensor electrode structure according to claim 1, wherein the heating resistor and the sensitive film electrode are alternately arranged in a comb shape with an insulator interposed therebetween. 3. A first step of forming a metal resistive film on an insulating substrate and processing it into a heating resistor, and forming an insulating layer covering both the insulating substrate and the heating resistor. Then, a second step of coating the surface with a material for forming a sensitive film electrode, a third step of coating the surface with a resin or a liquid glass component-containing material, and etching the multilayer-coated substrate A fourth step in which the heating resistor and the sensitive film electrode are arranged via an insulator so that at least a part of the electrodes overlaps in the thickness direction, and the flattened substrate. And a fifth step of coating with a material for forming a sensitive film. 4. A gas sensor electrode structure in which a heating resistor, a metal oxide semiconductor sensitive film, and an electrode for a sensitive film are formed on an insulating substrate, and a change in resistance value caused by adsorption and desorption of a gas to and from the semiconductor sensitive film is used. , The heating resistor,
A gas sensor electrode structure, wherein a temperature sensing film for temperature sensing is arranged between said semiconductor sensing film and said semiconductor sensing film. 5. A temperature-sensitive film electrode for measuring the temperature of the temperature-sensitive film is disposed via an insulator such that at least a part of the temperature-sensitive film electrode overlaps the heating resistor in a thickness direction. A gas sensor electrode structure characterized by the above-mentioned. 6. The gas sensor electrode structure according to claim 4, wherein the heating resistor and the temperature-sensitive film electrode are alternately arranged in a comb-tooth shape with an insulator interposed therebetween. 7. A first step of forming a metal resistive film on an insulating substrate and processing it into a heating resistor, and forming an insulating layer covering both the insulating substrate and the heating resistor. Further, a second step of coating the surface with a material for forming an electrode for a temperature-sensitive film, a third step of coating the surface with a resin or a liquid glass component-containing material, and etching the multilayer-coated substrate A fourth step of arranging the heating resistor and the temperature-sensitive film electrode via an insulator so that at least a part of the both overlap in the thickness direction, and the flattening is performed. A fifth step of coating the substrate with a material for forming a temperature-sensitive film, and further forming an insulating layer thereon, a sixth step of coating the surface of the insulating layer with the material for forming a sensitive film, Including the seventh step of installing a sensitive membrane electrode connected to the A method for manufacturing a gas sensor electrode structure.