JPS58102144A - Gas sensor - Google Patents

Abstract

PURPOSE:To manufacture an even, very small-sized gas sensor with low power consumption and high responsivity by a construction wherein the substrate is provided with an electrically insulating thin film which includes a gas sensitive film and an electrode for measuring its electric characteristic, and a thin film heater. CONSTITUTION:An insulating film 7 is composed of SiO2, AlO2, glass, Si3N4, a multilayer film comprising these components, or so. A thin film heater 2 is composed of the thin film of Pt or the like. If substrates 10', 10'' are thermal insulators, utilization efficiency of heat generated by the thin film heater 2 is enhanced. A gas sensitive film 5 is composed of a ultrafine particle film which has been formed using the in-water evaporation method. In this gas sensor, since the sensitive part and the heater part can be minimized, it becomes possible to, for example, provide a plurality of sensitive films adjacent to each other and to permit the normal operation at given temperature with the respective operating temperatures being varied. Thus, both detection precision and accuracy can be improved. Further, humidity can be also detected by operating one of sensitive films under about room temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved gas sensor, particularly an ultra-small gas sensor that consumes low power, has transparent response speed, has uniform characteristics, and is easy to achieve high precision and high reliability. This is what we are trying to provide.

Currently, various types of gas sensors are being proposed, including sintered bodies, thick film types, thin film types, and ultrafine particle film types.

Among these, the ultrafine particle film type proposed by the present inventor in, for example, Japanese Patent Application No. 103026/1983 has the highest gas sensitivity compared to other types. Generally, these semiconductor gas sensors are said to have a problem with accuracy. The inventor of the present invention conducted a detailed study on the cause and found that one of the major factors is variation in the operating temperature of the gas sensitive body or gas sensitive membrane. Therefore, the present inventor proposed a method for controlling the operating temperature of an ultrafine particle gas-sensitive membrane with high precision in, for example, Utility Application No. 56-182434 and Utility Model Application No. 55-182435. With this proposal, it is possible to manufacture a gas sensor with an ultrafine particle gas-sensitive film using the microfabrication technology used in current VLSI manufacturing, so it is smaller and smaller than other types. The accuracy and uniformity are also very good. The ability to control the operating temperature not only results in higher precision, but also reduces the heating response time of the gas-sensitive membrane due to the reduced heat capacity due to the smaller two dimensions. In addition, power consumption was also reduced.

However, the conventional proposals made by the present inventors still have unresolved problems. The problem will be specifically explained using FIG. 1. Note that the figure (,) is a top view, and the figure () is a top view.
b) is a sectional view taken along line AA' in FIG.

As shown in the figure, a p-type silicon substrate 1 is adhered to a support 9 made of alumina or the like, and an ultrafine particle gas-sensitive film 5 is provided with a Si◯2 film 7 interposed therebetween. 3′.

3'' is a wire connection electrode for applying power to the substrate 1, and 4' and 4'' 4111 are electrodes for measuring electrical characteristics such as electrical resistance or capacitance of the sensitive film 5. Now, it is necessary to heat only the gas-sensitive film 5, but in the case of the conventional example shown in FIG. 1, the entire silicon substrate 1 is heated. The problem was that the heat generated in the substrate 1 was transmitted through the ceramic support made of alumina or the like and escaped.

It was necessary to solve the contradictory problems of further reducing power consumption and heating only the gas-sensitive membrane 5 to a high temperature of several hundred degrees Celsius.

Furthermore, in the conventional example shown in FIG.
When trying to heat the temperature to several hundred degrees Celsius, the electrode 3'.

3" and the silicon substrate 1 (parts 8' and 8") are also heated to several hundred degrees Celsius, so over a long period of time, the alloy layer (Pt-8t, Pt-8t,
Another problem that remained unresolved was that the performance of electrodes a' and f deteriorated due to deterioration of the materials (Mo-8t, Au-3t, etc.) over time.

The present invention can solve the above-mentioned conventional problems. That is, by using the gas sensor of the present invention, power consumption can be further reduced, and the gas sensitive membrane 6 can be used.
The contradictory issues that remain with conventional gas sensors, such as heating gas sensors to high temperatures of several hundred degrees Celsius, can be solved in one fell swoop.

The present invention will be explained in detail below.

FIG. 2 shows an embodiment of the gas sensor of the present invention. Figure (,) is a top view, Figure (b) is A-A' in Figure (,).
FIG. Portions having the same functions as those of the conventional example shown in FIG. 1 will be given the same reference numerals to avoid redundant explanation. In the figure, 7 is an insulating film, SiO2, A
Q2o3. It is composed of multilayer films such as crow, 513N4, Ruihaso, etc. 2 is Pt, Mo.

TiN, TaN2. This is a thin film heater made of a well-known thin film such as NiCr. 10', 10'' are substrates made of metal, thermal insulator, silicon, Si02 film formed on silicon, etc. When using silicon itself for the substrates 10', 10'', ,
An alloy layer formed between silicon and an electrode material (for example, P t S
Although it cannot solve the problem that the electrode performance deteriorates in the heater electrodes 2' and 2'' due to aging of the silicon (such as Au Si system), it is possible to
If the o2 film is pre-coated (not shown), such problems will not occur. If the substrates 10', 10'' are thermal insulators, the heat generated by the thin film heater 2 can be used more efficiently.

In a thin film heater, if the heater 2 part is designed so that the resistance value is the highest (rJ) among the electric resistances between the electrodes 2' and 2'', it is easy to locally generate heat in the heater 2 part.

As is clear from a comparison with FIG. 1, the power consumption for heating the sensitive film 6 is reduced. Since heating is performed through the insulating film 7, it is advantageous for the insulating film 7 to be thinner from the viewpoint of reducing power consumption.

Needless to say, it is further desirable that the material be electrically insulating and thermally a good conductor. It goes without saying that the bonding pad d, 6'' may be provided on the substrate 1σ, 10''.

FIG. 3 shows another embodiment. Figure (,) is top view 2
FIG. 0)) is a sectional view taken along line A-A' of the figure (-).

For the sake of simplicity, the gas-sensitive membrane 6 is not shown in FIG. 3(,). A thin film heater 2 is placed on top of the insulating film 7.
, an electrically insulating and preferably thermally conductive coating 11, on top of which an electrode 4' for the gas-sensitive membrane.

all, 44F and gas-sensitive membranes 6 are provided, respectively.

8', 8'' are heaters 2', 2'' and electrodes 3', 3
”This is an opening for connecting with.

The portion of the heater 2 and the portions of the electrodes 2', 2'' may be formed from different electrode materials or may be formed to have different thicknesses.Also, they may be formed by a technique such as screen printing. It goes without saying that the pads 6', 6'' may be provided on the substrates 1σ, 10''.

Further, when the heater 2 is made of a thin platinum film, for example, it has a certain temperature dependence as is well known, so it can be used not only as a heater but also as a temperature sensor.

Therefore, the temperature of the gas-sensitive membrane 6 can be precisely controlled.

It is preferable that the insulating film 7 is a thermally poor conductor and the coating 11 is a thermally good conductor. In the embodiment shown in FIG. 3, the thin film heater 2 is an insulating film 7. Since it is coated with the film 11, there is an advantage that the proportion lost due to air convection is reduced.

If the film 11 in FIG. 3 is a SiO2 film or a Si3N4 film, it can be formed by the well-known CVD method.

Another advantage of the gas sensor of the present invention is that the thermal response speed for heating and cooling the gas-sensitive membrane 6 is orders of magnitude faster than that of the prior art.

In FIGS. 2 and 3, the gas-sensitive film 6 is composed of an ultrafine particle film formed using an evaporation method in a gas. Regarding the manufacturing method of such a membrane, for example, Japanese Patent Application No. 53-1
As already proposed in No. 00620, for example, a metal mask is used to selectively install the gas-sensitive film 5 in a specific location.

It goes without saying that the gist of the present invention will not be impaired even if a well-known film other than the film formed by the in-gas evaporation method is used as the gas-sensitive film 5, and various modifications other than those described above can be considered. Needless to say, it is possible.

For example, as shown in FIG. 4, which is a two-wheeled example of the embodiment shown in FIG. This has the advantage that the gas-sensitive membrane 6 can be exposed to air convection to a lesser extent. In this case, it is preferable that the performance of the insulating film 7 and the coating 11 be opposite to that shown in FIG.

In the above embodiments, a case has been described in which the heater also serves as a temperature sensor, but it goes without saying that a temperature sensor for detecting the ambient temperature may be provided at a location other than the heater.

The correlation between the emitted power or the emitted temperature of the thin film heater and the electrical characteristics of the sensitive film at various concentrations of the test gas is once stored in a memory element, and then the actual measured value and the stored value of the electrical property are stored. Since the gas to be detected can be detected by comparison, not only can gas detection be performed with higher precision, but also changes due to ambient temperature can be corrected through arithmetic processing.

Alternatively, for example, by providing a heater that is exactly the same as heater 2 in FIG. 3, but not providing a gas-sensitive film or providing a gas-insensitive film above it, the change in ambient temperature can be corrected. It goes without saying that it can be done.

As proposed by the present inventor in, for example, Japanese Patent Application No. 54-68138, a plurality of different gases can be detected with the Lee sensitive membrane by changing the operating temperature of the ultrafine particle gas sensitive membrane. In the gas sensor of the present invention, the sensitive part and the heater part can be miniaturized, so it has become practical to provide, for example, a plurality of sensitive films in close proximity and to vary the operating temperature of each to operate steadily at a predetermined temperature. Therefore, by operating multiple gas-sensitive membranes under the same conditions for gas detection, not only can detection accuracy and precision be improved, but also by operating at least one at room temperature, can be detected.

As described above, the gas sensor of the present invention has excellent features such as low power consumption, high-speed response, high accuracy, and high reliability, and can be manufactured uniformly and in a reduced size, so it has industrial value. It has a high value.

[Brief explanation of the drawing]

Figures 1(a) and 1(b) show conventional gas sensors, of which figure (→ is a top view and figure (b) is a sectional view taken along line AA' in figure (a). figure(,) , (
b) shows an embodiment of the gas sensor of the present invention, in which figures (,) are top views, and figures (tops) are taken along line A-A' in figures (,).
FIG. Figures 3 (,) and (b) show other embodiments of the present invention and gas sensors, in which figures (,) are top views and figures (,) are cross-sections taken along line A-A' in figures (,). It is a diagram. FIG. 4 is a sectional view showing a two-wheeled version of the embodiment shown in FIGS. 3(a) and 3(b). 1...Substrate, 2...Thin film heater,! ,
t'... Electrode (for heater), "?'", 4'.
...... Electrode (for gas-sensitive membrane), 6...
・・Gas sensitive membrane, 3 “・・・・・Electrode (for wire connection), 6.e/・・・・Bonding panode, 7
...Insulating film, Gi, Gi...Open hole, 1σ
, 10''...Substrate, 11...Coating. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure θ' Figure 2ff' 5 2・2''

Claims (7)

[Claims] (1) at least a portion of the substrate has an electrically insulating thin film held by the substrate, the thin film is provided with a gas-sensitive film and an electrode for measuring its electrical properties; A gas sensor comprising a thin film heater for heating a gas sensitive membrane. (2) The gas sensor according to claim 1, wherein a gas sensitive film is provided on one surface of the thin film, and a thin film heater is provided on the other surface of the thin film. (3) The gas sensor according to claim 1, wherein a gas sensitive film is provided on a thin film heater provided on the thin film via an electrically insulating thin film. . (4) The correlation between the emitted power or the emitted temperature of the thin film heater and the electrical characteristics of the gas-sensitive film at various concentrations of the test gas is temporarily stored in the storage means, and then the actual measured values of the electrical characteristics are stored. 2. The gas sensor according to claim 1, wherein the gas sensor is configured to detect the gas to be detected by comparing the value of the gas to be detected. (5) The gas sensor according to claim 1, wherein the gas-sensitive film is a film composed of ultrafine particles. (6) The gas sensor according to claim 1, characterized in that a plurality of thin films each having a thin film heater and a gas sensitive film are provided. (7) The gas sensor according to claim 6, wherein at least one of the gas-sensitive films provided on each of the plurality of thin films is configured to detect humidity.