JPH11344457A - Smell sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a smell sensor conserved in power, small in size and made continuously usable. SOLUTION: Electrodes 22, 23 are formed on an insulating substrate 21, and a metal oxide semiconductor layer 24 composed of nickel oxide or the like is formed between these electrodes 22, 23. A metal oxide insulating film 25 comprising nickel titanate is formed thereon, a sensitive film 26 comprising zinc oxide tin oxide or indium oxide is further formed thereon, and a reference element 31 same in structure and having a reference element 31 having a reference film 29 not almost responding to a malodorous gas formed to the sensitive film 26 is further formed thereon. By taking the difference between the detection values thereof, effect due to a change with lapse of time is removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an odor sensor which detects an odor gas and detects its presence.

[0002]

2. Description of the Related Art Conventional odor sensors include an odor sensor using a sensitive film made of an organic substance, which is excellent in that it has high selectivity. However, once used, it loses sensitivity and is disposable and cannot be used repeatedly. An odor sensor using a metal oxide can be used repeatedly. That is, as shown in FIG.
A pair of electrodes 12 and 13 are provided on a heat-resistant insulating substrate 11, and a sensitive portion 14 made of a metal oxide sensitive to odorous gas is formed between the electrodes 12 and 13. A heater 15 is provided on the opposite side of the insulating substrate 11.

When an odor gas is adsorbed on the sensitive part 14, the electrode 1
The electric resistance between 2 and 13 changes, and odorous gas can be detected. In order to increase the detection sensitivity, the sensitive unit 14
Is preferably raised to, for example, about 150 ° C. At this point, it is preferable to always heat the heater 15 to some extent.
In order to erase the odor gas once it has been adsorbed on the sensitive part 14, the heater 15 is heated to a considerably high temperature so that the sensitive part 14 becomes, for example, 400 ° C. 14 can be released. Therefore, it is possible to use the heater 15 repeatedly by raising the sensitive portion 14 to such a high temperature by the heater 15.

[0004]

In the conventional odor sensor shown in FIG. 3, in order to increase the detection sensitivity, the sensitive portion 1
Even in the case of heating the temperature of No. 4, it was necessary to constantly heat the whole including the insulating substrate 11 to, for example, 150 ° C., and the power consumption was large. Further, in order to regenerate the sensitive part 14, that is, to diffuse the adsorbed odor gas, it is necessary to raise the temperature of the sensitive part 14 to 400 ° C. A large power consumption is required, the heater 15 itself has a relatively large capacity and a large size, and the odor sensor may cause a fire.

An object of the present invention is to provide an odor sensor that consumes little power, is small and can be reused, that is, can be used continuously.

[0006]

According to the present invention, a pair of electrodes are formed on a heat-resistant insulating substrate, a metal oxide semiconductor layer is formed between the electrodes, and the metal oxide semiconductor layer is formed. A metal oxide insulating film is formed thereon, and a metal oxide film sensitive to an odor gas is formed thereon.

[0007]

FIG. 1 shows an embodiment of the present invention.
Electrodes 22 and 23 are formed on a heat-resistant insulating substrate 21 such as alumina at intervals. These electrodes 22, 23
In between, a metal oxide semiconductor layer 24, for example, nickel oxide,
For example, tin indium oxide is formed. An oxide insulating film 25 is formed on the semiconductor layer 24. As the oxide insulating film, for example, nickel titanate and aluminum oxide are formed, which constitute a so-called gate insulating film.
An odor gas-sensitive metal oxide insulating film, that is, a sensitive film 26 is formed thereon. As the sensitive film 26, the same as the sensitive portion 14 in the conventional device shown in FIG. 3 can be used, that is, tin oxide, indium oxide, zinc oxide, etc. are formed by a printing technique.

In this embodiment, the odor detecting elements 28A to 28G composed of the electrodes 22, 23, the metal oxide semiconductor layer 24, the metal oxide insulating film 25, and the metal oxide sensitive film 26 have the same process, the same size, Formed in multiple shapes and structures,
Just so that the sensitive film 26 is sensitive to different gases,
Different membranes are used. Further, in this example, the reference element 31 on which the reference film 29 having a sufficiently low sensitivity to the odorous gas as compared with the others is formed as one of the sensitive films.
Are configured. That is, seven of the detection elements 28 and one reference element 31 are formed simultaneously on the same insulating substrate 21, and only the composition and thickness of the uppermost sensitive film 26 and reference film 29 are different from each other. However, the same structure and material are used for the other parts.

In this embodiment, the electrode 23 is a common electrode, so that the electrodes 23 of the elements approaching each other, in this example, four elements, are formed in common. The electrodes 22 are independent from each other, a voltage is applied between the electrodes 22 and 23, the sensitive film 26 and the reference film 31 each act as a gate electrode, and the insulating film 25 acts as a gate insulating film. A channel is formed near the boundary of the insulating film 25 of the metal oxide semiconductor layer 24, and has a structure similar to that of a so-called MIS type semiconductor element.

As a method of manufacturing the semiconductor layer 24, a solution method, a sputtering method, a CVD method, or the like can be used. However, a solution method capable of selectively forming a film only in the semiconductor layer region is easily manufactured. In this case, an unnecessary portion of the semiconductor film is masked using a photoengraving technique, a semiconductor layer is applied, and then the mask portion is removed.
Can be manufactured. The thickness of the semiconductor layer 24 is
A film having a thickness of several tens nm to 1 μm, for example, 100 nm is used.

The insulating film 25 can be similarly manufactured by a solution method, a sputtering method, a CVD method, or the like, but is preferably manufactured by a sputtering method having excellent film characteristics. In this case, a stainless steel mask in which a portion to be formed is cut out is superimposed on the substrate in advance, and then a sputter film is formed only on a necessary portion by sputtering, thereby obtaining an insulating film 25 only on a necessary portion. The thinner the film, the better the responsiveness, but on the other hand, the insulation properties are reduced due to pinholes and the like, so that the thickness is about several nm to 100 nm, for example, a 20 nm film is used.

The method for manufacturing the sensitive film 26 can be a solution method, a sputtering method, a CVD method, or the like. In the case of manufacturing by the solution method with the lowest manufacturing equipment cost, the unnecessary parts of the semiconductor film are masked using a photoengraving technique, the sensitive film material is applied, and the mask part is removed, and the necessary parts are removed. The sensitive film 26 is obtained. This film thickness is changed by several nm to several μm depending on the concentration of the gas to be measured. The thinner the film thickness, the better the response characteristics at low concentrations, but on the other hand, it saturates at high concentrations, so that the concentration cannot be measured.
For example, there is a case where tin oxide having a thickness of 15 nm is used for one sensitive film, and a thickness of 800 nm is used for another sensitive film so that a higher concentration gas can be measured.

When the odorous gas sensitive to the sensitive film 26 is adsorbed, the resistance value between the electrodes 22 and 23 of the corresponding element 28 changes, that is, the current value flowing between these electrodes 22 and 23 changes, The odorous gas can be detected. In order to release the adsorbed odor gas and repeat it, that is, to continuously use it, for example, as shown in FIG.
A voltage is applied in the form of a pulse between the electrodes 3 and a current flows while the pulse voltage is being applied. In each of the elements 28 and 31, the channel portion is locally heated, and the temperature of the sensitive film 26 and the reference film 29 is increased. Rises to about 400 ° C. as shown in FIG. 2B. When the application of the pulse voltage is stopped, the temperature drops to about 150 ° C., but when the pulse voltage is applied again, the temperature rises again. It is used in such a state, and the arrival of the odorous gas is detected in a state where the temperature is about 150 ° C. and the sensitivity is high while the voltage pulse is not applied. When no odorous gas is present, a current varying with a waveform similar to this temperature flows between the electrodes 22 and 23 as shown in FIG. 2C.

In the state where the odor gas of each element has not arrived, and at the measurement temperature (in this example, 150 ° C.)
The current flowing in the degree) and I _0, a current when the smell gas has arrived and I, shall be measured its I / I _0. For example, when a certain gas A arrives, as shown in FIGS. 2D to 2F, the values of the two detection elements 28A and B and the reference element 31 respectively increase, but the detection current of the detection element 28A greatly changes, and the detection element 28B Is smaller than this, and the change in the detection current of the reference element 31 is slight.

On the other hand, when another gas B arrives, the detecting element 28
The current rise in A is small, the current in the detection element 28B changes greatly, and the change in current with respect to the reference element 31 is about the same as that of the odor gas A. For example, the sensitive film of the first detecting element 28 is tin oxide, and the sensitive film of the second detecting element 28 is zinc oxide. In this way, various odorous gases can be detected.

This kind of element, that is, a MIS element generally suffers from so-called drift in which the performance is deteriorated due to the influence of the ambient temperature or a change in the surface composition due to aging, etc. In this example, a reference element 31 is provided. Since the same drift occurs in this case, the influence of the drift can be eliminated by calculating the difference between the detection values of the reference element and each detection element. Similarly, by providing the reference element 31, it is possible to effectively detect a target odor gas while minimizing the influence of miscellaneous gas adsorption and water vapor at a low temperature.

In this embodiment, seven detecting elements 28A to 28A
The comparison was performed using one reference element 31 with respect to G. However, if the detection element 28 and the reference element 31 are provided so as to be one-to-one and the comparison is performed, the accuracy can be further improved. The effect of drift can be eliminated. For example, detecting element 2
8A is a sensor element having a high sensitivity to the test gas A, while a sensor element having a low sensitivity to the same test gas A is used by using the detection element 28B as a reference element. Similarly, a sensor element having high sensitivity to the test gas B is used as the detection element 28D, and a sensor element having low sensitivity to the same test gas B is used by using the detection element 28E as a reference element.

Further, in the present embodiment, the sensitivity of the reference film 29 of the reference element 31 is lower than the sensitivity of the other sensitive films 26, but may be higher. That is, it is only necessary that the sensitivities differ to such an extent that the difference between the detection element and the reference element can be obtained. The expression that the sensitivity of the reference film is sufficiently low indicates this.

[0019]

As described above, according to the present invention, the adsorbed gas can be released and can be used repeatedly, that is, continuously, and in that case, the gate insulating film, that is, the metal oxide insulating film 25 can It is a very thin film of about 500 °. Therefore, if a small amount of current is passed between the electrodes 22 and 23 to locally heat the metal oxide semiconductor layer 24 which is a channel portion, the sensitive film 26 is also heated and the sensitivity is increased. In addition, the temperature can be raised to release the adsorbed gas, the temperature can be increased, and the operation can be performed with low power. Further, the overall configuration does not require a large heater and can be formed in a small shape. .

Further, by providing the reference element, it is possible to avoid the influence of drift due to aging and the influence of water vapor and a non-detection target gas. In addition, the element configuration is simple, it can be produced by applying printing technology, and it is rich in mass productivity,
It can be made cheaply.

[Brief description of the drawings]

FIG. 1A is a plan view showing an embodiment of the present invention, and FIG. 1B is a sectional view thereof.

2A is a voltage applied between electrodes, B is a temperature of an element, FIG.
C is the current flowing between the electrodes, D, E and F are the first, respectively.
The figure which shows the sensitivity with respect to each different gas of a 2nd detection element and a reference element.

FIG. 3 is a diagram showing a conventional odor sensor.

Claims (3)

[Claims] An insulating substrate; a pair of electrodes formed at intervals on the insulating substrate; a metal oxide semiconductor layer formed between the two electrodes; An odor sensor comprising: a metal oxide insulating film formed on a substrate; and an odor gas-sensitive metal oxide film formed on the metal oxide insulating film. 2. The odorous gas formed on the insulating substrate and having the same structure as the pair of electrodes, the metal oxide semiconductor layer, and the metal oxide insulating film. The odor sensor according to claim 1, further comprising a reference element on which a reference metal film having a different sensitivity to an odor gas from the responsive metal oxide film is formed. 3. The pair of electrodes on the insulating substrate,
The metal oxide semiconductor layer, the metal oxide insulating film,
A plurality of elements comprising the odor gas-sensitive metal oxide are formed, and the odor gas-sensitive metal oxide film is formed to be sensitive to different odor gases. Or the odor sensor according to 2.