JP2988016B2 - Ozone sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ozone sensor using a metal oxide semiconductor thin film for controlling ozone concentration in an ozone generator or various ozone-using devices or detecting leaked ozone.

[0002]

2. Description of the Related Art Since ozone has a strong oxidizing effect,
It is used in many fields such as water and sewage water treatment, medical treatment, and food industry for the purpose of deodorization and sterilization. Recently, it has been spreading to ordinary households through use in various home appliances.
However, while having useful utility value, even a very small amount of ozone is extremely harmful to the human body, so it is necessary to reliably control the amount of ozone generated and detect leaked ozone.

In order to measure and detect the ozone concentration, in addition to the conventional oxidation-reduction method, absorption spectroscopy method, ultraviolet absorption spectrum method and the like, recently, a sensitive thin film made of a metal oxide semiconductor such as In ₂ O ₃ or SnO ₂ has been used. Practical application of the ozone sensor to be used is being actively promoted. This ozone sensor utilizes the fact that the electric resistance value of the sensitive body thin film changes according to the ozone concentration, and has many advantages of being small, lightweight, highly reliable, simple and relatively inexpensive. . However, for stable operation of this sensor element, 35
Since it is necessary to keep the temperature at about 0 to 450 ° C., a pair of platinum electrodes, for example, is provided on a plate-shaped ceramic substrate mainly composed of α-Al ₂ O ₃ which is heat-resistant and has excellent electrical insulation. The element is manufactured by forming the sensitive body thin film between the electrodes. This sensitive thin film can be formed by applying a film forming technique such as a vapor deposition method or a sputtering method using an electron beam.
A method is widely used in which a metal salt solution of indium, tin, or the like is wet-coated by a screen printing method, a spin coating method, or the like, dried, heated and fired in air to form an oxide thin film.

[0004]

As described above, when an ozone sensor composed of an element using a sensitive body thin film formed by a film forming method by wet coating is used for a long period of time, if an ozone sensor has been Some of the characteristics deteriorated with time. When the deteriorated sensor was observed in detail, it was found that the sensitive thin film of the element was partially peeled off from the ceramic substrate surface. An object of the present invention is to improve deterioration of characteristics over time due to peeling of the sensitive body thin film and the like.

[0005]

As described above, the present invention provides an ozone sensor comprising an element using a sensitive thin film mainly composed of a metal oxide semiconductor obtained by a film forming method by wet coating. In view of the fact that the characteristic thin film is deteriorated when used for a long period of time, the sensitive thin film is partially separated from the surface of the ceramic substrate, and the problem is solved by focusing on the roughness of the substrate surface. Specifically, the surface roughness (Ra)
By using an electrically insulating substrate in the range of 0.05 μm to 0.5 μm and forming a pair of electrodes and a sensitive thin film mainly composed of a metal oxide semiconductor between the electrodes on the substrate, the length is increased. In use for a period, not only the characteristic deterioration due to the peeling of the sensitive body thin film from the substrate surface due to the repetition of thermal shock is suppressed, but also the sensitivity and responsiveness of the sensor are improved by the uniform film thickness. is there.

[0006]

The main point of the present invention is that the surface roughness (Ra) is 0.05.
By using an electrically insulating substrate in the range of μm to 0.5 μm , the bonding strength between the sensitive thin film and the substrate formed by a film-forming method by wet coating is improved, and it is resistant to thermal shock and has stable characteristics. A sensor element to be maintained can be obtained. At the same time, the effective surface area of the sensitive element thin film formed by the wet film formation method can be increased, and the obtained sensor exhibits characteristics excellent in sensitivity and responsiveness.

[0007]

FIG. 1 is a schematic sectional view showing an embodiment of an ozone sensor element according to the present invention. In FIG. 1, reference numeral 1 denotes an alumina substrate (2 × 5 × 0.5 mm), and 2 denotes a coating liquid prepared mainly by metal salts such as chlorides of In and Sn, which is applied by dipping, dried, and dried in air. In ₂ O ₃ (95% by weight) and SnO ₂ (5% by weight)
%) Is a platinum electrode formed in advance on a substrate by a sputtering method or the like. The alumina substrate has a surface roughness (Ra) of 0.1.
05 μm, 0.1 μm, 0.3 μm, 0.5 μm, 0.
7 μm and 1.0 μm were used.

First, in order to check the bonding property between the sensitive element thin film of these sensor elements and the substrate, a film peeling test was performed using an adhesive tape. The results are shown in (Table 1). The symbols ○, △, and △ represent the order in which the bonding property is good. If the surface roughness exceeds 0.5 μm, part of the film will peel off on the adhesive tape,
Apparent attachment was observed. The area of the peeled film occupied about 2% of the apparent film formation area. When the surface roughness was 0.5 μm or less, the amount of peel adhesion to the tape was extremely small, and when the surface roughness was 0.5 μm and 0.05 μm, a very fine film piece was attached. At the surface roughness of 0.1 μm and 0.3 μm, no peeling was observed with the naked eye. In addition, surface roughness
If the substrate is smaller than 0.05 μm,
Immediately after that, peeling often occurs on a part of the film.
I didn't make it an elephant. In the thin film formed by the above method, extremely fine particles in the order of several to several + 数 are appropriately sintered to form a porous film. If the surface roughness of the substrate is large,
The coating liquid tends to accumulate in the concave portions of the substrate, the firing speed becomes non-uniform, distortion occurs, and the film easily floats in a fine region, and the so-called anchor effect decreases. Conversely, even if the surface roughness is too small, the anchor effect is considered to be reduced. It is determined that it is important to match the size and sintering state of the crystal grains constituting the sensitive body thin film with the substrate surface roughness.

[0009]

[Table 1]

Further, a thermal shock test in which the sensor element is placed in an electric furnace and the temperature is raised and lowered from room temperature to 500 ° C. in about 1 minute is performed.
00 cycles performed, results of examining the state of peeling sensitive thin film in the same manner as described above, the surface roughness is 0.05μ
It was confirmed that the bonding state between the film and the substrate was very good when a substrate having a size of m to 0.5 μm or less was used.

Next, the surface roughness of 0.3 μm and 1.0 μm
The response characteristics to ozone were determined by the method described below, using a sensor element manufactured in the same manner as described above using an alumina substrate of m. The sensor element was fixed to the heater for heating the element in close contact and set in a measuring box filled with clean air.
Set to. Next, ozone equivalent to 0.5 ppm was injected into the measurement box, uniformly diffused and brought into contact with the sensor element, and the change in the electric resistance value of the sensor element was measured. The result is shown in FIG. The change in the electric resistance value of the sensor using the substrate having a surface roughness of 0.3 μm was large, showing excellent characteristics in both response characteristics and return characteristics associated with exhaust. However, it was found that the change in resistance of the sensor using the substrate having a surface roughness of 1.0 μm was small, and both the response characteristics and the return characteristics were inferior. When a substrate with a surface roughness of 0.3 μm is used, the thickness of the sensitive body is relatively uniform, and the effective surface area of the sensitive body involved in the reaction is large, resulting in high sensitivity and excellent response characteristics. It is considered to be. On the other hand, when the surface roughness is increased to some extent, the film thickness becomes non-uniform, and a portion having a large film thickness occupies a considerable area, which substantially reduces the surface area.
It is considered that the effective surface area involved in the reaction is reduced.

Further, the surface roughness is 0.3 μm and 1.0 μm.
The change over time in sensor sensitivity was measured using a sensor element manufactured using a μm substrate. The sensor element was left in an air atmosphere at 450 ° C. and was taken out every 200 hours.
The change in electric resistance at 350 ° C. was measured in the measurement box in the same manner as described above, and the change over time in sensor sensitivity was determined. The sensor sensitivity was represented by a value (R _G / R _A ) obtained by dividing the sensor resistance (R _G ) in ozone mixed air by the sensor resistance (R _A ) in air. This was performed for a total of 1000 hours, and the results are shown in FIG. It was found that the sensitivity of a sensor using a substrate having a surface roughness of 0.3 μm was extremely stable, but the sensitivity of a sensor using a substrate having a surface roughness of 1.0 μm gradually decreased. The effective surface area of the sensitive body thin film when using a substrate having a surface roughness of 1.0 μm is greater than that when using a substrate having a surface roughness of 0.3 μm.
It is considered that the surface area is small from the beginning, and the degree of decrease in the surface area increases as the sintering progresses.

As is apparent from the above embodiments, the ozone sensor according to the present invention has extremely excellent characteristics. In the examples, the case where the dipping method was used as the method for producing the ozone sensitive substance thin film was described. However, a film forming method by screen printing, spin coating, brush coating, or other wet coating can be used as appropriate. The same effect as that of the embodiment can be obtained. Further, in the embodiment, only a case where a material having a ratio of In ₂ O ₃ to SnO ₂ of 95: 5 is used as the sensitive body thin film has been described. Can be. In addition, the starting material is not limited to the examples, and a material suitable for a film forming method can be appropriately selected and used. It is added that the structure and configuration of each part of the sensor element or the heat-resistant and electrically insulating substrate material and the electrode material can be freely designed or used as long as they do not contradict the gist of the invention.

[0014]

The ozone sensor according to the present invention is excellent in stability and long-term reliability due to thermal shock in addition to sensitivity and responsiveness of ozone detection, and is small, lightweight and inexpensive. It is suitable for applications such as ozone concentration control or ozone detection in equipment.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing one embodiment of an ozone sensor according to the present invention.

FIG. 2 is a characteristic diagram showing an ozone response.

FIG. 3 is a characteristic diagram showing a change over time in sensitivity.

[Explanation of symbols]

 Reference Signs List 1 alumina substrate 2 sensitive film 3 electrode

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Kunio Kimura 1006 Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (56) References JP-A-4-274749 (JP, A) JP-A-4-152258 (JP, A) JP-A-63-298148 (JP, A) JP-A-2-285246 (JP) , A) (58) Field surveyed (Int.Cl. ⁶ , DB name) G01N 27/12

Claims (3)

(57) [Claims] 1. An ozone sensor comprising: a pair of electrodes formed on an electrically insulating substrate; and a thin-film sensitive body mainly composed of a metal oxide semiconductor formed between the electrodes. Has a surface roughness (Ra) of 0.05 μm or more
An ozone sensor having a range of 0.5 μm . 2. The ozone sensor according to claim 1, wherein the sensitive body is formed by a film forming method by wet coating. 3. The main component of the sensitizer is In ₂ O ₃ and SnO.
Ozone sensor according to claim 1 or 2, wherein the _2.