JPH0668475B2 - Thin film ozone sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a thin film ozone sensor having high sensitivity to low concentration ozone.

[Conventional technology]

Ozone is used for many purposes such as medical use, food industry, wastewater treatment, semiconductor manufacturing process for the purpose of sterilization, deodorization, oxidation, etc. due to its strong oxidizing power, and the amount used is also increasing. There is. However, since ozone has a strong oxidizing power, it is highly toxic to the human body, and its permissible concentration is specified to be 0.1 ppm. Therefore, the development of a highly sensitive sensor that is easier to handle, more reliable, and cheaper than before Is desired.

Conventionally, as a method for measuring low-concentration ozone, a redox titration method, an absorptiometric method, an electrochemical method, an ultraviolet absorption spectrum method, etc. have been proposed, but they generally require a large measuring device and are expensive. In addition, it has drawbacks such as complicated handling.

[Problems to be solved by the invention]

On the other hand, a semiconductor gas sensor called a sintering type or a thick film type has been provided as a gas sensor that is cheaper than before and is easy to handle. However, the semiconductor gas sensor is almost insensitive to ozone and is not used as an ozone sensor. That is, since ozone has an extremely strong oxidizing power and has a property of spontaneously decomposing, ozone is reactively decomposed on the surface layer of the sensor before reaching the inside of the sensor, which does not contribute to the sensitivity of the sensor. It was a thing.

The present invention has been made by paying attention to the above situation,
An object of the present invention is to provide a semiconductor ozone sensor which is easy to handle and inexpensive and which is highly reliable and highly sensitive to low-concentration ozone.

[Means for solving problems]

That is, the characteristic configuration of the thin film type ozone sensor according to the present invention is that a semiconductor thin film layer of 300 Å to 1 μm containing In ₂ O ₃ as a main component is formed on the substrate, and its action and effect are as follows. Is.

[Work]

Since a thin film type sensor with a semiconductor thin film layer whose main component is In ₂ O ₃ is used on the substrate, a conventional semiconductor gas sensor called a sintered type or thick film type is used. In some cases, ozone may be reactively decomposed on the surface layer of the sensor and may not reach the sensing portion of the sensor, which may cause a situation in which the sensor does not function as a sensor. Since ozone can reach the sensing part of the sensor and reacts at the sensing part without causing a situation such as reaction decomposition by ozone, it can function as an ozone sensor with high sensitivity,
In addition, since it is formed of In ₂ O _{3 having} a film thickness of 300 Å or more, the change with time is small.

〔The invention's effect〕

In other words, as a result of trial production of various semiconductor thin films that are easy to handle and inexpensive, and thin films with various film pressures, an In ₂ O ₃ -based thin film sensor with a film thickness of 1 μm or less, for example, for low concentration ozone of 1 ppm or less Is highly sensitive and has excellent characteristics as a sensor, and the film thickness of the In ₂ O ₃ thin film sensor is 300
Those above Å have been found to show stable output with little change over time, so they have high reliability, can be detected with high sensitivity, and can be used stably for a long period of time.

〔Example〕

 Hereinafter, examples of the present invention will be described in detail.

Figure 1 and in Figure 2 there is shown a schematic perspective view and a schematic cross sectional view of a thin film type ozone sensor, surface In ₂ O of the sensor insulating substrate such as alumina (1) as shown in FIG. _This is formed by forming a semiconductor thin film layer (2) containing ₃ as a main component. Any substrate can be used as the substrate (1) as long as it has a heating function and a function capable of measuring a change in resistance value, and is not limited. Further, the thin film layer (2) can be formed on the surface of the substrate (1) by a thermal decomposition method, a chemical vapor deposition method, a physical vapor deposition method, or any other film production method. The film thickness of the semiconductor thin film layer (2) of the semiconductor thin film layer (2) is 300Å to 1 μm, which means that when the film thickness exceeds 1 μm, a sensor for low concentration ozone of, for example, about 1 ppm is used. Output is low and some are not practical, and when the thickness of the semiconductor thin film layer (2) is less than 300Å, it is highly sensitive to ozone, but has a large change over time and is inferior in long-term stability. Because there is. Also,
It is more preferable that the semiconductor thin film layer (2) has a thickness of 300Å to 5000Å. In the figure, (3) is a comb-shaped electrode formed on the surface of the substrate (1), (2) is a semiconductor thin film layer formed on the substrate (1) so as to cover the electrode (3), and (4). Is a heater attached to the back surface of the insulating substrate (1). As shown in FIG. 1, the electrode (3) is visible through the semiconductor thin film layer (2) from the front side.

Next, the present invention will be specifically described.

As shown in FIGS. 1 and 2, the alumina substrate (1)
This substrate (1) so as to cover the electrode (3) formed on it
A semiconductor thin film layer (2) containing In ₂ O ₃ as a main component was formed thereon by a vacuum vapor deposition method to prepare a thin film type ozone sensor.
Next, the film thickness dependence of ozone sensitivity in the thin film type ozone sensor having the above configuration was measured. Results are shown in FIG. From this figure, it is found that the ozone sensitivity tends to decrease as the film thickness of the semiconductor thin film layer increases, and particularly when the film thickness exceeds 1 μm, the sensitivity of low-concentration ozone greatly decreases. Was confirmed.

Further, in FIG. 4, when the film thickness of the semiconductor thin film layer is changed,
The normalized output over time is shown for 0.5 ppm ozone concentration. From this figure, it can be seen that the change over time increases as the film thickness decreases, and the long-term stability deteriorates. Further, FIG. 5 shows the response waveform and the reproducibility with respect to an ozone concentration of 0.5 ppm using a thin film type ozone sensor having a semiconductor thin film layer having a film thickness of 300 liters. From this figure, it was confirmed that the response speed and reproducibility were excellent.

[Another embodiment]

As shown in FIG. 6, a comb-shaped electrode (3) and a heater (4) are formed on the same surface of the substrate (1), and the semiconductor thin film is formed on the substrate (1) so as to cover the electrode (3). The layer (2) may be formed, and as shown in FIG. 7, an electrode (3) which also serves as a heater (4) is formed on the surface of the substrate (1) and the substrate (1) is covered so as to cover the electrode (3). A semiconductor thin film layer (2) may be formed on the surface. Further, the heater (4) may be embedded inside the substrate (1).

Incidentally, a thin film layer of silicon oxide is formed on the surface of the semiconductor thin film layer (2) to form a thin film type ozone sensor, or a thin layer of metal oxide is formed on the surface of the semiconductor thin film layer (2). It may be formed and the surface thereof may be covered with a thin film layer of silicon oxide. In this way, it can be used as an ozone sensor having excellent selectivity for reducing gas. That is, when a reducing gas coexists, the ozone output decreases, and accurate ozone concentration may not be measured, but the surface of this In ₂ O ₃ semiconductor thin film layer is covered with a thin film layer of silicon oxide. By doing so, the selectivity for ozone gas can be increased.

Further, although reference numerals are given in the claims for convenience of comparison with the drawings, the present invention is not limited to the structures of the accompanying drawings by the entry.

[Brief description of drawings]

The drawings show an embodiment of the thin-film ozone sensor according to the present invention. FIG. 1 is a perspective view of the thin-film ozone sensor, FIG. 2 is a cross-sectional view thereof, and FIG. 3 is a diagram showing film thickness dependence of ozone sensitivity. ,
FIG. 4 is a diagram showing long-term stability when the thickness of the semiconductor thin film layer of the thin film type ozone sensor is changed, and FIG. 5 is a diagram showing a response waveform and reproducibility of ozone of the thin film type ozone sensor, and FIG. 7 and 8 are schematic plan views of the thin film ozone sensor. (1) ... Substrate, (2) ... Semiconductor thin film layer.

Claims (2)

[Claims] 1. A thin film type ozone sensor comprising a substrate (1) and a semiconductor thin film layer (2) containing In ₂ O ₃ as a main component, wherein the semiconductor thin film layer (2) has a thickness of 300Å ~ 1 μm
Thin film type ozone sensor set to. 2. The semiconductor thin film layer (2) has a thickness of 300Å
The thin film ozone sensor according to claim 1, wherein the thin film ozone sensor has a thickness of up to 5000 Å.