JPH0711496B2 - Gas detection method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a gas detection method using a gas sensor that reacts with various gases, and more particularly to a method for detecting gas using porous silicon. Is.

[Prior art]

There are various materials for the gas sensor, and various structures have been considered. Among them, the one using a semiconductor substrate such as silicon has attracted attention because it has an advantage that an amplifier and the like can be integrally formed and can be downsized.

However, in order to use it as a gas sensor, there are problems that the structure is complicated and biochemical substances must be used, and there are few that are satisfactory in terms of cost.

Therefore, the inventor proposed to obtain a gas sensor using porous silicon, and to detect gas by a change in capacity (Japanese Patent Application No. 61-184506).

In such a gas detection device, it is preferable to be able to use as many detection methods as possible.

〔Purpose〕

The present invention aims to provide an easy measurement method by a method different from the detection method already proposed.

It is another object of the present invention to provide a gas detection method that does not require a complicated measuring circuit or changes the structure of the element.

[Technical means for solving problems]

The present invention achieves the above-mentioned object by measuring using an electromotive voltage generated between electrodes.

That is, an element having electrodes formed on the surface of the porous silicon layer of the single crystal silicon substrate having a porous silicon layer on one surface and on the surface of the single crystal silicon substrate on the back surface thereof is placed in a gas atmosphere, and It is characterized in that the gas is detected by the electromotive voltage generated.

[Action]

The present invention was made in the process of studying the properties of porous silicon, and although the principle thereof has not been clarified in many points, the results of the experiment confirmed changes in the properties with sufficient reproducibility.

It was confirmed that a voltage was generated between the electrodes of the device having a two-layer structure of the porous silicon layer and the single crystal silicon substrate in the polar gas atmosphere.

The present invention utilizes this phenomenon and applies it to a gas detection method.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a front sectional view showing an example of a sensor unit used in the present invention.

A porous silicon layer 11 is formed on one surface of the single crystal silicon substrate 10, an electrode 12 is formed on a part of the surface of the porous silicon layer 11, and a lead wire is connected. On the other hand, an electrode 13 is formed on the entire surface in contact with the single crystal silicon substrate 10 on the back surface.

The porous silicon layer 11 is formed by anodizing the surface of the single crystal silicon substrate 10. One surface of a P-type single crystal silicon substrate doped with polon is hydrogen fluoride (H
F) When anodization is performed in the solution, a porous silicon layer is formed on the surface of the single crystal silicon substrate. Although the thickness of the porous silicon layer is determined by the conditions of the anodizing treatment, the thickness was set to 7 to 45 microns when the present invention was carried out.

The electrode 12 formed on the porous silicon layer can be formed by a usual method using a solder alloy or gold. The porous silicon layer 11 is formed so that a part thereof is exposed, not the entire surface. It may be formed in a circular shape in the central portion or may be formed in a mesh shape or a stripe shape over the entire surface. Any electrode 13 can be used as the electrode 13 formed on the single crystal silicon substrate 10 as long as an ohmic contact can be made.

It has been confirmed that a voltage is generated between the electrode 12 and the electrode 13 when the element composed of the porous silicon layer 11 and the single crystal silicon substrate 10 as described above is placed in a certain gas atmosphere. The electromotive voltage was confirmed in the atmosphere of polar gases such as water vapor, ethanol vapor, and acetone vapor.

As a result of measuring in a gas atmosphere each of the 10 mm square element formed with the above electrode, the following results were obtained.

The current was measured in a short circuit in which electrodes 12 and 13 were connected to a resistance of 100 kΩ. In any gas atmosphere,
Always the electrode for the porous silicon layer side, that is, for electrode 13.
On the 12 side, the electromotive voltage was generated with the polarities of the corners. In dry air, the same polarity and the opposite polarity sometimes appeared.

Hereinafter, the measurement results will be described with reference to FIG.
The results are shown in which steam, ethanol vapor, and acetone vapor were introduced from the state of being placed in dry air, measurement was performed in each atmosphere after about 5 minutes, and then the state was returned to dry air.

When each gas was introduced, the voltage gradually increased, showed a peak, then gradually decreased, and tended to settle at a certain value. In this case, since the measurement was performed only for a short time of about 5 minutes, this constant value is not clearly shown.

As shown in FIG. 2, in water vapor, a peak value appeared after about 4 minutes, indicating a relatively large current (0.5 μA). On the other hand, in ethanol vapor, the peak value appears within 1 minute and decreases with the passage of time. Further, in the case of acetone vapor, although it has a low peak value, there is a tendency that the width of the decrease thereafter is small.

In both cases, the current value decreases significantly when returning to dry air. The vertical axis in FIG. 2 is based on the current value in dry air. An electromotive force is generated even in dry air, but its value is about 1/10 of that in the above gas atmosphere.

The above example is the result of measuring the electromotive voltage in a short time, but when measured over a longer time, there is no significant deterioration in the characteristics, and even after operating for about 12 hours, the electromotive voltage remains the same. It was happening.

Further, the result of repeating the dry air and the gas atmosphere alternately was the same, and the electromotive voltage of a substantially constant value was measured. FIG. 3 shows the result of repeating 300 times in acetone and dry air for about one and a half hours. At first, the value shows a tendency to decrease, but after about 10 minutes, there is almost no change.

From these results, it was confirmed that a stable electromotive voltage was obtained for a long time. A slight change in the characteristics was observed depending on the temperature, and the electromotive voltage tended to increase as the temperature decreased.

The electromotive voltage generated between the porous silicon layer and the single crystal silicon substrate can be measured, and the result can detect a gas having polarity. Since the current value is small, it may be amplified by an appropriate means.

The properties of porous silicon are still unknown. The mechanism of electromotive force generation used in the present invention has not been completely elucidated, but it is sufficient that porous silicon is an extremely active substance and exhibits unique electrical characteristics in a polar gas atmosphere. It has been confirmed.
As described above, changes in capacitance or resistance have also been measured, and it is considered that the phenomenon used in the present invention has something to do with these.

〔effect〕

According to the present invention, the gas can be detected by measuring the electromotive voltage generated in the gas atmosphere. Since voltage or current can be measured directly, a simple measuring circuit can be used.

There is also an advantage that an element having a simple structure can be used as a sensor element having good sensitivity.

[Brief description of drawings]

FIG. 1 is a front sectional view showing an example of a sensor element used for carrying out the present invention, and FIGS. 2 and 3 are explanatory views showing its characteristics. 10 …… Single crystal silicon substrate 11 …… Porous silicon layer 12, 13 …… Electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Motohashi 727, Katayanagi, Sakado, Saitama 1 (56) References JP-A-53-96891 (JP, A) JP-A-63-40847 (JP, A)

Claims (1)

[Claims] 1. A single crystal silicon substrate having a porous silicon layer on one surface thereof, wherein elements each having electrodes formed on the surface of the porous silicon layer and the surface of the single crystal silicon substrate on the back surface thereof are arranged in a gas atmosphere, A gas detection method, characterized in that gas is detected by an electromotive voltage generated in the element.