JPS63238545A - Gas detection method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a gas detection method using a gas sensor that reacts to various gases, and particularly to a method of detecting gas using porous silicon. It is.

[Prior art]

There are various materials that can be used as gas sensors, and various structures have been considered. Among these, those using semiconductor substrates such as silicon are attracting attention because they have the advantage of being able to integrate amplifiers and other components and can be made smaller.

However, in order to use it as a gas sensor, there were problems such as a complicated structure and the need to use biochemical substances, and there were few that were satisfactory in terms of cost.

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

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

〔the purpose〕

An object of the present invention is to provide an easy measurement method using a method different from the detection methods already proposed.

Another object of the present invention is to provide a gas detection method that does not require changing the structure of the element or requiring a complicated measurement circuit.

[Technical means to solve problems]

The present invention utilizes electromotive force generated between electrodes. Jtl
The above objective is achieved by determining the

That is, - an element having electrodes formed on the surface of the porous silicon layer and the surface of the single crystal silicon substrate on the back side of a single crystal silicon substrate having a porous silicon layer on the surface is placed in a gas atmosphere; The feature is that gas is detected by the generated electromotive force.

[Effect]

The present invention was made in the process of researching the properties of porous silicon, and although there are many aspects of its principles that have not yet been elucidated, experimental results confirmed changes in properties with sufficient reproducibility.

In a polar gas atmosphere, it was confirmed that voltage was generated between the electrodes of a device with a two-layer structure consisting of a porous silicon layer and a single-crystal silicon substrate.

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 section used in the present invention.

Porous silicon layer 1 on one surface of single crystal silicon substrate 10
1 is formed, an electrode 12 is formed on a part of the surface of the porous silicon layer 11, and a Riet wire is connected to the electrode 12.

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.

Porous silicon layer 11 is formed by anodizing the surface of single crystal silicon substrate 10 .

When one surface of a P-type crystal silicon substrate doped with boron is anodized in a hydrogen fluoride (HF) 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 carrying out the present invention.

The electrode 12 formed on the porous silicon layer can be formed using a solder alloy or gold by a normal method. The porous silicon layer 11 is formed so that not the entire surface but a portion thereof is exposed. It may be formed in a circular shape in the center, or may be formed in a mesoche shape or a stripe shape over the entire surface. Any material may be used as the electrode 13 formed on the single crystal silicon substrate 10 as long as it can make ohmic contact.

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

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

The current in a short circuit in which electrodes 12 and 13 were connected to a 100 Ω resistor was measured. In any gas atmosphere, an electromotive voltage was always generated with negative polarity on the porous silicon layer side, that is, on the electrode 12 side with respect to the electrode 13. In dry air, the same polarity and the opposite polarity sometimes appeared.

The measurement results will be explained below with reference to FIG.

The results show the results of introducing water vapor, ethanol vapor, and acetone vapor from a state in which the sample was placed in dry air, and after about 5 minutes, measurements were taken in each atmosphere, and then the sample was returned to dry air.

When each gas is introduced, the voltage gradually increases, and after reaching a peak, it gradually decreases and shows a tendency to settle at a constant value. In this case, since the measurement was only for a short time of about 5 minutes, this constant value is not clearly shown.

As shown in Figure 2, the peak value appears after about 4 minutes in water vapor, and the current is relatively large (0, 5/, 4).
It shows. On the other hand, in ethanol vapor, the peak value appears within 1 minute and decreases over time. Furthermore, although the peak value of acetone vapor is low, the subsequent decrease tends to be small.

In both cases, the current value significantly decreased when returned to dry air. In addition, in FIG. 2, the vertical axis is based on the current value in dry air. Although an electromotive force is generated even in dry air, the value is about 1/10 of that in the two gas atmospheres mentioned above.

The above example is the result of constant electromotive force over a short period of time, but even when measured over a longer period of time, there was no significant deterioration of the characteristics, and after opening at about 12 o'clock, The electromotive force was also the same.

Furthermore, the results of alternating between dry air and gas atmospheres were similar, and the electromotive force was measured at a fairly constant value. Figure 3 shows the results of measurements taken in acetone and dry air over a period of approximately 1.5 hours and 300 turns. 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 could be obtained over a long period of time. It should be noted that a slight change in characteristics was observed depending on the temperature, and as the temperature increased by 1, the electromotive voltage tended to increase.

The electromotive force generated between the porous silicon layer and the single-crystal silicon substrate is measured, and based on the results, it is possible to detect a polar gas.

Since the current value is small, appropriate means;
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There are still many aspects of the properties of porous silicon that are not yet understood. Although the mechanism of generating the electromotive force used in the present invention has not been completely elucidated, porous silicon is an extremely active material and exhibits unique electrical properties in a polar gas atmosphere. has been sufficiently confirmed. As mentioned above, changes in I capacitance or resistance have also been measured, and it is thought that the phenomena utilized in the present invention have something to do with these.

〔effect〕

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

Another advantage is that an element with a simple structure can be used as a sensor element with good sensitivity.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front sectional view showing an example of a sensor element used in carrying out the present invention, and FIGS. 2 and 3 are explanatory diagrams showing its characteristics. 10,...Single crystal silicon substrate 11...Porous silicon layer 12.13...Electrode%1 Figure

Claims (1)

[Claims] An element having electrodes formed on the surface of the porous silicon layer and the surface of the single crystal silicon substrate on the back side of a single crystal silicon substrate having a porous silicon layer on one surface is placed in a gas atmosphere, A gas detection method characterized by detecting gas by electromotive force.