JPH0623709B2 - Gas sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a gas sensor that reacts with various gases, and more particularly to a gas sensor that uses porous silicon.

[Prior art and its problems]

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 were some problems that the structure became complicated and biochemical substances had to be used, and few things were satisfactory in terms of cost.

〔Purpose〕

An object of the present invention is to solve the above problems and provide a gas sensor having a simple structure and a low cost.

Moreover, it aims at obtaining the gas sensor which can react with various gases.

[Means for solving problems]

The present invention achieves the above object by utilizing porous silicon.

That is, a single crystal silicon substrate having a porous silicon layer on one surface has electrodes formed on a part of the surface of the porous silicon layer and on the back surface of the single crystal silicon substrate.

Accordingly, it is intended to detect that the current value with respect to the voltage applied between the two electrodes changes due to the presence of the specific gas.

〔Example〕

The present invention was made in the process of studying the properties of porous silicon having a large surface area, and its principle has not yet been completely elucidated. Moreover, although there are unclear points about the properties of the porous silicon itself, it has an excellent effect and sufficient reproducibility. Examples will be described below.

FIG. 1 is a front sectional view showing an example of a gas sensor according to the present invention.

Porous silicon layer 1 on one surface of single crystal silicon substrate 10
1 is formed, the electrode 12 is formed on a part of the surface of the porous silicon layer 11, and the lead wire 13 is connected to the electrode 12. On the other hand, an electrode 14 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. Boron-doped P-type single crystal silicon substrate (ρ = 9.60 (Ω · c
m)) on one surface, hydrogen fluoride (HF) solution concentration 50vo1
%, The formation current was 100 mA / cm ² , and the formation time was 540 seconds, and the anodization treatment was performed to form the porous silicon layer 11. The porous silicon layer 11 was formed to have a relatively large thickness of about 45 μm.

The electrode 12 provided on the surface of the porous silicon layer 11 was formed by soldering, but since it did not adhere with the usual tin-lead solder, the dedicated solder for the ultrasonic soldering device was used. This solder has a composition of 35 wt% tin, 25 wt% lead, 20 wt% cadmium,
It is zinc 20 wt%. A lead wire 13 of a copper wire is soldered to the electrode 12 formed on the porous silicon layer 11, and at this time, heat treatment was performed at about 200 ° C. for about 1 minute using a trowel. It is not necessary to use the same solder for the electrodes 14 formed on the single crystal silicon substrate 10, and any electrode can be used as long as ohmic contact can be made.

It is considered that during the above heat treatment, the substance forming the solder diffuses or permeates into the porous silicon layer 11 and thereby changes the electrical properties of the porous silicon layer 11. Since porous silicon usually has a relatively high resistance, it is certain that the substance plays a major role in lowering the resistance.

It should be noted that the smaller the area of the electrode 12 formed on the porous silicon layer 11, the more advantageous the reaction and recovery time.

The results of measuring how the device formed as described above reacts to various gas atmospheres are shown in FIGS. 2 to 4. In the figure, the output obtained from each sample in the range of -5V to + 5V is shown before the reaction, during the reaction, and after the reaction.

FIG. 2 shows changes in saturated steam. A curve 21 shows the characteristics in a vacuum of 3 × 10 ⁻³ Torr, and a curve 22 shows the characteristics when this sample is placed in saturated steam for 2.5 hours. Curve 2
The change amount of the output current of the curve 22 is larger than that of 1. Then, in vacuum (3 × 10 ^-4 Torr), reapply 16
The curve 23 shows the characteristic after standing for a while, which is almost the same as the original characteristic. It should be noted that this is the result of measurement in the dark with the sample temperature set at 23 to 25 ° C.

Next, the change in saturated alcohol vapor is shown in FIG. The curve 31 shows the characteristic in a vacuum of 3 × 10 ⁻³ Torr, and the curve 3 shows the characteristic when this sample is placed in a saturated vapor of ethyl alcohol for 2.5 hours.
It is 2. Especially when a + voltage is applied, the output changes rapidly. The curve 33 shows the characteristics after being placed again in a vacuum (3 × 10 ⁻³ Torr) for 36 hours, but the characteristics have returned to values close to the initial values, if not perfect. In addition, in this example, the sample temperature is 22 to 25 ° C., and the measurement result is obtained in the dark.

FIG. 4 shows the response in oxygen gas at 1 atm. A curve 41 shows the characteristics in a vacuum of 4 × 10 ⁻³ Torr, and a curve 42 shows the characteristics after 5 minutes have elapsed in oxygen gas at 1 atm. In this case, unlike the above example, the resistance is changing to increase,
Moreover, the reaction appears in a short time. In vacuum again (4 x 1
The curve 43 shows the characteristics after 16 hours of passage at 0 ^-3 Torr). In this case, the sample temperature was 50 to 55 ° C. and the measurement was performed in the dark.

As is clear from the above examples, it was confirmed that the voltage-current characteristics of the saturated steam, the saturated alcohol vapor, and the oxygen greatly changed, and both the cases where the resistance decreased and the resistance increased were measured. From this, it is clear that it can be used as various gas sensors.

Although there are differences in the initial characteristics of each sample in the above example,
It is considered that this is influenced by factors such as the electrode area and the heat treatment time.

In addition, in each of the above examples, the measurement results after being placed in various gases for a relatively long time are shown, but in reality, the change in the characteristics appears within such a long time, and as a sensor, It can fulfill its function.

〔effect〕

According to the present invention, a gas sensor having a simple structure and easy to manufacture can be obtained.

As described above, it has been confirmed that the characteristics of the gas can be clearly discriminated from various gases, and a highly reliable gas sensor can be obtained.

Further, since the characteristic changes exist in any direction, it is possible to detect two kinds of gas with one gas sensor.

[Brief description of drawings]

FIG. 1 is a front sectional view showing an embodiment of the present invention, and FIGS. 2 to 4 are explanatory views showing voltage-current characteristics for various gases. 10 ... Single crystal silicon substrate, 11 ... Porous silicon layer, 12, 14 ... Electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-53-5695 (JP, A) JP-A-56-37547 (JP, A)

Claims (1)

[Claims] 1. A gas sensor comprising a single crystal silicon substrate having a porous silicon layer on one surface thereof, wherein electrodes are formed on a part of the surface of the porous silicon layer and on the back surface of the single crystal silicon substrate.