JPS6378049A - Humidity detector - Google Patents

Abstract

PURPOSE:To permit stable humidity detection by depositing a moisture sensitive expandable and contractable film on one main of a cantilever consisting of a thin semiconductor sheet and forming piezo-resistance regions on the other main plane of the cantilever. CONSTITUTION:This detector is formed by extending the cantilever 2 having about 20mum thickness integrally from a square annular base part 1 consisting of silicon and having about 300mum thickness. The piezo-resistance regions 3a-3d are formed on the surface of the cantilever and the moisture sensitive expandable and contractable film 4 consisting of a high-polymer material such as nylon and having about 20mum thickness is deposited on the rear surface. The film 4 is formed by coating and drying nylon which is made into a liquid for by a solvent such as hexafluoroisopropanol. the cantilever 2 is deflected by the expansion and contraction force of the film 4 and the resistance values of the regions 3a-3d change when the film expands or contracts according to the moisture of the atmosphere to be measured. The resistances are bridge-coupled by an external circuit. The strain of the cantilever 2; i.e., humidity, is detected by measuring the bridge voltage.

Description

[Detailed description of the invention] (b) Industrial application field This fifth article relates to a humidity detection device.

(b) Conventional technology Humidity detectors such as humidity-sensitive ceramics whose electrical characteristics change depending on humidity are known.

This detector utilizes the electrical characteristics of the gas-solid interface, and therefore, the interface is exposed to the atmosphere, susceptible to pollution, etc., and lacks long-term stability. On the other hand,
Moisture-sensitive stretchable materials such as hair and nylon, as disclosed in Japanese Patent Application Laid-Open No. 56-42126, are stable in terms of time, but it is difficult to convert their stretch into electrical signals.

1/M Problems to be Solved by the Invention The present invention provides a humidity detection device that uses a moisture-sensitive stretch film and can easily and sensitively convert the stretch into an electrical signal.

Means for Solving the Problems The humidity detecting device of the present invention has a cantilever made of a thin silicon plate.A moisture-sensitive stretchable film is applied to the main surface of the cantilever, and a piezoresistive region is formed on the other main surface of the cantilever. Characteristically.

(E) Function In the device of the present invention, the moisture-sensitive stretchable film expands and contracts in response to the humidity of the atmosphere to be measured, and the cantilever is bent by the stretching force. Then, the piezoresistor converts this amount of deflection into electric stitching.

(f) Example As shown in Fig. 1, the device according to the present invention has a rectangular howl base (1) made of silicon with a thickness of about 300 μm, and a cantilever (2) with a thickness of about 2071 m extending integrally from the body. The surface piezoresistance region (2) of the cantilever (2)
3a) (31))... (The surface of each surface is coated with a moisture-sensitive stretch film (4) made of a polymeric material such as nylon and having a thickness of approximately 2 μm.

When forming the cantilever (2), the thickness is approximately 300μ.
By anisotropic etching, a silicon single-crystal plate of 100 m thick was formed into a bulge with a thickness of about 20 μm only in the center, and as a result,
The periphery of the thin plate is supported by an annular base (1).

Next, the cantilever (2) is made by cutting grooves (51) on three sides of the thin plate.Furthermore, piezoresistive regions (3a), (3b), etc. are formed on the surface of the cantilever (2) by diffusion, and as shown in FIG. Although not shown, these regions are connected by wiring paths formed by diffusion or vapor deposition.

The etching technique, piezoresistive region formation, wiring path formation technique, etc. described above are similar to the manufacturing technique of a silicon diaphragm type pressure sensor disclosed in Japanese Patent Publication No. 58-7179&i+. The cantilever surface on which the piezoresistive head is formed may be covered with a water-resistant and soft molding material for protection.

When applying the moisture-sensitive stretch film (4), nylon made into a liquid with a solvent such as hexafluoroinpropertool is applied and dried.

In the above device, when the moisture-sensitive stretchable film (41) expands and contracts depending on the humidity of the atmosphere to be measured, the cantilever (2) is bent by the stretching force, and the piezoresistive regions (3a) (3b)
The resistance value of ... changes. Each of these resistors is connected to an external circuit IJ-7, and by measuring this bridge voltage, the degree of distortion of the cantilever (2), that is, the humidity can be detected.

In single crystal semiconductors, the piezoresistance characteristics have anisotropy, so
To increase the humidity detection sensitivity, each piezoresistive region (3
The arrangement of a) (3b)... is important.

Now, the cantilever (2) is made of P-type silicon single crystal (10
0) surface, and as shown in Figure 2, the longitudinal direction of the cantilever (2) is 71, the width direction is 71, and the direction perpendicular to the plane of the paper is 2.
The resistance value of each piezoresistive region in the direction and the X direction is Rx, R
Let it be y.

Consider a situation in which the free end of the cantilever moves in two axial directions due to expansion and contraction of the moisture-sensitive stretch film, and a stress σa is generated at the point X=a where the piezoresistive region exists.

Generally, the change in resistance value due to the piezoresistance effect △R is △R/R=
π(lC1!+πt) (where πl:l: upper resistance coefficient, πt:
Transverse piezoresistance coefficient, σ! = longitudinal stress, det: transverse stress). Assuming that the direction in which the cantilever (2) is deflected is its longitudinal direction, the stress generated is only .17'a in the X direction. On the other hand, if a current is passed through each resistance region in its longitudinal direction, then σg=(feL
, σt=0, for resistance Ry, El=0,
Since vt=cra, the change in both resistance values is expressed as △RX/RX=rr A' (ra △Ry/Ry=πtζa).

Assuming that these resistors are arranged in a very small range, and that the variations in resistance value and temperature coefficient of resistance between the resistors are negligibly small (i.e., Rx = Ry), the P'J- By connecting to
Rx=Ry). That is, maximum sensitivity is achieved when the signs of πl and πt are opposite and the absolute value is large. P-type silicon single crystal (100
The dependence of the piezoresistance coefficient on the crystal axis of the ) plane is shown in Figure 4.
The maximum value of πe1πt is in the [110] direction. If the value is L, the sign is reversed in the [1-10] direction perpendicular to this, and the maximum value is -,
-L. Therefore, Rx is in the (110') direction and Ry is [
1-10], Vo=(EC+L)7aIinR, and the sensitivity is maximized. Also, in reverse, Rx is [1-1
Similar results can be obtained even if Ry is placed at (110).

(G) Effects of the Invention According to the present invention, even if the moisture-sensitive stretchable film is contaminated by the atmosphere to be measured, it stably expands and contracts in response to the humidity, and the stretching force causes the cantilever to bend. It is converted into a 4-voice signal as a change in piezoresistance.

[Brief explanation of the drawing]

Figure 1A is a long side view of an embodiment of the present invention, and Figure 1B is the same B.
-B cross-sectional view, FIGS. 2 and 3 are coordinate diagrams for explaining the above-mentioned device, and B14 and Y-circuit diagrams, and FIG. 4 is a crystal orientation diagram. (2)...cantilever, (3a)(3t))...
Piezoresistance region, (4)...Moisture-sensitive stretch membrane.

Claims (1)

[Claims] (1) A humidity detection device characterized in that a moisture-sensitive stretch film is applied to one main surface of a cantilever made of a thin semiconductor plate, and a piezoresistive region is formed on the other main surface of the cantilever.