JPH07117485B2 - Humidity detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a humidity detector.

(B) Conventional Technology As temperature detectors, there are known temperature-sensitive bodies such as humidity-sensitive ceramics whose electrical characteristics change depending on humidity. This detector is
It utilizes the electrical characteristics of the gas-solid interface, and therefore the interface is exposed to the atmosphere, susceptible to pollution and the like, and lacks long-term stability. On the other hand, Japanese Unexamined Patent Publication No. 56-4212
Moisture-sensitive elastic materials such as hair and nylon as disclosed in Japanese Patent No. 6 are stable for a long period of time, but are difficult to convert the expansion and contraction into electric signals.

In order to solve such a problem, a piezoresistive region is provided on one surface of the silicon diaphragm, and a moisture-sensitive film stretchable body is attached to the same surface with an adhesive (silicon rubber, etc.). A humidity detecting device that detects humidity by changing the resistance value of the piezoresistive region in response to the change in resistance of the diaphragm by expanding and contracting according to the humidity is disclosed in JP-A-61-202152. Has been done.

(C) Problems to be Solved by the Invention However, in the humidity detecting device as shown in the prior art, when the moisture sensitive film stretcher is attached to the piezoresistive region, the moisture sensitive film stretcher itself and the adhesive (such as silicone rubber) are used. ) Moisture from itself affects the piezoresistive region and deteriorates its characteristics.

Further, in the publication, a structure is proposed in which a moisture-sensitive stretchable film is provided between the header and the base on the side opposite to the surface where the piezoresistive region is provided for the pellet.

However, in this configuration, the moisture-sensitive stretch film and the pellet are in point contact with each other via the base portion, and when the humidity detecting device having such a configuration is mass-produced, the stretch of the moisture-sensitive stretch film is transmitted to the piezoresistive region. There are variations in time characteristics. Furthermore, since the moisture-sensitive stretch film is in contact not only with the base but also with the header, the effects of expansion and contraction of the header itself due to friction with the header, temperature, etc. are directly transmitted to the moisture-sensitive stretch film, and the piezoresistive region There are variations in the characteristics when transmitted.

The present invention uses a moisture-sensitive film elastic body, and easily expands and contracts the same.
Moreover, the present invention provides a humidity detecting device that can be sensitively converted into an electric signal.

(D) Means for Solving the Problems In the humidity detecting device of the present invention, a stretch film is provided along one main surface of a cantilever made of a silicon thin plate, and a piezoresistive region is formed on the other main surface of the cantilever. Is characterized by.

(E) Operation In the device of the present invention, the moisture-sensitive stretchable film provided along one main surface of the cantilever expands and contracts according to the humidity of the atmosphere to be measured, and the cantilever bends due to the expanding and contracting force. Then, the piezoresistor provided on the other main surface of the cantilever converts this bending amount into an electric amount.

(F) Example As shown in FIG. 1, the apparatus of the present invention has a cantilever (2) having a thickness of about 200 μm integrally projected from a rectangular annular base (1) having a thickness of about 300 μm made of silicon. Piezoresistive region (3
While forming a) (3b), etc., a moisture-sensitive stretchable film (4) made of a polymer material such as nylon and having a thickness of about 20 μm is attached to the back surface.

When forming the cantilever (2), the thickness is about 300 μm.
The silicon single crystal plate (1) is anisotropically etched to form a thin plate having a thickness of about 20 μm only in the central portion, so that the periphery of the thin plate has the shape indicated by the annular base (1). Next, the cantilever (2) is made by inserting the cut grooves (5) in three directions of the thin plate. Further, piezoresistive regions (3a) (3b) ... Are formed on the surface of the cantilever (2) by diffusion, and although not shown, these regions are connected by wiring lines by diffusion or vapor deposition. The etching technique, the piezoresistive region forming technique and the wiring path forming technique are described in Japanese Patent Publication No.
This is the same as the manufacturing technology of the silicon diaphragm type pressure sensor disclosed in the publication. The surface of the cantilever (2) formed in the piezoresistive area is water resistant for protection.
Moreover, it may be covered with a soft molding material.

When the moisture-sensitive stretchable film (4) is applied, nylon that has been liquefied with a solvent such as hexafluoroisopropanol is applied and dried.

In the above device, when the moisture-sensitive stretchable film (4) expands and contracts according to the humidity of the atmosphere to be measured, the cantilever (2) bends due to the expanding and contracting force, and the piezoresistive regions (3a) (3b) ...
・ The resistance value of changes. Each of these resistors is bridge-coupled by an external circuit, and the skewness of the cantilever (2), that is, the humidity can be detected by measuring the bridge voltage.

Piezoresistive characteristics have anisotropy in single crystal semiconductors,
To increase the humidity detection sensitivity, increase the piezoresistive area (3
The arrangement of a) (3b) ... is important.

Now, the cantilever (2) is made of P-type silicon single crystal (10
0) surface is created by etching, and as shown in FIG. 2, the longitudinal direction of the cantilever (2) is x, the lateral direction is y, and the direction perpendicular to the paper surface is z.
The resistance value of each piezoresistive area in the x and y directions is Rx, Ry
And

Consider a state in which the free end of the cantilever (2) moves in the z-axis direction due to the expansion and contraction of the moisture-sensitive elastic film, and a stress of σa is generated at the point of x = a where the piezoresistive region exists.

Generally, the change in resistance value ΔR of the piezoresistive effect is expressed as ΔR / R = πl · σl + πt · σt (where πl: longitudinal piezoresistive coefficient, πt: lateral piezoresistive coefficient, σl: longitudinal stress, σt: Lateral stress). When the main bending direction of the cantilever (2) is its longitudinal direction, the stress generated is only σa in the x direction. On the other hand, if a current is applied to each resistance region in the longitudinal direction,
Since the resistance Rx is σl = σa, σt = 0, and the resistance Ry is σl = 0, σt = σa, the change in both resistance values is expressed as ΔRx / Rx = πl ・ σa ΔRy / Ry = πt ・ σa To be done.

These resistors are arranged in a very small range, and if the variations in the resistance value and the temperature coefficient of resistance between the resistors are so small as to be negligible (that is, Rx = Ry), make a bridge connection as shown in Fig. 3. Thus, the output voltage Vo is expressed as Vo = (ΔRx−Ry) Iin, and Vo = (πl−πt) σa · R · Iin (where R = Rx−Ry). That is, the maximum sensitivity is obtained when the signs of πl and πt are opposite and the absolute value is large. The crystal axis dependence of the piezoresistance coefficient of the (100) plane of a P-type silicon single crystal is shown in FIG. 4, and the maximum values of πl and πt are in the [110] direction. If the values are K and L, the sign is inverted in the [1-10] direction orthogonal to this, and the maximum values are -K and -L. Therefore, if Rx is arranged in the [110] direction and Ry is arranged in the [1-10] direction, Vo = (K + L) σaRIin and the sensitivity is maximized. In addition, Rx is [1-10] in reverse.
The same effect can be obtained by arranging the direction Ry in the [110] direction.

(G) Effect of the Invention According to the present invention, by using the moisture-sensitive stretchable film, processing is facilitated, and even when it is contaminated by the atmosphere to be measured, it is stably stretched according to humidity. Further, since the moisture-sensitive stretchable film is provided along one main surface, the sensitivity of sensing humidity is improved.
Furthermore, since the moisture-sensitive stretchable film does not come into contact with other members, it is possible to prevent deterioration of the characteristics of the moisture-sensitive stretchable film due to the influence of other members.
Furthermore, by providing the moisture-sensitive stretchable film and the piezoresistive region on different surfaces, it is possible to prevent deterioration of the characteristics of the piezoresistive region due to moisture in the moisture-sensitive stretchable film. Further, the expansion and contraction force of the moisture-sensitive expansion and contraction film bends the cantilever and is sensitively converted into an electric signal as a piezoresistance change. Further, since the base portion and the cantilever are integrally formed, the processing of the main body of the apparatus becomes easy and the mass production effect is improved.

[Brief description of drawings]

FIG. 1A is a rear view of the apparatus according to the present invention, and FIG.
-B sectional view, FIGS. 2 and 3 are a coordinate diagram and a bridge circuit diagram for explaining the above-mentioned device, respectively, and FIG. 4 is a crystal orientation diagram. (2) ... Cantilever, (3a) (3b) ... Piezoresistive region, (4) ... Moisture-sensitive stretch film.

Front page continuation (72) Inventor Yoshio Miyai 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. JP, Y1)

Claims (1)

[Claims] 1. A humidity detecting apparatus, wherein a moisture-sensitive stretchable film is provided along one main surface of a cantilever made of a semiconductor thin plate, and a piezoresistive region is formed on the other main surface of the cantilever.