JPH07176765A - Semiconductor strain transducer - Google Patents

Abstract

PURPOSE:To provide a semiconductor strain transducer where a gauge rate can be adjusted easily, the element with a large area can be manufactured simply and inexpensively, and measurement in a three-dimensional curved surface can be made. CONSTITUTION:Either p-type, i-type or n-type amorphous Si semiconductor thin film 2 is formed in insulated state from a thin-piece substrate 1 on either one of the thin-piece substrate 1 which is deformed according to external stress, a pair of input electrodes 5 and a pair of output electrodes 6 are provided on amorphous Si semiconductor thin film for forming a strain gauge 10, and at the same time a protection film 4 for insulation is formed on the surface of the amorphous Si semiconductor thin film 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor strain conversion element which is used as a pressure sensor, a strain sensor or the like and which utilizes a piezoresistive effect.

[0002]

2. Description of the Related Art Conventionally, a semiconductor strain conversion element has a diaphragm formed by thinning a part of a single crystal Si chip cut out from a Si wafer and cut into a predetermined size by polishing or etching to form a diffusion technique on the diaphragm. A strain sensitive element was formed by using the strain sensitive element, and this was bridge-wired to form a strain gauge. However, since the diaphragm is formed by polishing and etching, there is a problem in that a yield is reduced due to a polishing mistake and it takes time to manufacture, which causes a cost increase.

Further, since the size of the single crystal Si chip is limited by the area of the Si wafer, it has been impossible to manufacture an element having an area larger than that of the wafer. Moreover, when forming a strain gauge on a diaphragm made of single-crystal Si, it is difficult to make the diaphragm uniform in thickness, and the gauge ratio is controlled with high accuracy due to variations in the amount of impurities injected due to doping. Was difficult. In addition, since the strain is sensed on a single plane, there is a problem that the strain distribution on a three-dimensional curved surface cannot be practically measured and the usable range is limited.

[0004]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems, to easily adjust the gauge ratio, and to easily and inexpensively manufacture a large area product. An object of the present invention is to provide a semiconductor strain conversion element capable of measuring a three-dimensional curved surface.

[0005]

According to the present invention, a p-type, an i-type, and an n-type are provided on at least one surface of a flaky substrate which is deformed in response to an external stress while being insulated from the flaky substrate. An amorphous Si semiconductor thin film is formed, a pair of input electrodes and output electrodes are provided on the amorphous Si semiconductor thin film to form a strain gauge, and an insulating protective film is formed on the surface of the amorphous Si semiconductor thin film. Is formed.

[0006]

In the semiconductor strain conversion element of the present invention, the amorphous Si semiconductor thin film formed on the surface of the flaky substrate serves as a piezoresistive layer, and when the flaky substrate receives an external stress, the flaky substrate and the amorphous Si semiconductor The thin film is deformed, and a strain gauge consisting of a pair of input electrodes and output electrodes on the amorphous Si semiconductor thin film senses a stress in a direction perpendicular to the surface of the amorphous Si semiconductor thin film, and a piezoresistive effect causes an electrical signal of Output the displacement.

The piezoresistive effect is a phenomenon generally observed in crystals belonging to a limited crystal group such as a Si single crystal body. However, even in an amorphous Si semiconductor, depending on external stress, the valence band and the conductivity can be increased. Since the resistance value changes due to the change in energy difference between bands and the change in localized level between bands, it can be effectively used as a piezoresistive layer.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment in which a strain gauge is formed on one surface of the present invention will be described in detail below with reference to FIGS. 1
Is a flaky substrate that deforms in response to external stress,
An amorphous Si semiconductor thin film 2 of i-type, p-type, n-type or the like is deposited on the thin substrate 1 by plasma CVD of capacitive coupling type or inductive coupling type. The raw material gas for the amorphous Si semiconductor thin film 2 is SiH ₄ , Si ₂ H
_An i-type amorphous Si semiconductor thin film 2 is obtained by using ₆ , SiF ₄ , SiCl ₄ , SiCl ₄ -xHx and the like. On the other hand, diborane gas B ₂ H ₆ is usually used to obtain a p-type semiconductor, and phosphine gas PH ₃ or arsine gas AsH ₃ is usually used to obtain an n-type semiconductor.
It suffices to dope the respective source gases, and the conductivity of the amorphous Si semiconductor thin film 2 can be arbitrarily adjusted by adjusting the mixing ratio of these doping gases. In addition to this, the conductivity can also be adjusted by mixing GeH ₄ , CH _{4 and the} like with the raw material gas to form the alloy-type amorphous Si semiconductor thin film 2.

Since the plasma CVD can deposit and form the amorphous Si semiconductor thin film 2 at a relatively low temperature,
As the flaky substrate 1 that can be used, not only a glass or ceramic substrate but also a metal plate such as stainless steel or a thin plate or film such as resin can be used. When the flaky substrate 1 is used as a conductive material, in order to insulate it from the amorphous Si semiconductor thin film 2, as shown in FIG. 3, Si ₃ N ₄ or SiO _{2 is used.}
Prior to the formation of the amorphous Si semiconductor thin film 2, the insulating film 3 is formed on the thin substrate 1 by plasma CVD. After that, amorphous S is formed on the surface of the insulating film 3.
The i semiconductor thin film 2 is deposited, and the insulating protective film 4 such as Si ₃ N ₄ or SiO _{2 is} deposited on the surface of the amorphous Si semiconductor thin film 2. Amorphous S is formed by this protective film 4.
The i semiconductor thin film 2 is protected from the external environment to prevent deterioration. The insulating film 3, the amorphous Si semiconductor thin film 2, and the protective film 4 can be continuously formed on the flaky substrate 1 by changing the type of the raw material gas supplied to the CVD apparatus.

Then, a predetermined surface of the protective film 4 is masked and then etched to remove the protective film 4 at the input electrode and output electrode portions. Next, NiCr is applied to the removed portion.
A system alloy or a metal for electrodes such as a multilayer film having Mg as a base and Al as a base is vacuum-deposited. At this time, the arrangement pattern of the electrodes is such that the pair of input electrodes 5 and the pair of output electrodes 6 are provided to form the strain gauge 10. Although a pair of input electrodes 5 and a pair of output electrodes 6 are provided so as to intersect with each other in FIG. 1, the sensitivity characteristics are not limited by the crystal orientation of the single crystal Si, so that the electrodes can be freely set. The strain gauge 10 may be arranged to form the strain gauge 10. Furthermore, the electrode shape is
In order to increase the current area of the electrode, a comb type electrode may be used, and prior to the formation of the electrode, a control operation such as increasing the doping gas concentration is performed only on the amorphous Si semiconductor thin film portion corresponding to the electrode position. Therefore, the contact resistance with the electrode material can be reduced by increasing the conductivity somewhat higher than that of the base portion.

As shown in FIG. 4, the strain gauge 1 thus constructed has a strain gauge 1 on an amorphous Si semiconductor thin film 2.
By using a cantilever type in which one end of the flaky substrate 1 on which 0 is formed is fixed to the base 20, it can be used as an acceleration sensor, or as shown in FIG.
Strain gauge 10 on the amorphous Si semiconductor thin film 2 at the end of
When the flaky substrate 1 is subjected to external stress, it can be used as an absolute pressure or differential pressure type pressure sensor by fixing the peripheral edge of the flaky substrate 1 on which the thin flaky substrate 1 is formed. 2 is deformed, and the strain gauge 10 composed of a pair of input electrode 5 and output electrode 6 facing each other on the amorphous Si semiconductor thin film is amorphous S
i The stress in the direction perpendicular to the semiconductor thin film surface is sensed, and the displacement of the electric signal is output by the piezoresistance effect. If a thin metal plate, a resin film or the like is used as the flaky substrate 1, the completed sensor device can be provided along the surface to be measured having a three-dimensional curved surface as shown in FIG. It is possible to measure stress in a three-dimensional shape.

In FIG. 7, the output characteristics are different between the case where an external stress is applied as a compressive force and the case where it is applied as a tensile force. A second embodiment is shown in which the amorphous Si semiconductor thin films 2 and 2a are formed on both surfaces and the strain gauges 10 and 10a are provided on both surfaces. One of the amorphous Si semiconductor thin films 2 is resistant to external stress. Is applied to the amorphous Si semiconductor thin film 2a, and the strain gauges 10 and 10a on the respective surfaces simultaneously output respective output signals corresponding to these stresses.
A correction circuit for these two output signals can correct the difference in the output signals caused by the directionality of the stress applied to the amorphous Si semiconductor thin films 2 and 2a to perform more accurate measurement.

[0013]

As is apparent from the above description, the present invention provides a single crystal Si chip cut out from a single crystal Si wafer and cut into a predetermined size by forming an input electrode and an output electrode on an amorphous Si semiconductor thin film. Since it is not necessary to form the diaphragm by etching or polishing on a part, the manufacturing process is simplified and the yield is high, and it is also possible to use inexpensive materials such as metal and resin for the flaky substrate, reducing cost. Can be achieved. In addition, the amorphous Si semiconductor thin film that becomes the piezoresistive layer can precisely and easily adjust the specific resistance and the film thickness when it is deposited, and the strain gauge can be formed without using a bridge circuit, so that the output sensitivity is good. It can be anything. In addition, because amorphous Si does not have a crystal plane, it is possible to form multiple piezoresistive layers in any shape on the flaky substrate. Moreover, sensor devices using the flaky substrate as metal or resin are flexible. Since it can be deformed into a large area, it is possible to measure the stress distribution on a three-dimensional curved surface, and since there is no restriction due to the size of the Si wafer, it is possible to measure stress in a large area. The strain conversion element can be designed and the range of use can be expanded. Therefore, the present invention is a great advantage brought to the industry as a semiconductor strain conversion element which solves the conventional problems.

[Brief description of drawings]

FIG. 1 is a plan view showing a first embodiment of the present invention in which a strain gauge is formed on one surface.

FIG. 2 is a sectional view of the same.

FIG. 3 is a cross-sectional view showing a first embodiment in which an insulating film is formed.

FIG. 4 is a perspective view used as an acceleration sensor.

FIG. 5 is a partially cutaway side view used as a pressure sensor.

FIG. 6 is a cross-sectional view used for measuring a three-dimensional curved surface.

FIG. 7 is a sectional view showing a second embodiment of the present invention in which strain gauges are formed on both sides.

[Explanation of symbols]

 1 Flake substrate 2 Amorphous Si semiconductor thin film 4 Protective film 5 Input electrode 6 Output electrode 10 Strain gauge

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[Procedure amendment]

[Submission date] January 12, 1994

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

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Claims (1)

[Claims] 1. A p-type substrate, an i-type substrate, or an n-type substrate which is insulated from the flaky substrate (1) on at least one surface of the flaky substrate (1) that deforms in response to external stress. Of the amorphous Si semiconductor thin film (2), a pair of input electrodes (5) and output electrodes (6) are provided on the amorphous Si semiconductor thin film to form a strain gauge (10), and the amorphous Si semiconductor thin film (2) is formed. A semiconductor strain conversion element characterized in that a protective film (4) for insulation is formed on the surface of a semiconductor thin film (2).