JPS6410109B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to the piezoresistance effect characteristics of an amorphous silicon semiconductor thin film deposited on an insulating substrate using a glow discharge method, particularly the large longitudinal effect characteristics obtained. The present invention relates to a strain gauge constructed focusing on the gauge factor, and a strain gauge constructed focusing on the fact that longitudinal effects, horizontal effects, and diagonal effects are different from each other. Here, what is an amorphous silicon semiconductor?
A semiconductor that uses silicon as a base material, excludes liquids and gases, and does not exhibit three-dimensional periodicity crystallographically. In other words, it is a perfect amorphous silicon semiconductor that is irregular and amorphous and has no diffraction peaks that can be identified by an X-ray diffraction waveform.
Amorphous silicon semiconductors having a slight but identifiable diffraction peak and containing a so-called microcrystalline phase are collectively referred to as amorphous silicon semiconductors.

[Conventional technology]

Conventionally, sensor materials for strain gauges have generally been alloy foils such as Cu-Ni foil, Ni-Cr wires,
Cu-Ni wires are used, and semiconductors are used for those with high detection sensitivity.

Those using alloy foil are widely used because of their large dynamic range and good linearity, but they have the following drawbacks.

(1) Since the ratio of change in resistivity to strain, that is, the gauge factor G, is small, usually G=2 to 4, it is necessary to use an amplifier in the output section.

(2) It is necessary to provide a temperature compensation circuit to eliminate the temperature dependence of the gauge factor.

(3) Since the resistivity of the alloy foil is low, in order to make the resistance value of the strain detection part over a certain value (usually around 100Ω), the shape of the detection part needs to be a folded strip wire. The area becomes larger.

On the other hand, those using semiconductor crystals have a relatively large gauge factor, and the gauge factor G is |G|100, so the detection sensitivity is high. However, it has many drawbacks, such as the large temperature dependence of the gauge factor and nonlinearity.

Furthermore, in order to increase the detection sensitivity, it is necessary to reduce the thickness of the substrate, and methods for forming a diaphragm structure using polishing, anisotropic etching, and selective etching are used as methods for this purpose. In these methods, the former method is particularly prone to damage during polishing, and the latter method requires complicated and expensive semiconductor manufacturing equipment to achieve reproducibility. The disadvantage of old strain gauges was that they were expensive. Furthermore, these strain gauges are difficult to use by themselves, and generally need to be stably fixed to a pedestal provided on the strain detection target using an adhesive or the like. Moreover, creep is likely to occur due to the difference in thermal expansion coefficient between the strain-detected member and the crystalline semiconductor, so long-term stability is difficult to obtain. On top of that,
It requires a temperature compensation circuit and a nonlinear correction circuit, and furthermore, the operating temperature range is usually limited to -20°C to 140°C.

[Problem to be solved by the invention]

As described above, although strain gauges using crystalline semiconductors have many drawbacks, their excellent feature of high gauge factor is an irreplaceable property.

Therefore, efforts have been made to construct semiconductor thin film strain gauges using thermal chemical vapor deposition methods (hereinafter referred to as thermal CVD methods), vacuum evaporation methods, etc., which are easy to form thin films.

However, the thermal CVD method requires heating the substrate to 600°C or higher, while the vacuum evaporation method has the advantage of being able to deposit at a substrate heating temperature of around 400°C (for example, JP-A No. 47-3273, "Piezoelectric "Device with resistance converter and method for manufacturing the same")
It has the following drawbacks.

(1) Semiconductor thin films formed by vacuum evaporation lack long-term stability, resulting in gauge characteristic drift.

(2) Due to slight variations in the deposition conditions, the properties of the resulting semiconductor thin film varied widely, making it difficult to obtain reproducibility. Therefore, the elements have become expensive.

[Means to solve the problem]

On the other hand, with recent advances in plasma CVD technology, it has been confirmed that amorphous silicon semiconductor thin films can be formed on insulating substrates such as glass and mica at temperatures as low as 200°C (for example, "Electronic Materials", January 1981). No. PP.56-58), but unfortunately strain gauge characteristics were not studied. However, no one had verified whether the amorphous silicon semiconductor thin film described above had a gauge factor large enough to be of practical use. In view of the above points, the inventors first conducted experimental verification.
(Regarding this result, please refer to the Proceedings of the 2nd "Fundamentals and Applications of Sensors" Symposium sponsored by the Electronic Devices Technology Committee of the Institute of Electrical Engineers of Japan (Thursday, May 27, 1982).
Sunday (Friday)) Announced on B5-4. ) The present invention utilizes the fact discovered by the inventors, that is, in an amorphous silicon semiconductor thin film, the particle size
By including a fine crystalline phase consisting of about 100 Å, the gauge factor can be increased to 32 or more, and the amount of strain applied and the rate of change in resistance value exhibit a good proportional relationship (hereinafter referred to as "linearity"). good"
It is written as ), and aims to provide a small and highly accurate strain gauge constructed by taking advantage of the ease of thin film formation and microfabrication properties of amorphous silicon semiconductor thin film materials.

[Effect]

Figures 1 and 2 show the strain-resistance changes of an amorphous silicon semiconductor thin film deposited on a glass substrate by the CD glow discharge method, which is one of the plasma CVD methods, using a mixed gas of SiF ₄ and H ₂ . 3 is a drawing showing the rate characteristics, that is, the piezoresistance effect characteristics.

The strain gauges shown in FIGS. 4 and 5a were used for the measurements.

The strain gauge is composed of a glass substrate 1, an amorphous silicon semiconductor thin film resistor 2 for strain detection, a pair of electrodes 3, 3', and a pair of lead wires 5, 5'.

In the figure, the length L, width W, and thickness t of the amorphous silicon semiconductor thin film resistor are 10 mm, 1 mm, respectively.
It is 1μm. Furthermore, the length, width, and thickness of the glass substrate are 40 mm, 10 mm, and 500 μm, respectively.

FIG. 1 is a diagram showing an example of the characteristics of a p-type amorphous silicon semiconductor thin film (the specific formation method will be described later), and the horizontal axis represents the strain applied to the glass substrate, that is, the amorphous silicon semiconductor thin film resistor. The magnitude ε (=ΔL/L, elongation is t) and the vertical axis represents the magnitude ΔR/R of the rate of change in resistance. Here, L and R are the characteristic length and resistance value when no strain is applied, and △L and △R are the respective changes in length and resistance value due to strain, + means increase, - means decrease. are shown respectively. In the figure, the black circles indicate the longitudinal effect (the strain direction and the resistance measurement direction are the same), the △ marks indicate the horizontal effect (the strain direction and the resistance measurement direction are perpendicular), and the + marks indicate the diagonal effect (the strain direction is the same). and the length direction of the resistor (when the angle θ = 45°) is shown. From this result, the resistance change rate △R/R is directly proportional to the magnitude of strain ε,
For the gauge factor G (=(ΔR/R)/ε), a maximum value G=32.5 was obtained when the vertical effect was applied, and a negative gauge factor was obtained when the horizontal effect was applied. Furthermore, the temperature dependence of the gauge factor in this case is as small as 0.4%/°C or less.

FIG. 2 is a diagram showing an example of the characteristics of an n-type amorphous silicon semiconductor thin film (the specific formation method will be described later). The symbols in the figure are the same as in FIG. 1.

From this experimental result, even in n-type amorphous silicon semiconductor thin films, the magnitude of the resistance change rate ΔR/R is directly proportional to the magnitude of strain ε, the gauge factor is negative for both the longitudinal effect and the transverse effect, and the oblique effect is very small and almost equal to zero. The absolute value of the gauge factor was maximum when there was a longitudinal effect, and |G|=20 was obtained.
Further, the temperature dependence of the gauge factor in this case is small like in the p-type.

Figure 3 is a diagram showing the change characteristics of the gauge factor depending on the direction of strain. In the figure, the horizontal axis represents the magnitude θ between the strain direction and the resistance measurement direction, and the vertical axis represents the magnitude of the gauge factor. , + mark and black circle mark are p-type, respectively.
Each n-type amorphous silicon semiconductor thin film is shown.
Further, the magnitudes of θ=0°, 45°, and 90° correspond to the vertical effect, oblique effect, and horizontal effect, respectively.

From this experimental result, the absolute values of the gauge factors of both p-type and n-type amorphous silicon semiconductor thin films are maximum when the longitudinal effect is applied, and are positive for p-type and negative for n-type. The above experimental results show that the amorphous silicon semiconductor thin film resistor has an excellent piezoresistance effect, and in particular, the absolute value of the gauge factor G is maximum when there is a longitudinal effect for both p-type and n-type.
It was confirmed that the amorphous silicon semiconductor thin film resistor, which has a structure that takes advantage of the longitudinal effect of both p-type and n-type, exhibits excellent characteristics as a sensor material for strain gauges.

〔Example〕

4 and 5 are diagrams showing the configuration of an embodiment of the strain gauge according to the present invention. In particular, it is assumed that stress, that is, strain is applied in parallel to the direction of the arrow. FIG. 5a shows a plan view, and FIG. 5a shows a sectional view taken along line X-X'.

FIG. 5b is a sectional view showing an example in which a protective film is provided on the surface of the amorphous silicon semiconductor thin film resistor 2 shown in FIG. Here, the protective film covers the entire upper part except for the electrodes 3 and lead wires 5 to prevent the element from being affected by outside air or the like.

In the figure, 1 is an insulating substrate, 2 is a p-type (n-type) amorphous silicon semiconductor thin film resistor, 3 and 3' are electrodes, 4 is a surface protective film, 5 and 5' are output lead wires, and 6 is a Each strain gauge is shown.

A method for manufacturing the strain gauge 6 will be described next.

The material of the insulating substrate 1 has heat resistance,
CVDSiO ₂
It is preferable to cover the surface of a glass plate, polyimide film, metal _plate , or semiconductor with an insulating thin film (e.g. _, CVDSiO ₂ thin film or
(CVDSi ₃ N ₄ thin film) is used.
After thoroughly cleaning the insulating substrate 1 with an organic solvent or the like, it is instantly dried in a clean atmosphere.

Next, using a mixed gas of SiH ₄ or SiF ₄ and H ₂ ,
An amorphous silicon semiconductor thin film 2 is deposited using a DC glow discharge method or an RF glow discharge method.
In this case, the doping gas used is diborane (B ₂ H ₆ ) for p-type, and phosphine (PH ₃ ) or arsine (AsH ₃ ) for n-type.

In this case, the higher the conductivity σ of the amorphous semiconductor thin film resistor, the more desirable it is, and usually σ = 1S cm ^-1 or more is used.
The conductivity σ of each p-type and n-type amorphous silicon semiconductor thin film shown in the figure is 10S・cm ^-1 ,
It is 7.4S cm ^-1 . An example of deposition conditions using the DC glow discharge method is a discharge pressure of 0.1 to 10 Torr;
Discharge current ~100mA/ ^cm2 , discharge voltage 500~800V,
Electrode spacing 3cm, substrate temperature 250-450℃, SiF ₄ /H ₂
=1~10, _{B2H6 / SiF4} =100~2500ppm, _PH3 /
SiF ₄ =100 to 2500 ppm. As an amorphous silicon semiconductor thin film deposited under these conditions, a resistivity of σ=20S·cm ⁻¹ or higher can be easily obtained. As a method of increasing the electrical conductivity of an amorphous silicon semiconductor thin film, a method of increasing the discharge current or a method of increasing the proportion of doping gas is generally used.

When a semiconductor thin film is deposited using the above method, a fine crystal phase of around 100 Å is included in the amorphous film, but a large gauge factor characteristic is maintained.
Further, high conductivity can also be obtained from Si-Ge alloy type amorphous semiconductor thin films. In this case, _SiH4 and _GeH4
Using a mixed gas with B ₂ H ₆ or PH ₃ , AsH ₃ doping gas added, DC glow discharge method (method of applying direct current voltage) or RF glow discharge method (method of applying high frequency voltage) Deposit an amorphous semiconductor thin film using Next, a metal film for electrodes (for example, NiCr500) is coated using a vacuum evaporation method.
Å/Au1000Å) is deposited. Furthermore, unnecessary portions are removed using a photoetching technique to form the electrode pair 3, 3' and the amorphous silicon semiconductor thin film resistor 2.

The shape of the thin film resistor 2 is an amorphous silicon semiconductor thin film, which is particularly noticeable in the case of a semiconductor thin film containing a large amount of fine crystalline phase with high conductivity.
As a result of X-ray diffraction, a diffraction peak is obtained at <111> as the crystal axis direction of Considering that both the shape and the n-shape are maximized, it is desirable to have a shape in which the length L in the tensile or compressive direction is long and the length W in the lateral direction is short.
This L/W is determined in consideration of the conductivity, film thickness, output impedance, etc. of the amorphous semiconductor thin film, and is usually set to L/W=10 to 100. Next, a protective film 4 is deposited on the substrate surface. As the protective film, a CVDSiO ₂ film, a CVDSi ₃ N ₄ film, a polyimide resin, or the like is used. The protective film on the electrode pad is removed using photo-etching technology.
Finally, the lead wire pair 5, 5' for extraction is attached to the electrode pair 3, 3' to complete the process. The lead wire is constructed by a beam lead method or by wire bonding Au wire, Au ribbon wire, or the like.

In the above manufacturing method, photoetching technology was used to form the amorphous silicon semiconductor thin film resistor and the electrode pair, but they can also be formed by a method using a metal mask. In this case, a method is used in which unnecessary parts are covered with a metal mask when depositing an amorphous silicon semiconductor thin film or when depositing a thin electrode metal using a vacuum evaporation method.

6 and 7 are views showing other embodiments of the present invention, in which FIG. 6 is a plan view and FIG. 7 is a schematic cross-sectional view taken along line X-X' in FIG. 6.

In the figure, 11 is an insulating substrate, 12 is p-type (n-type)
Amorphous silicon semiconductor thin film resistor, 13,
13' is an electrode pair, 15, 15' is a lead wire pair, 16
indicate strain gauges. This strain gauge 16 has a shape that assumes that tensile stress or compressive stress will be applied in the direction of the arrow. The strain gauge 16 of this embodiment has a structure in which the pair of lead wires 5, 5' of the strain gauge 6 described above were separated in two directions, left and right, but are taken out in the same direction, and the manufacturing method is the same as that described above. It can be configured using the same thing.

FIG. 8 is a diagram showing another embodiment according to the present invention,
In the figure, 21 is an insulating substrate, 22A, 22B are amorphous silicon semiconductor thin film resistors, 23A,
23'A, 23B, 23'B are each electrode pair, 25A,
25'A, 25B, 25'B are each lead wire pair, 26
A and 26B represent each strain measurement resistor, and 27 represents a strain gauge. In this case, 26B is 26
Arranged by rotating A 90 degrees clockwise. This strain gauge 27 has a structure that allows measurement of both the longitudinal effect and the transverse effect with the same element.

As shown in Figure 3, the gauge factor due to the piezoresistance effect of an amorphous semiconductor thin film is different for the longitudinal effect and the transverse effect, so the strain gauge 27 is attached to the object to be measured to measure the change in each resistance value. By doing so, the direction and magnitude of strain applied to the strain gauge can be measured simultaneously.

FIG. 9 is a diagram showing another embodiment according to the present invention,
In the figure, 31 is an insulating substrate, 32 is an amorphous silicon semiconductor thin film resistor, 33, 33' is an electrode pair,
35, 35' are lead wire pairs, 36A, 36B, 3
Reference numeral 6C indicates each strain measuring resistor, which is arranged so as to be rotated counterclockwise by 45 degrees from each other, and 37 indicates a strain gauge. In this case, the longitudinal effect, horizontal effect, and diagonal effect can be measured simultaneously, so by attaching this strain gauge 37 to the object to be measured, you can measure the magnitude and direction of strain in the object to be measured with high precision. can be measured. The strain gauges 27 and 37 described in FIGS. 8 and 9 can be constructed using the same manufacturing method as the strain gauge 6 shown in FIGS. 4 and 5.

Next, we will briefly discuss the glow discharge method. The glow discharge method involves generating a glow discharge in a direct current electric field.
There are two methods: DC glow discharge method and RF glow discharge method, which generates glow discharge in a high frequency electric field. Figure 10 is
This is an example of an apparatus for depositing an amorphous silicon semiconductor thin film on an insulating substrate or the like using the RF glow discharge method.

This device heats a vacuum container 38, an anode 39 and a cathode 40 arranged in parallel inside the vacuum container, an air supply port 42 and an exhaust port 43 for supplying or exhausting gas 41 into the vacuum container, and the anode and cathode. It is composed of a heater 44 and the like. An insulating substrate 45 is placed on the anode or cathode. The gas 41 is usually SiH ₄ or SiF ₄ and H ₂
Doping gas (e.g. PH ₃ ,
(AsH ₃ , B ₂ H _6, etc.) is used.
The vacuum pressure during glow discharge is several Torr, the discharge voltage is almost constant, and the discharge current is 1 to 100 mA/ ^cm2 .
Most of the gas reactions occur within the positive column (plasma 46). In particular, this glow discharge method requires a substrate temperature of 400°C.
It has the characteristic of being able to deposit amorphous semiconductor thin films at temperatures as low as ℃ or below (conventional thermal CVD methods for thin film production require a substrate temperature of 600 to 700°C).
).

〔Effect of the invention〕

Next, the effects of the present invention will be described.

(1) An inexpensive strain gauge can be formed using a polymide film on an insulating substrate.

(2) Since an amorphous silicon semiconductor thin film resistor with high gauge factor and high conductivity is used, a highly sensitive strain gauge can be constructed.

(3) Since microfabrication technology represented by photoetching technology can be used, ultra-small strain gauges, etc. can be constructed.

(4) Since the manufacturing method is easy, inexpensive strain gauges can be manufactured.

(5) Since the gauge factor is large and the linearity is good, it is easy to configure the output amplifier and correction circuit.

(6) Resistance elements for measuring longitudinal, transverse, and diagonal effects can be configured on the same insulating substrate, and since the gauge factors for each effect are different, the magnitude and direction of strain in the strain-measured object can be determined with high precision. Strain gauges for detection can be configured.

(7) Because of its good temperature characteristics, it can be used as a strain gauge for relatively high temperatures.

As mentioned above, the strain gauge according to the present invention has many advantages over conventional ones.

[Brief explanation of drawings]

Figure 1 shows the piezoresistance effect characteristics of a p-type amorphous silicon semiconductor thin film, Figure 2 shows the piezoresistance effect characteristics of an n-type amorphous silicon semiconductor thin film, and Figure 3 shows the piezoresistance effect characteristics of an amorphous silicon semiconductor thin film. FIGS. 4 and 5 are diagrams showing changes in gauge factor with respect to the strain direction, and FIGS. 4 and 5 are diagrams showing an embodiment of the strain gauge according to the present invention. FIG. 4 is a plan view;
FIG. 5a is a cross-sectional view taken along line X-X' in FIG. 4, and FIG. 5b is a cross-sectional view showing an example in which a protective film is provided.
Figures 6 and 7 are diagrams showing other embodiments of the strain gauge, with Figure 6 being a plan view and Figure 7 being the line X-- in Figure 6.
A diagram showing a cross-sectional view at X', FIG. 8 is a diagram showing another embodiment of the strain gauge, FIG. 9 is a diagram showing another embodiment of the strain gauge, and FIG. 10 is an example of a device related to the glow discharge method. FIG. In the figure, 1, 11, 21, 31, 45 are insulating substrates, 2, 12, 22A, 22B, 32 are amorphous semiconductor thin film resistors, 3, 3', 13, 13',
23A, 23'A, 23B, 23'B, 33, 3
3' is an electrode pair, 4 is a protective film, 5, 5', 15, 1
5', 25A, 25'A, 25B, 25'B, 35,
35' is a lead wire pair, 6, 16, 27, 37 are strain gauges, 26A, 26B, 36A, 36B,
36C represents each strain measurement resistor, 39 represents an anode, and 40 represents a cathode.

Claims (1)

[Scope of Claims] 1. A strain gauge comprising a thin film resistor provided on an insulating substrate and a pair of electrodes for guiding current to the resistor, wherein the material constituting the resistor is A strain gauge characterized by being an amorphous silicon semiconductor formed by a glow discharge method. 2 an insulating substrate 21; provided on the substrate;
a first thin film 22A made of amorphous silicon semiconductor having a shape of a letter; a second thin film 22B made of amorphous silicon semiconductor having a U-shape and having a different orientation from the first thin film on the substrate; electrode pairs 23A, 23'A, 23 provided for introducing current into the first and second thin films, respectively;
B, 23'B; respective lead wire pairs 25A, 25'A, 25 provided in contact with each of the electrode pairs;
A strain gauge consisting of B and 25'B.