JPH06347345A - Load detector - Google Patents

Abstract

PURPOSE:To measure a load with high accuracy by a construction wherein a conductive base generating a compressive strain and a tensile strain on the same surface is provided in a strain generating body, semiconductor gages each having (n) and (p) layers are provided in strain generating parts respectively and a Wheatstone bridge is formed out of the gages and fixed resistors. CONSTITUTION:A strain generating body 1 constructs such a mechanism that a movable rigid body part 11 moves downward in parallel to a fixed rigid body part 10 when a load F is applied thereto. The opposite end parts 20 of a conductive base 2 are fixed to base fixing parts 14, respectively. The base 2 has a compressive strain part 22 and a tensile strain part 23 generating strains respectively in accordance with a change in the shape of the strain generating body 1 on the same surface and semiconductor strain gages 3 each prepared by laminating three layers of (n), (i) and (p) are formed on the surfaces of the two strain parts 22 and 23 respectively. The two gages 3 form a Wheatstone bridge with two fixed resistors 7 connected together at a point Ja. An electric signal corresponding to the load F is obtained from between points Jc and Jd and the load F can be measured therefrom. By this structure, temperature compensating properties of a load detector are improved remarkably.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load detector provided with a semiconductor strain gauge made of a thin film.

[0002]

2. Description of the Related Art A load detector using a semiconductor strain gauge is
It has advantages such as better strain sensitivity than those using a strain gauge made of a metal foil (for example, Japanese Patent Laid-Open No.
242901).

[0003]

However, since the semiconductor strain gauge has a large fluctuation in output due to a change in ambient temperature,
There is a drawback that the output becomes unstable. That is, the temperature dependence is high, and therefore the accuracy of the load detector is low.
In particular, a semiconductor strain gauge composed of a thin film of hydrogenated amorphous silicon having an i layer interposed between a p layer and an n layer has remarkably excellent strain sensitivity, but its temperature dependence is remarkably high. It has the drawback that it cannot be used for The present invention has been made in view of the above-mentioned conventional drawbacks, and an object of the present invention is to provide a load detector with high accuracy even if the ambient temperature changes.

[0004]

In order to achieve the above-mentioned object, the invention of each claim is such that a conductive substrate that produces compressive strain and tensile strain on the same surface is provided in a strain generating body, and p A semiconductor strain gauge formed of a thin film in which at least a layer and an n layer are laminated is provided at a portion of the conductive substrate where compressive strain and tensile strain are generated. A Whiston bridge circuit is formed by the two semiconductor strain gauges and two fixed resistors having a resistance temperature coefficient smaller than those of the semiconductor strain gauges.

According to the inventions of the respective claims, since the Hoiston bridge circuit is formed by the pair of semiconductor strain gauges and the two fixed resistors having a resistance temperature coefficient smaller than that of the semiconductor strain gauges, the ambient temperature is reduced. Even if it fluctuates, if the two semiconductor strain gauges have the same temperature change and have the same temperature coefficient of resistance, it is possible to prevent a decrease in accuracy due to the temperature change.

Here, according to the present invention, since the semiconductor strain gauge is provided in a portion where the compressive strain and the tensile strain are generated on the same surface of the conductive substrate, the conductive substrate is made small, Since the two semiconductor strain gauges can be brought close to each other, the temperature changes in the two semiconductor strain gauges can be equalized. Further, since the two semiconductor strain gauges are provided on the same surface of the conductive substrate, by manufacturing them in the same vacuum container,
Since the electrical and mechanical properties are the same, the temperature coefficient of resistance is also the same. In this way, the temperature change and the temperature coefficient of resistance of the two semiconductor strain gauges can be made equal, so that it is possible to prevent the accuracy from decreasing due to the temperature change.

The semiconductor strain gauge can be formed of a thin film of a hydrogenated amorphous silicon semiconductor having an i layer between a p layer and an n layer.

According to a fourth aspect of the present invention, two beam portions having two flexible portions are provided between the fixed rigid body portion at one end and the movable rigid body portion at the other end to form a flexure element. A pair of substrate fixing portions that fix both end portions of the conductive substrate are provided on both the rigid body portions. At least one of these substrate fixing portions projects toward the other.

According to the fourth aspect of the present invention, at least one of the pair of substrate fixing portions for fixing both end portions of the conductive substrate,
Since it projects toward the other side, the size of the conductive substrate can be made small so that the two semiconductor strain gauges can be brought close to each other. Therefore, similarly to the invention of claim 1, it is possible to prevent a decrease in accuracy due to a temperature change. obtain.

According to a fifth aspect of the invention, a pair of beam portions made of thin plates are provided between the fixed rigid body portion at one end and the movable rigid body portion at the other end to form a strain generating body. At least one of the beam portions constitutes the conductive substrate.

According to the invention of claim 5, the conductive substrate is composed of a beam portion made of a thin plate, and since the strain generating element can be made small and the conductive substrate can be made small,
Similar to the invention of claim 1, it is possible to prevent a decrease in accuracy due to a temperature change.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 4 show the first embodiment. Figure 1 (a)
In, the flexure element 1 has a pair of beam portions 12, 12 between the fixed rigid body portion 10 at one end and the movable rigid body portion 11 at the other end. The both beam portions 12 and 12 extend in parallel to the direction orthogonal to the direction in which the load F acts,
Two thin flexible portions 12a, 12a are formed at both ends thereof. Therefore, the flexure element 1 constitutes a Roberval mechanism in which when the load F acts on the movable rigid body portion 11, the movable rigid body portion 11 moves in parallel downward with respect to the fixed rigid body portion 10.

A through hole 13 at the center of the strain-flexing body 1 is provided with a pair of substrate fixing portions 14 and 14 projecting from both rigid body portions 10 and 11 toward the center. Both ends 20, 20 of the conductive substrate 2 are fixed to the substrate fixing portion 14 by welding or bolts.

In FIG. 1B, the conductive substrate 2 is
Has, for example, four notches 21 formed in a stainless steel plate. Therefore, as the strain element 1 is deformed, a compressive strain portion 22 that causes compressive strain and a tensile strain portion 23 that causes tensile strain are generated.
And on the same surface 24. Instead of the four cutouts 21, the plate thickness of the conductive substrate 2 may be partially reduced to form the strain concentration part. The surface 24 of both the strained portions 22 and 23 is mirror-finished, and the semiconductor strain gauge 3 made of a hydrogenated amorphous silicon thin film is formed on the surface 24.

The semiconductor strain gauge 3 has an i layer between an n layer and a p layer, and the n layer, the i layer, and the p layer are laminated in this order. The n layer has P (phosphorus) atoms substituted between Si (silicon) atoms, and has a thickness of, for example, 0.05 μm.
It has a film thickness of. The i layer is made of Si and has a film thickness of 0.8 μm, for example. The p layer has B (boron) atoms substituted between Si atoms, and has a film thickness of, for example, 0.05 μm. The pair of semiconductor strain gauges 3 are made to have the same electrical and mechanical characteristics by the manufacturing method described later. On the p-layer, an upper electrode 4 formed by laminating a chromium thin film and an indium thin film is vapor-deposited to have a film thickness of 0.2 μm, for example. The surface 24 of the upper electrode 4 and the conductive substrate 2
Signal lines 6A, 6B and 6C are connected to the via the well-known indium solders 5A, 5B and 5C.

In FIG. 2, the semiconductor strain gauges 3 and 3 described above are used.
Is two fixed resistors 7, which are connected to each other at the connection point Ja.
7 forms a Hoiston bridge circuit, and the semiconductor strain gauges 3, 3 with respect to a predetermined input voltage E applied between the connection point Ja and the conductive substrate 2 via the indium solder 5B. The output voltage e corresponding to the change in the current-voltage characteristic of No. 3 is obtained. That is, an electric signal (output voltage e) corresponding to the load F (FIG. 1) is obtained from between the two connection points Jc and Jd of the semiconductor strain gauge 3 and the fixed resistor 7, and the electric signal F (FIG. The size of 1) is measured.
The fixed resistor 7 is made of nichrome foil, for example, and has a resistance temperature coefficient smaller than that of the semiconductor strain gauge 3. The two fixed resistors 7, 7 are connected in parallel with each other with respect to the input voltage E, while the output voltage e
Are connected in series with each other. The two semiconductor strain gauges 3 and 3 are also connected to each other in parallel with respect to the input voltage E, and are connected to each other in series with respect to the output voltage e.

Next, a method of manufacturing the semiconductor strain gauge 3 and the like will be described. First, the surface 24 of the conductive substrate 2 shown in FIG. 1B is polished to a mirror surface state, and the surface 24 is covered with the mask plate 8 having the through holes 8a shown in FIG. 4A. Is attached to the first electrode 9A. Then, SiH ₄ (silane) gas is introduced into the vacuum container 30 and a voltage is applied to the two electrodes 9A and 9B to cause glow discharge and decompose the silane gas in the vacuum container 30. While introducing PH ₃ (phosphine) gas together with silane gas, doping treatment is performed to form n layer (FIG. 1).
To form. After forming the n layer, the i layer (FIG. 1) is formed by glow discharge while introducing only silane gas. Then, while introducing B ₂ H ₆ (diborane) gas together with the silane gas, a p-layer is formed by a doping process.

In this way, after the semiconductor strain gauge 3 is formed on the surface 24 of the conductive substrate 2, the vacuum state in the vacuum container 30 is released and the conductive substrate 2 is taken out. After this,
As shown in FIG. 4B, the conductive substrate 2 is set in another vacuum vapor deposition apparatus 31, and the upper electrode 4 formed by stacking a chromium thin film and an indium thin film is formed by a known vacuum vapor deposition method.
It is formed on the upper surface of the p layer of the semiconductor strain gauge 3. After this formation, on the conductive substrate 2 taken out from the vacuum vapor deposition device 31,
As shown in FIG. 4C, indium solders 5A, 5B,
5C is used to connect the copper electric signal lines 6A, 6B and 6C.

The above manufacturing method has been described in the case of being carried out in a laboratory. In the case of actual industrial production, a large mask plate 8 having a large number of through holes 8a shown in FIG. 4 (a) is used. Covering the surface of a large conductive substrate, forming a large number of semiconductor strain gauges 3 and upper electrodes 4 on one conductive substrate, and then cutting this large conductive substrate into the size shown in FIG. 1 (b). Thus, the conductive substrate 2 is obtained.

In the above structure, the output voltage e1 of the semiconductor strain gauge 3 alone in FIG. 1B has a very high temperature dependency of the semiconductor strain gauge 3 itself, and therefore, as shown in FIG. It fluctuates greatly. On the other hand, this load detector has two semiconductor strain gauges 3 as shown in FIG.
And a fixed resistance 7 having a resistance temperature coefficient smaller than those of the semiconductor strain gauges 3 form a Hoiston bridge circuit, so that even if the ambient temperature fluctuates, as shown in FIG. It is possible to prevent the output voltage e from changing due to the change.

Here, the load detector comprises a pair of semiconductor strain gauges 3 on a small conductive substrate 2 as shown in FIG.
Since the pair of semiconductor strain gauges 3 are close to each other, the temperature changes of the pair of semiconductor strain gauges 3 are equal. Also, a pair of semiconductor strain gauges 3
Are formed close to each other on the same surface 24 of the conductive substrate 2, the same vacuum container 3 as shown in FIG.
By forming within 0, the electrical and mechanical characteristics are equivalent, and the temperature coefficients of resistance are also equal to each other. As described above, since the temperature change and the temperature coefficient of resistance of the pair of semiconductor strain gauges 3 become equal, as shown in FIG. 3A, it is possible to obtain a load detector with stable output voltage e and excellent temperature compensation. You can

As described above, after forming a large number of semiconductor strain gauges 3 on a large conductive substrate, the large conductive substrate is cut to obtain the conductive substrate 2 shown in FIG. 1 (b). The manufacturing cost of the semiconductor strain gauge 3 can be reduced.

5 to 7 show modifications of the flexure element 1.
In the flexure element 1 of FIG. 5, one beam portion 12 is a separate body, and the beam portion 12 is joined to the fixed rigid body portion 10 and the movable rigid body portion 11 by bolts 15. The conductive substrate 2 is fixed to the substrate fixing portion 14 and the fixing piece 16 by the fastening force of the bolt 17.
It is sandwiched between and.

In the flexure element 1 of FIG. 6, the substrate fixing portion 14 is provided so as not to project through the through hole 13 of the flexure element 1 but to the outside. A recess 14a is formed in the substrate fixing portion 14.

The flexure element 1 in FIG. 7 is made of sheet metal, and a flat plate 19 is provided between a pair of upper and lower bent plates 18, 18. The flat plate 19 includes the board fixing portion 14 and both rigid body portions 10,
It constitutes a part of 11.

As described above, various types of flexure elements 1 can be used. For example, only one substrate fixing portion 14 in FIG. 1A is projected toward the other substrate fixing portion 14. Good. Further, the two openings of the through hole 13 of the strain generating element 1 may be covered with a cover or the like to further enhance the temperature compensation property.

FIG. 8 shows a second embodiment. In FIG.
In the flexure element 1, a pair of beam portions 12, 12 made of thin plates having a thickness of 1 mm or less, for example, are provided between a fixed rigid body portion 10 and a movable rigid body portion 11 made of a metal block. One of the thin plate beam portions 12, 12 constitutes the conductive substrate 2 of the present invention, and a pair of semiconductor strain gauges 3, 3 are formed on the surface 24 thereof. Compressive strain portion 22 and tensile strain portion 2 in which the semiconductor strain gauge 3 is formed.
On the back surface of 3, the groove 21A for forming the flexible portion 12a is formed.
Are formed. The metal block forming the fixed rigid body portion 10 and the movable rigid body portion 11 includes the beam portion 1
A positioning notch 1a for positioning 2 is formed. Other configurations are the same as those in the first embodiment described above,
The same parts or corresponding parts are designated by the same reference numerals, and detailed description thereof will be omitted.

In the load detector of the second embodiment, since the beam portion 12 is formed of a thin plate, the load detector is extremely small in total, and can be suitably used as a vibration or acceleration detector.

By the way, in the above embodiment, as shown in FIG. 1B, the thin film is laminated on the conductive substrate 2 in the order of the n layer, the i layer and the p layer. P layer,
The i layer and the n layer may be formed in this order. However, as in this embodiment, by forming the thin film on the conductive substrate 2 in the order of the n layer, the i layer, and the p layer, the semiconductor strain gauge 3 in the Hoiston bridge circuit of FIG. The effect of having an action is obtained. In addition, a thin film is formed on the conductive substrate 2
Even when the layers, the i layer, and the n layer are formed in this order, it is possible to easily give a forward rectification action to the semiconductor strain gauge 3 by changing the connection of the Hoiston bridge circuit in FIG.

In the above embodiment, the semiconductor strain gauge 3 shown in FIG. 1 (b) is formed of a thin film of hydrogenated amorphous silicon semiconductor. However, the invention of claim 1, 2, 4 or 5 is the semiconductor strain gauge 3 The material of is not limited.
Depending on future research, it is possible to construct the semiconductor strain gauge 3 using a thin film containing germanium, for example.

Further, in the above-mentioned embodiment, the semiconductor strain gauge 3 has the i layer between the p layer and the n layer. However, the invention of claim 1, 3, 4 or 5 includes at least the p layer and the n layer. It can also be applied to a semiconductor strain gauge in which layers are laminated, and temperature compensation can be improved.

The conductive substrate 2 need only have conductivity on the surface 24, and may be, for example, a ceramic substrate or a glass substrate on which a conductive material such as aluminum is formed. May be.

[0033]

As described above, according to the present invention, although the strain sensitivity is remarkably excellent, a pair of semiconductor strain gauges which are sensitive to temperature change are provided, and the temperature coefficient of resistance is smaller than that of the semiconductor strain gauge. Since the Hoiston bridge circuit is formed by the two fixed resistors and the semiconductor strain gauge, the temperature compensating property, which was remarkably low in the related art, is improved to a practical level. In particular, since a pair of semiconductor strain gauges are provided on a conductive substrate that produces compressive strain and tensile strain on the same surface, the temperature changes of the pair of semiconductor strain gauges become equal to each other, and Since the temperature coefficients of resistance are the same, the temperature compensation of the load detector is significantly improved.

[Brief description of drawings]

FIG. 1A is a schematic perspective view of a load detector showing a first embodiment of the present invention, and FIG. 1B is a perspective view of an essential part of the present invention schematically showing a semiconductor strain gauge.

FIG. 2 is a circuit diagram showing a load detection circuit.

FIG. 3 is a characteristic diagram showing characteristics of output voltage.

FIG. 4 is a process drawing showing the method for manufacturing a semiconductor strain gauge.

FIG. 5 is a cross-sectional view showing a first modification of the flexure element.

FIG. 6 is a perspective view showing a second modification of the flexure element.

FIG. 7 is a perspective view showing a third modified example of the flexure element with a part thereof broken away.

FIG. 8 is a schematic perspective view of a load detector showing a second embodiment.

[Explanation of symbols]

1 ... Strain element, 10 ... Fixed rigid body portion, 11 ... Movable rigid body portion, 1
2 ... Beam part, 12a flexible part, 14 ... Board fixing part, 2 ...
Conductive substrate, 20 ... Both ends, 22 ... Compressive strain part, 23 ... Tensile strain part, 24 ... Surface, 3 ... Semiconductor strain gauge, 7 ... Fixed resistance.

Claims (5)

[Claims] 1. A semiconductor strain gauge comprising a thin film in which at least a p layer and an n layer are laminated is provided on a conductive substrate in which a conductive substrate that produces a compressive strain and a tensile strain on the same surface is provided on the strain body. A load detector which is provided in a portion where the compressive strain and the tensile strain are generated, and which forms a Hoiston bridge circuit by the two semiconductor strain gauges and two fixed resistors having a resistance temperature coefficient smaller than those of the semiconductor strain gauges. 2. The load detector according to claim 1, wherein the semiconductor strain gauge is a thin film having an i layer between a p layer and an n layer. 3. The load detector according to claim 1, wherein the semiconductor strain gauge is formed of a thin film of hydrogenated amorphous silicon semiconductor. 4. The flexure element according to claim 1, wherein
Two beam portions having flexible portions are provided between a fixed rigid body portion at one end and a movable rigid body portion at the other end, and a pair of beam portions that fix both end portions of the conductive substrate to the both rigid body portions are provided. Load detector in which at least one of these substrate fixing portions projects toward the other. 5. The flexure body according to claim 1, wherein a pair of thin beam portions are provided between the fixed rigid body portion at one end and the movable rigid body portion at the other end, and at least one of the beam portions is provided. Is a load detector in which is the conductive substrate.