JPH04131721A - Stress sensor - Google Patents

Abstract

PURPOSE:To reduce the number of parts and significantly shorten the manufacturing process by providing a zero point temperature compensating resistance and a zero adjusting resistance on a circuit board. CONSTITUTION:A chip linear thermistor 9 as a zero point temperature compensating resistance is connected between connecting terminal parts 5B, 5C, and a chip resistance 11 for a zero adjusting resistance is connected between connecting terminal parts 5F, 5E. According to a determined calculating procedure, the used terminals as the whole bridge circuit, the resistance value and temperature coefficient of the linear thermistor 9, and the resistance value of the chip resistance 11 can be easily determined by calculation. A stress sensor in which the zero point temperature is thus compensated generates an output voltage according to a load between the used output terminals 17A-18A by changing the electric resistance of strain gauges 3A-3D when a load such as oil pressure acts on the strain part 1A of a diaphragm 1 to distort the strain part 1A, and it allows highly precise stress measurement.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is applicable to stress measurement, which is used, for example, to measure stress strain in structural members of civil engineering and construction machinery, stress measurement in various other equipment, pressure measurement in hydraulic circuits, etc. Regarding sensors.

[Prior Art] In general, metal gauges and semiconductor strain gauges are widely used as stress sensors applied as pressure sensors, strain sensors, torque sensors, load sensors, etc. Among these, the latter is particularly popular. Semiconductor strain gauges have been widely used in recent years because they have a higher gauge factor than the former metal gauges (and can generate a large change in resistance value in response to a small amount of mechanical strain).

Among these stress sensors, a diaphragm pressure sensor according to the prior art will be explained with reference to FIG. 9.

In the figure, 100 is a metal diaphragm, 101A, l0
IB, 10ICIOID are four semiconductor strain gauges (hereinafter referred to as strain gauges 101A to 101D) provided in the strain-generating portion of the diaphragm 100, and each strain gauge 101A
~101D is a piezoresistive element consisting of a thin film resistor on an insulating film (not shown) provided in a strain-generating part, for example, a P-CV.
A film is formed by the D method and molded by the photolithography method.

102A, 102B are zero point temperature compensation resistors made of thin film or thick film resistors having nonlinear temperature characteristics, which are also provided in the strain-generating portion of the diaphragm 100.

102B also has each of the strain gauges 101A to 101 on the insulating film.
The film is formed together with D.

103A and 103B are provided externally to the diaphragm 100, and are zero point temperature compensation resistors 1°2A and 102B.
The zero point adjustment resistors 103A and 103B are connected in parallel with the zero point temperature compensation resistor 102A,
104A and 104B are provided externally to the diaphragm 100 and are connected in parallel with the strain gauges 10IA and 101D. Temperature coefficient adjustment resistors 104A and 104B are temperature coefficient adjustment resistors 104A and 104B that are connected to strain gauges 10IA and 10I.
This is to adjust the temperature coefficient of D.

Here, if the connection point between the strain gauges 101A and 10ID is the power supply terminal 105, and the connection point between the strain gauges 101B and 1010 is the ground terminal 106, then the strain gauge is connected between the power supply terminal 105 and the ground terminal 106. 10IA, zero point temperature compensation resistor 102A, and strain gauge 101B are connected in series, and the zero point temperature compensation resistor 102A and strain gauge 101B are connected in series.
The connection point between the two becomes the output terminal 107 on one side, and the strain gauge 10 is connected between the power supply terminal 105 and the ground terminal 106.
1D, zero point temperature compensation resistor 102B, strain gauge 101C
are connected in series, and the connection point between the zero point temperature compensation resistor 102B and the strain gauge 10IC is the output terminal 108 on the other side.
Thus, the whole constitutes a bridge circuit.

Note that the zero point adjustment resistors 103A, 103B and the temperature coefficient adjustment resistors 104A, 104B are external resistors that have extremely low temperature dependence against temperature changes, and can be trimmed to perform zero point adjustment, temperature coefficient, etc. A resistor is used.

The stress sensor according to the conventional technology is configured as described above,
Regardless of whether the output voltage of the bridge circuit before zero-point temperature compensation shows positive or negative temperature characteristics, the temperature coefficient adjustment resistor 104A
, 104B, the temperature coefficients of the strain gauges 10IA, 10ID can be adjusted, and the zero point adjustment resistors 103A, 103B can adjust the temperature coefficients of the zero point temperature compensation resistors LO2A, 102B. In addition, the zero point adjustment resistor 10
3A and 103B, it is possible to adjust the zero point of the 8 voltages at no load.

As a result, even if a voltage is applied between the power supply terminal 105 and the ground terminal 106, no output voltage is generated between the output terminals 107108 if the strain-generating portion of the diaphragm 100 is in an unloaded state. On the other hand, when a load acts on the strain generating section and the strain generating section is distorted, the electrical resistance of the strain gauges 101A to 101D changes, and an output voltage corresponding to the load is generated between the output terminals 107 and 108.

[Problem to be solved by the invention]

However, in the stress sensor according to the prior art, the diaphragm 1
P-CV strain gauges 101A to 101D to the strain generating part of 00
The zero point temperature compensation resistors 102A and 102B are formed by depositing a resistive material with a high temperature coefficient at a predetermined position of the strain-generating portion after being formed by a film forming technique such as the D method or a forming technique such as photolithography. I try to do that.

However, after forming the strain gauges 10IA to 101D, a resistance material having the desired resistance value and temperature coefficient is deposited,
It is difficult to form the zero point temperature compensation resistors 102A and 102B, resulting in variations in resistance value and temperature coefficient. For this reason, in the prior art, the zero point temperature compensation resistor 10
After forming films 2A and 102B, in order to obtain the desired resistance value and temperature coefficient, zero point adjustment resistors 103A and 103B, which are externally attached separate resistors, are installed and correction is performed by laser trimming, reducing the number of parts. There is a problem in that the amount increases and correction work is required.

On the other hand, in order to form the zero point temperature compensation resistors 102A and 102B, control of film forming conditions, cleaning process, vapor deposition process, etc. are added, which has the disadvantage of significantly increasing the number of work steps. This has the disadvantage of causing a decrease in yield.

The present invention was developed in view of the above-mentioned drawbacks of the prior art, and eliminates the process of forming a film of the zero-point temperature compensation resistor on the diaphragm, and calculates the temperature coefficient and resistance value of the zero-point temperature compensation resistor using simple calculations. It is an object of the present invention to provide a stress sensor in which this resistor can be attached externally.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a diaphragm having a strain-generating portion, an insulating film provided on the diaphragm, a plurality of semiconductor strain gauges provided on the insulating film, and each semiconductor strain gauge. In a stress sensor comprising a plurality of conductors provided on the insulating film to be connected to form a Wheatstone bridge circuit, the diaphragm is provided with a circuit board located above each of the semiconductor strain gauges, the circuit board is provided with a zero point temperature compensation resistor made of a resistor with a large temperature dependence and a zero point adjustment resistor made of a resistor with a small temperature dependence, and the zero point temperature compensation resistor, the zero point adjustment resistor, and each of the conductors. are connected by lead wires to form a zero point temperature compensated Wheatstone bridge circuit.

Further, the zero point temperature compensation resistor used in the present invention is a linear thermistor with positive or negative characteristics whose resistance changes linearly with temperature changes, and the zero point adjusting resistor is a laser-trimmable chip resistor or thick film resistor. It can be done.

Furthermore, in the Wheatstone bridge circuit configured as described above, when the zero point temperature compensation resistor side is set as one output terminal and the zero point adjustment resistor side is set as the other output terminal, the output voltage before zero point temperature adjustment It is desirable that either the high voltage side or the low voltage side of the zero point temperature compensation resistor be used as one side output terminal depending on whether the temperature characteristic is positive or negative.

[Effect]

With this configuration, the resistance value and temperature coefficient of the zero point temperature compensation resistor are selected from the calculated values and mounted on the circuit board, and the zero point adjustment resistor is also selected from the calculated values and mounted on the circuit board, and the laser The zero point is adjusted by trimming.

At this time, since the zero-point temperature compensation resistor uses a resistor whose resistance value changes linearly with positive or negative characteristics with respect to the ambient temperature, the negative side will change depending on the temperature characteristics of the output voltage from the Wheatstone bridge circuit. Temperature compensation of the output voltage can be easily performed by selecting the output terminal of either the high voltage side or the low voltage side of the zero point temperature compensation resistor and appropriately determining the resistance value and temperature coefficient of the zero point temperature compensation resistor. can be done.

[Example] Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 8.

In the figure, reference numeral 1 denotes a metal diaphragm made of, for example, 5US630, and the diaphragm 1 includes a thin disc-shaped strain-generating portion IA and a thick cylindrical non-diaphragm integrally formed on the outer periphery of the strain-generating portion IA. The upper side surface in the figure is a flat film forming surface IC.

Reference numeral 2 denotes an insulating film formed on the film forming surface Ic of the diaphragm 1, and the insulating film 2 includes, for example, S, 02S, C, S, N
, etc., and is formed into a thin film by an appropriate film forming technique such as a vacuum evaporation method or a sputtering method. 3A, 3B, 3C
, 3D are four semiconductor strain gauges (hereinafter referred to as strain gauges 3 as a whole) located in the strain generating part IA and disposed on the insulating film 2, and the strain gauges 3 are made of, for example, P-CVD. A silicon thin film for a gauge doped with phosphorus or boron impurities is formed on an insulating film 2 by a method, and this is patterned as a thin film piezoresistive element by a photolithography method.

4A, 4B, 4C, 4D, 4E, 4F are the strain gauges 3
A thin film conductor (hereinafter referred to as the thin film conductor 4 as a whole) for connecting A to 3D to form a Wheatstone bridge circuit, and 4A is connected to one end of the strain gauge 3A and the other end of the fourth strain gauge 3D. 4B is a second thin film conductor connected to the other end of the first strain gauge 3A, and 4C is a third thin film conductor connected to one end of the second strain gauge 3B.
4D is a fourth thin film conductor connected to the other end of the second strain gauge 3B and one end of the third strain gauge 3C, and 4E is the other end of the third strain gauge 3C. The fifth thin film conductor 4F is connected to one end of the fourth strain gauge 3D, and the outer end thereof is connected to the connection terminal portions 5A, 5B, 5C, 5D. , 5E, and 5F.

Here, the thin film conductor 4 is formed of a good conductive material such as gold, aluminum, copper, etc. on the insulating film 2 using a vacuum deposition method, a sputtering method, or the like. The strain gauge 3 and the thin film conductor 4 are s.

It is integrally covered with a passivation film 6 consisting of two films and an S+sN- film.

Note that the above configuration is not particularly different from the basic configuration of a stress sensor according to the prior art.

Next, reference numeral 7 denotes a circuit board formed in the shape of a covered tube, such as a printed circuit board made of synthetic resin, and the circuit board 7 is bonded onto the diaphragm 1 via the insulating film 2 so as to cover the passivation film 6. It is fixed by means such as. The top surface 7A of the circuit board 7 has connection terminal portions 5A to 5A.
6 wiring insertion holes at positions corresponding to 5F 8.8. ...
In addition, a chip linear thermistor 9 and a chip resistor 11, which will be described later, are provided on the surface of the top surface portion 7A, and circuit components such as monolithic IC semiconductor elements and resistance elements are provided on the front or back surface. (not shown) is installed.

Further, reference numeral 9 denotes a chip linear thermistor (hereinafter referred to as linear thermistor 9) as a zero point temperature compensation resistor provided on the surface side of the top surface portion 7A of the circuit board 7, and the linear thermistor 9 has a positive resistance against temperature changes. It is constructed as a highly temperature-dependent positive characteristic linear thermistor that changes resistance linearly. The linear thermistor 9 is connected between the connection terminal portions 5B and 5C via lead wires 10A and IOB, such as bonding wires, which are inserted into the pair of wire insertion holes 8, 8.

On the other hand, 11 is a chip resistor as a zero point adjustment resistor provided on the surface side of the top surface portion 7A of the circuit board 7, similar to the linear thermistor 9 described above, and the chip resistor 11 does not change its resistance with respect to temperature changes. In other words, the temperature dependence is extremely small (
, and is configured as a laser trimmable resistor. The chip resistor 11 is connected between the connecting terminal portions 5F and 5B via lead wires 12A and 12B inserted through a pair of wiring insertion holes 8 and 8.

Furthermore, 13 is a connecting terminal portion 5A via a lead wire 14.
15 indicates a ground terminal connected via a lead wire 16. 17A and 17B are one side output terminals connected to both ends of the linear thermistor 90, and the output terminal 17A is a high voltage side output terminal located on the high voltage side (power supply terminal 13 side) of the linear thermistor 9, and the output terminal 1
7B is a low voltage side output terminal located on the low voltage side (earth terminal 15 side) of the linear thermistor 9. Also 18A18B
is the output terminal on the other side connected to both ends of the chip resistor 11, the output terminal 18A is the high voltage side output terminal located on the high voltage side (power supply terminal 13 side) of the chip resistor 11, and the output terminal 18B is the low voltage side output terminal of the chip resistor 11. This is a low voltage side output terminal located on the ground terminal 15 side (earth terminal 15 side).

The present embodiment is configured as described above, but next we will explain how to select the resistance value and temperature coefficient of the linear thermistor 9, which is the zero-point temperature compensation resistor, and the chip resistor 11, which is the zero-point adjustment resistor.
This section describes how to select the resistance value of .

First, with the linear thermistor 9 and chip resistor 11 removed, the - side output terminals 17A and 17B are short-circuited, and the other side output terminals 18A and 18B are short-circuited, and a bridge is created using only the strain gauges 3A to 3D. When a circuit is assembled and a predetermined voltage is applied between the power supply terminal 13 and the earth terminal 15, if the resistance value and temperature coefficient of each strain gauge 3A to 3D are known, the - side output terminal 17A, The output voltage output between the 17B side and the other output terminals 18A and 18B can be easily calculated.

As a result of this calculation, if the temperature characteristics of the output voltage from the bridge circuit change in the positive direction with respect to temperature rise, as shown by the solid line A in FIG. It is necessary to lower the output voltage to an output voltage that is not affected by temperature as shown by the dotted line B in FIG. Therefore, when the linear thermistor 9 is mounted on the circuit board 7, the low voltage side output terminal 17B is selected as the output terminal of the bridge circuit (see FIG. 6). As a result, when the temperature rises, the resistance value of the linear thermistor 9 having positive characteristics increases, so that the zero point temperature can be maintained at a constant value as indicated by the dotted line B in relation to the partial pressure ratio. Similarly, if the temperature characteristics of the output voltage from the bridge circuit change in the negative direction with respect to temperature rise, as shown by the solid line C in FIG. Since it is necessary to obtain an output voltage that is not affected by temperature as shown by the dotted line B in FIG. 7, the high voltage side output terminal 17A is selected as the output terminal of the bridge circuit (see FIG. 8). Thus, one output terminal 1 located on the linear thermistor 9 side
The terminals to be used for 7A and 17B are determined.

Second, assuming that a linear thermistor with a resistance value (for example, 100Ω) at a predetermined room temperature is connected between the lead wire 10A and IOB, the zero point should be set so that the output voltage from the bridge circuit is O■. Calculate and select the resistance value of the chip resistor 11, which is an adjustment resistor, and the output terminal 18A on the other side.

The output terminal to be used is determined from among the 18B.

Third, the chip resistor 11 selected by the calculation described above.
Calculate the resistance value of the linear thermistor such that the output voltage from the bridge circuit becomes 0 when the bridge circuit including the bridge circuit is heated to a predetermined high temperature. Note that this resistance value calculation can be easily performed because the chip resistor 11 has no temperature dependence (and the resistance values and temperature coefficients of the strain gauges 3A to 3D are known. The resistance value of the linear thermistor at a predetermined high temperature and the resistance value of the linear thermistor at a predetermined normal temperature (for example, 100
The temperature coefficient of the linear thermistor 9 to be actually used is calculated from the resistance difference between the linear thermistor 9 and the temperature difference.

According to the above calculation procedure, the terminals to be used for the entire bridge circuit, the resistance value and temperature coefficient of the linear thermistor 9, and the resistance value of the chip resistor 11 are calculated.

Therefore, the linear thermistor 9 selected in this way
is mounted on the circuit board 7 and connected to the connection terminal parts 5B and 5C via the lead wires 10A and 10B, and a chip resistor 11 is mounted on the circuit board 7 and connected to the connection terminal part 5F via the lead wires 12A and 12B. , 5E.

After that, a predetermined voltage is applied between the power supply terminal 13 and the earth terminal 15, and the - side output terminal 17A is applied.

17B and the output terminals 18A and 18B on the other side, one of which is determined as described above, for example, the output terminals 17A and 18A, is used as the respective output terminal, and the output voltage between the output terminals 17A and 18A is set as the respective output terminal. measure. If fine adjustment of the zero point is required, the chip resistor 11 may be laser trimmed.

In the stress sensor of this embodiment in which the zero point temperature is compensated as described above, when a load such as hydraulic pressure acts on the strain-generating portion IA of the diaphragm 1 and the strain-generating portion IA is distorted, the strain gauges 3A to 3
The electrical resistance of D changes, and the output terminals 17A-18 to be used
It generates an output voltage between A and A according to the load, making it possible to measure stress with high precision.

In addition, the zero point temperature compensation resistor according to this embodiment uses a chip linear thermistor 9, and the thermistor 9 has an insulating film 2.
(Since it only needs to be mounted on the circuit board 7, the number of parts can be reduced, and the manufacturing process can be significantly reduced.

Moreover, since the chip linear thermistor 9 can be a solid element having linear characteristics against temperature changes, the element can be easily selected.

Furthermore, the resistance values, temperature coefficients, etc. of the linear thermistor 9 and chip resistor 11 can be determined by simple calculation procedures, and those with predetermined characteristics can be selected, simplifying the adjustment process for zero point temperature compensation. can do.

In the embodiment, a chip linear thermistor 9 with positive characteristics was used as the zero point temperature compensation resistor, but a chip linear thermistor with negative characteristics with respect to temperature changes may also be used. The resistor is not limited to a thermistor as long as it has linear characteristics; for example, a thick film resistor may be used.

Furthermore, although the chip resistor 11 with extremely low temperature dependence is shown as an example of the zero point adjustment resistor, any resistor that has low temperature dependence and can be laser trimmed may be used, for example, a thick film or thin film resistor may be used. , on the other hand, a fixed metal film resistor or the like may be used.

Further, in the embodiment, the chip linear thermistor 9 and the chip resistor 11 have been described as being provided on the front surface of the circuit board 7, but it goes without saying that they may be provided on the back surface thereof.

〔Effect of the invention〕

As described in detail above, the stress sensor according to the present invention has a structure in which the zero-point temperature compensation resistor and the zero-point adjustment resistor are provided on a circuit board separate from the diaphragm, so that the number of parts is small, and The manufacturing process can be significantly shortened, and the resistance value, temperature coefficient, etc. of these resistors can be determined by simple calculation procedures, so the zero point temperature adjustment process can be simplified, and the zero point temperature Since the accuracy of compensation can be improved, the stress measurement accuracy can be improved.

[Brief explanation of the drawing]

1 to 6 relate to embodiments of the present invention, FIG. 1 is a longitudinal sectional view of the stress sensor according to the embodiment, and FIG. 2 is a front view of the stress sensor with the circuit board and passivation film removed. Figure 3 is a circuit diagram showing Figure 2 as a strain gauge connection circuit, Figure 4 is a circuit diagram showing the circuit in Figure 3 with a zero point temperature compensation resistor and a zero point adjustment resistor connected, and Figure 3 is a circuit diagram showing Figure 2 as a strain gauge connection circuit. Figure 5 is a diagram showing the case where the output voltage has positive characteristics before zero point temperature adjustment, Figure 6 is a circuit diagram showing the selection state of the output terminal in the case of Figure 5, and Figure 7 is a diagram showing the case where the output voltage has positive characteristics before zero point temperature adjustment. FIG. 8 is a diagram showing the case where the output voltage has a negative characteristic; FIG. 8 is a circuit diagram showing the selection state of the output terminal in the case of FIG. 7; FIG. 9 is a circuit diagram showing a bridge circuit of a stress sensor according to the prior art. be. l... diaphragm, IA... strain generating part, IC...
Film formation surface, 2... Insulating film, 3A to 3D... Semiconductor strain gauge 4A to 4E... Thin film conductor, 5A to 5F... Connection terminal portion, 7... Circuit board, 8...・Wiring insertion hole,
9...Chip linear thermistor (resistance for zero point temperature compensation), 10A, IOB, 12A, 12B, 14.16...
・Lead wire, 11...Chip resistor (resistance for zero point adjustment)
, 13...Power terminal, 15...Earth terminal, 17A
, 17B... - side output terminal, 18A, 18B...
Output terminal on the other side. Patent applicant: Hitachi Construction Machinery Co., Ltd. Patent attorney Kazuhiko Hirose

Claims (3)

[Claims] (1) A Wheatstone bridge circuit is constructed by connecting a diaphragm having a strain-generating portion, an insulating film provided on the diaphragm, a plurality of semiconductor strain gauges provided on the insulating film, and each of the semiconductor strain gauges. In the stress sensor, the diaphragm is provided with a circuit board located above each of the semiconductor strain gauges, and the circuit board includes a conductor having a large temperature dependence. A zero point temperature compensation resistor made of a resistor and a zero point adjustment resistor made of a resistor with small temperature dependence are provided, and the zero point temperature compensation resistor, the zero point adjustment resistor, and each of the conductors are connected by a lead wire, A stress sensor comprising a Wheatstone bridge circuit with zero point temperature compensation. (2) The zero point temperature compensation resistor is a linear thermistor with positive or negative characteristics whose resistance changes linearly with temperature changes, and the zero point adjustment resistor is a chip resistor or thick film resistor that can be laser trimmed. The stress sensor according to item (1). (3) In the Wheatstone bridge circuit, when the zero-point temperature compensation resistance side is used as one output terminal and the zero-point adjustment resistance side is used as the other output terminal, the temperature characteristics of the output voltage before zero-point temperature adjustment are , the stress sensor according to claim 1, wherein either the high voltage side or the low voltage side of the zero point temperature compensation resistor is configured as one output terminal depending on the negative value.