JP2017009490A - Distortion detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distortion detection device capable of performing output with high linearity.SOLUTION: A distortion detection device comprises: a deformable body distorted according to inputted loading; a piezoresistance 20 provided on the deformable body and changing a resistance value according to the distortion; an input resistance 30 having a predetermined resistance value; and a computing amplifier 40 including a non-inverting input terminal 41 to which a first electric potential composed of a predetermined constant potential is connected, an inverting input terminal 42 to which a second electric potential composed of a predetermined constant potential different from the first electric potential is connected via the input resistance 30 one terminal of which is connected with one terminal of the piezoresistance 20, and an output terminal 43 to which the other terminal of the piezoresistance 20 is connected.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a strain detection device that detects strain generated in a deformable body.

  Conventionally, for example, a technique described in Patent Document 1 is a technique for detecting distortion that has been used.

  The linear detection bridge circuit described in Patent Document 1 forms a Wheatstone bridge with three fixed resistors and one variable resistor, and a constant current circuit, a differential amplifier, and a current control circuit are connected to the Wheatstone bridge. When the constant current circuit supplies a constant current to the Wheatstone bridge, and the resistance value of the variable resistor changes due to the input of the load and the output voltage is generated in the Wheatstone bridge, the differential input voltage of the differential amplifier changes, and the constant current To control. By controlling the current supplied to the Wheatstone bridge in this way, the linearity of the output of the Wheatstone bridge is maintained even when the variable resistor has a large change width.

JP-A-53-45275

  In the technique described in Patent Document 1, a current proportional to one of the output voltages of the Wheatstone bridge is fed back as a drive current. However, since the linearity correction method varies depending on the proportionality constant between the output voltage and the feedback current, the proportionality constant is set depending on the value of the fixed resistance or variable resistance in order to maintain the linearity of the output voltage of the Wheatstone bridge. Individual adjustments are required.

  Therefore, there is a demand for a strain detection device that can perform output with high linearity without adjusting the proportionality constant.

  A characteristic configuration of the strain detection device according to the present invention includes a deformable body that is distorted according to an input load, a piezoresistor that is provided on the deformable body and changes a resistance value according to the strain, and a predetermined resistance value. A non-inverting input terminal to which a first potential having a predetermined constant potential is connected, and one terminal of the piezoresistor and one terminal of the input resistor are connected via the input resistor. And an operational amplifier having an inverting input terminal to which a second potential having a predetermined constant potential different from the first potential is connected, and an output terminal to which the other terminal of the piezoresistor is connected. It is in.

  With such a characteristic configuration, a voltage that is inversely proportional to the input resistance and proportional to the piezoresistor can be obtained as the output of the operational amplifier. Therefore, an output having high linearity with respect to the change in the resistance value of the piezoresistor can be obtained. can get. Therefore, an output with high linearity can be obtained with respect to a change in the resistance value of the piezoresistor without individually adjusting the linearity. Therefore, it is possible to detect the strain with high accuracy in the region where the resistance change of the piezoresistor with respect to the applied strain to the piezoresistor is linear. Further, by suppressing the non-linear variation of the resistance change of the piezoresistor with respect to the applied strain, the non-linear correction function can be made common, and the strain can be detected with high accuracy without individual adjustment.

  Preferably, the input resistance and the piezoresistor are semiconductors made of the same material and have the same conductivity, and the carrier concentration ratio between the input resistance and the piezoresistor is 0.5 or more and 2.0 or less. It is.

  With such a configuration, by arranging the input resistor and the piezoresistor so that the temperature difference between the input resistor and the piezoresistor becomes small, the change in the resistance value due to the temperature change at the time of no distortion is canceled, and the temperature Detection with good characteristics is possible.

  Further, the rate of change in resistance value of the input resistance when a predetermined load is input to the deformable body is the ratio of change in resistance value of the piezoresistor when the predetermined load is input to the deformable body. It is preferable that the ratio is smaller than the ratio.

  With such a configuration, it is possible to suppress non-linearity due to a change in the resistance value of the input resistance when a load is input in the output of the operational amplifier. As the change amount of the resistance value of the input resistance is smaller than the change amount of the resistance value of the piezoresistor, an output with higher linearity with respect to the change of the piezoresistance can be obtained.

  In addition, the input resistance is provided in the same adhesive structure as the piezoresistor in a portion where the amount of strain generated when a load is input to the deformable body is smaller than the amount of strain generated in the portion where the piezoresistor is provided. Preferably.

  With such a configuration, for example, the distortion amount of the input resistance can be made smaller than the distortion amount of the piezoresistor, and the change in the input resistance with respect to the input of the load can be suppressed. In addition, since the adhesive structure is the same, it is possible to make the amount of distortion caused by the thermal expansion coefficient difference between the adhesive and the deformed body close to each other by the input resistance and the piezo resistance, and no load is applied. The fluctuation of the ratio of the resistance value to the temperature of the piezoresistance and the input resistance at the time is suppressed. For this reason, it is effectively prevented that the strain detection result obtained by combining the piezoresistor and the input resistance when no load is applied varies with temperature, and accurate strain detection is possible.

  In addition, it is preferable that the piezoresistor and the input resistor are simultaneously manufactured in the same process and formed as a single semiconductor chip.

  With such a configuration, it becomes possible to make the temperature characteristics of the resistance value and the piezoresistance coefficient between the piezoresistor and the input resistor closer, and the temperature of the ratio between the piezoresistor and the resistance value of the input resistor when no load is applied. When there is no applied load, the input resistance and the piezo resistance can bring the amount of distortion due to the shrinkage of the adhesive during curing and the difference in thermal expansion coefficient between the adhesive and the deformed body close to each other. The variation of the strain amount applied to the piezoresistor and the input resistor due to temperature can be equivalent, and the resistance value of both resistors and the ratio of the resistance variation due to the piezoresistive effect can be made close. Variations in the ratio of the resistance values of the two resistors when no load is applied due to temperature are suppressed, and variations due to output temperature are suppressed.

  Further, a plurality of the piezoresistors, the input resistors, and the operational amplifiers are provided, and the piezoresistors are provided at a plurality of positions where the deformation amount of the deformable body is different, and based on the difference between the outputs of the plurality of operational amplifiers. It is preferable to calculate the input load. It is preferable that the distortion amount of the plurality of input resistors accompanying the deformation of the deformable body is smaller than the distortion amount of the most distorted piezoresistor among the piezoresistors.

  In this way, noise is applied equally to the outputs of multiple operational amplifiers by providing multiple distortion detection circuits with piezoresistors, input resistors, and operational amplifiers, and using the difference between the outputs of multiple operational amplifiers as detection signals. Can be canceled and detection with higher accuracy becomes possible.

It is the figure which showed an example of the deformation body with which a distortion | strain detector is provided. It is the figure which showed the state of the deformation body which has bent. It is a circuit diagram of a distortion detection circuit. It is the figure which showed the relationship between the thickness of the semiconductor chip with which a distortion detection circuit is comprised, and distortion. It is a circuit diagram of a distortion detection circuit according to another embodiment.

  The strain detection apparatus according to the present invention detects a load input to the deformable body. Hereinafter, the strain detection apparatus 1 of the present embodiment will be described.

  The strain detection apparatus 1 includes a deformable body 10 that is distorted according to an input load, and a strain detection circuit 50. A perspective view of the deformable body 10 is shown in FIG. The deformable body 10 is configured in, for example, a rectangular plate shape using a material that is distorted according to an input load. When a load is input to the load input unit 12 set at a predetermined position, the deformable body 10 is supported at a position where the deformable body 10 can be distorted as shown in FIG.

  FIG. 3 shows a circuit diagram of the distortion detection circuit 50. The strain detection circuit 50 includes a piezoresistor 20, an input resistor 30, and an operational amplifier 40. In the present embodiment, the piezoresistor 20, the input resistor 30, and the operational amplifier 40 are manufactured using a known semiconductor manufacturing process.

  The piezoresistor 20 is provided in a portion of the deformable body 10 where distortion occurs when a load is input, and the piezoresistor 20 is distorted according to the amount of strain of the deformable body 10. The piezoresistor 20 is made of a single crystal semiconductor and changes its resistance value according to the strain. If the deformable body 10 is fixed in a state in which both ends do not rotate, as shown in FIG. 2, a surface 13 on which the load in the deformable body 10 is input (the surface on which the load input portion 12 is set) is provided. When attention is paid, a pair of tensile parts A and a pair of compression parts B appear. In the part C between the tension part A and the compression part B, almost no distortion occurs. In the present embodiment, the piezoresistor 20 is provided in at least one of each of the pair of tension parts A and each of the pair of compression parts B. Thereby, it is possible to detect the strain generated in the deformable body 10 by the change in the resistance value.

  The input resistor 30 has a predetermined resistance value. The input resistor R may be formed using a semiconductor.

  The operational amplifier 40 has a non-inverting input terminal 41, an inverting input terminal 42, and an output terminal 43. The non-inverting input terminal 41 is connected with a first potential having a predetermined constant potential. The predetermined constant potential refers to a potential having a constant potential difference from a reference potential (ground potential). In the example of FIG. 3, a non-inverting input terminal 41 is connected to a constant voltage source 61 that outputs a first potential.

  Here, the piezoresistor 20 and the input resistor 30 are each provided with a pair of terminals. One terminal of the pair of piezoresistors 20 and one terminal of the pair of input resistors 30 are connected to the inverting input terminal 42. The inverting input terminal 42 is connected to a second potential having a predetermined constant potential different from the first potential via the input resistor 30. That is, the input resistor 30 has a second DC potential different from the first potential connected to the other terminal of the pair of terminals, and is connected to the inverting input terminal 42 to one terminal of the pair of terminals. . In the example of FIG. 3, a constant voltage source 62 that outputs the second potential is connected to the other terminal of the input resistor 30.

  The output terminal 43 is connected to the other of the pair of terminals of the piezoresistor 20. As described above, one terminal of the piezoresistor 20 is connected to the inverting input terminal 42. Therefore, the piezoresistor 20 is used as a feedback resistor provided across the output terminal 43 and the inverting input terminal 42 of the operational amplifier 40.

  By configuring the strain detection circuit 50 in this way, the strain detection circuit 50 is proportional to the potential difference between the first potential and the second potential and the resistance value of the piezoresistor 20, and inversely proportional to the resistance value of the input resistor 30. Output voltage. The resistance value of the piezoresistor 20 changes due to the load input to the deformable body 10, and as a result, the output voltage of the strain detection circuit 50 changes. At this time, the first potential connected to the non-inverting input terminal 41 of the operational amplifier 40 and the second potential connected to the inverting input terminal 42 of the operational amplifier 40 do not change, and therefore, according to the resistance value of the piezoresistor 20. The voltage output from the output terminal 43 of the operational amplifier 40 changes. As described above, the strain detection circuit 50 can extract a change in the resistance value according to the strain as a change in the voltage value. Therefore, the strain detection circuit 50 functions as a resistance-voltage conversion circuit, and based on the voltage output from the output terminal 43, Can be detected.

  According to the strain sensing device 1 having the above configuration, a voltage proportional to the piezoresistor 20 can be obtained as an output of the operational amplifier 40 in inverse proportion to the input resistor 30, so that a change in the resistance value of the piezoresistor 20 can be obtained. Output with high linearity can be obtained. Therefore, an output with high linearity can be obtained with respect to a change in resistance value of the piezoresistor 20 without individually adjusting the linearity. Therefore, the strain can be accurately detected in a region where the resistance change of the piezoresistor 20 with respect to the applied strain to the piezoresistor 20 is linear. Further, by suppressing the non-linear variation of the piezoresistor 20 with respect to the applied strain, the non-linear correction function can be made common, and the strain can be detected with high accuracy without individual adjustment.

  Further, in the strain detection device 1, the rate of change in the resistance value of the input resistor 30 when a predetermined load is input to the deformable body 10 is the same as that of the piezoresistor 20 when the predetermined load is input to the deformable body 10. What is smaller than the rate of change of the resistance value may be used. For example, the rate of change in the resistance value of the input resistor 30 when a predetermined load is input is sufficiently smaller than the rate of change in the resistance value of the piezoresistor 20, and preferably the rate of change in the resistance value of the input resistor 30. However, it is good that it is 1/100 or less of the rate of change of the resistance value of the piezoresistor 20. By doing so, the rate of change of the input resistance 30 with respect to the input of the load can be reduced relative to the rate of change of the piezoresistor 20, and the rate of change with respect to the input resistor 30 can also be reduced.

  According to the strain detection apparatus 1 having the above configuration, non-linearity due to a change in the resistance value of the input resistor 30 when a load is input can be suppressed in the output of the operational amplifier 40. As the change amount of the resistance value of the input resistor 30 is smaller than the resistance value of the input resistor 30, an output with higher linearity with respect to the change of the piezoresistor 20 is obtained.

  Further, in the strain detection device 1, the input resistor 30 is connected to the piezoresistor 20 at a portion where the amount of strain generated when a load is input to the deformable body 10 is smaller than the amount of strain generated at the portion where the piezoresistor 20 is provided. It is good to provide with the same adhesion structure. Desirably, the input resistor 30 is preferably provided in a portion having a distortion amount of 1/100 or less with respect to the distortion amount of the portion to which the piezoresistor 20 is bonded, with the same adhesive structure as the piezoresistor 20. . Specifically, the input resistor 30 is provided at a portion where the amount of strain generated is smaller than the tensile portion A or the compressed portion B of FIG. “Same bonding structure” means that when the piezoresistor 20 and the input resistor 30 are formed of different chips, the piezoresistor 20 is bonded to the deformable body 10 and the input resistor 30 is bonded to the deformable body 10. It means that the same adhesive, the same amount of use per unit area, and the same work environment are used.

  According to the strain detection device 1 having the above configuration, for example, the strain amount of the input resistor 30 can be made smaller than the strain amount of the piezoresistor 20, and the change of the input resistor 30 with respect to the input of the load can be suppressed. Further, since the adhesive structure is the same, it is possible to make the input resistor 30 and the piezoresistor 20 approach the amount of distortion caused by the shrinkage of the adhesive during curing and the difference in thermal expansion coefficient with respect to the adhesive and the deformable body 10 between the input resistor 30 and the piezoresistor 20. Variation in the ratio of the resistance value to the temperature of the piezoresistor 20 and the input resistor 30 when no voltage is applied is suppressed. For this reason, it is effectively prevented that the strain detection result obtained by combining the piezoresistor 20 and the input resistor 30 when no load is applied varies depending on the temperature, and accurate strain detection is possible.

  In the strain sensing device 1, the input resistor 30 and the piezoresistor 20 are semiconductors made of the same material and have the same conductivity, and the carrier concentration ratio between the input resistor 30 and the piezoresistor 20 is 0.5 or more. It is good if it is 0 or less.

  According to the strain detection device 1 having the above-described configuration, the strain detection circuit 50 is configured so as to have no strain by disposing the input resistance 30 and the piezoresistor 20 so that the temperature difference between the input resistance 30 and the piezoresistor 20 is reduced. The change in resistance value due to the temperature change is canceled, and detection with good temperature characteristics becomes possible.

  Further, in the strain sensing device 1, the piezoresistor 20 and the input resistor 30 are preferably manufactured simultaneously in the same process and formed as a single semiconductor chip.

  According to the strain detection device 1 having the above-described configuration, it is possible to make the resistance value of the piezoresistor 20 and the input resistor 30 and the temperature characteristics of the piezoresistive coefficient closer, and the piezoresistor 20 and the input resistor 30 when no load is applied. Variations in the resistance value ratio and fluctuations due to temperature can be reduced. Further, the shrinkage at the time of curing of the adhesive at the time of bonding, and the strain amount due to the difference in thermal expansion coefficient with respect to the adhesive and the deformable body 10 can be made closer to the input resistor 30 and the piezoresistor 20, and the piezo when there is no applied load. Variations in temperature of the strain applied to the resistor 20 and the input resistor 30 can be equivalent, and the resistance values of both resistors and the ratio of resistance variation due to the piezoresistance effect can be made close. Variations in the ratio of the resistance values of the two resistors when no load is applied due to temperature are suppressed, and variations due to output temperature are suppressed.

  Here, Japanese Patent Application Laid-Open No. 2006-266683 discloses a relationship between a chip surface position and a chip surface strain using a chip thickness as a parameter. This relationship is shown in FIG. 4 and it can be seen that strain is hardly transmitted to the end of the chip. From this, the input resistor 30 is arranged at the end of the chip, and the piezoresistor 20 is arranged at a position away from the end of the chip, so that the input resistance 30 is changed with respect to the change amount of the resistance value of the piezoresistor 20. The amount of change in resistance value can be made sufficiently small. Moreover, the influence of the resistance value of the input resistance 30 can be suppressed by arranging the input resistance 30 on the circuit board and holding the board so that the board is not deformed. Furthermore, by providing the deformable body 10 with a low Young's modulus (preferably 1 GPa or less) through a thick adhesive layer, transmission to the input resistor 30 can be suppressed.

  The input resistor 30 may be disposed at the end of the chip along the direction in which the tensile / compressive strain is applied on the semiconductor chip on which the piezoresistor 20 is formed, or may be disposed on the circuit board. Also good. Furthermore, you may adhere | attach on the deformation | transformation body 10 through a thick adhesive layer with a low Young's modulus.

[Other Embodiments]
In the above embodiment, the example in which the strain detection device 1 includes one strain detection circuit 50 has been described. However, the strain detection device 1 includes the piezoresistor 20, the input resistor 30, and the operational amplifier 40. It is also possible to have a configuration in which a plurality of positions are provided at different positions and the input load is calculated based on the difference between the outputs of the plurality of operational amplifiers 40.

  FIG. 5 shows an example in which two strain detection circuits 50 each including a piezoresistor 20, an input resistor 30, and an operational amplifier 40 are provided. One operational amplifier 40 is provided with an input resistor 31 as an input resistor 30 and a piezoresistor 21 as a feedback resistor. The other operational amplifier 40 is provided with an input resistor 32 as an input resistor 30 and a piezoresistor 22 as a feedback resistor. A constant voltage source 61 is connected to the non-inverting input terminal 41 of both operational amplifiers 40, and a constant voltage source 62 is connected to the inverting input terminal 42 of both operational amplifiers 40 via an input resistor 31 and an input resistor 32, respectively. Connected. It is possible to input the outputs of both operational amplifiers 40 connected in this way to the differential amplifier 70 and use the difference as a detection signal. In this way, by using the difference between the outputs of the two operational amplifiers 40 as a detection signal, it is possible to cancel the noise equally applied to the outputs of the two operational amplifiers 40 and to detect with higher accuracy. Become.

Note that the differential amplifier 70 is an example, and instead of the differential amplifier 70, a device that calculates the difference between the outputs of the two operational amplifiers 40 can be used.
In this case, the input resistor 31 and the input resistor 32 are preferably provided in the portion C in FIG. 2, and the piezoresistor 21 and the piezoresistor 22 are preferably provided in the tension portion A and the compression portion B in FIG. Also in this case, the input resistor 31, the input resistor 32, the piezoresistor 21, and the piezoresistor 22 are preferably provided on the deformable body 10 with the same adhesive structure.

  The present invention can be used in a strain detection device that detects strain generated in a deformable body.

1: Strain detector 10: Deformation body 20: Piezoresistor 30: Input resistance 40: Amplifier 41: Non-inverting input terminal 42: Inverting input terminal 43: Output terminal

Claims (6)

A deformable body that distorts according to the input load;
Piezoresistors that are provided on the deformable body and change a resistance value according to strain;
An input resistance having a predetermined resistance value;
A non-inverting input terminal to which a first potential consisting of a predetermined constant potential is connected, one terminal of the piezoresistor and one terminal of the input resistor are connected to the first potential via the input resistor. An operational amplifier having an inverting input terminal to which a second potential consisting of different predetermined constant potentials is connected, and an output terminal to which the other terminal of the piezoresistor is connected;
A strain detection device comprising:   The input resistance and the piezoresistor are semiconductors made of the same material and have the same conductivity, and a ratio of carrier concentration between the input resistance and the piezoresistor is 0.5 or more and 2.0 or less. The strain detection apparatus described.   The rate of change in resistance value of the input resistance when a predetermined load is input to the deformable body is greater than the rate of change of resistance value in the piezoresistor when the predetermined load is input to the deformable body. The strain detection device according to claim 1, wherein the strain detection device is smaller.   The input resistance is provided at a site where an amount of strain generated when a load is input to the deformable body is smaller than an amount of strain generated at a site where the piezoresistor is provided with the same adhesive structure as the piezoresistor. Item 4. The strain detection device according to any one of Items 1 to 3.   The strain detection apparatus according to any one of claims 1 to 4, wherein the piezoresistor and the input resistor are manufactured simultaneously in the same process and formed as a single semiconductor chip.   A plurality of the piezoresistors, the input resistors, and the operational amplifiers are provided, and a plurality of the piezoresistors are provided at positions where the distortion amount of the deformable body is different, and the input is performed based on a difference between outputs of the plurality of operational amplifiers. The strain detection apparatus according to any one of claims 1 to 5, wherein a load is calculated.

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