JP2016138844A - Strain sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a strain sensor capable of obtaining sufficient sensitivity relative to even comparatively low pressure.SOLUTION: A strain sensor includes: a fixing part 110; a diaphragm part 120 connected to the fixing part 110; a piezoresistance 130 provided to the diaphragm part 120; a first beam 121 connected to the fixing part 110; a second beam 122 which is connected to the fixing part 110 and which extends in a direction orthogonal to the first beam 121; and a connection part 123 for connecting the first beam 121 and the second beam 122.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a strain sensor including a detection unit that detects an input to an electronic device.

  Conventionally, pressure sensors have been used in electronic devices such as information devices that operate by detecting pressure. A conventional pressure sensor is shown in FIG.

  As shown in FIG. 5, the conventional pressure sensor includes a support frame 11 having a hollow portion, a diaphragm 12 formed on the bottom surface of the hollow portion and deformed by application of pressure, and provided on the diaphragm 12. A pressure detection unit 13 that detects pressure as an electrical signal by being distorted by deformation and an electrode 14 are provided. Diaphragm 12 includes a thin region and a thick region that includes part or all of pressure detector 13 and is thicker than the thickness of the thin region.

  The support frame 11 is formed in a substantially square shape, and SiO2 films 11b and 11b serving as masks for etching are formed on both surfaces of the silicon substrate 11a.

  The thick region is formed on one surface or both surfaces of the diaphragm 12 in a substantially flat or protruding shape, and is formed by providing a thick portion on the diaphragm 12 formed in a substantially uniform thickness.

  The pressure detection unit 13 includes a plurality of piezoresistive units 13 a to 13 d, and the plurality of piezoresistive units 13 a to 13 b are respectively arranged on the outer peripheral side of the diaphragm 12.

  Next, an operation example of the pressure sensor device will be described with reference to FIG. When the diaphragm 12 receives pressure from the outside, the diaphragm 12 is deformed according to the magnitude of the pressure. Then, the pressure detection unit 13 provided in the diaphragm 12 is also distorted together with the diaphragm 12, and the resistance values of the plurality of piezoresistors 13a to 13d arranged on the outer periphery of the diaphragm 12 are changed. By measuring the change in the resistance value, the pressure applied to the pressure sensor device 10 is measured. (Patent Document 1)

JP 2002-71492 A

  In the conventional pressure sensor shown in Patent Document 1, depending on the thickness and material of an object whose pressure is to be detected, there is a problem that the amount of strain transmitted to the pressure detection unit becomes small and sufficient sensitivity cannot be obtained. .

  Therefore, an object of the present disclosure is to provide a strain sensor that can obtain sufficient sensitivity even with a relatively small pressure.

  In order to solve the above-described problem, the present disclosure includes a fixed portion, a diaphragm portion connected to the fixed portion, and a piezoresistor provided in the diaphragm portion, and a first beam connected to the fixed portion. A second beam connected to the fixed portion and extending in a direction perpendicular to the first beam, and a connection portion connecting the first beam and the second beam; did.

  By making the diaphragm part of the strain sensor into a cross shape in which the first beam and the second beam are orthogonal to each other, and by providing a fixed part at the end of the diaphragm part, the cross-sectional area of the diaphragm part can be reduced. Become. Since the amount of distortion transmitted to the piezoresistor is inversely proportional to the cross-sectional area of the diaphragm portion, detection sensitivity can be improved by reducing the cross-sectional area.

Plan view of the strain sensor of the present disclosure Cross section of the same strain sensor AA line BB line cross section of the same strain sensor Diagram showing stress applied to the strain sensor Diagram showing a conventional pressure sensor

(Embodiment 1)
Hereinafter, an embodiment of a strain sensor of the present disclosure will be described in detail with reference to the accompanying drawings.

  FIG. 1 illustrates a configuration of a strain sensor according to an embodiment of the present disclosure. The strain sensor 100 has a fixed part 110 and a diaphragm part 120 connected to the fixed part 110. The fixed part 110 and the diaphragm part 120 are made of silicon. The diaphragm 120 includes a first beam 121 extending in the X-axis direction, a second beam 122 orthogonal to the X-axis direction and extending in the Y-axis direction, and the first beam 121 and the second beam 122. And a piezoresistor 130 and an electrode 140 are provided on top of the first beam 121 and the second beam 122. The first beam 121 and the second beam 122 are provided in pairs with the connecting portion 123 interposed therebetween. The fixed portion 110 is formed in a frame shape, and the first beam 121 is connected to the central portion of the fixed portion 110 in the X-axis direction, and the second beam 122 is connected to the central portion of the fixed portion 110 in the Y-axis direction. Has been. The strain sensor 100 is connected to a strain generating body (not shown) whose strain is measured by the fixed portion 110, and can measure strain generated in the strain generating body. In the embodiment, the fixing portion 110 is formed in a frame shape. However, the present invention is not limited to this. For example, the four fixing portions 110 having a rectangular parallelepiped shape that respectively support the first beam 121 and the second beam 122 are provided. It may be provided. However, the durability of the strain sensor 100 can be improved by forming the fixing portion 110 in a frame shape as in the embodiment.

  Next, an example of a method for manufacturing the strain sensor 100 will be described. The fixing part 110 and the diaphragm part 120 are formed by etching the silicon substrate. Thereafter, a piezoresistor 130 is formed in the diaphragm 120 by ion implantation.

  FIG. 2 is a cross-sectional view of the strain sensor 100 in FIG. The thickness of the fixing part 110 is formed so as to be larger than the thickness of the diaphragm part 120, and the thickness of the fixing part 110 and the thickness of the diaphragm part 120 are formed so as to be substantially uniform.

  The diaphragm unit 120 is provided with a piezoresistor 130 including a first piezoresistive element 131, a second piezoresistive element 132, a third piezoresistive element 133, and a fourth piezoresistive element 134. When the diaphragm 120 is deformed, the strain resistance value of the piezoresistor 130 changes. The first piezoresistive element 131, the second piezoresistive element 132, the third piezoresistive element 133, and the fourth piezoresistive element 134 form a bridge circuit. When a reference voltage is applied to the piezoresistor 130 and a load is applied from the strain generating body, a tensile stress F1 is applied in the X-axis direction, and a compressive stress F2 is applied in the Y-axis direction so as to follow it. Is done. As a result, the first beam 121 is deformed so as to extend in the X-axis direction, and the second beam 122 is deformed so as to be contracted in the Y-axis direction. The resistance value of the piezoresistor 130 changes due to the deformation of the diaphragm section 120, and the change in the resistance value is measured as a voltage change output from the bridge circuit via the electrode 140. Can be measured.

  FIG. 3 is a cross-sectional view of the strain sensor 100 in FIG. As shown in FIG. 3, the diaphragm portion 120 is formed by connecting a first beam 121, a second beam 122, and a connection portion 123, so that the first beam 121 or the second beam 122 is formed. The cross-sectional area of the portion provided with the piezoresistor 130 of the diaphragm portion 120 in the direction orthogonal to the direction in which the stub extends is reduced. Since the amount of strain of the diaphragm 120 when pressure is applied from the strain generating body is inversely proportional to the size of the cross-sectional area, compared to a structure in which the diaphragm is provided on the entire inner surface of the fixed portion like a conventional pressure sensor. The strain sensor 100 according to the embodiment can increase the strain amount of the diaphragm portion 120 when pressure is applied. Thereby, the amount of strain applied to the piezoresistor 130 increases, and the detection sensitivity of the strain sensor 100 can be improved.

  A first piezoresistive element 131 and a third piezoresistive element 133 are arranged on the first beam 121 so as to extend in the X-axis direction, and a second piezoresistive element 132 and a second piezoresistive element 132 are arranged on the second beam 122. The fourth piezoresistive element 134 is arranged so as to extend in the Y-axis direction. That is, the first piezoresistive element 131, the second piezoresistive element 132, the third piezoresistive element 133, and the fourth piezoresistive element 134 are arranged so that the longitudinal directions thereof face the connection portion.

  By arranging the piezoresistor 130 in this way, the detection sensitivity of the distortion generated in the diaphragm 120 due to the distortion generated in the strain generating body can be improved. For example, when a tensile stress F1 is applied from the strain generating body to the strain sensor 100 in the X-axis direction, a compressive stress F2 is applied to the Y-axis direction of the strain generating body. At this time, tensile stress is applied to the first piezoresistive element 131 and the third piezoresistive element 133 arranged so that the longitudinal direction is in the X-axis direction, and the resistance value is increased. On the other hand, compressive stress is applied to the second piezoresistive element 132 and the fourth piezoresistive element 134 that are arranged so that the longitudinal direction is in the Y-axis direction, and the resistance value decreases. Here, the first piezoresistive element 131 and the second piezoresistive element 132, and the third piezoresistive element 133 and the fourth piezoresistive element 134 are paired to form a bridge circuit, thereby detecting the sensitivity of the pressure sensor. Can be improved. Further, even if a bridge circuit is formed by pairing the first piezoresistive element 131 and the fourth piezoresistive element 134, and the second piezoresistive element 132 and the third piezoresistive element 133, the strain sensor 100 is similarly formed. Detection sensitivity can be improved.

  In this way, the first piezoresistive element 131 and the third piezoresistive element 133 are arranged so that the longitudinal direction is the X-axis direction, and the second piezoresistive element 132 and the fourth piezoresistive element 134 are longitudinally arranged. By arranging the direction so as to be in the Y-axis direction, it is possible to improve the detection sensitivity of the strain generated in the strain generating body.

  As shown in FIG. 1, the diaphragm 120 is formed such that the first beam 121 and the second beam 122 have the same length and intersect at the midpoints of the first beam 121 and the second beam 122. Has been. In addition, the first piezoresistive element 131 and the third piezoresistive element 133 are disposed in the central portion between the fixed portion 110 and the connection portion 123 of the first beam 121, and the second piezoresistive element 132 and The fourth piezoresistive element 134 is disposed in the central portion between the fixed portion 110 and the connecting portion 123 of the second beam 122. By adopting such a structure, the strain sensor 100 has a structure that is line-symmetric with respect to the X-axis direction and the Y-axis direction. With such a structure, output fluctuations caused by expansion and contraction due to temperature changes of the strain sensor 100 can be canceled, and detection accuracy can be improved.

  In addition, the electrode 140 is provided with electrodes necessary for measuring the amount of strain, for example, a reference voltage application electrode, an output voltage detection electrode, and a GND electrode. The number of electrodes formed on the sides can be the same. The arrangement of the dummy electrodes is formed so that the center of the strain sensor 100 is symmetrical with respect to the first beam 121 and the second beam 122.

  Next, the effect of the strain sensor of the embodiment will be described.

  In a conventional strain sensor, when there is an influence of environmental changes such as a temperature change, the diaphragm part may be deformed and the deformation of the diaphragm part due to the temperature change may be detected as a stress applied to the strain sensor. However, the strain sensor 100 according to the present disclosure can reduce the influence of temperature change.

  When a load is applied from the strain generating body to the strain sensor 100, a tensile stress F1 is applied to the diaphragm 120 in the X-axis direction, and a compressive stress F2 is applied in the Y-axis direction. On the other hand, when stress is applied to the diaphragm portion 120 due to temperature change, when the temperature of the strain sensor 100 rises, the diaphragm portion 120 expands, and therefore the stress applied to the diaphragm portion 120 in the X-axis direction and Y-axis direction is both tensile stress. (Expansion). When the temperature decreases, the stress applied to the diaphragm portion 120 in the X-axis direction and the Y-axis direction both becomes compressive stress (shrinkage). Here, since the piezoresistor 130 is disposed so as to be orthogonal to the X-axis direction and the Y-axis direction, the same stress is applied to the piezoresistor 130. Thereby, the output change by the deformation | transformation of the strain sensor 100 by a temperature change can be canceled.

  Further, the strain sensor 100 is symmetrical with respect to the center of the strain sensor 100 in the X axis direction and the Y axis direction. For this reason, the magnitudes of stress applied to the first piezoresistive element 131, the second piezoresistive element 132, the third piezoresistive element 133, and the fourth piezoresistive element 134 are the same. From this, an output change due to deformation of the strain sensor 100 due to a temperature change can be canceled more effectively.

  Since the strain sensor according to the present disclosure has excellent detection sensitivity, it can be used in information devices that can perform various controls by simple operations by input, and electronic devices such as refrigerators and washing machines that control operations based on the generated strain. Useful.

DESCRIPTION OF SYMBOLS 100 Strain sensor 110 Fixed part 120 Diaphragm part 121 1st beam 122 2nd beam 123 Connection part 130 Piezoresistor 131 1st piezoresistive element 132 2nd piezoresistive element 133 3rd piezoresistive element 134 4th Piezoresistive element 140 electrode

Claims (5)

A fixed part;
A diaphragm portion connected to the fixed portion;
Having a piezoresistor provided in the diaphragm portion;
A first beam connected to the fixed part;
A second beam connected to the fixed portion and extending in a direction perpendicular to the first beam;
A strain sensor having a connection portion connecting the first beam and the second beam. The strain sensor according to claim 1, wherein the first beam and the second beam have the same length. The piezoresistor is
The first beam is disposed in a direction in which the first beam extends;
The strain sensor according to claim 1, wherein the second beam is disposed in a direction in which the second beam extends. 2. The strain sensor according to claim 1, wherein the piezoresistor is arranged at the center of the intersection of the first beam and the second beam and the fixed portion. The strain sensor according to claim 1, wherein the fixing portion is formed in a frame shape.

Images