JP2011164042A - Physical quantity sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a physical quantity sensor which can be used for substantially all objects to be measured and which can accurately measure a strain or load on the objects to be measured regardless of changes in temperature. <P>SOLUTION: The physical quantity sensor includes: a strain element 28 that produces a strain by external force; and first and second vibrators 22a and 22b having first and second beam-shaped vibration part 23a and 23b, respectively. The first beam-shaped vibration part 23a of the first vibrator 22a has a long side substantially orthogonal to a long side of the second beam-shaped vibration part 23b of the second vibrator 22b, and by detecting a difference in vibration frequency between the two vibrators 22a and 22b, a mechanical quantity acting on the strain element 28 is detected. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a physical quantity sensor that detects strain and load acting on an object.

  In general, as physical quantity sensors for detecting strain and load acting on an object, those shown in FIGS. 5A and 5B are known (see Patent Document 1). FIG. 5A is a perspective view of a conventional physical quantity sensor. In FIG. 5 (a), reference numeral 1 denotes a vibrator composed of a crystal piece 2, and electrodes 3 that form pairs on both principal surfaces in both ends in the Z direction with the XZ plane of coordinate axes X, Y, and Z as the principal surface. , 3 'and electrodes 4 and 4' are formed, and these are used as a first vibrating part and a second vibrating part, respectively. The vibrator 1 is processed into a substantially square shape with a constant thickness, that is, the Y direction, and the electrodes 3, 3 ′ and the electrodes 4, 4 ′ are each in the X-axis direction where the main vibration of thickness shear vibration is excited. It is formed long. Therefore, the first vibration part and the second vibration part vibrate at the same vibration frequency. FIG. 5B is a block diagram showing the configuration of a pressure sensor system using this physical quantity sensor. In FIG. 5B, 5 is a measured object, 6 is the first vibrating section, and The connected first oscillation circuit, 7 is a second oscillation circuit connected to the second vibration unit, 8 is a mixer, 9 is an arithmetic circuit, and 10 is a display.

In FIG. 5 (a) (b), an external force to Q ₁ X direction is applied to the first vibrating portion in the vibrator 1 attached to the object to be measured 5, the first vibrating portion and the external force Q ₁ the A compressive force q _{1 in the} direction acts. At the same time, if an external force Q _{2 in the} direction opposite to the external force Q ₁ is applied to the second vibration portion of the vibrator 1, an extension force q _{2 in the} same direction as the external force Q ₂ acts on the second vibration portion. . As a result, distortion due to the compressive force q ₁ occurs in the first vibration part, and the oscillation frequency of the first oscillation circuit 6 including the first vibration part changes from, for example, f ₀ to f ₀ −f ₁ . . Further, the second vibrating part distortion occurs by extension force q _2, the oscillation frequency of the second oscillator circuit 7 including a second vibrating section changes from f ₀ to f ₀ + f _2. When the outputs of these two oscillation circuits are input to the mixer 8, the difference between the oscillation frequencies of the two oscillation circuits from the mixer 8 is Δ = (f ₀ + f ₂ ) − (f ₀ −f ₁ ) = f ₁ + f ₂ Is output. The arithmetic circuit 9 converts the frequency of this signal into a weight value and displays it on the display 10 as a digital value. Thereby, since a larger frequency difference can be obtained than in the case of using a physical quantity sensor having only the first vibration part or the second vibration part, measurement sensitivity can be increased. Furthermore, since fluctuations in the oscillation frequency due to temperature changes can be canceled, strain and load can be accurately measured regardless of temperature changes.

  As prior art document information relating to the invention of this application, for example, Patent Document 1 is known.

JP-A 61-57823

However, in the conventional physical quantity sensor shown in FIGS. 5A and 5B, the first vibration part and the second vibration part are arranged in parallel to each other. There was a problem of being limited. This problem will be described with reference to FIGS. FIG. 6 (a) connects the vibrator 1 of the conventional physical quantity sensor shown in FIG. 5 (a) on the side surface of the beam 11 having one end fixed and a vertical upward external force applied to the other end. Indicates the state. At this time, it is assumed that the vibrator 1 is disposed so as to straddle the neutral surface 12 of the beam. In such a case, since the compressive force acts on the first vibration part in the vibrator 1 and the extension force acts on the second vibration part, the first oscillation circuit including the first vibration part oscillation frequency of 6, for example, changes from f ₀ to f ₀ -f _1. The oscillation frequency of the second oscillator circuit 7 including a second vibrating section changes from f ₀ to f ₀ + f _2. By taking the difference between the outputs of these two oscillation circuits, it is possible to obtain a larger frequency difference than when using a physical quantity sensor having only the first vibration part or the second vibration part. Can be increased. Furthermore, since fluctuations in the oscillation frequency due to temperature changes can be canceled, strain and load can be accurately measured regardless of temperature changes.

FIG. 6B shows a state in which the vibrator 1 of the conventional physical quantity sensor is disposed above the neutral surface 12 on the side surface of the beam 11 shown in FIG. At this time, since the compressive force acts on both the first vibrating portion and the second vibrating portion in the vibrator 1, the oscillation frequency of the first oscillation circuit 6 including the first vibrating portion is, for example, from f _0. to f ₀ -f _1, the oscillation frequency of the second oscillator circuit 7 including a second vibrating section changes from f ₀ to f ₀ -f ₁ '. However, since the difference between the outputs of these two oscillation circuits is Δ = (f ₀ −f ₁ ′) − (f ₀ −f ₁ ) = f ₁ −f ₁ ′, the first vibrating section or the second The frequency difference is smaller than when a physical quantity sensor having only a vibrating part is used, and the measurement sensitivity is lowered.

FIG. 6C shows the vibrator 1 of the conventional physical quantity sensor shown in FIG. 5A arranged on the side surface of the column 13 with one end fixed and a vertical downward external force applied to the other end. Indicates the state. At this time, since substantially the same compressive force acts on both the first vibrating portion and the second vibrating portion in the vibrator 1, the oscillation frequency of the first oscillation circuit 6 including the first vibrating portion is, for example, from f ₀ to f ₀ -f _1, changes the oscillation frequency of the second oscillator circuit 7 including a second vibrating section from f ₀ to f ₀ -f _1. Therefore, since the difference between the outputs of these two oscillation circuits is Δ = (f ₀ −f ₁ ) − (f ₀ −f ₁ ) = 0, the external force cannot be measured. As described above, the transducer 1 of the conventional physical quantity sensor has a sensitivity for measuring strain and load, except in a special case where external forces acting in opposite directions act on the first and second vibrating parts arranged in parallel to each other. However, the range in which this physical quantity sensor can be applied is extremely limited.

  The present invention solves the above-mentioned conventional problems, and is applied to virtually all measured objects to measure the strain and load acting on the measured objects with high sensitivity and high accuracy regardless of temperature changes. It is an object of the present invention to provide a physical quantity sensor that can be used.

  In order to achieve the above object, the present invention has the following configuration.

  The invention according to claim 1 of the present invention includes a strain generating body that generates strain due to an external force, and a first beam-shaped vibrating section that is disposed on the strain generating body and has a vibration frequency that changes in accordance with the amount of strain. And a second vibrator having a second beam-like vibrating portion that is arranged on the strain generating body and has a vibration frequency that changes in accordance with the amount of strain. The longitudinal direction of the first beam-like vibration part in one vibrator and the longitudinal direction of the second beam-like vibration part in the second vibrator are substantially orthogonal, and the vibration frequency of the first vibrator A mechanical quantity acting on the strain generating body is detected by detecting a difference from the vibration frequency of the second vibrator. According to this configuration, the first vibrator in the first vibrator is detected. The longitudinal direction of the beam-like vibrating portion of the second vibrator and the longitudinal direction of the second beam-like vibrating portion of the second vibrator are substantially orthogonal to each other. Therefore, when an external force is applied to the strain generating body, the direction of the force acting on the first vibrator and the force acting on the second vibrator are always opposite to each other, and the first vibrator By detecting the difference between the vibration frequency of the second vibrator and the vibration frequency of the second vibrator, the mechanical quantity acting on the strain generating body is detected, so that the present invention is applied to substantially all measured objects. Thus, the strain and load acting on the measurement object can be measured with high sensitivity and high accuracy regardless of temperature change.

  According to the second aspect of the present invention, the first vibrator and the second vibrator are formed on a single semiconductor substrate. According to this configuration, the physical quantity sensor can be miniaturized. In addition, the mounting variation of the two vibrators can be eliminated, and this makes it possible to measure the strain and load acting on the minute part of the measured object with high sensitivity and high accuracy regardless of temperature changes. It has a working effect.

  As described above, the physical quantity sensor of the present invention includes a strain generating body that generates strain due to an external force, and a first beam-shaped vibrating section that is arranged on the strain generating body and whose vibration frequency changes according to the strain amount. A first vibrator having a second beam-like vibrating portion that is disposed on the strain generating body and has a vibration frequency that changes according to the amount of strain. The longitudinal direction of the first beam-like vibration part in the vibrator of FIG. 5 and the longitudinal direction of the second beam-like vibration part in the second vibrator are substantially orthogonal, and the vibration frequency of the first vibrator and the A mechanical quantity acting on the strain-generating body is detected by detecting a difference from the vibration frequency of the second vibrator, and the first beam-like vibrating portion of the first vibrator. And the longitudinal direction of the second beam-like vibrating portion of the second vibrator are substantially orthogonal to each other. When an external force is applied to the strain generating body, the direction of the force acting on the first vibrator and the force acting on the second vibrator are always in opposite directions, and the vibration of the first vibrator Since the mechanical quantity acting on the strain generating body is detected by detecting the difference between the frequency and the vibration frequency of the second vibrator, it can be applied to substantially all measured objects. Thus, the strain and load acting on the measurement object can be measured with high sensitivity and high accuracy regardless of the temperature change.

(A) Top view of physical quantity sensor according to Embodiment 1 of the present invention, (b) A-part enlarged view of (a), (c) (b) BB sectional view (A) Changes in the vibration frequency of the first and second vibrators when an external force is applied to the object to be measured in a state where the beam-like vibration parts of the first and second vibrators are vibrating in a string. The figure shown, (b) The figure which showed the change of the vibration frequency difference of the 1st, 2nd vibrator when external force acted on the to-be-measured body (A) Top view of physical quantity sensor according to Embodiment 2 of the present invention, (b) Enlarged view of part C of (a), (c) Cross sectional view along line DD of (b) (A) Top view of physical quantity sensor in Embodiment 3 of the present invention, (b) Enlarged view of E part of (a), (c) (b) GG cross-sectional view (A) Perspective view of conventional physical quantity sensor, (b) Block diagram showing the configuration of a pressure sensor system using the physical quantity sensor (A) The figure which shows the state which applied the vibrator | oscillator of the same physical quantity sensor across the neutral surface on the side of the beam where one end is fixed and the vertical upward external force is applied to the other end, (b) The figure which shows the state which has arrange | positioned the vibrator | oscillator of the physical quantity sensor located on the side surface of the beam where one end is fixed and the external force is applied to the other end above the neutral plane. The figure which shows the state which has arrange | positioned the vibrator | oscillator of the same physical quantity sensor on the side surface of the pillar to which one end is fixed and the external force perpendicular | vertical downward is applied to the other end.

(Embodiment 1)
Hereinafter, the first aspect of the present invention will be described with reference to the first embodiment. 1A is a top view of the physical quantity sensor according to Embodiment 1 of the present invention, FIG. 1B is an enlarged view of a portion A in FIG. 1A, and FIG. 1C is B in FIG. FIG. 1A to 1C, reference numeral 21 denotes a physical quantity sensor, 22a denotes a first vibrator, and the first vibrator 22a is formed by etching a semiconductor substrate such as silicon and has a mechanical quantity. The first beam-like vibrating portion 23a whose natural frequency changes by the action and the first beam-like vibrating portion 23a are surrounded and fixed to support both ends of the first beam-like vibrating portion 23a. Part 24a. In addition, a lower electrode, a piezoelectric layer made of PZT or the like, and a driving element 25a made of an upper electrode are formed in the center of the surface of the first beam-like vibrating portion 23a, and the first beam-like vibrating portion 23a is formed. Similarly, a lower electrode, a piezoelectric layer made of PZT or the like, and a detection element 26a made of an upper electrode are formed in order at the end of the vibration part 23a, and the drive element 25a and the detection element 26a have wiring patterns (not shown). Is electrically connected to the land 27a.

  In the same manner as described above, 22b is a second vibrator, and this second vibrator 22b is formed by etching a semiconductor substrate such as silicon, and the second vibration frequency is changed by the action of a mechanical quantity. The beam-like vibrating portion 23b and a fixing portion 24b surrounding the second beam-like vibrating portion 23b and supporting both ends of the second beam-like vibrating portion 23b. Further, a lower electrode, a piezoelectric layer made of PZT or the like, and a drive element 25b made of an upper electrode are formed in the center of the surface of the second beam-like vibrating portion 23b, and the second beam-like vibrating portion 23b is formed. Similarly, a lower electrode, a piezoelectric layer made of PZT or the like, and a detection element 26b made of an upper electrode are formed in order at the end of the vibration part 23b, and the drive element 25b and the detection element 26b are formed with a wiring pattern (not shown). Is electrically connected to the land 27b.

  The bottom surface of the first vibrator 22a is rigid such as a metal-based bonding material such as an Au-Au bond or an epoxy resin so that the strain generated in the strain generating body 28 is transmitted to the first vibrator 22a. It is fixedly connected by a substance 29a having At this time, the length direction of the beam-like vibrating portion 23 a in the first vibrator 22 a is arranged substantially parallel to the length direction of the strain generating body 28.

  In the same manner as described above, the bottom surface of the second vibrator 22b is made of a metal-based bonding material such as an Au-Au joint or epoxy so that the strain generated in the strain generating body 28 is transmitted to the second vibrator 22b. It is connected and fixed by a substance 29b having rigidity such as resin. At this time, the length direction of the beam-like vibrating portion 23b in the second vibrator 22b is arranged substantially parallel to the width direction of the strain generating body 28.

  Reference numeral 30 denotes a signal processing board electrically connected to the first and second vibrators 22a and 22b by a wiring pattern (not shown). The signal processing board 30 is disposed on the strain generating body 28. Yes. At this time, the signal processing board 30 is made of a flexible material such as silicone resin so that the distortion generated on the strain generating body 28 is not transmitted to the signal processing board 30 and the function of the signal processing board 30 is not impaired. A large substance is connected to the strain body 28. The strain body 28 of the physical quantity sensor 21 configured as described above is fixedly arranged on a measurement object (not shown).

In the above structure, when an AC voltage having a frequency close from the signal processing board 30 to the natural frequency f _a of the first beam-like vibrating portion 23a to the driving element 25a of the first vibrator 22a is applied, the drive The element 25a starts stretching vibration in the longitudinal direction of the first beam-like vibrating portion 23a. The first beam-like vibrating portion 23a by the stretching vibration starts string vibrates vertically at the natural frequency f _a with itself. The string vibration is received by the detection element 26a, and AC signals from the detecting elements 26a having a frequency equal to the natural frequency f _a of the first beam-like vibrating portion 23a is generated. This AC signal is phase-adjusted and amplified in the signal processing board 30 and fed back to the drive element 25a. Thus, the first beam-like vibrating portion 23a lasts string vibration at a frequency equal to the natural frequency f _a. Similarly, the signal processing of the signal processing board 30, the second beam-like vibrating portion 23b will be to sustain the string vibration at a frequency equal to the natural frequency f _b.

  FIG. 2A shows an external force applied to the measured object in a state where the first and second beam-like vibrating portions 23a and 23b of the first and second vibrators 22a and 22b vibrate vertically. It is the figure which showed the change of the vibration frequency of the 1st, 2nd vibrator | oscillators 22a, 22b when is working.

Assuming that a tensile force F in the longitudinal direction is applied to the strain body 28, the strain body 28 extends in the longitudinal direction and contracts in the width direction by a length corresponding to the Poisson's ratio of the strain body 28. Accordingly, since the stretching force to the first beam-like vibrating portion 23a acts in the first vibrator 22a, the vibration frequency 31a of the first vibrator 22a increases to f _a + f _a 'from f _a. At the same time, since the compressive force to the second beam-like vibrating portion 23b acts in the second vibrator 22b, the vibration frequency 31b of the second vibrator 22b to f _b -f _b 'from f _b Will be reduced. On the contrary, if a compressive force −F in the longitudinal direction is applied to the strain generating body 28, the strain generating body 28 contracts in the longitudinal direction, and the width direction is the length corresponding to the Poisson's ratio of the strain generating body 28. Will grow. Thus, since the compressive force to the first beam-like vibrating portion 23a acts in the first vibrator 22a, the vibration frequency of the first beam-like vibrating portion 23a to f _a -f _a 'from f _a descend. At the same time, since the tension acting on the second beam-like vibrating portion 23b of the second vibrator 22b, the vibration frequency of the second beam-like vibrating portion 23b is increased to f _b + f _b 'from f _b Will do.

In FIG. 2A, when the vibration frequency 31a of the first vibrator 22a and the vibration frequency 31b of the second vibrator 22b intersect, that is, when these two vibration frequencies match, the first vibrator 22a. And the vibration of the second vibrator 22b interfere with each other, which causes a problem that the measurement accuracy of external force and strain is lowered. Therefore, in the first embodiment of the present invention, the vibration frequency 31a of the first vibrator 22a and the vibration frequency 31b of the second vibrator 22b do not intersect within the range in which the external force or strain is to be measured. it is obtained by providing a vibration frequency f _a of the first resonator 22a, the difference between the oscillation frequency f _b of the second vibrator 22b.

  The AC signals generated from the first and second beam-like vibrating portions 23a and 23b of the first and second vibrators 22a and 22b are processed in the signal processing board 30, and the difference in vibration frequency between these two AC signals. A signal having Δ is output.

FIG. 2B is a diagram showing a change in the vibration frequency difference 32 between the first and second vibrators 22a and 22b when an external force is applied to the object to be measured. For example, if the longitudinal direction of the tensile force F is applied to the strain body 28, the vibration frequency difference △ is _{△ = (f a + f a} ') - (f b -f b') = (f a -f b) + (F _a ′ + f _b ′). By processing the second term of this equation that changes due to an external force in the signal processing board 30, a larger frequency difference is obtained than when a physical quantity sensor having only the first vibration part or the second vibration part is used. be able to. In this way, by measuring the output natural frequency difference, the strain and load acting on the strain generating body 28 can be measured with high sensitivity. When an external force is applied to the strain body 28, the direction of the force acting on the first vibrator 22a and the force acting on the second vibrator 22b is always opposite due to the Poisson's ratio. It can be applied to all measured objects. On the other hand, since the first and second vibrators 22a and 22b are formed from the same material semiconductor substrate, the direction and rate of change of the vibration frequency with respect to the temperature change are the same. As a result, fluctuations in the vibration frequency due to temperature changes can be canceled, so that strain and load can be accurately measured regardless of temperature changes.

(Embodiment 2)
The second aspect of the present invention will be described below with reference to the second embodiment. 3A is a top view of the physical quantity sensor according to the second embodiment of the present invention, FIG. 3B is an enlarged view of a portion C in FIG. 3A, and FIG. 3C is D in FIG. 3B. FIG. In the second embodiment, components having the same configurations as those of the first embodiment described above are denoted by the same reference numerals, and description thereof is omitted.

  3A to 3C, reference numeral 33 denotes a physical quantity sensor, and the second embodiment of the present invention is different from the first embodiment of the present invention described above on a single semiconductor substrate 34. Surrounding the first beam-like vibrating portion 23a, the second beam-like vibrating portion 23b, and the first and second beam-like vibrating portions 23a, 23b, and the first and second beams. The fixed portions 35 that support both ends of the oscillating portions 23a and 23b are formed, and the drive elements 25a and 25b and the detection elements 26a and 26b are electrically connected to the land 36 by a wiring pattern (not shown). In addition, the bottom surface of the semiconductor substrate 34 has rigidity such as metal-based bonding material such as Au-Au bonding or epoxy resin so that strain generated in the strain generating body 28 is transmitted to the first vibrator 22a. This is the point where the material 37 is connected and fixed. At this time, also in the second embodiment of the present invention, the length direction of the first beam-like vibrating portion 23a is the length of the strain generating body 28, as in the first embodiment of the present invention. The length direction of the second beam-like vibrating part 23b is arranged substantially parallel to the width direction of the strain generating body 28.

  With such a configuration, the physical quantity sensor 33 can be reduced in size, and the second beam-shaped vibrating portion 23b can be accurately and orthogonally arranged without mounting variation with respect to the first beam-shaped vibrating portion 23a. Thus, it is possible to obtain an effect that the strain and the load acting on the minute portion of the measurement object can be measured with high sensitivity and high accuracy regardless of the temperature change.

(Embodiment 3)
4A is a top view of the physical quantity sensor according to Embodiment 3 of the present invention, FIG. 4B is an enlarged view of a portion E in FIG. 4A, and FIG. 4C is G in FIG. 4B. FIG. In the third embodiment, components having the same configurations as those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  4A to 4C, reference numeral 40 denotes a physical quantity sensor, and the third embodiment of the present invention is different from the second embodiment of the present invention described above on a single semiconductor substrate 41. Surrounding the first beam-like vibrating portion 23a, the second beam-like vibrating portion 23b, and the first and second beam-like vibrating portions 23a, 23b, and the first and second beams. The fixed portions 42 that support both ends of the vibrating portions 23a and 23b are formed, and the drive elements 25a and 25b and the detection elements 26a and 26b are electrically connected to the land 36 by a wiring pattern (not shown). At the same time, only on the outer peripheral portion of the bottom surface of the semiconductor substrate 41, metal-based bonding material such as Au-Au bonding, epoxy resin, or the like so that the strain generated in the strain generating body 28 is transmitted to the first vibrator 22a. This is the point where the material 37 having the following rigidity is connected and fixed. At this time, the length direction of the first beam-like vibrating portion 23a is arranged substantially parallel to the width direction of the strain body 28, and the length direction of the second beam-like vibrating portion 23b is The strain body 28 is disposed substantially parallel to the length direction.

  With such a configuration, the physical quantity sensor 40 can be further reduced in size, and the second beam-shaped vibrating portion 23b can be accurately arranged orthogonal to the first beam-shaped vibrating portion 23a without mounting variation. As a result, it is possible to obtain an effect that the strain and load acting on the minute portion of the measurement object can be measured with high sensitivity and high accuracy regardless of the temperature change.

  The physical quantity sensor according to the present invention can always reverse the direction of the force acting on the first vibrator and the force acting on the second vibrator when an external force is applied to the strain generating body. By applying to virtually all measured objects, the strain and load acting on the measured objects can be measured with high sensitivity and high accuracy regardless of temperature changes. In particular, it is useful as a physical quantity sensor for detecting strain and load acting on an object.

21, 33, 40 Physical quantity sensor 22a First vibrator 22b Second vibrator 23a First beam-like vibration part 23b Second beam-like vibration part 28 Strain body 34, 41 Single semiconductor substrate

Claims (2)

A strain generating body that generates strain due to an external force, a first vibrator that is disposed on the strain generating body and has a first beam-shaped vibrating section that changes a vibration frequency according to the amount of strain, and the strain generating And a second vibrator having a second beam-like vibrating portion that is arranged on the body and whose vibration frequency changes according to the amount of strain, and the first beam-like vibration in the first vibrator The longitudinal direction of the first portion and the longitudinal direction of the second beam-like vibrating portion of the second vibrator are substantially orthogonal, and the difference between the vibration frequency of the first vibrator and the vibration frequency of the second vibrator A physical quantity sensor that detects a mechanical quantity acting on the strain-generating body by detecting the strain. The physical quantity sensor according to claim 1, wherein the first beam-like vibrating portion and the second beam-like vibrating portion are formed on a single semiconductor substrate.

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