JP2010281581A - Pressure sensor and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pressure sensor greatly improved in pressure detection precision. <P>SOLUTION: The pressure sensor 1 has: a pressure sensitive element 25 including base sections 27a, 27b across vibration sections 26a, 26b; a diaphragm 20 including a pair of support sections 23, 24 for fixing the pressure sensitive element 25 to one surface of a flexible section; a temperature sensor 12; a storage section 16; and an arithmetic processing section 17. The storage section 16 stores coefficients of a first approximation polynomial for relating temperature to frequencies in the pressure sensor 1 under environment of fixed pressure, coefficients of a second approximation polynomial for relating pressure to frequencies in the pressure sensor under a plurality of mutually different temperature environments, and coefficients of a third approximation polynomial for composing primary coefficients of the second approximation polynomial. The pressure sensor 1 outputs signals for compensating for frequency temperature characteristics that depend on pressure. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

The present invention relates to a pressure sensor and a method for manufacturing the same, and in particular, approximates a frequency temperature characteristic of a pressure-sensitive unit and a pressure frequency characteristic by a polynomial, measures the coefficients of these polynomials, stores them in a storage unit,
The present invention relates to a pressure sensor whose accuracy has been improved by calling up the coefficient every time the pressure is measured and processing it, and a method for manufacturing the same.

A pressure sensor using a relationship between a stress applied to a piezoelectric vibrator and a change in resonance frequency has been put into practical use. By using a double tuning fork type piezoelectric vibrator as the piezoelectric vibrator, sensitivity to stress is improved, and an altitude difference and a depth difference can be detected from a slight pressure difference.
Patent Document 1 discloses a pressure detection unit using a piezoelectric vibrating piece as a pressure sensitive element.
FIG. 14A is a side sectional view of the pressure detection unit, and FIG. 14B is a sectional view taken along line QQ in FIG.
The pressure detection unit 60 includes a diaphragm 6 having a pressure receiving surface on one main surface (outer main surface).
1, a base 75 provided to face the other main surface (inner main surface) of the diaphragm 61, and a piezoelectric vibrating piece 70 as a pressure sensitive element.
The pressure-sensitive element has a pressure-sensitive part and a pair of base parts connected to both ends of the pressure-sensitive part, sets the detection direction of force as a detection axis, and the direction in which the pair of base parts of the pressure-sensitive element are arranged is A parallel relationship with the detection axis. In the case of a double tuning fork type piezoelectric vibrator, the beam extending direction and the detection axis are in parallel relation.
As shown in FIG. 14A, the diaphragm 61 includes a thin portion 63 that deforms when the pressure receiving surface receives pressure from a direction perpendicular to the pressure receiving surface, and a peripheral edge of the thin portion 63. The frame part 69 is formed. On the other surface of the diaphragm 61 and on one main surface of the thin portion 63, there is a pair of support portions 65 for fixing the piezoelectric vibrating piece 70,
The piezoelectric vibrating piece 70 has a pair of base portions 71 supported by a support portion 65. Further, on the other main surface of the thin-walled portion 63, a protruding portion 67 is provided in a region including a portion facing the vibrating portion 72 that is a pressure-sensitive portion of the piezoelectric vibrating piece 70. By making a part of the thin part 63 thick and forming the protruding part 67, the deformation of the part can be prevented, and the center of the thin part 63 comes into contact with the piezoelectric vibrating piece 70 when pressure is applied. Can be prevented.

A so-called double tuning fork type vibration element is used for the piezoelectric vibrating piece 70. The double tuning fork type vibration element
Both ends have fixed ends (base portions) 71, and two vibration beams (vibration portions) are formed between the two fixed ends 71. The double tuning fork type vibration element is the pressure sensitive part (vibration part 72).
When a tensile stress (elongation stress) or a compressive stress is applied to two vibrating beams, there is a characteristic that the resonance frequency changes almost in proportion to the applied stress.
In the pressure detection unit 60 shown in FIG. 14, both fixed ends (base portions) 71 of the double tuning fork type vibration element 70 are fixed to the mounting surfaces 66 of the pair of support portions 65 formed in the thin portion 63 of the diaphragm 61. Yes. When pressure is applied to the upper portion of the diaphragm 61, the thin portion 63 is bent, and the thin portion 63 is deformed downward in FIG. The placement surface 66 of the support portion 65 is inclined with the deformation state of the thin portion 63, and the placement surface 66 is inclined outward with respect to the center of gravity of the diaphragm 61. For this reason, the interval between the two mounting surfaces 66 is widened, and the double tuning fork type vibration element 70 fixed to the mounting surface 66 is provided.
An extensional stress is applied to the vibrating portion 72 of the above. When an extension stress is applied to the vibration part 72, the resonance frequency of the double tuning fork type vibration element 70 increases.

However, since the frequency-temperature characteristic of the double tuning fork type vibration element 70 has an upward convex secondary characteristic,
When used in an environment with a large temperature change, there is a problem that an error occurs in pressure detection accuracy.
Therefore, a method for improving the pressure detection accuracy by compensating the frequency temperature characteristic of the double tuning fork type vibration element 70 by adding a temperature sensor for detecting temperature has been studied.
FIG. 15 is a block diagram of the pressure sensor 80. The change in the resonance frequency of the pressure detection unit 60 and the temperature detected by the temperature sensor 82 are taken into the processing device, and these are arithmetically processed to compensate for the frequency change in temperature. The pressure applied to the diaphragm 61 is detected.
As the temperature sensor, the tuning fork type crystal resonator disclosed in Patent Documents 2, 3, 4, and 5 is suitable in consideration of accuracy, shape, cost, and the like. The frequency-temperature characteristic of a tuning fork type crystal resonator is generally an upwardly convex secondary characteristic. In the above-mentioned patent document, as shown in FIG. The relationship between the tuning fork type quartz crystal rotated by θ around) and the apex temperature of the secondary temperature characteristic is disclosed.
According to Patent Document 5, the relationship between the primary factor alpha ₁ about the rotation angle θ and the frequency temperature characteristics of the X-axis is related as shown in FIG. 17.
FIG. 18 shows the frequency-temperature characteristics of a tuning-fork type crystal resonator for temperature detection.
On the other hand, the frequency change Δf / f changes almost linearly and the temperature change is obtained as a digital quantity, which is suitable as a temperature sensor.

JP 2007-327922 A Japanese Patent Laid-Open No. 53-2097 JP-A-54-158150 Japanese Examined Patent Publication No. 61-29652 Patent No. 3010922

The conventional pressure sensor 80 shown in FIG. 15 is configured to correct the frequency temperature characteristics of the double tuning fork type vibration element of the pressure detection unit 60 by using a tuning fork type crystal resonator as the temperature sensor 82.
When the pressure sensor 80 is used in an environment where there is no temperature change, the coefficient of the polynomial representing the pressure (stress) P-frequency f characteristic of the pressure detection unit 60 stored in the storage unit 85 is read out and processed by the processing device. The pressure P applied to the pressure sensor 80 is obtained by generating a polynomial of pressure P-frequency f and applying the changed frequency to the polynomial.
When the pressure sensor 80 is used in an environment with a temperature change, first, the temperature is calculated by receiving a temperature signal from the temperature sensor 82.
Next, the frequency temperature characteristic (temperature T−) of the pressure detection unit 60 stored in the storage unit 85.
The coefficient of the polynomial representing the frequency Δf / f characteristic) is read out, and the polynomial of the frequency temperature characteristic (temperature T−frequency Δf / f) is generated by the processing device, and the temperature is applied to this to detect the pressure due to the temperature change. The frequency variation of unit 60 is calculated. The frequency fluctuation is used to compensate the frequency of the pressure detection unit 60, and the compensated frequency change is generated by the processing device by the pressure (stress) P−.
By applying to the polynomial of frequency f, the pressure P applied to the pressure sensor is obtained.

By the way, in recent years, pressure sensors are used in various forms, and high-accuracy specifications are required according to them, and strict ones regarding specifications relating to detection error, variation, accuracy, etc. are required. It has become.
However, the pressure sensor 80 configured as described above has faced a new problem that it has become impossible to sufficiently satisfy such strict specifications.
The present invention has been made to solve the above problems, and it is an object of the present invention to provide a pressure sensor having high accuracy, high resolution, and high stability, and a method for manufacturing the same.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

Application Example 1 A pressure sensor according to the present invention includes a pressure-sensitive unit whose frequency changes according to pressure, and a storage unit, and the storage unit has a frequency of the pressure-sensitive unit under a constant pressure environment. A coefficient of a first approximate polynomial representing a temperature characteristic, a coefficient of a second approximate polynomial representing a pressure frequency characteristic of the pressure-sensitive unit under a plurality of different temperature environments, and a first order of the second approximate polynomial The coefficient of the third approximate polynomial constituting the coefficient is stored.

The frequency temperature characteristic of the pressure sensor is related by a first approximate polynomial, the pressure vs. frequency characteristic is related by a second approximate polynomial, the first order coefficient of the second approximate polynomial is related by a third approximate polynomial, All the coefficients of these polynomials are stored in the storage unit. And, when using the pressure sensor, all the coefficients are called up to compensate the frequency of the pressure sensor, so the pressure detection accuracy obtained by the measurement is greatly improved, both reproducibility and high stability can be improved, and the operating temperature There is an effect that the range and the working pressure range are expanded.

Application Example 2 The pressure sensor according to Application Example 1 is characterized in that the first approximate polynomial is a cubic polynomial.

By approximating the frequency temperature characteristic of the pressure sensor with a cubic polynomial, there is an effect that the detection accuracy of the pressure sensor is improved as compared with the case of approximating with a quadratic polynomial.

Application Example 3 The pressure sensor according to Application Example 1 is characterized in that the second approximate polynomial is a cubic polynomial.

By approximating the pressure vs. frequency characteristic of the pressure sensor with a cubic polynomial, there is an effect that the detection accuracy of the pressure sensor is improved as compared with the approximation of the conventional linear expression.

Application Example 4 The pressure sensor according to Application Example 1 is characterized in that the third approximate polynomial is a quadratic polynomial.

By making the first order coefficient of the second approximate polynomial temperature dependent and making it a second order polynomial,
Since the frequency is corrected by taking into account the temperature dependence that has not been considered in the past, the detection accuracy of the pressure sensor is improved.

Application Example 5 The pressure sensor of the present invention is operated based on a temperature sensor that detects the temperature of the pressure-sensitive unit, a frequency signal output from the pressure-sensitive unit, and a coefficient stored in the storage unit. The pressure sensor according to any one of Application Examples 1 to 4, further comprising: an arithmetic processing unit that performs processing.

By providing the temperature sensor and the arithmetic processing unit, it is possible to output a signal in which the frequency temperature characteristic depending on the pressure is compensated.

Application Example 6 In the pressure sensor, the pressure sensing unit includes a pressure sensing element having a pressure sensing part and a pair of bases connected to both ends of the pressure sensing part, and a pressure receiving surface on one main surface. And a back side of the pressure receiving surface covers one main surface side of the pressure sensitive element, and a diaphragm provided with a pair of support portions for supporting a pair of base portions of the pressure sensitive element, respectively, and the pressure receiving of the diaphragm The pressure sensor according to any one of Application Examples 1 to 5, further comprising a base that opposes the back side of the surface and covers the other main surface side of the pressure-sensitive element.

By providing a support portion for mounting the pressure sensitive element on one surface of the diaphragm, the pressure sensitive element can be easily held and the pressure sensitive unit can be easily sealed. Further, there is a feature that the deformation amount of the pressure receiving surface of the diaphragm is accurately converted by the pressure sensitive element.

Application Example 7 In the pressure sensor according to Application Example 6, the pressure sensor includes at least one columnar beam.

By using a columnar beam for the pressure-sensitive portion, there is an effect that the pressure-sensitive sensitivity can be greatly improved as compared with pressure-sensitive elements having other shapes.

Application Example 8 In the pressure sensor according to Application Example 6 or 7, the pressure sensor, the diaphragm, and the base are all made of a quartz material.

By making all of the pressure-sensitive elements, diaphragms, and bases that make up the pressure-sensitive unit from quartz, the linear expansion coefficient of each part can be made the same, so the degradation of detection accuracy due to strain caused by temperature changes can be reduced. effective.

Application Example 9 A pressure sensor manufacturing method according to the present invention is a pressure sensor manufacturing method including a pressure-sensitive unit whose frequency changes according to pressure, a storage unit, and a pressure sensor. Obtaining a coefficient of a first approximate polynomial representing a frequency temperature characteristic of the pressure sensor; obtaining a coefficient of a second approximate polynomial representing a pressure frequency characteristic of the pressure sensor under a plurality of different temperature environments; A pressure sensor comprising: a step of obtaining a coefficient of a third approximation polynomial constituting a first order coefficient of the second approximation polynomial; and a step of storing all the coefficients in the storage unit. It is a manufacturing method.

As described above, the coefficient that represents the frequency temperature characteristic, the coefficient that represents the pressure-frequency characteristic, the coefficient that represents the temperature dependence of the first-order coefficient of the pressure-frequency characteristic, and the coefficient that represents the temperature dependence are memorized. Manufacturing a pressure sensor that can greatly improve the pressure detection accuracy of the pressure sensor, improve reproducibility and high stability, and widen the operating temperature range and operating pressure range. Has the effect of becoming possible.

The block diagram which shows the structure of the pressure sensor which concerns on this invention. (A) is a vertical sectional view and (b) is a horizontal sectional view of a pressure sensitive unit. (A) is a top view of a diaphragm, (b) is sectional drawing. (A) of a base is a top view, (b) is sectional drawing. It is a figure explaining a double tuning fork type crystal vibration element, (a) is a vibration mode, (b) is an electrode composition, (c) is a figure showing wiring of an electrode. Frequency-temperature characteristics when the stress (pressure) applied to the double tuning fork crystal resonator is used as a parameter. The figure which shows the relationship between the pressure P and the frequency f of a pressure-sensitive unit when temperature is used as a parameter. The figure explaining qualitatively how a peak temperature of a frequency temperature characteristic shifts with pressure which pressurizes in a pressure sensing unit. (A) is the elastic constant of quartz, (b) is the temperature coefficient of each elastic constant. A graph showing the relationship between temperature and the rate of change in sensitivity. The diamond mark ◆ curve is calculated, and the square mark ■ curve is actually measured. The figure which calculated | required the frequency temperature characteristic when 0 atmosphere and 1 atmosphere were loaded to the pressure-sensitive unit using the finite element method. The figure which calculated | required the frequency temperature characteristic when 0 atmosphere and 1 atmosphere were loaded to the pressure-sensitive unit by measurement. The figure which shows the relationship between the pressure P of a pressure-sensitive unit, and the resonant frequency f. (A) is sectional drawing of the conventional stress detection unit, (b) is sectional drawing in QQ. The block diagram which shows the structure of a pressure sensor. The figure which shows the relationship between a tuning fork type piezoelectric vibrator and a crystal axis. The figure which shows the relationship between the cutting angle (theta) of a tuning fork type piezoelectric vibrator, and primary temperature coefficient (alpha) ₁ . Frequency-temperature characteristics of a tuning-fork type piezoelectric vibrator for temperature measurement.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of a pressure sensor 1 according to an embodiment of the present invention.
The pressure sensor 1 includes a pressure-sensitive unit 11 that changes in frequency according to pressure (atmospheric pressure), a temperature sensor (Ts) 12 that senses the temperature of the pressure-sensitive unit 11 and outputs a temperature signal, and a sensitivity of the pressure-sensitive unit 11. An oscillation circuit (OSC) 13 that excites the pressure element and a counter 14 that counts the output signal of the oscillation circuit 13 are provided. Further, a temperature compensated reference oscillator (TCXO) 15 that supplies a reference signal to the counter 14 and a storage unit (EEPROM) 16 that stores coefficients obtained by approximating various characteristics of the pressure-sensitive unit 11 with polynomials. An arithmetic processing unit (CPU) 17 that calculates a temperature signal of the temperature sensor 12, a frequency signal of the counter 14, and a coefficient signal from the storage unit 16, and an interface that electrically connects the arithmetic processing unit 17 and an external device. Part (I / F) 18.

FIG. 2A is a vertical cross-sectional view of the pressure-sensitive unit 11, and FIG. 2B is a horizontal cross-sectional view of Q1-Q1 as viewed from above Q1-Q1.
The pressure-sensitive unit 11 includes a diaphragm 20 that is flexible when pressure is applied thereto, a pressure-sensitive element 25 that changes in frequency when stress is applied thereto, and a base 3 that joins the diaphragm 20 to form a sealed space.
0.
FIG. 3A is a plan view of the diaphragm 20 of the pressure-sensitive unit 11, and FIG.
It is sectional drawing in 2-Q2.
The outer shape of the diaphragm 20 is rectangular and has a frame-shaped thick portion (frame portion) 21 at the periphery, a thin plate-like thin portion 22 connected to the thick portion 21, and a central portion on the thin portion 22. And a pair of support portions 23 and 24 that are symmetrical with respect to the center of gravity. That is, the thin portion 22 is provided with a pair of support portions 23 and 24 at portions corresponding to the pair of base portions 27 a and 27 b of the pressure sensitive element 25.
2 and 3 show an example of the diaphragm 20, but the pressure sensor 1 of the present invention may use another shape, for example, a concentric diaphragm.

4A is a plan view of the base 30 of the pressure-sensitive unit 11, and FIG. 4B is Q3-Q3.
FIG.
The base 30 is rectangular and has a peripheral frame portion 31, a flat plate portion 32 connected to the frame portion 31, and a hole 33 penetrating through the central portion of the flat plate portion 32. The end of the hole 33 is processed into a wide opening and is metallized. The frame portion 31 and the flat plate portion 32 have one plane side on the same plane, and on the other plane side, the thickness of the flat plate portion 32 is smaller than the thickness of the frame portion 31 and is flush with the plane of the plate portion 32. Instead, a recess is formed at the center of the base 30.
The outer dimensions of the diaphragm 20 shown in FIG. 3A and the outer dimensions of the base 30 shown in FIG. 4A are substantially the same, and the thick portion 21 at the periphery of the diaphragm 20 and the periphery of the base 30 Frame part 3
1 are formed in close contact with each other.
The diaphragm 20 applies, for example, a photolithographic technique and an etching technique to a flat crystal plate, and etches a predetermined portion (thin wall portion 22) from both sides of the crystal plate.
It can be easily configured. The base 30 is formed by etching a predetermined portion from one side of a flat crystal plate, for example, to form a flat plate portion 32, and further processing a hole 33 by etching in the center of the flat plate portion 32. Can do.

As the pressure sensitive element 25, for example, a double tuning fork type vibration element shown in FIG. The double tuning fork type vibration element 25 includes a pair of vibration parts (vibration beams) 26a and 26b extending in parallel with each other and a pair of base parts 27a connected and integrated to both ends of the pair of vibration parts 26a and 26b. 27b
And.
As shown in FIG. 2A, the pressure-sensitive unit 11 has a structure in which the base portions 27a and 27b of the pressure-sensitive element (double tuning fork type vibration element) 25 are bonded to the support portions 23 and 24 on one surface of the diaphragm 20, For example, low melting point glass is applied, heated and bonded and fixed. A thick part surface 21a on the side of the diaphragm 20 on which the pressure sensitive element (double tuning fork type vibration element) 25 is mounted and a frame part surface 31a of the base 30 are coated with an adhesive, for example, a low melting point glass, and heated. Glue and fix.
Then, the sealed space formed by the diaphragm 20 and the base 30 is evacuated through the through hole 33 formed in the flat plate portion 32 of the base 30, and a filling 34, for example, gold tin AuS, is formed in the through hole 33.
n, filled with gold germanium AuGe, and the sealed space is evacuated.
An example of low-melting glass has been shown as an adhesive, but other adhesives such as epoxy adhesives may be used, and direct bonding, bonding members containing alkoxides, organosiloxy groups, etc. may be used and bonded by ultraviolet or plasma irradiation. It is desirable that stress relaxation of the pressure-sensitive unit 11 is achieved, such as a bonding method to be performed and a eutectic bonding method using a metal film such as a gold-tin alloy film as a bonding member.
As the temperature sensor 12, for example, a tuning fork type vibration element shown in FIG. 16 is used. The oscillation circuit 13 can be composed of, for example, an amplification IC and a capacitor. The counter 14 uses a general counter IC. The reference signal reference oscillator 15 uses a temperature compensated crystal oscillator composed of an AT-cut crystal resonator element and a temperature compensation IC. The storage unit 16 uses, for example, an rewritable EEPROM, and the arithmetic processing unit 17 uses a general microprocessor. The interface (I / F) 18 selects a circuit appropriately according to an external circuit.

The double tuning fork type crystal vibrating element 25 will be briefly described with reference to FIG.
The double tuning fork type crystal vibrating element 25 includes a pair of base portions 27a and 27b as shown in FIG. 5A and a vibrating portion (pressure-sensitive portion) 26a composed of a pair of columnar beams connecting the base portions 27a and 27b.
A stress sensitive part made of a piezoelectric substrate provided with a piezoelectric element 26b, and an excitation electrode formed on the vibration region of the piezoelectric substrate.
A broken line in FIG. 5A is a plan view showing a vibration state of the double tuning fork type crystal vibrating element 25. The excitation electrodes are arranged so that the vibration mode of the double tuning fork type crystal resonator element 25 vibrates in a vibration mode symmetrical to each other with respect to the central axis in the longitudinal direction of the pair of vibration portions 26a and 26b. FIG. 5B is a plan view showing an example of the excitation electrode formed on the double tuning fork type crystal vibrating element 25 and the sign of the charge on the excitation electrode excited at a certain moment. FIG. 4C is a schematic cross-sectional view showing connection of excitation electrodes.
The double tuning fork type crystal vibrating element 25 is formed by processing a Z-cut quartz substrate or a Z′-cut quartz substrate (a substrate rotated around the X axis) into a desired shape by using, for example, a photolithography technique and an etching technique, and applying a vacuum An excitation electrode, a lead electrode, and the like are formed using a vapor deposition method or the like.

The double tuning fork type quartz vibrating element has good sensitivity to stretching (tensile) and compressive stress, and has excellent decomposing ability when used as a pressure sensitive element (stress sensitive element) for altimeter or depth gauge. Therefore, altitude difference and depth difference can be detected from a slight pressure difference.
The frequency-temperature characteristic of the double tuning fork type quartz resonator element is an upward convex quadratic curve, and the apex temperature depends on the rotation angle around the X axis (electric axis) of the quartz crystal. Generally, the peak temperature is room temperature (
Each parameter is set to be 25 ° C.
The resonance frequency f _F when an external force F is applied to the pair of vibrating parts of the double tuning fork crystal resonator element is as follows.
f _F = f ₀ × (1− (K × L ² × F) / (2 × E × I)) ^1/2 (1)
Here, f ₀ is the resonance frequency of the double tuning fork type quartz vibrating element when there is no external force, K is a constant according to the fundamental mode (= 0.0458), L is the length of the vibrating beam, E is the longitudinal elastic constant, I Is cross section 2
Next moment. Second moment I are from ^{I = d × w 3/12} , the equation (1) can be modified as follows. Here, d is the thickness of the vibration beam, and w is the width.
f _F = f ₀ × (1−S _F × σ) ^1/2 (2)
However, the stress sensitivity _SF and the stress σ are respectively expressed by the following equations.
S _F = 12 × (K / E) × (L / w) ² (3)
σ = F / (2 × A) (4)
Here, A is the cross-sectional area (= w × d) of the vibration beam.

From the above, when the force F acting on the double tuning fork type crystal resonator is negative in the compression direction and positive in the extension direction (tensile direction), the relationship between the force F and the resonance frequency f _F is that the force F resonates with the compression force. The frequency f _F decreases and increases with the stretching (tensile) force. The stress sensitivity S _F is proportional to the square of the vibration beam L / w.
Further, the pressure sensitive element is not limited to a double tuning fork type crystal resonator, and any piezoelectric vibration element whose frequency is changed by extension / compression stress can be used.
Further, the number of columnar beams constituting the pressure-sensitive portion is not limited to two, and it is only necessary that the number of columnar beams is composed of at least one columnar beam. It is easy to suppress vibration leakage etc. 2
A book is preferred. When the number of columnar beams is two, the above-described double tuning fork type vibrator is formed in which tuning fork type vibrating pieces are joined face to face.
Since the pressure-sensitive unit 11 uses the sealed space formed by the diaphragm 20 and the base 30 as a vacuum state, pressure, for example, 1 atm, is applied to the pressure receiving surface of the diaphragm 20 from the direction perpendicular to the pressure receiving surface. When pressure is applied to the pressure receiving surface of the diaphragm 20, the thin portion 22 is bent, and the thin portion 22 is bent and deformed toward the back side of the pressure receiving surface of the diaphragm 20. The placement surfaces 23a and 24a of the support portions 23 and 24 are inclined as the thin portion 22 is deformed, and the placement surfaces 23a and 24a are inclined outward from the center of gravity of the thin portion 22, respectively. For this reason, the space | interval between mounting surface 23a, 24a spreads, and the vibration parts 26a, 2 of the double tuning fork type crystal vibrating element 25 fixed to this mounting surface 23a, 24a.
An elongation (tensile) stress is applied to 6b. When an elongation stress is applied to the vibrating portions 26a and 26b, the resonance frequency of the double tuning fork type quartz vibrating element 25 increases.

In a state where an extension (tensile) stress or a compressive stress is applied to the double tuning fork type quartz vibrating element, the frequency temperature characteristic of the double tuning fork type quartz vibrating element is different from the frequency temperature characteristic in a state where no stress is applied. A curve S0 shown by a solid line in FIG. 6 is a frequency-temperature characteristic in a state where no stress is applied to the double tuning fork type quartz vibrating element 25, and various constants of the double tuning fork type quartz vibrating element so that the vertex temperature Tm0 becomes room temperature. For example, the cutting angle θ is set. A curved line S1 indicated by a broken line is a frequency temperature characteristic in a state where an extension (tensile) stress is applied to the double tuning fork type crystal vibrating element, and the apex temperature Tm1 is T
Shift to higher temperature than m0. A curve S2 indicated by a one-dot chain line is a frequency-temperature characteristic in a state where compressive stress is applied to the double tuning fork type crystal vibrating element, and the vertex temperature Tm2 shifts to a lower temperature side than Tm0.
The pressure (stress) P-frequency f characteristic of the pressure-sensitive unit 11 differs in pressure-frequency sensitivity (df / dP) depending on the temperature T in the environment where the pressure-sensitive unit 11 is exposed as shown in FIG.
Pressure vs. frequency sensitivity at room temperature (25 ° C) vs. pressure vs. frequency sensitivity (d
f / dP) decreases, and pressure vs. frequency sensitivity (df / dP) increases at high temperatures (85 ° C.). To this phenomenon, an extension (tensile) stress is applied to the double tuning fork type crystal resonator element.
As a result of thinking that the phenomenon that the frequency increases may be induced at the same time, it is thought that the phenomenon that the vertex temperature of the quadratic curve is shifted by the application of stress as shown in FIG. 6 can be explained. It was.

FIG. 8 illustrates a phenomenon in which the peak temperature of the frequency temperature characteristic (temperature T-frequency f characteristic) of the pressure sensitive unit 11 shifts to the high temperature side when the pressure applied to the pressure sensitive unit 11 changes from 0 atm to 1 atm. It is a figure to do. When the pressure applied to the pressure sensitive unit 11 is 0 atm, no stress is applied to the double tuning fork type crystal vibrating element 25 of the pressure sensitive unit 11 in which the inside of the sealed space is evacuated.
When the pressure applied to the pressure-sensitive unit 11 is 1 atm, an extension (tensile) stress is applied to the double tuning fork type crystal vibrating element 25, and the frequency of the double tuning fork type crystal vibrating element 25 increases. At this time, pressure vs. frequency sensitivity (df / dP) is small at low temperature, and pressure vs. frequency sensitivity (df / dP) at high temperature.
df / dP) increases. When these two phenomena are added, the frequency temperature characteristic (temperature T-frequency f characteristic) at 0 atm indicated by J ₀ becomes the frequency temperature characteristic at 1 atm indicated by J ₁ (temperature T-frequency f characteristic).
Temperature T-frequency f characteristic). That is, the phenomenon that the peak temperature of the frequency temperature characteristic is shifted to the high temperature side due to the pressure applied to the pressure-sensitive unit 11 can be qualitatively explained.

Therefore, the inventors of the present application analyze the pressure-sensitive unit 11 using a finite element method in order to compensate the shift of the apex temperature of the frequency temperature characteristic exhibited by the pressure-sensitive unit 11 due to the pressure and to improve the accuracy of the pressure sensor 1. Tried. Diaphragm 20 and pressure sensitive element (
The double tuning fork type quartz vibrating element) 25 and the base 30 are all made of quartz materials. As the quartz constant, a density ρ of 2.65 × 10 ³ (kg / m ³ ) and a Poisson's ratio of 0.135 were used.
The elastic constant (Young's modulus) Cij that links the relationship between the strain and stress of the equation of motion used for the analysis of the pressure-sensitive unit 11 is a matrix constant shown in FIG. The elastic constant (Young's modulus) Cij of quartz has anisotropy and temperature dependence.
Therefore, the elastic constant at an arbitrary temperature T was obtained using the following approximate expression. The constants shown in FIG. 9B are used for the first order coefficient α, the second order coefficient β, and the third order coefficient γ of the elastic constant Cij in the equation (5).
Cij (T) = Cij × (1 + α × T + β × T ² + γ × T ³ ) (5)

Next, intensive analysis was conducted on the cause of pressure-frequency sensitivity (df / dP) changing with temperature as shown in FIG. The elastic constant Cij is a function of the temperature T as shown in the equation (5), and the resonance frequency of the pressure-sensitive unit 11 is analyzed using the finite element method.
FIG. 10 is a diagram showing the relationship between the temperature T and the sensitivity change rate.
The frequency of the pressure sensitive unit 11 when the 0 atm frequency of f _0, 1 atm and f _1, | f ₀ -
f ₁ | / f ₁ is defined as the rate of change in sensitivity, and 0 at 25 ° C. A temperature T-sensitivity change rate curve obtained by changing the temperature T and analyzing the sensitivity change rate is indicated by a diamond mark ◆. A curve indicated by a square mark ■ is a temperature T-sensitivity change rate curve obtained by actually measuring the pressure-sensitive unit 11.
The reason why the apex temperature of the frequency temperature characteristic of the pressure-sensitive unit 11 changes due to the applied pressure is that the first-order coefficient of the polynomial representing the frequency temperature characteristic changes. That is, when the temperature rises,
The elastic coefficient Cij of the crystal is reduced, and the sensitivity change rate in FIG. 10 is increased. Since the sensitivity change rate increases almost linearly as the temperature T increases, the first-order coefficient of the polynomial representing the frequency temperature characteristic of the pressure-sensitive unit 11 changes. As a result, it was found that the apex temperature seemed to shift.

FIG. 11 is a diagram showing the frequency-temperature characteristics of the pressure-sensitive unit 11 obtained by simulation analysis when the pressure applied to the diaphragm 20 is 0 atm and 1 atm. The frequency change Δf / f of the pressure-sensitive unit 11 was calculated by changing the temperature T at each atmospheric pressure. The case of 0 atm is indicated by a diamond mark ◆, and the case of 1 atm is indicated by a square mark ■. The frequency change Δf / f was determined at 0 atm and 1 atm. The thin line is a curve obtained by plotting the frequency change Δf / f calculated by the finite element method at each temperature T and connecting with a smooth line. The thick line is a curve by a polynomial obtained by approximating the frequency change Δf / f calculated at each temperature T using the least square method. The apex temperature of the frequency temperature characteristic at 0 atm is −6 ° C., but the apex temperature is shifted to the high temperature side at 1 atm, and it is determined from the analysis result that it becomes 20 ° C. A polynomial y representing the frequency temperature characteristic of the pressure-sensitive unit 11 at 0 atmosphere and 1 atmosphere is shown in the lower part of the drawing.
At 0 atm: y = −0.0476x ² −0.595x + 41.498 (a)
At one atmosphere: y = −0.0464x ² + 1.737x-15.342 (b)

FIG. 12 is a curve when the pressure-sensitive unit 11 is subjected to a load of 0 atm and 1 atm by experiment and the frequency temperature characteristic of the pressure-sensitive unit 11 is measured.
The case of 1 atm is indicated by a square mark ■. In the case of 0 atm, the peak temperature of the frequency temperature characteristic is -7
Although it was ° C., in the case of 1 atm, the peak temperature is shifted to 20 ° C. A polynomial y representing the frequency temperature characteristic of the pressure-sensitive unit 11 at 0 atmosphere and 1 atmosphere is shown in the lower part of the drawing.
At 0 atm: y = −0.0383x ² −0.5123x + 32.126 (c)
At 1 atm: y = −0.0308x ² + 1.2514x-11.212 (d)
When the simulation analysis result shown in FIG. 11 is compared with the measurement result by the experiment shown in FIG. 12, when pressure (1 atm) is applied to the pressure-sensitive unit 11, the shift amount of the peak temperature to the high temperature side is: Simulation analysis also showed that it could be calculated with an error range of several percent.
From the analysis results and the actual measurement results, it has been proved that the reason why the peak temperature of the frequency temperature characteristic changes is due to the change of the first order coefficient of the polynomial representing the frequency temperature characteristic.
The inventors of the present application have arrived at the invention according to the present application based on the above-described research results.


In the present embodiment, the polynomial representing the frequency temperature characteristic of the pressure-sensitive unit 11 is the first approximate expression f, and the following third-order polynomial is used.
f = a ₁ T ³ + a ₂ T ² + a ₃ T + a ₄ (6)

FIG. 13 is a curve showing a pressure P-frequency f characteristic indicating a change in the resonance frequency f when pressure (stress) P is applied to the pressure-sensitive unit 11. A polynomial representing this pressure frequency characteristic is defined as a second approximate expression P, and the following cubic polynomial is used.
^{_{P = b 1 f 3 + b}} 2 f 2 + b 3 f + f c ··· (7)
Here, fc represents a frequency temperature characteristic when, for example, a pressure of 1 atm is applied to the pressure sensitive unit 11. The first-order coefficient b _{3 in} Expression (7) is a coefficient representing temperature dependence, and is set as a third approximate expression b ₃ , and the following second-order polynomial is used.
b ₃ = c ₁ T ² + c ₂ T + c ₃ (8)

Since the manufactured pressure-sensitive unit 11 varies slightly in electrical characteristics, the equations (6), (
7) All the coefficients of (8) were measured and stored in the storage unit 16 of the pressure sensor 1. First, the frequency temperature characteristic (Tf characteristic) is measured in an environment of a constant atmospheric pressure Po within the operating atmospheric pressure range, and the coefficients a ₁ , a ₂ , a 3, and a ₄ of Equation (6) are obtained. Next, the pressure frequency characteristic (Pf characteristic) is measured using the temperature T within the operating temperature range as a parameter (three or more points, for example, −35 ° C., 25 ° C., 85 °), and the coefficient b of the equation (7) Find ₁ , b ₂ , b ₃ .
Then, the temperature Ti is used as a parameter, the pressure P is changed, the resonance frequency of the pressure-sensitive unit 11 is obtained, and the pressure-to-frequency sensitivity (df / dP) i is obtained. Temperature Ti and pressure vs. frequency sensitivity (
df / dP) i is plotted, and the coefficients c ₁ , c ₂ , and c ₃ of Equation (8) are obtained from this curve.
All the coefficients a _{1 to} a ₄ , b _{1 to} b ₃ , and c _{1 to} c ₃ obtained by the measurement are stored in the storage unit 16 of the pressure sensor 1.

Thus, the frequency temperature characteristic (Tf characteristic) and pressure frequency characteristic (P-) of the pressure sensitive unit 11 are as follows.
f characteristic) is approximated by a polynomial, and the coefficient of the first-order term of the pressure frequency characteristic (Pf characteristic) is approximated by a polynomial, and the coefficient of these polynomials is measured and stored in the storage unit 16 to store the pressure sensor 1. Configured. The operation of the pressure sensor 1 of the present invention is performed by fetching the temperature signal from the temperature sensor 12 and the frequency signal of the pressure sensitive unit 11 through the counter 14 into the arithmetic processing unit 17 and storing the frequency temperature characteristic (T -f characteristic), pressure frequency characteristic (P-f characteristic), by calling the coefficients of temperature dependence term b _3, by adding a correction to the signal, it is possible to determine the pressure applied to the pressure sensor 1. It has been found that when the pressure sensor 1 is configured in this way, the pressure detection accuracy is greatly improved.
For example, the working pressure range is about 0.5 to 1.5 atmospheres. In FIG. 11, when the temperature is 15 ° C., the frequency difference (Δf / f) between 0 atm and 1 atm is about 80 ppm, which is about 200 Pa.
It corresponds to. At 0.5 atm, the pressure is about 100 Pa. In the pressure sensor 1 according to the present invention, the accuracy is about 5 Pa, and the pressure detection accuracy is greatly improved to about 1/20.

In the above description, the expression (6) representing the frequency temperature characteristic (Tf characteristic) is a cubic polynomial, the expression (7) representing the pressure frequency characteristic is a cubic polynomial, and the expression (8) representing the temperature dependence characteristic expression is Although approximated by a quadratic polynomial, a higher order polynomial may be used to increase the accuracy of the pressure sensor. However, when the degree is increased, the storage unit for storing these coefficients becomes larger and the IC becomes larger, and the degree of each polynomial is determined in consideration of the required accuracy.
The frequency temperature characteristic of the pressure sensor is related by a first approximate polynomial, the pressure vs. frequency characteristic is related by a second approximate polynomial, the first order coefficient of the second approximate polynomial is related by a third approximate polynomial, After measuring and calculating all the coefficients of these polynomials, store them in the storage unit and call up all the coefficients when using the pressure sensor to compensate the frequency of the pressure sensor, so the pressure obtained by measurement Detection accuracy is greatly improved, both reproducibility and high stability can be improved, and the operating temperature range and operating pressure range are widened.

In the present embodiment, the pressure sensor 1 is configured as shown in FIG. 1, but this is merely an example, and in order to reduce the power consumption of the pressure sensor 1, the arithmetic processing unit 17 that consumes a large amount of current. The interface unit (I / F) 18 may have a function in an external device to be electrically connected, and the pressure sensor may be configured except for the arithmetic processing unit 17 and the interface unit (I / F) 18. By transferring the function of the arithmetic processing unit 17 having the largest power consumption among the pressure sensors to the CPU of the external device, it is possible to reduce the size of the pressure sensor and reduce power consumption. . In this case, if the temperature sensor 11 connected to the arithmetic processing unit 17 is disposed in the vicinity of the pressure-sensitive unit 11, it can be provided in an external device.
Therefore, the pressure sensor 1 of the present embodiment can be configured by the pressure-sensitive unit 11 and the storage unit 16, and the pressure sensor 1 can be reduced in size and power consumption can be reduced.

Like the pressure sensor 1 of the present embodiment, since the pressure-sensitive element 25, the diaphragm 20, and the base 30 constituting the pressure-sensitive unit 11 are all made of quartz, the linear expansion coefficients of the respective parts can be made the same. There is an effect that deterioration in detection accuracy due to distortion caused by temperature change can be reduced.
Further, by approximating the frequency temperature characteristic of the pressure sensor 1 of the present embodiment with a cubic polynomial, there is an effect that the detection accuracy of the pressure sensor is improved as compared with the case of approximation with a quadratic polynomial. Further, by approximating the pressure-frequency characteristic of the pressure sensor 1 with a cubic polynomial, there is an effect that the detection accuracy of the pressure sensor is improved as compared with the approximation of the conventional linear expression. In addition, since the first order coefficient of the second approximate polynomial has a temperature dependency and is a second order polynomial, the temperature is corrected by taking into account the temperature dependency that has not been considered in the past. Has the effect of improving.

In the present embodiment, a pressure-sensitive unit 11 whose frequency changes according to pressure, and a pressure-sensitive unit 11
1 is a method for manufacturing a pressure sensor 1 comprising a storage unit that stores various characteristics of the first and second frequency temperature characteristics that relate the temperature and the frequency of the pressure sensor 1 under a constant pressure environment. A step of obtaining a coefficient of an approximate polynomial, a step of obtaining a coefficient of a second approximate polynomial representing a pressure-frequency characteristic relating the pressure and frequency of the pressure sensor 1 under a plurality of different temperature environments, and the second A method for manufacturing a pressure sensor, comprising: a step of obtaining a coefficient of a third approximation polynomial constituting a first order coefficient of the approximation polynomial; and a step of storing all the obtained coefficients in the storage unit.
As described above, the coefficient that represents the frequency temperature characteristic, the coefficient that represents the pressure-frequency characteristic, the coefficient that represents the temperature dependence of the first-order coefficient of the pressure-frequency characteristic, and the coefficient that represents the temperature dependence are memorized. Pressure sensor 1 that can greatly improve the pressure detection accuracy of the pressure sensor, improve reproducibility and high stability, and can widen the operating temperature range and the operating pressure range. There is an effect that it becomes possible.

DESCRIPTION OF SYMBOLS 1 ... Pressure sensor, 11 ... Pressure-sensitive unit, 12 ... Temperature sensor (Ts), 13 ... Oscillation circuit (OSC), 14 ... Counter, 15 ... Reference oscillator (TCXO), 16 ... Memory | storage part, 17 ...
Arithmetic processing unit (CPU), 18 ... interface unit (I / F), 20 ... diaphragm, 2
DESCRIPTION OF SYMBOLS 1 ... Thick part, 22 ... Thin part, 23, 24 ... Support part, 25 ... Pressure-sensitive element (double tuning fork vibration element),
26a, 26b ... vibrating portion, 27a, 27b ... base, 30 ... base, 31 ... frame portion, 32 ... flat plate portion, 33 ... hole

Claims (9)

A pressure-sensitive unit whose frequency changes according to pressure,
A storage unit,
The storage unit
A coefficient of a first approximate polynomial representing a frequency temperature characteristic of the pressure-sensitive unit under a constant pressure environment;
A second frequency characteristic of the pressure sensitive unit in a plurality of different temperature environments.
The coefficients of the approximate polynomial of
A pressure sensor storing a coefficient of a third approximate polynomial constituting a first-order coefficient of the second approximate polynomial. The pressure sensor according to claim 1, wherein the first approximate polynomial is a cubic polynomial. The pressure sensor according to claim 1, wherein the second approximate polynomial is a cubic polynomial. The pressure sensor according to claim 1, wherein the third approximate polynomial is a quadratic polynomial. A temperature sensor for detecting the temperature of the pressure sensitive unit;
An arithmetic processing unit that performs arithmetic processing based on a frequency signal output from the pressure-sensitive unit and a coefficient stored in the storage unit;
The pressure sensor according to any one of claims 1 to 4, further comprising: The pressure sensitive unit is:
A pressure sensitive element having a pressure sensitive part and a pair of bases connected to both ends of the pressure sensitive part;
There is a pressure receiving surface on one main surface, a back side of the pressure receiving surface covers one main surface side of the pressure sensitive element, and a pair of support portions that respectively support a pair of base portions of the pressure sensitive element are provided. With a diaphragm
6. The pressure sensor according to claim 1, further comprising a base that opposes the back side of the pressure-receiving surface of the diaphragm and covers the other main surface side of the pressure-sensitive element. . The pressure sensor according to claim 6, wherein the pressure-sensitive portion includes at least one columnar beam. The pressure sensor according to claim 6 or 7, wherein the pressure-sensitive element, the diaphragm, and the base are all made of a quartz material. A pressure-sensitive unit whose frequency changes according to pressure, a storage unit, and a method of manufacturing a pressure sensor,
Obtaining a coefficient of a first approximate polynomial representing a frequency temperature characteristic of the pressure sensor under a constant pressure environment;
Second pressure representing the pressure frequency characteristics of the pressure sensor in a plurality of different temperature environments.
Obtaining a coefficient of an approximate polynomial of
Obtaining a coefficient of a third approximate polynomial constituting a first-order coefficient of the second approximate polynomial;
Storing all the coefficients in the storage unit;
A method for manufacturing a pressure sensor, comprising:

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