Pressure sensor

Abstract

To obtain a pressure sensor that is able to measure a pressure with higher accuracy by reducing the influence of the error factor strain of a uniaxial strain sensor caused by a temperature change.SOLUTION: A pressure sensor includes: a base; a silicon sensor chip 30 having a diaphragm 31 formed on a detection surface 30b; a first uniaxial strain sensor 41 provided at a center of the diaphragm 31; and a second uniaxial strain sensor 42 provided at an outer edge of the diaphragm 31. When a Y axis is set in a direction in which the first uniaxial strain sensor 41 and the second uniaxial strain sensor 42 are arranged and a center of the diaphragm 31 is set as an origin, a cantilever structure including a region in which at least a part of the diaphragm 31 is formed, is formed in the silicon sensor chip 30. In the cantilever structure, a second uniaxial strain sensor 42 side along the Y axis is a tip side, and a first uniaxial strain sensor 41 side is a root side. If Y coordinates of a position of the outer edge of the diaphragm 31 on the Y axis are r and - r, a Y coordinate of a position of a root of the cantilever structure is - r<Y<r.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a pressure sensor. [Background technology]

[0002] There is known a pressure sensor in which a uniaxial strain sensor such as a vibrator is provided on a diaphragm that deforms with a change in pressure. In a pressure sensor provided with a uniaxial strain sensor, strain occurs in the uniaxial strain sensor as the diaphragm deforms. The pressure sensor measures the pressure applied to the diaphragm by detecting changes in the resonant frequency of the uniaxial strain sensor caused by the generated strain (see, for example, Patent Document 1).

[0003] Some of these pressure sensors are equipped with a silicon sensor chip in which a cavity is formed inside the silicon, and the area covering the cavity serves as a diaphragm. The silicon sensor chip is fixed to a base. To prevent distortion of the diaphragm from factors other than pressure, the base is made of a material that relieves distortion that occurs between the silicon and the base. Also, to suppress deformation due to temperature changes, the base is made of a material with a linear expansion coefficient close to that of silicon. The base is made of, for example, glass.

[0004] The linear expansion coefficients of the silicon sensor chip and the base are close to each other, which reduces the error-causing strain caused by the difference in the linear expansion coefficients when temperature changes, but since the linear expansion coefficients do not match, the error-causing strain does not become zero. Therefore, in order to further suppress the effects of error-causing strain, two uniaxial strain sensors are provided: one that generates compressive strain when pressure is applied to the diaphragm, and the other that generates tensile strain, and pressure can be measured with higher accuracy by using the difference in strain sensitivity of the two uniaxial strain sensors through differential calculation. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2015-38433 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, because the error-cause strains generated in the two one-axis strain sensors do not match, there was a problem in that the influence of the error-cause strains remained slightly even when differential calculation was performed.

[0007] An object of the present invention is to obtain a pressure sensor that can perform more accurate pressure measurement by reducing the effect of error-causing strain on a one-axis strain sensor. [Means for solving the problem]

[0008] The pressure sensor according to the present invention includes a base, a silicon sensor chip bonded to the base and having a circular diaphragm formed on a detection surface that is the opposite surface to the bonding surface bonded to the base, a first one-axis strain sensor provided at the center of the diaphragm on the detection surface, and a second one-axis strain sensor provided on the outer edge of the diaphragm on the detection surface. A Y-axis is set in the direction in which the first one-axis strain sensor and the second one-axis strain sensor are aligned, with the center of the diaphragm as the origin and a ... from the origin to the second one-axis strain sensor. When the direction toward the 1-axis strain sensor is set as the negative direction and the X-axis perpendicular to the Y-axis on the detection surface is set, a cantilever structure including an area where at least a part of a diaphragm is formed is formed on the silicon sensor chip, and the cantilever structure has the second 1-axis strain sensor side along the Y-axis as the tip side and the first 1-axis strain sensor side as the base side, and when the Y coordinates of the positions of the outer edges of the diaphragm on the Y-axis are r and -r, the Y coordinate of the base position of the cantilever structure is -r. <Y<rとなる。 Effect of the Invention

[0009] According to the present invention, it is possible to obtain a pressure sensor capable of reducing the influence of error-causing distortion and performing pressure measurement with higher accuracy. [Brief description of the drawings]

[0010] [Figure 1] 1 is a side view showing a schematic configuration of a pressure sensor according to a first embodiment. [Diagram 2] FIG. 2 is a diagram showing the silicon sensor chip in the first embodiment as viewed from the detection surface side. [Diagram 3] 3 is a cross-sectional view of the pressure sensor taken along a plane including the Y-axis shown in FIG. 2. [Figure 4] 4 is a cross-sectional view showing a state of the silicon sensor chip when a positive temperature change is applied to the entire configuration in the first embodiment. FIG. [Diagram 5] FIG. 13 is a diagram showing the relationship between the distortion of the first and second oscillators caused by a change in temperature when the temperature is increased by 1° C., and the position of the positive side end portion. [Figure 6] FIG. 2 is a diagram showing a first modified example of a cantilever structure, as viewed from the detection surface side of the silicon sensor chip in the first embodiment. [Figure 7] FIG. 2 is a diagram showing a second modified example of a cantilever structure, as viewed from the detection surface side of the silicon sensor chip in the first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A differential pressure transmitter according to an embodiment of the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiment described below.

[0012] [Embodiment 1] [Configuration of pressure sensor] 1 is a side view showing a schematic configuration of a pressure sensor according to embodiment 1. The pressure sensor 1 includes a base 10, a seat 20, and a silicon sensor chip 30. The base 10 is a member for fixing the pressure sensor 1 to a measurement target. The base 10 is made of metal, for example, Kovar. The seat 20 is attached and fixed to the base 10. The seat 20 is made of, for example, glass.

[0013] The silicon sensor chip 30 is bonded and fixed to the base 20. The silicon sensor chip 30 has a bonding surface 30a bonded to the base 20 and a detection surface 30b which is the surface opposite to the bonding surface 30a.

[0014] Fig. 2 is a view of the silicon sensor chip in the first embodiment as seen from the detection surface side. Fig. 3 is a cross-sectional view of the pressure sensor cut along a plane including the Y-axis shown in Fig. 2. A circular diaphragm 31 is formed on the detection surface 30b. The diaphragm 31 is a region that covers a cavity 32 formed inside the silicon sensor chip 30, and is a circular thin film. As the cavity 32 is provided inside, the diaphragm 31 is deformed by changes in pressure applied to the detection surface 30b.

[0015] A first oscillator 41 is provided at the center of the diaphragm 31 on the detection surface 30b. A second oscillator 42 is provided at the outer edge of the diaphragm 31 on the detection surface 30b. The first oscillator 41 is a first uniaxial strain sensor. The second oscillator 42 is a second uniaxial strain sensor. In addition to the oscillator, a piezoelectric element, which is a uniaxial strain sensor similar to a vibration sensor such as an oscillator, or a strain gauge using a metal thin film can be used for the first uniaxial strain sensor and the second uniaxial strain sensor. The deformation amount of the diaphragm 31 changes depending on the pressure applied to the diaphragm 31. Strain occurs in the first oscillator 41 and the second oscillator 42 as the diaphragm 31 deforms. The resonance frequency of the first oscillator 41 and the second oscillator 42 changes depending on the strain. Therefore, in the pressure sensor 1, the pressure applied to the diaphragm 31 can be measured by detecting the change in the resonance frequency of the first oscillator 41 and the second oscillator .

[0016] Here, the Y axis is set in the direction in which the first oscillator 41 and the second oscillator 42 are aligned. The center of the diaphragm 31 is set as the origin, the direction from the origin toward the second oscillator 42 is set as the negative direction, and the opposite direction is set as the positive direction. The X axis is set on the detection surface 30b, perpendicular to the Y axis. The unit of the Y coordinate is [mm].

[0017] The silicon sensor chip 30 is formed with a first groove 51, a second groove 52, and a connecting space 53. The first groove 51 is a pair of grooves extending parallel to the Y axis. The pair of first grooves 51 are arranged side by side along the X axis direction, and are provided on both sides of the second vibrator 42. The negative end portions of the pair of first grooves 51 are located on the negative side of the second vibrator 42.

[0018] The second groove 52 is a groove that connects the negative end portions of the pair of first grooves 51. The first groove 51 and the second groove 52 are formed to a depth such that their respective bottoms are closer to the bonding surface 30a than the cavity 32. The second groove 52 is located on the negative side of the second vibrator 42.

[0019] The connecting space 53 connects the bottom of the pair of first grooves 51 and the bottom of the second groove 52. The connecting space 53 is formed on the bonding surface 30a side of the cavity 32. In the silicon sensor chip 30, an area surrounded by the pair of first grooves 51, second grooves 52, and the connecting space 53 extends along the Y-axis direction and has a cantilever structure with the end on the positive side supported.

[0020] In the pressure sensor 1, silicon oil is filled around the entire periphery except for the bottom surface of the base 10. Pressure is applied to the silicon oil through a pressure-receiving diaphragm (not shown). When pressure is applied to the silicon oil, the pressure applied to the diaphragm 31 formed on the silicon sensor chip 30 also changes, and the diaphragm 31 is deformed. When the diaphragm 31 is deformed, distortion occurs in the first oscillator 41 provided at the center of the diaphragm 31 and the second oscillator 42 provided on the outer edge. The occurrence of distortion changes the resonant frequencies of the first oscillator 41 and the second oscillator 42. In the pressure sensor 1, the pressure applied to the pressure-receiving diaphragm is measured by detecting the change in the resonant frequencies of the first oscillator 41 and the second oscillator 42.

[0021] Here, in order to accurately measure the pressure applied to the pressure-receiving diaphragm 31, it is desirable that the distortion occurring in the first oscillator 41 and the second oscillator 42 is caused only by the pressure applied to the diaphragm 31.

[0022] However, since the linear expansion coefficient of the base 20 to which the silicon sensor chip 30 is fixed differs from the linear expansion coefficient of the base 20, a strain is applied to the silicon sensor chip 30 due to the difference in the linear expansion coefficient when the temperature changes.

[0023] For example, if the base 20 is made of glass, the linear expansion coefficient of the base 20 is 3.2 ppm / °C, and the linear expansion coefficient of the silicon sensor chip 30 is 2.6 ppm / °C. In this case, when the temperature rises, compressive strain occurs on the detection surface 30b. When compressive strain occurs on the detection surface 30b, strain occurs on the first oscillator 41 and the second oscillator 42. In other words, when the temperature changes, strain other than strain caused by pressure occurs on the first oscillator 41 and the second oscillator 42, and the change in temperature becomes a factor of measurement error of the pressure sensor 1.

[0024] FIG. 4 is a cross-sectional view showing the state of the silicon sensor chip when a positive temperature change is applied to the entire configuration in the first embodiment. Since the linear expansion coefficient of the base 20 is larger than that of the silicon sensor chip 30, the entire silicon sensor chip 30 is deformed into a downward convex shape due to the so-called bimetal effect. In FIG. 4, the deformation of the detection surface 30b is exaggerated for ease of understanding. The area of ​​the detection surface 30b surrounded by the first groove 51 and the second groove 52 is part of the surface of the cantilever beam, so that the compressive strain caused by the temperature change is smaller than that of the other area of ​​the detection surface 30b. Therefore, as shown in FIG. 4, even if the compressive strain occurs in the detection surface 30b due to the temperature change, the deformation of the part having the cantilever beam structure is small. In this way, the first groove 51, the second groove 52, and the connection space 53 are formed, so that the error-causing strain of the first oscillator 41 and the second oscillator 42 due to the temperature change can be reduced, thereby reducing the measurement error.

[0025] Returning to FIG. 2, the first oscillator 41 is provided in the center of the diaphragm 31, and the second oscillator 42 is provided on the outer edge of the diaphragm 31. Therefore, when the diaphragm 31 is deformed, the strains generated in the first oscillator 41 and the second oscillator 42 are in opposite directions. For example, when the diaphragm 31 is deformed so as to be recessed due to the application of pressure, a compressive strain is generated in the first oscillator 41, and a tensile strain is generated in the second oscillator 42. Therefore, by utilizing the difference between the strains of the first oscillator 41 and the second oscillator 42, it is possible to eliminate the influence of the strain caused by the change in temperature and reduce the measurement error.

[0026] Here, since the first oscillator 41 is provided closer to the base of the cantilever structure and the second oscillator 42 is provided closer to the tip of the cantilever structure, the compressive strain generated in the oscillators when the temperature changes is smaller in the second oscillator 42 than in the first oscillator 41. Therefore, the error factor strain when the temperature changes is smaller in the second oscillator 42 than in the first oscillator 41. As a result, the error factor strain of the first oscillator 41 and the error factor strain of the second oscillator 42 do not match, and it is difficult to completely eliminate the error factors even if the difference in strain is utilized.

[0027] In the first embodiment, the difference between the error-causing strain of the first oscillator 41 and the error-causing strain of the second oscillator 42 when the temperature changes is reduced by the position of the end of the pair of first grooves 51 on the positive side along the Y axis, and the measurement error due to the change in temperature when the difference in strain is used is further reduced. In the following description, the end of the pair of first grooves 51 on the positive side along the Y axis is simply referred to as the positive side end 51a. The positive side end 51a is the base position of the cantilever structure.

[0028] FIG. 5 is a diagram showing the relationship between the distortion of the first and second oscillators caused by the change in temperature when the temperature is increased by 1° C. and the position of the positive side end. Here, the detection surface 30b of the silicon sensor chip 30 is assumed to be a square with a side length of 6 mm as shown in FIG. 2. The length of the first oscillator 41 along the Y axis is assumed to be 0.7 mm (700 μm). The length of the second oscillator 42 along the Y axis is assumed to be 0.59 mm (590 μm). The radius of the diaphragm 31 is assumed to be 1.5 mm.

[0029] The leftmost part of FIG. 5 shows the error-causing distortion when the first groove 51, the second groove 52, and the connecting space 53 are not formed. As shown in FIG. 5, the first groove 51, the second groove 52, and the connecting space 53 are formed, so that the distortion of the first oscillator 41 and the second oscillator 42 caused by temperature changes is reduced. The distortion of the first oscillator 41 and the second oscillator 42 tends to be reduced as the Y coordinate of the position of the positive-side end 51a of the first groove 51 is increased toward the positive side. Therefore, if the positive-side end 51a is increased, the influence of the distortion caused by temperature changes can be reduced. In particular, by making the Y coordinate of the positive-side end 51a larger than the radius of the diaphragm 31, the distortion of the first oscillator 41 and the second oscillator 42 can be reduced, and the influence of the error-causing distortion caused by temperature changes can be reduced.

[0030] However, in many ranges of the position of the positive-side end portion 51a, there is a difference between the strain of the first oscillator 41 and the strain of the second oscillator 42. Therefore, even if the difference between the strain of the first oscillator 41 and the strain of the second oscillator 42 is used to reduce the measurement error, the error factor remains.

[0031] Here, as shown in FIG. 5, the strain of the first vibrator 41 and the strain of the second vibrator 42 coincide where the Y coordinate of the position of the positive-direction side end portion 51a becomes a specific value. In the example shown in FIG. 5, the Y coordinate that becomes the specific value is -0.1. Also, the farther the positive-direction side end portion 51a is from the specific value in both the positive and negative directions, the greater the difference between the strain of the first vibrator 41 and the strain of the second vibrator 42. That is, the closer the Y coordinate of the position of the positive-direction side end portion 51a is to the specific value, the smaller the difference between the error factor strain of the first vibrator 41 and the error factor strain of the second vibrator 42, and the error factor when using the difference in strain also becomes smaller.

[0032] Therefore, in the pressure sensor 1 according to Embodiment 1, in order to further reduce the influence of the error factor strain caused by the temperature change of the first vibrator 41 and the second vibrator 42, when the radius of the diaphragm 31 is r, the Y coordinate of the position of the positive-direction side end portion 51a of the first groove 51 is set to -r < Y < r (range A1 shown in FIG. 2). r and -r can also be said to be the Y coordinates of the positions of the outer edges of the diaphragm 31 on the Y axis.

[0033] Also, in order to make the difference between the error factor strain of the first vibrator 41 and the error factor strain of the second vibrator 42 smaller, when the Y coordinate of the position of the positive-direction side end portion of the second vibrator 42 is -a, it is desirable that the Y coordinate of the position of the positive-direction side end portion 51a of the first groove 51 be -a < Y < a (range A2 shown in FIG. 2).

[0034] Furthermore, in order to make the difference between the strain of the first vibrator 41 and the strain of the second vibrator 42 smaller, when the Y coordinate of the position of the positive-direction side end portion of the first vibrator 41 is b, it is more desirable that the Y coordinate of the position of the positive-direction side end portion 51a of the first groove 51 be -a < Y < b (range A3 shown in FIG. 2).

[0035] In this way, the closer the Y coordinate of the position of the positive side end 51a of the first groove 51 is to the specific position where the distortion of the first oscillator 41 and the distortion of the second oscillator 42 coincide, the more the influence of error-causing distortion due to temperature change can be reduced, resulting in a pressure sensor 1 that can perform pressure measurements with higher accuracy.

[0036] 5, the strain of the first oscillator 41 is more affected by changes in the position of the positive end 51a than the strain of the second oscillator 42. This is because the first oscillator 41 is provided closer to the base of the cantilever structure, and therefore the Poisson's ratio of the strain in the X-axis direction that is applied to the strain in the Y-axis direction changes depending on the position of the positive end 51a. In contrast, the second oscillator 42 is provided closer to the tip of the cantilever, and therefore the effect of changes in the position of the positive end 51a on the strain is smaller.

[0037] Another example (modification) of the cantilever structure formed on the silicon sensor chip 30 is shown. FIG. 6 is a view of the silicon sensor chip in the first embodiment as seen from the detection surface side, showing a first modification of the cantilever structure. As shown in FIG. 6, the first groove 51 may be formed in a crank shape, and the tip side of the cantilever structure may be thinner than the base side. FIG. 7 is a view of the silicon sensor chip in the first embodiment as seen from the detection surface side, showing a second modification of the cantilever structure. As shown in FIG. 7, the distance between the first grooves 51 may be smaller toward the tip of the cantilever structure, and the tip side of the cantilever structure may be thinner than the base side.

[0038] 〔others〕 Some examples of combinations of the disclosed technical features are set out below.

[0039] (1) A pressure sensor comprising a pedestal, a silicon sensor chip joined to the pedestal and having a circular diaphragm formed on a detection surface which is the opposite surface of the joint surface joined to the pedestal, a first uniaxial strain sensor provided at the center of the diaphragm on the detection surface, and a second uniaxial strain sensor provided at the outer edge of the diaphragm on the detection surface. When a Y-axis is set in the direction in which the first uniaxial strain sensor and the second uniaxial strain sensor are aligned with the center of the diaphragm as the origin, and the direction from the origin to the second uniaxial strain sensor is defined as the negative direction, a cantilever beam structure including at least a region where a part of the diaphragm is formed is formed in the silicon sensor chip. In the cantilever beam structure, the side on the second uniaxial strain sensor side along the Y-axis is the tip side, and the side on the first uniaxial strain sensor side is the root side. When the Y-coordinates of the positions of the outer edge of the diaphragm on the Y-axis are r and -r, the Y-coordinate of the position of the root of the cantilever beam structure satisfies -r < Y < r.

[0040] (2) The pressure sensor according to (1), wherein when the Y-coordinate of the end position on the positive direction side of the second uniaxial strain sensor is -a, the Y-coordinate of the position of the root of the cantilever beam structure satisfies -a < Y < a.

[0041] (3) The pressure sensor according to (2), wherein when the Y-coordinate of the end position on the positive direction side of the first uniaxial strain sensor is b, the Y-coordinate of the position of the root of the cantilever beam structure satisfies -a < Y < b.

Description of Reference Numerals

[0042] 1 Pressure sensor 10 Base 20 Pedestal 30 Silicon sensor chip 30a Joint surface 30b Detection surface 31 Diaphragm 32 Cavity 41 First vibrator 42 Second vibrator 51 First groove 51a Positive direction side end 52 The Second Groove 53 Connected Space

Claims

1. With a pedestal, a silicon sensor chip that is bonded to the base and has a circular diaphragm formed on a detection surface that is the opposite surface to the bonding surface bonded to the base; a first uniaxial strain sensor provided at the center of the diaphragm on the detection surface; a second uniaxial strain sensor provided on an outer edge of the diaphragm on the detection surface; When the Y axis is set in the direction in which the first uniaxial strain sensor and the second uniaxial strain sensor are aligned, the center of the diaphragm is set as the origin, and the direction from the origin toward the second uniaxial strain sensor is set as the negative direction, a cantilever structure including a region in which at least a portion of the diaphragm is formed is formed on the silicon sensor chip; The cantilever structure has a tip side on the second uniaxial strain sensor side along the Y axis and a base side on the first uniaxial strain sensor side, A pressure sensor in which, when the Y coordinates of the positions of the outer edge of the diaphragm on the Y axis are r and -r, the Y coordinate of the position of the base of the cantilever beam structure satisfies -r<Y<r.

2. The pressure sensor according to claim 1, wherein when the Y coordinate of the end position on the positive side of the second uniaxial strain sensor is -a, the Y coordinate of the base position of the cantilever beam structure satisfies -a<Y<a.

3. The pressure sensor according to claim 2, wherein when the Y coordinate of the end position on the positive side of the first uniaxial strain sensor is b, the Y coordinate of the base position of the cantilever beam structure satisfies -a<Y<b.

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