pressure sensor
The pressure sensor employs a cantilever structure with aligned strain sensors to minimize temperature-induced strain errors, improving measurement accuracy by leveraging differential strain sensitivity.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- YOKOGAWA ELECTRIC CORP
- Filing Date
- 2023-09-04
- Publication Date
- 2026-06-30
AI Technical Summary
Existing pressure sensors with uniaxial strain sensors suffer from residual error factors due to mismatched strains in the strain sensors, leading to inaccuracies in pressure measurement despite differential calculations.
A pressure sensor design with a cantilever structure incorporating a first uniaxial strain sensor at the center and a second uniaxial strain sensor at the edge of the diaphragm, aligned along the Y-axis, where the grooves and connection spaces reduce strain errors by minimizing the influence of temperature-induced strains through differential strain sensitivity.
The design achieves more accurate pressure measurements by effectively reducing strain errors caused by temperature changes, enhancing the precision of pressure detection.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to a pressure sensor.
Background Art
[0002] A pressure sensor provided with a uniaxial strain sensor such as a vibrator on a diaphragm that is deformed by a change in pressure is known. In a pressure sensor provided with a uniaxial strain sensor, strain occurs in the uniaxial strain sensor as the diaphragm deforms. In the pressure sensor, the pressure applied to the diaphragm is measured by detecting a change in the resonance frequency or the like of the uniaxial strain sensor due to the generated strain (see, for example, Patent Document 1).
[0003] Some of such pressure sensors include a silicon sensor chip in which a cavity is formed inside silicon and a region covering the cavity serves as a diaphragm. The silicon sensor chip is fixed to a pedestal. In order to prevent strain from occurring in the diaphragm due to factors other than pressure, the pedestal is formed of a member that relaxes the strain generated between the silicon and the pedestal. Also, in order to suppress deformation due to temperature change, the pedestal is formed of a material having a linear expansion coefficient close to that of silicon. The pedestal is formed of, for example, glass.
[0004] Since the linear expansion coefficients of the silicon sensor chip and the pedestal are close, error factor strain caused by the difference in linear expansion coefficients during temperature change can be reduced. However, since the linear expansion coefficients do not match exactly, the error factor strain does not become zero. Therefore, in order to further suppress the influence of the error factor strain, two uniaxial strain sensors, a uniaxial strain sensor that generates compressive strain and a uniaxial strain sensor that generates tensile strain when pressure is applied to the diaphragm, are provided, and by using the difference in strain sensitivity of the two uniaxial strain sensors through differential calculation, pressure is measured with higher accuracy.
Prior Art Documents
Patent Documents
[0005] [Patent Document 1] Japanese Patent Publication No. 2015-38433 [Overview of the project] [Problems that the invention aims to solve]
[0006] However, because the error-causing strains generated in the two uniaxial strain sensors did not match, there was a problem in that even after performing differential calculations, a slight influence of the error-causing strain remained.
[0007] The present invention aims to provide a pressure sensor that can perform more accurate pressure measurement by reducing the influence of error-causing strain on a uniaxial strain sensor. [Means for solving the problem]
[0008] The pressure sensor according to the present invention comprises a base, a silicon sensor chip bonded to the base and having a circular diaphragm formed on the detection surface opposite to the bonding surface bonded to the base, 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, with the Y-axis set in the direction in which the first and second uniaxial strain sensors are aligned, the center of the diaphragm as the origin, and the second from the origin When the direction toward the uniaxial strain sensor is defined as the negative direction, and the X-axis is set to be perpendicular to the Y-axis on the detection surface, the silicon sensor chip has a cantilever structure that includes at least a region in which a part of the diaphragm is formed, and the cantilever structure has the second uniaxial strain sensor side along the Y-axis as the tip side and the first uniaxial strain sensor side as the base side, and 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 structure is -r <Y<rとなる。 [Effects of the Invention]
[0009] According to the present invention, it is possible to obtain a pressure sensor that can perform more accurate pressure measurement by reducing the influence of strain, which is an error factor. [Brief explanation of the drawing]
[0010] [Figure 1] This is a side view showing the schematic configuration of a pressure sensor according to Embodiment 1. [Figure 2] This is a view of the silicon sensor chip in Embodiment 1, seen from the detection side. [Figure 3] Figure 2 is a cross-sectional view of the pressure sensor cut along a plane containing the Y-axis. [Figure 4] This 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 Embodiment 1. [Figure 5] This figure shows the relationship between the strain of the first and second oscillators caused by the temperature change when the temperature is increased by 1°C, and the position of the positive-direction end. [Figure 6] This diagram shows the silicon sensor chip in Embodiment 1 as viewed from the detection surface side, and is a first modified example of a cantilever beam structure. [Figure 7] This diagram shows a silicon sensor chip in Embodiment 1 as viewed from the detection surface side, and illustrates a second modified example of the cantilever beam structure. [Modes for carrying out the invention]
[0011] A differential pressure transmitter according to one embodiment of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to the embodiments described below.
[0012] [Embodiment 1] [Configuration of the pressure sensor] Figure 1 is a side view showing a schematic configuration of a pressure sensor according to Embodiment 1. The pressure sensor 1 comprises a base 10, a pedestal 20, and a silicon sensor chip 30. The base 10 is a member for fixing the pressure sensor 1 to the object to be measured. The base 10 is made of metal, for example, Kovar. The pedestal 20 is attached to and fixed to the base 10. The pedestal 20 is made of glass, for example.
[0013] The silicon sensor chip 30 is bonded and fixed to the base 20. The silicon sensor chip 30 has a bonding surface 30a that is bonded to the base 20, and a detection surface 30b which is the opposite side of the bonding surface 30a.
[0014] Figure 2 is a view of the silicon sensor chip in Embodiment 1, seen from the detection surface side. Figure 3 is a cross-sectional view of the pressure sensor cut along a plane containing the Y-axis shown in Figure 2. A circular diaphragm 31 is formed on the detection surface 30b. The diaphragm 31 is a circular thin film that covers the cavity 32 formed inside the silicon sensor chip 30. Because the cavity 32 is provided inside, the diaphragm 31 deforms as the pressure applied to the detection surface 30b changes.
[0015] A first vibrator 41 is provided at the center of the diaphragm 31 on the detection surface 30b. A second vibrator 42 is provided at the outer edge of the diaphragm 31 on the detection surface 30b. The first vibrator 41 is a first uniaxial strain sensor. The second vibrator 42 is a second uniaxial strain sensor. In addition to vibrators, the first and second uniaxial strain sensors can also be uniaxial strain sensors similar to vibrating sensors, such as piezoelectric elements or strain gauges using thin metal films. The amount of deformation of the diaphragm 31 changes according to the pressure applied to the diaphragm 31. Strain is generated in the first vibrator 41 and the second vibrator 42 in accordance with the deformation of the diaphragm 31. The resonant frequencies of the first vibrator 41 and the second vibrator 42 change according to the strain. Therefore, the pressure sensor 1 can measure the pressure applied to the diaphragm 31 by detecting changes in the resonant frequencies of the first oscillator 41 and the second oscillator 42.
[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 defined as the negative direction, and the opposite direction is defined as the positive direction. Furthermore, the X-axis is set on the detection surface 30b, perpendicular to the Y-axis. The unit of the Y-coordinate value is [mm].
[0017] The silicon sensor chip 30 is formed with a first groove 51, a second groove 52, and a connection 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 provided on both sides of the second vibrator 42. The end portions on the negative direction side of the pair of first grooves 51 are located on the negative direction side of the second vibrator 42.
[0018] The second groove 52 is a groove connecting the end portions on the negative direction side of the pair of first grooves 51. The bottoms of the first groove 51 and the second groove 52 are formed at a depth where the bottom of each is on the bonding surface 30a side of the cavity 32. The second groove 52 is located on the negative direction side of the second vibrator 42.
[0019] The connection space 53 connects the bottoms of the pair of first grooves 51 and the bottom of the second groove 52. The connection space 53 is formed on the bonding surface 30a side of the cavity 32. In the silicon sensor chip 30, the region surrounded by the pair of first grooves 51, the second groove 52, and the connection space 53 extends along the Y-axis direction and has a structure of a cantilever beam with the end portion on the positive direction side supported.
[0020] In the pressure sensor 1, silicon oil is filled around all of the base 10 except for the bottom surface. 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, causing the diaphragm 31 to deform. When the diaphragm 31 deforms, strain occurs in the first vibrator 41 provided at the center of the diaphragm 31 and the second vibrator 42 provided at the outer edge. When strain occurs, the resonance frequencies of the first vibrator 41 and the second vibrator 42 change. In the pressure sensor 1, by detecting the change in the resonance frequencies of the first vibrator 41 and the second vibrator 42, the pressure applied to the pressure-receiving diaphragm is measured.
[0021] In order to accurately measure the pressure applied to the pressure-receiving diaphragm, it is desirable that the strain generated in the first oscillator 41 and the second oscillator 42 be solely due to the pressure applied to the diaphragm 31.
[0022] However, because the coefficient of thermal expansion of the base 20 on which the silicon sensor chip 30 is fixed is different from the coefficient of thermal expansion of the base 20, when the temperature changes, strain caused by the difference in the coefficients of thermal expansion is applied to the silicon sensor chip 30.
[0023] For example, if the base 20 is made of glass, the coefficient of linear expansion of the base 20 will be 3.2 ppm / °C, and the coefficient of linear expansion of the silicon sensor chip 30 will be 2.6 ppm / °C. In this case, as the temperature rises, compressive strain will occur on the detection surface 30b. When compressive strain occurs on the detection surface 30b, strain will occur in the first oscillator 41 and the second oscillator 42. In other words, changes in temperature will cause strain other than that caused by pressure to occur in the first oscillator 41 and the second oscillator 42, and the change in temperature will become a factor in the measurement error of the pressure sensor 1.
[0024] Figure 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 Embodiment 1. Because the linear expansion coefficient of the base 20 is greater than that of the silicon sensor chip 30, the entire silicon sensor chip 30 deforms into a downward convex shape due to the so-called bimetallic effect. In Figure 4, the deformation of the detection surface 30b is exaggerated for ease of understanding. The region of the detection surface 30b surrounded by the first groove 51 and the second groove 52 is part of the surface of a cantilever beam, so the compressive strain that occurs when the temperature changes is smaller in this region compared to other regions of the detection surface 30b. Therefore, as shown in Figure 4, even if compressive strain occurs in the detection surface 30b due to a change in temperature, the deformation of the cantilever beam structure is small. In this way, the formation of the first groove 51, the second groove 52 and the connecting space 53 reduces the error-causing strain of the first oscillator 41 and the second oscillator 42 due to temperature changes, thereby reducing measurement errors.
[0025] Returning to Figure 2, the first oscillator 41 is located in the center of the diaphragm 31, and the second oscillator 42 is located on the outer edge of the diaphragm 31. Therefore, when the diaphragm 31 deforms, the strains generated in the first oscillator 41 and the second oscillator 42 are in opposite directions. For example, if the diaphragm 31 deforms in a concave manner due to pressure application, compressive strain is generated in the first oscillator 41 and tensile strain is generated in the second oscillator 42. Therefore, by utilizing the difference between the strain of the first oscillator 41 and the strain of the second oscillator 42, the effects of strain caused by temperature changes can be eliminated, thereby reducing measurement errors.
[0026] Here, the first oscillator 41 is located closer to the base of the cantilever structure, and the second oscillator 42 is located closer to the tip of the cantilever structure. Therefore, when the temperature changes, the compressive strain generated in the oscillator is smaller for the second oscillator 42 than for the first oscillator 41. Consequently, the error-causing strain when the temperature changes is smaller for the second oscillator 42 than for the first oscillator 41. As a result, the error-causing strain of the first oscillator 41 and the error-causing strain of the second oscillator 42 do not match, and it is difficult to completely eliminate the error factors even by utilizing the difference in strain.
[0027] In this embodiment 1, the position of the positive-direction ends of the pair of first grooves 51 along the Y-axis reduces 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, thereby further reducing measurement errors due to temperature changes when utilizing the difference in strain. In the following description, the positive-direction ends of the pair of first grooves 51 along the Y-axis will simply be referred to as the positive-direction ends 51a. The positive-direction ends 51a are located at the base of the cantilever beam structure.
[0028] Figure 5 shows the relationship between the strain of the first and second oscillators caused by the temperature change when the temperature is increased by 1°C, and the position of the positive-direction end. Here, the detection surface 30b of the silicon sensor chip 30 is assumed to be a square with sides of 6 mm, as shown in Figure 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 Figure 5 shows the error-causing strain when the first groove 51, the second groove 52, and the connecting space 53 are not formed. As shown in Figure 5, the formation of the first groove 51, the second groove 52, and the connecting space 53 reduces the strain of the first oscillator 41 and the second oscillator 42 caused by temperature changes. The larger the Y-coordinate of the positive-direction end 51a of the first groove 51 is in the positive direction, the smaller the strain of the first oscillator 41 and the second oscillator 42 tends to be. Therefore, increasing the size of the positive-direction end 51a can reduce the effect of strain caused by temperature changes. In particular, by making the Y-coordinate of the positive-direction end 51a larger than the radius of the diaphragm 31, the strain of the first oscillator 41 and the second oscillator 42 can be reduced, thereby reducing the effect of error-causing strain caused by temperature changes.
[0030] However, in many areas, there is a difference between the strain of the first oscillator 41 and the strain of the second oscillator 42 at the position of the positive-direction end 51a. Therefore, even when attempting to reduce measurement errors by utilizing the difference between the strain of the first oscillator 41 and the strain of the second oscillator 42, error factors remain.
[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, as the positive-direction side end portion 51a moves away from the specific value in both the positive direction and the negative direction, the difference between the strain of the first vibrator 41 and the strain of the second vibrator 42 increases. 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 smaller the error factor when using the difference in strain.
[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 regarded as 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] Thus, the closer the Y-coordinate of the positive-direction end 51a of the first groove 51 is to a specific position where the strain of the first oscillator 41 and the strain of the second oscillator 42 coincide, the more the influence of error-causing strain due to temperature changes can be reduced, resulting in a pressure sensor 1 that can perform more accurate pressure measurements.
[0036] As shown in Figure 5, the strain of the first oscillator 41 is more affected by changes in the position of the positive-direction end 51a than the strain of the second oscillator 42. This is because the first oscillator 41 is located closer to the base of the cantilever beam structure, and the position of the positive-direction end 51a changes the Poisson's ratio of the strain in the X-axis direction that is applied to the strain in the Y-axis direction. In contrast, the second oscillator 42 is located closer to the tip of the cantilever beam, so changes in the position of the positive-direction end 51a have less effect on the strain.
[0037] Other examples (modified versions) of the cantilever structure formed on the silicon sensor chip 30 are shown. Figure 6 is a view of the silicon sensor chip in Embodiment 1 from the detection surface side, and shows a first modified version of the cantilever structure. As shown in Figure 6, the first groove 51 is formed in a crank shape, and the cantilever structure may be thinner at the tip than at the base. Figure 7 is a view of the silicon sensor chip in Embodiment 1 from the detection surface side, and shows a second modified version of the cantilever structure. As shown in Figure 7, the distance between the first grooves 51 is formed to decrease towards the tip of the cantilever structure, and the cantilever structure may be thinner at the first-order side than at the base.
[0038] 〔others〕 Some examples of the combinations of technical features that will be disclosed are listed 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 joining 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. The cantilever beam structure has the second uniaxial strain sensor side along the Y-axis as the tip side and the first uniaxial strain sensor side as 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.
Explanation of Signs
[0042] 1 Pressure sensor 10 Base 20 Pedestal 30 Silicon sensor chip 30a Joining 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 Connecting Space
Claims
1. The base and A silicon sensor chip is joined to the base, and a circular diaphragm is formed on the detection surface, which is the opposite side of the joining surface to the base. A first uniaxial strain sensor is provided at the center of the diaphragm on the detection surface, The system comprises a second uniaxial strain sensor provided on the 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 taken as the origin, and the direction from the origin toward the second uniaxial strain sensor is taken as the negative direction, The silicon sensor chip has a cantilever structure formed on it, which includes at least a region where a part of the diaphragm is formed. In the cantilever beam structure, the side with the second uniaxial strain sensor along the Y-axis is the tip side, and the side with the first uniaxial strain sensor is the base 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 is -r < Y < r.
2. The pressure sensor according to claim 1, wherein when the Y-coordinate of the positive-direction end position of the second uniaxial strain sensor is -a, the Y-coordinate of the base position of the cantilever beam structure is -a < Y < a.
3. The pressure sensor according to claim 2, wherein when the Y-coordinate of the positive-direction end position of the first uniaxial strain sensor is b, the Y-coordinate of the base position of the cantilever beam structure is -a < Y < b.