CN117607489B - Sensitive structure of piezoresistive acceleration sensor and acceleration sensor - Google Patents
Sensitive structure of piezoresistive acceleration sensor and acceleration sensor Download PDFInfo
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- CN117607489B CN117607489B CN202410063803.5A CN202410063803A CN117607489B CN 117607489 B CN117607489 B CN 117607489B CN 202410063803 A CN202410063803 A CN 202410063803A CN 117607489 B CN117607489 B CN 117607489B
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- 230000001133 acceleration Effects 0.000 title claims abstract description 56
- 230000009471 action Effects 0.000 claims abstract description 8
- 238000002955 isolation Methods 0.000 claims description 32
- 230000004308 accommodation Effects 0.000 claims description 5
- 239000010410 layer Substances 0.000 description 10
- 230000009286 beneficial effect Effects 0.000 description 6
- 230000035945 sensitivity Effects 0.000 description 6
- 238000001514 detection method Methods 0.000 description 5
- 238000010586 diagram Methods 0.000 description 5
- 238000005259 measurement Methods 0.000 description 4
- 230000035939 shock Effects 0.000 description 4
- 230000001808 coupling effect Effects 0.000 description 3
- 230000004044 response Effects 0.000 description 3
- 239000002356 single layer Substances 0.000 description 3
- 230000008859 change Effects 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000004806 packaging method and process Methods 0.000 description 2
- 230000002093 peripheral effect Effects 0.000 description 2
- 229910052710 silicon Inorganic materials 0.000 description 2
- 239000010703 silicon Substances 0.000 description 2
- 230000004075 alteration Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000004880 explosion Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 238000009863 impact test Methods 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
- G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
- G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
- G01P15/12—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by alteration of electrical resistance
- G01P15/122—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by alteration of electrical resistance by metal resistance strain gauges, e.g. wire resistance strain gauges
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
- G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
- G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
- G01P15/0802—Details
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Abstract
The invention belongs to the technical field of acceleration sensors. The invention provides a sensitive structure of a piezoresistive acceleration sensor and the acceleration sensor. The sensitive structure comprises a frame and a sensitive unit, wherein the frame is provided with a first accommodating space, and the sensitive unit is arranged in the first accommodating space. The sensing unit comprises a mass block, a first support beam and a second support beam. The mass has a main body and a protrusion fixed to the main body; one ends of the first support beam and the second support beam are respectively connected to a first longitudinal position and a second longitudinal position of the main body of the mass; the longitudinal direction of the mass block is the sensitive direction of the mass block, and the extending direction of the convex part of the mass block is parallel to the extending directions of the first supporting beam and the second supporting beam; the mass block generates acting force on the first supporting beam and the second supporting beam under the action of acceleration. The anti-impact capability and the transverse anti-interference capability of the sensitive structure are improved. The spatial position can be fully utilized, thereby reducing the volume of the sensitive structure.
Description
Technical Field
The invention relates to the technical field of sensors, in particular to a piezoresistive acceleration sensor.
Background
Piezoresistive acceleration sensors based on micro-nano processing technology are widely applied to the fields of automobile collision, explosion impact test and the like. The piezoresistive acceleration sensor includes a frame, a mass block, a connection beam, and a strain resistor (resistive strain gauge), one end of the connection beam is fixed to the frame, and the other end of the connection beam is fixed to the mass block. The connecting beam is provided with a strain resistor, and the mass block deforms the connecting beam under the action of acceleration, so that the resistance value of the strain resistor on the connecting beam is changed.
In the prior art, a single-layer connecting beam is usually arranged, so that the shock resistance of the acceleration sensor is weak, and the transverse anti-interference capability is also weak. In addition, gaps are formed among the connecting beams, the mass blocks and the frame, and the space arrangement of the connecting beams, the mass blocks and the frame often limits the volume of the acceleration sensor, so that the acceleration sensor cannot further optimize the volume. In addition, the sensitive structure has no stress isolation frame, external interference stress is easy to act on the strain resistor part, so that temperature drift is serious, and measurement error is large.
Disclosure of Invention
In order to solve the technical problems, the invention provides a sensing structure of a piezoresistive acceleration sensor and the acceleration sensor, which can not only improve the shock resistance of the sensor, but also reduce the volume of the sensor.
In a first aspect of the present disclosure, a sensing structure of a piezoresistive acceleration sensor is provided, including a frame and a sensing unit, where the frame is formed with a first accommodating space, and the sensing unit is disposed in the first accommodating space. The sensing unit comprises a mass block, a first support beam and a second support beam. The mass block is provided with a main body and a convex part protruding out of the main body; one end of the first support beam is connected to a first longitudinal position of the main body of the mass, and the other end is connected to the frame; one end of the second support beam is connected to the second longitudinal position of the body of the mass and the other end is connected to the frame. Wherein the longitudinal direction of the mass block is the sensitive direction of the mass block; the first supporting beam and the second supporting beam are respectively arranged at two opposite sides of the main body of the mass block, and the extending direction of the convex part of the mass block is parallel to the extending directions of the first supporting beam and the second supporting beam; the mass block generates acting force on the first supporting beam and the second supporting beam under the action of acceleration.
Further, the mass block is provided with two convex parts which are respectively arranged at two sides of the main body of the mass block.
Further, the sensitive structure further comprises a strain resistor, wherein the strain resistor is arranged on the first supporting beam, and the rigidity of the first supporting beam is higher than that of the second supporting beam.
Further, the sensitive structure is provided with two first supporting beams and two second supporting beams, a first supporting beam and a second supporting beam are respectively arranged on two sides of the mass block, and the first supporting beam on one side is opposite to the second supporting beam on the other side.
Further, the width of the first support beam is greater than the width of the second support beam.
Further, the width of the gap between the convex part of the mass block and the first supporting beam and the second supporting beam on the same side is equal.
Further, the thickness of the first supporting beam and the second supporting beam is smaller than that of the mass block, the upper surface of the first supporting beam is flush with the upper surface of the sensitive structure, two strain resistors are arranged on the upper surface of each first supporting beam, and the two strain resistors are respectively arranged at two ends of the first supporting beam.
Further, four bonding pads are arranged on the upper surface of the frame, each bonding pad is electrically connected with one strain resistor, and the four strain resistors are electrically connected to form a Wheatstone full bridge circuit.
Further, the sensitive structure further comprises an isolation frame and a connecting beam, wherein the isolation frame and the connecting beam are arranged in the first accommodating space, and the isolation frame is connected to the frame through the connecting beam. The isolation frame is provided with a second accommodating space, and the sensitive unit is arranged in the second accommodating space; the other end of the first supporting beam and the other end of the second supporting beam are both fixed to the isolation frame, and the first supporting beam and the second supporting beam are connected to the frame through the isolation frame.
In a second aspect of the present disclosure, an acceleration sensor is provided, which includes an upper cover plate, a bottom plate, and the foregoing sensitive structure, where the sensitive structure is disposed between the upper cover plate and the bottom plate.
The sensitive structure layer of the piezoresistive acceleration sensor and the acceleration sensor have the following characteristics and advantages:
1. the sensitive structure is provided with a double-layer supporting beam, which is beneficial to improving the shock resistance of the sensitive structure; the double-layer supporting beam can effectively limit the transverse swing of the mass block, namely inhibit the transverse coupling effect of the sensitive structure, and is beneficial to improving the transverse anti-interference capability of the sensitive structure;
2. in addition, the first supporting beam, the second supporting beam and the convex parts of the mass block are staggered, so that the space position can be fully utilized, and the volume of the sensitive structure is reduced;
3. the rigidity of the first supporting beam is greater than that of the second supporting beam, and a strain resistor is arranged on the first supporting beam, so that larger stress can be obtained by the strain resistor; in addition, the frequency and the mode of the sensitive structure can be modulated by adjusting the width, the thickness or the length of the second support beam, so that the sensitivity of the sensitive structure is improved, and the optimal dynamic response characteristic is obtained;
4. the sensitive structure is provided with the isolation frame, so that the peripheral packaging stress, temperature stress, impact stress and other interference stress of the acceleration sensor can be completely isolated, and the interference on the strain resistance is reduced, thereby ensuring that the acceleration sensor obtains better temperature stability and acceleration measurement precision.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 shows a schematic perspective view of an acceleration sensor of the present invention;
FIG. 2 shows a schematic perspective view of one of the sensing structures of FIG. 1;
FIG. 3 shows a schematic top view of the sensing structure shown in FIG. 2;
FIG. 4 shows a schematic view of the sensitive structure taken along the direction AA in FIG. 3;
FIG. 5 shows a schematic perspective view of another sensitive structure of FIG. 1;
FIG. 6 shows a schematic top view of the sensing structure shown in FIG. 5;
FIG. 7 shows a schematic view of the sensitive structure taken along the BB direction in FIG. 6;
FIG. 8 shows a schematic diagram of the distribution of strain resistances of FIG. 5;
FIG. 9 shows a schematic view of the isolation bezel and the sense unit at rest;
FIG. 10 is a schematic diagram of an isolated frame and a sensitive unit under acceleration;
fig. 11 shows a schematic diagram of the electrical connection of the wheatstone full bridge of the present embodiment.
Reference numerals illustrate:
100-acceleration sensor, 10-upper cover plate, 30-bottom plate;
20-sensitive structures, 21-frames, 23-first supporting beams, 24-second supporting beams, 26-mass blocks, 262-main bodies, 264-convex parts, 27-strain resistors, 28-bonding pads and 212-first accommodating spaces;
42-isolation frame, 45-connecting beam, 422-second accommodation space.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention discloses an acceleration sensor 100, which at least comprises a sensitive structure 20, wherein the sensitive structure is provided with a first supporting beam, a second supporting beam and a mass block, and the mass block deforms the two supporting beams under the action of acceleration. The mass of the sensitive structure 20 is shaped, the mass has a main body and a protrusion protruding from the main body, one end of the first support beam is connected to a first longitudinal position of the main body of the mass, and one end of the second support beam is connected to a second longitudinal position of the main body of the mass. Compared with the traditional single-layer support beam structure, the support beam with two longitudinal positions is connected to the mass block (namely the double-layer support beam structure), so that the shock resistance is better; on the premise of ensuring the sensitivity of the sensitive structure 20, the double-layer supporting beam can effectively limit the transverse swing of the mass block, namely inhibit the transverse coupling effect of the sensitive structure 20, and is beneficial to improving the transverse anti-interference capability of the sensitive structure 20. In addition, the mass block is of a special-shaped structure, the extending directions of the first supporting beam and the second supporting beam are parallel to the extending directions of the convex parts of the mass block, and the first supporting beam, the second supporting beam and the convex parts of the mass block are staggered, so that the space position can be fully utilized, and the volume of the sensitive structure 20 is reduced.
Referring to fig. 1, in some embodiments, the acceleration sensor 100 includes an upper cover plate 10, a sensing structure 20, and a bottom plate 30, wherein the sensing structure 20 is located between the upper cover plate 10 and the bottom plate 30, and the three are connected in a bonding manner. The upper cover plate 10 and the bottom plate 30 are used to support and seal the sensitive structure 20, and the central areas of both can be provided with grooves to provide a movement space for the mass of the sensitive structure 20. The material of the upper cover plate 10 and the bottom plate 30 may be glass or silicon, and the material of the sensitive structure 20 is silicon. Sensitive structure 20 is described in detail below.
In one embodiment, referring to fig. 2-4, a sensing structure 20 includes a frame 21 and a sensing unit. The frame 21 forms a first accommodating space 212, and the sensing unit is disposed in the first accommodating space 212. The sensitive unit comprises in particular a first support beam 23, a second support beam 24 and a mass 26. The mass 26 has a body 262 and a protrusion 264 protruding from the body 262. One end of the first support beam 23 is connected to the first longitudinal position of the main body 262, and the other end is connected to the frame 21; one end of the second support beam 24 is connected to the second longitudinal position of the main body 262, and the other end is connected to the frame 21; the longitudinal direction of the mass 26 is the sensitive direction of the mass 26. The protruding portion 264 of the mass 26, the first support beam 23, and the second support beam 24 extend in parallel, for example, in a direction perpendicular to the longitudinal direction. The mass 26 generates a force on the first support beam 23 and the second support beam 24 under the action of acceleration, and when the force reaches a threshold value, the first support beam 23 and the second support beam 24 can be deformed. Wherein the X-axis direction, the Y-axis direction and the Z-axis direction are three mutually perpendicular directions, and the Z-axis direction is longitudinal. Referring to fig. 2, the extending direction of the main body 262 is the X-axis direction, the extending directions of the convex portion 264, the first support beam 23, and the second support beam 24 are the Y-axis direction, and the sensitive direction of the sensitive structure 20 is the Z-axis direction. In the X-axis direction, the convex parts 264 on the same side are staggered with the supporting beam, and the projection of the convex parts 264 on the same side and the projection of the supporting beam onto the Y-axis are at least partially overlapped.
Specifically, the sensing structure 20 is configured in a flat plate shape, and the sensing unit is disposed in the first accommodating space 212 of the frame 21, that is, the frame 21 surrounds the sensing unit. That is, the first accommodating space 212 can accommodate the mass 26, the first support beam 23, and the second support beam 24, and provide space for movement of the mass 26 and deformation of both support beams. The frame 21 may be constructed in a regular or irregular ring shape such as a circular ring shape or a square ring shape. Referring to fig. 2, the frame 21 is configured in a square ring shape, and the first receiving space 212 is square. The square refers to a rectangle or a square.
With continued reference to fig. 2-4, the mass 26 is configured as a contoured shape including a body 262 and a protrusion 264. In some embodiments, the thickness of the mass 26 is consistent with the thickness of the frame 21. Preferably, the upper and lower surfaces of the mass 26 and the frame 21 are flush, respectively. The main body 262 is configured as a rectangular or substantially rectangular shape, and the protruding portion 264 is provided at least on one side of the rectangular shape. In some embodiments, the mass 26 has one protrusion 264, and the protrusion 264, the first support beam 23, and the second support beam 24 are all located on the same side of the body 262. For example, in the X-axis direction, the convex portion 264 is provided between the first support beam 23 and the second support beam 24. In other embodiments, referring to fig. 2 to 4, the mass 26 has two protrusions 264, the two protrusions 264 are disposed on opposite sides of the main body 262, and the first support beam 23 and the second support beam 24 are also disposed on different sides of the main body 262. Preferably, the first support beam 23 is disposed opposite one of the protrusions 264, and the second support beam 24 is disposed opposite the other protrusion 264. In some embodiments, the length of projection of the protrusion 264 to the Y-axis is greater than the length of projection of the body 262 to the Y-axis. In the embodiment shown in fig. 2-4, the length of projection of the protrusion 264 onto the Y-axis is approximately equal to 2 times the length of projection of the body 262 onto the Y-axis. Preferably, in the X-axis direction, the gap between the mass 26 and the frame 21 is equal to the gap between the first support beam 23, the second support beam 24 and the frame 21. In some embodiments, among the same-side protrusion 264, the first support beam 23, and the second support beam 24, the protrusion 264 is located between the first support beam 23 and the second support beam 24; more preferably, the convex portion 264 of the mass 26 is equal to the gap between the first support beam 23 and the second support beam 24 on the same side. In the X-axis direction, the width of the convex portion 264 is related to the widths of the first support beam 23 and the second support beam 24.
The sensitive structure 20 includes a strain resistor 27, and the strain resistor 27 is disposed on a surface of the first support beam 23 or the second support beam 24. The mass 26 is subjected to acceleration to deform the first support beam 23 and the second support beam 24, thereby causing the resistance value of the strain resistor 27 to change. By detecting the resistance value, the acceleration value can be calculated.
The detection direction of the acceleration sensor 100 may be the Z-axis direction (i.e., the mass 26 performs out-of-plane motion), or may be any direction parallel to the X-Y plane (i.e., the mass 26 performs in-plane motion). The detection direction of the acceleration sensor 100 is the sensitive direction of the mass 26, the first support beam 23, and the second support beam 24.
In some embodiments, referring specifically to fig. 2 and 4, the detection direction of the acceleration sensor 100 is the Z-axis direction, and the thicknesses of the first support beam 23 and the second support beam 24 are smaller than the thickness of the mass 26. The strain resistor 27 is provided on the upper surface or the lower surface of the first support beam 23 or on the upper surface or the lower surface of the second support beam 24. Preferably, the strain resistors 27 are provided on the outer side surfaces of the first support beam 23 and the second support beam 24. The first support beam 23 is close to the upper surface of the sensitive structure 20, the outer side surface of the first support beam 23 is the upper surface of the first support beam 23, and the outer side surface of the second support beam 24 is the lower surface of the second support beam 24. In some embodiments, along the Z-axis, the upper surface of the first support beam 23 is flush with the upper surface of the mass 26, and the lower surface of the second support beam 24 is flush with the lower surface of the mass 26.
The rigidity of the first support beam 23 and the second support beam 24 may be the same or different. In some embodiments, referring to fig. 3 and 4, the first support beam 23 and the second support beam 24 are the same in rigidity. Specifically, the first support beam 23 and the second support beam 24 have uniform widths and thicknesses, and the strain resistors 27 may be disposed on the upper surface of the first support beam 23 and the lower surface of the second support beam 24. For example, the upper surface of the first support beam 23 is provided with two strain resistors 27, the lower surface of the second support beam 24 is provided with two strain resistors 27, and four strain resistors 27 may be configured as a wheatstone bridge to facilitate measuring the resistance value. More specifically, the strain resistor 27 is configured to be long and extend along the X-axis. Wherein, two strain resistors 27 are respectively arranged at the joints of the first supporting beam 23, the frame 21 and the mass block 26; the other two strain resistors 27 are respectively arranged at the joints of the second supporting beam 24, the frame 21 and the mass block 26. That is, two of the strain resistors 27 are provided at both ends of the first support beam 23, and the other two strain resistors 27 are provided at both ends of the second support beam. The strain resistor is arranged at the joint, which is beneficial to improving the detection sensitivity.
In other embodiments, where the first support beam 23 and the second support beam 24 are different in rigidity, the strain resistor 27 may be provided on the surface of one of the two that is strong in rigidity. The strain resistor 27 is provided on one of the rigid members so that a larger stress can be obtained in the strain resistor 27. In addition, by adjusting the width, thickness or length of the other, the frequency and mode of the sensitive structure 20 can be modulated, the sensitivity of the sensitive structure is improved, and the optimal dynamic response characteristic is obtained. Specifically, for example, the widths or thicknesses of the first support beam 23 and the second support beam 24 are different, so that the first support beam 23 is relatively rigid. Preferably, the widths of the first support beam 23 and the second support beam 24 are consistent, the thickness of the first support beam 23 is greater than that of the second support beam 24, and the strain resistor 27 is disposed on the upper surface of the first support beam 23.
Referring to fig. 1, 2 and 3, in some embodiments, the frame 21 is provided with pads 28 electrically connected to the strain resistors 27, and the strain resistors 27 may be connected to an external circuit through the pads 28. Specifically, the sensing structure 20 has four strain resistors 27, the frame 21 is provided with four pads 28, and the four pads 28 are electrically connected with the four strain resistors 27 to form a Wheatstone full bridge circuit. The four pads 28 are equally divided into two groups, respectively provided on both sides of the frame 21 parallel to the extending direction of the first support beam 23, and located on the upper surfaces of both sides.
The invention also provides another embodiment of the sensitive structure, see fig. 5 to 7, in which the sensitive structure 20 has two first support beams 23, two second support beams 24, compared to the previous embodiment. Sensitive structure 20 comprises a frame 21, two first support beams 23, two second support beams 24 and a mass 26. The frame 21 has a first accommodation space 212, and the first support beam 23, the second support beam 24, and the mass 26 are disposed in the first accommodation space 212. Specifically, the main body 262 of the mass 26 is configured as a rectangular or nearly rectangular shape, the length direction of the main body 262 extends along the X-axis, the width direction of the main body 262 extends along the Y-axis, and two protrusions 264 are provided on opposite sides of the width direction of the main body 262, respectively, each of which is further provided with the first support beam 23 and the second support beam 24. Preferably, the convex portion 264 is disposed between the first support beam 23 and the second support beam 24 in the X-axis direction. More preferably, the first support beam 23 on one side is disposed opposite to the second support beam 24 on the other side in the Y-axis direction. In some embodiments, among the same-side protrusion 264, the first support beam 23, and the second support beam 24, the protrusion 264 is located between the first support beam 23 and the second support beam 24; more preferably, the distances between the first support beam 23, the second support beam 24 and the frame 21 are equal in the X-axis direction. The protrusion 264 of each mass 26 is equal to the gap width between the first support beam 23 and the second support beam 24 on the same side.
Referring to fig. 5, in the Y-axis direction, two protrusions 264 are arranged offset; in the X-axis direction, the two convex portions 264 are partially arranged in a staggered manner, that is, the projection portions of the two convex portions 264 projected to the X-axis coincide; in the X-axis direction, the convex part 264, the first supporting beam 23 and the second supporting beam 24 on the same side are arranged in a staggered way; projections of the convex portion 264, the first supporting beam 23 and the second supporting beam 24 on the same side, projected to the Y axis, are at least partially overlapped; this arrangement can reduce the volume of the sensitive structure while ensuring the sensitivity of the sensitive structure.
Referring to fig. 6 and 7, the upper surface of each first support beam 23 is provided with two strain resistors 27, specifically, one strain resistor 27 is provided at each end of each first support beam 23. In some embodiments, the rigidity of the first support beam 23 is greater than the rigidity of the second support beam 24. Specifically, referring to fig. 6, the width of the first support beam 23 is greater than the width of the second support beam 24. Preferably, referring to fig. 7, the thickness of the first support beam 23 is greater than the thickness of the second support beam 24. More preferably, referring to fig. 6, the length of the first support beam 23 is smaller than the length of the second support beam 24. The width direction of the supporting beam is the X-axis direction, the thickness direction of the supporting beam is the Z-axis direction, and the length direction of the supporting beam is the Y-axis direction.
In some embodiments, sensing structure 20 further includes an isolation bezel 42, isolation bezel 42 is disposed in first receiving space 212 of frame 21, and isolation bezel 42 is connected to frame 21 via connection beams 45. The isolation frame 42 is formed with a second accommodating space 422, and the sensing unit is disposed in the second accommodating space 422, i.e. the first supporting beam 23, the second supporting beam 24 and the mass block 26 are disposed in the second accommodating space 422. The first and second support beams 23, 24 are fixed to the isolation rims 42, respectively, and the first and second support beams 23, 24 are connected to the frame 21 through the isolation rims 42. The sensitive units are arranged inside the isolating frame 42, and a gap is formed between the isolating frame 42 and the frame 21, which gap is beneficial to prevent interference stress applied to the frame 21 from being transmitted to the isolating frame 42 or the inner part of the isolating frame 42. For example, the foregoing structure can prevent peripheral disturbance stresses such as package stress, temperature stress, etc. from being transferred to the position where the strain resistor 27 is arranged, and the strain resistor 27 is only stressed by the inertial action of the mass block and is not affected by the disturbance stress, so that the acceleration sensor 100 can obtain good temperature stability and measurement accuracy, and then the detection reliability of the acceleration sensor 100 is improved.
Preferably, in some embodiments, with continued reference to fig. 5 and 6, in the X-axis direction, the gap between the body 262 of the mass 26 and the isolation frame 42 is equal to the gap between the first support beam 23, the second support beam 24, and the isolation frame 42. The gaps between the convex portions 264 of the mass 26 and the isolation rims 42, the first support beam 23, and the second support beam 24 are equal, and the gaps between the first support beam 23 and the isolation rims 42 and the convex portions 264 of the mass 26 on both sides thereof are equal. The arrangement is that the acceleration sensor 100 not only meets the deformation space requirements of the mass block 26, the first supporting beam 23 and the second supporting beam 24, but also can fully utilize the space position, thereby reducing the volume of the acceleration sensor 100.
In some embodiments, two connection beams 45 extending along the X-axis direction are disposed on two sides of the isolation frame 42, respectively, and the extending direction of the connection beams 45 is perpendicular to the extending direction (length direction) of the first support beam 23. The frame 21 is configured in a square ring shape, and the connection beam 45 is fixed to the frame 21. In some embodiments, two pads 28 are further provided on the upper surfaces of the two sides of the frame 21 connected to the connection beam 45, and each pad 28 is electrically connected to one strain resistor 27. Specifically, both ends of each first support beam 23 are provided with strain resistors 27. More specifically, the upper surface of the connection between each first support beam 23 and the isolation frame 42 and the mass 26 is provided with a strain resistor 27. Referring to fig. 8, the strain resistances of the resistances R4, R3, R2, R1 are sequentially distributed along the Y-axis direction.
The operation of the acceleration sensor 100 with the sensitive structure 20 will be described in detail below with reference to fig. 9 and 10. Fig. 9 shows a schematic view of the isolation border 42 and the sensing unit at rest, with the upper surface of the first support beam 23 being flush with the upper surface of the isolation border 42 and the lower surface of the second support beam 24 being flush with the lower surface of the isolation border 42. Fig. 10 shows a schematic diagram of the isolation border 42 and the sensitive unit under the action of the acceleration a. When the mass 26 receives the acceleration a, the mass 26 is displaced along the Z-axis direction of the sensitive structure 20 by the inertial force, so that the first support beam 23 and the second support beam 24 are completely deformed. The root of the first support beam 23 close to the isolating frame 42 will generate a corresponding tensile stress and the root of the first support beam 23 close to the mass 26 will generate a corresponding compressive stress, the magnitude of which is proportional to the acceleration. When the first support beam 23 is bent and deformed, the first support beam 23 will generate tensile and compressive stresses perpendicular to the cross section. In the deformation shown in fig. 10, the strain resistors with the resistances R1 and R4 receive tensile stress along the length direction of the strain resistor, and the strain resistors with the resistances R2 and R3 receive compressive stress along the length direction of the strain resistor, so that the two groups of resistance stresses have the same magnitude and opposite directions.
As shown in FIG. 11, the strained resistors with resistances R1-R4 are connected as a Wheatstone full bridge circuit. According to the wheatstone bridge principle, the output signal of the acceleration sensor 100 is in direct proportion to the change of the resistance value, so that the output signal is in direct proportion to the acceleration to be measured, and the acceleration is measured. Fig. 11 shows a schematic diagram of the electrical connection of the wheatstone full bridge of the present embodiment. Through V out = V in The ΔR can be calculated by the ratio of ΔR/R, thereby obtaining an acceleration value. Wherein V is in For input voltage, V out For the output voltage, R is the base resistance value of the strain resistor, and Δr is the variable resistance value of the strain resistor.
The sensitive structure 20 disclosed by the invention is provided with a double-layer supporting beam, and has better impact resistance than a single-layer mass beam; and the double-layer supporting beam can effectively limit the transverse swing of the mass block, namely inhibit the transverse coupling effect of the sensitive structure 20, and is beneficial to improving the transverse anti-interference capability of the sensitive structure 20. In addition, the first support beam, the second support beam and the mass block are arranged in a staggered manner, so that the space position can be fully utilized, and the volume of the sensitive structure 20 is reduced. The rigidity of the first support beam is greater than the rigidity of the second support beam. A strain resistor is arranged on the first supporting beam, so that larger stress can be obtained by the strain resistor. In addition, the frequency and the mode of the sensitive structure can be modulated by adjusting the width, the thickness or the length of the second supporting beam, so that the sensitivity of the sensitive structure is improved, and the optimal dynamic response characteristic is obtained. The sensitive structure 20 is provided with the isolation frame 42, so that the packaging stress, the temperature stress, the impact stress and the like at the periphery of the acceleration sensor 100 can be completely isolated, and the interference on the strain resistance is reduced, so that the acceleration sensor 100 can obtain better temperature stability and acceleration measurement accuracy.
It should be appreciated that the sensitive structure 20 may be integral with either the upper cover plate 10 or the bottom plate 30. Thus, in some embodiments, the sensitive structure 20 is not an intermediate layer of the acceleration sensor 100, but an upper layer or a lower layer constituting the acceleration sensor 100.
The foregoing is merely a few embodiments of the present invention and those skilled in the art may make various modifications or alterations to the embodiments of the present invention in light of the disclosure herein without departing from the spirit and scope of the invention.
Claims (6)
1. A sensing structure of a piezoresistive acceleration sensor, characterized by comprising:
a frame formed with a first accommodation space;
the sensitive unit, sensitive unit set up in the first accommodation space, sensitive unit includes:
the mass block is provided with a main body and two convex parts protruding out of two opposite sides of the main body;
two first support beams, one end of which is connected to a first longitudinal position of the body of the mass and the other end is connected to the frame;
two second support beams, one end of which is connected to a second longitudinal position of the body of the mass and the other end of which is connected to the frame; and
The strain resistor is arranged on the first supporting beam;
the longitudinal direction of the mass block is the sensitive direction of the mass block, and the first longitudinal position and the second longitudinal position are different longitudinal positions;
the extending direction of the convex part of the mass block is parallel to the extending directions of the first supporting beam and the second supporting beam;
the mass block generates acting force on the first supporting beam and the second supporting beam under the action of acceleration;
the two opposite sides of the main body are respectively provided with a first supporting beam and a second supporting beam, and the first supporting beam on one side is opposite to the second supporting beam on the other side;
the rigidity of the first support beam is greater than that of the second support beam, and the width of the first support beam is greater than that of the second support beam.
2. The sensing structure of claim 1, wherein the protrusion of the mass has an equal gap width with the first and second support beams on the same side.
3. The sensing structure of claim 2, wherein the thickness of the first support beam and the second support beam is smaller than the thickness of the mass block, the upper surface of the first support beam is flush with the upper surface of the sensing structure, and two strain resistors are arranged on the upper surface of each first support beam and are respectively arranged at two ends of the first support beam.
4. A sensitive structure according to claim 3, wherein four pads are provided on the upper surface of said frame, and four of said strain resistors are electrically connected to four of said pads to form a wheatstone full bridge circuit.
5. The sensitive structure of any one of claims 1 to 4, further comprising an isolation bezel and a connection beam disposed within the first receiving space, the isolation bezel being connected to the frame by the connection beam;
the isolation frame is provided with a second accommodating space, and the sensitive unit is arranged in the second accommodating space;
the other end of the first supporting beam and the other end of the second supporting beam are both fixed to the isolation frame, and the first supporting beam and the second supporting beam are connected to the frame through the isolation frame.
6. An acceleration sensor, characterized by comprising an upper cover plate, a bottom plate and the sensitive structure of any one of claims 1-5, wherein the sensitive structure is arranged between the upper cover plate and the bottom plate.
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