A low stress structure suitable for monolithic integrated pressure sensor arrays

Abstract

The application relates to a low-stress structure suitable for a monolithic integrated pressure sensor array, which comprises, from top to bottom, a pressure sensing structure layer, a fixed support layer, a longitudinal stress buffer layer and a connecting plate; the pressure sensing structure layer comprises a group of piezoresistive bridge structure unit arrays arranged on the surface, and each piezoresistive bridge structure unit is provided with a back cavity on the lower side and a first ring groove on the peripheral side; the fixed support layer is provided with a first through hole corresponding to each back cavity; the longitudinal stress buffer layer comprises a group of bosses corresponding to the piezoresistive bridge structure units on the lower surface, each boss is provided with a second through hole corresponding to each first through hole, and the surfaces of the bosses are connected with the connecting plate to form a dot matrix contact connection; and the connecting plate is provided with a third through hole corresponding to each second through hole. The application realizes horizontal and longitudinal buffering of external stress, and the structure does not significantly increase the process processing difficulty of the MEMS pressure sensor array chip, is flexible to apply, and is easy to realize.

Description

Technical Field

[0001] This invention relates to the field of MEMS sensor chip structure technology, and specifically to a low-stress structure suitable for monolithic integrated pressure sensor arrays. Background Technology

[0002] MEMS (Micro-Electro-Mechanical Systems) sensors are now widely used in consumer electronics, automotive electronics, the Internet of Things (IoT), defense industries, and numerous industrial products. With technological advancements, increasingly higher demands are being placed on the performance of MEMS sensors. External stress has a particularly significant impact on the performance of MEMS sensors. Changes in external stress inevitably cause corresponding strain, which, when transmitted to the sensitive structure, leads to changes in the sensor's output signal, especially for MEMS sensors based on capacitive, piezoresistive, and resonant detection principles.

[0003] The advantages of silicon piezoresistive MEMS pressure sensors are high sensitivity, no hysteresis, high frequency response, high output level, and ease of use. The disadvantage is their high sensitivity to external stress. Currently, pressure sensing components used in pressure scanning valves of smart MEMS pressure modules, such as the pressure scanning valve with publication number CN114777992A, integrate multiple independent pressure sensor chips onto a drive control circuit board. The advantage is that there is no crosstalk between each independent pressure sensor chip, achieving good stress isolation. The disadvantages are large size and the lack of longitudinal buffering for external stress on each independent pressure sensor chip, making it susceptible to interference from external stress.

[0004] While MEMS pressure sensor array chips can effectively reduce the size of pressure module products, this structure is susceptible to external stress interference, affecting product performance. Summary of the Invention

[0005] To address the problem that pressure sensor array chips in existing technologies are easily affected by external stress interference, this invention provides a low-stress structure suitable for monolithic integrated pressure sensor arrays.

[0006] It adopts the following technical solution:

[0007] A low-stress structure suitable for monolithic integrated pressure sensor arrays: comprising a pressure sensing structure layer, a fixed support layer, a longitudinal stress buffer layer, and a connecting plate stacked sequentially from top to bottom;

[0008] The pressure sensing structure layer includes an array of piezoresistive bridge structure units disposed on its upper surface. Each piezoresistive bridge structure unit has a back cavity on its lower side and a first annular groove on its periphery. The depth of the first annular groove is greater than the thickness of the piezoresistive bridge structure unit.

[0009] The fixed support layer is provided with a first through hole corresponding to each back cavity;

[0010] The longitudinal stress buffer layer includes protrusions arranged in an array on its lower surface, corresponding to the piezoresistive bridge structure unit. Each protrusion is provided with a second through hole that communicates with each first through hole. The surface of this set of protrusions is connected to the connecting plate to form a dot matrix contact connection.

[0011] The connecting plate is provided with a third through hole that communicates with each of the second through holes.

[0012] Furthermore, the second through hole includes at least one coaxially arranged folded through hole unit, which is a hole-type structure with small opening sizes at both ends and a large cross-sectional size in the middle, and the parameters of the opening size at both ends to the maximum cross-sectional size in the middle increase linearly.

[0013] Furthermore, a second annular groove is provided on the periphery of each boss, and the groove depth direction of the second annular groove is arranged along the axial direction of the second through hole.

[0014] Furthermore, the depth of the second annular groove exceeds the location of the maximum cross-sectional dimension of the lowermost folded through-hole unit in the second through hole.

[0015] Furthermore, the cross-sectional shape of the second through hole is rectangular.

[0016] Furthermore, the lower surface of the connecting plate is also provided with an air guide nozzle that communicates with each third through hole.

[0017] Furthermore, the pressure sensing structure layer is provided with multiple layers of metal wiring, which are electrically connected to the chip bonding area. Each piezoresistive bridge structure unit is interconnected with the multiple layers of metal wiring through bonding leads, and the chip bonding area is connected to a multi-channel switch selection chip.

[0018] Compared with the prior art, the present invention has the following advantages: The present invention provides a low-stress structure suitable for monolithic integrated pressure sensor arrays. By setting a first annular groove on the periphery of each piezoresistive bridge structural unit, the transverse stress influence between the piezoresistive bridge structural units is effectively isolated. By setting a boss on the longitudinal stress buffer layer, dot matrix contact with the connecting plate is achieved. At the same time, in conjunction with the set second annular groove and folded through-hole unit, the present invention achieves longitudinal buffering of external stress. Moreover, this structure does not significantly increase the manufacturing difficulty of MEMS pressure sensor array chips, can be flexibly applied, and is easy to implement. Attached Figure Description

[0019] Figure 1 This is a cross-sectional structural diagram of a low-stress structure suitable for a monolithic integrated pressure sensor array according to an embodiment of the present invention;

[0020] Figure 2 yes Figure 1 A top-view structural diagram;

[0021] Figure 3 yes Figure 1 Schematic diagram of the cross-sectional structure along the AA direction;

[0022] Figure 4 This is a schematic cross-sectional view of the second through hole in this embodiment;

[0023] Figure 5 This is a schematic diagram of the force applied to the experimental model;

[0024] Figure 6 This is a schematic diagram of the force application in the control group model;

[0025] Figure 7 This is a comparison diagram of surface stress distribution in the test group and the control group under lateral force;

[0026] Figure 8 This is a comparison chart of the transverse stress distribution data in the experimental and control groups.

[0027] Figure 9 This is a comparison diagram of the stress distribution at the location of the piezoresistive bridge structural unit in the test group and the control group under longitudinal force.

[0028] Figure 10 This is a comparison chart of longitudinal stress distribution data in the experimental and control groups.

[0029] Explanation of reference numerals in the attached drawings: 100, sensing structure layer; 101, piezoresistive bridge structure unit; 102, back cavity; 103, first annular groove; 104, multilayer metal wiring; 105, chip bonding area; 106, multi-channel switch selection chip; 107, bonding wire; 200, fixing support layer; 201, first through hole; 300, stress buffer layer; 301, boss; 302, second annular groove; 310, second through hole; 311, folded through hole unit; 400, connecting plate; 401, third through hole; 402, air guide needle. Detailed Implementation

[0030] To make the present invention clearer, a low-stress structure suitable for monolithic integrated pressure sensor arrays is further described below with reference to the accompanying drawings. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the present invention.

[0031] like Figures 1 to 3 As shown, a low-stress structure suitable for monolithic integrated pressure sensor arrays includes a pressure sensing structure layer 100, a fixed support layer 200, a longitudinal stress buffer layer 300, and a connecting plate 400 stacked sequentially from top to bottom.

[0032] The pressure-sensing structural layer 100 uses a double-polished silicon wafer as its main body, and an array of piezoresistive bridge structural units 101 are fabricated on its upper surface. The number of rows and columns of the piezoresistive bridge structural units 101 can be arbitrarily set according to requirements. A corresponding back cavity 102 is provided directly below each piezoresistive bridge structural unit 101, and a first annular groove 103 is provided around the periphery of each piezoresistive bridge structural unit 101. The first annular groove 103 is preferably rectangular, and its depth is greater than the thickness of the piezoresistive bridge structural unit 101. Preferably, the depth of the first annular groove 103 extends beyond the top wall of the back cavity 102 by a certain distance, which can effectively isolate the lateral stress influence between the piezoresistive bridge structural units 101. The piezoresistive bridge structural unit 101 is a prior art technique, formed by photolithography, etching, ion implantation, and other processes on the silicon wafer to create resistive strips to form a Wheatstone bridge for sensing strain in the corresponding region.

[0033] The silicon wafer is also provided with multilayer metal wiring 104 located on both sides of the piezoresistive bridge structure unit 101. The multilayer metal wiring 104 is electrically connected to the chip bonding area 105 located on the silicon wafer. Each piezoresistive bridge structure unit 101 is interconnected with the multilayer metal wiring 104 through bonding leads 107. The chip bonding area 105 is connected to the multichannel switch selection chip 106.

[0034] The fixed support layer 200 is mainly made of glass, and a first through hole 201 is provided on the glass that is connected to the center of each back cavity 102 region. The first through hole 201 is preferably a straight hole.

[0035] The longitudinal stress buffer layer 300 is based on a double-polished silicon wafer. On its lower surface, protrusions 301 are arrayed, each corresponding to a piezoresistive bridge structural unit 101. Each protrusion 301 has a second through-hole 310 communicating with each first through-hole 201. A second annular groove 302 is also provided around each protrusion 301, with the groove depth direction along the axial direction of the second through-hole 310. The protrusions 301 can be formed by etching shallow cavities on the lower surface of the silicon wafer, outside the area surrounding the second through-hole 310. This ensures that when the longitudinal stress buffer layer 300 is connected to the connecting plate 400, only the surfaces of the protrusions 301 are in contact, while other areas are non-contact areas, thus forming a dot matrix contact between the longitudinal stress buffer layer 300 and the connecting plate 400. The second annular groove 302 is also formed by deep trench etching. The specific cross-sectional shape of the second annular groove 302 can be set according to the cross-sectional shape of the boss 301. For example, in this embodiment, the cross-sectional outline of the boss is rectangular, and the second annular groove 302 is the corresponding rectangular frame shape.

[0036] The connecting plate 400 is provided with a third through hole 401 corresponding to each second through hole 310. In some embodiments, in order to facilitate the introduction of external gas pressure, a gas guide nozzle 402 corresponding to each third through hole 401 is also provided on the lower surface of the connecting plate 400. The gas guide nozzle 402 is tubular.

[0037] Preferably, the second through hole 310 includes at least one folded through hole unit 311. For example... Figure 3 The second through hole 310 shown includes only one folded through hole unit 311. The folded through hole unit 311 is a hole-shaped structure with small opening sizes at both ends and a large cross-sectional size in the middle. Furthermore, the opening size at both ends increases linearly to the maximum cross-sectional size in the middle. That is, its longitudinal cross-section presents a combination shape of two trapezoids with their long bases collinear. The short bases of the two trapezoids are located at the two ends, and the sides of the trapezoids are hypotenuses. When subjected to external longitudinal stress, the folded through hole unit 311 provides deformable space for longitudinal stress deformation, thereby buffering the external longitudinal stress.

[0038] Of course, the second through hole 310 may also include multiple folded through hole units 311, such as Figure 4 As shown, the second through hole 310 includes two coaxially connected folded through hole units 311. Here, the stress buffer layer 300 is based on two bonded double-polished silicon wafers, and each silicon wafer is provided with a folded through hole unit 311. By increasing the number of folded through hole units 311, the buffering effect of the external longitudinal stress of this device is improved.

[0039] Accordingly, the depth of the second annular groove 302 exceeds the position where the maximum cross-sectional dimension of the lowermost folded through-hole unit 311 of the second through-hole 310 is located, further improving the ability to buffer external longitudinal stress. The cross-section of the second through-hole 310 is preferably rectangular, but other cross-sectional shapes are also acceptable for ease of manufacturing.

[0040] like Figure 5 As shown, the structural model of this embodiment is used as the test group, and simulation tests are conducted by applying a transverse force F1 and a longitudinal force F2 to the structural model respectively; as Figure 6 The control group is shown. Compared with the structure in this embodiment, the structural model used has the first annular groove 103, boss 301, second annular groove 302 and folded through hole unit 311 removed. The rest of the structure is the same. A simulation test was conducted on the structural model by applying a transverse force F1 and a longitudinal force F2. The test conditions of this group are the same as those of the test group.

[0041] The results obtained from the simulation experiment are as follows Figures 7 to 10 As shown, where, Figure 7This is a comparison diagram of surface stress distribution in the experimental and control groups under lateral force. The area marked by the box in the diagram is the periphery of the piezoresistive bridge structural unit 101. Figure 8 This is a comparison chart of the transverse stress distribution data in the experimental and control groups. The boxed area in the chart represents the transverse stress value at the periphery of the piezoresistive bridge structural unit 101. Obviously, the transverse stress in the experimental group structural model between the piezoresistive bridge structural units 101 (boxed area) is smaller, about 0.1 MPa, while the transverse stress in the control group structural model between the piezoresistive bridge structural units 101 (boxed area) is larger, about 0.7 MPa. This indicates that the structural model in this embodiment can effectively reduce the influence of transverse stress crosstalk.

[0042] Figure 9 This is a comparison diagram of surface stress distribution in the experimental and control groups under longitudinal force. Figure 10 This is a comparison chart of longitudinal stress distribution data in the experimental and control groups. The chart shows the longitudinal stress value at position 101 of the piezoresistive bridge structural unit; obviously, from... Figure 9 It can be seen that the experimental group structural model is less affected by the applied longitudinal force, and the surface stress distribution is uniform, while the control group structural model has a chaotic and uneven surface stress distribution. Figure 10 The stress values ​​show the longitudinal stress transmitted to the piezoresistive bridge structural unit 101. The experimental structural model is an order of magnitude smaller than the control structural model. This indicates that the structural model in this embodiment can effectively reduce the influence of longitudinal stress.

[0043] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. However, obvious variations or modifications derived from the essential spirit of the present invention still fall within the protection scope of the present invention.

Claims

1. A low-stress structure suitable for monolithic integrated pressure sensor arrays, characterized in that: It includes a pressure-sensing structural layer (100), a fixed support layer (200), a longitudinal stress buffer layer (300), and a connecting plate (400) stacked from top to bottom. The pressure sensing structure layer (100) includes an array of piezoresistive bridge structure units (101) disposed on its upper surface. A back cavity (102) is provided on the lower side of each piezoresistive bridge structure unit (101), and a first annular groove (103) is provided on the periphery of each piezoresistive bridge structure unit (101). The depth of the first annular groove (103) is greater than the thickness of the piezoresistive bridge structure unit (101). The fixed support layer (200) is provided with a first through hole (201) corresponding to each back cavity (102); The longitudinal stress buffer layer (300) includes bosses (301) arranged in an array on its lower surface corresponding to the piezoresistive bridge structure unit (101). Each boss (301) is provided with a second through hole (310) corresponding to each first through hole (201). The surface of the boss (301) is connected to the connecting plate (400) to form a dot matrix contact connection. The connecting plate (400) is provided with a third through hole (401) corresponding to each second through hole (310). The second through hole (310) includes at least one coaxially arranged folded through hole unit (311). The folded through hole unit (311) is a hole structure with small opening size at both ends and large cross-sectional size in the middle, and the opening size at both ends increases linearly to the maximum cross-sectional size in the middle. The pressure sensing structure layer (100) is provided with multi-layer metal wiring (104), which is electrically connected to the chip bonding area (105). Each piezoresistive bridge structure unit (101) is interconnected with the multi-layer metal wiring (104) through bonding leads (107). The chip bonding area (105) is connected to a multi-channel switch selection chip (106).

2. The low-stress structure suitable for monolithic integrated pressure sensor arrays according to claim 1, characterized in that: A second annular groove (302) is provided on the periphery of each of the bosses (301), and the groove depth direction of the second annular groove (302) is arranged along the axial direction of the second through hole (310).

3. The low-stress structure suitable for monolithic integrated pressure sensor arrays according to claim 2, characterized in that: The groove depth of the second annular groove (302) exceeds the location of the maximum cross-sectional dimension of the lowermost folded through hole unit (311) in the second through hole (310).

4. A low-stress structure suitable for monolithic integrated pressure sensor arrays according to claim 3, characterized in that: The cross-sectional shape of the second through hole (310) is rectangular.

5. A low-stress structure suitable for monolithic integrated pressure sensor arrays according to claim 1 or 4, characterized in that: The lower surface of the connecting plate (400) is also provided with an air guide nozzle (402) that communicates with each third through hole (401).

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