Pressure Sensor and Its Preparation Method

Abstract

Embodiments of the present disclosure provide a pressure sensor and a preparation method thereof. The pressure sensor includes a silicon strain diaphragm, on which a cross beam, a strain film and a back cavity are sequentially formed from top to bottom. The cross beam divides the silicon strain diaphragm into four symmetrically arranged hollow parts, the hollow parts are petal-shaped, piezoresistors are respectively arranged at four ends of the cross beam, a Wheatstone bridge is formed between the piezoresistors, and a groove is arranged on the cross beam. In the pressure sensor of the present disclosure, a groove is arranged on the cross beam of the strain film, and the groove can increase the deformation deflection of the cross beam, so as to increase the concentrated stress of the piezoresistors at the four ends of the cross beam, and further improve the sensitivity of the pressure sensor. The petal-shaped hollow parts can increase the exposed area of the strain film below them. The larger the contact area between the strain film and the external pressure, the greater the deformation deflection of the strain film, and the sensitivity of the pressure sensor is further improved.

Description

Technical Field

[0001] The embodiments of the present disclosure belong to the field of micro-electromechanical systems (MEMS) technology, and specifically relate to a pressure sensor and a method for preparing the same. Background Art

[0002] MEMS (Micro-Electro-Mechanical System) pressure sensors are widely used in automotive electronics, medical electronics, aerospace and other fields due to their advantages such as miniaturization, high sensitivity and easy integration.

[0003] In the related technology, the MEMS pressure sensor adopts a whole membrane structure. When the whole membrane is subjected to external pressure, the diaphragm deforms, and the four sides of the diaphragm are subjected to certain stress. The piezoresistors arranged at the edges of the diaphragm are subjected to less concentrated stress. When the diaphragm produces a small deformation, the piezoresistors may not sense the stress at the edges of the diaphragm, thereby affecting the sensitivity of the pressure sensor. Summary of the invention

[0004] The embodiments of the present disclosure aim to solve at least one of the technical problems existing in the prior art and provide a pressure sensor and a method for manufacturing the same.

[0005] An embodiment of the present disclosure provides a pressure sensor, which includes a silicon strain diaphragm, on which a cross beam, a strain membrane and a back cavity are formed in sequence from top to bottom, the cross beam divides the silicon strain diaphragm into four symmetrically arranged hollow portions, the hollow portions are in the shape of petals, four ends of the cross beam are respectively provided with varistors, a Wheatstone bridge is formed between the varistors, and a groove is provided on the cross beam.

[0006] In some embodiments of the present disclosure, the groove includes a first groove and four groups of second grooves, the first groove is arranged at the center of the cross beam, and the four groups of second grooves are respectively arranged at four beam arms of the cross beam.

[0007] In some embodiments of the present disclosure, each group of the second grooves is arranged close to the first grooves.

[0008] In some embodiments of the present disclosure, the first groove is a circular groove, a rectangular groove or other groove that is symmetrical about the center of the cross beam.

[0009] In some embodiments of the present disclosure, the first groove is a rectangular groove, a circular groove or a triangular groove.

[0010] In some embodiments of the present disclosure, the shape of the back cavity is similar to the shape of the hollow portion.

[0011] In some embodiments of the present disclosure, each end of the cross beam is provided with a heavily doped contact area and a metal lead, the varistor at each end of the cross beam is connected in series with the heavily doped contact area, the metal lead is connected to the heavily doped contact area, and a Wheatstone bridge is formed between the varistors.

[0012] In some embodiments of the present disclosure, the silicon strain diaphragm further includes a cross mass, the cross mass is disposed in the back cavity, and the cross mass and the cross beam are disposed opposite to the strain diaphragm.

[0013] In some embodiments of the present disclosure, a thermistor is provided on the silicon strain diaphragm.

[0014] A second aspect of the present disclosure provides a method for preparing a pressure sensor, which is used to prepare the pressure sensor described in any of the above embodiments, and the preparation method comprises the following steps:

[0015] growing an oxide layer on a silicon substrate;

[0016] Performing a photolithography patterning process on the front side of the silicon substrate to form a varistor;

[0017] Photolithographically forming a heavily doped contact region on the front side of the silicon substrate;

[0018] forming contact holes on a silicon substrate using a chemical vapor deposition process;

[0019] Using sputtering and photolithography process to prepare metal leads in the contact holes, and preparing metal welding blocks with exposed oxide layers on the silicon substrate;

[0020] A thermistor is fabricated on the front side of a silicon substrate;

[0021] etching a cross beam on a silicon substrate and etching a groove on the cross beam;

[0022] A back cavity and a cross-mass block are etched on the back side of the silicon substrate;

[0023] The back side of the silicon substrate is bonded to the glass substrate.

[0024] The pressure sensor and preparation method of the embodiment of the present disclosure include a silicon strain diaphragm, which is formed with a cross beam, a strain membrane and a back cavity from top to bottom in sequence, and the cross beam silicon strain diaphragm is divided into four hollow parts, and the four ends of the cross beam are respectively provided with piezoresistors, and the cross beam is provided with a groove, and the deformation deflection of the cross beam when subjected to external pressure can be increased by setting the groove, thereby increasing the concentrated stress at the four ends of the cross beam, that is, increasing the concentrated stress of the piezoresistors, and thus improving the sensitivity of the pressure sensor. In addition, the hollow part is specifically petal-shaped, and the petal-shaped hollow part can increase the exposed area of ​​the strain membrane below it. The larger the contact area between the strain membrane and the external pressure, the greater the deformation deflection of the strain membrane, and the greater the deformation deflection of the cross beam above the strain membrane, further increasing the concentrated stress of the piezoresistors, and improving the sensitivity of the pressure sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is an axonometric diagram of a pressure sensor according to an embodiment of the present disclosure;

[0026] Figure 2 for Figure 1 A cross-sectional view of the pressure sensor shown;

[0027] Figure 3 for Figure 1 A front view of the pressure sensor shown;

[0028] Figure 4(a)~4(i) The present invention is a flow chart of a method for preparing a pressure sensor according to an embodiment of the present invention.

[0029] The reference numerals in the accompanying drawings represent the following:

[0030] 100. Pressure sensor;

[0031] 10. Silicon strain diaphragm; 11. Cross beam; 111. First groove; 112. Second groove; 12. Strain membrane; 13. Back cavity; 14. Hollow portion; 15. Varistor; 16. Heavily doped contact area; 17. Metal lead; 18. Metal welding block; 19. Cross mass block;

[0032] 20. glass base; 201. through hole;

[0033] 30. Thermistor;

[0034] 101, silicon substrate; 102, silicon oxide layer; 103, contact hole;

[0035] 200. Photoresist. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the technical solution of the present disclosure, the present disclosure is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0037] like Figures 1 to 3 As shown, the present disclosure proposes a pressure sensor 100, which includes a silicon strain diaphragm 10. The silicon strain diaphragm 10 is sequentially formed with a cross beam 11, a strain membrane 12 and a back cavity 13 from top to bottom. The cross beam 11 divides the silicon strain diaphragm 10 into four symmetrically arranged hollow portions 14, and the hollow portions 14 are in the shape of petals. Piezoresistors 15 are respectively provided at the four ends of the cross beam 11, and a Wheatstone bridge is formed between the piezoresistors 15. A groove is provided on the cross beam 11.

[0038] The pressure sensor 100 of the embodiment of the present disclosure includes a silicon strain diaphragm 10, which is formed with a cross beam 11, a strain film 12 and a back cavity 13 from top to bottom. The cross beam 11 divides the silicon strain diaphragm 10 into four hollow parts 14, and the four ends of the cross beam 11 are respectively provided with piezoresistors 15, and the cross beam 11 is provided with a groove. The arrangement of the groove can increase the deformation deflection of the cross beam 11 when it is subjected to external pressure, thereby increasing the concentrated stress at the four ends of the cross beam 11, that is, increasing the concentrated stress of the piezoresistors 15, and further improving the sensitivity of the pressure sensor 100. In addition, the hollow part 14 is specifically petal-shaped, and the petal-shaped hollow part 14 can increase the exposed area of ​​the strain film 12 below it. The larger the contact area of ​​the strain film 12 with the external pressure, the larger the deformation deflection of the strain film 12, and the larger the deformation deflection of the cross beam 11 above the strain film 12, further increasing the concentrated stress of the piezoresistors 15, and improving the sensitivity of the pressure sensor 100.

[0039] The edge of the cross beam 11 of the silicon strain diaphragm 10 in this embodiment is connected to the fixed part, the thickness of the fixed part is the same as that of the cross beam 11, the shape of the fixed part is annular, the four ends of the cross beam 11 are respectively connected to the inner ring of the fixed part, and the cross beam 11 and the fixed part together form four hollow parts 14 symmetrical about the center of the cross beam 11. The varistor 15 is arranged at the end of the cross beam 11 and close to the fixed part. When the cross beam 11 is subjected to pressure and deformed, the end of the cross beam 11 is subjected to a large concentrated stress, that is, the varistor 15 is subjected to a large concentrated stress.

[0040] The structure of each hollow portion 14 is a polygonal groove, and the polygon includes two right-angled sides and an arc-shaped side, wherein the two right-angled sides are formed by two adjacent beam arms of the cross beam 11, and the arc-shaped side is formed by the fixed portion. Specifically, the arc-shaped side is convex from the cross beam 11 toward the fixed portion, and the arc-shaped sides of the two adjacent hollow portions 14 form a convexity in the fixed portion, and the convexity is connected to the end of the corresponding cross beam 11, that is, the inner ring of the fixed portion is formed with four convexities, and each convexity is connected to the end of the corresponding cross beam 11. When the strain membrane 12 and the cross beam 11 are subjected to external pressure, the strain membrane 12 and the cross beam 11 are deformed together, and the end of the cross beam 11 is subjected to a large concentrated stress, and the fixed portion connected to the end is a convexity, and the convex structure further increases the stress at the end of the cross beam 11, thereby improving the sensitivity of the pressure sensor 100.

[0041] In some embodiments of the present disclosure, each end of the cross beam 11 is provided with a heavily doped contact area 16 and a metal lead 17, the varistor 15 at each end of the cross beam 11 is connected in series with the heavily doped contact area 16, the metal lead 17 is connected to the heavily doped contact area 16, and a Wheatstone bridge is formed between each varistor 15. Specifically, the metal lead 17 is introduced into the fixed part from the end of the cross beam 11, the metal lead 17 is arranged along the edge of the hollow part 14 in the fixed part, and a metal welding block 18 is provided between the metal leads 17 respectively led out from two adjacent ends, and the varistor 15 outputs the resistance value through the metal welding block 18.

[0042] In some embodiments of the present disclosure, a cross mass 19 is provided on the side of the strain film 12 facing the back cavity 13. The cross mass 19 is convex from the strain film 12 toward the back cavity 13, and the cross mass 19 is located in the back cavity 13. The cross mass 19 is arranged correspondingly to the cross beam 11. The cross mass 19 and the cross beam 11 can both increase the difference between the transverse and longitudinal stresses, and improve the stress concentration effect of the pressure sensor 100. At the same time, the cross mass 19 and the cross beam 11 jointly increase the stiffness of the pressure sensor 100, increase the natural frequency of the pressure sensor 100, and improve the linearity of the pressure sensor 100.

[0043] In some embodiments of the present disclosure, the groove includes a first groove 111, wherein the first groove 111 is disposed at the center of the cross beam 11. By disposing the first groove 111 in the center and west of the cross beam 11, the deformation deflection of the cross beam 11 when subjected to external pressure can be increased, thereby improving the sensitivity of the pressure sensor 100.

[0044] Furthermore, the first groove 111 is a circular groove, a rectangular groove or other grooves symmetrical about the center of the cross beam 11. The first groove 111 symmetrical about the cross beam 11 can make each beam arm of the cross beam 11 bear force evenly, thereby ensuring that each piezoresistors 15 bear force evenly, thereby improving the accuracy of the pressure sensor 100.

[0045] In some embodiments of the present disclosure, the groove also includes a second groove 112, which is disposed on the beam arm of the cross beam 11. The second groove 112 can further increase the deformation deflection of the cross beam 11 when subjected to external pressure, thereby further improving the sensitivity of the pressure sensor 100.

[0046] Specifically, there are four groups of second grooves 112 , and the four groups of second grooves 112 are respectively disposed on four beam arms of the cross beam 11 to ensure that the deformation deflection of each beam arm is the same, thereby improving the accuracy of the pressure sensor 100 .

[0047] Furthermore, each group of second grooves 112 is arranged close to the first grooves 111 , that is, each second groove 112 is far away from the end of the corresponding cross beam 11 , which can ensure the rigidity of the end of the cross beam 11 while improving the deformation deflection of the cross beam 11 .

[0048] Specifically, the second groove 112 is a rectangular groove, a circular groove or a triangular groove. When the second groove 112 is a rectangular groove, the length direction of the rectangular groove is arranged along the length of the corresponding beam arm; when the second groove 112 is a circular groove, the circular groove is symmetrically arranged about the width center of the beam arm to ensure that the two sides of the beam arm are evenly stressed; when the second groove 112 is a triangular groove, the apex angles of two adjacent triangular grooves arranged along the length direction of the beam arm face in opposite directions. Each group of second grooves 112 can be one, two, three, four, five, six or more, and this embodiment does not specifically limit the number of each group of second grooves 112.

[0049] In some embodiments of the present disclosure, a thermistor 30 is further provided on the silicon strain diaphragm 10. The thermistor 30 is provided on the front, side or back of the silicon strain diaphragm 10. The thermistor 30 is used to sense the ambient temperature and change the resistance value according to the ambient temperature to provide a temperature reference for the user.

[0050] In some embodiments of the present disclosure, the pressure sensor 100 further includes a glass substrate, which is disposed on a side of the silicon strain diaphragm 10 where the back cavity 13 is formed, and the glass substrate is connected to the silicon strain diaphragm 10 by bonding.

[0051] like Figure 4(a) to Figure 4(i) As shown, the second aspect of the present disclosure proposes a method for preparing a pressure sensor 100 , and the method for preparing the pressure sensor 100 is used to prepare the pressure sensor 100 of any of the above embodiments.

[0052] The method for preparing the pressure sensor 100 comprises the following steps:

[0053] S10: growing an oxide layer on the silicon substrate 101;

[0054] As shown in Fig. 4(a), the silicon substrate 1011 is an N-type silicon substrate 101, and its thickness is 300um-600um. A silicon oxide layer 102 is grown on the surface of the silicon substrate 101 by thermal oxidation growth. The thickness of the silicon oxide layer 102 is 200-500nm.

[0055] S20: performing a photolithography patterning process on the front side of the silicon substrate 101 to form a varistor 15;

[0056] As shown in FIG. 4( b ), a photolithography patterning process is performed on the front side of the silicon substrate 101 , and the photoresist 200 is directly used as a mask material for boron ion implantation, followed by annealing to form the varistor 15 .

[0057] S30: forming a heavily doped contact region on the front side of the silicon substrate 101 by photolithography;

[0058] As shown in FIG. 4( c ), a heavily doped contact region 16 pattern is formed on the front side of the silicon wafer by photolithography, and ion implantation and annealing are performed to obtain the heavily doped contact region.

[0059] S40: forming a contact hole 103 on the silicon substrate 101 by using a chemical vapor deposition process;

[0060] As shown in FIG4(d), a 500 nm thick silicon dioxide protective layer is deposited on the front of the silicon substrate 101 by plasma enhanced chemical vapor deposition (PECVD), and then a photolithography patterning process is performed, and a buffered oxide etchant (BOE) is used at room temperature to etch the silicon dioxide layer 102 to form a contact hole 103. After the etching is completed, an ion beam etching process (IBE) is used to etch at a low speed to ensure that the impurities in the contact hole 103 are completely removed.

[0061] S50: using sputtering and photolithography to prepare metal leads 17 in the contact holes 103, and to prepare metal solder bumps 18 with the oxide layer exposed on the silicon substrate 101;

[0062] As shown in FIG. 4( e ), a 1 μm thick Al metal layer is deposited on the front side of the silicon substrate 101 by magnetron sputtering (PVD), and then a photolithography patterning process is performed, and the metal layer is corroded using an Al etching solution to form leads.

[0063] S60: preparing a thermistor 30 on the front side of the silicon substrate 101;

[0064] As shown in FIG. 4( f ), a thermistor 30 is prepared on the front surface of the silicon substrate 101 .

[0065] S70: etching the cross beam 11 and its groove on the silicon substrate 101;

[0066] As shown in FIG4(g), a photolithography patterning process is performed on the front side of the silicon substrate 101 to define an etching window, and the silicon dioxide layer 102 is first etched using a 7:1 BOE solution at room temperature. After the etching is completed, the cross beam 11 is subjected to ICP deep silicon etching to form a petal-shaped membrane, and a first groove 111 and a second groove 112 are etched on the cross beam 11. After the etching is completed, the wafer is removed for degumming and cleaning.

[0067] S80: etching a back cavity 13 and a cross mass 19 on the back side of the silicon substrate 101;

[0068] As shown in FIG. 4( h ), photolithography is performed on the back of the silicon wafer to define an etching window, and then ICP deep silicon etching is performed to form a back cavity 13 and a cross mass 19 , and a strain film 12 is formed between the back cavity 13 and the cross beam 11 .

[0069] S90: Bonding the back side of the silicon substrate 101 to the glass substrate.

[0070] As shown in FIG. 4( i ), the back side of the silicon wafer is anodically bonded to a BF33 glass substrate. A through hole 201 is formed on the glass substrate. The through hole 201 is located directly opposite to the center of the silicon wafer back cavity 13 . After the bonding is completed, the wafer is diced to complete the preparation of the pressure sensor 100 .

[0071] According to the method for preparing a pressure sensor of an embodiment of the present disclosure, the prepared pressure sensor 100 includes a silicon strain diaphragm 10, and the silicon strain diaphragm 10 is sequentially formed with a cross beam 11, a strain film 12 and a back cavity 13 from top to bottom. The cross beam 11 divides the silicon strain diaphragm 10 into four hollow parts 14, and the four ends of the cross beam 11 are respectively provided with piezoresistors 15, and the cross beam 11 is provided with a groove. The arrangement of the groove can increase the deformation deflection of the cross beam 11 when subjected to external pressure, thereby increasing the concentrated stress at the four ends of the cross beam 11, that is, increasing the concentrated stress of the piezoresistors 15, and thus improving the sensitivity of the pressure sensor 100. In addition, the hollow part 14 is specifically petal-shaped, and the petal-shaped hollow part 14 can increase the exposed area of ​​the strain film 12 below it. The larger the contact area of ​​the strain film 12 with the external pressure, the larger the deformation deflection of the strain film 12, and the larger the deformation deflection of the cross beam 11 above the strain film 12, further increasing the concentrated stress of the piezoresistors 15, and improving the sensitivity of the pressure sensor 100.

[0072] The pressure sensor prepared in this embodiment is a MEMS pressure sensor.

[0073] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present disclosure, but the present disclosure is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and substance of the present disclosure, and these modifications and improvements are also considered to be within the scope of protection of the present disclosure.

Claims

1. A pressure sensor, characterized in that: The pressure sensor comprises a silicon strain diaphragm, wherein the silicon strain diaphragm is sequentially formed with a cross beam, a strain membrane and a back cavity from top to bottom, wherein the cross beam divides the silicon strain diaphragm into four symmetrically arranged hollow portions, wherein the hollow portions are in the shape of petals, and four ends of the cross beam are respectively provided with piezoresistors, wherein a Wheatstone bridge is formed between the piezoresistors, and a groove is provided on the cross beam; The grooves include a first groove and four groups of second grooves. The first groove is arranged at the center of the cross beam, and the four groups of second grooves are respectively arranged at four beam arms of the cross beam; each group of the second grooves is arranged close to the first groove.

2. The pressure sensor according to claim 1, characterized in that: The first groove is a circular groove, a rectangular groove or other grooves that are symmetrical about the center of the cross beam.

3. The pressure sensor according to claim 1, characterized in that: The second groove is a rectangular groove, a circular groove or a triangular groove.

4. The pressure sensor according to claim 1, characterized in that: The shape of the back cavity is similar to the shape of the hollow portion.

5. The pressure sensor according to claim 1, characterized in that: Each end of the cross beam is provided with a heavily doped contact area and a metal lead, the varistor at each end of the cross beam is connected in series with the heavily doped contact area, the metal lead is connected to the heavily doped contact area, and a Wheatstone bridge is formed between the varistors.

6. The pressure sensor according to claim 1, characterized in that: The silicon strain diaphragm further comprises a cross mass block, the cross mass block is arranged in the back cavity, and the cross mass block and the cross beam are arranged opposite to the strain diaphragm.

7. The pressure sensor according to claim 1, characterized in that: The silicon strain diaphragm is provided with a thermistor.

8. A method for preparing a pressure sensor according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: growing an oxide layer on a silicon substrate; Performing a photolithography patterning process on the front side of the silicon substrate to form a varistor; Photolithographically forming a heavily doped contact region on the front side of the silicon substrate; forming contact holes on a silicon substrate using a chemical vapor deposition process; Using sputtering and photolithography process to prepare metal leads in the contact holes, and preparing metal welding blocks with exposed oxide layers on the silicon substrate; A thermistor is fabricated on the front side of a silicon substrate; etching a cross beam on a silicon substrate and etching a groove on the cross beam; A back cavity and a cross-mass block are etched on the back side of the silicon substrate; The back side of the silicon substrate is bonded to the glass substrate.

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