Piezoresistive pressure sensor and preparation method thereof
By setting up direct contact and completely isolation sensing membrane in the pressure -resistant pressure sensor, and using the voltage detection circuit for signal compensation, the problem of low output accuracy of traditional pressure -resistant pressure sensors is solved, and higher accuracy and higher accuracy and higher accuracy and higher accuracy and accuracy.
Patent Information
- Application Number
- CN202411529486.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-30
- Publication Date
- 2025-01-28
AI Technical Summary
The output of a traditional piezoresistive pressure sensor is affected by vibration and acceleration, resulting in a decrease in output accuracy and inability to achieve accurate pressure sensing results.
By setting the first sensor compression membrane directly contacting the strong media to test the strong medium and the second sensing film completely isolated from the outside of the outside world, the two -sensitive compression membrane completely isolated by the external pressure medium is used to complete the mutual compensation of the output signal to eliminate the vibration and acceleration. Error.
Effectively improve the output accuracy of the pressure -resistant pressure sensor, and completely eliminate errors caused by vibration and acceleration.
Smart Images
Figure CN119374765A_ABST
Abstract
Description
Technical Field
[0001] The present disclosure relates to the technical field of MEMS sensors, and in particular to a piezoresistive pressure sensor and a preparation method thereof. Background Art
[0002] Piezoresistive pressure sensors are the most widely used type of sensors. They play an important role in aerospace, military industry, energy collection, automotive technology, medical equipment and other fields. They also have a wide range of market application needs in nuclear power, metallurgy, chemical industry, engine monitoring and other fields. Piezoresistive pressure sensors mainly use the piezoresistive effect of silicon. When pressure is applied to the pressure-sensitive film, the resistivity of the piezoresistors on the pressure-sensitive film will change, and then the output signal of the Wheatstone bridge formed by the resistor connection will change.
[0003] However, the output of traditional piezoresistive pressure sensors will be affected by vibration and acceleration, resulting in reduced output accuracy and failure to achieve accurate pressure sensing results. Summary of the invention
[0004] The purpose of the embodiments of the present disclosure is to provide a piezoresistive pressure sensor and a method for preparing the same, so as to solve the problem in the prior art that the output of the piezoresistive pressure sensor is affected by vibration and acceleration, resulting in reduced output accuracy.
[0005] The embodiments of the present disclosure adopt the following technical scheme: a piezoresistive pressure sensor, comprising: a substrate, a device layer arranged on a first surface of the substrate, and an upper cover arranged on a second surface of the substrate, wherein the first surface and the second surface are two opposite surfaces of the substrate; wherein the second surface of the substrate is provided with a first cavity and a second cavity, so that the remaining substrate portion between the bottom surface of the first cavity and the first surface forms a first pressure-sensitive film, and the remaining substrate portion between the bottom surface of the second cavity and the first surface forms a second pressure-sensitive film; the upper cover is provided with a through hole corresponding to the first cavity; the device layer includes at least: a first piezoresistor and a second piezoresistor for sensing stress conditions on the first pressure-sensitive film, a third piezoresistor and a fourth piezoresistor for sensing stress conditions on the second pressure-sensitive film, and a pressure detection circuit formed by connecting a plurality of piezoresistors.
[0006] In some embodiments, the first pressure-sensitive film and the second pressure-sensitive film have the same film size.
[0007] In some embodiments, the first varistor and the second varistor are arranged at the maximum stress on the first pressure-sensitive film; the third varistor and the fourth varistor are arranged at the maximum stress on the second pressure-sensitive film; one of the first varistor and the second varistor is a transverse varistor, and the other is a longitudinal varistor; one of the third varistor and the fourth varistor is a transverse varistor, and the other is a longitudinal varistor.
[0008] In some embodiments, the distance between any varistor and the center point of the corresponding pressure-sensitive film is the same.
[0009] In some embodiments, the first varistor, the second varistor, the third varistor, and the fourth varistor have the same size and electrical characteristics.
[0010] In some embodiments, the pressure detection circuit is a semi-open loop Wheatstone bridge circuit.
[0011] In some embodiments, the pressure detection circuit includes at least: a first conduction part, a second conduction part, a third conduction part, a fourth conduction part, a fifth conduction part, a first metal plate, a second metal plate, a third metal plate, a fourth metal plate and a fifth metal plate, and any two conduction parts are insulated; wherein, the first conduction part is configured to achieve electrical connection between the third varistor, the fourth varistor and the first metal plate, the second conduction part is configured to achieve electrical connection between the first varistor, the fourth varistor and the second metal plate, the third conduction part is configured to achieve electrical connection between the first varistor, the second varistor and the third metal plate, the fourth conduction part is configured to achieve electrical connection between the second varistor and the fourth metal plate, and the fifth conduction part is configured to achieve electrical connection between the third varistor and the fifth metal plate.
[0012] In some embodiments, the first conductive portion, the second conductive portion, the third conductive portion, the fourth conductive portion, and the fifth conductive portion are a plurality of heavily doped regions having different shapes and insulated from each other.
[0013] In some embodiments, each varistor includes a first connection area and a second connection area electrically connected to the varistor; the first conductive portion includes a first connection area of the third varistor, a second connection area of the fourth varistor, and a first wire connected to the first connection area of the third varistor, the second connection area of the fourth varistor, and the first metal disk at the same time; the second conductive portion includes a first connection area of the fourth varistor, a second connection area of the first varistor, and a second wire connected to the first connection area of the fourth varistor, the second connection area of the first varistor, and the second metal disk at the same time; the third conductive portion includes a first connection area of the first varistor, a first connection area of the second varistor, and a third wire connected to the first connection area of the first varistor, the first connection area of the second varistor, and the third metal disk at the same time; the fourth conductive portion includes a second connection area of the second varistor and a fourth wire connected to the second connection area of the second varistor and the fourth metal disk at the same time; the fifth conductive portion includes a second connection area of the third varistor and a fifth wire connected to the second connection area of the third varistor and the fifth metal disk at the same time.
[0014] The present embodiment also provides a method for preparing a piezoresistive pressure sensor as described above, comprising: providing a silicon-on-insulator structure as a substrate, wherein the top surface of the top silicon of the silicon-on-insulator structure is used as the first surface of the substrate, and the bottom surface of the bottom silicon of the silicon-on-insulator structure is used as the second surface of the substrate; opening a first cavity and a second cavity on the second surface, so that the remaining substrate portion between the bottom surface of the first cavity and the first surface forms a first pressure-sensitive film, and the remaining substrate portion between the bottom surface of the second cavity and the first surface forms a second pressure-sensitive film; preparing a device layer on the first surface; and bonding an upper cover on the second surface, wherein the upper cover is provided with a through hole corresponding to the first cavity.
[0015] The beneficial effect of the embodiments of the present disclosure is that by providing a first pressure-sensitive film that is in direct contact with the external pressure medium to be measured and a second pressure-sensitive film that is completely isolated from the external pressure medium to be measured, when external pressure is applied, the first pressure-sensitive film that is in direct contact with the external pressure medium to be measured simultaneously responds to the stress generated by the external pressure, vibration and acceleration, while the second pressure-sensitive film that is completely isolated from the external pressure medium to be measured only responds to the stress generated by vibration and acceleration, and mutual compensation of output signals is completed through the piezoelectric detection circuit to completely eliminate the errors caused by vibration and acceleration, thereby effectively improving the output accuracy of the piezoresistive pressure sensor. BRIEF DESCRIPTION OF THE DRAWINGS
[0016] In order to more clearly illustrate one or more embodiments of this specification or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this specification. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.
[0017] Figure 1 Schematic diagram of the hierarchical structure of the piezoresistive pressure sensor in the first embodiment of the present disclosure;
[0018] Figure 2 A schematic top view of a piezoresistive pressure sensor in the first embodiment of the present disclosure;
[0019] Figure 3 Schematic diagram of a circuit of a semi-open-loop Wheatstone bridge circuit in the first embodiment of the present disclosure;
[0020] Figure 4 Another schematic top view of the piezoresistive pressure sensor in the first embodiment of the present disclosure;
[0021] Figure 5 for Figure 2 Schematic diagram of the cross section at AA';
[0022] Figure 6 for Figure 2 Schematic diagram of the cross section at BB';
[0023] Figure 7 Another schematic top view of the piezoresistive pressure sensor in the first embodiment of the present disclosure;
[0024] Figure 8 is a flow chart of a method for preparing a piezoresistive pressure sensor in a second embodiment of the present disclosure;
[0025] Fig. 9 This is a hierarchical diagram after step 11 and step 21 are completed in the second embodiment of the present disclosure;
[0026] Figures 10 to 15 This is a hierarchical diagram after each step from step 12 to step 17 in the second embodiment of the present disclosure is completed;
[0027] Figures 16 to 23 This is a hierarchical diagram after each step from step 22 to step 29 is completed in the second embodiment of the present disclosure. DETAILED DESCRIPTION
[0028] In order to enable those skilled in the art to better understand the technical solutions in one or more embodiments of this specification, the following will be combined with the drawings in one or more embodiments of this specification to clearly and completely describe the technical solutions in one or more embodiments of this specification. Obviously, the described embodiments are only part of the embodiments of this specification, not all of the embodiments. Based on one or more embodiments of this specification, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this document.
[0029] Piezoresistive pressure sensors are the most widely used type of sensors. They play an important role in aerospace, military industry, energy collection, automotive technology, medical equipment and other fields. They also have a wide range of market application needs in nuclear power, metallurgy, chemical industry, engine monitoring and other fields. Piezoresistive pressure sensors mainly use the piezoresistive effect of silicon. When pressure is applied to the pressure-sensitive film, the resistivity of the piezoresistors on the pressure-sensitive film will change, and then the output signal of the Wheatstone bridge formed by the resistor connection will change.
[0030] However, the output of traditional piezoresistive pressure sensors will be affected by vibration and acceleration, resulting in reduced output accuracy and failure to achieve accurate pressure sensing results.
[0031] In order to solve the above problems, the first embodiment of the present disclosure provides a piezoresistive pressure sensor, which specifically provides a first pressure-sensitive membrane that is in direct contact with the external pressure medium to be measured and a second pressure-sensitive membrane that is completely isolated from the external pressure medium to be measured. When external pressure is applied, the first pressure-sensitive membrane that is in direct contact with the external pressure medium to be measured responds to the stress generated by the external pressure, vibration and acceleration at the same time, while the second pressure-sensitive membrane that is completely isolated from the external pressure medium to be measured only responds to the stress generated by vibration and acceleration. The output signals are compensated by the piezoelectric detection circuit to completely eliminate the errors caused by vibration and acceleration, thereby effectively improving the output accuracy of the piezoresistive pressure sensor. Figures 1 to 7 The piezoresistive pressure sensor of this embodiment will be described in detail.
[0032] Figure 1 FIG. 2 shows a schematic diagram of the hierarchical structure of the piezoresistive pressure sensor in this embodiment. Figure 1 As shown, the piezoresistive pressure sensor mainly includes a substrate 1, a device layer 4 arranged on a first surface of the substrate 1, and an upper cover 8 arranged on a second surface of the substrate 1, wherein the first surface and the second surface are two opposite surfaces of the substrate 1, corresponding to Figure 1The upper surface and the lower surface of the substrate 1. Specifically, a first cavity 71 and a second cavity 72 are provided on one side of the second surface of the substrate 1, so that the remaining substrate portion between the bottom surface of the first cavity 71 and the first surface forms the first pressure-sensitive film 11, and the remaining substrate portion between the bottom surface of the second cavity 72 and the first surface forms the second pressure-sensitive film 12; accordingly, the upper cover 8 is provided with a through hole 81 corresponding to the first cavity 71, so that the first pressure-sensitive film 11 is in contact with the outside world, while the second pressure-sensitive film 12 is completely isolated from the outside world; at the same time, at least a first piezoresistor 41 and a second piezoresistor 42 for sensing the stress condition on the first pressure-sensitive film 11, a third piezoresistor 43 and a fourth piezoresistor 44 for sensing the stress condition on the second pressure-sensitive film 12, and a pressure detection circuit formed by connecting multiple piezoresistors are provided in the device layer 4.
[0033] In this embodiment, the substrate 1 can be implemented by a silicon-on-insulator (SOI) structure, which is actually a stacked structure of a bottom silicon (SOI-handle), a buried oxide layer (SOI-BOX) and a top silicon (SOI-top), wherein the top surface of the top silicon is used as the first surface, the bottom surface of the bottom silicon is used as the second surface, the cavities 71 and 72 are both opened in the bottom silicon, and the device layer is prepared in the top silicon. When the cavity is actually prepared, a first cavity 71 and a second cavity 72 are formed on the substrate by back etching. The first cavity 71 and the second cavity 72 should have the same shape and size, so that the film layer size of the two pressure-sensitive films formed after etching the cavity is the same, so as to achieve the same pressure feedback to vibration or acceleration and ensure the measurement accuracy. The upper cover 8 is also formed based on silicon material, and can be connected to the substrate 1 by silicon-silicon bonding to form a strong combination. The through hole 81 corresponding to the position of the first cavity 71 exposes the first pressure-sensitive film 11 to the external environment, while the second cavity 72 is completely closed and can only sense the stress caused by vibration and / or acceleration to compensate for the error on the first pressure-sensitive film 11.
[0034] It should be noted that Figure 1 The cross-sectional shapes of the first cavity 71 and the second cavity 72 are not shown in the figure. When actually preparing the cavity, a circular, square or other regular shape can be selected as the cross-sectional shape of the cavity, and this shape is also the shape of the sensing film. Usually, when preparing a circular sensing film, dry etching is often used. The side wall of the cavity is as follows: Figure 1In the vertical state shown, if a square pressure-sensitive film is used, wet etching can be used, and the side walls of the cavity are inclined. A square pressure-sensitive film with more concentrated stress can be selected for a small range, and a circular pressure-sensitive film can be selected for a large range. The specific thickness of the pressure-sensitive film (i.e., substrate thickness-cavity depth) is also determined in combination with the shape of the cavity cross-section and the range requirements, such as a circular pressure-sensitive film with a thickness of 160μm or a square pressure-sensitive film with a thickness of 130μm. This embodiment is introduced using a circular cavity cross-section as an example, but the shape and size of the pressure-sensitive film can actually be selected in combination with the requirements, and this embodiment does not limit it.
[0035] In addition, when designing and implementing the first cavity 71 and the second cavity 72, it should be ensured that the first pressure-sensitive film 11 and the second pressure-sensitive film 12 are completely isolated from each other, that is, a certain distance should be ensured between the two to avoid mutual influence or air leakage; at the same time, it should also be ensured that there is a certain distance between the first pressure-sensitive film 11 and the second pressure-sensitive film 12 and the edge of the substrate to avoid the above-mentioned edge being too thin and causing the cavity to contact with the outside world and leak. When actually implementing the cavity, the spacing between the pressure-sensitive films and the spacing between the pressure-sensitive films and the edge of the substrate should be simulated and calculated in combination with the substrate size, the accuracy requirements of the sensing, the shape of the pressure-sensitive film, etc., and this embodiment does not impose specific restrictions.
[0036] Figure 2 FIG. 1 shows a top view of a piezoresistive pressure sensor, which mainly shows a specific layout of each piezoresistor and a pressure detection circuit in a device layer 4. Figure 2 As shown, the dotted lines correspond to the positions of the first cavity 71 and the second cavity 72, that is, the positions of the first pressure-sensitive film 11 and the second pressure-sensitive film 12. The first piezoresistors 41 and the second piezoresistors 42 are arranged within the sensing range of the first pressure-sensitive film 11, and the third piezoresistors 43 and the fourth piezoresistors 44 are arranged within the sensing range of the second pressure-sensitive film 12. Specifically, the piezoresistors corresponding to each pressure-sensitive film are respectively arranged at the maximum stress of the pressure-sensitive film area, and different piezoresistors are used to sense pressure conditions in different directions. In this embodiment, the first piezoresistors 41 and the second piezoresistors 42 are arranged at the edge of the first pressure-sensitive film 11, that is, at the maximum stress of the first pressure-sensitive film 11; at the same time, the third piezoresistors 43 and the fourth piezoresistors 44 are arranged at the edge of the second pressure-sensitive film 12, that is, at the maximum stress of the second pressure-sensitive film 12.
[0037] The varistor in this embodiment can be a p-type silicon material formed by lightly doping the top silicon, and its piezoresistance coefficient is anisotropic. Combined with the positional relationship between the length direction of the piezoresistance strip and the edge of the pressure-sensitive film, the varistor in this embodiment is divided into a transverse varistor and a longitudinal varistor. Taking the circular pressure-sensitive film of this embodiment as an example, the length direction of the piezoresistance strip of the transverse varistor is perpendicular to the edge of the film, while the length direction of the piezoresistance strip of the longitudinal resistor is tangent to the edge of the film. In specific implementation, one of the first varistor 41 and the second varistor 42 is a transverse varistor, and the other is a longitudinal varistor. Similarly, one of the third varistor 43 and the fourth varistor 44 is a transverse varistor, and the other is a longitudinal varistor. When the pressure on the pressure-sensitive film is actually sensed by a Wheatstone bridge formed by connecting the varistor, due to the anisotropy of the piezoresistance coefficient of the p-type silicon material, the resistance changes of the longitudinal varistor and the transverse varistor will be different, thereby generating a resistance difference, which can be converted into an output signal as a sensing result through the Wheatstone bridge.
[0038] It should be understood that the distances between all the above-mentioned varistors and the center points of the corresponding pressure-sensitive films are the same, and on the basis of the consistent shape and size of the pressure-sensitive films, the positions of the pressure changes sensed by the varistors are also the same; in addition, the first varistor 41, the second varistor 42, the third varistor 43 and the fourth varistor 44 have the same size and electrical characteristics, thereby obtaining more accurate measurement results. In actual preparation, attention should be paid to the consistency of the lightly doped position and concentration to ensure the uniform electrical characteristics of the varistors.
[0039] In this embodiment, the pressure detection circuit is a semi-open loop Wheatstone bridge circuit. Figure 3As shown, the device area corresponding to each pressure-sensitive film forms half a Wheatstone bridge, thereby coupling the pressure signals output by the two pressure-sensitive films to offset the outputs related to vibration and acceleration. Specifically, the pressure detection circuit at least includes: a first conduction part, a second conduction part, a third conduction part, a fourth conduction part, a fifth conduction part, a first metal plate 61, a second metal plate 62, a third metal plate 63, a fourth metal plate 64 and a fifth metal plate 65, and any two conduction parts are insulated, wherein the conduction part is used to realize the electrical connection between the varistor and the metal plate, and the metal plate is used as a terminal to be electrically connected to the downstream acquisition device; wherein the first conduction part is configured to realize the electrical connection between the third varistor 43, the fourth varistor 44 and the first metal plate 61, the second conduction part is configured to realize the electrical connection between the first varistor 41, the fourth varistor 44 and the second metal plate 62, the third conduction part is configured to realize the electrical connection between the first varistor 41, the second varistor 42 and the third metal plate 63, the fourth conduction part is configured to realize the electrical connection between the second varistor 42 and the fourth metal plate 64, and the fifth conduction part is configured to realize the electrical connection between the third varistor 43 and the fifth metal plate 63.
[0040] Combination Figure 2 The layout shown in FIG. 1 is a schematic diagram of a first conductive portion, a second conductive portion, a third conductive portion, a fourth conductive portion, and a fifth conductive portion. The first conductive portion, the second conductive portion, the third conductive portion, the fourth conductive portion, and the fifth conductive portion are heavily doped regions having different shapes and insulated from each other, respectively corresponding to Figure 2 The first heavily doped region 51, the second heavily doped region 52, the third heavily doped region 53, the fourth heavily doped region 54 and the fifth heavily doped region 55 are designed in accordance with the position design of the first pressure-sensitive film 11 and the second pressure-sensitive film 12 and the position layout of the varistors corresponding to the pressure-sensitive films. The shapes of the heavily doped regions are not fixed, and the design standard is to ensure the electrical connection effect of the corresponding varistors and the metal disk. Figure 4 A schematic top view of another piezoresistive pressure sensor is shown. Figure 2 The layout method, Figure 4 The position of the middle pressure-sensitive film has changed, and the corresponding varistor position and the shape of the heavily doped area have changed accordingly. It should be noted that when the area difference between the designed multiple heavily doped areas is smaller, the initial resistance difference between the two Wheatstone half-bridges is smaller, and the zero-point output is also smaller; and when the volume of the long strip etched isolation area between the two pressure-sensitive films is smaller, the possibility of stress mutual influence or resonance between the two pressure-sensitive films is smaller. In actual design, the layout setting of the piezoresistive pressure sensor can be completed in combination with actual needs.
[0041] Further Figure 2 As shown, the periphery of the surface of the device layer 4 is etched to form an isolation ring 50, that is, Figure 2In the middle shaded area, etching stops when it reaches the buried oxide layer surface of the SOI substrate, so in fact, the shaded area should be the surface of the buried oxide layer exposed after the isolation ring is etched. The design of the isolation ring can not only achieve physical isolation between the chip device layer and the external pressure medium to be measured, but also increase the area of the heavily doped area as much as possible. Figure 5 Shows Figure 2 Schematic diagram of the cross section at AA', Figure 6 It shows Figure 2 The cross-sectional schematic diagram at BB' is used to show the structure of the piezoresistive pressure sensor of this embodiment in detail.
[0042] Figure 7 A top view schematic diagram of another piezoresistive pressure sensor is shown, in which the varistors are no longer connected through heavily doped regions, but the two connection areas connected to each varistor and the metal wire are combined to achieve the construction of a Wheatstone bridge. Specifically, each varistor includes a first connection area and a second connection area electrically connected to the varistor, the first conductive portion includes the first connection area 431 of the third varistor 43, the second connection area 442 of the fourth varistor 44, and a first wire 91 simultaneously connected to the first connection area 431 of the third varistor 43, the second connection area 442 of the fourth varistor 44, and the first metal disk 61; the second conductive portion includes the first connection area 441 of the fourth varistor 44, the second connection area 412 of the first varistor 41, and a first wire 91 simultaneously connected to the first connection area 441 of the fourth varistor 44, the second connection area 412 of the first varistor 41, and the second metal disk 62 The third conducting portion includes the first connecting area 411 of the first varistor 41, the first connecting area 421 of the second varistor 42, and the third conducting portion 93 connected to the first connecting area 411 of the first varistor 41, the first connecting area 421 of the second varistor 42, and the third metal disk 63; the fourth conducting portion includes the second connecting area 422 of the second varistor 42 and the fourth conducting portion 94 connected to the second connecting area 422 of the second varistor 42 and the fourth metal disk 64; the fifth conducting portion includes the second connecting area 432 of the third varistor 43 and the fifth conducting portion 95 connected to the second connecting area 432 of the third varistor 43 and the fifth metal disk 65.
[0043] It should be noted that, whether Figure 2 The method of using heavily doped regions to complete electrical connection is shown in FIG. Figure 7 The methods of completing electrical connection through wires shown are all specific implementation methods when actually designing piezoresistive pressure sensors. Different varistor layouts and connection methods can be selected accordingly based on actual needs, process levels, and different packaging methods.
[0044] In this embodiment, a first pressure-sensitive film that is in direct contact with the external pressure medium to be measured and a second pressure-sensitive film that is completely isolated from the external pressure medium to be measured are provided. When external pressure is applied, the first pressure-sensitive film that is in direct contact with the external pressure medium to be measured simultaneously responds to the stress generated by the external pressure, vibration and acceleration, while the second pressure-sensitive film that is completely isolated from the external pressure medium to be measured only responds to the stress generated by vibration and acceleration. The output signals are compensated by each other through the piezoelectric detection circuit to completely eliminate the errors caused by vibration and acceleration, thereby effectively improving the output accuracy of the piezoresistive pressure sensor.
[0045] Based on the same inventive concept, the second embodiment of the present disclosure provides a method for preparing the piezoresistive pressure sensor provided in the first embodiment, and its flow chart is as follows: Figure 8 As shown, it mainly includes steps S10 to S40:
[0046] S10, providing a silicon-on-insulator structure as a substrate; wherein a top surface of a top silicon layer of the silicon-on-insulator structure is used as a first surface of the substrate, and a bottom surface of a bottom silicon layer of the silicon-on-insulator structure is used as a second surface of the substrate;
[0047] S20, opening a first cavity and a second cavity on the second surface, so that the remaining substrate portion between the bottom surface of the first cavity and the first surface forms a first pressure-sensitive film, and the remaining substrate portion between the bottom surface of the second cavity and the first surface forms a second pressure-sensitive film;
[0048] S30, preparing a device layer on the first surface;
[0049] S40, bonding an upper cover on the second surface, wherein the upper cover is provided with a through hole corresponding to the first cavity.
[0050] It should be noted that, in the actual execution process of the above steps S20 and S30, step S20 can be executed first and then step S30, and there is no necessary logical connection between the execution steps. Similarly, step S40 only needs to be executed after S20 is executed, and it does not necessarily have to be executed after S30 is completed in the order of the step numbers.
[0051] Combine the following Figures 9 to 15 For example Figure 2 The preparation process of the piezoresistive pressure sensor shown is described in detail:
[0052] Step 11: Clean the prepared SOI wafer to remove impurities and particles adsorbed on the surface of the wafer, such as Fig. 9 As shown;
[0053] Step 12: Lightly doped ions are implanted into the top silicon layer of the SOI wafer in step 11 to prepare a p-type varistor 4, such as Fig.10 As shown;
[0054] Step 13: Perform heavy doping ion implantation on the heavily doped region of the p-type piezoresistor interconnection formed in step 12 to form a heavily doped region 5, such as Fig.11 As shown;
[0055] Step 14: Etch the top silicon layer of the SOI wafer to remove the portion not protected by the mask material, forming an isolation ring 50 around the heavily doped region 5 and the device layer. Fig.12 As shown;
[0056] Step 15: Use metal plating technology to make reliable ohmic contacts at the electrical interfaces leading out of the five heavily doped regions, forming five metal plates 6, such as Fig.13 As shown;
[0057] Step 16: Back-etch the bottom silicon of the SOI to form a back-etched first cavity 71 that is in direct contact with the external pressure medium to be measured, and a back-etched second cavity 72 that is completely isolated from the external pressure medium to be measured, such as Fig.14 As shown;
[0058] Step 17: Using silicon-silicon direct bonding technology, the silicon cover 8 is bonded to the SOI back-etched surface to form a strong bond. Fig.15 shown.
[0059] Combine the following Fig. 9 , Figures 16 to 23 For example Figure 7 The preparation process of the piezoresistive pressure sensor shown is described in detail:
[0060] Step 21: Clean the prepared SOI wafer to remove impurities and particles adsorbed on the surface of the wafer, such as Fig. 9 As shown;
[0061] Step 22: Perform lightly doped ion implantation and heavily doped ion implantation on the top silicon layer of the SOI wafer in step 21, such as Fig.16 As shown;
[0062] Step 23: Etch the top silicon layer of the SOI wafer to form lightly doped connecting strips connected by heavily doped connecting layers, such as Fig.17 As shown;
[0063] Step 24: Deposit an insulating layer 10 on the top silicon layer of the SOI wafer, such as Fig.18 As shown;
[0064] Step 25: Etching an ohmic contact hole on the insulating layer 10 to prepare for the next step of making a reliable ohmic contact, such as Fig.19 As shown;
[0065] Step 26: Perform metal wiring on the top layer of SOI by metal plating and high temperature annealing process to form wire 9, such as Fig. 20 As shown;
[0066] Step 27: Deposit a passivation layer 13 on the top silicon layer of SOI and etch out a metal disk 6, such as Fig.21 As shown;
[0067] Step 28: Back-etch the bottom silicon of the SOI to form a back-etched first cavity 71 that is in direct contact with the external pressure medium to be measured, and a back-etched second cavity 72 that is completely isolated from the external pressure medium to be measured, such as Fig. 22 As shown;
[0068] Step 29: Use silicon-silicon direct bonding technology to bond the silicon cover 8 to the SOI back-etched surface to form a strong bond. Fig.23 shown.
[0069] In this embodiment, a first pressure-sensitive film that is in direct contact with the external pressure medium to be measured and a second pressure-sensitive film that is completely isolated from the external pressure medium to be measured are provided. When external pressure is applied, the first pressure-sensitive film that is in direct contact with the external pressure medium to be measured simultaneously responds to the stress generated by the external pressure, vibration and acceleration, while the second pressure-sensitive film that is completely isolated from the external pressure medium to be measured only responds to the stress generated by vibration and acceleration. The output signals are compensated by each other through the piezoelectric detection circuit to completely eliminate the errors caused by vibration and acceleration, thereby effectively improving the output accuracy of the piezoresistive pressure sensor.
[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present disclosure, rather than to limit them. Although the present disclosure has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present disclosure.
Claims
1. A piezoresistive pressure sensor, characterized in that: include: A substrate, a device layer disposed on a first surface of the substrate, and an upper cover disposed on a second surface of the substrate, wherein the first surface and the second surface are two opposite surfaces of the substrate; wherein A first cavity and a second cavity are formed on the second surface of the substrate, so that the remaining substrate portion between the bottom surface of the first cavity and the first surface forms a first pressure-sensitive film, and the remaining substrate portion between the bottom surface of the second cavity and the first surface forms a second pressure-sensitive film; The upper cover is provided with a through hole corresponding to the first cavity; The device layer includes at least: a first piezoresistor and a second piezoresistor for sensing stress on the first pressure-sensitive film, a third piezoresistor and a fourth piezoresistor for sensing stress on the second pressure-sensitive film, and a pressure detection circuit formed by connecting multiple piezoresistors.
2. The piezoresistive pressure sensor according to claim 1, characterized in that: The first pressure-sensitive film and the second pressure-sensitive film have the same film size.
3. The piezoresistive pressure sensor according to claim 1, characterized in that: The first varistor and the second varistor are arranged at the maximum stress position on the first pressure-sensitive film; the third varistor and the fourth varistor are arranged at the maximum stress position on the second pressure-sensitive film; One of the first varistor and the second varistor is a transverse varistor, and the other is a longitudinal varistor; One of the third varistor and the fourth varistor is a transverse varistor, and the other is a longitudinal varistor.
4. The piezoresistive pressure sensor according to claim 3, characterized in that: The distance between any varistor and the center point of the corresponding pressure-sensitive film is the same.
5. The piezoresistive pressure sensor according to claim 1, characterized in that: The first varistor, the second varistor, the third varistor, and the fourth varistor have the same size and electrical characteristics.
6. The piezoresistive pressure sensor according to any one of claims 1 to 5, characterized in that: The pressure detection circuit is a semi-open loop Wheatstone bridge circuit.
7. The piezoresistive pressure sensor according to claim 6, characterized in that: The pressure detection circuit at least includes: a first conduction part, a second conduction part, a third conduction part, a fourth conduction part, a fifth conduction part, a first metal disk, a second metal disk, a third metal disk, a fourth metal disk and a fifth metal disk, and any two conduction parts are insulated; wherein, The first conductive portion is configured to achieve electrical connection between the third varistor, the fourth varistor and the first metal disk, the second conductive portion is configured to achieve electrical connection between the first varistor, the fourth varistor and the second metal disk, the third conductive portion is configured to achieve electrical connection between the first varistor, the second varistor and the third metal disk, the fourth conductive portion is configured to achieve electrical connection between the second varistor and the fourth metal disk, and the fifth conductive portion is configured to achieve electrical connection between the third varistor and the fifth metal disk.
8. The piezoresistive pressure sensor according to claim 7, characterized in that: The first conductive portion, the second conductive portion, the third conductive portion, the fourth conductive portion, and the fifth conductive portion are a plurality of heavily doped regions having different shapes and insulated from each other.
9. The piezoresistive pressure sensor according to claim 7, characterized in that: Each varistor includes a first connection area and a second connection area electrically connected to the varistor; The first conductive portion includes a first connection area of the third varistor, a second connection area of the fourth varistor, and a first wire connected to the first connection area of the third varistor, the second connection area of the fourth varistor, and the first metal plate at the same time; The second conductive portion includes a first connection area of the fourth varistor, a second connection area of the first varistor, and a second wire connected to the first connection area of the fourth varistor, the second connection area of the first varistor, and the second metal plate at the same time; The third conducting portion includes a first connection area of the first varistor, a first connection area of the second varistor, and a third wire connected to the first connection area of the first varistor, the first connection area of the second varistor, and the third metal plate at the same time; The fourth conductive portion includes a second connection area of the second varistor and a fourth wire connected to the second connection area of the second varistor and the fourth metal plate at the same time; The fifth conductive portion includes a second connection region of the third varistor and a fifth conductive line connected to both the second connection region of the third varistor and the fifth metal plate.
10. A method for preparing a piezoresistive pressure sensor according to any one of claims 1 to 9, characterized in that: include: Providing a silicon-on-insulator structure as a substrate, wherein a top surface of a top silicon layer of the silicon-on-insulator structure is used as a first surface of the substrate, and a bottom surface of a bottom silicon layer of the silicon-on-insulator structure is used as a second surface of the substrate; A first cavity and a second cavity are formed on the second surface, so that the remaining substrate portion between the bottom surface of the first cavity and the first surface forms a first pressure-sensitive film, and the remaining substrate portion between the bottom surface of the second cavity and the first surface forms a second pressure-sensitive film; preparing a device layer on the first surface; An upper cover is bonded to the second surface, and the upper cover is provided with a through hole corresponding to the first cavity.