CN117007220A

CN117007220A - MEMS piezoresistive pressure sensor and preparation method thereof

Info

Publication number: CN117007220A
Application number: CN202310983665.8A
Authority: CN
Inventors: 李维平; 兰之康; 管武干
Original assignee: Nanjing Gaohua Technology Co ltd
Current assignee: Nanjing Gaohua Technology Co ltd
Priority date: 2023-08-07
Filing date: 2023-08-07
Publication date: 2023-11-07

Abstract

The embodiment of the disclosure discloses a MEMS piezoresistive pressure sensor and a preparation method thereof, wherein the MEMS piezoresistive pressure sensor comprises a first substrate, a second substrate, a first passivation layer, a second passivation layer, a first inverse piezoelectric unit, a piezoresistive unit, a first lead and a bonding pad; the first substrate is provided with a cavity and is fixed on the second substrate; the first passivation layer is arranged on one side of the first substrate, which is away from the second substrate, and piezoresistive units corresponding to the cavities are embedded in the first passivation layer; the first inverse piezoelectric unit is arranged on one side of the first passivation layer, which is away from the second substrate; the first inverse piezoelectric unit, the first passivation layer and the piezoresistive unit form a pressure sensitive film in the area corresponding to the cavity; the second passivation layer is arranged on one side of the first inverse piezoelectric unit, which is away from the first substrate, and one side of the second passivation layer, which is away from the second substrate, is provided with a first lead and a bonding pad which are respectively electrically connected with the piezoresistive unit and the first inverse piezoelectric unit. The pressure sensor can effectively improve the linearity, the measuring range and the overload resistance of the sensor.

Description

MEMS piezoresistive pressure sensor and preparation method thereof

Technical Field

The embodiment of the disclosure belongs to the technical field of pressure sensors, and particularly relates to a MEMS piezoresistive pressure sensor and a preparation method thereof.

Background

MEMS piezoresistive pressure sensors are widely used in the pressure measurement field due to their advantages of high sensitivity, good frequency response, high accuracy, good stability, small size, easy integration, etc.

The traditional MEMS piezoresistive pressure sensor is prepared by firstly doping the surface of a silicon substrate to form a piezoresistor strip, then etching a cavity on the back surface of the silicon substrate to form a pressure sensitive film in a square area where the piezoresistor strip is positioned, and finally bonding an area where the back surface is not corroded on a glass substrate.

For the traditional MEMS piezoresistive pressure sensor structure, the deflection effect of the pressure sensitive film can enable the output voltage and the input pressure of the sensor to be in a nonlinear relation, so that the sensor generates nonlinear errors which are increased along with the increase of the input pressure, the linearity and the measuring range of the sensor are mutually restricted, and the overall improvement of the performance of the sensor is limited. In addition, the thermal expansion coefficients of the silicon substrate and the glass substrate of the traditional MEMS piezoresistive pressure sensor are different, so that bonding thermal stress can be generated at the normal working temperature of the sensor at a bonding interface connecting the two substrates, thereby causing temperature drift of the sensor and reducing the measurement accuracy of the sensor.

Disclosure of Invention

Embodiments of the present disclosure aim to solve at least one of the technical problems existing in the prior art, and disclose a MEMS piezoresistive pressure sensor and a method for manufacturing the same.

In a first aspect, embodiments of the present disclosure provide a MEMS piezoresistive pressure sensor, the MEMS piezoresistive pressure sensor comprising a first substrate, a second substrate, a first passivation layer, a second passivation layer, a first inverse piezoelectric unit, a piezoresistive unit, and a first lead and pad;

the first substrate is provided with a cavity penetrating through the thickness of the first substrate and is fixed on the second substrate;

the first passivation layer is arranged on one side of the first substrate, which is away from the second substrate, and the piezoresistive unit corresponding to the cavity is embedded in the first passivation layer;

the first inverse piezoelectric unit is arranged on one side of the first passivation layer, which is away from the second substrate; the first inverse piezoelectric unit, the first passivation layer and the piezoresistive unit form a pressure sensitive film in the area corresponding to the cavity;

the second passivation layer is arranged on one side of the first inverse piezoelectric unit, which is away from the first substrate, and the first lead and the bonding pad are arranged on one side of the second passivation layer, which is away from the second substrate, and are respectively and electrically connected with the piezoresistive unit and the first inverse piezoelectric unit.

In some embodiments, the first inverse piezoelectric unit includes a first lower plate, a first inverse piezoelectric layer, and a first upper plate sequentially stacked to be disposed on the first passivation layer.

In some embodiments, the MEMS piezoresistive pressure sensor further comprises a second inverse piezoelectric unit and a second lead and pad;

the second inverse piezoelectric unit is arranged on one side of the second substrate facing the first substrate and corresponds to the cavity;

the second lead and the bonding pad are arranged on one side of the second substrate, which is away from the first substrate, and are electrically connected with the second inverse piezoelectric unit.

In some embodiments, the second inverse piezoelectric unit includes a second lower plate, a second inverse piezoelectric layer, and a second upper plate sequentially stacked to be disposed on the second substrate.

In some embodiments, a groove is disposed on a side of the second substrate facing the first substrate, and the groove accommodates the second inverse piezoelectric unit.

In some embodiments, a gap is provided between the second inverse piezoelectric unit and the groove, and the MEMS piezoresistive pressure sensor further comprises a filling layer filled in the gap.

In some embodiments, the piezoresistive units include N-type piezoresistive units and P-type piezoresistive units;

the N-type piezoresistor unit comprises an N-type piezoresistor strip, N-type electrode leading-out areas positioned at two ends of the N-type piezoresistor strip, and a P-type area arranged at one side of the N-type piezoresistor strip, which faces the second substrate;

the P-type piezoresistor unit comprises a P-type piezoresistor strip, P-type electrode leading-out areas positioned at two ends of the P-type piezoresistor strip, and an N-type area arranged at one side of the P-type piezoresistor strip, which faces the second substrate.

In a second aspect, embodiments of the present disclosure provide a method of making a MEMS piezoresistive pressure sensor as described in the foregoing, the method comprising:

providing an SOI wafer; the SOI wafer comprises a first substrate, an oxide layer and a device layer which are sequentially stacked;

doping the device layer of the SOI sheet to form a piezoresistance unit;

oxidizing a device layer area outside the piezoresistive unit to obtain a first passivation layer;

forming a first inverse piezoelectric unit on the first passivation layer, specifically: forming a first lower electrode plate on the first passivation layer; forming a first inverse piezoelectric layer on the first lower electrode plate; forming a first upper plate on the first counter electrode layer;

forming a second passivation layer on the first inverse piezoelectric unit;

patterning the second passivation layer to form a first through hole;

forming a second through hole at a position of the first inverse piezoelectric unit corresponding to the first through hole;

forming a first lead and a bonding pad on the second passivation layer, and filling a metal layer in the first through hole and the second through hole so that the first lead and the bonding pad are respectively electrically connected with the first inverse piezoelectric unit and the piezoresistive unit;

forming a cavity on the back surface of the first substrate to form a pressure sensitive film;

providing a second substrate;

and bonding the second substrate and the first substrate to prepare the MEMS piezoresistive pressure sensor.

In some embodiments, prior to bonding the second substrate to the first substrate, the method further comprises: forming a second inverse piezoelectric unit on the second substrate, specifically:

forming a deep through hole on the first surface of the second substrate;

forming a groove on the second surface of the second substrate;

forming a second lower polar plate in the groove;

forming a second inverse piezoelectric layer on the second lower electrode plate;

forming a filling layer in the groove, and patterning the filling layer to form a through hole;

forming a second upper polar plate on the surface of the groove and a lead in the filling layer through hole;

etching the deep through hole until the lead in the filling layer through hole leaks out;

and forming a second lead and a bonding pad on the first surface of the second substrate, so that the second lead and the bonding pad are electrically connected with the second inverse piezoelectric layer.

In some embodiments, doping the device layer of the SOI sheet forms a piezoresistive cell, comprising:

n-type doping and P-type doping are carried out on the device layer of the SOI sheet to form an N-type region and a P-type region respectively;

p-type doping and N-type doping are carried out on the surface areas of the N-type area and the P-type area to respectively form a P-type piezoresistor strip and an N-type piezoresistor strip;

p-type heavy doping and N-type heavy doping are carried out on two ends of the P-type piezoresistor strip and the N-type piezoresistor strip to respectively form a P-type electrode lead-out area and an N-type electrode lead-out area.

Compared with the traditional MEMS piezoresistive pressure sensor, the MEMS piezoresistive pressure sensor of the embodiment of the disclosure has the following advantages:

1. the MEMS piezoresistive pressure sensor of the embodiments of the present disclosure adopts a new mode of operation based on a first inverse piezoelectric unit. When the sensor measures the external pressure in the mode, the pressure sensitive film does not need to deform, so that the pressure sensitive film of the sensor has no deflection effect, the linearity and the measuring range of the sensor are greatly improved, and the linearity and the measuring range of the sensor are not mutually restricted;

2. when the external pressure input by the MEMS piezoresistive pressure sensor of the embodiment of the disclosure exceeds the measuring range, the pressure sensitive film of the sensor can use the whole deformation range of the pressure sensitive film to accommodate overload pressure. This greatly improves the overload resistance of the sensor for conventional MEMS piezoresistive pressure sensors that can only use a small portion of the deformation range of the pressure sensitive membrane to accommodate overload pressures.

3. The resistance change of the piezoresistor strip in the MEMS piezoresistor type pressure sensor of the embodiment of the disclosure is not only from piezoresistance effect, but also from the influence of the piezoresistance effect of the first inverse piezoelectric layer area without the polar plate. The sensitivity of the piezoresistor strip is effectively improved, the negative feedback effect in the new working mode is enhanced, the sensitivity of the sensor is improved, and the linearity and the measuring range of the sensor are further increased.

4. In the structure of the MEMS piezoresistive pressure sensor in the embodiment of the disclosure, the second inverse piezoelectric unit is disposed in the central square groove of the second substrate, and when the upper and lower polar plates of the second inverse piezoelectric unit are subjected to appropriate voltage controlled by temperature, an inverse piezoelectric effect is generated, so that the structure generates horizontal shrinkage controlled by temperature, and drives the second substrate to also generate horizontal shrinkage controlled by temperature, so as to reduce the difference of shrinkage degrees between the two substrate layers, further reduce bonding thermal stress, effectively reduce temperature drift of the MEMS piezoresistive pressure sensor in the embodiment of the disclosure, and improve measurement accuracy of the sensor.

Drawings

The above and other features, advantages, and aspects of embodiments of the present disclosure will become more apparent by reference to the following detailed description when taken in conjunction with the accompanying drawings. The same or similar reference numbers will be used throughout the drawings to refer to the same or like elements. It should be understood that the figures are schematic and that elements and components are not necessarily drawn to scale.

FIG. 1 is a cross-sectional view of a MEMS piezoresistive pressure sensor according to an embodiment of the present disclosure;

FIG. 2 is a top view of the MEMS piezoresistive pressure sensor shown in FIG. 1;

FIG. 3 is a bottom view of the MEMS piezoresistive pressure sensor shown in FIG. 1;

fig. 4 to 37 are process flow diagrams of a method of manufacturing a MEMS piezoresistive pressure sensor according to an embodiment of the present disclosure.

Detailed Description

In order that those skilled in the art will better understand the technical solutions of the present disclosure, the present disclosure will be described in further detail with reference to the accompanying drawings and detailed description.

Embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While certain embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete. It should be understood that the drawings and embodiments of the present disclosure are for illustration purposes only and are not intended to limit the scope of the present disclosure.

It should be further noted that, for convenience of description, only a portion relevant to the present disclosure is shown in the drawings. Embodiments of the present disclosure and features of embodiments may be combined with each other without conflict.

The present disclosure will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.

As shown in fig. 1-3, embodiments of the present disclosure relate to a MEMS piezoresistive pressure sensor that includes a first lead and pad 1, a second passivation layer 2, a first inverse piezoelectric unit, a piezoresistive unit, a first passivation layer 12, a first substrate 13, a pressure sensitive film 14, and a second substrate 16.

As illustrated in fig. 1 and 2, the first lead and the pad 1 are located at the uppermost layer of the sensor, and in some embodiments, the material of the first lead and the pad 1 is at least one of aluminum, copper, platinum, titanium, gold, or the like, and the thickness of the first lead and the pad 1 ranges from 50nm to 500nm. The first lead wire and the bonding pad 1 are respectively and electrically connected with the first inverse piezoelectric unit and the piezoresistance unit through the through holes of the second passivation layer and the first inverse piezoelectric unit.

With continued reference to fig. 1, the second passivation layer 2 is located under the first lead and the pad 1, and in some embodiments, the material of the second passivation layer 2 is at least one of silicon oxide or silicon nitride, and the thickness of the second passivation layer 2 ranges from 50nm to 2000nm.

Next, as shown in fig. 1, a first inverse piezoelectric unit is located below the second passivation layer 2, and in some embodiments, the first inverse piezoelectric unit is formed by stacking a first upper plate 3, a first inverse piezoelectric layer 4, and a first lower plate 5 in order from top to bottom. The first upper polar plate 3 is positioned below the second passivation layer 2, the material of the first upper polar plate 3 is at least one of aluminum, copper, platinum, titanium or gold, and the thickness of the first upper polar plate 3 ranges from 50nm to 500nm. The material of the first inverse piezoelectric layer 4 is one of aluminum nitride, lead zirconate titanate or zinc oxide, and the thickness ranges from 5 μm to 100 μm. The first lower plate 5 is the same material and thickness as the first upper plate 3.

With continued reference to fig. 1 and 2, the first passivation layer 12 is located below the first inverse piezoelectric element, and in some embodiments, the material of the first passivation layer 12 may be silicon oxide or silicon nitride, and the thickness of the first passivation layer 12 ranges from 2 μm to 50 μm, and the first passivation layer 12 has a piezoresistive element embedded therein. In some embodiments, the piezoresistive unit comprises an N-type piezoresistive unit and a P-type piezoresistive unit, and in combination with fig. 13, the N-type piezoresistive unit comprises an N-type piezoresistive strip 9, N-type electrode lead-out regions 11 at two ends of the N-type piezoresistive strip, and a P-type region 10 below the N-type piezoresistive strip; the P-type piezoresistance unit comprises a P-type piezoresistance strip 6, P-type electrode leading-out areas 8 at two ends of the P-type piezoresistance strip and an N-type area 7 below the P-type piezoresistance strip. The N-type piezoresistance unit and the P-type piezoresistance unit are made of one of monocrystalline silicon or polycrystalline silicon, and the N-type piezoresistance unit and the P-type piezoresistance unit are respectively distributed at the middle points of four sides of the pressure sensitive film 14, and the four piezoresistance strips are connected into a Wheatstone bridge through metal leads.

Illustratively, as shown in fig. 1, the first substrate 13 is located below the first passivation layer 12, and in some embodiments, the material of the first substrate 13 is one of monocrystalline silicon or polycrystalline silicon, and the thickness of the first substrate 13 ranges from 400 μm to 1000 μm. The first substrate 13 is provided with a closed cavity 15 through its thickness, which cavity 15 may be in the shape of a "trapezoidal table". The square upper surface of the closed cavity 15 projects upwards on the first passivation layer 12, the first inverse piezoelectric element and the area on the second passivation layer 2 together constitute the pressure sensitive film 14.

With continued reference to fig. 1, a second substrate 16 is positioned below the first substrate 13. In some embodiments, the material of the second substrate 16 is one of borosilicate glass, etc., and the thickness of the second substrate 16 ranges from 400 μm to 1000 μm. In some embodiments, the MEMS piezoresistive pressure sensor further includes a second inverse piezoelectric unit disposed on an upper surface of the second substrate 16, and a second lead and pad 21 disposed on a lower surface of the second substrate 16, the second lead and pad 21 being electrically connected to the second inverse piezoelectric unit.

Illustratively, as shown in fig. 1, the second inverse piezoelectric unit includes a second upper plate 17, a second inverse piezoelectric layer 18, and a second lower plate 19. A square groove is arranged at the central position of the second substrate 16, and the second upper polar plate 17, the second inverse piezoelectric layer 18 and the second lower polar plate 19 are sequentially arranged in the square groove from top to bottom to form a second inverse piezoelectric unit. The gap between the second inverse piezoelectric unit and the square groove is filled with the filling layer 20.

In some embodiments, the materials of the second upper electrode plate 17 and the second lower electrode plate 19 are at least one of aluminum, copper, platinum, titanium, gold, etc., and the thickness ranges from 50nm to 500nm. The second inverse piezoelectric layer 18 is made of one of aluminum nitride, silicon oxide, lead zirconate titanate, zinc oxide, and the like, and has a thickness ranging from 50 μm to 200 μm. The material of the filling layer 20 is one of silicon oxide or silicon nitride.

Further, the first inverse piezoelectric unit and the second inverse piezoelectric unit can further improve the performance of the sensor by increasing the number of layers.

The working principle of the MEMS piezoresistive pressure sensor according to the embodiments of the present disclosure will be described below:

as shown in fig. 1, in the MEMS piezoresistive pressure sensor according to the embodiment of the present disclosure, the first inverse piezoelectric unit has an inverse piezoelectric effect, and the upper and lower plates thereof are stretched in a horizontal direction after a suitable voltage is applied. The square area in the middle of the first inverse piezoelectric unit forms a part of the pressure sensitive film 14, so that the horizontal stretching of the first inverse piezoelectric unit drives the pressure sensitive film 14 to horizontally stretch. Because the peripheral edge of the pressure sensitive film 14 is fixed on the first substrate 13 through the first passivation layer 12, and the middle square area of the pressure sensitive film 14 is in a suspended state, when the pressure sensitive film 14 stretches horizontally, a vertical upward force is generated on the middle square area suspended in the middle.

Based on the foregoing, the MEMS piezoresistive pressure sensor according to the embodiments of the present disclosure adopts a new operation mode: when the external pressure is vertically applied to the pressure sensitive film 14, stress is generated in the region where the piezoresistive unit is located, and after the piezoresistive strips forming the piezoresistive unit sense the stress, the resistance value changes and the voltage is output through the wheatstone bridge. The sensor external circuit amplifies the output voltage and applies the amplified output voltage to the upper and lower polar plates of the first inverse piezoelectric unit, so that the pressure sensitive film 14 generates vertical upward force, and the vertical downward external pressure is counteracted. Finally, the voltage values of the upper polar plate and the lower polar plate of the first inverse piezoelectric unit are detected, and the value of the external pressure can be converted to be obtained to finish measurement. In this process, the voltage of the upper and lower plates of the first inverse piezoelectric unit and the vertical upward force generated by the voltage on the pressure sensitive film 14 always follow the vertical downward external pressure variation suffered by the pressure sensitive film 14. Because the transmission of the electric signal and the response of the inverse piezoelectric effect are instantaneous relative to the change of the external pressure, the pressure sensitive film 14 does not deform in the process of detecting the external pressure by the sensor, so that the pressure sensitive film 14 of the sensor does not have deflection effect, the linearity and the measuring range of the sensor are greatly improved, and the linearity and the measuring range of the sensor are not mutually restricted. In addition, the pressure sensitive membrane 14 of the sensor may use its entire deformation range to accommodate overload pressures when the external pressure input by the sensor exceeds the span. This greatly improves the overload resistance of the sensor for conventional MEMS piezoresistive pressure sensors that use only a small portion of the deformation range of the pressure sensitive membrane 14 to accommodate overload pressures.

When external pressure is applied to the pressure sensitive film 14 and stress is concentrated in the piezoresistive unit area, not only the P-type piezoresistive strip 6 (the N-type piezoresistive strip 9) will have its resistance reduced (increased) due to the piezoresistive effect, but also the area of the first inverse piezoelectric layer 4 without the polar plate covered on the piezoresistive unit will have the piezoelectric effect, so that negative charges and vertically upward electrostatic fields are generated above the piezoresistive unit. The electrostatic field enables PN junctions at the interfaces of the P-type piezoresistor strips 6 and the N-type areas 7 in the P-type piezoresistor units to move downwards, so that the thickness of the P-type piezoresistor strips 6 is increased, and the resistance value is further reduced after piezoresistance effect; the PN junction at the interface of the N-type piezoresistor strip 9 and the P-type region 10 in the N-type piezoresistor unit moves upwards, so that the thickness of the N-type piezoresistor strip 9 is reduced, and the resistance value is further increased after the piezoresistor effect. Therefore, the sensitivity of the piezoresistor strip can be effectively improved, the negative feedback effect in the new working mode is enhanced, the sensitivity of the sensor is improved, and the linearity and the measuring range of the sensor are further increased.

The first substrate 13 and the second substrate 16 are hermetically connected together by anodic bonding to form a bonding interface. This process is typically performed in a process environment above 400 c and after bonding is completed, after the sensor is placed from a high temperature process environment to a low temperature normal operating environment, the first substrate 13 will shrink to a greater extent than the second substrate 16 due to the fact that the first substrate 13 has a higher coefficient of thermal expansion than the second substrate 16, thereby creating a temperature dependent bond thermal stress at the bonding interface. The thermal stress can be transferred to the piezoresistor strip to generate temperature drift for the sensor, and the measurement accuracy of the sensor is reduced. In view of this problem, in the MEMS piezoresistive pressure sensor structure according to the embodiments of the present disclosure, the second inverse piezoelectric unit is disposed in the central square groove of the second substrate 16, and when the upper and lower plates of the second inverse piezoelectric unit are subjected to a suitable voltage controlled by temperature, the inverse piezoelectric effect controlled by temperature is generated, so that the structure is shrunk horizontally under temperature control. Also, because the second inverse piezoelectric unit is tightly connected in the second substrate 16 through the filling layer 20, the temperature-controlled horizontal shrinkage of the second inverse piezoelectric unit will drive the second substrate 16 to also undergo temperature-controlled horizontal shrinkage. Therefore, the difference of shrinkage degree between the two substrate layers can be reduced, and bonding thermal stress is effectively reduced, so that the temperature drift of the sensor is effectively reduced, and the measurement accuracy of the sensor is improved.

In summary, the MEMS piezoresistive pressure sensor of the embodiments of the present disclosure has the following advantages over conventional MEMS piezoresistive pressure sensors:

Based on the same inventive concept, the embodiments of the present disclosure further provide a method for manufacturing the MEMS piezoresistive pressure sensor as described above, and the structure of the MEMS piezoresistive pressure sensor may be specifically described with reference to the foregoing related description, which is not repeated herein. The method specifically comprises the following steps:

step one, providing an SOI sheet; the SOI wafer comprises a first substrate, an oxide layer and a device layer which are sequentially stacked.

Specifically, in this step, as shown in fig. 4, an SOI wafer is prepared, and a device layer, an oxide layer, and a first substrate 13 are sequentially provided from top to bottom.

And step two, carrying out N-type doping and P-type doping on the device layer of the SOI sheet to respectively form an N-type region and a P-type region.

Specifically, in this step, as shown in fig. 5 and 6, N-type region 7 and P-type region 10 are formed by N-type doping and P-type doping, respectively, on the device layer of the SOI wafer.

And thirdly, P-type doping and N-type doping are carried out on the surface areas of the N-type area and the P-type area to respectively form a P-type piezoresistor strip and an N-type piezoresistor strip.

Specifically, in this step, as shown in fig. 7 and 8, P-type doping and N-type doping are performed on the surface areas of the N-type region 7 and the P-type region 10, so as to form P-type varistor strips 6 and N-type varistor strips 9 and PN junctions thereunder, respectively.

And step four, P-type heavy doping and N-type heavy doping are carried out on two ends of the P-type piezoresistor strip and the N-type piezoresistor strip to respectively form a P-type electrode lead-out area and an N-type electrode lead-out area.

Specifically, in this step, as shown in fig. 9 and 10, P-type heavy doping and N-type heavy doping are performed on two ends of the P-type piezo-resistor strip 6 and the N-type piezo-resistor strip 9, so as to form the P-type electrode lead-out region 8 and the N-type electrode lead-out region 11, respectively, so as to complete the preparation of the four piezo-resistive units.

And fifthly, oxidizing the device layer area outside the piezoresistive unit to obtain a first passivation layer.

Specifically, in this step, as shown in fig. 11, the device layer region outside the four piezoresistive cells is oxidized, thereby expanding the oxide layer in the SOI wafer to form the first passivation layer 12.

And step six, forming a first lower polar plate on the first passivation layer.

Specifically, in this step, as shown in fig. 12 and 13, metal is sputtered on the upper surface of the first passivation layer 12 and photolithography is performed to form the first lower plate 5.

And step seven, forming a first inverse piezoelectric layer on the first lower polar plate.

Specifically, in this step, as shown in fig. 14, aluminum nitride is deposited on the upper surface of the first lower plate 5 to form the first counter piezoelectric layer 4.

And step eight, forming a first upper polar plate on the first inverse piezoelectric layer.

Specifically, in this step, as shown in fig. 15 and 16, metal is sputtered on the upper surface of the first counter electrode layer 4 and photolithography is performed to form the first upper plate 3.

And step nine, forming a second passivation layer on the first inverse piezoelectric unit.

Specifically, in this step, as shown in fig. 17, silicon oxide is deposited on the upper surface of the first upper plate 3 to form the second passivation layer 2.

And step ten, patterning the second passivation layer to form a first through hole.

Specifically, in this step, as shown in fig. 18 and 19, the second passivation layer 2 is subjected to photolithography to form a via hole, so as to prepare for the electrical connection of the first upper plate 3 and the formation of the via hole of the first counter piezoelectric layer 4.

And step eleven, forming a second through hole at the position of the first inverse piezoelectric unit corresponding to the first through hole.

Specifically, in this step, as shown in fig. 20 and 21, the first inverse piezoelectric layer 4 is subjected to photolithography to form a through hole, so as to prepare for forming an electrical connection of the first lower electrode plate 5, the N-type electrode lead-out region 11 and the P-type electrode lead-out region 8.

And twelve, forming a first lead and a bonding pad on the second passivation layer, and filling a metal layer in the first through hole and the second through hole so that the first lead and the bonding pad are respectively electrically connected with the first inverse piezoelectric unit and the piezoresistive unit.

Specifically, in this step, as shown in fig. 22, metal is sputtered on the upper surface of the second passivation layer 2 and photolithography is performed to form the first lead and the pad 1, and the metal is filled in the through holes of the second passivation layer 2 and the first counter electrode layer 4, so as to complete the electrical connection between the pad and the first upper electrode plate 3, the first lower electrode plate 5, the N-type electrode lead-out region 11 and the P-type electrode lead-out region 8.

And thirteenth, forming a cavity on the back surface of the first substrate to form a pressure sensitive film.

Specifically, in this step, as shown in fig. 23 and 24, the back surface of the first substrate 13 is wet-etched to prepare a "trapezoidal mesa" cavity with a downward opening in the first substrate 13, to form the pressure-sensitive film 14.

Step fourteen, providing a second substrate.

Specifically, in this step, as shown in fig. 25, a sheet of borosilicate glass having a thickness of 500 μm is prepared as the second substrate 16.

Fifteen, forming a deep through hole on the first surface of the second substrate.

Specifically, in this step, as shown in fig. 26, etching is performed under the second substrate 16 to form two deep through holes.

Sixthly, forming a groove on the second surface of the second substrate.

Specifically, in this step, as shown in fig. 27, etching is performed on the upper surface of the second substrate 16 to form a square groove.

Seventeenth, forming a second lower polar plate in the groove;

specifically, in this step, as shown in fig. 28 and 29, metal is sputtered at the bottom of the square groove of the second substrate 16 and photolithography is performed to form the second lower plate 19.

Eighteenth, forming a second inverse piezoelectric layer on the second lower polar plate.

Specifically, in this step, as shown in fig. 30, aluminum nitride is deposited on the surface of the second lower plate 19 and the second inverse piezoelectric layer 18 is formed by photolithography.

Nineteenth, forming a filling layer in the groove, and patterning the filling layer to form a through hole.

Specifically, in this step, as shown in fig. 31, silicon oxide is deposited in the square groove to form the filling layer 20, and then the filling layer 20 is subjected to photolithography to form a via hole.

And twenty, forming a second upper polar plate on the surface of the groove and leading wires in the filling layer through holes.

Specifically, in this step, as shown in fig. 32 and 33, metal is sputtered on the upper surface of the groove and photolithography is performed to form the second upper plate 17 and the lead-in-fill via.

And twenty-one, etching the deep through hole until the lead in the filling layer through hole is leaked out.

Specifically, in this step, as shown in fig. 34, a deep via hole is further etched in preparation for forming an electrical connection of the second upper plate 17 and the second lower plate 19.

And twenty-two steps, forming a second lead and a bonding pad on the first surface of the second substrate, so that the second lead and the bonding pad are electrically connected with the second inverse piezoelectric layer.

Specifically, in this step, as shown in fig. 35 and 36, the lower surface of the second substrate 16 is sputtered with metal and subjected to photolithography to form the second lead and the pad 21, and the electrical connection of the bottom pad and the second upper plate 17 and the second lower plate 19 is completed.

And twenty-third, bonding the second substrate and the first substrate to prepare the MEMS piezoresistive pressure sensor.

Specifically, in this step, as shown in fig. 37, the lower surface of the thirteenth corresponding structure is bonded to the upper surface of the twenty-second corresponding structure by an anodic bonding process to form the closed cavity 15, so as to complete the preparation of the MEMS piezoresistive pressure sensor according to the embodiments of the present disclosure.

Compared with the traditional MEMS piezoresistive pressure sensor, the MEMS piezoresistive pressure sensor prepared by the embodiment of the disclosure has the following advantages:

It is to be understood that the above embodiments are merely exemplary embodiments employed to illustrate the principles of the present disclosure, however, the present disclosure is not limited thereto. Various modifications and improvements may be made by those skilled in the art without departing from the spirit and substance of the disclosure, and are also considered to be within the scope of the disclosure.

Claims

1. The MEMS piezoresistive pressure sensor is characterized by comprising a first substrate, a second substrate, a first passivation layer, a second passivation layer, a first inverse piezoelectric unit, a piezoresistive unit, a first lead and a bonding pad;

2. The MEMS piezoresistive pressure sensor according to claim 1, wherein the first inverse piezoelectric unit comprises a first lower plate, a first inverse piezoelectric layer and a first upper plate, which are sequentially stacked on the first passivation layer.

3. The MEMS piezoresistive pressure sensor according to claim 1, wherein the MEMS piezoresistive pressure sensor further comprises a second inverse piezoelectric unit and a second lead and pad;

4. The MEMS piezoresistive pressure sensor according to claim 3, wherein the second inverse piezoelectric unit comprises a second lower plate, a second inverse piezoelectric layer and a second upper plate, which are sequentially stacked on the second substrate.

5. The MEMS piezoresistive pressure sensor according to claim 3, wherein a side of the second substrate facing the first substrate is provided with a recess, the recess housing the second inverse piezoelectric unit.

6. The MEMS piezoresistive pressure sensor according to claim 5, wherein a void is provided between the second inverse piezoelectric unit and the groove, the MEMS piezoresistive pressure sensor further comprising a filling layer filling the void.

7. The MEMS piezoresistive pressure sensor according to any of claims 1-6, wherein the piezoresistive cells comprise N-type piezoresistive cells and P-type piezoresistive cells;

8. A method of manufacturing a MEMS piezoresistive pressure sensor according to any of claims 1 to 7, wherein the method comprises: