Pressure sensor, preparation method thereof and electronic equipment

Abstract

A pressure sensor comprises a substrate (10) and a plurality of sensing units (100) located on the substrate (10), each sensing unit (100) comprises a pressure sensing cavity (21), and the orthographic projection areas of at least two pressure sensing cavities (21) on the substrate (10) are different. The invention further discloses a preparation method of the pressure sensor and electronic equipment.

Description

Pressure sensor, manufacturing method thereof, and electronic device Technical Field

[0001] The present disclosure belongs to the field of sensor technology, and particularly relates to a pressure sensor, a preparation method thereof, and an electronic device. Background Art

[0002] With the development of semiconductor technology, MEMS (micro-electromechanical systems) devices, which are a descendant of the same, are widely used in more and more fields such as aerospace, petroleum, chemical industry, automobile, consumer electronics, etc. due to their small size, high integration and mass production. For example, pressure sensors, temperature sensors, accelerometers, gyroscopes, image sensors, and photoelectric sensors that use MEMS manufacturing technology.

[0003] Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art and provides a pressure sensor and a preparation method thereof, and an electronic device.

[0005] An embodiment of the present disclosure provides a pressure sensor, which includes a substrate and a plurality of sensing units located on the substrate. Each of the sensing units includes a pressure-sensing cavity. The orthographic projection areas of at least two of the pressure-sensing cavities on the substrate are unequal.

[0006] In which, the pressure sensor also includes a first pressure-sensitive layer and a second pressure-sensitive layer; the first pressure-sensitive layer and the second pressure-sensitive layer are respectively arranged on both sides of the pressure-sensitive cavity along the depth direction; the first pressure-sensitive layer includes the first electrode plate of each of the sensing units, and the second pressure-sensitive layer includes the second electrode plate of each of the sensing units.

[0007] The pressure sensor further includes the substrate comprising a silicon substrate, and the first electrode plate is obtained by ion implantation of the silicon substrate.

[0008] Wherein, the material of the second pressure-sensitive layer is single crystal silicon.

[0009] The pressure sensor further includes a first connection portion electrically connected to the first electrode layer and a second connection portion electrically connected to the second electrode layer.

[0010] The first connecting portion is located on a side of the first pressure-sensitive layer close to the second pressure-sensitive layer, and the second connecting portion is located on a side of the second pressure-sensitive layer away from the first pressure-sensitive layer.

[0011] In which, the pressure sensor also includes the pressure-sensing cavity arranged on the substrate, and a pressure-sensing layer on the side of the pressure-sensing cavity facing away from the substrate; each of the sensing units includes four piezoresistors formed on the pressure-sensing layer and connected in series, and the four piezoresistors constitute a Wheatstone bridge.

[0012] The piezoresistor in the sensing unit is obtained by ion implantation into the pressure-sensitive layer.

[0013] Each of the sensing units further includes a conductive line connected in series with a piezoresistor, and the conductive line is located on a side of the pressure-sensitive layer away from the base substrate.

[0014] Wherein, the substrate is a silicon base.

[0015] The sensing units are arranged in an array; the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same row on the substrate monotonically increase or decrease, and / or the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same column on the substrate monotonically increase or decrease.

[0016] When the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same row on the substrate monotonically increase or decrease, the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same row on the substrate change proportionally or arithmetic differences.

[0017] When the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same column on the substrate monotonically increase or decrease, the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same column on the substrate change proportionally or arithmetically.

[0018] The orthographic projection of the pressure-sensing cavity on the base substrate is rectangular or circular.

[0019] An embodiment of the present disclosure provides a method for preparing a pressure sensor, which includes forming a plurality of sensing units on a substrate; forming the sensing units includes forming pressure-sensing cavities, and the areas of the orthographic projections of at least two pressure-sensing cavities on the substrate are unequal.

[0020] The step of forming the pressure-sensing cavity includes forming a support layer on the base substrate, and patterning the support layer to form a plurality of the pressure-sensing cavities.

[0021] In which, the preparation method of the pressure sensor also includes forming a first pressure-sensitive layer and a second pressure-sensitive layer on both sides of the pressure-sensitive cavity in the depth direction, respectively, the first pressure-sensitive layer includes a first electrode plate arranged in a one-to-one correspondence with the pressure-sensitive cavity, and the second pressure-sensitive layer includes a second electrode plate arranged in a one-to-one correspondence with the pressure-sensitive cavity.

[0022] Wherein, the base substrate is a silicon substrate, and the first pressure-sensitive layer is formed by ion implantation of the silicon substrate.

[0023] The step of forming a second pressure-sensitive layer on the pressure-sensitive cavity includes:

[0024] Providing an SOI wafer; wherein the SOI wafer comprises an auxiliary substrate, a transition layer and a single crystal silicon film layer disposed on the auxiliary substrate;

[0025] Bonding the side of the SOI wafer having the single crystal silicon film layer to the substrate having the pressure sensing cavity formed thereon;

[0026] The auxiliary substrate and the transition layer are removed, and the single crystal silicon film layer remains to form the second pressure-sensitive layer.

[0027] The method for preparing the pressure sensor further includes forming a pressure-sensitive layer on the side of the pressure-sensitive cavity away from the substrate, and performing ion implantation on the pressure-sensitive layer to form a Wheatstone bridge for each sensing unit, wherein the Wheatstone bridge includes four piezoresistors connected in series.

[0028] The method for preparing the pressure sensor further includes the step of forming a conductive line on the side of the pressure-sensitive layer facing away from the base substrate, and the conductive line in the sensing unit is connected in series with the piezoresistor.

[0029] The sensing units are arranged in an array; the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same row on the substrate are equal and monotonically increase or decrease, and / or the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same column on the substrate are monotonically increase or decrease.

[0030] When the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same row on the substrate monotonically increase or decrease, the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same row on the substrate change proportionally or arithmetic differences.

[0031] When the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same column on the substrate monotonically increase or decrease, the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same column on the substrate change proportionally or arithmetically.

[0032] The orthographic projection of the pressure-sensing cavity on the base substrate is rectangular or circular.

[0033] An embodiment of the present disclosure provides an electronic device, which includes any of the pressure sensors described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a top view of a single square film.

[0035] FIG2 is a top view of a single circular film.

[0036] FIG3 is a cross-sectional view of a single-pressure-sensitive film resistive or capacitive pressure sensor.

[0037] FIG4 is a top view of a pressure sensor comprising array-arranged square membrane sensing units of equal area.

[0038] FIG5 is a top view of a pressure sensor comprising sensing units of circular membranes arranged in an array and having equal areas.

[0039] FIG6 is an output characteristic curve of a pressure sensor comprising array-arranged square membrane sensing units of equal area;

[0040] FIG7 is a top view of a capacitive pressure sensor comprising sensing units of square films arranged in an array and having proportionally variable areas.

[0041] FIG8 is a top view of a capacitive pressure sensor comprising sensing units of circular membranes arranged in an array and having proportionally variable areas.

[0042] FIG9 is a cross-sectional view of a capacitive pressure sensor having a sensing unit of a square film with a proportionally variable area.

[0043] FIG10 is an output characteristic curve of a capacitive pressure sensor comprising sensing units of square thin films arranged in an array and having proportionally variable areas;

[0044] FIG11 is a flow chart for preparing a capacitive pressure sensor having a sensing unit of a square film with a variable area in equal proportion.

[0045] FIG12 is a top view of a piezoresistive pressure sensor comprising sensing units of square films arranged in an array and having proportionally variable areas.

[0046] FIG13 is a circuit diagram of a Wheatstone bridge.

[0047] FIG14 is a cross-sectional view of a piezoresistive pressure sensor having a sensing unit of a square film with a proportionally variable area.

[0048] FIG15 is a flow chart for preparing a piezoresistive pressure sensor having a sensing unit of a square film with a proportionally variable area. DETAILED DESCRIPTION

[0049] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0050] Unless otherwise defined, the technical or scientific terms used in this disclosure should have the usual meanings understood by people with ordinary skills in the field to which this disclosure belongs. The words "first", "second" and similar words used in this disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "one", "an" or "the" do not indicate a quantity limitation, but rather indicate the existence of at least one. Words such as "include" or "comprise" mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0051] For MEMS pressure sensors, the two most mainstream technical principles are to use the piezoresistive effect or the capacitive effect to convert pressure into a corresponding electrical signal: the former generally implants ions in a specific area of ​​a single-crystal silicon thin film to achieve a silicon resistor strip with a certain doping concentration. Pressure causes the film to deform, resulting in a change in silicon resistance; the latter forms a capacitor through two parallel and opposing low-resistance thin films. Pressure causes the film to deform and the relative spacing changes, resulting in a change in capacitance. The two have in common that the physical structure that senses pressure is a thin film 30, but it should be understood that the pressure sensor includes a pressure-sensing cavity 21 that supports and provides deformation space for the thin film 30. The pressure-sensing cavity 21 is arranged on the substrate 10, and a support layer 20 is arranged on the substrate 10. The pressure-sensing cavity 21 is formed on the support layer 20. The shape of the thin film is usually circular or square, as shown in Figures 1 and 2, and the cross-sectional view is shown in Figure 3. The shape of the thin film 30 is consistent with the outline of the positive projection of the pressure-sensing cavity 21 on the substrate 10.

[0052] When designing a pressure sensor with a diaphragm as the sensitive element, two main principles must usually be met, namely, at full scale: 1) the maximum deflection does not exceed 20% of the diaphragm, and 2) the maximum stress does not exceed 20% of the allowable stress.

[0053] For circular diaphragms,

[0054] For square diaphragms,

[0055] When the film material is selected, Young's modulus E, Poisson's ratio v, allowable stress σ lare all constant values, and the deflection is only related to the applied pressure p, radius R or side length l, and thickness h. Generally speaking, for a single-deformation film, its radius (or side length) is limited by the use requirements and directly determines the size of the sensitive device; (1) When it is necessary to measure a smaller pressure, if the thickness remains unchanged, although the above formula can be satisfied, the sensitivity of the sensor will be greatly reduced, resulting in an increase in the amplification factor during signal processing, and the noise signal will inevitably be amplified, which has a great impact on the accuracy of the sensor. In other words, the range of the sensor is limited to a certain range; (2) If the thickness is reduced simultaneously and the above formula is satisfied, it will increase the difficulty of the preparation process, and the inevitable thickness deviation will lead to poor product consistency; (3) In order to simultaneously meet the measurement pressure p and thickness h and comprehensively consider the feasibility of the process, it is often required to expand the film radius R or side length l, making the product size larger, which may not meet some use scenarios; (4) In addition, the nonlinearity of single film deformation is often relatively large, which requires the signal fitting to use multiple data points and a more complex multi-order fitting formula.

[0056] To address any of the aforementioned issues with existing pressure sensors, the present disclosure provides the following technical solutions. The pressure sensor in the present disclosure can be either a capacitive pressure sensor or a piezoresistive pressure sensor. The following describes the pressure sensor in the present disclosure using capacitive and piezoresistive pressure sensors as examples.

[0057] First example: Figure 4 is a top view of a pressure sensor including sensing units 100 of equal-area square thin films arranged in an array; Figure 5 is a top view of a pressure sensor including sensing units 100 of equal-area circular thin films arranged in an array; Figure 7 is a top view of a capacitive pressure sensor including sensing units 100 of equal-area square thin films arranged in an array; Figure 8 is a top view of a capacitive pressure sensor including sensing units 100 of equal-area circular thin films arranged in an array; and Figure 9 is a cross-sectional view of a capacitive pressure sensor including sensing units 100 of equal-area square thin films. As shown in Figures 4-5 and 7-9, the pressure sensor is a capacitive pressure sensor that includes a substrate 10, a first pressure-sensing layer 31, a support layer 20, and a second pressure-sensing layer 32 formed on the substrate 10. Of the first and second pressure-sensing layers 31 and 32, only the second pressure-sensing layer deforms when subjected to pressure. The support layer 20 is formed with a plurality of pressure-sensing cavities 21, the first pressure-sensing layer 31 includes a plurality of first electrodes 311, and the second pressure-sensing layer 32 includes a plurality of second electrodes 321. The first electrodes 311 and the second electrodes 321 are both arranged corresponding to the pressure-sensing cavities 21, that is, a first electrode 311 and a second electrode 321 are respectively arranged on both sides of a pressure-sensing cavity 21 along its depth direction. At this time, the first electrode 311, the second electrode 321 and the pressure-sensing cavity 21 between the two constitute a sensing unit 100. By dividing the pressure sensor with one pressure-sensing cavity 21 into a pressure sensor with multiple pressure-sensing cavities 21, the second pressure-sensing layer 32 can be made relatively thin, so that the maximum deflection and maximum stress of the film satisfy formulas (3) and (4) while ensuring sensitivity; if the thickness of the second pressure-sensing layer 32 is not changed, then under the premise of satisfying the formula, the pressure sensor can measure a larger pressure than the pressure sensor with a single pressure-sensing cavity 21.

[0058] In some examples, among the multiple sensing units 100 of the pressure sensor, there are at least two pressure-sensing cavities 21 whose orthographic projections on the substrate 10 are unequal in area. It should be noted that the size of the orthographic projection of the pressure-sensing cavity 21 on the substrate 10 determines the size of the area of ​​the first electrode plate 311 and the second electrode plate 321 in the sensing unit 100. Since the first electrode plate 311 and the second electrode plate 321 of each sensing unit 100 are arranged on both sides of the depth direction of the pressure-sensing cavity 21, the larger the orthographic projection area of ​​the pressure-sensing cavity 21 on the substrate 10, the larger the area of ​​the first electrode plate 311 / second electrode plate 321 of the sensing unit 100, and vice versa. That is, in the embodiment of the present disclosure, there are at least two pressure-sensing cavities 21 whose orthographic projections on the substrate 10 are unequal in area, that is, the areas of the first electrode plate 311 / second electrode plate 321 of at least two sensing units 100 are unequal. The first electrode plate 311 and the second electrode plate 321 of the sensor unit 100 are both pressure-sensitive layers. The pressure-sensitive layers of at least two sensor units 100 mentioned below have different areas, that is, the areas of the first electrode plate 311 / the second electrode plate 321 of at least two sensor units 100 are different.

[0059] In one example, the sensing units 100 are arranged in an array; the areas of the orthographic projections of the pressure-sensing cavities 21 of the sensing units 100 in the same row on the substrate 10 monotonically increase or decrease, and / or the areas of the orthographic projections of the pressure-sensing cavities 21 of the sensing units 100 in the same column on the substrate 10 monotonically increase or decrease. For example:

[0060] When the areas of the orthographic projections of the pressure-sensing cavities 21 of the sensing units 100 in the same row on the substrate 10 monotonically increase or decrease, the areas of the orthographic projections of the pressure-sensing cavities 21 of the sensing units 100 in the same row on the substrate 10 change proportionally or arithmetically. When the areas of the orthographic projections of the pressure-sensing cavities 21 of the sensing units 100 in the same column on the substrate 10 change monotonically or monotonically, the areas of the orthographic projections of the pressure-sensing cavities 21 of the sensing units 100 in the same column on the substrate 10 change proportionally or arithmetically.

[0061] Specifically, referring to Figure 7, the pressure sensor includes 9 sensing units 100 in a 3*3 pattern. The orthographic projection of each pressure-sensing cavity 21 on the substrate 10 is a square. The orthographic projection areas of the pressure-sensing layers in the same row on the substrate 10 are proportionally reduced, and the orthographic projection areas of the pressure-sensing layers in the same column on the substrate 10 are proportionally reduced. Taking the example of a 2% difference in the orthographic projection area of ​​each pressure-sensing layer on the substrate 10, the maximum area of ​​a single pressure-sensing layer is 0.04mm 2 , the minimum area is 0.04*(0.98)^ 4 mm 2The linearity of the pressure-sensitive layer of the sensing unit 100 located in the same column of the pressure sensor is greatly improved compared with the traditional single film or equal-area film group (the nonlinear value is reduced by 70%); the film deviation introduced by processing is equivalent to affecting one or several pressure-sensitive layers rather than the entire pressure sensor, and the process consistency is well guaranteed. For example, the thickness of the film after processing is 1.3% larger than the design value. According to formulas (1) and (3), it can be seen that When the area and input pressure remain unchanged, the ratio of the processed film deflection to the design value is 1:1.04, which is exactly the ratio of the square of the area of ​​the pressure-sensing layer of any two sensing units 100. For variable-pitch flat-plate capacitive pressure sensors, when the two plates come into contact, the capacitance often changes suddenly, causing the overall output to have a significant inflection point deviation that limits the range. The output characteristic curve of the capacitance value of the capacitive pressure sensor embodiment as it changes with air pressure is shown in Figure 10. It can be seen that the capacitance no longer has the inflection point of the output characteristic curve of the pressure sensor shown in Figure 4 of Figure 6, greatly improving the measurement accuracy of the sensor. Examining the capacitance output value in the 30-120kPa air pressure range, its capacitance nonlinearity is about 1.5%, which is only 30% of that in Example 1, greatly reducing the nonlinearity of the device and the difficulty of compensation.

[0062] The above is only an exemplary pressure sensor structure. Alternatively, the pressure-sensitive layers of the sensing units 100 in the same row may be arranged in an arithmetic progression. For example, the area of ​​the pressure-sensitive layers of the sensing units 100 may decrease from top to bottom, with the difference between any two adjacent pressure-sensitive layers being equal. Another example is the area of ​​the pressure-sensitive layers of the sensing units 100 may decrease from top to bottom, with the difference between any two adjacent pressure-sensitive layers being equal. This arrangement can also achieve the aforementioned effect of proportionally varying the pressure-sensitive layers of the sensing units 100 in the same row, and therefore will not be described in detail here.

[0063] In some examples, the orthographic projection of the pressure-sensing cavity 21 of each sensing unit 100 on the base substrate 10 is not limited to the aforementioned square, but may also be circular.

[0064] In some examples, the base substrate 10 uses a silicon substrate, and the first electrode 311 of each sensor unit 100 is obtained by ion implantation of the silicon substrate, that is, the first electrode 311 of the sensor unit 100 can be obtained by processing the silicon substrate, thereby making the device lighter and thinner.

[0065] When the silicon substrate is a P-type silicon substrate, phosphorus ions can be implanted through the P-type silicon substrate, followed by high-temperature annealing to form an N-well. Then, boron ions are implanted through a high-concentration ion column on the surface, and rapid thermal annealing is performed to form a P+ layer, thereby forming the first electrode 311 of each sensor unit 100. When the silicon substrate is an N-type silicon substrate, boron ions can be implanted through the N-type silicon substrate, followed by high-temperature annealing to form a P-well. Then, phosphorus ions are implanted through a high-concentration ion column on the surface, and rapid thermal annealing is performed to form an N+ layer, thereby forming the first electrode 311 of each sensor unit 100.

[0066] In some embodiments, the material of the support layer 20 in the pressure sensor may specifically be silicon oxide.

[0067] To further clarify the structure of the capacitive pressure sensor, the following describes the capacitive pressure sensor in conjunction with a method for manufacturing the capacitive pressure sensor. The following description uses an example in which the substrate 10 is a silicon substrate and the first electrode 311 of the sensor unit 100 is obtained by processing the silicon substrate.

[0068] FIG11 is a flow chart for preparing a capacitive pressure sensor having a sensing unit 100 of a square thin film with a proportionally variable area. As shown in FIG11 , the method for preparing the capacitive pressure sensor according to the embodiment of the present disclosure specifically includes the following steps:

[0069] S11 , providing a silicon substrate, and performing ion implantation on the silicon substrate to form a first electrode plate 311 of each sensing unit 100 . A plurality of first electrode plates 311 are connected into an integrated structure, namely forming a first pressure-sensing layer 31 .

[0070] In some examples, when the silicon substrate is a P-type silicon substrate, step S11 may include: injecting phosphorus ions into the P-type silicon substrate, forming an N well through high-temperature annealing at 1100°C, and then injecting boron ions into the surface with high concentration ions, forming a P+ layer through rapid thermal annealing. At this time, the first electrode 311 is completed.

[0071] When the silicon substrate is an N-type silicon substrate, step S11 may include: implanting boron ions on the N-type silicon substrate, forming a P well through high-temperature annealing at 1100° C., and then implanting phosphorus ions at a high concentration on the surface, and forming an N+ layer through rapid thermal annealing.

[0072] S12 , forming a support layer 20 on the silicon substrate after completing the above steps, wherein the support layer 20 has pressure-sensing cavities 21 corresponding to the first electrode plates 311 .

[0073] In some examples, the support layer 20 may be made of silicon oxide with a thickness ranging from 100 nm to 5 μm, for example, 400 nm. When the support layer 20 is made of silicon oxide, step S12 may include depositing a layer of silicon oxide on the first electrode plate 311 using PECVD, and then photolithographically exposing the desired array arrangement of the first electrode plates 311 on the silicon oxide surface using a photoresist as a mask, thereby forming the pressure-sensing cavities 21.

[0074] S13. Provide an SOI wafer. The SOI wafer includes an auxiliary substrate 50, a transition layer 51 disposed on the auxiliary electrode 50, and a single crystal silicon film layer 52 disposed on the side of the transition layer 51 facing away from the auxiliary substrate 50. The single crystal silicon film layer 52 serves as the second pressure-sensing layer 32. The transition layer 51 can be made of silicon oxide.

[0075] S14, bonding the SOI wafer and the support layer 20 together through low-temperature silicon-silicon bonding.

[0076] S15 , removing the SOI auxiliary substrate 50 by grinding and thinning, and then removing the silicon oxide transition layer 51 by hydrofluoric acid, leaving only the single crystal silicon film layer 52 , thus forming the second pressure-sensitive layer 32 including a plurality of second electrodes 321 .

[0077] S16 , forming a first connecting portion 41 electrically connected to the first pressure-sensing layer 31 and a second connecting portion 42 electrically connected to the second pressure-sensing layer 32 .

[0078] In some examples, step S16 includes: exposing the required area of ​​the first electrode by photolithography, protecting other areas with photoresist, and then etching the second pressure-sensitive layer 32 and the support layer 20 in the area exposed by the photoresist by a dry etching process to expose part of the first pressure-sensitive layer 31.

[0079] Next, a Ti / Al metal layer is deposited across the entire substrate using metal sputtering. The Ti layer serves as an adhesion layer to improve adhesion, with a thickness of 50nm to 100nm, and the Al layer serves as a low-resistance electrode layer, with a thickness of 300nm to 1μm. Finally, photoresist lithography is used to protect the first and second connectors 41, 42 to be formed, leaving the remaining areas exposed without photoresist protection. Finally, the Ti / Al layer is dry-etched, and the photoresist is removed, forming the first and second connectors 41, 42.

[0080] The preparation of the capacitive pressure sensor is now completed.

[0081] Second example: Figure 12 is a top view of a piezoresistive pressure sensor comprising an array of square thin film sensing units 100 with proportionally variable areas; Figure 13 is a circuit diagram of a Wheatstone bridge; and Figure 14 is a cross-sectional view of a piezoresistive pressure sensor comprising a square thin film sensing unit 100 with proportionally variable areas. As shown in Figures 12-14, the pressure sensor is a piezoresistive pressure sensor comprising a support layer 20 disposed on a substrate 10. The support layer 20 has a plurality of pressure-sensing cavities 21. A pressure-sensing layer is formed on the side of the support layer 20 facing away from the substrate 10. The pressure-sensing layer has a plurality of Wheatstone bridges corresponding to the pressure-sensing cavities 21. Each Wheatstone bridge comprises four series-connected piezoresistors 61. A pressure-sensing cavity 21 and the corresponding Wheatstone bridge disposed on the pressure-sensing layer constitute a sensing unit 100. The orthographic projection areas of the pressure-sensing cavities 21 of at least two sensing units 100 on the substrate 10 are different. In this example, the thickness of the pressure-sensitive layer is the same, and the different sizes of the pressure-sensitive cavity 21 determine the different sizes of the effective pressure-sensitive layer. Each piezoresistive sensing unit 100 is adapted to a different range and linearity, forming a multi-range pressure sensor that corresponds to high-precision measurement requirements of different ranges.

[0082] In some examples, the varistor 61 can be formed by ion implantation of the pressure-sensing layer. For example, the pressure-sensing film is made of a P-type single-crystal silicon film layer. First, the entire surface of the P-type single-crystal silicon pressure-sensing layer is modified by N implantation. Then, P- implantation is performed in sections to form the varistor 61, which is located at the inner edge of the pressure-sensing cavity 21. Then, P+ implantation is performed in sections to form the ohmic contact area of ​​the varistor 61, so that the varistor 61 can be connected via conductive wires 62 to form a Wheatstone bridge.

[0083] Furthermore, a conductive line 62 and a connecting pad 63 are formed on the side of the pressure-sensing layer facing away from the substrate. The conductive line 62 is electrically connected to the ohmic contact area of ​​the varistor 61, forming a Wheatstone bridge. The four varistor 61 in the Wheatstone bridge are respectively referred to as the first varistor R1, the second varistor R2, the third varistor R3, and the fourth varistor R4. The connecting pads 63 include a first connecting pad VDD, a second connecting pad VSS, a third connecting pad OUT+, and a fourth connecting pad OUT-. The first end of the first varistor R1 and the first end of the second varistor R2 are electrically connected to the first connecting pad VDD, the second end of the first varistor R1 and the first end of the third varistor R3 are electrically connected to the third connecting pad OUT+, the second end of the third varistor R3 and the second end of the fourth varistor R4 are connected to the second connecting pad VSS, and the second end of the second varistor R2 and the first end of the fourth varistor R4 are connected to the fourth connecting pad OUT-. The conductive wire 62 and the connecting pad 63 are made of metal.

[0084] In some examples, the sensing units 100 are arranged in an array; the areas of the orthographic projections of the pressure-sensitive cavities 21 of the sensing units 100 in the same row on the substrate 10 are equal, and the areas of the orthographic projections of the pressure-sensitive cavities 21 of the sensing units 100 in the same column on the substrate 10 monotonically increase or decrease, that is, the areas of the pressure-sensitive layers of the sensing units 100 in the same column are not equal. For example: the areas of the orthographic projections of the pressure-sensitive cavities 21 (pressure-sensitive layers) of the sensing units 100 in the same column on the substrate 10 change proportionally or arithmetic differences. The thickness of the pressure-sensitive layers is the same, but the different sizes of the pressure-sensitive cavities 21 determine the different sizes of the effective pressure-sensitive layers. Each piezoresistive sensing unit 100 is adapted to a different range and linearity, forming a multi-range pressure sensor that corresponds to high-precision measurement requirements of different ranges.

[0085] In order to make the structure of the piezoresistive pressure sensor of the embodiment of the present disclosure clearer, the structure of the piezoresistive pressure sensor is further described below in conjunction with the preparation method of the pressure sensor.

[0086] FIG15 is a flow chart of manufacturing a piezoresistive pressure sensor having a sensing unit 100 of a square thin film with a proportionally variable area. As shown in FIG15 , the manufacturing method of the piezoresistive pressure sensor according to an embodiment of the present disclosure includes the following steps:

[0087] S21 , providing a base substrate 10 .

[0088] In some examples, the base substrate 10 may be a silicon substrate.

[0089] S22 , forming a support layer 20 on the base substrate 10 , wherein the support layer 20 has a plurality of pressure-sensing cavities 21 .

[0090] S23, providing an SOI wafer, the SOI wafer comprising an auxiliary substrate 70, a transition layer 71, and a single crystal silicon film layer 72 disposed on a side of the transition layer 71 away from the auxiliary substrate, wherein the transition layer 72 is made of silicon oxide.

[0091] S24: The single crystal silicon film layer 72 of the SOI wafer is bonded to the support layer 20 via low-temperature silicon-silicon bonding. S25: The auxiliary substrate 70 is removed by grinding and thinning, and the silicon oxide transition layer 71 is removed using hydrofluoric acid, leaving only the single crystal silicon film layer 72, thus forming the pressure-sensitive layer 30.

[0092] S26 , the pressure-sensitive layer 30 may be made of P-type single crystal silicon. The entire surface of the P-type single crystal silicon pressure-sensitive layer is modified by N implantation to form a modified single crystal silicon pressure-sensitive layer 301 .

[0093] S27 , partition P-injection to form a piezoresistor 61 , which is located at the edge of the pressure sensing cavity 21 .

[0094] S28 , performing P+ implantation on the varistor 61 to form an ohmic contact region 611 of the varistor 61 , so as to facilitate subsequent connection of the varistor 61 through the conductive wire 62 to form a Wheatstone bridge.

[0095] S29 , forming conductive lines 62 and connecting pads 63 .

[0096] In some examples, the four piezoresistors 61 in the Wheatstone bridge are respectively referred to as the first piezoresistor 61 , the second piezoresistor 61 , the third piezoresistor 61 , and the fourth piezoresistor 61 . The connecting pads 63 include a first connecting pad 63 , a second connecting pad 63 , a third connecting pad 63 , and a fourth connecting pad 63 ; wherein the first end of the first piezoresistor 61 and the first end of the second piezoresistor 61 are electrically connected to the first connecting pad 63 , the second end of the first piezoresistor 61 and the first end of the third piezoresistor 61 are electrically connected to the third connecting pad 63 , the second end of the third piezoresistor 61 and the second end of the fourth piezoresistor 61 are connected to the second connecting pad 63 , and the second end of the second piezoresistor 61 and the first end of the third piezoresistor 61 are connected to the fourth connecting pad 63 . The conductive wires 62 and the connecting pads 63 are made of metal. Step S25 may include depositing a metal film layer on the side of the pressure-sensitive layer facing away from the base substrate 10 , and then coating photoresist, exposing, developing, and etching to form the conductive lines 62 and the connecting pads 63 .

[0097] The preparation of the piezoresistive pressure sensor is now completed.

[0098] An embodiment of the present disclosure provides an electronic device, which may include any of the above-mentioned pressure sensors.

[0099] It will be understood that the above embodiments are merely exemplary embodiments for illustrating the principles of the present invention, and the present invention is not limited thereto. Those skilled in the art will appreciate that various modifications and improvements can be made without departing from the spirit and substance of the present invention, and such modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A pressure sensor, comprising a substrate, a plurality of sensing units located on the substrate, each of the sensing units comprising a pressure-sensing cavity; and the areas of the orthographic projections of at least two of the pressure-sensing cavities on the substrate are unequal.

2. The pressure sensor according to claim 1, wherein: It also includes a first pressure-sensitive layer and a second pressure-sensitive layer; the first pressure-sensitive layer and the second pressure-sensitive layer are respectively arranged on both sides of the pressure-sensitive cavity along the depth direction; the first pressure-sensitive layer includes a first electrode plate of each of the sensing units, and the second pressure-sensitive layer includes a second electrode plate of each of the sensing units.

3. The pressure sensor according to claim 2, wherein: It also includes that the substrate includes a silicon substrate, and the first electrode plate is obtained by ion implantation of the silicon substrate.

4. The pressure sensor according to claim 2, wherein: The material of the second pressure-sensitive layer is single crystal silicon.

5. The pressure sensor according to claim 2, wherein: The invention also includes a first connection part electrically connected to the first electrode layer and a second connection part electrically connected to the second electrode layer.

6. The pressure sensor according to claim 5, wherein: The first connecting portion is located on a side of the first pressure-sensitive layer close to the second pressure-sensitive layer, and the second connecting portion is located on a side of the second pressure-sensitive layer away from the first pressure-sensitive layer.

7. The pressure sensor according to claim 1, wherein: It also includes a pressure-sensitive layer on the side of the pressure-sensitive cavity away from the substrate, wherein the pressure-sensitive cavity is arranged on the substrate; each of the sensing units includes four piezoresistors formed on the pressure-sensitive layer and connected in series, and the four piezoresistors constitute a Wheatstone bridge.

8. The pressure sensor according to claim 7, wherein: The varistor in the sensing unit is obtained by ion implantation of the pressure-sensitive layer.

9. The pressure sensor according to claim 7, wherein: Each of the sensing units further comprises a conductive line connected in series with a piezoresistor, and the conductive line is located on a side of the pressure-sensitive layer away from the substrate.

10. The pressure sensor according to claim 7, wherein: The substrate is a silicon substrate.

11. The pressure sensor according to any one of claims 1 to 10, wherein: The sensing units are arranged in an array; the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same row on the substrate monotonically increase or decrease, and / or the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same column on the substrate monotonically increase or decrease.

12. The pressure sensor according to claim 11, wherein: When the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same row on the substrate monotonically increase or decrease, the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same row on the substrate change in equal proportion or in equal difference; When the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same column on the substrate monotonically increase or decrease, the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same column on the substrate change in equal proportion or in equal difference.

13. The pressure sensor according to any one of claims 1 to 10, wherein: The orthographic projection of the pressure sensing cavity on the base substrate is a rectangle or a circle.

14. A method for preparing a pressure sensor, comprising forming a plurality of sensing units on a substrate; forming the sensing units comprises forming pressure-sensing cavities, and the areas of the orthographic projections of at least two pressure-sensing cavities on the substrate are unequal.

15. The method for preparing a pressure sensor according to claim 14, wherein: The step of forming the pressure-sensitive cavity includes forming a support layer on the base substrate, and patterning the support layer to form a plurality of the pressure-sensitive cavities.

16. The method for preparing a pressure sensor according to claim 14, wherein: It also includes forming a first pressure-sensitive layer and a second pressure-sensitive layer on both sides of the pressure-sensitive cavity in the depth direction, wherein the first pressure-sensitive layer includes a first electrode plate arranged in a one-to-one correspondence with the pressure-sensitive cavity, and the second pressure-sensitive layer includes a second electrode plate arranged in a one-to-one correspondence with the pressure-sensitive cavity.

17. The method for preparing a pressure sensor according to claim 16, wherein: The base substrate is a silicon substrate, and the first pressure-sensitive layer is formed by ion implantation of the silicon substrate.

18. The method for preparing a pressure sensor according to claim 16, wherein: The step of forming a second pressure-sensitive layer on the pressure-sensitive cavity comprises: Providing an SOI wafer; wherein the SOI wafer comprises an auxiliary substrate, a transition layer and a single crystal silicon film layer disposed on the auxiliary substrate; Bonding one side of the SOI wafer having the single crystal silicon film layer to the substrate having the pressure sensing cavity formed thereon; The auxiliary substrate and the transition layer are removed, and the single crystal silicon film layer remains to form the second pressure-sensitive layer.

19. The method for preparing a pressure sensor according to claim 14, wherein: The method further comprises forming a pressure-sensitive layer on a side of the pressure-sensitive cavity away from the substrate, and performing ion implantation on the pressure-sensitive layer to form a Wheatstone bridge of each sensing unit, wherein the Wheatstone bridge comprises four piezoresistors connected in series.

20. The method for preparing a pressure sensor according to claim 14, wherein: The method also includes forming a conductive line on a side of the pressure-sensitive layer away from the base substrate, and the conductive line is connected in series with the varistor in the sensing unit.

21. The method for preparing a pressure sensor according to any one of claims 14 to 20, wherein: The sensing units are arranged in an array; the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same row on the substrate are equal and monotonically increase or decrease, and / or the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same column on the substrate are monotonically increase or decrease.

22. The method for preparing a pressure sensor according to claim 21, wherein: When the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same row on the substrate monotonically increase or decrease, the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same row on the substrate change in equal proportion or in equal difference; When the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same column on the substrate monotonically increase or decrease, the areas of the orthographic projections of the pressure-sensing cavities of the sensing units in the same column on the substrate change in equal proportion or in equal difference.

23. The method for preparing a pressure sensor according to any one of claims 14 to 20, wherein: The orthographic projection of the pressure sensing cavity on the base substrate is a rectangle or a circle.

24. An electronic device comprising the pressure sensor according to any one of claims 1 to 13.

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