A MEMS pressure sensor and a manufacturing method thereof

Abstract

The present invention discloses a MEMS pressure sensor and a method for manufacturing the same. The MEMS pressure sensor comprises: four strip-shaped protrusions arranged on a first plane, each of which includes a heavily P-type doped layer; a plurality of electrodes, each of which is used to connect the strip-shaped protrusions to input and output electrical signals, and each of the electrodes and the strip-shaped protrusions forms a Wheatstone bridge; and a strained film layer disposed between a cavity and the Wheatstone bridge. This structure improves the sensitivity and stability of the pressure sensor while reducing its size.

Description

[0001] The application number of this invention is: 202110710324.4, the application date is: June 25, 2021, and the name of the invention is: A MEMS pressure sensor and its manufacturing method. Technical Field

[0002] The embodiments of the present invention relate to the field of sensor technology, and in particular to a MEMS pressure sensor and a manufacturing method thereof. Background Art

[0003] Pressure sensors are widely used in numerous industries, including defense and military, automotive electronics, petrochemicals, aerospace, medical devices, and consumer electronics. They account for one-third of the total sensor market. Based on their operating principles, pressure sensors can be categorized as piezoresistive, capacitive, piezoelectric, surface acoustic wave, and Hall effect. Piezoresistive pressure sensors, manufactured using MEMS technology, are widely used due to their high sensitivity and low cost.

[0004] The piezoresistor in a traditional MEMS piezoresistive pressure sensor is fabricated by fabricating a P-type lightly doped region within a specific area of ​​an N-type lightly doped device layer as the piezoresistive strip. A P-type heavily doped region is then fabricated at the ohmic contact location of the P-type lightly doped region. Ohmic contact holes are formed in the P-type heavily doped region to establish ohmic contact between the metal interconnect layer and the Wheatstone bridge. This traditional method forms the P-type lightly doped and P-type heavily doped regions embedded within the N-type lightly doped device layer. This PN junction structure, due to numerous parasitic parameters and surface defects, results in a low breakdown voltage and high leakage current, which can compromise the pressure sensor's measurement stability over long-term use. Furthermore, this structure makes it difficult to minimize the piezoresistive strip width. To maintain a certain resistance value for the Wheatstone bridge arm, the arm resistors must be formed using lightly P-type doping, which results in significant temperature drift in the sensor's sensitivity. Furthermore, with traditional embedded piezoresistors, when the strain film is deformed under stress, the stress is not well concentrated in the piezoresistor itself, resulting in low sensor sensitivity. Finally, traditional embedded PN junction structures require at least three photomasks, which are costly. Summary of the Invention

[0005] The present invention provides a MEMS pressure sensor and a manufacturing method thereof, so as to improve the sensitivity and stability of the pressure sensor and reduce the size of the pressure sensor.

[0006] To achieve the above-mentioned objectives, an embodiment of the first aspect of the present invention proposes a MEMS pressure sensor, comprising: four strip-shaped protrusions arranged on a first plane, wherein each of the strip-shaped protrusions includes a P-type heavily doped layer; a plurality of electrodes, wherein each of the electrodes is used for each of the strip-shaped protrusions to connect input electrical signals and output electrical signals, and each of the electrodes and each of the strip-shaped protrusions constitutes a Wheatstone bridge; and a strained thin film layer, which is arranged between a cavity and the Wheatstone bridge.

[0007] According to an embodiment of the present invention, an N-type device layer is located below the four strip-shaped protrusions, and the N-type device layer is a low-doped N-type silicon layer. The sidewalls of the four protrusions at least expose the P-type heavily doped layer.

[0008] According to one embodiment of the present invention, each strip-shaped protrusion further includes: a P-type lightly doped layer located below the P-type heavily doped layer, the sidewalls of the four protrusions expose at least the P-type heavily doped layer and the P-type lightly doped layer, and below the four strip-shaped protrusions is an N-type device layer, which is a low-doped N-type silicon layer.

[0009] According to one embodiment of the present invention, each of the strip-shaped protrusions includes a varistor portion and two wire portions; the two ends of the varistor portion are respectively connected to one of the wire portions; wherein, in the opposite direction to the first direction, the line width of the varistor portion is smaller than the line width of the wire portion.

[0010] According to one embodiment of the present invention, the four strip-shaped protrusions are arranged in parallel, and include a first strip-shaped protrusion, a second strip-shaped protrusion, a third strip-shaped protrusion and a fourth strip-shaped protrusion in sequence; each of the strip-shaped protrusions includes a first wire portion and a second wire portion, the first wire portion and the second wire portion are symmetrically arranged, and the first wire portion and the second wire portion are offset by a preset distance relative to the axis of symmetry, for connecting the varistor portion.

[0011] According to one embodiment of the present invention, the varistor portion in the first strip-shaped protrusion protrudes outward from a side of the first strip-shaped protrusion away from the second strip-shaped protrusion; the varistor portion in the second strip-shaped protrusion protrudes outward from a side of the second strip-shaped protrusion away from the first strip-shaped protrusion; the varistor portion in the third strip-shaped protrusion protrudes outward from a side of the third strip-shaped protrusion away from the fourth strip-shaped protrusion; and the varistor portion in the fourth strip-shaped protrusion protrudes outward from a side of the fourth strip-shaped protrusion away from the third strip-shaped protrusion.

[0012] According to one embodiment of the present invention, the varistor portion includes a varistor; the shape of the varistor in each of the strip-shaped protrusions is one of a U-shape, a V-shape, or a cascade shape composed of multiple V-shapes or U-shapes, and the arrangement shapes of the varistors are all axially symmetrically distributed with the symmetry axis as the central axis.

[0013] According to an embodiment of the present invention, the shapes of the varistors in the strip-shaped protrusions are the same.

[0014] According to one embodiment of the present invention, the varistor portion includes a plurality of strip varistors and a third wire portion for connecting the plurality of strip varistors in series; the line width of the strip varistors is smaller than the line width of the third wire portion; the plurality of strip varistors are all parallel to the axis of symmetry and are symmetrically distributed with the axis of symmetry as the central axis, and the plurality of third wire portions are all perpendicular to the axis of symmetry.

[0015] According to one embodiment of the present invention, the four strip-shaped protrusions are arranged in parallel, and sequentially include a first strip-shaped protrusion, a second strip-shaped protrusion, a third strip-shaped protrusion, and a fourth strip-shaped protrusion; the plurality of electrodes include: a first input electrode, a second input electrode, a first output electrode, a second output electrode, a first ground electrode, and a second ground electrode;

[0016] One end of the first strip-shaped protrusion is connected to the first input electrode, and the other end is connected to the first output electrode; one end of the second strip-shaped protrusion is connected to the first output electrode, and the other end is connected to the first ground electrode; one end of the third strip-shaped protrusion is connected to the second input electrode, and the other end is connected to the second output electrode; one end of the fourth strip-shaped protrusion is connected to the second output electrode, and the other end is connected to the second ground electrode.

[0017] According to an embodiment of the present invention, the first input electrode, the second input electrode, the first output electrode, the second output electrode, the first ground electrode and the second ground electrode are all metal electrodes.

[0018] According to one embodiment of the present invention, the first input electrode, the second input electrode, the first output electrode, the second output electrode, the first ground electrode and the second ground electrode are all arranged in the same layer as the first strip-shaped protrusion, the second strip-shaped protrusion, the third strip-shaped protrusion and the fourth strip-shaped protrusion.

[0019] According to one embodiment of the present invention, four strip-shaped raised areas, a first input electrode area, a first output electrode area, a second output electrode area, a second input electrode area, a first ground electrode area and a second ground electrode area are arranged on the first plane, and each of the electrode areas is separated by a groove.

[0020] To achieve the above-mentioned objectives, an embodiment of the second aspect of the present invention proposes a method for manufacturing a MEMS pressure sensor, which is applied to the MEMS pressure sensor as described above, and includes the following steps: providing a substrate, wherein the substrate includes an N-type device layer; performing P-type dense doping on the entire surface of one side of the N-type device layer to form a P-type dense doping layer; using an etching process to form four strip-shaped protrusions, wherein the side walls of the four strip-shaped protrusions at least expose the P-type dense doping layer; forming a plurality of electrodes, each of the electrodes is used for each of the strip-shaped protrusions to input and output electrical signals; each of the electrodes and each of the strip-shaped protrusions constitutes a Wheatstone bridge; etching the substrate to form a cavity, and forming a strained thin film layer between the cavity and the Wheatstone bridge.

[0021] According to the MEMS pressure sensor and its manufacturing method proposed in the embodiment of the present invention, by setting four strip-shaped protrusions, when the strain film layer is subjected to pressure, the stress is maximum at the edge and center of the strain film layer, and the stress is more concentrated on the surface of the protruding strip-shaped varistor, with high sensitivity and good linearity. In addition, the parasitic parameters between the heavily doped layer and the substrate are smaller, and the layer is closer to an ideal PN junction with the substrate, so it has a higher breakdown voltage and lower leakage current, and thus has higher reliability and long-term stability. Due to the high doping concentration on the surface of the strip-shaped protrusions, the device can achieve lower sensitivity temperature drift. The MEMS pressure sensor has a simple structure, and the preparation process of the varistor strip only requires one mask, with low process cost and can be mass-produced. In addition, in the two embodiments of the present invention, the embodiment in which the first cavity is an open cavity can be used to measure relative differential pressure; the embodiment in which the first cavity is a vacuum-sealed cavity can be used to measure absolute pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a top view of a MEMS pressure sensor provided in an embodiment of the present invention;

[0023] Figure 2 yes Figure 1 A cross-sectional view of an embodiment along the AA' direction;

[0024] Figure 3 yes Figure 1 A cross-sectional view of another embodiment along the AA' direction;

[0025] Figure 4 yes Figure 1 A cross-sectional view of another embodiment along the AA' direction;

[0026] Figure 5 is a top view of a MEMS pressure sensor according to one embodiment of the present invention;

[0027] Figure 6 is a top view of a MEMS pressure sensor provided in another embodiment of the present invention;

[0028] Figure 7 is a top view of a MEMS pressure sensor provided in yet another embodiment of the present invention;

[0029] Figure 8 is a top view of a MEMS pressure sensor provided in yet another embodiment of the present invention;

[0030] Figure 9 is a top view of a MEMS pressure sensor provided in yet another embodiment of the present invention;

[0031] Figure 10 This is a circuit schematic diagram of a Wheatstone bridge in a MEMS pressure sensor according to one embodiment of the present invention;

[0032] Figure 11 1 is a schematic structural diagram of a MEMS pressure sensor proposed in one embodiment of the present invention;

[0033] Figure 12 is a top view of a MEMS pressure sensor provided in yet another embodiment of the present invention;

[0034] Figure 13 is a flow chart of a method for manufacturing a MEMS pressure sensor proposed in an embodiment of the present invention;

[0035] Figure 14 This is a flow chart of a method for manufacturing a MEMS pressure sensor according to one embodiment of the present invention;

[0036] Figure 15 is a flow chart of a method for manufacturing a MEMS pressure sensor according to another embodiment of the present invention;

[0037] Figure 16 is a flow chart of a method for manufacturing a MEMS pressure sensor according to another embodiment of the present invention;

[0038] Figure 17 1 is a step diagram of a method for manufacturing a MEMS pressure sensor according to one embodiment of the present invention;

[0039] Figure 18 1 is a step diagram of a method for manufacturing a MEMS pressure sensor according to one embodiment of the present invention;

[0040] Figure 19 1 is a step diagram of a method for manufacturing a MEMS pressure sensor according to one embodiment of the present invention;

[0041] Figure 20 1 is a step diagram of a method for manufacturing a MEMS pressure sensor according to one embodiment of the present invention;

[0042] Figure 211 is a step diagram of a method for manufacturing a MEMS pressure sensor according to one embodiment of the present invention;

[0043] Figure 22 is a step diagram of a method for manufacturing a MEMS pressure sensor according to another embodiment of the present invention;

[0044] Figure 23 is a step diagram of a method for manufacturing a MEMS pressure sensor according to another embodiment of the present invention;

[0045] Figure 24 is a step diagram of a method for manufacturing a MEMS pressure sensor according to another embodiment of the present invention;

[0046] Figure 25 1 is a step diagram of a method for manufacturing a MEMS pressure sensor according to another embodiment of the present invention;

[0047] Figure 26 This is a step diagram of a method for manufacturing a MEMS pressure sensor proposed in yet another embodiment of the present invention. DETAILED DESCRIPTION

[0048] The present invention will be further described in detail below with reference to the accompanying drawings and examples. It will be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention. It should also be noted that, for ease of description, the accompanying drawings only illustrate portions relevant to the present invention, not all structures.

[0049] Figure 1 FIG. 1 is a top view of the MEMS pressure sensor proposed in an embodiment of the present invention. Figure 1 and Figure 2 As shown, the MEMS pressure sensor 100 includes:

[0050] A support layer 101, an insulating layer 102, an N-type device layer 103, and a P-type heavily doped layer 104 are sequentially stacked along a first direction; wherein the first direction is a direction from the support layer 101 perpendicularly to the P-type heavily doped layer 104;

[0051] Four strip-shaped protrusions are arranged on a first plane, along a first direction, each strip-shaped protrusion includes at least a P-type heavily doped layer 104, and the first plane is a plane perpendicular to the first direction;

[0052] Multiple electrodes 112, each electrode 112 is used for each strip-shaped protrusion to receive input electrical signals and output electrical signals; each electrode and each strip-shaped protrusion constitutes a Wheatstone bridge 105;

[0053] The support layer 101 is provided with a first cavity 106 , and a strained film layer 107 is provided between the first cavity 106 and the Wheatstone bridge 105 .

[0054] It should be noted that the vertical projection of the bottom surface of the first cavity 106 on the insulating layer 102 covers the vertical projection of the Wheatstone bridge 105 on the insulating layer 102. As a result, when the strain film layer 107 is deformed through the first cavity 106, the four strip-shaped protrusions in the Wheatstone bridge 105 above the strain film layer 107 may also be deformed. Due to the deformation of the four strip-shaped protrusions, the resistance value changes. In addition, the strip-shaped protrusions at the edge of the strain film layer 107 and the strip-shaped protrusions at the center of the strain film layer 107 are subjected to opposite forces (e.g., Figure 1 As shown in , if the strained film layer 107 is subjected to an upward force direction, the strip protrusions at the center are subjected to tensile stress, and the strip protrusions at the edge are subjected to compressive stress; conversely, the strip protrusions at the center are subjected to compressive stress, and the strip protrusions at the edge are subjected to tensile stress. Figure 2 Only one example is shown. (A circle with a dot points outward perpendicular to the paper, while a circle with a cross points inward perpendicular to the paper.) The resistance changes have opposite polarities. Due to the characteristics of a Wheatstone bridge, the two output ports of the Wheatstone bridge, formed by the various strip-shaped protrusions, output a potential difference. This output potential difference is proportional to the pressure applied to the strained film layer 107, thereby detecting the pressure applied to the strained film layer 107.

[0055] The support layer 101 may be a silicon layer, the insulating layer 102 may be a silicon dioxide layer, and the N-type device layer 103 may be a low-doped N-type silicon layer. The lightly doped element may be boron. The P-type heavily doped layer 104 may be a P-type heavily doped silicon layer, wherein the heavily doped element may be boron.

[0056] It can be understood that along the first direction (ie Figure 2 The support layer 101, the insulating layer 102 and the N-type device layer 103 together constitute a substrate, as shown in FIG. Figure 1 As shown, the substrate can be rectangular. Four strip-shaped protrusions (a first strip-shaped protrusion 108, a second strip-shaped protrusion 109, a third strip-shaped protrusion 110, and a fourth strip-shaped protrusion 111) are arranged on a first plane, wherein the resistance values ​​of the four strip-shaped protrusions are equal, and the first plane can be the top surface of the substrate. Because the four strip-shaped protrusions protrude from the substrate surface, after the strain film layer 107 is deformed by force, the induced stress is more concentrated in the P-type densely doped layer on the surface of the piezoresistive portion of the four strip-shaped protrusions, thereby improving the sensitivity and linearity of the pressure sensor.

[0057] The higher the doping concentration on the surface of each strip-shaped protrusion, the lower the sensitivity temperature coefficient of the pressure sensor and the smaller the temperature drift. In addition, a higher doping concentration can achieve higher doping uniformity, thereby achieving better device consistency. Therefore, the four strip-shaped protrusions all include at least a P-type densely doped layer 104, which achieves a lower sensor sensitivity temperature coefficient and higher linearity. Thus, the P-type densely doped layer 104 acts as a resistor in the Wheatstone bridge 105, which makes the MEMS pressure sensor relatively less sensitive to temperature changes and is less affected by ambient temperature changes. The low sensitivity temperature coefficient and high linearity make the detection results more accurate and broaden the use environment of the pressure sensor.

[0058] The PN junction formed between the P-type heavily doped layer 104 and the N-type device layer 103 is a parallel plane junction, and the parasitic parameters between the raised P-type heavily doped layer 104 and the N-type device layer 103 are smaller, and can be regarded as an ideal PN junction. This PN junction has lower leakage current and higher breakdown voltage, which is reflected in the pressure sensor. The pressure sensor has better long-term reliability and higher tolerance to operating temperature, thereby broadening the use environment of the pressure sensor.

[0059] According to one embodiment of the present invention, Figure 2 As shown, the first cavity 106 is located on the surface of the support layer 101 facing away from the insulating layer 102 , and the first cavity 106 is an open cavity; thus, the MEMS pressure sensor of this structure can measure open differential pressure.

[0060] Or, as Figure 3 As shown, the first cavity 106 is located on the surface of the support layer 101 adjacent to the insulating layer 102. In this structure, the first cavity 106 is sealed by the insulating layer 102 and the support layer 101 to form a vacuum sealed cavity, which can measure absolute pressure.

[0061] According to one embodiment of the present invention, Figure 4 As shown, along the first direction, each strip-shaped protrusion further includes: a P-type lightly doped layer 113 , and the P-type lightly doped layer 113 is located between the N-type device layer 103 and the P-type heavily doped layer 104 .

[0062] It is understood that the P-type lightly doped layer 113 may be a P-type lightly doped silicon layer, wherein the lightly doping element may be boron. On the first plane, a PN junction is formed between the P-type lightly doped layer 113, the P-type heavily doped layer 104, and the N-type device layer 103. The PN junction including the P-type lightly doped layer 113 has a deeper junction depth, and therefore a higher breakdown voltage.

[0063] According to one embodiment of the present invention, Figure 5As shown, each strip-shaped protrusion includes a varistor portion 114 and two wire portions 115; the two ends of the varistor portion 114 are respectively connected to a wire portion; wherein, along the opposite direction of the first direction, the line width of the varistor portion 114 is smaller than the line width of the wire portion 115.

[0064] It can be understood that the line width of the varistor part 114 is much smaller than the line width of the wire part 115, so that the resistance of the varistor part 114 is much greater than the resistance of the wire part 115, and the wire part and the varistor part are set on the same layer.

[0065] According to one embodiment of the present invention, Figure 5 As shown, four strip-shaped protrusions are arranged in parallel, including a first strip-shaped protrusion 108, a second strip-shaped protrusion 109, a third strip-shaped protrusion 110 and a fourth strip-shaped protrusion 111 in sequence; each strip-shaped protrusion includes a first wire portion 1151 and a second wire portion 1152, and the first wire portion 1151 and the second wire portion 1152 are symmetrically arranged, and the first wire portion 1151 and the second wire portion 1152 are both offset by a preset distance relative to the axis of symmetry, for connecting the varistor portion 114.

[0066] The four strip-shaped protrusions are symmetrical with respect to the transverse axis of the substrate, so that the resistances on both sides of the Wheatstone bridge 105 are symmetrically distributed, thereby achieving accurate detection results.

[0067] According to one embodiment of the present invention, Figure 5 As shown, the varistor portion 114 in the first strip-shaped protrusion 108 protrudes outward from the side of the first strip-shaped protrusion 108 away from the second strip-shaped protrusion 109; the varistor portion 114 in the second strip-shaped protrusion 109 protrudes outward from the side of the second strip-shaped protrusion 109 away from the first strip-shaped protrusion 108; the varistor portion 114 in the third strip-shaped protrusion 110 protrudes outward from the side of the third strip-shaped protrusion 110 away from the fourth strip-shaped protrusion 111; and the varistor portion 114 in the fourth strip-shaped protrusion 111 protrudes outward from the side of the fourth strip-shaped protrusion 111 away from the third strip-shaped protrusion 110.

[0068] It can be understood that when the strain film layer 107 is deformed by pressure, the force on the surface of the strain film layer is mainly concentrated in the center and the middle of the edge of the strain film layer, and then the piezoresistive resistor portion 114 in the second strip protrusion 109 and the third strip protrusion 110 is arranged as follows: Figure 5 and the piezoresistive resistor portion 114 of the first strip-shaped protrusion 108 and the fourth strip-shaped protrusion 111 is arranged at the edge, so that the stress distribution is more concentrated on the piezoresistive resistor portion 114, which can improve the sensitivity of the pressure sensor.

[0069] According to one embodiment of the present invention, Figure 6As shown, the piezoresistive portion 114 includes a piezoresistive resistor 1141; the piezoresistive resistors 1141 in each strip-shaped protrusion are arranged in a U-shape, a V-shape, or a cascade of multiple V-shapes or U-shapes. The arrangement of the piezoresistive resistors 1141 is axially symmetrical with the symmetry axis as the central axis. It should be noted that the arrangement of the piezoresistive resistors 1141 in each strip-shaped protrusion can also be in a straight line. The piezoresistive resistors 1141 in the first strip-shaped protrusion 108 and the fourth strip-shaped protrusion 111 cannot be in a straight line. If the piezoresistive resistors 1141 are directly connected to the two wires in a straight line, when the strain film layer 107 deforms, the stress direction at the piezoresistive resistor 1141 is along the symmetry axis. If the piezoresistive resistors are arranged perpendicular to the symmetry axis, there will be no stress component in the direction of the symmetry axis, and no deformation signal can be detected. Therefore, the piezoresistive resistors 1141 in the first strip-shaped protrusion 108 and the fourth strip-shaped protrusion 111 cannot be in a straight line, and must have a component in the direction along the symmetry axis. The stress distribution of the piezoresistors in the second strip-shaped protrusions 109 and the third strip-shaped protrusions 110 is in all directions, so the shape of the piezoresistors in the second strip-shaped protrusions 109 and the third strip-shaped protrusions 110 can be a straight line.

[0070] Furthermore, the piezoresistors 1141 in the first and fourth strip-shaped protrusions 108, 111 are shaped like a U, a V, or a cascade of multiple V- or U-shaped shapes. The piezoresistors 1141 in the second and third strip-shaped protrusions 109, 110 are shaped like a straight line, a U, a V, or a cascade of multiple V- or U-shaped shapes. The shapes of the piezoresistors in the four strip-shaped protrusions can be freely matched or combined, as long as the resistance values ​​of the resistors on both sides of the symmetry axis of the Wheatstone bridge 105 are the same. Figure 6 That is, the shape of the piezoresistor 1141 in the first strip-shaped protrusion 108 and the fourth strip-shaped protrusion 111 is U-shaped, and the shape of the piezoresistor 1141 in the second strip-shaped protrusion 109 and the third strip-shaped protrusion 110 is straight.

[0071] According to one embodiment of the present invention, Figure 7 As shown, the shapes of the varistors in each strip-shaped protrusion are the same.

[0072] In order to improve the detection accuracy of the pressure sensor, the resistance values ​​of the four strip-shaped protrusions can be kept the same, that is, the shape of the pressure-sensitive resistor portion of each strip-shaped protrusion is set to be the same. Figure 7 That is, the varistor 1141 in each strip-shaped protrusion is cascaded in two V shapes.

[0073] In other embodiments, the shape of the varistor portion 114 can also be wavy or broken line, so that the resistance of the varistor 1141 in the varistor portion 114 can be increased, and setting it to a wavy or broken line shape can further reduce the size of the pressure sensor.

[0074] According to one embodiment of the present invention, Figure 5 As shown, the varistor portion 114 includes a plurality of strip varistors and a third wire portion for connecting the plurality of strip varistors in series; the line width of the strip varistors is much smaller than the line width of the third wire portion; the plurality of strip varistors are all parallel to the axis of symmetry and are axially symmetrically distributed with the axis of symmetry as the center axis, and the plurality of third wire portions are all perpendicular to the axis of symmetry.

[0075] Take two strip varistors and a third conductor as an example. Figure 8 As shown, the varistor portion 114 includes a first strip varistor 1142, a second strip varistor 1143 and a third wire portion 1144. The resistance of the first strip varistor 1142 and the second strip varistor 1143 is much greater than the resistance of the third wire portion 1144. The third wire portion 1144 can be regarded as a wire. In addition, the length of the first strip varistor 1142 and the second strip varistor 1143 along the symmetry axis can be adjusted according to actual needs. The larger the required resistance value, the longer the set length.

[0076] In other embodiments, a plurality of strip-shaped varistors may be provided and connected in series via a third conductive line portion.

[0077] Each strip-shaped varistor is parallel to the axis of symmetry, and the third conductor portion is perpendicular to the axis of symmetry, which is conducive to adjusting the total resistance of the entire strip-shaped protrusion by length according to actual needs.

[0078] The electrodes in the Wheatstone bridge 105 are described below.

[0079] According to one embodiment of the present invention, Figure 9 As shown, four strip-shaped protrusions are arranged in parallel, including a first strip-shaped protrusion 108, a second strip-shaped protrusion 109, a third strip-shaped protrusion 110 and a fourth strip-shaped protrusion 111 in sequence; a plurality of electrodes 112 include: a first input electrode 1121, a second input electrode 1122, a first output electrode 1123, a second output electrode 1124, a first ground electrode 1125 and a second ground electrode 1126;

[0080] One end of the first strip-shaped protrusion 108 is connected to the first input electrode 1121, and the other end is connected to the first output electrode 1123; one end of the second strip-shaped protrusion 109 is connected to the first output electrode 1123, and the other end is connected to the first ground electrode 1125; one end of the third strip-shaped protrusion 110 is connected to the second input electrode 1122, and the other end is connected to the second output electrode 1124; one end of the fourth strip-shaped protrusion 111 is connected to the second output electrode 1124, and the other end is connected to the second ground electrode 1126.

[0081] The first input electrode 1121 and the second input electrode 1122 have the same input electrical signal and can be the same electrode. The first ground electrode 1125 and the second ground electrode 1126 can be the same electrode. Figure 10 and Figure 11 As shown, the four strip-shaped protrusions and the electrodes form a Wheatstone bridge, wherein the first input electrode 1121 and the second input electrode 1122 are Vcc electrodes, the first output electrode 1123 is a Vout+ electrode, the second output electrode 1124 is a Vout- electrode, and the first ground electrode 1125 and the second ground electrode 1126 are GND electrodes.

[0082] According to one embodiment of the present invention, the first input electrode 1121 , the second input electrode 1122 , the first output electrode 1123 , the second output electrode 1124 , the first ground electrode 1125 and the second ground electrode 1126 are all metal electrodes.

[0083] The material of the metal electrode may be Cu, Pt, Au, or the like.

[0084] According to one embodiment of the present invention, the first input electrode 1121, the second input electrode 1122, the first output electrode 1123, the second output electrode 1124, the first ground electrode 1125 and the second ground electrode 1126 are all arranged in the same layer as the first strip-shaped protrusion 108, the second strip-shaped protrusion 109, the third strip-shaped protrusion 110 and the fourth strip-shaped protrusion 111.

[0085] According to one embodiment of the present invention, Figure 12 As shown, the four strip-shaped protrusion areas, the first input electrode 1121 area, the first output electrode 1122 area, the second output electrode 1123 area, the second input electrode 1124 area, the first ground electrode 1125 area and the second ground electrode 1126 area arranged on the first plane are separated by grooves 116. It can be seen that Figure 10 Since the P-type heavily doped layer 104 has good conductivity, the P-type heavily doped layer 104 can be directly used as an electrode to increase material utilization.

[0086] According to an embodiment of the present invention, along a direction opposite to the first direction, the bottom surface of the trench 116 at least contacts a surface of the N-type device layer 103 that is not doped with the P type and faces away from the insulating layer 102 .

[0087] That is, the depth of the groove 116 is at least the same as the height of each strip-shaped protrusion. It should be noted that the depth of the groove 116 needs to be greater than the overall thickness of the doped layer, so that each strip-shaped protrusion can be separated.

[0088] According to one embodiment of the present invention, the support layer 101 may be a silicon layer, the insulating layer 102 may be a silicon dioxide layer, the N-type device layer 103 may be a low-doped N-type silicon layer, the P-type highly doped layer 104 may be a P-type highly doped silicon layer, and the P-type lightly doped layer 113 may be a P-type lightly doped silicon layer. The insulating layer 102 may electrically insulate the support layer 101. The support layer 101, the insulating layer 102, and the N-type device layer 103 may form an SOI substrate.

[0089] Figure 13 FIG. 1 is a flow chart of a method for manufacturing a MEMS pressure sensor according to an embodiment of the present invention. The method is applied to the above-mentioned MEMS pressure sensor. Figure 13 As shown, the method includes the following steps:

[0090] S101 , providing a substrate, wherein the substrate includes a support layer 101 , an insulating layer 102 and an N-type device layer 103 ; the substrate may be an SOI substrate.

[0091] S102, the entire surface of the N-type device layer 103 facing away from the insulating layer 102 is subjected to P-type dense doping to form a P-type dense doping layer 104 (no mask is required); it should be noted that the formation of the P-type dense doping layer 104 can be achieved by diffusion doping or ion implantation and other doping methods well known to those skilled in the art, and the present invention does not make any specific limitations on this.

[0092] The doping element of the P-type heavily doped layer 104 may be boron, which is beneficial for reducing the temperature coefficient of sensitivity of the pressure sensor surface, reducing temperature drift, and improving the detection accuracy of the pressure sensor.

[0093] S103, an etching process is used to form four strip-shaped protrusions, wherein the sidewalls of the four strip-shaped protrusions expose at least the P-type heavily doped layer 104. The etching process can be dry or wet etching. The four strip-shaped protrusions formed protrude from the surface of the N-type device layer 103, which helps concentrate stress on the four strip-shaped protrusions and improve the sensitivity of the pressure sensor. The etching process can control the line width of the four strip-shaped protrusions, thereby making the piezoresistors in the four strip-shaped protrusions very thin, increasing the resistance of each strip-shaped protrusion, reducing the size of the pressure sensor, and reducing costs.

[0094] S104, forming a plurality of electrodes, each electrode is used for each strip-shaped protrusion to input and output electrical signals; each electrode and each strip-shaped protrusion constitutes a Wheatstone bridge 105; the Wheatstone bridge 105 can realize the conversion between force and electrical signal, thereby realizing the function of the pressure sensor.

[0095] S105: A first cavity 106 is formed by etching the surface of the support layer 101 facing away from the insulating layer 102. A strain film layer 107 is formed between the first cavity 106 and the Wheatstone bridge 105. The thickness of the strain film layer 107 is related to the size of the pressure sensor and the magnitude of the pressure being measured. If the pressure to be detected is high, the strain film layer 107 can be thicker. Conversely, if the pressure to be detected is low, the strain film layer 107 can be thinner. The maximum depth of the first cavity 106 is etched through the support layer 101, preferably in the range of 20 microns to 800 microns. The sidewalls of the four strip-shaped protrusions at least expose the P-type heavily doped layer 104 and can at most etch through the N-type device layer 103. The specific value is set according to actual needs. This allows the chip area to be further reduced, reducing costs, while maintaining the same measurement range. Alternatively, a thicker strain film layer can be used to improve the linearity of the pressure sensor while maintaining the same chip area.

[0096] According to another embodiment of the present invention, the method comprises the following steps:

[0097] Providing a substrate as a support layer 101;

[0098] A first cavity 106 is formed by etching a surface of one side of the support layer 101;

[0099] An N-type single crystal silicon wafer is provided as an N-type device layer 103, and an insulating layer 102 is formed on one surface of the device layer 103;

[0100] The outer surface of the support layer 101 having the first cavity 106 etched thereon is bonded to the surface of the insulating layer 102 away from the device layer 103 under a vacuum environment, so that the first cavity 106 is a vacuum-sealed cavity;

[0101] Thinning the device layer 103;

[0102] The entire surface of the N-type device layer 103 facing away from the insulating layer 102 is heavily doped with P-type to form a P-type heavily doped layer 104;

[0103] Four strip-shaped protrusions are formed by an etching process, wherein the sidewalls of the four strip-shaped protrusions at least expose the P-type heavily doped layer 104;

[0104] A plurality of electrodes are formed, each electrode being used for each strip-shaped protrusion to input and output electrical signals; each electrode and each strip-shaped protrusion constitutes a Wheatstone bridge 105;

[0105] A strained thin film layer 107 is formed between the first cavity 106 and the Wheatstone bridge 105 .

[0106] This embodiment differs from the previous embodiment in that, before forming the Wheatstone bridge 105, a first cavity 106 is first formed on a surface of the support layer 101 adjacent to the insulating layer 102. After forming the first cavity 106, the support layer 101 and the insulating layer 102 are bonded together, an N-type device layer 103 is formed on the insulating layer 102, and then a Wheatstone bridge 105 is formed on the N-type device layer 103. This structure can measure absolute pressure.

[0107] According to one embodiment of the present invention, Figure 14 As shown, before performing P-type dense doping on the entire surface of the N-type device layer facing away from the insulating layer to form a P-type dense doped layer in S102, the method further includes:

[0108] S1011 , lightly doping the entire surface of the N-type device layer 103 on one side facing away from the insulating layer 102 with P-type to form a P-type lightly doped layer 113 (no photomask required);

[0109] After performing P-type dense doping on the entire surface of the N-type device layer 103 facing away from the insulating layer 102 to form the P-type dense doped layer 104 in S102 , the method further includes:

[0110] S1031 , forming four strip-shaped protrusions by an etching process, wherein sidewalls of the four strip-shaped protrusions at least expose the P-type lightly doped layer 113 and the P-type heavily doped layer 104 .

[0111] The P-type lightly doped layer 113 can be a P-type lightly doped silicon layer, wherein the lightly doped element can be a boron element. On the first plane, a PN junction is formed between the P-type lightly doped layer 113, the P-type heavily doped layer 104, and the N-type device layer 103. The PN junction of the P-type lightly doped layer 113 has a deeper junction depth, is a body breakdown, and has a higher breakdown voltage, thereby enabling the MEMS pressure sensor to operate at a higher temperature (e.g., an ambient temperature of 175 degrees). In addition, the provision of the P-type heavily doped layer 104 reduces temperature drift, thereby increasing sensor calibration accuracy and reducing test and calibration costs.

[0112] According to one embodiment of the present invention, Figure 15 As shown, S104 forms a plurality of electrodes including:

[0113] S1041, forming a plurality of electrodes by electroplating or sputtering.

[0114] According to one embodiment of the present invention, Figure 16 As shown, S104 forms a plurality of electrodes including:

[0115] S1042 , forming a plurality of electrodes by etching, with the trench sidewalls between the electrodes exposed to at least the surface of the N-type device layer 103 that is not doped with P-type and faces away from the insulation 102 .

[0116] In this embodiment, forming a plurality of electrodes and forming four strip-shaped protrusions are completed in the same step, thereby saving process steps and simplifying the process flow. The structure of the four strip-shaped protrusions is the same as that in the structural embodiment.

[0117] Specifically, Figures 17 to 21 This is a flow chart of a method for manufacturing a MEMS pressure sensor according to one embodiment of the present invention. Figure 17 、 Figure 18 、 Figure 19 、 Figure 22 、 Figure 23 This is a flow chart of a method for manufacturing a MEMS pressure sensor according to another embodiment of the present invention. Figures 24 to 26 This is a flow chart of a method for fabricating a MEMS pressure sensor according to another embodiment of the present invention. In this embodiment, steps common to the previous two embodiments are not shown; please refer to the previous two embodiments. In each of the aforementioned examples, only a single photomask is used, making it easy to achieve a small chip area, low process cost, and mass production feasible.

[0118] In summary, according to the MEMS pressure sensor and its manufacturing method proposed in the embodiment of the present invention, the MEMS pressure sensor includes a support layer, an insulating layer, an N-type device layer and a P-type highly doped layer stacked in sequence along a first direction; wherein the first direction is the direction in which the support layer points perpendicularly to the P-type highly doped layer; four strip-shaped protrusions are arranged on the first plane, and along the first direction, each strip-shaped protrusion includes a P-type highly doped layer, and the first plane is a plane perpendicular to the first direction; a plurality of electrodes, each electrode is used for each strip-shaped protrusion to input and output electrical signals; each electrode and each strip-shaped protrusion constitutes a Wheatstone bridge; the support layer is provided with a first cavity, and a strain film layer is provided between the first cavity and the Wheatstone bridge, so that by providing four strip-shaped protrusions, when the strain film layer is subjected to pressure, the surface stress is the largest at the edge middle and center positions of the strain film layer, and the stress is more concentrated on the surface of the protruding strip-shaped varistor, with high sensitivity and good linearity. In addition, the parasitic parameters between the P-type heavily doped layer and the substrate are smaller, and the layer is closer to an ideal PN junction with the substrate, resulting in a higher breakdown voltage and lower leakage current. Furthermore, the introduction of a lightly doped P-type layer between the P-type heavily doped layer and the N-type device layer deepens the PN junction, further increasing the breakdown voltage and resulting in higher reliability and long-term stability. Due to the high doping concentration on the surface of the strip-shaped protrusions, the device can achieve lower sensitivity temperature drift. This MEMS pressure sensor has a simple structure, and the preparation process for the piezoresistive strips requires only one photomask, resulting in low process costs and suitable for mass production.

[0119] Note that the above are only preferred embodiments of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments, and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments and may include many other equivalent embodiments without departing from the concept of the present invention. The scope of the present invention is determined by the scope of the appended claims.

Claims

1. A MEMS pressure sensor, characterized in that: include: Four strip-shaped protrusions arranged on the first plane, wherein each of the strip-shaped protrusions includes a P-type heavily doped layer; A plurality of electrodes, wherein each of the electrodes is used for each of the strip-shaped protrusions to receive input electrical signals and output electrical signals, and each of the electrodes and each of the strip-shaped protrusions constitutes a Wheatstone bridge; A strained film layer is provided between the cavity and the Wheatstone bridge, Each of the strip-shaped protrusions includes a varistor portion and two wire portions; two ends of the varistor portion are respectively connected to one of the wire portions; wherein the line width of the varistor portion is smaller than the line width of the wire portion.

2. The MEMS pressure sensor according to claim 1, wherein: An N-type device layer is located below the four strip-shaped protrusions. The N-type device layer is a low-doped N-type silicon layer. A PN junction is formed between the P-type heavily doped layer and the N-type device layer. The side walls of the four protrusions at least expose the P-type heavily doped layer.

3. The MEMS pressure sensor according to claim 1, wherein: Each strip-shaped protrusion further includes: a P-type lightly doped layer located below the P-type heavily doped layer, and the sidewalls of the four protrusions at least expose the P-type heavily doped layer and the P-type lightly doped layer. Below the four strip-shaped protrusions is an N-type device layer, which is a low-doped N-type silicon layer. A PN junction is formed between the P-type lightly doped layer, the P-type heavily doped layer and the N-type device layer.

4. The MEMS pressure sensor according to claim 1, wherein: The four strip-shaped protrusions are arranged in parallel, and include a first strip-shaped protrusion, a second strip-shaped protrusion, a third strip-shaped protrusion and a fourth strip-shaped protrusion in sequence; each of the strip-shaped protrusions includes a first wire portion and a second wire portion, the first wire portion and the second wire portion are symmetrically arranged, and the first wire portion and the second wire portion are offset by a preset distance relative to the axis of symmetry, for connecting the varistor portion.

5. The MEMS pressure sensor according to claim 4, wherein: The varistor portion in the first strip-shaped protrusion protrudes outward from the side of the first strip-shaped protrusion away from the second strip-shaped protrusion; the varistor portion in the second strip-shaped protrusion protrudes outward from the side of the second strip-shaped protrusion away from the first strip-shaped protrusion; the varistor portion in the third strip-shaped protrusion protrudes outward from the side of the third strip-shaped protrusion away from the fourth strip-shaped protrusion; the varistor portion in the fourth strip-shaped protrusion protrudes outward from the side of the fourth strip-shaped protrusion away from the third strip-shaped protrusion.

6. The MEMS pressure sensor according to claim 5, characterized in that The varistor portion includes a varistor; the arrangement shape of the varistor in each of the strip-shaped protrusions is one of a U-shape, a V-shape, or a cascade shape composed of multiple V-shapes or U-shapes, and the arrangement shapes of the varistor are all axially symmetrically distributed with the symmetry axis as the central axis.

7. The MEMS pressure sensor according to claim 6, wherein: The shapes of the varistors in the strip-shaped protrusions are the same.

8. The MEMS pressure sensor according to claim 5, wherein: The varistor portion includes a plurality of strip varistors and a third wire portion for connecting the plurality of strip varistors in series; the line width of the strip varistors is much smaller than the line width of the third wire portion; the plurality of strip varistors are all parallel to the axis of symmetry and are axially symmetrically distributed with the axis of symmetry as the central axis, and the plurality of third wire portions are all perpendicular to the axis of symmetry.

9. The MEMS pressure sensor according to claim 1 or 3, characterized in that: The four strip-shaped protrusions are arranged in parallel, and sequentially include a first strip-shaped protrusion, a second strip-shaped protrusion, a third strip-shaped protrusion and a fourth strip-shaped protrusion; The plurality of electrodes include: a first input electrode, a second input electrode, a first output electrode, a second output electrode, a first ground electrode, and a second ground electrode; One end of the first strip-shaped protrusion is connected to the first input electrode, and the other end is connected to the first output electrode; one end of the second strip-shaped protrusion is connected to the first output electrode, and the other end is connected to the first ground electrode; one end of the third strip-shaped protrusion is connected to the second input electrode, and the other end is connected to the second output electrode; one end of the fourth strip-shaped protrusion is connected to the second output electrode, and the other end is connected to the second ground electrode.

10. The MEMS pressure sensor according to claim 9, wherein: The first input electrode, the second input electrode, the first output electrode, the second output electrode, the first ground electrode, and the second ground electrode are all metal electrodes.

11. The MEMS pressure sensor according to claim 9, wherein: The first input electrode, the second input electrode, the first output electrode, the second output electrode, the first ground electrode and the second ground electrode are all arranged in the same layer as the first strip-shaped protrusion, the second strip-shaped protrusion, the third strip-shaped protrusion and the fourth strip-shaped protrusion.

12. The MEMS pressure sensor according to claim 11, wherein: The four strip-shaped protruding regions, the first input electrode region, the first output electrode region, the second output electrode region, the second input electrode region, the first ground electrode region and the second ground electrode region are arranged on the first plane, and the electrode regions are isolated by grooves.

13. A method for manufacturing a MEMS pressure sensor, characterized in that: The method is applied to the MEMS pressure sensor according to any one of claims 1 to 12, comprising the following steps: Providing a substrate, wherein the substrate includes an N-type device layer; Performing P-type dense doping on one side surface of the N-type device layer to form a P-type dense doped layer; Forming four strip-shaped protrusions by an etching process, wherein sidewalls of the four strip-shaped protrusions at least expose the P-type heavily doped layer; forming a plurality of electrodes, each of the electrodes being used for each of the strip-shaped protrusions to input and output electrical signals; each of the electrodes and each of the strip-shaped protrusions forming a Wheatstone bridge; The substrate is etched to form a cavity, and a strained thin film layer is formed between the cavity and the Wheatstone bridge.

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