A TFT-PMUTs based on KNN and stress release grooves, preparation method, application and ultrasonic tactile sensing detection device

Abstract

The present invention discloses a TFT-PMUTs based on KNN and stress release grooves, a preparation method, an application and an ultrasonic tactile sensing detection device, wherein the TFT-PMUTs include a piezoelectric micromechanical ultrasonic transducer and a thin film transistor, wherein the axis of the bottom electrode of each unit in the piezoelectric micromechanical ultrasonic transducer is provided with a unit central pillar, and the center of each piezoelectric micromechanical ultrasonic transducer array element is provided with an array element central pillar; the KNN piezoelectric layer is provided with an array element central pillar in a blank area at the center position of the piezoelectric micromechanical ultrasonic transducer array element; a stress release groove is provided on the structural layer; the array element central pillar and the unit central pillar are connected one by one to the voltage switch of the thin film transistor, and the top electrode at each array element central pillar and the bottom electrode corresponding to each unit central pillar are electrically connected to the voltage switch on the thin film transistor that is opposite to their position; the unit boundary pillar is bonded to the surface of the thin film transistor. The sensor of the present invention can perform tactile perception and track detection, and has high sensitivity, and can be mass-produced.

Description

Technical Field

[0001] The present invention relates to MEMS and ultrasonic transducer technology, and in particular to a TFT-PMUTs based on KNN and stress release grooves for the application field of human-like five-sense tactile perception, a preparation method, an application and an ultrasonic tactile perception detection device. Background Art

[0002] Touch is one of the five senses of human beings, which is used to perceive environmental pressure, temperature, humidity, strain and other stimuli, and realize the information exchange between the human body and the external environment. Inspired by human skin, tactile sensors similar to human sense organs have been rapidly developed in recent years due to their wide applications in medical health, intelligent robots, human-computer interaction and other fields, and have become the forefront and hot spot of research in the field of sensor technology. At present, the common tactile perception principles are mainly based on capacitance, piezoelectricity, piezoresistiveness, optics, ultrasound, etc. Among them, contact tactile sensors such as capacitance, piezoelectricity, and piezoresistiveness have been widely studied, while ultrasonic touch is an emerging perception technology, which is still in its infancy and has little public research. Therefore, there is an urgent need for a tactile perception ultrasonic transducer sensor with high detection sensitivity that is technically feasible and can be mass-produced. Summary of the invention

[0003] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a TFT-PMUTs based on KNN and stress release grooves, a preparation method, an application and an ultrasonic tactile sensing detection device. The sensor of the present invention can perform tactile perception and trajectory detection, has high sensitivity, and can be mass-produced.

[0004] The technical solution adopted by the present invention is as follows:

[0005] A TFT-PMUTs based on KNN and stress release grooves, including a piezoelectric micromechanical ultrasonic transducer and a thin film transistor;

[0006] The piezoelectric micromechanical ultrasonic transducer comprises a plurality of piezoelectric micromechanical ultrasonic transducer array elements distributed in an array, each of which comprises four piezoelectric micromechanical ultrasonic transducer units distributed at the four corners of a square and an array element central support column located at the center of the square;

[0007] The piezoelectric micromechanical ultrasonic transducer unit comprises a structural layer, an insulating layer, a top electrode, a KNN piezoelectric layer, a bottom electrode and a unit boundary pillar, wherein the structural layer, the insulating layer, the top electrode, the KNN piezoelectric layer and the unit boundary pillar are arranged in sequence, a cavity is formed between the unit boundary pillar and the KNN piezoelectric layer, the bottom electrode is arranged on the KNN piezoelectric layer and is located at the axis of the cavity, a unit center pillar is arranged at the axis of the bottom electrode, and a metal pad connected to the bottom electrode is arranged on the unit center pillar;

[0008] All piezoelectric micromechanical ultrasonic transducer units share the structural layer, insulating layer, top electrode, and KNN piezoelectric layer. The KNN piezoelectric layer is provided with a blank area at the center of the piezoelectric micromechanical ultrasonic transducer array element. The blank area extends to the surface of the top electrode. The array element central pillar is arranged in the blank area. The array element central pillar is provided with a metal pad connected to the top electrode. The structural layer is provided with a stress release groove at a position opposite to the unit boundary pillar around each cavity.

[0009] The array form formed by the array element central pillar and all the unit central pillars in the array element of the piezoelectric micromechanical ultrasonic transducer is the same as the array distribution form of the voltage switch on the thin film transistor. The array element central pillar and all the unit central pillars in the array element of the piezoelectric micromechanical ultrasonic transducer are directly opposite to the voltage switches of the thin film transistor one by one, and the voltage switch is bonded to the metal pads on the array element central pillar and the unit central pillar through the conductive metal layer;

[0010] The cell boundary pillar is bonded to the surface of the thin film transistor.

[0011] Preferably, in each piezoelectric micromechanical ultrasonic transducer unit, the lateral dimension of the bottom electrode is smaller than the lateral dimension of the cavity, and the coverage rate of the bottom electrode in the area enclosed by the KNN piezoelectric layer and the cavity is 70%-80%.

[0012] Preferably, the stress release groove is annular in shape, and the stress release groove penetrates the entire structural layer along its depth direction and extends to the surface of the insulating layer.

[0013] Preferably, the inner diameter of the stress release groove is not less than the diameter of the cavity;

[0014] The stress release grooves of two adjacent piezoelectric micromechanical ultrasonic transducer units intersect or have outer circles that are tangent to each other. When intersecting, one stress release groove intersects with the outer circle of the other stress release groove, but the inner circle does not intersect.

[0015] Preferably, the metal pad is made of gold; and the conductive metal layer is made of gold-tin alloy.

[0016] Preferably, all piezoelectric micromechanical ultrasonic transducer array elements share the structural layer, insulating layer, top electrode, and KNN piezoelectric layer.

[0017] Preferably, the structural layer is provided with a protective layer having a buffering effect.

[0018] The present invention uses TFT-PMUTs based on KNN and stress release grooves as signal detection units for fingerprint detection and motion trajectory route detection.

[0019] The present invention also provides an ultrasonic tactile perception detection device, including a data processing unit and a signal detection unit, wherein the signal detection unit adopts the TFT-PMUTs based on KNN and stress release grooves as described above in the present invention, and the data processing unit is connected to the circuit of the thin film transistor and can process the electrical signal sent by the thin film transistor.

[0020] The method for preparing TFT-PMUTs based on KNN and stress release grooves of the present invention as described above comprises the following steps:

[0021] Step (1), oxidizing the lower surface of the single crystal silicon as a structural layer to form a silicon dioxide layer as an insulating layer;

[0022] Step (2), sputtering a top electrode material on the surface of the insulating layer by a magnetron sputtering method to obtain a top electrode;

[0023] Step (3), sputtering a KNN piezoelectric layer material on the surface of the top electrode by a magnetron sputtering method to obtain a KNN piezoelectric layer; photolithography and patterning the KNN piezoelectric layer, and then etching the KNN piezoelectric layer, and stopping the etching at the top electrode to form the blank area;

[0024] Step (4), sputtering a bottom electrode material on the surface of the KNN piezoelectric layer by a magnetron sputtering method, and then dry etching the patterned bottom electrode material to form a bottom electrode;

[0025] Step (5), using a PECVD method to deposit a silicon dioxide insulating layer on the KNN piezoelectric layer, the blank area and the bottom electrode surface;

[0026] Step (6), photolithography the silicon dioxide insulating layer, and etching the silicon dioxide insulating layer using a dry etching method to form a unit boundary pillar, a cavity, an array element center pillar, and a unit center pillar;

[0027] Step (7), sputtering metal pad material by magnetron sputtering, and then preparing metal pads on the array element central pillar and the unit central pillar by dry etching;

[0028] Step (8), sputtering a conductive metal layer material by magnetron sputtering, and then performing photolithography and patterning to prepare a conductive metal layer on the unit boundary pillars, cavities, array element center pillars and unit center pillar surfaces of the piezoelectric micromechanical ultrasonic transducer, as well as the voltage switches on the thin film transistors and the surfaces where the thin film transistors are bonded to the unit boundary pillars;

[0029] Step (9), spin coating a photoresist protective layer on one side of the cavity of the piezoelectric micromechanical ultrasonic transducer, wherein the photoresist protective layer fills all spaces, and the thickness of the photoresist protective layer is higher than the height of the unit boundary pillar, the array element center pillar, and the unit center pillar;

[0030] Step (10), etching the structural layer by a wet etching method to form a stress release groove;

[0031] Step (11), removing the photoresist protective layer;

[0032] Step (12), bonding the array element center pillar and the unit center pillar to the voltage switch, and bonding the unit boundary pillar to the surface of the thin film transistor.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The present invention combines piezoelectric micromechanical ultrasonic transducers (PMUTs) and thin film transistors (TFT) based on KNN and stress release grooves, wherein the thin film transistor is a field effect semiconductor device prepared by micromachining technology, and various circuit functions can be formed by realizing conduction (disconnection) between electrodes. By integrating TFT and PMUTs, the characteristics of TFT as a switching device and a driving device can be used to realize flexible conduction and management of array elements. At the same time, the programmability of the thin film transistor can be used to locally amplify and process the signal generated by each array element separately. As the TFT of the control circuit itself, the parasitic capacitance and crosstalk generated by other components in the circuit can be further avoided, the power consumption and delay of the entire circuit system can be reduced, and the performance of the sensor system can be improved. The TFT-PMUTs of the present invention has a stress release groove, which changes the circumferential fixed support boundary condition of the piezoelectric film of the PMUTs unit to a boundary condition similar to that of a simple support, and can effectively reduce the stiffness of the vibrating film without affecting the piezoelectric drive bending moment, release the edge stress of the film, and greatly increase the amplitude of the film. In addition, compared with the situation that the ultrasonic waves transmitted or received between the traditional PMUTs array elements will propagate in the structural layer and suppress the ultrasonic performance of the surrounding array elements, the isolation groove can reduce the acoustic crosstalk between adjacent array elements and improve the ultrasonic transceiver performance of PMUTs. The present invention has a KNN new piezoelectric material (i.e., a KNN piezoelectric layer is used). Compared with the PZT piezoelectric material, the KNN new piezoelectric material does not contain the toxic heavy metal lead, and the PMUTs prepared by it have significant advantages in the medical and health fields and environmental protection.

[0035] The high-performance TFT-PMUTs preparation process based on KNN and stress release grooves of the present invention is simple, and the prepared PMUT has good structure and performance consistency. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A top view of an array element of a piezoelectric micromechanical ultrasonic transducer of the present invention;

[0037] Figure 2 for Figure 1Longitudinal section along section AA;

[0038] Figure 3 for Figure 1 Bottom view of

[0039] Figure 4 A schematic diagram of a thin film transistor array circuit drive used in the present invention;

[0040] Figure 5 The figure is a process flow chart of preparing TFT-PMUTs based on KNN and stress release grooves of the present invention;

[0041] Figure 6 This is a schematic diagram of the application of TFT-PMUTs based on KNN and stress release grooves for ultrasonic tactile fingerprint detection in the present invention;

[0042] Figure 7 This is a schematic diagram of the application of TFT-PMUTs based on KNN and stress release grooves for ultrasonic slip trajectory detection in the present invention.

[0043] In the figure, 1- piezoelectric micromechanical ultrasonic transducer, 2- thin film transistor, 2-1- voltage switch, 3- TFT glass substrate, 4- structural layer, 5- insulating layer, 6- top electrode, 7- KNN piezoelectric layer, 8- bottom electrode, 9- cavity, 10- unit boundary pillar, 11- stress release groove, 12- single crystal silicon, 13- silicon dioxide insulating layer, 14- pad, 15- gold-tin alloy, 16- photoresist protection layer, 17- bottom electrode connecting wires of each unit, 18- top electrode lead wire, 19- control switch, 20- gate, 21- drain, 22- source, 23- array element center pillar, 24- gold pad, 25- unit center pillar, 26- buffer layer. DETAILED DESCRIPTION

[0044] The present invention is described in detail below with reference to the accompanying drawings and embodiments:

[0045] Reference Figure 1-Figure 4 The present invention is based on KNN and stress release groove TFT-PMUTs, including a piezoelectric micromechanical ultrasonic transducer 1 and a thin film transistor 2; the piezoelectric micromechanical ultrasonic transducer 1 includes a plurality of piezoelectric micromechanical ultrasonic transducer array elements distributed in an array, such as Figure 1-Figure 3 As shown, each piezoelectric micromechanical ultrasonic transducer array element includes four piezoelectric micromechanical ultrasonic transducer units distributed at the four corners of a square and an array element central support 23 located at the center of the square; see Figure 2The piezoelectric micromechanical ultrasonic transducer unit comprises a structural layer 4, an insulating layer 5, a top electrode 6, a KNN piezoelectric layer 7, a bottom electrode 8 and a unit boundary support 10. The structural layer 4, the insulating layer 5, the top electrode 6, the KNN piezoelectric layer 7 and the unit boundary support 10 are arranged in sequence. A cavity 9 is formed between the unit boundary support 10 and the KNN piezoelectric layer 7. The bottom electrode 8 is arranged on the KNN piezoelectric layer 7 and is located at the axis of the cavity 9. A unit central support 25 is arranged at the axis of the bottom electrode 8. The unit central support 25 is provided with a support having a connection with the bottom electrode 8. All piezoelectric micromechanical ultrasonic transducer units share the structural layer 4, insulating layer 5, top electrode 6, and KNN piezoelectric layer 7. All piezoelectric micromechanical ultrasonic transducer array elements also share the structural layer 4, insulating layer 5, top electrode 6 and KNN piezoelectric layer 7. The KNN piezoelectric layer 7 is provided with a blank area at the center of the piezoelectric micromechanical ultrasonic transducer array element. The blank area extends to the surface of the top electrode 6. The array element central pillar 23 is arranged in the blank area. A metal pad connected to the top electrode 6 is provided; a stress release groove 11 is provided on the structural layer 4 at a position opposite to the unit boundary pillar 10 around each cavity 9, and the stress release groove 11 can reduce the influence of mutual crosstalk between each piezoelectric micromechanical ultrasonic transducer unit; the array form formed by the array element central pillar 23 and all unit central pillars 25 in the piezoelectric micromechanical ultrasonic transducer array element is the same as the array distribution form of the voltage switch on the thin film transistor 2, and the array element central pillars 23 and unit central pillars 25 in all piezoelectric micromechanical ultrasonic transducer array elements are distributed in a rectangular form, and the row and column distance of the rectangle is the same as the row and column distance of the array where the voltage switch on the thin film transistor 2 is located, so that it can be ensured that the array element central pillar 23 and the unit central pillar 25 correspond to the voltage switch of the thin film transistor 2 one by one and are directly opposite, and the voltage switch is bonded to the metal pads on the array element central pillar 23 and the unit central pillar 25 through the conductive metal layer; the unit boundary pillar 10 is bonded to the surface of the thin film transistor 2 through the conductive metal layer. Among them, the material of the metal pad is gold, which has good conductivity, and the conductive metal layer adopts gold-tin alloy, which has good conductivity on the one hand and good bonding effect with the metal pad on the other hand.

[0046] The working principle of the TFT-PMUTs based on KNN and stress release grooves of the above structure of the present invention is as follows:

[0047] The outside world generates pressure on the vibrating film of the piezoelectric micromechanical ultrasonic transducer 1. Based on the piezoelectric effect, the unit KNN piezoelectric film (i.e., the KNN piezoelectric layer 7) is deformed in sequence under the drive of the sound pressure and generates a charge change between the upper and lower electrodes. The signal is transmitted to the thin film transistor 2 via the pad 14 and the gold-tin alloy 15. Figure 4When a positive voltage is applied to the horizontal scanning line, the switches of several transistors in the same horizontal direction are turned on, the source and drain are connected, and the vertical data line can send data to the processing circuit connected to the source end, and the TFT circuit uses this to identify and integrate the PMUT unit signal. In the structure of the present invention, the circuit array of the thin film transistor 2 can accurately identify the signal of the piezoelectric micromechanical ultrasonic transducer and accurately collect it to complete the reception of ultrasonic waves.

[0048] Based on the PMUTs of the TFT substrate, the homologous control of ultrasonic emission and reception is realized, and the PMUTs are precisely addressed through the TFT array scanning lines and data lines. The PMUTs excitation voltage is controlled to reach the threshold voltage, so that electrons or holes can form a conduction channel between the source and the drain to form a current, thereby completing the driving of the PMUTs array element. Furthermore, through the addressable array, a specific PMUTs unit is designed to realize ultrasonic emission and reception, and ultrasonic waves with high penetration are emitted to the surface of the skin, and the ultrasonic waves produce echoes of different sizes depending on the depth of the tissue. By using the difference in acoustic wave impedance between the skin and the air, the uneven image of the fingerprint can be distinguished, and the dermis, blood vessels, etc. inside the finger can be penetrated through the epidermis to obtain the physiological information of the dermis layer, and live and 3D fingerprint detection can be performed.

[0049] In the above scheme of the present invention, in each piezoelectric micromechanical ultrasonic transducer unit, the lateral dimension of the bottom electrode 8 is smaller than the lateral dimension of the cavity 9, and the coverage rate of the bottom electrode 8 in the area enclosed by the KNN piezoelectric layer 7 and the cavity 9 is 70%-80%. The shape of the stress release groove 11 is annular, and the stress release groove 11 penetrates the entire structural layer 4 along its depth direction and extends to the surface of the insulating layer 5. This structure can further facilitate the deformation of the vibrating film of the entire piezoelectric micromechanical ultrasonic transducer 1, reduce the influence of mutual crosstalk, and make the detection more sensitive. The inner diameter of the stress release groove 11 is not less than the diameter of the cavity 9; the stress release grooves 11 of two adjacent piezoelectric micromechanical ultrasonic transducer units intersect or are tangent to each other. When intersecting, one stress release groove 11 intersects with the outer circle of the other stress release groove 11, and the inner circle does not intersect. This structure can further facilitate the deformation of the vibrating film of the entire piezoelectric micromechanical ultrasonic transducer 1, reduce the influence of mutual crosstalk, and make the detection more sensitive.

[0050] The present invention can also provide a protective layer with a buffering effect on the surface of the structural layer 4 to prevent the structural layer 4 from being scratched, thereby increasing the service life of the entire device.

[0051] The TFT-PMUTs based on KNN and stress release grooves of the present invention are used as a signal detection unit during fingerprint detection and motion trajectory route detection.

[0052] The present invention also provides an ultrasonic tactile perception detection device, including a data processing unit and a signal detection unit, wherein the signal detection unit adopts the TFT-PMUTs based on KNN and stress release grooves as described above in the present invention, and the data processing unit is connected to the circuit of the thin film transistor 2 and can process the electrical signal sent by the thin film transistor 2.

[0053] See also Figure 5 The method for preparing TFT-PMUTs based on KNN and stress release grooves of the present invention as described above comprises the following steps:

[0054] Step (1), taking a low-resistance double-sided polished single crystal silicon wafer (resistivity less than 0.001Ω·cm), using the single crystal silicon 12 as the structural layer 4, and oxidizing the lower surface of the single crystal silicon 12 by a wet oxidation or dry oxidation combined process to generate a silicon dioxide layer as the insulating layer 5;

[0055] Step (2), using a magnetron sputtering method to sputter a top electrode material on the surface of the insulating layer 5 to obtain a top electrode 6, wherein the top electrode material may be metal molybdenum;

[0056] Step (3), sputtering a KNN piezoelectric layer material on the surface of the top electrode 6 by a magnetron sputtering method to form a 1 μm thick KNN piezoelectric film, the KNN piezoelectric film being used as the KNN piezoelectric layer 7; photolithography and patterning the KNN piezoelectric layer 7, and then etching the KNN piezoelectric layer 7, the etching stopping at the top electrode 6, to form the blank area;

[0057] Step (4), using a magnetron sputtering method to sputter a bottom electrode material on the surface of the KNN piezoelectric layer 7, and then patterning the bottom electrode material by photolithography and dry etching to form a bottom electrode 8, where the bottom electrode material can be made of metal molybdenum;

[0058] Step (5), using a PECVD method to deposit a silicon dioxide insulating layer 13 on the surface of the KNN piezoelectric layer 7, the blank area and the bottom electrode 8;

[0059] Step (6), photolithography the silicon dioxide insulating layer 13, and etching the silicon dioxide insulating layer 13 using a dry etching method to form a unit boundary pillar 10, a cavity 9, an array element center pillar 23, and a unit center pillar 25;

[0060] Step (7), sputtering the metal pad material gold by magnetron sputtering, and then patterning the gold layer by dry etching to obtain metal pads on the array element central pillar 23 and the unit central pillar 25;

[0061] Step (8), sputtering a conductive metal layer material of gold-tin alloy by magnetron sputtering, and then patterning by photolithography, to prepare a conductive metal layer on the surface of the unit boundary pillar 10, the cavity 9, the array element center pillar 23 and the unit center pillar 25 of the piezoelectric micromechanical ultrasonic transducer 1, and the voltage switch on the thin film transistor 2 and the surface where the thin film transistor 2 is bonded to the unit boundary pillar 10;

[0062] Step (9), spin coating a photoresist protective layer 16 on one side of the cavity 9 of the piezoelectric micromechanical ultrasonic transducer 1, wherein the photoresist protective layer 16 fills all spaces, and the thickness of the photoresist protective layer 16 is higher than the height of the unit boundary pillar 10, the array element center pillar 23, and the unit center pillar 25;

[0063] Step (10), etching the structural layer 4 by a wet etching method to form a stress release groove 11;

[0064] Step (11), removing the photoresist protection layer 16;

[0065] Step (12), bonding the array element central pillar 23 and the unit central pillar 25 to the voltage switch, and bonding the unit boundary pillar 10 to the surface of the thin film transistor 2.

[0066] In the above-mentioned preparation process of the present invention, the electrical connection between the upper and lower electrodes of the PMUTs and the TFT circuit is achieved by means of the flip-chip isolation trench technology.

[0067] Secondly, KNN piezoelectric layer materials can achieve high piezoelectricity similar to PZT (d31=140×10 -12 C / N), high Curie temperature (Tc=420℃) and high electromechanical coupling coefficient can improve the transmit and receive sensitivity of PMUT. In addition, KNN film can be prepared by sputtering, sol-gel method and other methods, with dense and uniform structure, small nano size, good electrical insulation and excellent MEMS process compatibility.

[0068] Example

[0069] like Figure 1-Figure 5 As shown, in this embodiment, the coverage of the bottom electrode 8 in the area enclosed by the KNN piezoelectric layer 7 and the cavity 9 is 70%. The shape of the stress release groove 11 is annular, and the stress release groove 11 penetrates the entire structural layer 4 along its depth direction and extends to the surface of the insulating layer 5. The stress release groove 11 of this structure makes the circumferential fixed support boundary condition of the PMUT unit piezoelectric film become a boundary condition close to that of a simple support, which can effectively reduce the stiffness of the vibrating film without affecting the piezoelectric driving bending moment, release the edge stress of the film, greatly increase the amplitude of the film, and reduce the crosstalk between adjacent array elements, thereby improving the PMUT ultrasonic transceiver performance.

[0070] Figure 4 The figure shows a schematic diagram of the TFT-PMUTs array circuit drive. The rectangle is the voltage switch 2-2 of the TFT, the horizontal line is the scan line, and the horizontal line is connected to the gate end of the TFT; the vertical line is the data line, and the vertical line is connected to the drain end of the TFT. When a positive voltage is applied to each horizontal scan line, the switches of several transistors in the same horizontal direction are turned on, the source and drain are connected, and the vertical data line can send data to the processing circuit connected to the source end. The combination of the horizontal scan line and the data line realizes the index similar to the matrix row and column, completes the addressable excitation of the PMUTs array element, and then realizes the excitation control of the high-pixel PMUTs array element.

[0071] See also Figure 5 The method for preparing TFT-PMUTs based on KNN and stress release grooves in this embodiment specifically includes the following steps:

[0072] (1) taking a low-resistance double-sided polished single-crystalline silicon wafer as the structural layer 4, and using a wet oxidation or dry oxidation combined process to oxidize the lower surface of the single-crystalline silicon wafer to form a silicon dioxide insulating layer, and the silicon dioxide insulating layer is used as the insulating layer 5;

[0073] (2) magnetron sputtering, sputtering a layer of molybdenum top electrode on the surface of the insulating layer 5;

[0074] (3) preparing a KNN piezoelectric material target, sputtering a layer of KNN piezoelectric film on the molybdenum top electrode layer by magnetron sputtering, the KNN piezoelectric film being used as the KNN piezoelectric layer 7, and the sputtering thickness being 1 μm; photolithography, patterning the KNN piezoelectric film, and then etching the KNN piezoelectric film, stopping the etching at the molybdenum top electrode layer, and processing the blank area on the surface of the KNN piezoelectric layer 7;

[0075] (4) sputtering a molybdenum bottom electrode layer on the surface of the KNN piezoelectric layer 7 and the blank area by magnetron sputtering; photolithography and dry etching to form a bottom electrode 8;

[0076] (5) depositing a silicon dioxide insulating layer 13 on the lower portion of the structure processed in step (4) by using a PECVD method;

[0077] (6) photolithography of the silicon dioxide insulating layer 13, and etching the silicon dioxide insulating layer 13 by dry etching to form the unit boundary pillar 10, the cavity 9, the array element center pillar 23 and the unit center pillar 25;

[0078] (7) sputtering a layer of gold on the lower surface of the structure obtained in step (6) by magnetron sputtering, and patterning the gold layer by dry etching to form gold pads on the surfaces of the array element central pillar 23 and the unit central pillar 25;

[0079] (8) magnetron sputtering a layer of gold-tin alloy 15 on the lower surface of the structure obtained in step (7), photolithography and patterning are performed so that the gold-tin alloy 15 on the surface of the unit boundary pillar 10, the cavity 9, the array element center pillar 23 and the unit center pillar 25 is retained; magnetron sputtering a layer of gold-tin alloy 15 on the voltage switch on the thin film transistor 2 and the surface where the thin film transistor 2 is bonded to the unit boundary pillar 10, the gold-tin alloy 15 on the voltage switch is consistent in area with the gold-tin alloy 15 on the array element center pillar 23 and the unit center pillar 25, and the gold-tin alloy 15 on the unit boundary pillar 10 is consistent in area with the gold-tin alloy 15 at the bonding connection portion between the thin film transistor 2 and the unit boundary pillar 10;

[0080] (9) On the back of PMUT ( Figure 5 The lower part of the structure obtained in step (8) is spin-coated with a photoresist protective layer 16, which fills all cavities and has a thickness higher than the height of all pillars;

[0081] (10) etching the top structural layer 4 by a wet etching method to form a stress release groove 11;

[0082] (11) removing the photoresist protective layer 16;

[0083] (12) Bonding: performing gold-tin bonding on corresponding positions of the piezoelectric micromechanical ultrasonic transducer 1 and the thin film transistor 2.

[0084] like Figure 6 As shown, when tactile applications are performed, the thin film transistor 2 is located at the bottom layer, the piezoelectric micromechanical ultrasonic transducer 1 is correspondingly combined with the array of the thin film transistor 2, and the buffer layer 26 is a protective layer to prevent the surface of the TFT-PMUTs device from being damaged by direct contact with the finger. The specific implementation method is that the finger is located on the surface of the buffer layer to apply pressure, and at the same time, the PMUTs emit ultrasonic waves with high penetration. The sound waves penetrate the buffer layer to reach the skin surface, and different echoes are generated with different depths of the finger skin tissue. The difference in acoustic impedance between the skin and the air can be used to receive different signals of the thin film transistor 2, and the signal of the thin film transistor 2 is processed to distinguish the uneven image of the fingerprint.

[0085] like Figure 7As shown in the figure, the specific implementation process of slide rail posture perception and recognition is as follows: the finger slides non-contact on the surface of the TFT-PMUTs sensor, and an AC voltage is loaded to excite the TFT array. The excitation signal is transmitted to the corresponding PMUT unit through the TFT array. The KNN piezoelectric vibrates due to the inverse piezoelectric effect. The PMUTs array element emits ultrasonic waves outward. The ultrasonic waves propagate to the surface of the sliding finger and are reflected. The reflected waves are received by the PMUT array elements. After the signal is transmitted to the TFT array, the reflected signals are collected and post-processed, and each delayed signal is inverted to obtain a finger motion trajectory map, thereby sensing the sliding trajectory of the fingertip on the sensor surface.

[0086] It can be seen from the above scheme that the present invention can effectively improve the main performances of PMUT such as electromechanical coupling coefficient and transceiver sensitivity. The present invention develops a TFT-PMUTs preparation process and develops a new type of PMUTs based on TFT substrate with high performance and flexible array element control. The specific PMUTs unit is designed through the TFT addressable array to realize ultrasonic emission and reception. The difference in acoustic wave impedance between skin and air is used to distinguish the uneven image of fingerprints. The dermis and blood vessels inside the finger can pass through the epidermis to obtain the physiological information of the dermis, and live and 3D fingerprint detection can be performed, thereby realizing the application in the field of ultrasonic tactile perception.

[0087] The above are only several embodiments of the present invention, not all or the only embodiments. Any equivalent changes made to the technical solution of the present invention by ordinary technicians in this field after reading the specification of the present invention are covered by the claims of the present invention.

Claims

1. A TFT-PMUTs based on KNN and stress release grooves, characterized in that: It comprises a piezoelectric micromechanical ultrasonic transducer (1) and a thin film transistor (2); The piezoelectric micromechanical ultrasonic transducer (1) comprises a plurality of piezoelectric micromechanical ultrasonic transducer array elements distributed in an array, each of the piezoelectric micromechanical ultrasonic transducer array elements comprising four piezoelectric micromechanical ultrasonic transducer units distributed at the four corners of a square and an array element central support (23) located at the center of the square; The piezoelectric micromechanical ultrasonic transducer unit comprises a structural layer (4), an insulating layer (5), a top electrode (6), a KNN piezoelectric layer (7), a bottom electrode (8) and a unit boundary pillar (10), wherein the structural layer (4), the insulating layer (5), the top electrode (6), the KNN piezoelectric layer (7) and the unit boundary pillar (10) are arranged in sequence, a cavity (9) is formed between the unit boundary pillar (10) and the KNN piezoelectric layer (7), the bottom electrode (8) is arranged on the KNN piezoelectric layer (7) and is located at the axis of the cavity (9), a unit center pillar (25) is provided at the axis of the bottom electrode (8), and a metal pad connected to the bottom electrode (8) is provided on the unit center pillar (25); All piezoelectric micromechanical ultrasonic transducer units share the structural layer (4), the insulating layer (5), the top electrode (6), and the KNN piezoelectric layer (7); the KNN piezoelectric layer (7) is provided with a blank area at the center position of the piezoelectric micromechanical ultrasonic transducer array element, the blank area extends to the surface of the top electrode (6), the array element center pillar (23) is arranged in the blank area, and the array element center pillar (23) is provided with a metal pad connected to the top electrode (6); the structural layer (4) is provided with a stress release groove (11) at a position opposite to the unit boundary pillar (10) around each cavity (9); The array form formed by the array element central pillar (23) and all the unit central pillars (25) in the piezoelectric micromechanical ultrasonic transducer array element is the same as the array distribution form of the voltage switch on the thin film transistor (2); the array element central pillar (23) and all the unit central pillars (25) in the piezoelectric micromechanical ultrasonic transducer array element are directly opposite to the voltage switches of the thin film transistor (2), and the voltage switches are bonded to the metal pads on the array element central pillar (23) and the unit central pillar (25) through the conductive metal layer; The cell boundary pillar (10) is bonded to the surface of the thin film transistor (2).

2. The TFT-PMUTs based on KNN and stress release grooves according to claim 1, characterized in that: In each piezoelectric micromechanical ultrasonic transducer unit, the lateral dimension of the bottom electrode (8) is smaller than the lateral dimension of the cavity (9), and the coverage rate of the bottom electrode (8) in the area enclosed by the KNN piezoelectric layer (7) and the cavity (9) is 70%-80%.

3. The TFT-PMUTs based on KNN and stress release grooves according to claim 1, characterized in that: The stress release groove (11) is annular in shape, and the stress release groove (11) penetrates the entire structural layer (4) along its depth direction and extends to the surface of the insulating layer (5).

4. The TFT-PMUTs based on KNN and stress release grooves according to claim 1, characterized in that: The inner diameter of the stress release groove (11) is not less than the diameter of the cavity (9); The stress release grooves (11) of two adjacent piezoelectric micromechanical ultrasonic transducer units intersect or have outer circles that are tangent to each other. When intersecting, one stress release groove (11) intersects with the outer circle of the other stress release groove (11), but the inner circle does not intersect.

5. The TFT-PMUTs based on KNN and stress release grooves according to claim 1, characterized in that: The material of the metal pad is gold; the conductive metal layer is made of gold-tin alloy.

6. The TFT-PMUTs based on KNN and stress release grooves according to claim 1, characterized in that: All piezoelectric micromechanical ultrasonic transducer array elements share the structural layer (4), insulating layer (5), top electrode (6), and KNN piezoelectric layer (7).

7. The TFT-PMUTs based on KNN and stress release grooves according to claim 1, characterized in that: The structural layer (4) is provided with a protective layer having a buffering effect.

8. The application of TFT-PMUTs based on KNN and stress release grooves according to any one of claims 1 to 7, characterized in that: The KNN- and stress-releasing groove-based TFT-PMUTs are used as signal detection units for fingerprint detection and motion trajectory detection.

9. An ultrasonic tactile sensing detection device, characterized in that: It comprises a data processing unit and a signal detection unit, the signal detection unit adopts the TFT-PMUTs based on KNN and stress release grooves according to any one of claims 1 to 7, and the data processing unit is connected to the circuit of the thin film transistor (2) and can process the electrical signal sent by the thin film transistor (2).

10. The method for preparing TFT-PMUTs based on KNN and stress release grooves according to any one of claims 1 to 7, characterized in that: The steps include: Step (1), oxidizing the lower surface of the single crystal silicon (12) as the structural layer (4) to form a silicon dioxide layer as the insulating layer (5); Step (2), sputtering a top electrode material on the surface of the insulating layer (5) by a magnetron sputtering method to obtain a top electrode (6); Step (3), sputtering a KNN piezoelectric layer material on the surface of the top electrode (6) by a magnetron sputtering method to obtain a KNN piezoelectric layer (7); photolithography and patterning the KNN piezoelectric layer (7), and then etching the KNN piezoelectric layer (7), wherein the etching stops at the top electrode (6) to form the blank area; Step (4), using a magnetron sputtering method to sputter a bottom electrode material on the surface of the KNN piezoelectric layer (7), and then dry-etching the patterned bottom electrode material to form a bottom electrode (8); Step (5), using a PECVD method to deposit a silicon dioxide insulating layer (13) on the surface of the KNN piezoelectric layer (7), the blank area and the bottom electrode (8); Step (6), photolithography of the silicon dioxide insulating layer (13), etching the silicon dioxide insulating layer (13) using dry etching to form a unit boundary pillar (10), a cavity (9), an array element center pillar (23), and a unit center pillar (25); Step (7), sputtering a metal pad material by magnetron sputtering, and then preparing a metal pad on the array element central pillar (23) and the unit central pillar (25) by dry etching; Step (8), sputtering a conductive metal layer material by magnetron sputtering, and then performing photolithography and patterning to prepare a conductive metal layer on the surface of the unit boundary pillar (10), the cavity (9), the array element center pillar (23) and the unit center pillar (25) of the piezoelectric micromechanical ultrasonic transducer (1), as well as the voltage switch on the thin film transistor (2) and the surface where the thin film transistor (2) is bonded to the unit boundary pillar (10); Step (9), spin coating a photoresist protective layer (16) on one side of the cavity (9) of the piezoelectric micromechanical ultrasonic transducer (1), wherein the photoresist protective layer (16) fills all spaces, and the thickness of the photoresist protective layer (16) is higher than the height of the unit boundary pillar (10), the array element center pillar (23), and the unit center pillar (25); Step (10), etching the structural layer (4) by a wet etching method to form a stress release groove (11); Step (11), removing the photoresist protective layer (16); Step (12), bonding the array element central pillar (23) and the unit central pillar (25) to the voltage switch, and bonding the unit boundary pillar (10) to the surface of the thin film transistor (2).

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