An ultrasonic sensor based on TFT transistor and a preparation process thereof

Abstract

The application relates to the technical field of semiconductor processes, in particular to an ultrasonic sensor based on a TFT transistor and a preparation process thereof, and the structure comprises a substrate, a functional layer and a TFT transistor, the substrate has opposite front and back surfaces; the functional layer is arranged on the front surface of the substrate, and the TFT transistor is arranged on the front surface of the functional layer; the process comprises: growing the functional layer on the front surface of the substrate and growing the TFT transistor on the front surface of the functional layer. The functional layer is arranged in the functional layer between the TFT transistor and the substrate, the propagation path of the sound wave in the sensor is optimized, the energy loss is reduced, and the sound wave energy conversion efficiency of the piezoelectric layer is significantly improved. Meanwhile, the PZT material is used to replace the PVDF material to grow on the substrate as the piezoelectric material, the PZT material has the characteristics of high piezoelectric constant and high dielectric constant, and the whole sensor has the characteristics of high resolution, high signal-to-noise ratio, high sensitivity and high penetration.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of TFT transistor-based ultrasonic sensor, and particularly relates to a TFT transistor-based ultrasonic sensor and a preparation process thereof. BACKGROUND

[0002] At present, an ultrasonic sensor is a sensor for converting an ultrasonic signal into other energy signals. The ultrasonic wave is a mechanical wave with a vibration frequency higher than 20 kHz. It has the characteristics of high frequency, short wavelength, small diffraction, good directionality, directional propagation as a ray, and the like. The ultrasonic wave has great penetration power for liquids and solids, especially in sunlight opaque solids. The ultrasonic wave will produce a significant reflection to form a reflected echo when it encounters impurities or interfaces, and will produce a Doppler effect when it encounters moving objects. The ultrasonic sensor is widely used in industry, national defense, biomedicine and the like.

[0003] As an important structure of the existing ultrasonic sensor, PVDF and PZT are two kinds of piezoelectric materials widely used in the fields of sensors, transducers and energy collection, but the use of PVDF piezoelectric film on the substrate is the mainstream product at present. However, compared with PZT material, the PVDF material has low piezoelectric constant, low electromechanical coupling efficiency and low dielectric constant, is not suitable for high energy density application, and has poor temperature stability and durability.

[0004] The ultrasonic fingerprint identification technology can be applied to user authentication of mobile phones and tablet computers, access control systems and identity confirmation of mobile payment, has a wide application field, and can provide a high-security biometric authentication method. The ultrasonic fingerprint identification technology adopts an ultrasonic sensor combined with a TFT transistor. The piezoelectric layer of the current ultrasonic sensor is arranged on the front surface of the TFT transistor, and the upper buffer layer is arranged on the functional layer of the front surface of the substrate, and then the TFT transistor is arranged. Such a structure limits the sound wave energy conversion efficiency of the piezoelectric layer, and the existence of the upper buffer layer may affect the electrical connection stability between the piezoelectric layer and the TFT transistor.

[0005] For example, the thesis document of the University of Electronic Science and Technology entitled "Research on Ultrasonic Fingerprint Identification Technology Based on TFT Transistor", the author is Shang Fei, which mentions that a piezoelectric layer is prepared on the surface of the TFT transistor. Although the process does not easily damage the TFT thin film device, it is not conducive to improving the conversion efficiency of the piezoelectric layer.

[0006] Therefore, in order to improve the performance of the ultrasonic sensor, the application proposes an innovative design, that is, the piezoelectric layer is arranged in the special functional layer between the TFT transistor and the substrate. Such a layout not only can optimize the propagation path of the sound wave inside the sensor, reduce the energy loss, but also can enhance the interaction between the piezoelectric layer and the TFT transistor, improve the conversion efficiency and stability of the electrical signal, so that the sensor has the characteristics of high resolution, high signal-to-noise ratio, high sensitivity and high penetration. SUMMARY

[0007] In view of the above problems, the application aims to provide a TFT transistor-based ultrasonic sensor and a preparation process thereof. Through specific structural design, the propagation path of the sound wave and the interaction between the piezoelectric layer and the TFT transistor are optimized. Meanwhile, PZT material is used to replace PVDF material to grow on the substrate as a piezoelectric material. By using the characteristics of high piezoelectric constant and high dielectric constant of the PZT material, the entire sensor has the characteristics of high resolution, high signal-to-noise ratio, high sensitivity and high penetration.

[0008] The object of the application can be achieved by the following technical solution: a TFT transistor-based ultrasonic sensor, comprising:

[0009] a substrate, the substrate having opposite front and back surfaces;

[0010] a functional layer, the functional layer being grown on the front surface of the substrate; and

[0011] a TFT transistor, the TFT transistor being grown on the front surface of the functional layer.

[0012] The functional layer comprises a first piezoelectric layer.

[0013] In an embodiment of the application, the functional layer comprises a first buffer layer, a first piezoelectric layer and a second buffer layer, which are sequentially stacked on the front surface of the substrate.

[0014] In an embodiment of the application, the first piezoelectric layer comprises a first metal layer, a first piezoelectric film and a second metal layer which are sequentially stacked on the first buffer layer, wherein the material of the first piezoelectric film is PZT.

[0015] In an embodiment of the application, the front surface of the TFT transistor is provided with a second piezoelectric layer.

[0016] In an embodiment of the application, the back surface of the substrate is provided with a third buffer layer and a third piezoelectric layer, which are sequentially stacked on the back surface of the substrate.

[0017] The application also provides a preparation process of the TFT transistor-based ultrasonic sensor, comprising the following steps:

[0018] S1a, preparing a substrate having opposite front and back surfaces, and growing the functional layer on the front surface of the substrate;

[0019] S2a, growing the TFT transistor on the front surface of the functional layer and making a via hole on the TFT transistor for connecting the TFT transistor with the first piezoelectric layer.

[0020] In an embodiment of the application, the preparation process further comprises:

[0021] S3a, growing the second piezoelectric layer on the TFT transistor and patterning the second piezoelectric layer, wherein the second piezoelectric layer is connected with the TFT transistor through the via hole.

[0022] The application also provides a preparation process of the TFT transistor-based ultrasonic sensor, comprising the following steps:

[0023] S1b, preparing a substrate having opposite front and back surfaces, and growing the functional layer on the front surface of the substrate;

[0024] S2b, growing the third buffer layer on the back surface of the substrate

[0025] S3b, growing the third piezoelectric layer on the back surface of the third buffer layer and patterning the third piezoelectric layer; and

[0026] S4b, growing the TFT transistor on the front surface of the functional layer and making a TGV on the TFT transistor for connecting the third piezoelectric layer with the TFT transistor and connecting the functional layer with the TFT transistor.

[0027] In an embodiment of the application, the preparation process further comprises the following steps:

[0028] S5b, growing the second piezoelectric layer on the front surface of the TFT transistor and patterning the second piezoelectric layer, wherein the second piezoelectric layer is connected with the TFT transistor through a via hole.

[0029] In an embodiment of the application, the growing of the functional layer in the S1a or the S1b comprises the following steps:

[0030] S1-1, growing the first buffer layer on the front surface of the substrate;

[0031] S1-2, growing the first metal layer, the first piezoelectric thin film and the second metal layer on the front surface of the first buffer layer in sequence and patterning the first metal layer, the first piezoelectric thin film and the second metal layer; and

[0032] S1-3, growing the second buffer layer on the front surface of the second metal layer.

[0033] In an embodiment of the present application, the preparation process further comprises the following steps:

[0034] S4a, growing the third buffer layer on the back surface of the substrate;

[0035] S5a, growing the third piezoelectric layer on the back surface of the third buffer layer and patterning the third piezoelectric layer, the third piezoelectric layer being connected to the TFT transistor through TGV.

[0036] Advantages of the present application:

[0037] 1. The piezoelectric layer is arranged in the functional layer between the TFT transistor and the substrate, which optimizes the propagation path of the acoustic wave inside the sensor, reduces the energy loss, significantly improves the acoustic wave energy conversion efficiency of the piezoelectric layer, and makes the sensor have the characteristics of high resolution, high signal-to-noise ratio, high sensitivity and high penetration. The synergistic design of the upper buffer layer and the piezoelectric layer in the functional layer reduces the lattice mismatch between the substrate and the piezoelectric layer, improves the crystalline quality of the piezoelectric layer, and further ensures the stability of energy conversion. The layer-by-layer layout of the functional layer and the TFT transistor strengthens the interaction between the piezoelectric layer and the TFT transistor, and improves the conversion efficiency and connection stability of the electrical signal.

[0038] 2. The present application adopts high-performance piezoelectric materials such as PZT (compared with traditional PVDF materials, it has higher piezoelectric constant, electromechanical coupling efficiency and dielectric constant), which is suitable for high energy density application scenarios and enhances the sensing sensitivity of the sensor to ultrasonic signals.

[0039] 3. The design of the third piezoelectric layer on the back surface of the substrate and the second piezoelectric layer on the front surface of the TFT transistor realizes the bidirectional reception and conversion of ultrasonic signals, widens the dynamic response range of the sensor, and at the same time, through the mutual support of the multi-layer structure, enhances the mechanical stability of the overall structure.

[0040] 4. The process of the present application takes into account the quality of the thin film and the bonding force between the layers, reduces the risk of layer peeling or performance degradation. The application of sol-gel process and magnetron sputtering process fully utilizes the advantages of each process, simplifies the preparation steps and reduces the process complexity while ensuring performance. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 Structure diagram of ultrasonic sensor proposed for embodiment 1 of the present application;

[0042] Figure 2 Structure diagram of ultrasonic sensor proposed for embodiment 2 of the present application;

[0043] Figure 3 Structure diagram of ultrasonic sensor proposed for embodiment 3 of the present application;

[0044] Figure 4 Structure diagram of ultrasonic sensor proposed for embodiment 4 of the present application;

[0045] Figures 5 to 9 Process flow diagram of ultrasonic sensor preparation proposed for embodiment 5 of the present application;

[0046] Figure 10 and Figure 11 Process flow diagram of ultrasonic sensor preparation proposed for embodiment 6 of the present application;

[0047] Figures 12 to 14 Process flow diagram of ultrasonic sensor preparation proposed for embodiment 7 of the present application;

[0048] Figures 15 to 19 Process flow diagram of ultrasonic sensor preparation proposed for embodiment 8 of the present application;

[0049] Figure 20 Process flow diagram of ultrasonic sensor preparation proposed for embodiment 9 of the present application;

[0050] 10, substrate;

[0051] 20, functional layer; 201, first buffer layer; 202, first piezoelectric layer; 203, second buffer layer; 2021, first metal layer; 2022, first piezoelectric film; 2023, second metal layer;

[0052] 30, TFT transistor;

[0053] 40, TGV / via hole;

[0054] 50, second piezoelectric layer; 501, third metal layer; 502, second piezoelectric film; 503, fourth metal layer;

[0055] 60, third buffer layer;

[0056] 70 third piezoelectric layer; 701, fifth metal layer; 702, third piezoelectric film; 703, sixth metal layer. DETAILED DESCRIPTION

[0057] Embodiments of the present application are described below by way of example with reference to the accompanying drawings, in which like or similar elements or components are designated by like reference numerals, and in which the various elements whose function can be the same are generally designated by the same reference numerals throughout the drawings. The embodiments described below are examples only, and are not to be construed as limiting the present application.

[0058] Embodiment 1

[0059] Please refer to Figure 1 The TFT transistor-based ultrasonic sensor proposed in this embodiment includes a substrate 10, a functional layer 20, and a TFT transistor 30 arranged in sequence.

[0060] Optionally, the thickness of the substrate 10 is 150-1500 μm, the material of the substrate 10 is a glass substrate, the substrate 10 can also be made of sapphire, and the functional layer 20 is arranged on the front surface of the substrate 10. Specifically, the functional layer 20 includes a first buffer layer 201, a first piezoelectric layer 202, and a second buffer layer 203, which are grown in sequence on the front surface of the substrate 10.

[0061] Specifically, the first piezoelectric layer 202 includes a first metal layer 2021, a first piezoelectric film 2022, and a second metal layer 2023, which are grown in sequence on the front surface of the first buffer layer, and the material of the first piezoelectric film 2022 is PZT.

[0062] Finally, the TFT transistor 30 is arranged on the front surface of the first piezoelectric layer 202, and a via hole 40 is formed on the TFT transistor 30 to realize the communication between the TFT transistor 30 and the first piezoelectric layer 202. The ultrasonic sensor in this embodiment can realize signal transmission.

[0063] When this structure is adopted, the material of the first piezoelectric film 2022 is PZT, which has higher piezoelectric constant, electromechanical coupling efficiency, and dielectric constant than PVDF material, which is conducive to improving the signal-to-noise ratio and resolution of the sensor. In addition, the PZT material also has good stability and durability, and can maintain stable performance in various environments, which is conducive to the long-term stable operation of the ultrasonic sensor.

[0064] When the piezoelectric film of the sensor with a conventional structure adopts a PVDF polymer, the penetration ability of the ultrasonic fingerprint to the sensor cover plate is generally not more than 400 µm, while when the piezoelectric film of the sensor with the structure of the present application adopts PZT material, the penetration ability of the ultrasonic fingerprint to the sensor cover plate can be greater than 1000 µm.

[0065] Embodiment 2

[0066] Please refer to Figure 2 The ultrasonic sensor in this embodiment is based on the preferred scheme of the ultrasonic sensor in Embodiment 1. The ultrasonic sensor further comprises a second piezoelectric layer 50 grown on the front surface of the TFT transistor 30, and the second piezoelectric layer 50 is communicated with the TFT transistor 30 through the via 40. Specifically, the second piezoelectric layer 50 comprises a third metal layer 501, a second piezoelectric film 502, and a fourth metal layer 503, which are grown on the front surface of the TFT transistor 30. In this embodiment, the material of the second piezoelectric film 502 can be PZT or PVDF.

[0067] The ultrasonic sensor in this embodiment can realize signal transmission and reception. The second piezoelectric layer 50 is arranged to improve the receiving sensitivity of the ultrasonic signal. Since the first piezoelectric layer 202 is closely combined with the TFT transistor 30, the electric charge converted by the piezoelectric effect can be quickly collected by the TFT transistor 30, thereby improving the signal conversion efficiency. At the same time, the design of the multi-layer piezoelectric film can enhance the piezoelectric effect, thereby further improving the receiving strength of the ultrasonic signal.

[0068] Embodiment 3:

[0069] Please refer to Figure 3 The ultrasonic sensor in this embodiment is based on the preferred scheme of the ultrasonic sensor in Embodiment 1. The ultrasonic sensor further comprises a third buffer layer 60 and a third piezoelectric layer 70. Specifically, the third buffer layer 60 and the third piezoelectric layer 70 are sequentially grown on the back surface of the substrate 10.

[0070] Optionally, the third piezoelectric layer 70 comprises a fifth metal layer 701, a third piezoelectric film 702, and a sixth metal layer 703. Specifically, the fifth metal layer 701, the third piezoelectric film 702, and the sixth metal layer 703 are sequentially grown on the back surface of the third buffer layer 60. The material of the third piezoelectric film 702 is PZT or PVDF. The third piezoelectric layer 70 can be communicated with the TFT transistor 30 through the TGV (Through-Glass-Via) 40, or can be communicated with the TFT transistor 30 through subsequent packaging wire bonding.

[0071] The ultrasonic sensor in this embodiment can also realize signal transmission and reception, that is, the first piezoelectric layer 202 transmits signals, and the second piezoelectric layer 50 and the third piezoelectric layer 70 receive signals, and the structural signal is stronger. By setting the third piezoelectric layer 70, the reception and conversion of ultrasonic signals can be realized, and the signal-to-noise ratio and resolution of the ultrasonic sensor are improved. By precisely controlling the composition and structure of the third piezoelectric layer 70, the piezoelectric effect of the sensor can be effectively improved, thereby enhancing the response capability to ultrasonic signals. At the same time, the stable structure of the third piezoelectric layer 70 helps to reduce the influence of environmental factors on the performance of the sensor, and improves the long-term stability and reliability of the sensor.

[0072] Embodiment 4:

[0073] Please refer to Figure 4 The ultrasonic sensor based on the TFT transistor in this embodiment is based on a preferred scheme proposed in Embodiment 1 of the present application, and further includes a third buffer layer 60 and a third piezoelectric layer 70. In this embodiment, the structure of the third buffer layer 60 and the third piezoelectric layer 70 is the same as that in Embodiment 3, which will not be repeated here.

[0074] The ultrasonic sensor in this embodiment can also realize signal transmission and reception, that is, the first piezoelectric layer 202 transmits signals, and the third piezoelectric layer 70 receives signals.

[0075] Embodiment 5:

[0076] Please refer to Figures 5 to 9 This embodiment is based on the preparation process proposed in Embodiment 1 above, which includes the following steps:

[0077] S1a, preparing a substrate 10 having opposite front and back surfaces, and growing a functional layer 20 on the front surface of the substrate 10. Specifically, the functional layer 20 includes the following steps:

[0078] S1-1, growing a first buffer layer 201 on the front surface of the substrate 10. The grown first buffer layer 201 can serve as a bottom layer for growing the first piezoelectric layer 202, improving the bonding force between the first piezoelectric layer 202 and the substrate 10 and the stability of the overall structure, and ensuring high performance of the entire ultrasonic sensor.

[0079] S1-2, growing a first metal layer 2021, a first piezoelectric film 2022, and a second metal layer 2023 in sequence on the front surface of the first buffer layer 201, and patterning the first metal layer 2021, the first piezoelectric film 2022, and the second metal layer 2023. In this embodiment, the first piezoelectric film 2022 is made of PZT, and the first piezoelectric layer 202 can be grown by a magnetron sputtering process or a sol-gel process.

[0080] S1-3, growing a second buffer layer 203 on the front side of the second metal layer 2023. The second buffer layer 203 can serve as a bottom layer for growing the TFT transistor 30, improving the bonding force between the first piezoelectric layer 202 and the TFT transistor 30 and the stability of the overall structure, ensuring high performance of the entire ultrasonic sensor.

[0081] S2a, growing the TFT transistor 30 on the front side of the functional layer 20 and making a via hole 40 on the TFT transistor 30 for connecting the TFT transistor 30 with the first piezoelectric layer 202.

[0082] In the above process, the first buffer layer 201 is first grown on the front side of the substrate 10, and then the first piezoelectric layer 202 is grown. The combination of the first buffer layer 201 and the first piezoelectric layer 202 can improve the performance of the ultrasonic sensor. The first buffer layer 202 can effectively reduce the lattice mismatch between the substrate 10 and the first piezoelectric layer 202, thereby improving the quality of the first piezoelectric layer 202. At the same time, the first buffer layer 201 can also increase the adhesion between the first piezoelectric layer 202 and the substrate 10, preventing the first piezoelectric layer 202 from falling off or being damaged during use. The second buffer layer 203 can further enhance the stability of the structure, help to balance the internal stress, and ensure the tight bonding between the layers.

[0083] The first piezoelectric layer 202, as the core working part of the ultrasonic sensor, can serve as the signal emitting part. By using high-quality piezoelectric materials and combining with a fine growth process, the first piezoelectric layer 202 can have excellent piezoelectric properties and stability, making the sensor have the characteristics of high resolution, high signal-to-noise ratio, high sensitivity, and high penetration. This process of combining the first buffer layer 201, the first piezoelectric layer 202, and the second buffer layer 203 provides an effective way to prepare high-performance ultrasonic sensors based on TFT transistors 30.

[0084] Example 6

[0085] Please refer to Figure 10 and Figure 11 , this embodiment is based on the preparation process proposed in the above-mentioned embodiment 2 and embodiment 5, which further comprises the following steps:

[0086] S3a, growing a second piezoelectric layer 50 on the TFT transistor 30 and patterning the second piezoelectric layer 50, the second piezoelectric layer 50 is connected with the TFT transistor 30 through the via hole 40. In this embodiment, the second piezoelectric layer 50 can be grown on the front side of the TFT transistor 30 by sol-gel process. The specific growth method of the second piezoelectric layer 50 is as follows:

[0087] S3a-1, the third metal layer 501, the second piezoelectric film 502 and the fourth metal layer 503 are sequentially grown on the front surface of the TFT transistor 30 by a sol-gel process and are patterned, and the material of the second piezoelectric film 502 is PZT or PVDF in this embodiment.

[0088] The ultrasonic sensor prepared in this embodiment can realize self-emission and self-reception, i.e., the first piezoelectric layer 202 emits a signal, and the second piezoelectric layer 50 receives the signal. The second piezoelectric layer 50 not only improves the sensitivity of the ultrasonic sensor but also widens the application range thereof. This embodiment provides an innovative solution for preparing a high-signal-to-noise-ratio and high-resolution TFT transistor-based ultrasonic sensor.

[0089] Embodiment 7

[0090] Please refer to Figures 12 to 14 , this embodiment is based on the preparation process proposed in Embodiments 3 and 6 above, which includes the following steps:

[0091] S4a, growing a third buffer layer 60 on the back surface of the substrate 10; the third buffer layer 60 grown can serve as a bottom layer for growing the third piezoelectric layer 70, improve the bonding force between the third piezoelectric layer 70 and the substrate 10 and the stability of the overall structure, and ensure the high performance of the entire ultrasonic sensor.

[0092] S5a, growing a third piezoelectric layer 70 on the back surface of the third buffer layer 60 and patterning the third piezoelectric layer 70, and the third piezoelectric layer 70 is connected to the TFT transistor 30 through the TGV 40. In this embodiment, the third piezoelectric layer 70 can be grown on the back surface of the substrate 10 by a sol-gel process. The specific growth method of the third piezoelectric layer 70 is as follows:

[0093] S5a-1, the fifth metal layer 701, the third piezoelectric film 702 and the sixth metal layer 703 are sequentially grown on the back surface of the substrate 10 by a sol-gel process and are patterned, and the material of the third piezoelectric film 702 is PZT or PVDF in this embodiment.

[0094] The ultrasonic sensor prepared in this embodiment can realize self-emission and self-reception, i.e., the first piezoelectric layer 202 emits a signal, and the second piezoelectric layer 50 and the third piezoelectric layer 70 receive the signal. The second piezoelectric layer 50 and the third piezoelectric layer 70 simultaneously receive the signal, which can improve the performance of the ultrasonic sensor. This embodiment provides an innovative solution for preparing a high-signal-to-noise-ratio and high-resolution TFT transistor-based ultrasonic sensor.

[0095] Embodiment 8

[0096] Please refer to Figures 15 to 19 , this embodiment is based on the preparation process proposed in Embodiment 4 above, which includes the following steps:

[0097] S1b, preparing the substrate 10, the substrate 10 has opposite front and back surfaces, and the functional layer 20 is grown on the front surface of the substrate 10. Specifically, the growth process of the functional layer 20 is described in S1-1 to S1-3 of Embodiment 5, which will not be repeated here.

[0098] S2b, growing the third buffer layer 60 on the back surface of the substrate 10; the grown third buffer layer 60 can serve as a bottom layer for growing the third piezoelectric layer 70, improving the bonding force between the third piezoelectric layer 70 and the substrate and the stability of the overall structure, and ensuring high performance of the entire ultrasonic sensor.

[0099] S3b, growing the third piezoelectric layer 70 on the back surface of the third buffer layer 60 and patterning the third piezoelectric layer 70. In this embodiment, the third piezoelectric layer 70 can be grown on the back surface of the substrate 10 by a magnetron sputtering process. The specific growth method of the third piezoelectric layer 70 is as follows:

[0100] S3b-1, sequentially stacking and growing the fifth metal layer 701, the third piezoelectric film 702, and the sixth metal layer 703 on the back surface of the substrate 10 by a magnetron sputtering process and patterning, and in this embodiment, the material of the third piezoelectric film 702 is PZT.

[0101] S4b, growing the TFT transistor 30 on the front surface of the functional layer 20 and making the TGV 40 on the TFT transistor 30, for connecting the third piezoelectric layer 70 and the TFT transistor 30 and connecting the functional layer 20 and the TFT transistor 30.

[0102] The ultrasonic sensor prepared in this embodiment can realize self-emission and self-reception, i.e., the first piezoelectric layer 30 emits signals and the third piezoelectric layer 70 receives signals. The third piezoelectric layer 70 is grown by a magnetron sputtering process, and the material of the third piezoelectric film 702 is PZT, so that the performance of the third piezoelectric layer 70 is better and the signal is stronger, and the sensor has the characteristics of high resolution, high signal-to-noise ratio, high sensitivity, and high penetration. In this embodiment, the functional layer 20 and the third piezoelectric layer 70 are grown first, and then the TFT transistor 30 is regrown, which can avoid damaging the TFT transistor 30 when growing the third piezoelectric layer 70 by a magnetron sputtering process. This embodiment provides an innovative solution for preparing a high signal-to-noise ratio, high resolution, and TFT transistor-based ultrasonic sensor.

[0103] In the above process, the combination of the third buffer layer 60 and the third piezoelectric layer 70 can improve the performance of the ultrasonic sensor. The third buffer layer 60 can effectively reduce the lattice mismatch between the substrate and the third piezoelectric layer 70, thereby improving the quality of the third piezoelectric layer 70. At the same time, the third buffer layer 60 can also increase the adhesion between the third piezoelectric layer 70 and the substrate 10, preventing the third piezoelectric layer 70 from falling off or being damaged during use.

[0104] Example 9

[0105] Please refer to Figure 20 , the present embodiment is based on the preparation process proposed in the above-mentioned example 3 and example 8, comprising the following steps:

[0106] S5b, a second piezoelectric layer 50 is grown on the front surface of the TFT transistor 30 and the second piezoelectric layer 50 is patterned, and the second piezoelectric layer 50 is connected with the TFT transistor 30 through the via hole 40. In this embodiment, the preparation process of the second piezoelectric layer 50 is the same as S3a-1 in example 6, which will not be repeated here.

[0107] The ultrasonic sensor prepared in this embodiment can realize self-emission and self-reception, that is, the first piezoelectric layer 202 emits signals, and the second piezoelectric layer 50 and the third piezoelectric layer 70 receive signals. The second piezoelectric layer 50 and the third piezoelectric layer 70 receive signals at the same time, which can improve the performance of the ultrasonic sensor.

[0108] The above describes only the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can make equivalent replacements or changes within the technical range disclosed in the present application according to the technical solution and the inventive concept of the present application, which should be covered within the protection scope of the present application.

[0109] One or more embodiments of the present specification are intended to cover all such replacements, modifications and variations falling within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent replacements, improvements, etc. made within the spirit and principles of one or more embodiments of the present specification should be included within the protection scope of the present disclosure.

[0110] It should be understood that the terms "upper", "lower", "front", "back", "left", "right", etc. indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0111] In addition, the terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, such as two, three, etc., unless otherwise specifically limited.

[0112] In the present invention, unless specifically stated and limited otherwise, a first feature is "on", "above", or "over" a second feature can mean that the first and second features are in direct contact, or the first and second features are in indirect contact with an intervening medium. Also, a first feature "on", "above", and "over" a second feature can mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is horizontally higher than the second feature. A first feature "under", "below", and "underneath" a second feature can mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is horizontally lower than the second feature.

Claims

1. A fabrication process for an ultrasonic sensor, characterized in that, The ultrasonic sensor based on TFT transistors includes: A substrate having opposing front and back sides; A functional layer, the functional layer being grown on the front side of the substrate; and TFT transistor, the TFT transistor being grown on the front side of the functional layer; The functional layer includes a first piezoelectric layer; The fabrication process includes the following steps: S1b, preparing a substrate having a front side and a back side, and growing the functional layer on the front side of the substrate; S2b, a third buffer layer is grown on the back side of the substrate; S3b, a third piezoelectric layer is grown on the back side of the third buffer layer, and the third piezoelectric layer is patterned; and S4b, the TFT transistor is grown on the front side of the functional layer and a TGV is formed on the TFT transistor to connect the third piezoelectric layer with the TFT transistor and to connect the functional layer with the TFT transistor; The preparation process further includes the following steps: S5b, a second piezoelectric layer is grown on the front side of the TFT transistor and patterned, wherein the second piezoelectric layer is connected to the TFT transistor through a via.

2. The fabrication process for an ultrasonic sensor according to claim 1, characterized in that, The functional layer includes a first buffer layer, a first piezoelectric layer, and a second buffer layer, which are sequentially stacked on the front side of the substrate.

3. The fabrication process for an ultrasonic sensor according to claim 2, characterized in that, The first piezoelectric layer includes a first metal layer, a first piezoelectric film, and a second metal layer sequentially stacked on the first buffer layer, wherein the material of the first piezoelectric film is PZT.

4. The fabrication process for an ultrasonic sensor according to claim 1, characterized in that, A second piezoelectric layer is disposed on the front side of the TFT transistor.

5. The fabrication process for an ultrasonic sensor according to claim 1, characterized in that, A third buffer layer and a third piezoelectric layer are disposed on the back side of the substrate, and the third buffer layer and the third piezoelectric layer are stacked sequentially on the back side of the substrate.

6. The preparation process according to claim 3, characterized in that, Growing the functional layer in S1b includes the following steps: S1-1, The first buffer layer is grown on the front side of the substrate; S1-2, the first metal layer, the first piezoelectric film, and the second metal layer are sequentially grown on the front side of the first buffer layer, and the first metal layer, the first piezoelectric film, and the second metal layer are patterned; and S1-3, the second buffer layer is grown on the front side of the second metal layer.

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