Micro-machined acoustic wave transducer based on through-silicon via single crystal piezoelectric thin film and preparation method

Abstract

The application discloses a micro-mechanical acoustic wave transducer based on a through-silicon via single-crystal piezoelectric film and a preparation method thereof. The micro-mechanical acoustic wave transducer comprises, from top to bottom, an electrode, a piezoelectric film, a substrate and a bottom silicon. The electrode comprises two groups of electrodes which are separately arranged on the upper surface of the piezoelectric film. The bottom silicon surrounds the lower surface of the substrate and forms a cavity with the substrate for vibration of the piezoelectric film of the micro-mechanical acoustic wave transducer. TSVs are arranged on the substrate and the bottom silicon for leading out the electrode. The micro-mechanical acoustic wave transducer based on the through-silicon via single-crystal piezoelectric film is characterized in that the two groups of electrodes are arranged on the upper surface of the piezoelectric crystal, and the through holes are arranged on the substrate and the bottom silicon, so that the leading-out of the electrode is facilitated, the three-dimensional integration of the micro-mechanical acoustic wave transducer and a circuit is realized, and the problem that the traditional micro-mechanical piezoelectric ultrasonic transducer is difficult to be integrated in three dimensions is solved.

Description

Technical Field

[0001] This invention belongs to the field of micromechanical acoustic transducers, and particularly relates to a micromechanical acoustic transducer based on a through-silicon via single-crystal piezoelectric thin film and its preparation method. Background Technology

[0002] Traditional piezoelectric micromechanical acoustic transducers mainly consist of a top electrode, a piezoelectric thin film, a bottom electrode, a top silicon layer, a silicon dioxide layer, and a bottom silicon layer, arranged from top to bottom. Their working principle is as follows: after applying pulse excitation to the upper and lower electrode layers of the transducer, the piezoelectric material deforms due to the inverse piezoelectric effect, thereby generating periodic oscillations and emitting sound waves. The piezoelectric thin film is often made of materials such as PZT or aluminum nitride, while the top silicon layer, silicon dioxide layer, and bottom silicon layer use an SOI substrate, with a back cavity formed by deep etching of the lower silicon layer.

[0003] The aforementioned piezoelectric micromechanical acoustic transducer is integrated with the circuit primarily through wire bonding to the underlying circuit board. Traditional piezoelectric micromechanical acoustic transducers are fabricated by growing piezoelectric thin films such as PZT / AlN on an SOI substrate and then deeply etching the underlying silicon to form a back cavity. Therefore, for the three-dimensional integration of this type of piezoelectric micromechanical ultrasonic transducer, one approach could be to first perform an SOI TSV process followed by a MEMS process to etch the back cavity and fabricate the diaphragm structure on the SOI; or first fabricate the device structure using a MEMS process and then perform a TSV process on the SOI. However, both of these three-dimensional integration methods have significant drawbacks.

[0004] For the approach of performing TSV on SOI first and then MEMS, the subsequent MEMS process requires high temperatures of 200-400℃ during structural fabrication. This results in severe stress accumulation in the SOI wafer after TSV, leading to stress mismatch between the top and bottom silicon layers and significantly impacting device performance. Conversely, the approach of fabricating the structure using MEMS first and then performing TSV on SOI has two drawbacks: first, the device structure is relatively fragile after MEMS processing, posing a risk of damage during SOI TSV; second, the TSV process requires electroplating, which can easily contaminate the device.

[0005] The fundamental reason for the defects in the above three-dimensional integration process lies in the incompatibility between SOI TSV process and MEMS process. This makes the traditional three-dimensional integration process of piezoelectric micromechanical ultrasonic transducers and circuits very complex, costly, and not conducive to large-scale mass production. Summary of the Invention

[0006] In view of this, the present invention creatively proposes a micromechanical acoustic transducer based on a through-silicon via (TSV) single-crystal piezoelectric thin film and its fabrication method. The micromechanical acoustic transducer uses a single-crystal piezoelectric thin film material as the piezoelectric layer, and places two sets of electrodes (each set of electrodes is connected to an electrical signal) on top of the piezoelectric layer. The piezoelectric micromechanical ultrasonic transducer with this structure does not require SOI, and can achieve signal fan-out using traditional TSV technology, and has integration compatibility.

[0007] To achieve this objective, the first aspect of the present invention proposes the following technical solution: a micromechanical acoustic transducer based on a through-silicon via single-crystal piezoelectric thin film, wherein the micromechanical acoustic transducer comprises an electrode, a piezoelectric thin film, a substrate, and a bottom silicon layer arranged sequentially from top to bottom;

[0008] The electrode includes two sets of electrodes, which are located separately on the upper surface of the piezoelectric film;

[0009] The bottom silicon surrounds the lower surface of the substrate and forms a cavity with the substrate for the vibration of the piezoelectric film of the micromechanical acoustic transducer.

[0010] The substrate and the underlying silicon have TSVs for electrode lead-out.

[0011] Preferably, the two sets of electrodes are arranged in a "semi-open" shape on the upper surface of the piezoelectric film.

[0012] Preferably, the substrate is made of any one of alumina, silicon nitride, and silicon dioxide.

[0013] The second aspect of this invention proposes the following technical solution: a method for fabricating a micromechanical acoustic transducer based on a through-silicon via (TSV) single-crystal piezoelectric thin film, the method comprising:

[0014] S1: Obtain a bottom silicon with through-holes through the TSV process, and then perform surface planarization on the bottom silicon.

[0015] S2: Prepare a substrate layer on the upper surface of the silicon substrate and perform planarization treatment;

[0016] S3: Obtain a piezoelectric single crystal implantation wafer;

[0017] S4: Perform wafer-level bonding, bond the piezoelectric single crystal implantation wafer to the substrate-bound silicon at the wafer level, and perform surface planarization;

[0018] S5: The surface of the piezoelectric single crystal implantation wafer is etched to complete the patterning, and two sets of electrodes are prepared on the upper surface of the piezoelectric single crystal implantation wafer;

[0019] S6: Perform back cavity etching on the bottom silicon to obtain a micromechanical acoustic transducer based on a silicon through-hole single-crystal piezoelectric thin film.

[0020] Preferably, the surface medium is any one or more of alumina, silicon nitride, and silicon dioxide.

[0021] Preferably, the piezoelectric single crystal material is lithium niobate.

[0022] Preferably, in step S4, before performing the surface planarization operation, the piezoelectric single crystal implanted wafer is annealed, peeled off, and thinned.

[0023] Preferably, the etching patterning in S5 is performed using laser etching, FIB etching, or photolithography.

[0024] Preferably, in S6, the back cavity etching of the bottom silicon is performed using the DRIE process.

[0025] The beneficial effects of this invention are as follows: The micromechanical acoustic transducer based on a through-silicon via (TSV) single-crystal piezoelectric thin film proposed in this invention has two sets of electrodes disposed on the upper surface of the piezoelectric crystal, and through-holes are simultaneously formed on the substrate and the bottom silicon, which facilitates the lead-out of the electrodes, thereby realizing the three-dimensional integration of the micromechanical acoustic transducer and the circuit, solving the problem of the difficulty in 3D integration of traditional micromechanical piezoelectric ultrasonic transducers. The fabrication method of the micromechanical acoustic transducer based on a TSV single-crystal piezoelectric thin film proposed in this invention directly uses silicon as the substrate without requiring SOI, and the device can use TSV technology to achieve electrode lead-out. Therefore, the fabrication method proposed in this application does not require SOI TSV technology, overcoming the disadvantage of incompatibility between MEMS technology and SOI TSV technology in the traditional device fabrication process, making the three-dimensional integration of large-scale piezoelectric micromechanical ultrasonic transducers and circuits possible. Attached Figure Description

[0026] Figure 1 This is a schematic cross-sectional view of the micromechanical acoustic transducer based on a through-silicon via single-crystal piezoelectric thin film in an embodiment of the present invention.

[0027] Figure 2 This is a schematic diagram showing the arrangement of two sets of electrodes in an embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram of the three-dimensional integrated structure of a micromechanical acoustic transducer based on a through-silicon via single-crystal piezoelectric thin film in an embodiment of the present invention;

[0029] Figure 4 This is a schematic flowchart illustrating the fabrication process of the micromechanical acoustic transducer based on a through-silicon via single-crystal piezoelectric thin film in an embodiment of the present invention.

[0030] In the figure: 1. Electrode I 2. Electrode II 3. Piezoelectric film 4. Substrate 5. Underlying silicon 6. Lead wire 7. Circuit 8. TSV. Detailed Implementation

[0031] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

[0032] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0033] A micromechanical acoustic transducer based on a through-silicon via (TSV) single-crystal piezoelectric thin film, as an example, has the following structure: Figure 1 As shown, the micromechanical acoustic transducer includes, from top to bottom, electrodes, a piezoelectric thin film 3, a substrate 4, and a silicon substrate 5; wherein the electrodes include two sets of electrodes, namely... Figure 1 Electrodes I1 and II2 are shown, with the two sets of electrodes located separately on the upper surface of the piezoelectric film 3. As an example, [the following is an example / example]. Figure 2 As shown, two sets of electrodes are arranged in a semi-open pattern on the upper surface of the piezoelectric film 3. The bottom silicon 5 surrounds the lower surface of the substrate 4, forming a cavity for the vibration of the micromechanical acoustic wave transducer piezoelectric film 3. TSV8s for electrode leads are formed on the substrate 4 and the bottom silicon 5 to directly lead out the two sets of electrodes located on the upper surface, thereby realizing the three-dimensional integration of the micromechanical acoustic wave transducer and the circuit. The arrangement of its electrode leads is as follows. Figure 3 As shown.

[0034] As an example, the material of substrate 4 is any one of alumina, silicon nitride, and silicon dioxide.

[0035] A method for fabricating a micromechanical acoustic transducer based on a through-silicon via (TSV) single-crystal piezoelectric thin film, as an example, is as follows: Figure 4 As shown, the method includes:

[0036] S1: A bottom silicon with through-holes is obtained through the TSV process, and the surface of the bottom silicon is planarized to obtain the wafer for subsequent bonding.

[0037] S2: A substrate layer is prepared on the upper surface of the silicon substrate and planarized. In this example, the surface medium is any one or more of alumina, silicon nitride, and silicon dioxide.

[0038] S3: Obtain a piezoelectric single crystal implantation sheet. As an example, the piezoelectric single crystal material is lithium niobate.

[0039] S4: Perform wafer-level bonding, bonding the piezoelectric single crystal implantation wafer to the substrate silicon at the wafer level. Since lithium niobate is relatively thick, the piezoelectric single crystal implantation wafer needs to be annealed, peeled off, and thinned before surface planarization.

[0040] S5: The surface of the piezoelectric single crystal injection wafer is etched and patterned using methods such as laser etching, FIB etching or photolithography, and two sets of electrodes are prepared on the upper surface of the piezoelectric single crystal injection wafer.

[0041] S6: The back cavity of the bottom silicon is etched by DRIE process to obtain a micromechanical acoustic transducer based on a silicon through-hole single crystal piezoelectric thin film.

[0042] Through the above six steps, the micromechanical acoustic transducer based on a silicon through-hole single-crystal piezoelectric thin film was prepared, which solved the problem that traditional micromechanical piezoelectric ultrasonic transducers are difficult to integrate in 3D.

Claims

1. A method for fabricating a micromechanical acoustic transducer based on a through-silicon via (TSV) single-crystal piezoelectric thin film, characterized in that, The micromechanical acoustic transducer includes, from top to bottom, electrodes, a piezoelectric thin film, a substrate, and a silicon substrate; The electrode includes two sets of electrodes, which are located separately on the upper surface of the piezoelectric film; The bottom silicon surrounds the lower surface of the substrate and forms a cavity with the substrate for the vibration of the piezoelectric film of the micromechanical acoustic transducer. TSVs for electrode lead-out are formed on the substrate and the bottom silicon. The two sets of electrodes are arranged in a "semi-open" shape on the upper surface of the piezoelectric film; The method includes: S1: Obtain a bottom silicon with through-holes through the TSV process, and then perform surface planarization on the bottom silicon. S2: Prepare a substrate layer on the upper surface of the silicon substrate and perform planarization treatment; S3: Obtain a piezoelectric single crystal implantation wafer; S4: Perform wafer-level bonding, bond the piezoelectric single crystal implantation wafer to the substrate-bound silicon at the wafer level, and perform surface planarization; S5: The surface of the piezoelectric single crystal implantation wafer is etched to complete the patterning, and two sets of electrodes are prepared on the upper surface of the piezoelectric single crystal implantation wafer; S6: Perform back cavity etching on the bottom silicon to obtain a micromechanical acoustic transducer based on a silicon through-hole single-crystal piezoelectric thin film; The substrate is made of any one of alumina, silicon nitride, and silicon dioxide. The piezoelectric single crystal material is lithium niobate. In step S4, before the surface planarization operation, the piezoelectric single crystal implantation wafer is annealed, peeled off, and thinned. The etching patterning in S5 is achieved by laser etching, FIB etching, or photolithography. In S6, the back cavity etching of the bottom silicon is performed using the DRIE process.

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