Lamb wave resonator and method of making the same

Abstract

The application discloses a Lamb wave resonator, comprising: a first substrate; a piezoelectric layer, a cavity is formed between the first substrate and the piezoelectric layer, the piezoelectric layer is a C-axis inclined piezoelectric film, the angle of C-axis inclination is 48°-68° or -68°-48° by rotating the C-axis orientation of the piezoelectric film, the piezoelectric layer is suitable for exciting the first-order anti-symmetry mode Lamb wave under the action of a transverse electric field; a first metal electrode layer, comprising a metal electrode array formed by a plurality of positive and negative metal electrodes arranged alternately, the metal electrode array forms a transverse electric field, the first metal electrode layer is formed on the piezoelectric layer, and the direction of the transverse electric field is 70°-90° or -90°-70° with the +X axis direction of the global coordinate system of the C-axis inclined piezoelectric film; wherein the piezoelectric layer excites the A1 vibration mode Lamb wave under the action of the transverse electric field, so that the Lamb wave resonator realizes an electromechanical coupling coefficient greater than 15% under the condition that the resonant frequency is greater than 3 GHz.

Description

Technical Field

[0001] At least one embodiment of the present invention relates to a Lamb wave resonator, and more particularly to a Lamb wave resonator based on a C-axis tilted scandium-doped aluminum nitride piezoelectric thin film and a method thereof for fabrication. Background Technology

[0002] With the advent of the 5G / 6G era, the demand for mobile communication systems, especially cellular phone applications, is constantly increasing, placing higher requirements on the components of wireless communication systems. In 5G / 6G wireless communication systems, radio frequency (RF) front-end technology is considered a key technology, and RF filters, as a core component of the RF front-end, enable specific frequency components of the signal to pass through with low loss while significantly suppressing other frequency components, thereby improving the system's anti-interference capability and signal-to-noise ratio. Therefore, how to achieve high-performance filters at higher frequencies will be an important research goal for both academia and industry in the future.

[0003] Electromechanical coupling coefficient (k) 2 As a crucial indicator of filter and resonator performance, a high electromechanical coupling coefficient ensures a sufficiently large passband bandwidth, enabling the transmission of larger amounts of data. Therefore, achieving a resonator with a high electromechanical coupling coefficient in the 5G band is key to realizing wideband filters. Summary of the Invention

[0004] In view of this, in order to obtain a wide-bandwidth acoustic filter for the 5G FR1 (450MHz~6GHz) frequency band, while reducing the complexity of the acoustic resonator fabrication process, this invention provides a Lamb wave resonator and its fabrication method. By forming a piezoelectric layer with a C-axis tilted within a specific angle range on a first substrate, and making the +X axis direction of the global coordinate system where the C-axis tilted piezoelectric film is located form a specific angle range with the direction of the transverse electric field formed by the first metal electrode layer, Lamb waves of the A1 vibration mode are excited under the action of the transverse electric field, thereby realizing a high electromechanical coupling coefficient and high-frequency acoustic resonator.

[0005] This invention provides a Lamb wave resonator, comprising:

[0006] First substrate;

[0007] A piezoelectric layer is formed on a first substrate, and a cavity is formed between the first substrate and the piezoelectric layer. The piezoelectric layer is a C-axis tilted piezoelectric thin film. The C-axis tilt angle is 48° to 68° or -68° to -48° by rotating Euler angles. The piezoelectric layer is suitable for exciting the first antisymmetric mode Lamb wave under the action of a transverse electric field.

[0008] The first metal electrode layer includes a metal electrode array composed of multiple alternating positive and negative metal electrodes. The metal electrode array forms a transverse electric field, which forms the first metal electrode layer on the piezoelectric layer, such that the direction of the transverse electric field is 70° to 90° or -90° to -70° with the +X axis of the global coordinate system where the piezoelectric film is tilted along the C-axis.

[0009] The piezoelectric layer, under the action of a transverse electric field, excites Lamb waves of the A1 vibration mode, enabling the Lamb wave resonator to achieve an electromechanical coupling coefficient of more than 15% under the condition that the resonant frequency is greater than 3GHz.

[0010] This invention also provides a method for fabricating a Lamb wave resonator, applicable to the fabrication of the aforementioned Lamb wave resonator, comprising: placing a first substrate at an angle; depositing a piezoelectric layer on the first substrate using magnetron sputtering, wherein the piezoelectric layer is a piezoelectric thin film with a C-axis tilt angle of 48° to 68° or -68° to -48°; depositing a first metal electrode layer on the piezoelectric layer, wherein the transverse electric field direction formed by the metal electrodes of the first metal electrode layer forms an angle of 70° to 90° or -90° to -70° with the +X axis direction of the global coordinate system where the C-axis tilted piezoelectric thin film is located; depositing a mask layer on the first metal electrode layer and graphically defining the mask etching region; etching the piezoelectric layer using inductively coupled plasma etching; dry etching the first substrate using xenon difluoride (XeF2) gas to form a cavity on the side of the first substrate near the piezoelectric layer; and removing the mask layer using a buffered oxide etchant.

[0011] The present invention also provides a method for fabricating a Lamb wave resonator, applicable to the fabrication of the aforementioned Lamb wave resonator, comprising: depositing a release layer on a first substrate; tilting the first substrate on which the release layer is formed to deposit a piezoelectric layer on the release layer, wherein the piezoelectric layer is a piezoelectric thin film with a C-axis tilt angle of 48° to 68° or -68° to -48°; depositing a first bonding layer on the piezoelectric layer; depositing a second bonding layer on a second substrate and etching a region on the second substrate where the second bonding layer is not formed to form a cavity on the second substrate; aligning the first bonding layer and the second bonding layer and then performing wafer bonding; using laser to lift off the release layer to peel the first substrate from the piezoelectric layer; and forming a first metal electrode layer on the piezoelectric layer, wherein the lateral electric field direction formed by the first metal electrode layer forms an angle of 70° to 90° or -90° to -70° with the +X axis direction of the global coordinate system where the C-axis tilted piezoelectric thin film is located.

[0012] According to the Lamb resonator provided in the above embodiments of the present invention, a piezoelectric layer with a C-axis tilt angle of 48° to 68° or -68° to -48° is formed on a first substrate, and a cavity is formed between the first substrate and the piezoelectric layer. The direction of the transverse electric field formed by the first metal electrode layer is at an angle of 70° to 90° or -90° to -70° with the +X axis of the global coordinate system where the C-axis tilted piezoelectric film is located. Under the action of the transverse electric field, the piezoelectric layer excites a Lamb wave of the A1 vibration mode. Thus, the Lamb resonator achieves an electromechanical coupling coefficient of more than 15% under the condition that the resonant frequency is greater than 3GHz, so as to achieve a large electromechanical coupling coefficient in the 5G band and meet the requirements of wide bandwidth filters. Attached Figure Description

[0013] Figure 1 This is a schematic cross-sectional view of a Lamb wave resonator according to an embodiment of the present invention;

[0014] Figure 2 This is a schematic diagram showing the piezoelectric thin film tilted at a specific angle θ according to an embodiment of the present invention;

[0015] Figure 3 The curve showing the electromechanical coupling coefficient of the Lamb wave resonator that excites the A1 vibration mode according to an embodiment of the present invention as a function of the C-axis tilt angle of the piezoelectric thin film;

[0016] Figure 4 The curve showing the change of the electromechanical coupling coefficient of the Lamb wave resonator according to an embodiment of the present invention as a function of the direction of sound wave propagation.

[0017] Figure 5 This is a schematic diagram of the Lamb wave of the A1 vibration mode excited by the Lamb wave resonator according to an embodiment of the present invention;

[0018] Figure 6 The curve showing the resonant frequency of a Lamb wave resonator in the A1 vibration mode according to an embodiment of the present invention as a function of the piezoelectric thin film thickness.

[0019] Figure 7 This is a flowchart of a method for fabricating a Lamb wave resonator according to an embodiment of the present invention;

[0020] Figures 8(a) to 8(f) This is a schematic diagram illustrating the fabrication process of a Lamb wave resonator according to an embodiment of the present invention;

[0021] Figure 9 The simulation performance diagram of a Lamb wave resonator that excites the A1 vibration mode without metal electrode optimization design according to an embodiment of the present invention;

[0022] Figure 10 The simulation performance diagram of the Lamb wave resonator that excites the A1 vibration mode after the metal electrode optimization design according to an embodiment of the present invention is shown.

[0023] Figure 11 A flowchart illustrating a method for fabricating a Lamb wave resonator according to another embodiment of the present invention; and

[0024] Figure 12(a)~12(e) This is a schematic diagram illustrating the fabrication process of a Lamb wave resonator according to another embodiment of the present invention.

[0025] [Explanation of Labels in the Attached Image]

[0026] 1-First substrate;

[0027] 2-Release layer;

[0028] 3-Piezoelectric layer;

[0029] 41 - First metal electrode layer;

[0030] 5-Mask layer;

[0031] 6-Cavity;

[0032] 7-Bonding layer;

[0033] 71 - First bonding layer;

[0034] 72 - Second bonding layer;

[0035] 8-Second substrate. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. However, this invention can be implemented in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to make the invention thorough and complete, and to fully convey the scope of the invention to those skilled in the art. In the accompanying drawings, for clarity, the dimensions and relative dimensions of layers and regions may be exaggerated, and the same reference numerals denote the same elements throughout.

[0037] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0038] Currently, the piezoelectric materials used in acoustic resonators mainly include lead zirconate titanate (PZT), aluminum nitride (AlN), scandium-doped aluminum nitride (AlScN), lithium niobate (LiNbO3 / LN), and lithium tantalate (LiTaO3 / LT). Among them, C-axis oriented scandium-doped aluminum nitride (AlScN) has a larger piezoelectric parameter (ep). 33This can well meet the requirements of 5G / 6G frequency bands for high quality factor (Q) and large electromechanical coupling coefficient (k). 2 The demand for scanning aluminum nitride (SAM) films is increasing. Meanwhile, compared to lithium niobate films, SAM films offer CMOS-compatible and relatively simple film fabrication processes, making them a popular material for acoustic resonator fabrication. Traditional C-axis oriented SAM films only exhibit the highest electromechanical coupling coefficient (kΩ) when fabricating FBARs (Bulk Acoustic Resonators). 2 However, the fabrication process of FBAR resonators is relatively complex, which greatly increases the fabrication cost.

[0039] In view of this, the present invention provides a Lamb wave resonator based on a C-axis tilted scandium-doped aluminum nitride piezoelectric thin film and its fabrication method, so as to achieve a large electromechanical coupling coefficient in the 5G band.

[0040] Figure 1 This is a schematic cross-sectional view of a Lamb wave resonator according to an embodiment of the present invention.

[0041] According to an exemplary embodiment of the present invention, the present invention provides a Lamb wave resonator, with reference to... Figure 1 As shown, it includes:

[0042] First substrate 1;

[0043] A piezoelectric layer 3 is formed on a first substrate 1, and a cavity 6 is formed between the first substrate 1 and the piezoelectric layer 3. The piezoelectric layer 3 is a piezoelectric thin film tilted along the C-axis. The tilt angle of the C-axis is 48° to 68° or -68° to -48° by rotating the Euler angle. The piezoelectric layer 3 is suitable for generating a Lamb wave of the first antisymmetric mode under the action of a transverse electric field.

[0044] The first metal electrode layer 41 includes a metal electrode array composed of multiple alternating positive and negative metal electrodes. The metal electrode array forms a transverse electric field, and the first metal electrode layer 41 is formed on the piezoelectric layer 3, such that the direction of the transverse electric field is 70° to 90° or -90° to -70° with the +X axis direction of the global coordinate system where the piezoelectric film tilted by the C axis is located.

[0045] Among them, the piezoelectric layer 3 is excited by the transverse electric field to generate the first antisymmetric mode Lamb wave, so that the Lamb wave resonator can achieve an electromechanical coupling coefficient of more than 15% under the condition that the resonant frequency is greater than 3GHz.

[0046] It should be noted that the Lamb wave antisymmetric mode excited by the Lamb wave resonator can be at least one of the following: the first antisymmetric mode (A1 vibration mode), the third antisymmetric mode (A3 vibration mode), the fifth antisymmetric mode (A5 vibration mode), and the seventh antisymmetric mode (A7 vibration mode). Since the piezoelectric coefficient, dielectric constant, elastic modulus, and other parameters of the piezoelectric material change with the C-axis tilt angle, they affect the electromechanical coupling coefficient (k) of its acoustic resonator. 2 Therefore, different vibration modes can be excited by changing the tilt angle of the C-axis of the piezoelectric film. Furthermore, the higher the order of the vibration mode of the Lamb wave resonator, the higher the resonant frequency of the Lamb wave resonator and the lower the electromechanical coupling coefficient. The A1 vibration mode is a first-order antisymmetric shear wave mode of piezoelectric film vibration in the thickness direction, possessing a very high sound velocity. Since the resonant frequency of the first-order antisymmetric mode (A1 vibration mode) meets the requirements within the 5G frequency band, sound waves using the A1 vibration mode can achieve a high electromechanical coupling coefficient within the 5G frequency band.

[0047] It should be noted that the spacing between two adjacent metal electrodes and the width of the metal electrodes have an approximate correspondence with the wavelength of the generated sound wave. Because the A1 mode Lamb resonator has a higher sound velocity than a traditional surface acoustic wave (SAW) resonator, an A1 mode Lamb resonator fabricated with the same device size will have a higher resonant frequency. Furthermore, for A1 mode Lamb resonators with the same resonant frequency, the width between the metal electrodes is wider than that of traditional SAW resonators. Since narrower spacing between metal electrodes makes device fabrication more difficult, the fabrication process for A1 mode Lamb resonators is simpler than that for traditional SAW resonators.

[0048] According to an embodiment of the present invention, the material of the first substrate 1 can be one of the following: silicon, glass, quartz, sapphire (Al2O3), gallium nitride (GaN), silicon carbide (SiC), or lithium niobate (LN). The first substrate 1 serves to support the resonator.

[0049] According to an embodiment of the present invention, the piezoelectric layer 3 is made of scandium-doped aluminum nitride, or a composite layer material composed of aluminum nitride and scandium-doped aluminum nitride; the doping concentration of scandium in the scandium-doped aluminum nitride is 0-40%, for example, it can be 10%, 20%, 30%, or 40%. Increasing the doping concentration of scandium will reduce the resonant frequency of the fabricated Lamb wave resonator and increase the electromechanical coupling coefficient, but excessively high doping concentration is not conducive to forming a resonator with a high electromechanical coupling coefficient. The thickness of the piezoelectric layer 3 is 100-500 nm; for example, the thickness can be 100 nm, 200 nm, 300 nm, 400 nm, or 500 nm.

[0050] According to an embodiment of the present invention, the metal electrodes of the first metal electrode layer 41 are interdigitated electrodes, and the number of metal electrodes is 2 to 50; the spacing between two adjacent metal electrodes is half the wavelength of the sound wave; the width of each metal electrode is one-sixth or one-eighth of the wavelength of the sound wave; the length of each metal electrode is ten or ten and a half wavelengths of the sound wave; for example, the width of the metal electrode can be 5 μm.

[0051] According to embodiments of the present invention, the material of the metal electrode includes one of the following: gold, aluminum, molybdenum, platinum, copper, titanium-gold alloy, titanium-aluminum alloy, titanium-copper alloy, chromium-gold alloy, chromium-aluminum alloy, and chromium-copper alloy; the thickness of the metal electrode is 10 to 100 nm; for example, the thickness of the metal electrode can be 10 nm, 20 nm, 50 nm, 80 nm, or 100 nm.

[0052] It should be noted that a cavity 6 is formed on the side of the first substrate 1 near the piezoelectric layer 3. By forming a cavity 6 between the first substrate 1 and the piezoelectric layer 3, since the cavity 6 is an empty space and has an impedance close to infinity, the sound waves generated in the piezoelectric layer 3 can be confined within the piezoelectric layer 3, thereby reducing the loss or attenuation of the sound waves.

[0053] Figure 2 This is a schematic diagram of the piezoelectric thin film tilted at a specific angle θ according to an embodiment of the present invention.

[0054] refer to Figure 2 As shown, the XYZ coordinate system represents the global coordinate system, the C-axis orientation of the piezoelectric crystal represents the Z-axis of the global coordinate system, the Euler angles of the ZXZ rotation are (0, θ, α), and the X' axis direction represents the direction of the transverse electric field after Euler rotation.

[0055] According to an embodiment of the present invention, θ represents the tilt angle of the piezoelectric thin film of the piezoelectric layer 3 along the C-axis, and α represents the angle between the direction of the transverse electric field (X' direction) and the +X-axis direction (X direction) of the global coordinate system where the piezoelectric thin film tilted along the C-axis is located. According to an embodiment of the present invention, θ is 48° to 68° or -68° to -48°, and α is 70° to 90° or -90° to -70°.

[0056] Figure 3 The curve shows the electromechanical coupling coefficient of the Lamb wave resonator that excites the A1 vibration mode according to an embodiment of the present invention as a function of the tilt angle of the C-axis of the piezoelectric thin film.

[0057] It should be noted that by tilting the substrate, a piezoelectric thin film with a C-axis tilted at a certain angle can be deposited on the substrate. By selecting the optimal C-axis tilt angle, the piezoelectric thin film can achieve optimal performance on the substrate. 15 Electromechanical coupling coefficient (k) of piezoelectric parameter excitation2 15 Maximize, based on the ability to e 15 The piezoelectric parameters excite the maximum electromechanical coupling coefficient (k). 2 15 A Lamb wave antisymmetric A1 vibration mode acoustic resonator was fabricated using a piezoelectric thin film. This acoustic resonator exhibits a high electromechanical coupling coefficient. The specific trend of the electromechanical coupling coefficient with the C-axis tilt angle of the piezoelectric thin film can be found in [reference needed]. Figure 3 .

[0058] refer to Figure 3 As shown, by depositing a piezoelectric layer 3 with a C-axis tilt angle θ of 48° to 68° or -68° to -48° on the first substrate 1, the piezoelectric thin film is made to... 15 Electromechanical coupling coefficient (k) under piezoelectric parameters 2 15 To maximize this, the Lamb wave resonator of the piezoelectric layer 3 is used to excite acoustic waves in the antisymmetric A1 vibration mode of the Lamb wave, achieving an electromechanical coupling coefficient greater than 15% under the condition that the resonant frequency is greater than 3 GHz. Figure 3 The horizontal axis represents the C-axis tilt angle of the piezoelectric thin film, and the vertical axis represents the electromechanical coupling coefficient of the Lamb wave resonator, k. 2 11 Indicates that the piezoelectric film is in e 11 The electromechanical coupling coefficient, k, under piezoelectric parameters. 2 15 Indicates that the piezoelectric film is in e 15 The electromechanical coupling coefficient, k, under piezoelectric parameters. 2 33 Indicates that the piezoelectric film is in e 33 Electromechanical coupling coefficient of excitation under piezoelectric parameters.

[0059] Figure 4 This is a curve showing the electromechanical coupling coefficient of a Lamb wave resonator according to an embodiment of the present invention as a function of the direction of sound wave propagation.

[0060] refer to Figure 4 As shown, when using a piezoelectric crystal with a C-axis tilt angle of 60° as the piezoelectric layer, the Lamb waves of the A1 vibrational modes excited by different interdigitated electrode directions (i.e., different transverse electric field directions) in the plane have different electromechanical coupling coefficients. When the transverse electric field direction forms an angle of 70° to 90° or -90° to -70° with the +X axis of the global coordinate system where the C-axis-tilted piezoelectric film is located, the electromechanical coupling coefficient (k...) of the Lamb wave resonator... 2 15() greater than 15%. Wherein, the horizontal axis represents the propagation direction of the sound wave generated by the Lamb resonator, that is, the direction of the transverse electric field formed by the metal electrode, which is represented by the angle between the piezoelectric film tilted to the C-axis and the +X-axis direction of the global coordinate system, and the vertical axis represents the electromechanical coupling coefficient of the Lamb resonator.

[0061] Figure 5 This is a schematic diagram of the Lamb wave of the A1 vibration mode excited by the Lamb wave resonator according to an embodiment of the present invention.

[0062] refer to Figure 5 As shown, a Lamb wave is a plate wave. Antisymmetric Lamb waves are antisymmetric with respect to the neutral plane at x=0, meaning that the displacements of particles perpendicular to the plate at the upper and lower interfaces are equal in magnitude and direction. Lateral displacements are equal in magnitude but opposite in direction.

[0063] Figure 6 The curve shows the resonant frequency of the Lamb wave resonator of the A1 vibration mode according to an embodiment of the present invention as a function of the piezoelectric film thickness.

[0064] refer to Figure 6 As shown, a Lamb wave resonator was fabricated using scandium-doped aluminum nitride with a scandium doping concentration of 40% as the piezoelectric layer. The ratio of the piezoelectric film thickness to the Lamb wave wavelength was in the range of (2~10)*10. -3 Within a certain range, the resonant frequency of the Lamb wave resonator is always greater than 3 GHz. By studying the relationship between the resonant frequency of the A1 vibration mode and the thickness of the piezoelectric film, the thickness of the piezoelectric film that meets the requirements of 5G ultra-high frequency bands was determined. In this figure, the horizontal axis represents the ratio of the piezoelectric film thickness to the wavelength of the Lamb wave, and the vertical axis represents the resonant frequency of the Lamb wave resonator.

[0065] It should be noted that by rotating the Euler angles, the high e is selected. 15 A piezoelectric thin film with a C-axis tilt within a specific angle range under piezoelectric parameters is used. A first metal electrode layer with metal electrode arrangement within the specific angle range is deposited on the piezoelectric thin film. A mask layer is deposited on the surface of the first metal electrode layer and an etching region is defined. The resonator is released from the substrate and suspended. The first antisymmetric mode Lamb wave of the piezoelectric layer with a C-axis tilt of 48° to 68° or -68° to -48° is excited by a transverse electric field, resulting in a high electromechanical coupling coefficient (k). 2 The 5G FR1 band acoustic resonator can effectively improve the electromechanical coupling coefficient (k) of the acoustic resonator while ensuring a high resonant frequency. 2 This well meets the performance requirements of high frequency and high bandwidth filters in the current 5G frequency band.

[0066] Figure 7 This is a flowchart of a method for fabricating a Lamb wave resonator according to an embodiment of the present invention.

[0067] Figures 8(a) to 8(f) This is a schematic diagram illustrating the fabrication process of a Lamb wave resonator according to an embodiment of the present invention.

[0068] According to an exemplary embodiment of the present invention, the present invention provides a method for fabricating a Lamb wave resonator, with reference to... Figure 7 and Figures 8(a) to 8(f) As shown, it includes steps S01 to S06.

[0069] Step S01: The first substrate 1 is placed at an angle, and a piezoelectric layer 3 is deposited on the first substrate 1 by magnetron sputtering. The piezoelectric layer 3 is a piezoelectric thin film with a C-axis tilt angle of 48° to 68° or -68° to -48°.

[0070] According to an embodiment of the present invention, a first substrate 1 is placed in the vacuum reaction chamber of a magnetron sputtering apparatus, and a piezoelectric layer 3 with a C-axis tilt angle of 48° to 68° or -68° to -48° is deposited on the first substrate 1 by rotating and tilting the first substrate 1.

[0071] Step S02: Deposit a first metal electrode layer 41 on the piezoelectric layer 3. The direction of the transverse electric field formed by the metal electrodes of the first metal electrode layer 41 is at an angle of 70° to 90° or -90° to -70° with the +X axis direction of the global coordinate system where the piezoelectric thin film is tilted along the C-axis.

[0072] According to an embodiment of the present invention, the method for depositing a first metal electrode layer 41 on the piezoelectric layer 3 includes at least one of the following: electron beam evaporation, magnetron sputtering.

[0073] It should be noted that the first metal electrode layer 41 is formed on the piezoelectric layer 3, or, in the case where the first metal electrode layer 41 is formed on the piezoelectric layer 3, the above-mentioned Lamb wave resonator also includes a second metal electrode layer (not shown in the figure) formed on the lower surface of the piezoelectric layer 3.

[0074] According to an embodiment of the present invention, the A1 vibration mode can be excited by applying a transverse electric field through the interdigitated electrodes of the first metal electrode layer 41, and a second metal electrode layer does not need to be deposited under the piezoelectric layer 3. Therefore, it has greater advantages in material preparation and device fabrication compared to FBAR resonators.

[0075] Step S03: Deposit mask layer 5 on first metal electrode layer 41 and graphically define mask etching region.

[0076] According to an embodiment of the present invention, the material of the mask layer 5 can be at least one of the following: photoresist, silicon oxide, or silicon nitride. The thickness of the mask layer 5 is 0.5 μm to 10 μm.

[0077] According to an embodiment of the present invention, photolithography is used to pattern the mask etching area, and the photolithography can be electron beam lithography and / or ultraviolet lithography.

[0078] Step S04: The piezoelectric layer 3 is etched using inductively coupled plasma etching.

[0079] Step S05: Dry etching is performed on the first substrate 1 using xenon difluoride (XeF2) gas to form a cavity 6 on the side of the first substrate 1 near the piezoelectric layer 3.

[0080] Step S06: Remove the mask layer 5 using a buffered oxide etching solution.

[0081] Figure 9 The simulation performance diagram shows the Lamb wave resonator that excites the A1 vibration mode without metal electrode optimization design according to an embodiment of the present invention.

[0082] refer to Figure 9 As shown, the admittance characteristic curve of the Lamb wave resonator obtained without optimized design and fabrication of metal electrodes shows that there are many stray modes, and the spacing between two adjacent metal electrodes is 10 μm; where the horizontal axis represents the resonant frequency of the Lamb wave resonator and the vertical axis represents the admittance.

[0083] It should be noted that the spurious characteristics of the acoustic resonator are controlled by adjusting the spacing between two adjacent metal electrodes of the first metal electrode layer 41 formed on the piezoelectric layer 3. According to an embodiment of the present invention, the spacing between two adjacent metal electrodes is adjusted to 30-100 μm to suppress the spurious characteristics of the acoustic resonator.

[0084] Figure 10 The simulation performance diagram shows the Lamb wave resonator that excites the A1 vibration mode after the metal electrode optimization design according to an embodiment of the present invention.

[0085] refer to Figure 10As shown, a piezoelectric thin film with a C-axis tilt of 48°–68° or -68°–-48° is used as the piezoelectric layer. The direction of the transverse electric field formed by the first metal electrode layer 41 forms an angle of 70°–90° or -90°–-70° with the +X axis of the global coordinate system where the C-axis-tilted piezoelectric thin film is located. The arrangement of the metal electrodes in the first metal electrode layer 41 is optimized to achieve a spacing of 50 μm between adjacent metal electrodes. This results in a Lamb wave resonator with an electromechanical coupling coefficient of 15.4% near the resonant frequency of 3.76 GHz, far exceeding that of traditional AlN FBAR resonators and fully meeting the performance requirements of filters in the current 5 GFRI band. Furthermore, by optimizing the design of the first metal electrode layer 41, spurious modes of the Lamb wave resonator are suppressed, thus obtaining a Lamb wave resonator with A1 vibration modes free of spurious characteristics. Wherein, f p f represents the anti-resonant frequency. s The x-axis represents the resonant frequency, the y-axis represents the resonant frequency of the Lamb wave resonator, and the y-axis represents the admittance.

[0086] Figure 11 This is a flowchart of a method for fabricating a Lamb wave resonator according to another embodiment of the present invention.

[0087] Figure 12(a)~12(e) This is a schematic diagram illustrating the fabrication process of a Lamb wave resonator according to another embodiment of the present invention.

[0088] According to an exemplary embodiment of the present invention, the present invention also provides a method for fabricating a Lamb wave resonator by wafer bonding, referring to... Figure 11 and Figure 12(a)~12(e) As shown, it includes steps S11 to S17.

[0089] Step S11: Deposit release layer 2 on first substrate 1.

[0090] According to an embodiment of the present invention, the material of the first substrate 1 can be one of the following: silicon, glass, quartz, sapphire (Al2O3), gallium nitride (GaN), silicon carbide (SiC), or lithium niobate (LN). The material of the release layer 2 can be gallium nitride (GaN), and the thickness of the release layer 2 is 1 μm to 10 μm, for example, 1 μm, 2 μm, 5 μm, 8 μm, or 10 μm.

[0091] Step S12: The first substrate 1, on which the release layer 2 is formed, is tilted to deposit a piezoelectric layer 3 on the release layer 2. The piezoelectric layer 3 is a piezoelectric thin film with a C-axis tilt angle of 48° to 68° or -68° to -48°.

[0092] According to an embodiment of the present invention, a first substrate 1 having a release layer 2 is placed at an angle in the vacuum reaction chamber of a magnetron sputtering apparatus, and a piezoelectric layer 3 with a C-axis tilt angle of 48° to 68° or -68° to -48° is deposited on the release layer 2 by magnetron sputtering.

[0093] Step S13: Deposit a first bonding layer 71 on the piezoelectric layer 3.

[0094] According to an embodiment of the present invention, the material of the first bonding layer 71 can be one of the following: silicon dioxide, silicon nitride, or gold; the thickness of the first bonding layer 71 is 1 μm to 50 μm, for example, the thickness can be 1 μm, 10 μm, 20 μm, 40 μm, or 50 μm.

[0095] In step S14, a second bonding layer 72 is deposited on the second substrate 8, and the area on the second substrate 8 where the second bonding layer 72 is not formed is etched to form a cavity 6 on the second substrate 8.

[0096] According to an embodiment of the present invention, the material of the second substrate 8 may be one of the following: silicon, sapphire (Al2O3), gallium nitride (GaN), silicon carbide (SiC), or lithium niobate (LN).

[0097] Step S15: Align the first bonding layer 71 and the second bonding layer 72 and then perform wafer bonding.

[0098] According to an embodiment of the present invention, the first bonding layer 71 formed on the piezoelectric layer 3 is inverted, and the first bonding layer 71 and the second bonding layer 72 are aligned and wafer bonding is performed.

[0099] It should be noted that the material of the second bonding layer 72 is the same as that of the first bonding layer 71.

[0100] Step S16: The first substrate 1 is peeled off from the piezoelectric layer 3 by laser stripping release layer 2.

[0101] Step S17: A first metal electrode layer 41 is formed on the piezoelectric layer 3, wherein the direction of the electric field formed by the first metal electrode layer 41 is at an angle of 70° to 90° or -90° to -70° with the +X axis direction of the global coordinate system where the piezoelectric thin film is tilted by the C axis.

[0102] According to the Lamb resonator provided in the above embodiments of the present invention, a piezoelectric layer with a C-axis tilt angle of 48° to 68° or -68° to -48° is formed on a first substrate, and a cavity is formed between the first substrate and the piezoelectric layer. The direction of the transverse electric field formed by the first metal electrode layer is at an angle of 70° to 90° or -90° to -70° with the +X axis of the global coordinate system where the C-axis tilted piezoelectric film is located. Under the action of the transverse electric field, the piezoelectric layer excites a Lamb wave of the A1 vibration mode. Thus, the Lamb resonator achieves an electromechanical coupling coefficient of more than 15% under the condition that the resonant frequency is greater than 3GHz, so as to achieve a large electromechanical coupling coefficient in the 5G band and meet the requirements of wide bandwidth filters.

[0103] The use of ordinal numbers such as "first," "second," "third," etc., in the specification and claims to modify the corresponding elements does not imply that the element has any ordinal number, nor does it represent the order of one element with another element, or the order of manufacturing methods. The use of these ordinal numbers is only to enable a named element to be clearly distinguished from another element with the same name.

[0104] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A Lamb wave resonator, characterized in that, include: First substrate (1); A piezoelectric layer (3) is formed on the first substrate (1), and a cavity (6) is formed between the first substrate (1) and the piezoelectric layer (3). The piezoelectric layer (3) is a piezoelectric thin film tilted along the C-axis. The tilt angle of the C-axis is 48°~68° or -68°~-48° by rotating the Euler angle. The piezoelectric layer (3) is suitable for generating a Lamb wave of the first antisymmetric mode under the action of a transverse electric field. The first metal electrode layer (41) includes a metal electrode array composed of multiple positive and negative metal electrodes arranged alternately. The metal electrode array forms the transverse electric field. The first metal electrode layer (41) is formed on the piezoelectric layer (3) such that the direction of the transverse electric field is 70°~90° or -90°~-70° with the +X axis direction of the global coordinate system where the piezoelectric film tilted by the C axis is located. A release layer (2) is formed between the first substrate (1) and the piezoelectric layer (3) and is adapted to form the cavity (6) to release the space between the first substrate (1) and the piezoelectric layer (3); The release layer (2) comprises one or more layers, and the material of each layer includes one of the following: silicon dioxide, silicon nitride, gallium nitride; The thickness of the release layer (2) is 1μm~10μm; A second metal electrode layer is formed on the lower surface of the piezoelectric layer (3); The piezoelectric layer (3) generates a first-order antisymmetric mode Lamb wave under the action of the transverse electric field, so that the Lamb wave resonator achieves an electromechanical coupling coefficient of more than 15% under the condition that the resonant frequency is greater than 3GHz.

2. The Lamb wave resonator according to claim 1, characterized in that, The material of the piezoelectric layer (3) includes: scandium-doped aluminum nitride, or a composite layer material composed of aluminum nitride and scandium-doped aluminum nitride; The thickness of the piezoelectric layer (3) is 100~500nm.

3. The Lamb wave resonator according to claim 2, characterized in that, The doping concentration of scandium in the scandium-doped aluminum nitride is 0-40%.

4. The Lamb wave resonator according to claim 2, characterized in that, The scandium doping concentration in the scandium-doped aluminum nitride is 40%.

5. The Lamb wave resonator according to claim 1, characterized in that, The metal electrodes of the first metal electrode layer (41) are interdigitated electrodes, and the number of metal electrodes is 2 to 50. The distance between two adjacent metal electrodes is half the wavelength of the sound wave; The width of each of the metal electrodes is one-sixth or one-eighth of the wavelength of the sound wave; The length of each of the metal electrodes is ten wavelengths or ten and a half wavelengths of the sound wave.

6. The Lamb wave resonator according to claim 5, characterized in that, The material of the metal electrode includes one of the following: gold, aluminum, molybdenum, platinum, copper, titanium-gold alloy, titanium-aluminum alloy, titanium-copper alloy, chromium-gold alloy, chromium-aluminum alloy, and chromium-copper alloy. The thickness of the metal electrode is 10~100nm.

7. A method for fabricating a Lamb wave resonator, applicable to fabricating the Lamb wave resonator as described in any one of claims 1 to 6, characterized in that, include: The first substrate (1) is placed at an angle, and a piezoelectric layer (3) is deposited on the first substrate (1) by magnetron sputtering. The piezoelectric layer (3) is a piezoelectric thin film with a C-axis tilt angle of 48°~68° or -68°~-48°. A first metal electrode layer (41) is deposited on the piezoelectric layer (3), wherein the direction of the transverse electric field formed by the metal electrode of the first metal electrode layer (41) is 70°~90° or -90°~-70° with the +X axis direction of the global coordinate system where the piezoelectric film is tilted by the C axis; A mask layer (5) is deposited on the first metal electrode layer (41), and the mask etching area is graphically defined; The piezoelectric layer (3) was etched using inductively coupled plasma etching. The first substrate (1) is dry-etched using xenon difluoride gas to form a cavity (6) on the side of the first substrate (1) near the piezoelectric layer (3); and The mask layer (5) is removed using a buffered oxide etching solution.

8. A method for fabricating a Lamb wave resonator, applicable to fabricating the Lamb wave resonator as described in any one of claims 1 to 6, characterized in that, include: A release layer (2) is deposited on the first substrate (1); A first substrate (1) on which the release layer (2) is formed is tilted to deposit a piezoelectric layer (3) on the release layer (2), wherein the piezoelectric layer (3) is a piezoelectric thin film with a C-axis tilt angle of 48°~68° or -68°~-48°; A first bonding layer (71) is deposited on the piezoelectric layer (3); A second bonding layer (72) is deposited on the second substrate (8), and the area on the second substrate (8) where the second bonding layer (72) is not formed is etched to form a cavity (6) on the second substrate (8). After aligning the first bonding layer (71) and the second bonding layer (72), wafer bonding is performed; The first substrate (1) is peeled off from the piezoelectric layer (3) by laser ablation of the release layer (2); and A first metal electrode layer (41) is formed on the piezoelectric layer (3), wherein the direction of the transverse electric field formed by the first metal electrode layer (41) is 70°~90° or -90°~-70° with the +X axis direction of the global coordinate system where the piezoelectric film is tilted by the C axis.

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