A surface acoustic wave resonator and a spurious mode suppression method

Abstract

The application provides a surface acoustic wave resonator and a stray mode suppression method. The surface acoustic wave resonator comprises a substrate layer, a modulation layer arranged on the substrate layer, a piezoelectric layer arranged on the modulation layer, and an electrode layer arranged on the piezoelectric layer and used for exciting a surface acoustic wave mode. The modulation layer is used for reducing one or more of equivalent sound velocity, equivalent Young's modulus and equivalent elastic coefficient of a structure below the piezoelectric layer, thereby adjusting an acoustic boundary condition between the piezoelectric layer and the substrate layer and suppressing excitation of a stray mode. In the scheme, the modulation layer is arranged between the substrate layer and the piezoelectric layer, so that the purpose of suppressing high-order stray modes such as SAW modes is achieved.

Description

Technical Field

[0001] This invention relates to the field of resonator technology, specifically to a surface acoustic wave resonator and a method for suppressing stray modes. Background Technology

[0002] As mobile communication systems evolve towards higher frequencies, wider bandwidths, and higher integration, radio frequency (RF) front-end filters need to simultaneously achieve low insertion loss, wide passband bandwidth, high out-of-band rejection, and high power tolerance at higher operating frequencies. Surface acoustic wave (SAW) resonators, as a crucial fundamental unit of RF filters, have specific frequency response characteristics and electromechanical coupling coefficients (k...). 2 The level of spurious modes directly affects the passband performance and out-of-band suppression performance of the filter.

[0003] Piezoelectric thin film materials such as aluminum nitride and scandium-doped aluminum nitride (AlScN) are widely used in high-frequency acoustic devices due to their good process compatibility, high sound velocity, and good power tolerance. Introducing scandium into aluminum nitride can improve the piezoelectric response, thus enhancing the electromechanical coupling coefficient of surface acoustic wave resonators. However, as the scandium content increases, the effective sound velocity of the piezoelectric layer decreases, and higher-order stray modes (such as the Sezawa mode) are easily excited in the device, in addition to the main resonant mode. These higher-order stray modes typically appear on the high-frequency side of the main resonant peak, leading to additional peaks in the admittance curve, which in turn affects out-of-band rejection and passband flatness during filter synthesis.

[0004] In existing technologies, most solutions for improving the performance of scandium-doped aluminum nitride surface acoustic wave (SAW) devices focus on enhancing the crystal quality of the piezoelectric thin film, adjusting electrode dimensions, altering the reflective grating structure, or optimizing the layout design. While these solutions can improve device performance to some extent, their effectiveness in suppressing higher-order stray modes is limited. Summary of the Invention

[0005] In view of this, embodiments of the present invention provide a surface acoustic wave resonator and a stray mode suppression method to achieve the purpose of suppressing higher-order stray modes such as the Sizawa mode while maintaining or improving the quality of the piezoelectric layer and the electromechanical coupling coefficient.

[0006] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0007] The first aspect of this invention discloses a surface acoustic wave resonator, comprising:

[0008] Substrate layer;

[0009] A modulation layer is disposed on the substrate layer;

[0010] A piezoelectric layer is disposed on the modulation layer;

[0011] An electrode layer, disposed on the piezoelectric layer, is used to excite surface acoustic wave modes;

[0012] The modulation layer is used to reduce one or more of the equivalent sound velocity, equivalent Young's modulus, and equivalent elastic coefficient of the structure below the piezoelectric layer, thereby adjusting the acoustic boundary conditions between the piezoelectric layer and the substrate layer and suppressing the excitation of stray modes.

[0013] Optionally, the equivalent elastic modulus of the modulation layer is lower than that of the substrate layer, or lower than that of the structure below the piezoelectric layer when the modulation layer is not provided;

[0014] The thickness of the modulation layer is 1 nm to 10 μm;

[0015] The structure of the modulation layer includes one of a single layer, a composite layer, and a stacked structure;

[0016] The modulation layer is composed of one or more materials selected from aluminum nitride, silicon dioxide, silicon nitride, aluminum oxide, amorphous silicon, glass, polymer, low modulus nitride, and low-velocity medium.

[0017] Optionally, the modulation layer includes a single-crystal aluminum nitride layer formed by metal-organic chemical vapor deposition or molecular beam epitaxy.

[0018] Optionally, the substrate layer is composed of one or more materials selected from silicon, silicon-on-insulator, high-resistivity silicon, silicon carbide, sapphire, glass, and quartz.

[0019] Optionally, the total thickness of the piezoelectric layer is from 1 nm to 10 μm;

[0020] The piezoelectric layer includes one or more of the following: an aluminum nitride layer, a scandium-doped aluminum nitride layer, an aluminum nitride / scandium-doped aluminum nitride composite piezoelectric layer, and a scandium-doped aluminum nitride stack; the scandium-doped aluminum nitride stack is composed of scandium-doped aluminum nitride layers with different scandium doping concentrations.

[0021] The scandium-doped aluminum nitride layer is represented as Al. 1-x Sc x N, 0 <x≤0.45。

[0022] Optionally, the electrode layer includes: interdigitated electrodes, or a combination of interdigitated electrodes and reflective gate electrodes;

[0023] The materials of the interdigitated electrodes and / or the reflective grid electrodes include one or more of the following: gold, silver, copper, aluminum, molybdenum, chromium, nickel, platinum, titanium gold, titanium aluminum, chromium gold, chromium aluminum, titanium copper, and chromium copper, or alloys thereof, or composite metal layers.

[0024] Optionally, the interdigitated electrodes are arranged periodically, and one period of the interdigitated electrodes is the sum of one electrode width and the distance between adjacent electrodes. Twice the period is equal to the wavelength of the surface acoustic wave resonator. The ratio of the electrode width to the period is the electrode duty cycle, which is greater than or equal to 10% and less than or equal to 90%.

[0025] The number of interdigitated electrodes is from 2 to 500 pairs;

[0026] The aperture of the interdigitated electrode is from 1 nm to 1000 μm;

[0027] The width of the interdigitated electrode is 10 nm to 10 μm;

[0028] The spacing between two adjacent interdigitated electrodes is 10 nm to 10 μm;

[0029] The thickness of the interdigitated electrodes is 1 nm to 5 μm.

[0030] Optionally, the number of pairs of the reflective grid electrodes is from 2 to 500;

[0031] The aperture of the reflective grating electrode is from 1 nm to 1000 μm;

[0032] The electrode width of the reflective gate electrode is 10 nm to 10 μm;

[0033] The spacing between two adjacent reflective gate electrodes is 10 nm to 10 μm;

[0034] The thickness of the reflective gate electrode is 1 nm to 5 μm.

[0035] Optionally, the surface acoustic wave resonator further includes: an additional layer disposed above the electrode layer and / or above the piezoelectric layer;

[0036] The additional layer includes one or more of a passivation layer, a protective layer, a temperature compensation layer, or an encapsulation layer.

[0037] A second aspect of this invention discloses a stray mode suppression method applied to a surface acoustic wave (SAW) resonator, wherein the SAW resonator includes a substrate layer, a piezoelectric layer, and an electrode layer, and the stray mode suppression method includes:

[0038] A modulation layer is disposed between the substrate layer and the piezoelectric layer;

[0039] The modulation layer reduces one or more of the equivalent sound velocity, equivalent Young's modulus, and equivalent elastic coefficient of the structure beneath the piezoelectric layer.

[0040] The acoustic boundary conditions between the piezoelectric layer and the substrate layer are adjusted by the modulation layer to suppress the excitation of stray modes.

[0041] A surface acoustic wave resonator and stray mode suppression method based on the above embodiments of the present invention include: a substrate layer; a modulation layer disposed on the substrate layer; a piezoelectric layer disposed on the modulation layer; and an electrode layer disposed on the piezoelectric layer for exciting surface acoustic wave modes. The modulation layer is used to reduce one or more of the equivalent sound velocity, equivalent Young's modulus, and equivalent elastic coefficient of the structure below the piezoelectric layer, thereby adjusting the acoustic boundary conditions between the piezoelectric layer and the substrate layer and suppressing the excitation of stray modes. In this scheme, a modulation layer is disposed between the substrate layer and the piezoelectric layer. This modulation layer is used to reduce one or more of the equivalent sound velocity, equivalent Young's modulus, and equivalent elastic coefficient of the structure below the piezoelectric layer to adjust the acoustic boundary conditions between the piezoelectric layer and the substrate layer, thereby achieving the purpose of suppressing higher-order stray modes such as the Sizawa mode. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0043] Figure 1 This is a cross-sectional view of a surface acoustic wave resonator disclosed in an embodiment of the present invention;

[0044] Figure 2 This is a top view of a surface acoustic wave resonator disclosed in an embodiment of the present invention;

[0045] Figure 3 This is an X-ray diffraction full width at half maximum (FWHM) result of an AlScN thin film in a stacked structure disclosed in an embodiment of the present invention;

[0046] Figure 4 The image shows the X-ray diffraction full width at half maximum (FWHM) of an AlScN thin film in a comparative stacked structure disclosed in an embodiment of the present invention.

[0047] Figure 5 This is a comparative device simulation admittance curve disclosed in an embodiment of the present invention;

[0048] Figure 6 This is a vibration displacement distribution diagram of a comparative Rayleigh mode and a Sizawa mode disclosed in an embodiment of the present invention;

[0049] Figure 7 The above are simulation admittance curves of the embodiments and comparative examples disclosed in this invention after changing the Young's modulus or equivalent elastic coefficient of the aluminum nitride layer.

[0050] Figure 8 The measured admittance curves of scandium-doped aluminum nitride surface acoustic wave devices disclosed in the embodiments and comparative examples of the present invention are shown.

[0051] Figure 9 A comparison diagram of the electromechanical coupling coefficients of scandium-doped aluminum nitride surface acoustic wave devices disclosed in the embodiments of the present invention and comparative examples;

[0052] Figure 10 This is a flowchart of a stray mode suppression method disclosed in an embodiment of the present invention. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] In this application, the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0055] As the background technology indicates, existing technologies for improving the performance of scandium-doped aluminum nitride surface acoustic wave (SAW) devices primarily focus on enhancing the crystal quality of the piezoelectric thin film, adjusting electrode dimensions, altering the reflector grating structure, or optimizing the layout design. While these approaches can improve device performance to some extent, their effectiveness in suppressing higher-order stray modes is limited. Especially in high-frequency ASW devices with large electromechanical coupling coefficients, it is difficult to simultaneously achieve a large electromechanical coupling coefficient and a low level of higher-order stray modes through conventional electrode design or conventional piezoelectric thin film optimization alone.

[0056] Therefore, this invention discloses a surface acoustic wave resonator and a method for suppressing stray modes. In this scheme, a modulation layer is disposed between the substrate layer and the piezoelectric layer. The modulation layer is used to reduce one or more of the equivalent sound velocity, equivalent Young's modulus, and equivalent elastic coefficient of the structure below the piezoelectric layer, so as to adjust the acoustic boundary conditions between the piezoelectric layer and the substrate layer, thereby achieving the purpose of suppressing higher-order stray modes such as the Sizawa mode.

[0057] like Figure 1The image shown is a cross-sectional view of a surface acoustic wave resonator disclosed in an embodiment of the present invention.

[0058] First, it should be noted that the specific structural parameters, material combinations, thicknesses, and frequencies described below are only used to illustrate the embodiments of the present invention and are not intended to limit the scope of protection of this application.

[0059] The surface acoustic wave resonator 100 includes a substrate layer 101, a modulation layer 102, a piezoelectric layer 103, and an electrode layer 104. The modulation layer 102 is disposed on the substrate layer 101, the piezoelectric layer 103 is disposed on the modulation layer 102, and the electrode layer 104 is disposed on the piezoelectric layer 103.

[0060] In some embodiments, the surface acoustic wave resonator 100 can be formed by forming a modulation layer 102 on a substrate layer 101; forming a piezoelectric layer 103 on the modulation layer 102; and forming an electrode layer 104 on the piezoelectric layer 103. The modulation layer 102 and the piezoelectric layer 103 can be obtained by metal-organic chemical vapor deposition, physical vapor deposition, chemical vapor deposition, atomic layer deposition, molecular beam epitaxy, or other thin film formation methods. The electrode layer 104 can be formed by deposition, photolithography, etching, lift-off, or a combination thereof. The above description is only used to illustrate one implementation of the surface acoustic wave resonator 100 of the present invention and does not limit the present invention to a specific fabrication process.

[0061] In one embodiment, the substrate 101 is composed of one or more materials selected from silicon, silicon-on-insulator, high-resistivity silicon, silicon carbide, sapphire, glass, and quartz.

[0062] Specifically, the substrate layer 101 can be one or more of the following: silicon substrate, silicon-on-insulator substrate, high-resistivity silicon substrate, silicon carbide substrate, sapphire substrate, glass substrate, and quartz substrate.

[0063] Optionally, the substrate 101 is high-resistivity silicon, and the resistivity of high-resistivity silicon is greater than 10 kΩ·cm.

[0064] The modulation layer 102 is located between the substrate layer 101 and the piezoelectric layer 103. The modulation layer 102 is used to reduce one or more of the equivalent sound velocity, equivalent Young's modulus, and equivalent elastic coefficient of the structure below the piezoelectric layer 103, resulting in a lower equivalent sound velocity, a lower equivalent Young's modulus, or a lower equivalent elastic coefficient, thereby modulating the acoustic boundary conditions of the structure below the piezoelectric layer 103. This suppresses the excitation of stray modes, i.e., reduces the excitation of higher-order acoustic modes 302 in the piezoelectric layer 103 or the piezoelectric stack.

[0065] In a specific implementation, the equivalent elastic coefficient of the modulation layer 102 is lower than that of the substrate layer 101, or lower than that of the structure below the piezoelectric layer 103 when no modulation layer is provided. Through the above configuration, the modulation layer 102 can reduce the equivalent sound velocity on the substrate side, thereby suppressing higher-order stray modes.

[0066] It should be noted that the working mechanism of the modulation layer 102 can be understood as follows: when the modulation layer 102 below the piezoelectric layer 103 has a low equivalent elastic coefficient or a low equivalent sound velocity, the acoustic boundary conditions between the piezoelectric layer 103 and the substrate layer 101 change, causing higher-order modes that would normally easily form standing waves in the piezoelectric layer 103 to leak to the substrate side or become difficult to excite effectively. Consequently, the amplitude of higher-order stray modes such as the Sizawa mode in the admittance response decreases.

[0067] In one embodiment, the structure of the modulation layer 102 includes one of a single layer, a composite layer, and a stacked structure;

[0068] The modulation layer 102 can be a low-velocity layer, a low Young's modulus layer, a low elastic coefficient layer, a low equivalent elastic constant layer, or a material layer with tensile strain that reduces the equivalent elastic constant. Specifically, the material of the modulation layer 102 can include one or more of the following: aluminum nitride, silicon dioxide, silicon nitride, alumina, amorphous silicon, glass, polymer, low-modulus nitride, and low-velocity dielectric materials, in a single-layer, composite, or stacked structure.

[0069] The thickness of the modulation layer 102 can be from 1 nm to 10 μm. For example, the thickness of the modulation layer 102 can be 1 nm, 5 nm, 10 nm, 50 nm, 100 nm, 200 nm, 500 nm, 1 μm, 5 μm or 10 μm.

[0070] Preferably, the modulation layer 102 is a single-crystal aluminum nitride layer formed by metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).

[0071] In existing technologies, especially in high-frequency, large electromechanical coupling coefficient aluminum scandium nitride surface acoustic wave devices, it is difficult to simultaneously achieve a large electromechanical coupling coefficient and a low level of higher-order stray modes by simply using conventional electrode design or conventional piezoelectric thin film optimization.

[0072] Therefore, in the preferred embodiment, the modulation layer 102 is a single-crystal aluminum nitride layer formed by MOCVD or MBE, which can have high crystal quality and low equivalent elastic modulus. It can also serve as the bottom layer of the upper piezoelectric layer 103, enabling the subsequently formed aluminum nitride or scandium-doped aluminum nitride piezoelectric layer to have better crystal orientation and smaller X-ray diffraction full width at half maximum (FWHM). Thus, the modulation layer 102 can simultaneously play two roles: first, reducing the equivalent sound velocity or equivalent elastic modulus on the substrate side to suppress the excitation of higher-order stray modes such as the Sizawa mode while maintaining or improving the quality of the piezoelectric layer and the electromechanical coupling coefficient; second, improving the crystal quality of the upper piezoelectric layer 103 to enhance the electromechanical coupling coefficient of the main resonant modes such as the Rayleigh mode.

[0073] In another embodiment, the modulation layer 102 may also be a low Young's modulus aluminum nitride layer formed by physical vapor deposition (PVD), chemical vapor deposition, atomic layer deposition, or other methods. As long as the modulation layer 102 can reduce one or more of the equivalent sound velocity, equivalent Young's modulus, and equivalent elastic coefficient of the structure beneath the piezoelectric layer 103, suppression of higher-order stray modes can be achieved.

[0074] The piezoelectric layer 103 can be a single-layer piezoelectric layer or a composite piezoelectric layer.

[0075] In one embodiment, the piezoelectric layer 103 includes one or more of the following: an aluminum nitride layer, a scandium-doped aluminum nitride layer, an aluminum nitride / scandium-doped aluminum nitride composite piezoelectric layer, and a scandium-doped aluminum nitride stack, wherein the scandium-doped aluminum nitride stack is composed of scandium-doped aluminum nitride layers with different scandium doping concentrations.

[0076] Specifically, scandium-doped aluminum nitride layers are represented as Al 1-x Sc x N, 0 <x≤0.45。

[0077] For example, Al 1-x Sc x x in N can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, or 0.45.

[0078] The total thickness of the piezoelectric layer 103 is from 1 nm to 10 μm; for example, the total thickness of the piezoelectric layer 103 can be 50 nm, 100 nm, 200 nm, 300 nm, 500 nm, 800 nm, 1 μm, 2 μm, 5 μm, or 10 μm. When the piezoelectric layer 103 is a composite piezoelectric layer or a stacked piezoelectric layer, the above-mentioned total thickness is the sum of the thicknesses of each piezoelectric material layer in the composite piezoelectric layer or the stacked piezoelectric layer; the single-layer thickness, number of layers, material combination, arrangement order, and stacking structure of each piezoelectric material layer are not limited.

[0079] like Figure 2The image shown is a top view of a surface acoustic wave resonator disclosed in an embodiment of the present invention.

[0080] The electrode layer 104 includes: interdigitated electrodes 1041, or a combination of interdigitated electrodes 1041 and reflective gate electrodes 1042.

[0081] Specifically, the interdigitated electrode 1041 is used to excite surface acoustic waves in the piezoelectric layer 103. The reflective grating electrode 1042 can be disposed on both sides of the interdigitated electrode 1041 to reflect the acoustic wave energy propagating along the surface acoustic layer, thereby forming a resonant structure.

[0082] In one embodiment, the electrode layer 104 may also include other electrode structures capable of exciting surface acoustic wave modes.

[0083] In one embodiment, the materials of the interdigital electrode 1041 and / or the reflective gate electrode 1042 (i.e., electrode layer 104) include one or more of the following: gold, silver, copper, aluminum, molybdenum, chromium, nickel, platinum, titanium gold, titanium aluminum, chromium gold, chromium aluminum, titanium copper, and chromium copper, or alloys of the above materials, or composite metal layers composed of the above materials.

[0084] Preferably, the electrode layer 104 can be a chromium / gold composite metal layer.

[0085] Optionally, the electrode width of the interdigital electrode 1041 can be from 10 nm to 10 μm. The spacing between two adjacent interdigital electrodes 1041 can be from 10 nm to 10 μm. The number of pairs of interdigital electrodes 1041 can be from 2 to 500. The thickness of the interdigital electrode 1041 can be from 1 nm to 5 μm. The aperture of the interdigital electrode 1041 can be from 1 nm to 1000 μm.

[0086] Among them, the interdigital electrodes 1041 are arranged periodically. One period of the interdigital electrodes 1041 is the sum of one electrode width and the distance between adjacent electrodes. Twice the period is equal to the wavelength of the surface acoustic wave resonator 100. The ratio of the electrode width to the period is the electrode duty cycle, which is greater than or equal to 10% and less than or equal to 90%.

[0087] It should be noted that the electrode duty cycle can be understood as the proportion of the electrode width of the interdigitated electrode 1041 in one electrode cycle. One electrode cycle can include one electrode width and one spacing between adjacent electrodes. An electrode duty cycle greater than or equal to 10% and less than or equal to 90% indicates that the electrode width can be adjusted according to the target frequency of the device, the target electromechanical coupling coefficient, and the target spurious mode suppression effect, and is not limited to a structure where the electrode width and the spacing between adjacent electrodes are equal.

[0088] The representative wavelength of the surface acoustic wave resonator 100 can be 600 nm or 640 nm. In other embodiments, the wavelength of the surface acoustic wave resonator 100 can also be 320 nm, 360 nm, 400 nm, 440 nm, 480 nm, 520 nm or 560 nm.

[0089] Optionally, the electrode width of the reflective gate electrode 1042 can be from 10 nm to 10 μm. The spacing between two adjacent reflective gate electrodes 1042 can be from 10 nm to 10 μm. The number of pairs of reflective gate electrodes 1042 can be from 2 to 500. The thickness of the reflective gate electrode 1042 can be from 1 nm to 5 μm. The aperture of the reflective gate electrode 1042 can be from 1 nm to 1000 μm.

[0090] In one embodiment, the electrode widths of the interdigitated electrode 1041 and the reflective grid electrode 1042 are equal to the spacing between adjacent electrodes, resulting in an electrode duty cycle of 50%. The wavelength of the surface acoustic wave resonator 100 is equal to twice the sum of the electrode width and the electrode spacing.

[0091] It should be noted that the interdigitated electrode 1041 and the reflective grid electrode 1042 can have the same electrode width, the same electrode spacing, the same thickness and the same aperture; or they can be set to different electrode widths, electrode spacings, thicknesses or apertures according to the target operating frequency, target reflection intensity, target electromechanical coupling coefficient and target stray mode suppression effect.

[0092] In one embodiment, the surface acoustic wave resonator 100 further includes: an additional layer disposed above the electrode layer 104 and / or above the piezoelectric layer 103, or at other locations of the device;

[0093] Additional layers include one or more of passivation layers, protective layers, temperature compensation layers, or encapsulation layers, used to improve device environmental stability, temperature stability, or package reliability.

[0094] The above technical solution will be described in detail below with reference to specific embodiments and comparative examples.

[0095] like Figure 3 The figure shown is an X-ray diffraction full width at half maximum (FWHM) result of an AlScN thin film in a stacked structure disclosed in an embodiment of the present invention.

[0096] like Figure 4 The figure shown is an X-ray diffraction full width at half maximum (FWHM) result of an AlScN thin film in a comparative stacked structure disclosed in an embodiment of the present invention.

[0097] In the following examples and comparative examples, the piezoelectric layer material is a single scandium-doped aluminum nitride layer, which is formed by magnetron sputtering. The scandium-doped aluminum nitride is Al. 1-x Sc xN, where x = 0.3, i.e., Al 0.7 Sc 0.3 N.

[0098] In the following embodiments and comparative examples, the number of interdigitated electrodes is 50 pairs, and the number of reflective gate electrodes is 20 pairs on each side. The electrode material is a chromium / gold composite metal layer, wherein the chromium thickness is 2 nm and the gold thickness is 20 nm.

[0099] In this embodiment, the stacked structure includes a high-resistivity silicon substrate, a 100nm MOCVD aluminum nitride modulation layer, and a 500nm Al layer. 0.7 Sc 0.3 The structure consists of an N-piezoelectric layer and an electrode layer. It can be represented as: high-resistivity silicon / 100nm MOCVD aluminum nitride layer / 500nm Al 0.7 Sc 0.3 N piezoelectric layer / electrode layer.

[0100] In the comparative example, the stacked structure includes a high-resistivity silicon substrate, a 100nm PVD aluminum nitride layer, a 500nm Al0.7Sc0.3N piezoelectric layer, and an electrode layer. This structure can be represented as: high-resistivity silicon / 100nm PVD aluminum nitride layer / 500nm Al0.7Sc0.3N piezoelectric layer. 0.7 Sc 0.3 N piezoelectric layer / electrode layer.

[0101] like Figure 3 As shown, at 500nm Al 0.7 Sc 0.3 Under N-piezoelectric layer conditions, Al in the examples 0.7 Sc 0.3 The X-ray diffraction full width at half maximum (FWHM) of the N piezoelectric layer is 0.81°; For example... Figure 4 As shown, in the comparative example, Al 0.7 Sc 0.3 The X-ray diffraction full width at half maximum (FWHM) of the N piezoelectric layer is 1.86°; this indicates that the N piezoelectric layer exhibits high resistivity on a silicon substrate and Al... 0.7 Sc 0.3 Introducing an MOCVD aluminum nitride modulation layer between N piezoelectric layers can significantly improve Al 0.7 Sc 0.3 Crystal orientation quality of the N piezoelectric layer.

[0102] like Figure 5 The figure shown is a comparative device simulation admittance curve disclosed in an embodiment of the present invention.

[0103] The interdigitated electrodes can excite the main resonant mode 301, which can be a Rayleigh mode. Simultaneously, at the high-frequency side of the main resonant peak, a higher-order stray mode 302, induced by the Sizawa mode, may appear. This higher-order stray mode 302 will form an additional peak in the admittance curve, thus affecting the frequency response purity of the surface acoustic wave resonator.

[0104] like Figure 6 The diagram shows the vibration displacement distribution of Rayleigh mode and Sizawa mode, respectively, according to an embodiment of the present invention. The left side shows the vibration displacement distribution of the Rayleigh mode, and the right side shows the vibration displacement distribution of the Sizawa mode.

[0105] Among them, the Rayleigh mode, as the main resonant mode of the surface acoustic wave resonator, has its acoustic energy mainly concentrated near the surface of the piezoelectric layer and propagating along the surface of the device. Compared with the Rayleigh mode, the Sizawa mode has a more complex vibration displacement distribution in the thickness direction, and its vibration displacement exhibits a multi-order distribution in the piezoelectric layer and the underlying structure.

[0106] like Figure 7 The figure shown is a simulation admittance curve of the embodiment and comparative example of the present invention after changing the Young's modulus or equivalent elastic coefficient of the aluminum nitride layer.

[0107] Specifically, when the equivalent elastic modulus of the aluminum nitride layer was reduced from 450 GPa to 250 GPa, the peak value of the higher-order stray modes was significantly weakened. The simulation results indicate that reducing the equivalent elastic modulus of the modulation layer can effectively suppress the excitation of higher-order stray modes.

[0108] like Figure 8 The figure shows the measured admittance curves of scandium-doped aluminum nitride surface acoustic wave (SAW) devices according to the embodiments and comparative examples disclosed in this invention. The wavelengths of the SAW devices are 600 nm and 640 nm.

[0109] Among them, in the same 500nm Al 0.7 Sc 0.3 Under the same electrode design conditions and with an N-piezoelectric layer, compared with the comparative example using a PVD aluminum nitride layer, the embodiment using a MOCVD aluminum nitride modulation layer significantly suppresses higher-order stray modes on the high-frequency side of the main resonance peak.

[0110] like Figure 9 The figure shown is a comparison of the electromechanical coupling coefficients of the scandium-doped aluminum nitride surface acoustic wave devices disclosed in the embodiments of the present invention and the comparative examples.

[0111] Among them, the embodiment using MOCVD aluminum nitride modulation layer, compared to the comparative embodiment using PVD aluminum nitride layer, shows that the k of the surface acoustic wave resonator... 2 Significantly improved. In some embodiments, k 2The average improvement is approximately 40%, with a maximum improvement of approximately 64%. At operating frequencies above 6 GHz, surface acoustic wave resonators can achieve a k-value greater than 2%. 2 A quality factor (Q) greater than 500 and a merit value (FOM=k) greater than 10. 2 ·Q).

[0112] The beneficial effects of the above-described embodiments of the present invention are as follows: by setting a modulation layer between the substrate layer and the piezoelectric layer, the acoustic boundary conditions can be adjusted at the stacked structure level without significantly changing the conventional interdigitated electrode and reflective gate electrode layout structure. This allows for the suppression of higher-order stray modes such as the Sizawa mode while maintaining or improving the quality of the piezoelectric layer and the electromechanical coupling coefficient. This solution is applicable to scandium-doped aluminum nitride high-frequency surface acoustic wave resonators, especially those requiring a large k-value. 2 And low spurious response RF front-end filters. When the modulation layer uses an MOCVD aluminum nitride layer, the MOCVD aluminum nitride layer can improve the crystal quality of the upper scandium-doped aluminum nitride piezoelectric layer and further improve the device's k-value. 2 Therefore, the embodiments of the present invention can simultaneously achieve high-order stray mode suppression and electromechanical coupling performance improvement.

[0113] like Figure 10 The diagram shows a flowchart of a stray mode suppression method disclosed in an embodiment of the present invention. This method is applied to a surface acoustic wave (SAW) resonator, which includes a substrate layer, a piezoelectric layer, and an electrode layer. The stray mode suppression method includes the following steps:

[0114] Step S1: Set a modulation layer between the substrate layer and the piezoelectric layer.

[0115] Specifically, a modulation layer is introduced above the substrate and below the piezoelectric layer, making the modulation layer an intermediate layer between the two. Unlike conventional structures where the piezoelectric layer is formed directly on the substrate, by additionally setting a modulation layer between the substrate and the piezoelectric layer, a structural basis is provided for subsequent adjustment of the acoustic boundary conditions at the bottom of the piezoelectric layer. The modulation layer can be formed in the same way or differently from the piezoelectric layer. For example, the modulation layer and the piezoelectric layer can be formed continuously using the same deposition equipment or in steps using different processes.

[0116] Step S2: Reduce one or more of the equivalent sound velocity, equivalent Young's modulus, and equivalent elastic coefficient of the structure below the piezoelectric layer by using the modulation layer.

[0117] It should be noted that the modulation layer, through its own material properties (such as a lower equivalent elastic modulus than the substrate layer), reduces the overall equivalent stiffness of the structure beneath the piezoelectric layer, which is composed of the modulation layer and the substrate layer. It should be understood that any reduction in one or more of the above three factors implies that the modulation layer reduces the equivalent stiffness of the structure beneath the piezoelectric layer.

[0118] Step S3: Adjust the acoustic boundary conditions between the piezoelectric layer and the substrate layer through the modulation layer to suppress the excitation of stray modes.

[0119] When the equivalent stiffness beneath the piezoelectric layer decreases, the mechanical constraints (i.e., acoustic boundary conditions) that the sound waves satisfy when propagating between the piezoelectric layer and the underlying structure change accordingly.

[0120] Specifically, higher-order modes (such as the Sizawa mode), which are originally easy to excite in the piezoelectric layer and form standing wave distributions in the thickness direction, are more likely to radiate and leak their acoustic energy to the substrate side after the boundary conditions are changed, making it difficult to form strong resonance enhancement in the piezoelectric layer. Therefore, the peak intensity of higher-order stray modes in the admittance response is effectively weakened, and the frequency response purity of the surface acoustic wave resonator is improved.

[0121] Based on the stray mode suppression method disclosed in the above embodiments of the present invention, a modulation layer is disposed between the substrate layer and the piezoelectric layer. This modulation layer is used to reduce one or more of the equivalent sound velocity, equivalent Young's modulus, and equivalent elastic coefficient of the structure beneath the piezoelectric layer, thereby adjusting the acoustic boundary conditions between the piezoelectric layer and the substrate layer. This achieves the goal of suppressing higher-order stray modes such as the Sizawa mode while maintaining or improving the quality of the piezoelectric layer and the electromechanical coupling coefficient.

[0122] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for system or system embodiments, since they are basically similar to method embodiments, the description is relatively simple, and relevant parts can be referred to the descriptions in the method embodiments. The systems and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0123] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A surface acoustic wave resonator, characterized in that, include: Substrate layer; A modulation layer is disposed on the substrate layer; A piezoelectric layer is disposed on the modulation layer; An electrode layer, disposed on the piezoelectric layer, is used to excite surface acoustic wave modes; The modulation layer is used to reduce one or more of the equivalent sound velocity, equivalent Young's modulus, and equivalent elastic coefficient of the structure below the piezoelectric layer, thereby adjusting the acoustic boundary conditions between the piezoelectric layer and the substrate layer and suppressing the excitation of stray modes.

2. The surface acoustic wave resonator according to claim 1, characterized in that, The equivalent elastic coefficient of the modulation layer is lower than that of the substrate layer, or lower than that of the structure below the piezoelectric layer when the modulation layer is not provided. The thickness of the modulation layer is 1 nm to 10 μm; The structure of the modulation layer includes one of a single layer, a composite layer, and a stacked structure; The modulation layer is composed of one or more materials selected from aluminum nitride, silicon dioxide, silicon nitride, aluminum oxide, amorphous silicon, glass, polymer, low modulus nitride, and low-velocity medium.

3. The surface acoustic wave resonator according to claim 1, characterized in that, The modulation layer includes a single-crystal aluminum nitride layer formed by metal-organic chemical vapor deposition or molecular beam epitaxy.

4. The surface acoustic wave resonator according to claim 1, characterized in that, The substrate is composed of one or more materials selected from silicon, silicon-on-insulator, high-resistivity silicon, silicon carbide, sapphire, glass, and quartz.

5. The surface acoustic wave resonator according to claim 1, characterized in that, The total thickness of the piezoelectric layer is 1 nm to 10 μm; The piezoelectric layer includes one or more of the following: an aluminum nitride layer, a scandium-doped aluminum nitride layer, an aluminum nitride / scandium-doped aluminum nitride composite piezoelectric layer, and a scandium-doped aluminum nitride stack; the scandium-doped aluminum nitride stack is composed of scandium-doped aluminum nitride layers with different scandium doping concentrations. The scandium-doped aluminum nitride layer is represented as Al. 1-x Sc x N, 0 <x≤0.45。 6. The surface acoustic wave resonator according to claim 1, characterized in that, The electrode layer includes: interdigitated electrodes, or a combination of interdigitated electrodes and reflective grid electrodes; The materials of the interdigitated electrodes and / or the reflective grid electrodes include one or more of the following: gold, silver, copper, aluminum, molybdenum, chromium, nickel, platinum, titanium gold, titanium aluminum, chromium gold, chromium aluminum, titanium copper, and chromium copper, or alloys thereof, or composite metal layers.

7. The surface acoustic wave resonator according to claim 6, characterized in that, The interdigitated electrodes are arranged periodically, and one period of the interdigitated electrodes is the sum of one electrode width and the distance between adjacent electrodes. Twice the period is equal to the wavelength of the surface acoustic wave resonator. The ratio of the electrode width to the period is the electrode duty cycle, which is greater than or equal to 10% and less than or equal to 90%. The number of interdigitated electrodes is from 2 to 500 pairs; The aperture of the interdigitated electrode is from 1 nm to 1000 μm; The width of the interdigitated electrode is 10 nm to 10 μm; The spacing between two adjacent interdigitated electrodes is 10 nm to 10 μm; The thickness of the interdigitated electrodes is 1 nm to 5 μm.

8. The surface acoustic wave resonator according to claim 6, characterized in that, The number of pairs of the reflective grating electrodes is from 2 to 500; The aperture of the reflective grating electrode is from 1 nm to 1000 μm; The electrode width of the reflective gate electrode is 10 nm to 10 μm; The spacing between two adjacent reflective gate electrodes is 10 nm to 10 μm; The thickness of the reflective gate electrode is 1 nm to 5 μm.

9. The surface acoustic wave resonator according to any one of claims 1 to 8, characterized in that, The surface acoustic wave resonator further includes: an additional layer disposed above the electrode layer and / or above the piezoelectric layer; The additional layer includes one or more of a passivation layer, a protective layer, a temperature compensation layer, or an encapsulation layer.

10. A method for suppressing stray modes, characterized in that, The method for suppressing stray modes, applied to a surface acoustic wave (SAW) resonator comprising a substrate layer, a piezoelectric layer, and an electrode layer, includes: A modulation layer is disposed between the substrate layer and the piezoelectric layer; The modulation layer reduces one or more of the equivalent sound velocity, equivalent Young's modulus, and equivalent elastic coefficient of the structure beneath the piezoelectric layer; The acoustic boundary conditions between the piezoelectric layer and the substrate layer are adjusted by the modulation layer to suppress the excitation of stray modes.

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