A high frequency acoustic wave resonator and a method for preparing the same

Abstract

The present invention relates to the field of microelectronic devices, and in particular to a high-frequency acoustic wave resonator and a preparation method thereof. The high-frequency acoustic wave resonator comprises a supporting substrate, a piezoelectric film and an interdigital transducer stacked in sequence from bottom to top; wherein the sound velocity of the supporting substrate is not less than 5000 m / s; the target mode of the high-frequency acoustic wave resonator is a quasi-bulk wave mode generated by longitudinal electric field excitation; the thickness of the interdigital transducer is inversely proportional to the material density of the interdigital transducer; and the sound velocity of the target mode is less than the sound velocity of the supporting substrate. Based on a heterogeneous integrated substrate, while simplifying the structure of the acoustic wave resonator, the ohmic loss is reduced and the electromechanical coupling coefficient of the high-order mode is improved.

Description

Technical Field

[0001] The invention relates to the field of microelectronic devices, and in particular to a high-frequency acoustic wave resonator and a preparation method thereof. Background Art

[0002] The modern communication industry has higher and higher requirements for signal quality and the competition for communication spectrum resources is becoming more and more intense. Low loss, wide bandwidth, tunability and temperature stability have become the common goals pursued by the communication industry. Acoustic resonators have been widely used in the communication field due to their small size, large bandwidth and high Q value. Acoustic resonators include surface acoustic wave (SAW) resonators and bulk acoustic wave (BAW) resonators.

[0003] In the related art, since the resonant frequency of the BAW resonator is inversely proportional to the thickness of the device, the thickness of the piezoelectric film is usually reduced to increase the frequency of the resonator. However, as the frequency increases, the suspended piezoelectric film gradually becomes thinner, the structure becomes more fragile and heat dissipation becomes more difficult. And usually the first-order plate wave mode is excited by the structure of the top interdigitated electrode and the suspended bottom electrode to meet the high-frequency requirements. However, for single-crystal piezoelectric materials, it is very difficult to form a patterned suspended bottom electrode, and the electrode width is small at high frequencies, and the ohmic loss is large. Therefore, how to simplify the resonator structure, reduce the ohmic loss, and make the resonator have a larger electromechanical coupling coefficient has become the key to achieving high-performance high-frequency applications. Summary of the invention

[0004] To solve the above technical problems, the present application discloses, on one hand, a high-frequency acoustic wave resonator, which includes a supporting substrate, a piezoelectric film and an interdigital transducer stacked sequentially from bottom to top;

[0005] Among them, the sound velocity of the supporting substrate is not less than 5000 meters per second; the target mode of the high-frequency acoustic wave resonator is a quasi-bulk wave mode generated by longitudinal electric field excitation; the thickness of the interdigital transducer is inversely proportional to the material density of the interdigital transducer; and the sound velocity of the target mode is less than the sound velocity of the supporting substrate.

[0006] In a feasible embodiment, the product of the period of the IDT and the frequency of the target mode is greater than or equal to 80% of the sound velocity of the supporting substrate and less than the sound velocity of the supporting substrate.

[0007] In a feasible embodiment, the quasi-bulk wave modes include horizontal shear wave modes, Lamb wave modes, and first-order and higher-order modes of Rayleigh modes.

[0008] In a feasible embodiment, the thickness of the IDT is the product of a preset value and the thickness of a reference IDT;

[0009] The preset value is a ratio of the material density of the reference IDT to the material density of the IDT;

[0010] When the material of the reference IDT is pure aluminum or an alloy with an aluminum content exceeding 95%, the thickness of the reference IDT is greater than or equal to 15% of the wavelength of the high-frequency acoustic wave resonator.

[0011] In a feasible embodiment, when the material of the IDT is aluminum, the material of the piezoelectric film is X-cut lithium niobate, and the material of the supporting substrate is 6H-silicon carbide, the thickness of the IDT is 0.2 times the wavelength.

[0012] In a feasible embodiment, when the material of the IDT is aluminum, the material of the piezoelectric film is X-cut lithium niobate, and the material of the supporting substrate is sapphire, the thickness of the IDT is 0.18 to 0.19 times the wavelength.

[0013] In a feasible embodiment, when the material of the IDT is aluminum, the material of the piezoelectric film is X-cut lithium tantalate, and the material of the supporting substrate is sapphire, the thickness of the IDT is 0.19 to 0.2 times the wavelength.

[0014] In a feasible embodiment, the piezoelectric film includes at least one of lithium niobate, lithium tantalate, potassium niobate, aluminum nitride, scandium-doped aluminum nitride, zinc oxide, lead zirconate titanate, or lead magnesium niobate-lead titanate crystal.

[0015] In a feasible embodiment, the IDT is any one of a single-layer metal film, a multi-layer metal film, and a composite film composed of metal and non-metal.

[0016] On the other hand, the present application also discloses a method for preparing a high-frequency acoustic wave resonator, which comprises:

[0017] Providing a supporting substrate with a piezoelectric film on the top layer; the sound velocity of the supporting substrate is not less than 5000 m / s;

[0018] An IDT is prepared on a piezoelectric film; the thickness of the IDT is inversely proportional to the material density of the IDT; the target mode of the high-frequency acoustic wave resonator is a quasi-bulk wave mode generated by longitudinal electric field excitation; and the sound velocity of the target mode is less than the sound velocity of the supporting substrate.

[0019] By adopting the above technical solution, the high-frequency acoustic wave resonator provided by the present application has the following beneficial effects:

[0020] The high-frequency acoustic wave resonator includes a supporting substrate, a piezoelectric film and an interdigital transducer stacked in sequence from bottom to top; wherein the sound velocity of the supporting substrate is not less than 5000 m / s; the target mode of the high-frequency acoustic wave resonator is a quasi-bulk wave mode generated by longitudinal electric field excitation; the thickness of the interdigital transducer is inversely proportional to the material density of the interdigital transducer; the sound velocity of the target mode is less than the sound velocity of the supporting substrate. In this way, the electromechanical coupling coefficient of the first-order mode can be effectively reduced, and the electromechanical coupling coefficient of the high-order mode is relatively improved, and by setting the sound velocity of the high-order mode to be lower than the sound velocity of the supporting substrate, the sound wave can be prevented from leaking to the supporting substrate, so that the sound wave energy is constrained on the substrate surface. At the same time, the setting of the thickness of the interdigital transducer means lower ohmic loss, which is very important for high-frequency resonators with small wavelengths and small electrode widths, and the high-frequency acoustic wave resonator also has the advantage of simple structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 is a structural schematic diagram of a high-frequency acoustic wave resonator provided in an embodiment of the present application;

[0023] Figure 2 is a simulated admittance curve corresponding to different thicknesses of the interdigital transducers provided in the embodiment of the present application;

[0024] Figure 3 yes Figure 2 The vibration mode diagram corresponding to the S1 mode;

[0025] Figure 4 is a simulated admittance curve corresponding to the first high-frequency acoustic wave resonator provided in an embodiment of the present application;

[0026] Figure 5 yes Figure 4 The vibration mode diagram corresponding to the target mode;

[0027] Figure 6 is a simulated admittance curve corresponding to the second high-frequency acoustic wave resonator provided in an embodiment of the present application;

[0028] Figure 7 yes Figure 6 The vibration mode diagram corresponding to the target mode;

[0029] Figure 8 is a simulated admittance curve corresponding to the third high-frequency acoustic wave resonator provided in an embodiment of the present application;

[0030] Fig. 9 is a simulated admittance curve corresponding to the fourth high-frequency acoustic wave resonator provided in an embodiment of the present application;

[0031] Fig.10 yes Figure 8 The vibration mode diagram corresponding to the target mode;

[0032] Fig.11 yes Fig. 9 The vibration mode diagram corresponding to the target mode;

[0033] Fig.12 It is a schematic flow chart of a method for preparing a high-frequency acoustic wave resonator provided in an embodiment of the present application.

[0034] The following is a supplementary description of the attached drawings:

[0035] 1-support substrate; 2-piezoelectric film; 3-interdigital transducer. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0037] The term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure or characteristic that may be included in at least one implementation of the present application. In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "top", "bottom", etc. is based on the orientation or positional relationship shown in the accompanying drawings, which is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present application. In addition, the terms "first" and "second" are used only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may include one or more of the features explicitly or implicitly. Moreover, the terms "first", "second", etc. are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described here can be implemented in an order other than those illustrated or described here.

[0038] For the purpose of the following detailed description, it should be understood that the present invention may adopt various alternative changes and step sequences, unless expressly specified to the contrary. In addition, except in any operating examples, or otherwise indicated, all numbers representing the amount of ingredients used in the specification and claims should be understood to be modified by the term "about" in all cases. Therefore, unless otherwise indicated, the numerical parameters set forth in the following specification and the attached claims are approximate values ​​that vary according to the desired performance to be obtained by the present invention. At least it is not intended to limit the application of the doctrine of equivalents to the scope of the claims, and each numerical parameter should at least be interpreted according to the number of reported significant figures and by applying ordinary rounding techniques.

[0039] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values ​​set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0040] When a numerical range is disclosed herein, the above range is deemed to be continuous and includes the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise indicated, all ranges disclosed herein should be understood to include any and all sub-ranges included therein. For example, a specified range from "1 to 10" should be deemed to include any and all sub-ranges between a minimum of 1 and a maximum of 10. Exemplary sub-ranges of ranges 1 to 10 include, but are not limited to, 1 to 6.1, 3.5 to 7.8, 5.5 to 10, etc.

[0041] The frequency of the acoustic wave resonator is mainly determined by the thickness of the piezoelectric film, the velocity of the bulk acoustic wave of the piezoelectric material, and the load. Therefore, the general structure of the resonator is a substrate, a suspended bottom electrode, a piezoelectric film, and a top electrode arranged in sequence from bottom to top. The top electrode and the suspended bottom electrode structure are used to excite the first-order plate wave mode to meet the high-frequency requirements. However, for single-crystal piezoelectric materials, it is very difficult to form a patterned suspended bottom electrode, and the electrode width is small at high frequencies, resulting in large ohmic losses. The frequency is also increased by reducing the thickness of the piezoelectric film, but this method will cause the suspended piezoelectric film structure to become fragile and have poor heat dissipation. This makes it the key to simplify the resonator structure, reduce ohmic losses, and make the resonator have a larger electromechanical coupling coefficient while becoming a key to achieving high-performance high-frequency applications. To this end, please refer to Figure 1The present application provides a high-frequency acoustic wave resonator, which includes a supporting substrate 1, a piezoelectric film 2 and an interdigital transducer 3 stacked in sequence from bottom to top; wherein the sound velocity of the supporting substrate 1 is not less than 5000 m / s; the target mode of the high-frequency acoustic wave resonator is a quasi-bulk wave mode generated by longitudinal electric field excitation; the thickness of the interdigital transducer 3 is inversely proportional to the material density of the interdigital transducer 3; the sound velocity of the target mode is less than the sound velocity of the supporting substrate 1. Since the resonator has no bottom electrode, the parasitic capacitance and parasitic mode caused by the bottom electrode are effectively avoided, the structure of the acoustic wave resonator is simplified, the ohmic loss can be reduced, and the electromechanical coupling coefficient of the high-order mode can be improved, so that it can be better applied to high frequency and high performance.

[0042] In a feasible embodiment, the product of the period of the interdigital transducer 3 and the frequency of the target mode (i.e., the sound velocity of the target mode) is greater than or equal to 80% of the sound velocity of the supporting substrate 1, and less than the sound velocity of the supporting substrate 1. Thus, while preventing the acoustic wave energy from leaking to the supporting substrate 1, the electromechanical coupling coefficient of the high-order plate wave is increased while the electromechanical coupling coefficient of the low-order mode is reduced, thereby reducing the ohmic loss and improving the power capacity.

[0043] The interdigital transducer 3 includes a first bus bar and a second bus bar opposite to each other; the first bus bar is provided with a plurality of first electrodes arranged at intervals; the second bus bar is provided with a plurality of second electrodes arranged at intervals, and the plurality of first electrodes and the plurality of second electrodes are arranged in an interlaced manner to form interdigital electrodes; optionally, the distance between adjacent second electrodes is equal to the distance between adjacent first electrodes. Optionally, the period of the interdigital transducer 3 is the interval distance between the centers of adjacent first electrodes among the plurality of first electrodes, or the interval distance between the centers of adjacent second electrodes among the plurality of second electrodes.

[0044] In a feasible embodiment, the quasi-body wave modes include first-order and higher-order modes of horizontal shear wave modes, Lamb wave modes and Rayleigh modes, such as first-order symmetric Lamb wave (S1), higher-order mode of first-order horizontal shear wave (SH1), first-order antisymmetric Lamb wave (A1) and first-order Rayleigh mode (Sezawa).

[0045] In a feasible embodiment, the thickness of the IDT 3 is the product of a preset value and the thickness of the reference IDT; the preset value is the ratio of the material density of the reference IDT to the material density of the IDT 3; when the material of the reference IDT is pure aluminum or an alloy with an aluminum content exceeding 95%, the thickness of the reference IDT is greater than or equal to 15% of the wavelength of the high-frequency acoustic wave resonator. Specifically, assuming that the material of the reference IDT is pure aluminum or an alloy with an aluminum content exceeding 95%, the thickness of the IDT 3 is d≥(ρ0 / ρ1)×0.15λ, where ρ0 is the material density of the reference IDT, ρ1 is the material density of the IDT 3 in the present application, and λ is the wavelength of the high-frequency acoustic wave resonator; for example, when the material of the IDT is platinum, ρ0 / ρ1 is 1 / 8, and the required thickness can be set to 1 / 4 times the thickness of the reference IDT. When the material of the IDT is copper, ρ0 / ρ1 is 1 / 3.3, and the required thickness can be set to 1 / 2 times the thickness of the reference IDT. The above setting of the IDT thickness means lower ohmic loss, which is very important for high-frequency resonators with small wavelengths and small electrode widths, and the high-frequency acoustic wave resonator also has the advantage of a simple structure.

[0046] In a feasible embodiment, when the material of the interdigital transducer 3 is aluminum, the material of the piezoelectric film 2 is X-cut lithium niobate, and the material of the supporting substrate 1 is 6H-silicon carbide, the thickness of the interdigital transducer 3 is 0.2 times the wavelength. In another feasible embodiment, when the material of the interdigital transducer 3 is aluminum, the material of the piezoelectric film 2 is X-cut lithium niobate, and the material of the supporting substrate 1 is sapphire, the thickness of the interdigital transducer 3 is 0.18 to 0.19 times the wavelength. In another feasible embodiment, when the material of the interdigital transducer 3 is aluminum, the material of the piezoelectric film 2 is X-cut lithium tantalate, and the material of the supporting substrate 1 is sapphire, the thickness of the interdigital transducer 3 is 0.19 to 0.2 times the wavelength. Thereby, the obtained resonator can have the advantages of simple structure, that is, no bottom electrode is required, lower ohmic loss, and can avoid leakage of sound waves to the supporting substrate, so that the sound wave energy is confined to the surface of the substrate.

[0047] In a feasible embodiment, the piezoelectric film 2 is at least one of lithium niobate, lithium tantalate, potassium niobate, aluminum nitride, scandium-doped aluminum nitride, zinc oxide, lead zirconate titanate, or lead magnesium niobate-lead titanate crystal.

[0048] In a feasible embodiment, the IDT 3 is any one of a single-layer metal film, a multi-layer metal film, and a composite film composed of metal and non-metal. Optionally, the material of the metal film can be any one of pure metal, alloy, and doped non-metallic elements.

[0049] In order to facilitate understanding of the technical solution of the present application and illustrate the beneficial effects of the present application, specific embodiments will be described below.

[0050] Example 1

[0051] Provide a Figure 1 For an acoustic wave resonator of the structure shown, see Figure 2 and Figure 3 , Figure 2 Shown are simulated admittance curves corresponding to different thicknesses of interdigital transducers; Figure 3 Shown Figure 2 The vibration mode diagram corresponding to the S1 mode. The piezoelectric film 2 of the acoustic wave resonator is an X-cut lithium niobate film, the Euler angle of lithium niobate is (30, 90, -90), the supporting substrate 1 is 6H-silicon carbide, and the material of the interdigital transducer 3 is aluminum; the target mode is a high-order plate wave mode, and the wavelength of the resonator is 1.6 microns. Among them, Figure 2 Curve a in FIG. 1 corresponds to the simulated admittance curve when the thickness of the IDT 3 is 80 nanometers. It can be seen that when the thickness of the IDT 3 is 80 nanometers, the modes include S0 and SH1. Further comparison shows that the admittance ratio of the S0 mode is about 90 dB, while the admittance ratio of the SH1 mode is about 40 dB. Therefore, the S0 mode when the thickness of the IDT 3 is 80 nanometers is the strongest. Under the action of the high sound velocity 6H-silicon carbide, the sound velocity of the S0 mode reaches 7544 m / s. Figure 2 Curve b in the figure corresponds to the simulated admittance curve when the thickness of the IDT 3 is 160 nm. It can be seen that when the thickness of the IDT 3 reaches 160 nm, the SH1 mode is the strongest. At this time, the sound velocity of the S0 mode decreases and the electromechanical coupling coefficient decreases significantly. In addition, the existence of the SH1 mode at the adjacent frequency causes the S0 mode to no longer be suitable as the target mode. This shows that the S0 mode is only suitable as a target mode when the thickness of the IDT 3 is thinner, but a thinner IDT 3 means greater ohmic loss, which limits the quality factor of the resonator, and the SH1 mode cannot be used as a target mode because its resonant frequency is close to that of S0. When the thickness is further increased to 240 nm, new high-order plate wave modes appear, such as Figure 2 Curve c in FIG. 1 corresponds to the simulated admittance curve when the thickness of the interdigital transducer 3 is 240 nanometers. It can be seen that the target mode at this time is the S1 mode, and its vibration shape is as follows: Figure 3 As shown, the S1 mode is mainly excited by the longitudinal electric field, and a large amount of its vibration energy enters the IDT 3. At this time, the resonant cavity is composed of the piezoelectric film 2 and the IDT 3. Figure 2Curve d in the figure corresponds to the simulated admittance curve when the thickness of the IDT 3 is 320 nm. It can be seen that when the thickness of the IDT 3 reaches 320 nm, the thickness of the IDT 3 reaches 0.2 times the wavelength, and the SH1 and S0 modes are greatly weakened and far away from the target mode S1. The high-order plate waves excited at this time are expected to be used in high-performance high-frequency filters, and their sound speed is as high as 8576 m / s, which is higher than the target mode S0 when the thickness of the IDT 3 is 80 nm. Under the existing photolithography technology conditions, it can easily meet the frequency requirements of all frequency bands below 7 GHz.

[0052] It is understandable that the above only illustrates the case where the material of the IDT 3 is aluminum. In fact, if the material of the IDT 3 is a metal material such as gold, silver, platinum or alloy, since its material density is higher than that of aluminum, the thickness of the IDT 3 corresponding to the target mode generated by the high-order plate wave mode is smaller than that of aluminum. For example, when the thickness of aluminum is set to be greater than 0.15 times the wavelength, the aluminum is replaced with gold, and the thickness of the IDT 3 can be set to 0.05 times the wavelength. The thick electrode in this application refers to the thickness of the electrode of the same material that is usually set.

[0053] Through the above Figure 2 It can be understood from the analysis that the thick electrode solution provided by the present application is helpful to reduce ohmic loss, improve power capacity, and realize a resonator with a high quality factor. The high-order mode is mainly excited by the longitudinal electric field, but only the longitudinal electric field component provided by the top interdigital transducer 3 is used to obtain a large electromechanical coupling coefficient, so the bottom electrode is not required and the structure is very simple. Therefore, the process of the high-order plate wave resonator is very simple, and it has the characteristics of high sound velocity and low ohmic loss, and is suitable for realizing high-frequency and high-performance acoustic wave resonators.

[0054] Example 2

[0055] See also Figure 4 and Figure 5 , Figure 4 Shown is the simulated admittance curve corresponding to the first high-frequency acoustic wave resonator; Figure 5 Shown Figure 4 The vibration mode diagram corresponding to the target mode in the acoustic wave resonator. The piezoelectric film 2 of the acoustic wave resonator is an X-cut lithium niobate film, the Euler angle of lithium niobate is (30, 90, -90), the supporting substrate 1 is sapphire, the Euler angle of sapphire is (44.5, 125, 0), the material of the interdigital transducer 3 is aluminum, and the thickness is 230 nanometers, reaching 0.184 times the wavelength; the wavelength of the resonator is 1.25 microns; from Figure 4 It can be seen that the high-frequency acoustic wave resonator not only achieves a resonant frequency close to 5 GHz, but also has an electromechanical coupling coefficient of 14.1%, which is sufficient to meet the needs of some high-frequency bands. Figure 5 It can be seen that the target mode is the S1 mode, and a considerable portion of its vibration energy enters the IDT 3. At this time, the resonant cavity is composed of the piezoelectric film 2 and the IDT 3, which further verifies that it has a high electromechanical coupling coefficient.

[0056] Example 3

[0057] See also Figure 6 and Figure 7 , Figure 6 Shown is the simulated admittance curve corresponding to the second high-frequency acoustic wave resonator; Figure 7 Shown Figure 6 The vibration mode diagram corresponding to the target mode in the middle. The piezoelectric film 2 of the acoustic wave resonator is X-cut lithium tantalate, the Euler angle of lithium tantalate is (30, 90, -90), the supporting substrate 1 is sapphire, the Euler angle of sapphire is (44.5, 125, 0), the material of the interdigital transducer 3 is aluminum, and the thickness is 230 nanometers, reaching 0.192 times the wavelength; the wavelength of the resonator is 1.2 microns; from Figure 4 It can be seen that the high-frequency acoustic wave resonator not only achieves a resonance frequency close to 5 GHz, but also has an electromechanical coupling coefficient of 5.9%, which is comparable to that of aluminum nitride-based FBAR. Figure 5 It can be seen that the target mode is the S1 mode, and a large amount of vibration energy enters the IDT 3. At this time, the resonant cavity is composed of the piezoelectric film 2 and the IDT 3, which further verifies that it has a high electromechanical coupling coefficient.

[0058] Example 4

[0059] The piezoelectric film 2 of the acoustic wave resonator is Y36-cut lithium niobate, the Euler angle of lithium niobate is (0, 54, 0), the supporting substrate 1 is sapphire, the Euler angle of sapphire is (48, 125, 0), the material of the interdigital transducer 3 is aluminum, and the thickness is 260 nanometers, reaching 0.186 times the wavelength; assuming that the wavelength of the resonator is 1.4 microns; from Figure 8 It can be seen that the high-frequency acoustic wave resonator not only achieves a resonant frequency close to 4.5 GHz, but also has an electromechanical coupling coefficient of 13.1%. Its target mode is the first-order Rayleigh mode (Sezawa mode). When the electrode material is a platinum electrode, the required electrode thickness is reduced. The thickness of the platinum electrode is 0.046 times the wavelength. The corresponding simulated admittance curve and target mode vibration shape diagram are shown in Fig. 9 As shown, the frequency and Fig. 9 The electromechanical coupling coefficient is 11.6%. Figure 8 and Fig. 9 The vibration mode diagram corresponding to the target mode in Fig.10 and Fig.11) It can be seen that the target mode is the first-order Rayleigh mode (Sezawa), and a large amount of vibration energy enters into the IDT 3. At this time, the resonant cavity is composed of the piezoelectric film 2 and the IDT 3, which further verifies that it has a high electromechanical coupling coefficient.

[0060] Example 5

[0061] See also Fig.12 The present application also discloses a method for preparing a high-frequency acoustic wave resonator, which comprises:

[0062] S1201: Provide a supporting substrate 1 with a piezoelectric film 2 on the top layer; the sound velocity of the supporting substrate 1 is not less than 5000 m / s.

[0063] Optionally, the supporting substrate 1 with a piezoelectric film 2 on the top layer in step S1201 can be prepared by an ion implantation stripping process, a bonding and grinding process or a thin film growth process; wherein, the ion implantation stripping process can specifically be, first providing a piezoelectric wafer; performing ion implantation on the piezoelectric wafer from the implantation surface, thereby forming a defect layer in the middle of the piezoelectric wafer, and then bonding with the supporting substrate 1 through the implantation surface, and then performing annealing, stripping and polishing along the defect layer to obtain a supporting substrate 1 with a piezoelectric film 2 on the top layer; the bonding and grinding process can specifically be, directly bonding the piezoelectric wafer to the supporting substrate 1, and then grinding the piezoelectric wafer until the required thickness is reached; the thin film growth process can specifically be, directly epitaxially growing the piezoelectric film 2 on the supporting substrate 1.

[0064] S1202: preparing an IDT 3 on the piezoelectric film 2; the thickness of the IDT 3 is inversely proportional to the material density of the IDT 3; the target mode of the high-frequency acoustic wave resonator is a quasi-bulk wave mode generated by longitudinal electric field excitation; the sound velocity of the target mode is less than the sound velocity of the supporting substrate 1.

[0065] In step S1202 , a metal electrode layer may be formed on the piezoelectric film 2 by sputtering or deposition process, and then patterned by photolithography process to obtain the interdigital transducer 3 .

[0066] The above description is only an optional embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A high-frequency acoustic wave resonator, characterized in that: It includes a supporting substrate, a piezoelectric film and an interdigital transducer which are stacked in sequence from bottom to top; Wherein, the sound velocity of the supporting substrate is not less than 5000 m / s; the target mode of the high-frequency acoustic wave resonator is a quasi-bulk wave mode generated by longitudinal electric field excitation; the thickness of the interdigital transducer is inversely proportional to the material density of the interdigital transducer; the sound velocity of the target mode is less than the sound velocity of the supporting substrate; The thickness of the IDT is the product of a preset value and the thickness of a reference IDT; The preset value is a ratio of the material density of the reference IDT to the material density of the IDT; The product of the period of the IDT and the frequency of the target mode is greater than or equal to 80% of the sound velocity of the supporting substrate and less than the sound velocity of the supporting substrate.

2. The high-frequency acoustic wave resonator according to claim 1, characterized in that: When the material of the reference IDT is pure aluminum or an alloy with an aluminum content exceeding 95%, the thickness of the reference IDT is greater than or equal to 15% of the wavelength of the high-frequency acoustic wave resonator.

3. The high-frequency acoustic wave resonator according to claim 1, characterized in that: The quasi-body wave modes include first-order symmetrical Lamb waves, higher-order modes of first-order horizontal shear waves, first-order anti-symmetrical Lamb waves and first-order Rayleigh modes.

4. The high-frequency acoustic wave resonator according to claim 3, characterized in that: When the material of the IDT is aluminum, the material of the piezoelectric film is X-cut lithium niobate, and the material of the supporting substrate is 6H-silicon carbide, the thickness of the IDT is 0.2 times the wavelength.

5. The high-frequency acoustic wave resonator according to claim 3, characterized in that: When the material of the IDT is aluminum, the material of the piezoelectric film is X-cut lithium niobate, and the material of the supporting substrate is sapphire, the thickness of the IDT is 0.18 to 0.19 times the wavelength.

6. The high-frequency acoustic wave resonator according to claim 3, characterized in that: When the material of the IDT is aluminum, the material of the piezoelectric film is X-cut lithium tantalate, and the material of the supporting substrate is sapphire, the thickness of the IDT is 0.19 to 0.2 times the wavelength.

7. The high-frequency acoustic wave resonator according to claim 1, characterized in that: The piezoelectric film includes at least one of lithium niobate, lithium tantalate, potassium niobate, aluminum nitride, scandium-doped aluminum nitride, zinc oxide, lead zirconate titanate, or lead magnesium niobate-lead titanate crystal.

8. The high-frequency acoustic wave resonator according to claim 1, characterized in that: The interdigital transducer is any one of a single-layer metal film, a multi-layer metal film, and a composite film composed of metal and non-metal.

9. A method for preparing a high-frequency acoustic wave resonator, characterized in that: include: Providing a support substrate with a piezoelectric film on the top layer; the sound velocity of the support substrate is not less than 5000 m / s; An interdigital transducer is prepared on the piezoelectric film; the thickness of the interdigital transducer is inversely proportional to the material density of the interdigital transducer; the target mode of the high-frequency acoustic wave resonator is a quasi-bulk wave mode generated by longitudinal electric field excitation; the sound velocity of the target mode is less than the sound velocity of the supporting substrate; The thickness of the IDT is the product of a preset value and the thickness of a reference IDT; The preset value is a ratio of the material density of the reference IDT to the material density of the IDT; The product of the period of the IDT and the frequency of the target mode is greater than or equal to 80% of the sound velocity of the supporting substrate and less than the sound velocity of the supporting substrate.

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