Acoustic resonator and preparation method thereof
By embedding interdigital electrode pairs in a heterogeneous structure design, the problems of insufficient performance and temperature drift of acoustic resonators in the high-frequency range are solved, and the improvement of high electromechanical coupling and mechanical stability is achieved.
Patent Information
- Application Number
- CN202511466786.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-14
- Publication Date
- 2025-11-21
AI Technical Summary
Existing acoustic resonators struggle to maintain excellent performance at high frequencies, especially Lamb wave resonators which suffer from poor mechanical stability and frequency drift with temperature changes.
By embedding interdigital electrode pairs in a heterostructure design within a dielectric layer, the electromechanical coupling coefficient of the excited acoustic modes is enhanced, and temperature compensation is performed. In particular, for Lamb wave resonators, mechanical robustness and the excitation of Lamb wave acoustic modes with high electromechanical coupling coefficients are improved.
The electromechanical coupling coefficient of the acoustic resonator was improved, the mechanical stability was enhanced, and the frequency-temperature characteristics were improved to meet different application requirements.
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Figure CN121000189A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present disclosure relates to the technical field of high-frequency piezoelectric acoustic wave resonators, and particularly relates to a high electromechanical coupling coefficient temperature-compensated resonator based on a dielectric layer and a metal electrode structure with an interdigital cross distribution on the surface of a piezoelectric layer. BACKGROUND
[0002] With the evolution of 5G to Beyond 5G (B5G) and 6G era, the requirements for the performance of radio frequency front-end devices of wireless and mobile communication systems are increasingly stringent. The development of multi-band and high-band communication has dramatically increased the demand for high-frequency filters, and the performance of the filter is fundamentally determined by the performance of its core unit, the acoustic wave resonator.
[0003] The mainstream acoustic wave resonators on the market at present mainly include surface acoustic wave (SAW) resonators and bulk acoustic wave (BAW) resonators. The working frequency of the SAW resonator is mainly determined by the spacing of the interdigital electrodes, which is limited by the precision of the photolithography process, and it is difficult to maintain good performance at high frequencies (for example, more than 3 GHz), and its phase velocity is relatively low. The BAW resonator, especially the film bulk acoustic resonator (FBAR), has the advantages of low insertion loss, good power handling capability, high quality factor (Q), etc., but is limited by the piezoelectric coefficient of the piezoelectric material, and its limited electromechanical coupling coefficient k 2 is difficult to be applied to a wideband scenario.
[0004] Lamb wave resonators, as a new type of piezoelectric micro-electro-mechanical system (MEMS) acoustic wave resonator, combine the technical characteristics of SAW (simple electrode process) and BAW (film bulk acoustic wave technology platform). On the other hand, based on thin film piezoelectric materials such as lithium niobate (LiNbO3 / LN) and lithium tantalate (LiTaO3 / LT) with a large piezoelectric coefficient (e), a multi-order Lamb wave mode with a high Q value and a large electromechanical coupling coefficient k 2 can be excited, and it has design flexibility. However, it also faces challenges: the large negative temperature frequency coefficient of the piezoelectric material itself leads to a drift in the characteristics of the resonator / filter with temperature changes; the thin film of the high-frequency resonator is too thin, resulting in poor mechanical stability of the resonator and easy collapse. SUMMARY
[0005] Therefore, in order to at least partially solve at least one of the above-mentioned technical problems, the present disclosure provides an acoustic wave resonator and a preparation method thereof, which embeds a heterostructure of interdigital electrode pairs in a dielectric layer to enhance the electromechanical coupling coefficient of the excited acoustic wave mode while temperature-compensating the resonator. In particular, for a Lamb wave resonator, this structure can also enhance the mechanical robustness and excite a Lamb wave acoustic wave mode with a high electromechanical coupling coefficient k 2 .
[0006] To achieve the above object, the technical scheme of the present disclosure is as follows:
[0007] According to an embodiment of the present disclosure, a sound wave resonator is provided, comprising: a dielectric layer, in which an interdigital electrode pair is vertically arranged; a piezoelectric layer, the dielectric layer is arranged on the surface of the piezoelectric layer, and the surface of the piezoelectric layer is in contact with a surface of the interdigital electrode pair; and a substrate layer; wherein the thickness of the dielectric layer is 0.1-6 times the thickness of the piezoelectric layer.
[0008] According to an embodiment of the present disclosure, the sound wave resonator type can be a surface acoustic wave resonator, or a bulk acoustic wave resonator, or a Lamb wave resonator, or an XBAR resonator.
[0009] According to an embodiment of the present disclosure, when the resonator is a Lamb wave resonator, the thickness ratio of the dielectric layer and the piezoelectric layer is set to excite different Lamb wave high-order modes in the piezoelectric layer.
[0010] According to an embodiment of the present disclosure, the Lamb wave high-order modes that can be excited in the piezoelectric layer include: a second-order symmetric mode S2, a third-order anti-symmetric mode A3, a fourth-order symmetric mode S4, a fifth-order anti-symmetric mode A5, a sixth-order symmetric mode S6, or a seventh-order anti-symmetric mode A7.
[0011] When the thickness ratio of the dielectric layer and the piezoelectric layer is set to 0.5-1.7:1, the electromechanical coupling coefficient k 2 of the S2 Lamb wave mode excited by the sound wave resonator is greater than 30%; when the thickness ratio of the dielectric layer and the piezoelectric layer is set to 1.5-2.8:1, the electromechanical coupling coefficient k 2 of the A3 Lamb wave mode excited by the sound wave resonator is greater than 20%; when the thickness ratio of the dielectric layer and the piezoelectric layer is set to 2.6-3.5:1, the electromechanical coupling coefficient k 2 of the S4 Lamb wave mode excited by the sound wave resonator is greater than 15%.
[0012] According to the embodiment of the present disclosure, the preparation material of the interdigital electrode pair is selected from gold, aluminum, molybdenum, platinum, copper, or alloys of titanium gold, titanium aluminum, titanium copper, chromium gold, chromium aluminum, chromium copper; the thickness of the interdigital electrode pair is 10 nm-600 nm, thereby reducing the parasitic resistance of the resonator and improving the Q value; the number of metal fingers in each interdigital electrode is N, 2≤N≤700; the length of the metal finger is 10-20 wavelengths, the distance between two adjacent metal fingers is half a wavelength, and the width of each metal finger is one-eighth to one-quarter of a wavelength; the thickness of the piezoelectric layer is 10 nm-1000 nm; the tangential direction of the piezoelectric layer film is 110°Y-130°Ycut, 10°Z-30°Zcut; the preparation material of the piezoelectric layer is selected from lithium niobate, lithium tantalate, or a composite layer material of lithium niobate, aluminum nitride, scandium-doped aluminum nitride, lithium tantalate, and zinc oxide; and the preparation material of the dielectric layer is selected from silicon oxide, silicon nitride, aluminum nitride, zirconium tungstate, aluminum titanate, a silicon oxide / silicon nitride stack, or a silicon oxide / aluminum nitride stack.
[0013] According to the embodiment of the present disclosure, when the resonator is a bulk acoustic wave resonator, a Lamb wave resonator, or an XBAR resonator, a release region is provided under the piezoelectric layer to form a cavity structure for suspending the piezoelectric layer, or a Bragg mirror structure of the substrate layer is used to limit acoustic energy.
[0014] According to the embodiment of the present disclosure, the release region forms a cavity structure by etching the substrate layer or a sacrificial layer embedded in the substrate layer; or forms a cavity structure by etching the substrate layer through a back etching process to the piezoelectric layer.
[0015] According to the embodiment of another aspect of the present disclosure, a preparation method of an acoustic wave resonator is provided, including: preparing a piezoelectric layer on a substrate layer; growing a dielectric layer on the piezoelectric layer; and patterning the dielectric layer to define an electrode region and preparing an interdigital electrode pair, one surface of the interdigital electrode pair being in contact with a surface of the piezoelectric layer.
[0016] When the resonator to be prepared is a bulk acoustic wave resonator, a Lamb wave resonator, or an XBAR resonator, a release region is prepared or a Bragg mirror structure of the substrate layer is used to limit acoustic energy, the release region can form a cavity structure by etching the substrate layer, or form a cavity structure by etching a sacrificial layer embedded in the substrate layer, or form a cavity structure by etching through the substrate layer through a back etching process to release the piezoelectric layer, thereby obtaining a final acoustic wave resonator. BRIEF DESCRIPTION OF DRAWINGS
[0017] The above and other objects, features and advantages of the present disclosure will become more apparent from the following description of the embodiments of the present disclosure taken in conjunction with the accompanying drawings, in which:
[0018] Figure 1A stress distribution diagram of different Lamb wave modes in a double-layer film structure of a medium layer and a piezoelectric layer of an acoustic wave resonator.
[0019] Figure 2 A structure diagram of an acoustic wave resonator according to an embodiment of the present application.
[0020] Figure 3 A stress distribution diagram of different Lamb wave modes in a double-layer film structure of a medium layer and a piezoelectric layer of an acoustic wave resonator. Figure 2 A preparation method flow diagram of an acoustic wave resonator.
[0021] Figure 4 A structure diagram of an acoustic wave resonator according to another embodiment of the present application.
[0022] Figure 5 A stress distribution diagram of different Lamb wave modes in a double-layer film structure of a medium layer and a piezoelectric layer of an acoustic wave resonator. Figure 4 A simulation curve diagram of admittance of an acoustic wave resonator when the thickness of a medium layer is twice the thickness of a piezoelectric layer.
[0023] Figure 6 A stress distribution diagram of different Lamb wave modes in a double-layer film structure of a medium layer and a piezoelectric layer of an acoustic wave resonator. Figure 4 A specific preparation step diagram of an acoustic wave resonator.
[0024] Figure 7 A stress distribution diagram of different Lamb wave modes in a double-layer film structure of a medium layer and a piezoelectric layer of an acoustic wave resonator. Figure 4 A specific process preparation flow diagram of an acoustic wave resonator.
[0025] Figure 8 A structure diagram of an acoustic wave resonator according to still another embodiment of the present application.
[0026] Figure 9 A stress distribution diagram of different Lamb wave modes in a double-layer film structure of a medium layer and a piezoelectric layer of an acoustic wave resonator. Figure 8 A specific preparation step diagram of an acoustic wave resonator.
[0027] Figure 10 A stress distribution diagram of different Lamb wave modes in a double-layer film structure of a medium layer and a piezoelectric layer of an acoustic wave resonator. Figure 8 A specific process preparation flow diagram of an acoustic wave resonator.
[0028] Figure 11 A structure diagram of an acoustic wave resonator according to still another embodiment of the present application.
[0029] Figure 12 A stress distribution diagram of different Lamb wave modes in a double-layer film structure of a medium layer and a piezoelectric layer of an acoustic wave resonator. Figure 11 A specific preparation step diagram of an acoustic wave resonator structure.
[0030] Figure 13 A stress distribution diagram of different Lamb wave modes in a double-layer film structure of a medium layer and a piezoelectric layer of an acoustic wave resonator. Figure 11 A specific process preparation flow diagram of an acoustic wave resonator structure. DETAILED DESCRIPTION
[0031] The present disclosure provides an acoustic wave resonator and a preparation method thereof. The acoustic wave resonator is obtained by depositing an oxide (dielectric layer) on a piezoelectric layer film, and then etching the dielectric layer and depositing a metal interdigital electrode in the etching groove. In the structure, one side surface of the metal interdigital electrode pair directly contacts the surface of the piezoelectric layer, so that the electric field in the piezoelectric layer is more coupled with the stress field, thereby increasing the electromechanical coupling coefficient of the excited mode of the acoustic wave resonator.
[0032] The acoustic wave resonator structure has the freedom to adjust the thickness of the dielectric layer (such as SiO2) in the design stage to adapt to different operating frequencies or different levels of TCF (Temperature Coefficient of Frequency) compensation. In the microfabrication process, if the dielectric layer is deposited on the top of the thick interdigital electrode, the large step height of the edge of the interdigital electrode will reduce the film deposition quality, thereby finally reducing the performance of the resonator. Compared with the complete dielectric layer prepared on the top of the electrode, the structure of the interdigital electrode embedded in the dielectric layer can make the interdigital electrode very thick to obtain better resonator performance. In addition, taking a Lamb wave resonator as an example, the structure of the above resonator can also excite high-order Lamb wave modes (S2, A3, S4, etc.), work at N times the frequency of the A1 mode under the condition of the same thickness, and through the design of the film parameters of the heterostructure, the maximum electromechanical coupling coefficient k 2 of the excited high-order mode can be realized. Figure 1 As shown in the stress distribution diagram of the A1, S2, A3 mode Lamb wave in the core structure (dielectric layer and piezoelectric layer) of the acoustic wave resonator, other high-order mode cases are similar. According to the Berlincourt formula and the piezoelectric constitutive equation, the electromechanical coupling coefficient (k 2 ) of different acoustic wave modes is proportional to the coupling strength of the transverse electric field E and the stress mode T, so the structure of the electrode directly contacting the piezoelectric layer can excite high-order Lamb wave modes with large electromechanical coupling coefficients.
[0033] In order to make the purpose, technical scheme and advantages of the present disclosure clearer, the present disclosure is further described in detail below in combination with specific embodiments and with reference to the drawings.
[0034] According to the embodiments of the present disclosure, an acoustic wave resonator is provided, as shown in Figure 2 The acoustic wave resonator comprises a substrate layer 1, a piezoelectric layer 2, a dielectric layer 3, and an interdigital electrode pair 4 provided in the dielectric layer 3 in a penetrating manner from top to bottom. The dielectric layer 3 is arranged on the surface of the piezoelectric layer 2, and the surface of the piezoelectric layer 2 contacts one surface of the interdigital electrode pair 4.
[0035] The thickness of the dielectric layer is 0.1 to 6 times the thickness of the piezoelectric layer.
[0036] According to the embodiments of the present disclosure, a preparation method of the above-mentioned acoustic wave resonator is also provided, which comprises the following operations in combination with Figure 3 and Figure 2 The preparation method comprises the following operations:
[0037] S1: preparing a piezoelectric layer 2 on a substrate layer 1;
[0038] S2: growing a dielectric layer 3 on the piezoelectric layer 2; and
[0039] S3: patterning the dielectric layer 3 to define an electrode region and preparing an interdigital electrode pair 4, one surface of the interdigital electrode pair 4 being in contact with a surface of the piezoelectric layer 2.
[0040] According to the embodiments of the present disclosure, the acoustic wave resonator can be an acoustic surface wave resonator, a bulk acoustic wave resonator, a Lamb wave resonator or an XBAR resonator.
[0041] When the resonator is a Lamb wave resonator, the thickness ratio of the dielectric layer and the piezoelectric layer is set to excite different high-order modes of Lamb waves in the piezoelectric layer. The high-order modes of Lamb waves that can be excited in the piezoelectric layer include: a second-order symmetric mode S2, a third-order anti-symmetric mode A3, a fourth-order symmetric mode S4, a fifth-order anti-symmetric mode A5, a sixth-order symmetric mode S6 or a seventh-order anti-symmetric mode A7. For example, when the thickness ratio of the dielectric layer and the piezoelectric layer is set to 0.5-1.7:1, the electromechanical coupling coefficient k 2 of the S2 Lamb wave mode excited by the acoustic wave resonator is greater than 30%; when the thickness ratio of the dielectric layer and the piezoelectric layer is set to 1.5-2.8:1, the electromechanical coupling coefficient k 2 of the A3 Lamb wave mode excited by the acoustic wave resonator is greater than 20%; when the thickness ratio of the dielectric layer and the piezoelectric layer is set to 2.6-3.5:1, the electromechanical coupling coefficient k 2 of the S4 Lamb wave mode excited by the acoustic wave resonator is greater than 15%.
[0042] According to the embodiments of the present disclosure, the material of the substrate layer can be one of the following materials: silicon, sapphire (Al2O3), gallium nitride (GaN) and silicon carbide (SiC).
[0043] According to the embodiments of the present disclosure, the material for preparing the interdigital electrode pair can be selected from gold, aluminum, molybdenum, platinum, copper or an alloy composed of titanium gold, titanium aluminum, titanium copper, chromium gold, chromium aluminum and chromium copper; the thickness of the interdigital electrode pair is 10-600 nm, thereby reducing the parasitic resistance of the resonator and improving the Q value; the number of metal fingers in each interdigital electrode is N, 2≤N≤700; the length of each metal finger is 10-20 wavelengths, the distance between two adjacent metal fingers is half a wavelength, and the width of each metal finger is one-eighth to one-quarter of a wavelength.
[0044] According to the embodiment of the present disclosure, the thickness of the piezoelectric layer is 10 nm to 1000 nm; the tangential direction of the piezoelectric layer film is 110°Y~130°Y cut, 10°Z~30°Z cut; and the preparation material of the piezoelectric layer is selected from lithium niobate, lithium tantalate, or a composite layer material of lithium niobate, aluminum nitride, scandium-doped aluminum nitride, lithium tantalate, and zinc oxide.
[0045] According to the embodiment of the present disclosure, the preparation material of the medium layer is selected from silicon oxide, silicon nitride, aluminum nitride, zirconium tungstate, aluminum titanate, silicon oxide / silicon nitride stack, or silicon oxide / aluminum nitride stack.
[0046] According to the embodiment of the present disclosure, when the resonator is a bulk acoustic wave resonator, a Lamb wave resonator, or an XBAR resonator, a release area is further included, which is arranged below the piezoelectric layer to form a cavity structure for suspending the piezoelectric layer. For example, the release area forms a cavity structure by etching a substrate layer or a sacrificial layer pre-embedded in the substrate layer; or forms a cavity structure by etching the substrate layer to the piezoelectric layer through a back etching process. Figure 4 、 Figure 6 、 Figure 7 As shown in FIGS. 1, 2, and 3, the substrate layer below the piezoelectric layer of the acoustic wave resonator is etched to form a cavity structure to obtain a release area 5. The interdigital electrode pair 4 is prepared in the medium layer 3 and directly contacts the upper surface of the piezoelectric layer 2. By designing the thickness of the piezoelectric layer 2 and the medium layer 3, a high-order Lamb wave mode with a high electromechanical coupling coefficient can be excited. For example, when the piezoelectric layer 2 is selected as 128°Y-cut lithium niobate, the interdigital electrode pair is selected as aluminum material, and the medium layer 3 is selected as silicon oxide, the thickness of the medium layer 3 can be 0.1 to 6 times the thickness of the piezoelectric layer 2. Among them, when the thickness ratio of the medium layer to the piezoelectric layer is set to 0.5 to 1.7:1, the electromechanical coupling coefficient k 2 >30% of the S2 Lamb wave mode excited by the acoustic wave resonator; when the thickness ratio of the medium layer to the piezoelectric layer is set to 1.5 to 2.8:1, the electromechanical coupling coefficient k 2 >20% of the A3 Lamb wave mode excited by the acoustic wave resonator; and when the thickness ratio of the medium layer to the piezoelectric layer is set to 2.6 to 3.5:1, the electromechanical coupling coefficient k 2 >15% of the S4 Lamb wave mode excited by the acoustic wave resonator. Figure 5 As shown in FIG. 4, a two-dimensional simulation admittance curve is shown when the thickness of the silicon dioxide medium layer 3 to the thickness of the piezoelectric layer 2 is 2:1, the resonance frequency is as high as 17.9 GHz, and the electromechanical coupling coefficient is as high as 32.65% under the A3 vibration mode. This structure not only enhances the mechanical stability of the resonator, but also breaks through the limitation of the electromechanical coupling coefficient when the high-order Lamb wave mode is excited by the traditional single-layer film structure.
[0047] More specifically, as shown in FIGS. 5 and 6, a two-dimensional simulation admittance curve is further shown when the thickness of the silicon dioxide medium layer 3 to the thickness of the piezoelectric layer 2 is 2:1, the resonance frequency is as high as 17.9 GHz, and the electromechanical coupling coefficient is as high as 32.65% under the A3 vibration mode. Figure 6 and Figure 7 Figure 4 The specific preparation steps and process flow diagram of the acoustic wave resonator of the shown structure are as follows:
[0048] Step S11, preparing a double-layer structure of the substrate layer 1 and the piezoelectric layer 2.
[0049] For example, the substrate layer is a silicon substrate. The piezoelectric layer can be lithium niobate (LN), lithium tantalate (LT), or a composite layer material of lithium niobate, aluminum nitride, scandium-doped aluminum nitride, lithium tantalate, and zinc oxide.
[0050] Step S12: depositing a dielectric layer 3 on the piezoelectric layer 2; for example, the dielectric layer is silicon oxide.
[0051] Step S13: using photolithography mask technology to pattern and define the electrode deposition area, and using reactive ion etching technology to etch the silicon oxide dielectric layer 3 to the upper surface of the piezoelectric layer 2.
[0052] Step S14, depositing metal in the etched groove of the dielectric layer 3 by plating technology to obtain the interdigital electrode pair 4.
[0053] Step S15, using hard mask technology to make a mask layer 6 above the resonator for mask protection of piezoelectric layer etching, and further defining the etching area of the acoustic wave resonator by overlaying.
[0054] Step S16, using reactive ion etching technology to etch the dielectric layer 3, and using inductive coupling plasma etching method to etch the piezoelectric layer 2.
[0055] Step S17, etching the substrate layer to form a cavity structure to obtain a release area 5, suspending the piezoelectric layer 2, and completing the preparation of the acoustic wave resonator.
[0056] More specifically, as shown in Figure 8 , Figure 9 and Figure 10 The specific preparation steps and process flow diagram of another acoustic wave resonator with a pre-embedded sacrificial layer 7 of the substrate layer are shown as follows:
[0057] Step S21, preparing a substrate layer 1 with a pre-embedded sacrificial layer 7 and a piezoelectric layer 2.
[0058] For example, the substrate layer is a silicon substrate. The pre-embedded sacrificial layer 7 can include one or more layers, and each layer can be selected from one of the following: silicon dioxide, silicon nitride, lithium niobate, porous silicon. The piezoelectric layer can be lithium niobate (LN), lithium tantalate (LT), or a composite layer material of lithium niobate, aluminum nitride, scandium-doped aluminum nitride, lithium tantalate, and zinc oxide.
[0059] Step S22: depositing a dielectric layer 3 on the piezoelectric layer 2; for example, the dielectric layer is silicon oxide.
[0060] Step S23: define the electrode deposition area by photolithography mask technology, and etch the silicon oxide dielectric layer 3 to the upper surface of the piezoelectric layer 2 by reactive ion etching technology;
[0061] Step S24: deposit metal in the etching groove of the dielectric layer 3 by plating technology to obtain the interdigital electrode pair 4;
[0062] Step S25: make a mask layer 5 above the resonator by hard mask technology, which is used for mask protection of piezoelectric layer etching, and further define the etching area of the acoustic resonator by overlaying;
[0063] Step S26: etch the dielectric layer 3 by reactive ion etching technology, and etch the piezoelectric layer 2 by inductively coupled plasma etching method;
[0064] Step S27: etch the sacrificial layer 7 of the substrate layer to form a cavity structure to obtain the release area 5, and suspend the piezoelectric layer 2, thereby completing the preparation of the acoustic resonator.
[0065] More specifically, as shown in Figure 11 、 Figure 12 and Figure 13 , another acoustic resonator structure with suspended piezoelectric layer realized by back etching process is also shown, as well as the specific preparation steps and process flow diagram as follows:
[0066] Step S31: prepare a double-layer structure of the substrate layer 1 and the piezoelectric layer 2;
[0067] For example, the substrate layer 1 is a silicon substrate. The piezoelectric layer 2 can be lithium niobate (LN), lithium tantalate (LT), or a composite layer material of lithium niobate, aluminum nitride, scandium-doped aluminum nitride, lithium tantalate, and zinc oxide;
[0068] Step S32: deposit a dielectric layer 3 on the piezoelectric layer 2; for example, the dielectric layer is silicon oxide.
[0069] Step S33: define the electrode deposition area by photolithography mask technology, and etch the silicon oxide dielectric layer 3 to the upper surface of the piezoelectric layer 2 by reactive ion etching technology;
[0070] Step S34: deposit metal in the etching groove of the dielectric layer 3 by plating technology to obtain the interdigital electrode pair 4;
[0071] Step S35: make a mask layer 6 above the resonator by hard mask technology, which is used for mask protection of the electrode;
[0072] Step S36: etch the substrate layer to form a cavity structure to obtain the release area 5, and suspend the piezoelectric layer 2, thereby completing the preparation of the acoustic resonator.
[0073] It should be noted that the medium layer and the embedded interdigital electrode pair can also be arranged on the lower surface of the piezoelectric layer.
[0074] As can be seen from the above, for the Lamb wave resonator (LWR), the release area can be obtained by etching the pre-embedded sacrificial layer in the substrate layer, or can be obtained by directly etching the substrate layer, so that the lower surface boundary condition of the piezoelectric layer is electrically open; for the Lamb wave resonator (LWR), the sacrificial layer can not be used, but a back etching process is used to release the device, or a Bragg mirror structure of the substrate layer is used to limit acoustic energy; the acoustic wave resonator can be a surface acoustic wave (SAW) resonator, and for the SAW resonator, the release area is not needed at this time; the resonator can also be a bulk acoustic wave (BAW) resonator, and for the BAW resonator, the release area can be used to suspend the resonator, or a Bragg reflection layer structure in the substrate layer can be used without a release operation.
[0075] In summary, the present application provides an acoustic wave resonator and a preparation method thereof, the acoustic wave resonator maximizes the coupling of the transverse electric field and the stress mode in the piezoelectric layer by embedding a metal interdigital electrode in a medium layer and directly contacting the upper surface of the piezoelectric layer, thereby exciting a high-order Lamb wave acoustic wave mode with a high-frequency large electromechanical coupling coefficient. By adjusting the thickness of the piezoelectric layer and the medium layer, the distribution of the stress mode in the resonator can be changed, thereby affecting the electromechanical coupling coefficient of the resonator. Therefore, by adjusting the thickness of the piezoelectric layer and the medium layer, different high-order Lamb wave vibration modes of different frequencies can be obtained to meet different application requirements. At the same time, the structure also improves the problems of poor mechanical stability and poor frequency temperature stability existing in the traditional Lamb wave resonator.
[0076] Thus far, the embodiments of the present disclosure have been described in detail with reference to the accompanying drawings. It should be noted that the implementation manners not shown or described in the drawings or the specification are known to those skilled in the art, and are not described in detail. In addition, the definitions of the elements and methods described above are not limited to the various specific structures, shapes or manners mentioned in the embodiments, and can be simply changed or replaced by those skilled in the art.
[0077] It should be noted that, in this document, unless specifically indicated otherwise, having "one" element is not limited to having only one of the element, but can have one or more of the element.
[0078] In this document, unless specifically indicated otherwise, the so-called feature A "or" (or) or "and / or" (and / or) feature B means that A exists alone, B exists alone, or A and B exist simultaneously; the so-called feature A "and" (and) or "with" (and) or "and" (and) feature B means that A and B exist simultaneously; the so-called "includes", "contains", "has", "contains" means including but not limited to.
[0079] Furthermore, terms such as "upper", "lower", "left", "right", "front", "back", or "between" used herein are only used to describe a relative position between elements and can be extended to include translation, rotation, or mirroring in interpretation. Furthermore, unless specifically stated or otherwise necessary, "one element on another element" or similar recitations do not necessarily indicate that the element contacts the other element.
[0080] Furthermore, unless specifically described or steps necessarily occur in sequence, the order of steps in the above description is not limited to the above recited order, and can be varied or rearranged according to design and reliability considerations. Also, the above-described embodiments can be used in combination with each other or with other embodiments, based on design and reliability considerations, i.e., technical features in different embodiments can be freely combined to form more embodiments.
[0081] The above-described specific embodiments further illustrate the purpose, technical solutions, and beneficial effects of the present disclosure. It should be understood that the above-described embodiments are merely specific embodiments of the present disclosure and are not intended to limit the present disclosure. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.
Claims
1. A sound wave resonator, comprising: a dielectric layer, in which a pair of interdigital electrodes is disposed vertically and horizontally; a piezoelectric layer, the dielectric layer is disposed on the surface of the piezoelectric layer, and the surface of the piezoelectric layer is in contact with a surface of the pair of interdigital electrodes; and a substrate layer; wherein the thickness of the dielectric layer is 0.1-6 times the thickness of the piezoelectric layer. 2.The sound wave resonator according to claim 1, which is a surface acoustic wave resonator, a bulk acoustic wave resonator, a Lamb wave resonator, or an XBAR resonator. 3.The sound wave resonator according to claim 1 or 2, when the resonator is a Lamb wave resonator, different high-order modes of Lamb waves are excited in the piezoelectric layer by setting the thickness ratio of the dielectric layer and the piezoelectric layer.
4. The acoustic wave resonator of claim 3, wherein, The high-order modes of Lamb waves that can be excited in the piezoelectric layer include: second-order symmetric mode S2, third-order anti-symmetric mode A3, fourth-order symmetric mode S4, fifth-order anti-symmetric mode A5, sixth-order symmetric mode S6, or seventh-order anti-symmetric mode A7. 5.The sound wave resonator according to claim 3, wherein When the thickness ratio of the medium layer to the piezoelectric layer is set to 0.5-1.7:1, the electromechanical coupling coefficient k of the S2 Lamb wave mode excited by the acoustic wave resonator 2 >30%; When the thickness ratio of the medium layer to the piezoelectric layer is set to 1.5-2.8:1, the electromechanical coupling coefficient k 2 >20%; When the thickness ratio of the medium layer to the piezoelectric layer is set to 2.6-3.5:1, the electromechanical coupling coefficient k 2 >15%. 6.The sound wave resonator according to claim 1, wherein The material of the pair of interdigital electrodes is selected from gold, aluminum, molybdenum, platinum, copper, or alloys of titanium gold, titanium aluminum, titanium copper, chromium gold, chromium aluminum, and chromium copper; the thickness of the pair of interdigital electrodes is 10-600 nm, thereby reducing the parasitic resistance of the resonator and increasing the Q value; the number of metal fingers in each interdigital electrode is N, 2≤N≤700; the length of the metal fingers is 10-20 wavelengths, the distance between adjacent two metal fingers is half a wavelength, and the width of each metal finger is one-eighth to one-quarter of a wavelength; The thickness of the piezoelectric layer is 10-1000 nm; the tangential direction of the piezoelectric layer film is 110°Y-130°Y cut, 10°Z-30°Z cut; and the material of the piezoelectric layer is selected from lithium niobate, lithium tantalate, or a composite layer material of lithium niobate, aluminum nitride, scandium-doped aluminum nitride, lithium tantalate, and zinc oxide; The material of the dielectric layer is selected from silicon oxide, silicon nitride, aluminum nitride, zirconium tungstate, aluminum titanate, silicon oxide / silicon nitride stack, or silicon oxide / aluminum nitride stack. 7.The sound wave resonator according to claim 2, when the resonator is a bulk acoustic wave resonator, a Lamb wave resonator, or an XBAR resonator, further comprising a release area or a Bragg mirror structure using the substrate layer to limit acoustic energy, the release area is disposed below the piezoelectric layer to form a cavity structure for suspending the piezoelectric layer.
8. The acoustic wave resonator of claim 7, wherein, The release area forms a cavity structure by etching the substrate layer or a sacrificial layer pre-embedded in the substrate layer; or forms a cavity structure by etching the substrate layer to the piezoelectric layer through a back etching process. 9.A method for preparing a sound wave resonator, comprising: preparing a piezoelectric layer on a substrate layer; growing a dielectric layer on the piezoelectric layer; and defining an electrode area by patterning the dielectric layer and preparing a pair of interdigital electrodes, a surface of the pair of interdigital electrodes is in contact with the surface of the piezoelectric layer.
10. The method of fabricating an acoustic resonator of claim 9, wherein, When the resonator to be prepared is a bulk acoustic wave resonator, a Lamb wave resonator, or an XBAR resonator, a release region needs to be prepared or a Bragg mirror structure of a substrate layer is used to limit acoustic energy, the release region can form a cavity structure by etching a substrate layer, or form a cavity structure by etching a sacrificial layer embedded in the substrate layer, or etch through the substrate layer by a back etching process to release the piezoelectric layer to obtain the final acoustic wave resonator.