Thin film surface acoustic wave resonator element for implementing intermediate bandwidth and related electronic device
By employing a LiTa(1-x)Nb(x)O3 piezoelectric thin film layer and a specific Nb concentration growth orientation in SAW devices, the electromechanical coupling coefficient was improved, solving the problem of insufficient bandwidth in existing SAW devices and achieving performance enhancement of intermediate bandwidth RF filters.
Patent Information
- Application Number
- CN202480090342.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-03-28
- Publication Date
- 2026-11-06
AI Technical Summary
Existing SAW devices are insufficient in terms of electromechanical coupling and cannot meet the wide bandwidth requirements of new RF filters such as band 41 and band 75.
A thin-film surface acoustic wave resonator is used, which utilizes a piezoelectric thin film layer of LiTa(1-x)Nb(x)O3 crystal composition, combined with a specific Nb concentration and growth orientation, to achieve electromechanical coupling between LiTaO3 and LiNbO3, thereby increasing the electromechanical coupling coefficient to 12% to 25%, and then fabricates interdigital transducers through processes such as chemical vapor deposition.
It achieves improved RF filter performance in the intermediate bandwidth, suppresses spurious modes, and is suitable for RF filters in bands 41 and 75.
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Figure CN123057697A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of surface acoustic wave (SAW) devices, and more specifically, to a thin-film SAW resonator and related electronic device for achieving intermediate bandwidth. Background Technology
[0002] Surface acoustic wave (SAW) devices are devices that utilize elastic waves propagating on the surface of a material or at the interface of multiple materials. They are commonly used in micromechanical resonators and filters. SAW devices employ so-called interdigitated transducers (IDTs) to convert radio frequency (RF) signals into sound waves, or vice versa.
[0003] SAW devices are commonly used in RF filters. However, in at least some cases, existing SAW devices may not always meet the requirements of new RF filters under development. For example, RF filters for band 41 (B41, 2496 MHz to 2690 MHz) or band 75 (B75, 1432 MHz to 1517 MHz) may require wide bandwidths. However, existing SAW devices may be insufficient in electromechanical coupling (i.e., the fractional frequency distance from resonance to anti-resonance is relatively small) to meet the bandwidth requirements of these new RF filters.
[0004] Therefore, in at least some cases, a solution that can improve the bandwidth capability of SAW devices may be needed. Summary of the Invention
[0005] This invention provides a brief overview of some concepts, which will be further described in the detailed description below. This invention is not intended to identify key or essential features of the claimed subject matter, nor is it intended to limit the scope of the claimed subject matter.
[0006] One object of the present invention is to provide a thin-film surface acoustic wave resonator for achieving an intermediate bandwidth. The above and other objects are achieved through the features of the independent claims. Other embodiments will be apparent from the dependent claims, the specification, and the drawings.
[0007] According to a first aspect, a thin-film surface acoustic wave (FSAW) resonator is provided. The FSAW resonator includes a substrate layer. The FSAW resonator further includes an intermediate layer disposed on the substrate layer. The FSAW resonator further includes a piezoelectric thin film layer disposed on the intermediate layer. The FSAW resonator further includes an interdigital transducer (IDT) arrangement disposed on the piezoelectric thin film layer. The IDT arrangement includes two conductive elements, an active region disposed between the two conductive elements, and a plurality of interdigital electrodes. Each electrode extends from one of the conductive elements through the active region to the other conductive element. The distance between the central axes of every two adjacent electrodes is the electrode pitch. The piezoelectric thin film layer comprises a crystalline composition of a lithium tantalate (LT) compound and a lithium niobate (LN) compound. The electromechanical coupling coefficient of the crystalline composition is within the electromechanical coupling coefficient range. This invention realizes a structure for a thin-film surface acoustic wave resonator to achieve an intermediate bandwidth. More specifically, the disclosed stacked FSAW resonant element employs a piezoelectric thin film layer of LT and LN compounds with a specific niobium (Nb) concentration, thereby enabling electromechanical coupling between the LT and LN compounds.
[0008] In one implementation of the first aspect, the crystal composition comprises LiTa (1-x) Nb (x) O3. This implementation allows for the selection of Nb concentration, thereby enhancing electromechanical coupling to the optimal level for RF filters while mitigating and suppressing spurious modes in the structure.
[0009] In one implementation of the first aspect, the LiTa (1-x) Nb (x) The x value in O3 is between 0.3 and 0.7. This implementation can linearly change the properties of the crystalline composition.
[0010] In one implementation of the first aspect, the electromechanical coupling coefficient can be selected within the range of the electromechanical coupling coefficient based on the ratio of the LT compound and the LN compound. This implementation allows for selection of the electromechanical coupling coefficient as needed.
[0011] In one implementation of the first aspect, the electromechanical coupling coefficient ranges from approximately 12% to 25%. This implementation allows for selection of the electromechanical coupling coefficient as needed.
[0012] In an implementation of the first aspect, the crystal composition has approximately 33°YX(01) 2) Growth orientation. This implementation allows the main SAW mode to have relatively strong electromechanical coupling, and the growth orientation coincides with one of the crystal planes, making it suitable for epitaxial growth.
[0013] In one implementation of the first aspect, the growth orientation has a tolerance of 5 degrees. This implementation can mitigate the influence of initial growth conditions on the actual crystal orientation, which may deviate slightly from the 33° Y plane.
[0014] In one implementation of the first aspect, the thickness of the piezoelectric thin film layer is 1 micrometer or less. This implementation can grow a piezoelectric thin film with sufficiently low residual stress (which is necessary for growing a macroscopically defect-free film) while also covering the optimal thickness range required to achieve high-performance devices in the lower GHz range.
[0015] According to a second aspect, an electronic device is provided. The electronic device includes the FSAW resonant element described in the first aspect. This implementation provides an FSAW resonant element for an electronic device.
[0016] In one implementation of the second aspect, the FSAW resonant element is included in a radio frequency (RF) filter. RF filters require precise design parameters, and the FSAW resonant element can improve the performance of the RF filter.
[0017] The numerous accompanying features can be better understood by referring to the following detailed description in conjunction with the accompanying drawings; as the understanding deepens, the advantages of these features will also be more readily appreciated. Attached Figure Description
[0018] In the following description, exemplary embodiments are described in more detail with reference to the accompanying drawings, in which: Figure 1A This is a schematic diagram of a thin-film surface acoustic wave resonator element provided in one embodiment of the present invention; Figure 1B This is a schematic diagram of an interdigital transducer arrangement provided in one embodiment of the present invention; Figure 2 This is a block diagram of an electronic device provided in one embodiment of the present invention.
[0019] In the following text, the same reference numerals refer to the same or at least functionally equivalent features. Detailed Implementation
[0020] In the following description, reference is made to the accompanying drawings, which form part of the invention, and illustrate specific aspects by way of illustration that may be practiced. It will be understood that other aspects may be used without departing from the scope of the invention, and structural or logical changes may be made. Therefore, the following detailed description should not be construed in a limiting sense, as the scope of the invention is defined in the appended claims.
[0021] For example, it is understood that the disclosure relating to the described method applies equally to the corresponding device or system for performing the method, and vice versa. For instance, if a specific method step is described, the corresponding device may include units for performing the described method steps, even if such units are not explicitly described or illustrated in the accompanying drawings. On the other hand, for example, if a particular apparatus is described based on functional units, the corresponding method may include steps for performing the described function, even if such steps are not explicitly described or illustrated in the accompanying drawings. Furthermore, it is understood that, unless otherwise explicitly stated, features of the various exemplary aspects described herein can be combined with each other.
[0022] As detailed below, at least some of the disclosed embodiments can realize a structure for a thin-film surface acoustic wave (FSAW) resonator that can achieve an intermediate bandwidth.
[0023] At least some of the disclosed embodiments can realize a stacked FSAW device employing LiTa with specific Nb concentration and crystal orientation. (1 - X) Nb (X) O3 (LTN) piezoelectric thin film. The disclosed FSAW design enables electromechanical coupling between LiTaO3 and LiNbO3.
[0024] In other words, at least some of the disclosed embodiments can employ LTN piezoelectric materials to design FSAW resonators with an intermediate R-aR frequency bandwidth (intervening between LT and LN). In at least some of the disclosed embodiments, these intermediate R-aR bandwidths may be more advantageous for RF filter performance with bandwidths between 4% and 10%.
[0025] In at least some of the disclosed embodiments, the disclosed LTN material can help to better control Rayleigh SAW (RSAW) spurious emissions away from the filter passband.
[0026] In at least some of the disclosed embodiments, LTN material can be deposited in the form of an epitaxial submicron thin film using chemical vapor deposition (CVD), metal-organic chemical vapor deposition (MOCVD), pulsed laser deposition (PLD), or similar processes.
[0027] At least some of the disclosed embodiments can be fabricated using layer transfer technology for FSAW.
[0028] Next, combined Figure 1A and Figure 1B An exemplary embodiment of the FSAW resonant element 100 is described. Some characteristics of the described device are optional and may provide further advantages. In this document, a thin-film SAW (FSAW) resonant element refers to a type of SAW resonant element whose piezoelectric layer is made of a thin film material.
[0029] Figure 1A This is a schematic diagram of an FSAW resonant element 100 provided in one embodiment of the present invention. Figure 1B It is used for Figure 1A A schematic diagram of the interdigital transducer (IDT) arrangement 140 in the FSAW resonant element 100.
[0030] The FSAW resonant element 100 includes a substrate layer (or base substrate) 110. The substrate layer 110 may contain at least one of, for example, silicon (Si), sapphire, quartz, silicon carbide (SiC), or yttrium aluminum garnet (YAG).
[0031] The FSAW resonant element 100 also includes an intermediate layer 120 disposed on the substrate layer 110. The intermediate layer 120 may contain, for example, silicon dioxide (SiO2).
[0032] The FSAW resonant element 100 also includes a piezoelectric thin film layer 130 disposed on an intermediate layer 120. In at least some embodiments, the piezoelectric thin film layer 130 can be epitaxially grown (e.g., by chemical vapor deposition (CVD) or pulsed laser deposition (PLD)). For example, such a piezoelectric thin film layer can be grown on a seed layer, then polarized, and then transferred to an acoustic substrate using a suitable layer transfer technique.
[0033] In at least some embodiments, the substrate layer 110 may be thicker than the intermediate layer 120 and the piezoelectric thin film layer 130. In at least some embodiments, the substrate layer 110 may be several times thicker than either the intermediate layer 120 or the piezoelectric thin film layer 130.
[0034] The FSAW resonant element 100 also includes an interdigital transducer (IDT) arrangement 140 disposed on the piezoelectric thin film layer 130. The IDT arrangement 140 includes two conductive elements (such as busbars) 141 and 142. The IDT arrangement 140 also includes an active region 143 disposed between the two conductive elements 141 and 142. The IDT arrangement 140 also includes a plurality of interdigital electrodes 144 and 145. Each electrode extends from one of the conductive elements through the active region to the other conductive element. The distance between the central axes of any two adjacent electrodes is the electrode pitch. For example, electrodes 144 and 145 may comprise aluminum.
[0035] In other words, the active region 143 constitutes the central region of the IDT arrangement 140, while the conductive elements 141 and 142 constitute the relative edge regions of the IDT arrangement 140.
[0036] The term "interdigitation" refers to the fact that the active region 143 includes two sets of electrodes, which are arranged in such a way that the electrodes in the first set of electrodes and the electrodes in the second set of electrodes are arranged alternately, and each first electrode is separated from its adjacent first electrode by a second electrode; similarly, each second electrode is separated from its adjacent second electrode by a first electrode.
[0037] The piezoelectric thin film layer 130 comprises a crystalline composition of a lithium tantalate (LT) compound (such as LiTaO3) and a lithium niobate (LN) compound (such as LiNbO3). The electromechanical coupling coefficient of this crystalline composition is within an electromechanical coupling coefficient range. For example, the electromechanical coupling coefficient range can be approximately 12% to 25%. In some embodiments, the electromechanical coupling coefficient range can be approximately 12% to 24%.
[0038] In at least some embodiments, the crystal composition may include LiTa. 1-x Nb x O3. For example, LiTa 1-x Nb x The x value in O3 can be between 0.3 and 0.7. In at least some embodiments, LiTa 1-x Nb x The x value in O3 can be 0.5. In other words, LiTaO3 (LT) and LiNbO3 (LN) can be mixed in crystalline compositions with different concentrations of tantalum (Ta) and Nb.
[0039] In at least some embodiments, the electromechanical coupling coefficient can be selected within a range based on the ratio of the LT compound and the LN compound.
[0040] In at least some embodiments, the crystal composition may have approximately 33°YX(01) 2) Growth orientation (33° Y cut). For example, the growth orientation can have a tolerance of 5 degrees. In other words, a (33°±5°) YX cut can be used.
[0041] In at least some embodiments, the thickness of the piezoelectric thin film layer 130 may be 1 micrometer (µm) or less.
[0042] Figure 2 This is a block diagram of an electronic device 200 provided in one embodiment of the present invention. The electronic device 200 includes the FSAW resonant element 100 disclosed above. The electronic device 200 may also include a radio frequency (RF) filter 201. More specifically, in at least some embodiments, one or more FSAW resonant elements 100 may be included in the RF filter 201. For example, the RF filter 201 may include a B41 filter or a B75 filter.
[0043] Any ranges or device values given herein can be extended or modified without affecting the desired effect. Furthermore, unless expressly prohibited, any embodiment can be combined with other embodiments.
[0044] Although the subject matter has been described in language specific to structural features and / or actions, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or actions described above. Rather, the specific features and actions described above are disclosed as examples of implementing the claims, and other equivalent features and actions are intended to be included within the scope of the claims.
[0045] It should be understood that the advantages and benefits described above may relate to one or more embodiments. The embodiments are not limited to solving any or all of the described problems, nor are they limited to embodiments having any or all of the described advantages and benefits. It should also be understood that reference to "a" may refer to one or more of these items.
[0046] Aspects of any of the embodiments described above can be combined with aspects of any other embodiments described to form more embodiments without affecting the desired effect.
[0047] The term “including / comprising” is used herein to mean including the identified method, box, or element, but such box or element does not include an exclusive list, and the method or apparatus may include additional boxes or elements.
[0048] It should be understood that the above description is provided by way of example only, and various modifications can be made by those skilled in the art. The above specification, examples, and data provide a complete description of the structure and use of exemplary embodiments. Although various embodiments have been described above with a degree of specificity or in combination with one or more individual embodiments, those skilled in the art can make numerous modifications to the disclosed embodiments without departing from the spirit or scope of this specification.
Claims
1. A thin-film surface acoustic wave (FSAW) resonator (100), characterized in that, include: Substrate (110); An intermediate layer (120) is disposed on the substrate layer (110). A piezoelectric thin film layer (130) is disposed on the intermediate layer (120). An interdigital transducer (IDT) arrangement (140) is disposed on the piezoelectric thin film layer (130), wherein the IDT arrangement (140) includes two conductive elements (141, 142), an active region (143) disposed between the two conductive elements (141, 142), and a plurality of interdigital electrodes (144, 145), each electrode extending from one of the conductive elements through the active region to the other conductive element, and the distance between the central axes of every two adjacent electrodes is the electrode pitch. The piezoelectric thin film layer (130) comprises a crystalline composition of lithium tantalate (LT) compound and lithium niobate (LN) compound, wherein the electromechanical coupling coefficient of the crystalline composition is within the range of electromechanical coupling coefficients.
2. The FSAW resonant element (100) according to claim 1, characterized in that, The crystal composition includes LiTa (1-x) Nb (x) O3.
3. The FSAW resonant element (100) according to claim 2, characterized in that, The LiTa (1-x) Nb (x) The x value in O3 is between 0.3 and 0.
7.
4. The FSAW resonant element (100) according to any one of claims 1 to 3, characterized in that, The electromechanical coupling coefficient can be selected within the range of the electromechanical coupling coefficient based on the ratio of the LT compound and the LN compound.
5. The FSAW resonant element (100) according to any one of claims 1 to 4, characterized in that, The electromechanical coupling coefficient ranges from approximately 12% to 25%.
6. The FSAW resonant element (100) according to any one of claims 1 to 5, characterized in that, The crystal composition has approximately 33°YX(01) 2) Growth orientation.
7. The FSAW resonant element (100) according to claim 6, characterized in that, The growth orientation has a tolerance of 5 degrees.
8. The FSAW resonant element (100) according to any one of claims 1 to 7, characterized in that, The thickness of the piezoelectric thin film layer (130) is 1 micrometer or less.
9. An electronic device (200), characterized in that, Includes a thin-film surface acoustic wave (FSAW) resonator (100) according to any one of the preceding claims.
10. The electronic device (200) according to claim 9, characterized in that, The FSAW resonant element (100) is included in the radio frequency (RF) filter (201).