A thin-film surface acoustic wave resonator element structured to enable intermediate bandwidths, and a related electronic apparatus

Abstract

The invention allows a structure for a thin-film surface acoustic wave (FSAW) resonator to enable intermediate bandwidths. More specifically, a disclosed layered FSAW resonator element employing a piezoelectric thin-film layer with specific niobium (Nb) concentrations of lithium tantalate (LT) and lithium niobate (LN) compounds allows achieving an electromechanical coupling intermediate between the LT and LN compounds.

Description

[0001] A THIN-FILM SURFACE ACOUSTIC WAVE RESONATOR ELEMENT STRUCTURED TO ENABLE INTERMEDIATE BAND WIDTHS, AND A RELATED ELECTRONIC APPARATUS

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to the field of surface acoustic wave devices, and, more particularly, to a thin-film surface acoustic wave resonator structured to enable intermediate bandwidths, and a related electronic apparatus.

[0004] BACKGROUND

[0005] A SAW (surface acoustic wave) device is a device using propagation of elastic waves on a surface of a material or at an interface between several materials, and is commonly used in micro-mechanical resonators and filters. SAW devices use so-called interdigitated transducers (IDTs) to transform radio frequency (RF) signals into acoustic waves or acoustic waves into RF signals.

[0006] SAW devices are often used in RF filters. However, at least in some situations current SAW devices may not always meet the requirements of new RF filters being developed. For example, RF filters for use in band 41 (B41 , 2496 MHz - 2690 MHz) or band 75 (B75, 1432 MHz - 1517 MHz) may require wide bandwidths. Yet, current SAW devices may have insufficient electromechanical coupling (i.e., relatively small resonance-to-antiresonance fractional frequency distance) compared to bandwidth requirements of these new RF filters, for example.

[0007] Accordingly, at least in some situations, there may be a need for solutions that improve bandwidth capabilities of SAW devices.

[0008] SUMMARY

[0009] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0010] It is an object of the invention to allow a thin-film surface acoustic wave resonator structured to enable intermediate bandwidths. The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

[0011] According to a first aspect, a thin-film surface acoustic wave, FSAW, resonator element is provided. The FSAW resonator element comprises a substrate layer. The FSAW resonator element further comprises an intermediate layer arranged on the substrate layer. The FSAW resonator element further comprises a piezoelectric thin-film layer arranged on the intermediate layer. The FSAW resonator element further comprises an interdigital transducer, IDT, arrangement arranged on the piezoelectric thin-film layer. The IDT arrangement comprises two conductive elements, an active area arranged between the two conductive elements, and a plurality of interdigitating electrodes. Each electrode extends from one of the conductive elements across the active area towards the other of the conductive elements. Center axes of each two adjacent electrodes has a distance of an electrode pitch. The piezoelectric thin-film layer comprises a crystalline composition of lithium tantalate, LT, compounds and lithium niobate, LN, compounds. The crystalline composition has an electromechanical coupling coefficient within an electromechanical coupling coefficient range. The present disclosure allows a structure for a thin-film surface acoustic wave resonator to enable intermediate bandwidths. More specifically, the disclosed layered FSAW resonator element employing the piezoelectric thin-film layer with specific niobium (Nb) concentrations of the LT and LN compounds allows achieving an electromechanical coupling intermediate between the LT and LN compounds.

[0012] In an implementation form of the first aspect, the crystalline composition comprises LiTa<i-x)Nb(x)O3. This implementation form allows a selection of Nb concentration that boosts the electrotechnical coupling to optimum levels for an RF filter, while keeping away and suppressing spurious modes in the structure.

[0013] In an implementation form of the first aspect, the LiTa<i-x)Nb(x)O3 has an x value between 0.3 and 0.7. This implementation form allows properties of the crystalline composition to vary linearly.

[0014] In an implementation form of the first aspect, the electromechanical coupling coefficient is selectable within the electromechanical coupling coefficient range depending on proportions of the LT compounds and the LN compounds. This implementation form allows selection of the electromechanical coupling coefficient according to needs.

[0015] In an implementation form of the first aspect, the electromechanical coupling coefficient range is substantially from 12 percent to 25 percent. This implementation form allows selection of the electromechanical coupling coefficient according to needs.

[0016] In an implementation form of the first aspect, the crystalline composition has a growth orientation of substantially 33°Y- X(0112). This implementation form allows for relatively strong electromechanical coupling of a main SAW mode, while it coincides with one of the crystal planes and thus is feasible for being epitaxially grown.

[0017] In an implementation form of the first aspect, the growth orientation has a margin of five degrees. This implementation form allows for mitigating the influence of initial growing conditions on the actual crystal orientation, which may slightly deviate from the 33°Y plane.

[0018] In an implementation form of the first aspect, the piezoelectric thin-film layer has a thickness of one micrometer or less. This implementation form allows for growing a piezoelectric film with sufficiently low residual stresses required for growing films free of macro defects, while on the other it hand covers an optimal thickness range for achieving high performance devices in the lower GHz range.

[0019] According to a second aspect, an electronic apparatus is provided. The electronic apparatus comprises the FSAW resonator element according to the first aspect. This implementation form allows an FSAW resonator element for an electronic apparatus.

[0020] In an implementation form of the second aspect, the FSAW resonator element is comprised in a radio frequency, RF, filter. RF filters require precise design parameters, and the FSAW resonator element allows an improved performance of an RF filter. Many of the attendant features will be more readily appreciated as they become better understood by reference to the following detailed description considered in connection with the accompanying drawings.

[0021] DESCRIPTION OF THE DRAWINGS

[0022] In the following, example embodiments are described in more detail with reference to the attached figures and drawings, in which:

[0023] Fig. 1A is a diagram illustrating a thin-film surface acoustic wave resonator element according to an embodiment of the disclosure;

[0024] Fig. IB is a diagram illustrating an interdigital transducer arrangement according to an embodiment of the disclosure; and

[0025] Fig. 2 is a block diagram illustrating an electronic apparatus according to an embodiment of the disclosure.

[0026] In the following, identical reference signs refer to identical or at least functionally equivalent features.

[0027] DETAILED DESCRIPTION

[0028] In the following description, reference is made to the accompanying drawings, which form part of the disclosure, and in which are shown, by way of illustration, specific aspects in which the invention may be placed. It is understood that other aspects may be utilized, and structural or logical changes may be made without departing from the scope of the invention. The following detailed description, therefore, is not to be taken in a limiting sense, as the scope of the invention is defined in the appended claims.

[0029] For instance, it is understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if a specific method step is described, a corresponding device may include a unit to perform the described method step, even if such unit is not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on functional units, a corresponding method may include a step performing the described functionality, even if such step is not explicitly described or illustrated in the figures. Further, it is understood that the features of the various example aspects described herein may be combined with each other, unless specifically noted otherwise.

[0030] As will be discussed in more detail below, at least some of the disclosed embodiments may allow a structure for a thin-film surface acoustic wave (FS AW) resonator that enables intermediate bandwidths.

[0031] At least some of the disclosed embodiments may allow a layered FSAW device employing an LiTa i-xjNbtxjOs (LTN) piezoelectric thin film with specific Nb concentration and crystal orientation. The disclosed FSAW design may allow achieving an electromechanical coupling intermediate between the LiTaCh and LiNbCh. In other words, at least some of the disclosed embodiments may allow an LTN piezoelectric material for designing FSAW resonators with intermediate (between LT and LN) R-aR frequency bandwidths. At least in some of the disclosed embodiments, these intermediate R-aR bandwidths may be more favorable with respect to the performance of RF filters with bandwidths between 4% and 10%.

[0032] At least in some of the disclosed embodiments, the disclosed LTN material may enable a better control of Rayleigh SAW (RSAW) spurs keeping them away from the filter band.

[0033] At least in some of the disclosed embodiments, it may be possible to deposit the LTN material as an epitaxial sub-micrometer thin-film using chemical vapor deposition (CVD), metal-organic chemical vapor deposition (MOCVD), pulsed laser deposition (PLD), or the like.

[0034] At least some of the disclosed embodiments may allow using a layer transfer technique for FSAW manufacture.

[0035] Next, example embodiments of FSAW resonator element 100 are described based on Figs. 1A and IB. Some of the features of the described devices are optional features which provide further advantages. Herein, a thin-film SAW (FSAW) resonator element refers to a category of SAW resonator elements that use a thin-film material for a piezoelectric layer.

[0036] Fig. 1A is a diagram illustrating FSAW resonator element 100 according to an embodiment of the disclosure. Fig. IB is a diagram illustrating interdigital transducer (IDT) arrangement 140 employed in FSAW resonator element 100 of Fig. 1 A.

[0037] FSAW resonator element 100 comprises substrate layer (or base substrate) 110. Substrate layer 110 may comprise, e.g., at least one of silicon (Si), sapphire, quartz, silicon carbide (SiC), or yttrium aluminum garnet (YAG).

[0038] FSAW resonator element 100 further comprises intermediate layer 120 arranged on substrate layer 110. Intermediate layer 120 may comprise, e.g., silicon dioxide (SiCh).

[0039] FSAW resonator element 100 further comprises piezoelectric thin-film layer 130 arranged on intermediate layer 120. At least in some embodiments, piezoelectric thin-film layer 130 may be epitaxially grown (e.g., via chemical vapor deposition (CVD) or pulsed laser deposition (PLD)). For example, such layers may be grown on a seed layer, subsequently poled and then transferred to an acoustic substrate by a suitable layer transfer technique.

[0040] At least in some embodiments, substrate layer 110 may be thicker than intermediate layer 120 and piezoelectric thin-film layer 130. At least in some embodiments, substrate layer 110 may be multiple times thickerthan either of intermediate layer 120 or piezoelectric thin-film layer 130.

[0041] FSAW resonator element 100 further comprises interdigital transducer (IDT) arrangement 140 arranged on piezoelectric thin- film layer 130. IDT arrangement 140 comprises two conductive elements (e.g., busbars) 141, 142. IDT arrangement 140 further comprises active area 143 arranged between two conductive elements 141, 142. IDT arrangement 140 further comprises a plurality of interdigitating electrodes 144, 145. Each electrode extends from one of the conductive elements across the active area towards the other of the conductive elements. Center axes of each two adjacent electrodes has a distance of an electrode pitch. For example, electrodes 144, 145 may comprise aluminum.

[0042] In other words, active area 143 forms a center area of IDT arrangement 140, and the conductive elements 141, 142 form opposite edge areas of IDT arrangement 140.

[0043] By interdigitating it is meant that active area 143 comprises two sets of electrodes which are arranged such that the electrodes of the first set of electrodes alternate with the electrodes of the second set of electrodes, each first electrode being separated from a neighboring first electrode by a second electrode and, correspondingly, each second electrode being separated from a neighboring second electrode by a first electrode.

[0044] Piezoelectric thin-film layer 130 comprises a crystalline composition of lithium tantalate (LT) compounds (e.g., LiTaCh) and lithium niobate (LN) compounds (e.g., LiNbCh). The crystalline composition has an electromechanical coupling coefficient within an electromechanical coupling coefficient range. For example, the electromechanical coupling coefficient range may be substantially from 12 percent to 25 percent. In some embodiments, the electromechanical coupling coefficient range may be substantially from 12 percent to 24 percent.

[0045] At least in some embodiments, the crystalline composition may comprise LiTai-xNbxOs. For example, the LiTai-xNbxOs may have an x value between 0.3 and 0.7. At least in some embodiments, the LiTai-xNbxOs may have an x value of 0.5. In other words, LiTaO3 (LT) and LiNbO3 (LN) may be mixed in crystalline compositions with various concentrations of tantalum (Ta) and Nb.

[0046] At least in some embodiments, the electromechanical coupling coefficient may be selectable within the electromechanical coupling coefficient range depending on proportions of the LT compounds and the LN compounds.

[0047] At least in some embodiments, the crystalline composition may have a growth orientation (33° Y cut) of substantially 33°Y- X(0112). For example, the growth orientation may have a margin of five degrees. In other words, a (33°±5°) Y-X cut may be used.

[0048] At least in some embodiments, piezoelectric thin-film layer 130 may have a thickness of one micrometer (pm) or less.

[0049] Fig. 2 is a block diagram illustrating electronic apparatus 200 according to an embodiment of the disclosure. Electronic apparatus 200 comprises FSAW resonator element 100 disclosed above. Electronic apparatus 400 may further comprise radio frequency (RF) filter 201. More specifically, at least in some embodiments, one or more of the FSAW resonator elements 100 may be comprised in RF filter 201. For example, RF filter 201 may comprise a B41 filter or a B75 filter.

[0050] Any range or device value given herein may be extended or altered without losing the effect sought. Also, any embodiment may be combined with another embodiment unless explicitly disallowed. Although the subject matter has been described in language specific to structural features and / or acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as examples of implementing the claims and other equivalent features and acts are intended to be within the scope of the claims.

[0051] It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. It will further be understood that reference to 'an' item may refer to one or more of those items.

[0052] Aspects of any of the embodiments described above may be combined with aspects of any of the other embodiments described to form further embodiments without losing the effect sought.

[0053] The term 'comprising' is used herein to mean including the method, blocks or elements identified, but that such blocks or elements do not comprise an exclusive list and a method or apparatus may contain additional blocks or elements.

[0054] It will be understood that the above description is given by way of example only and that various modifications may 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 certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this specification.

Claims

CLAIMS1. A thin-film surface acoustic wave, FSAW, resonator element (100), comprising: a substrate layer (110); an intermediate layer (120) arranged on the substrate layer (110); a piezoelectric thin-film layer (130) arranged on the intermediate layer (120); and an interdigital transducer, IDT, arrangement (140) arranged on the piezoelectric thin-film layer (130), the IDT arrangement (140) comprising two conductive elements (141, 142), an active area (143) arranged between the two conductive elements (141, 142), and a plurality of interdigitating electrodes (144, 145), each electrode extending from one of the conductive elements across the active area towards the other of the conductive elements, center axes of each two adjacent electrodes having a distance of an electrode pitch, wherein the piezoelectric thin-film layer (130) comprises a crystalline composition of lithium tantalate, LT, compounds and lithium niobate, LN, compounds, the crystalline composition having an electromechanical coupling coefficient within an electromechanical coupling coefficient range.

2. The FSAW resonator element (100) according to claim 1, wherein the crystalline composition comprises LiTa<i-x)Nb(x)O3.

3. The FSAW resonator element (100) according to claim 2, wherein the LiTa<i-x)Nb(x)O3 has an x value between 0.3 and 0.7.

4. The FSAW resonator element (100) according to any of claims 1 to 3, wherein the electromechanical coupling coefficient is selectable within the electromechanical coupling coefficient range depending on proportions of the LT compounds and the LN compounds.

5. The FSAW resonator element (100) according to any of claims 1 to 4, wherein the electromechanical coupling coefficient range is substantially from 12 percent to 25 percent.

6. The FSAW resonator element (100) according to any of claims 1 to 5, wherein the crystalline composition has a growth orientation of substantially 33°Y-X(0112).

7. The FSAW resonator element (100) according to claim 6, wherein the growth orientation has a margin of five degrees.

8. The FSAW resonator element (100) according to any of claims 1 to 7, wherein the piezoelectric thin-film layer (130) has a thickness of one micrometer or less.

9. An electronic apparatus (200) comprising the thin-film surface acoustic wave, FSAW, resonator element (100) according to any one of the previous claims.

10. The electronic apparatus (200) according to claim 9, wherein the FSAW resonator element (100) is comprised in a radio frequency, RF, filter (201).

Images