An acoustic resonator device, an electronic apparatus and a manufacturing method

Abstract

The disclosure allows a structure for an acoustic resonator device, more speficially, a bulk acoustic wave (BAW) resonator that enables improved mass loading of the resonator and enables to be comprised in a ladder filter. These effects, among others, are achieved by configuring an intermediate electrode in a boundary between two piezoelectric layers and a common electrode on one side of the acoustic wave resonator and two separate electrodes on the other side of the acoustic wave resonator. Further- more, methods for manufacturing the acoustic resonator device are disclosed.

Description

[0001] AN ACOUSTIC RESONATOR DEVICE, AN ELECTRONIC APPARATUS AND A MANUFACTURING METHOD

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to the field of acoustic wave resonators, and, more particularly, to a bulk acoustic wave resonator with two piezoelectric layers of opposite wave polarization and an intermediate electrode.

[0004] BACKGROUND

[0005] A BAW (Bulk Acoustic Wave) resonator is an electromechanical device in which a standing acoustic wave is generated by an electric signal in a bulk of piezoelectric material. An example configuration comprises two electrodes arranged on opposite surfaces of the piezoelectric material, wherein the material choice and the thickness of the piezoelectric material layer generally define the operating frequency.

[0006] BAW devices may be classified into two categories: a thin film bulk acoustic wave resonator (FBAR) and a solidly mounted resonator (SMR).

[0007] At least in some situations, there may be a need for solutions that co-integrate multiple ladder filter components on a same die and compensate for a frequency offset.

[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 at least allow a bulk acoustic wave resonator structured to enable to comprise two impedance components of a ladder filter. Furthermore, an intermediate electrode configured in an interface between two piezoelectric layers may enable a significant mass loading effect on the resonant frequency of the bulk acoustic wave resonator. 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, an acoustic resonator device is provided. The acoustic resonator device may comprise a first piezoelectric layer and a second piezoelectric layer, wherein a first surface of the first piezoelectric layer is configured to a first surface of the second piezoelectric layer and the first piezoelectric layer and the second piezoelectric layer comprises opposite phase wave excitation for a given wave polarization. Furthermore, the acoustic resonator device may comprise at least four electrodes, wherein: a first electrode is configured on a second surface of the first piezoelectric layer; a second electrode is configured on a second surface of the second piezoelectric layer; a third electrode is configured on the second surface of the first piezoelectric layer; and a fourth electrode is configured in a portion of a boundary between the first surface of the first piezoelectric layer and the first surface of the second piezoelectric layer. Utilizing two piezoelectric layers with opposite phase wave excitation for a given polarization may enable power handling of bulk acoustic wave resonators. Additionally, the fourth electrode may enable a significant resonant frequency downshift e.g., of about 10% while retaining and even improving the electromechanical factor. In an implementation form of the first aspect, one or more border frame structures are configured at least partially underneath one or more electrodes of the at least four electrodes, such that the border frame structure extends along edges of a corresponding electrode. The border frame structure may enable suppression of spurious modes.

[0012] In an implementation form of the first aspect, the first piezoelectric layer and the second piezoelectric layer each comprises a stack layer, and a portion of the stack layer is removed substantially near at least one of the electrodes. Removing a portion from the stack layer may improve the energy confinement of the resonator.

[0013] In an implementation form of the first aspect, the first piezoelectric layer (102) and the second piezoelectric layer (104) comprise alternatively Aluminium Scandium Nitride (AlScN) and Lithium Niobate (LiNbO3). This combination of materials may enable an easy control of the mutual polarizations. While AlScN grows with a preferable polarization, the LiNbO3 can be specifically selected to have an opposite one.

[0014] In an implementation form of the first aspect, the AlScN comprises compression negative or compression positive C-Axis AlScN (c-AlScN), and the LiNbO3 comprises 36°Y LiNbO3 or (36°-180°)Y LiNbO3. The proposed stack allows two piezoelectric layers with mutually opposite polarizations and similar acoustic impedances.

[0015] In an implementation form of the first aspect, at least one of the first electrode and the third electrode is substantially rectangularly shaped and is configured in 0° rotation with respect to the OX crystal axis of the first piezoelectric layer. Adjusting orientation of an electrode may enable improving suppression of spurious modes. In this implementation form, the spurious modes formed along OX and 90°-OX lateral propagations may be with slightly different dispersions and interfere destructively at the electrical port.

[0016] In an implementation form of the first aspect, at least one of the first electrode and the third electrode is substantially rectangularly shaped and is configured in 45° rotation with respect to the OX crystal axis of the first piezoelectric layer. In this implementation form, the spurious modes formed along 45°-OX and -45°-OX lateral propagations may be with same dispersions and allow for the design of identical spurious mode suppression structures in the vicinity of each of the edges of the electrode. In an implementation form of the first aspect, at least one of the first electrode and the third electrode is multi -angle asymmetrically shaped. An asymmetrical electrode may improve suppression of spurious modes.

[0017] In an implementation form of the first aspect, at least three physically separate grated portions are configured to at least one side of at least one of the first electrode and the third electrode. The three physically separate grated portions may improve energy confinement of the acoustic resonator device.

[0018] In an implementation form of the first aspect, the at least three physically separate grated portions are of the same material than the first electrode the third electrode. Using the same material for the three grated portions may enable better reflectivity and thus, energy confinement.

[0019] In an implementation form of the first aspect, the physical separation of each grated portion from the at least three physically separate grated portions is between 0.3 micrometers and 2 micrometers. Alternating the separation distance may enable better energy confinement.

[0020] In an implementation form of the first aspect, a Bragg reflector stack is configured to the second surface of second piezoelectric layer. Bragg reflector stack. A Bragg reflector improves the structural integrity of the acoustic resonator device and may improve the energy confinement of longitudinal modes. According to a second aspect, an electronic apparatus is provided. The electronic apparatus may comprise the acoustic resonator device according to the first aspect. This implementation form allows an acoustic resonator device for radio frequency filter applications.

[0021] In an implementation form of the second aspect, the acoustic resonator device is comprised in a radio frequency filter. Radio frequency filters require precise design parameters, wherein the acoustic resonator device may enable improved performance of an RF filter.

[0022] According to a third aspect, there is provided a method for manufacturing the acoustic resonator device according to the first aspect. The method may comprise: configuring the first piezoelectric layer to a first surface of abase substrate; configuring the fourth electrode to the first surface of the first piezoelectric layer; configuring the second piezoelectric layer to the first surface of the first piezoelectric layer; configuring the second electrode to the second surface of the second piezoelectric layer; removing the base substrate; and configuring the first electrode and the third electrode on the second surface of the first piezoelectric layer. Disclosed manufacturing method(s) may enable faster implementation of the acoustic resonator device according to the first aspect.

[0023] In an implementation form of the third aspect, after the configuring of the second electrode to the second surface of the second piezoelectric layer, the method further comprises: configuring two or more bonding pedestals to the second surface of the second piezoelectric layer; and configuring a carrier substrate to the two or more bonding pedestals. A rigid carrier substrate bonded to the bonding pedestals may improve performance of acoustic resonator device.

[0024] In an implementation form of the third aspect, after the configuring of the second electrode to the second surface of the second piezoelectric layer, the method may further comprise configuring a substrate with a cavity to the second surface of the second piezoelectric layer such, that the cavity encloses the second electrode. A cavity may improve the resonance characteristics of the acoustic resonator device.

[0025] In an implementation form of the third aspect, after the configuring of the second electrode to the second surface of the second piezoelectric layer, the method further comprises: configuring a Bragg reflector stack to the second surface of the second piezoelectric layer; and configuring a carrier substrate to the Bragg reflector stack. A Bragg reflector improves the structural integrity of the acoustic resonator device and may improve the energy confinement of longitudinal modes.

[0026] 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.

[0027] DESCRIPTION OF THE DRAWINGS

[0028] In the following, example embodiments are described in more detail with reference to the attached figures and drawings, in which:

[0029] Fig. 1 is a diagram illustrating an acoustic resonator device according to embodiments of the disclosure;

[0030] Fig. 2 illustrates an electrode according to an example embodiment and an acoustic resonator device employing the electrode;

[0031] Fig. 3A illustrates example embodiments of electrodes;

[0032] Fig 3B illustrates three physically separate grated portions and an electrode according to an example embodiment; Fig. 4 illustrates an acoustic resonator device according to an example embodiment comprising a removed portion;

[0033] Fig. 5 illustrates a ladder filter according to an example embodiment;

[0034] Figs. 6A-6D are flow diagrams illustrating manufacturing methods according to example embodiments; and

[0035] Fig. 7 is a block diagram illustrating an electronic apparatus according to an embodiment of the disclosure.

[0036] In the following, identical reference signs refer to identical or at least functionally equivalent features.

[0037] DETAILED DESCRIPTION

[0038] 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.

[0039] 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.

[0040] As will be discussed in more detail below, at least some of the disclosed embodiments may allow a structure for a bulk acoustic wave (BAW) resonator that enables compensating for significant frequency offset of different resonator devices used in a same filter. The disclosed acoustic resonator device proposes a BAW structure with two piezoelectric material layers of opposite wave polarizations for a given input polarization, wherein an electrode configured in a boundary of the two piezoelectric materials increases mass loading of the BAW structure. Furthermore, using a common electrode for two separate electrodes on the same surface enables component matching in an RF filter and reduces the total area required by the RF filter.

[0041] In other words, at least some of the disclosed embodiments may allow a thin-film BAW resonator device employing two piezoelectric layers and an intermediate electrode in the piezoelectric layer boundary. Additionally, some disclosed embodiments may allow a solidly mounted resonator with a Bragg reflector stack. Furthermore, at least some of the disclosed embodiments may enable co-integration of multiple BAW resonators on the same die, which may be used in a ladder-filter configuration of an RF filter, for example.

[0042] Some disclosed embodiments may retain resonance to antiresonance fractional offset while reducing resonance frequency in the range of 5%-l 5%.

[0043] Some disclosed embodiments may enable a rectangularly shaped electrodes for BAW excitation with a variable rotation with respect to OX crystal axis of one of the two piezoelectric layers. Some disclosed embodiments may enable a multi -angle (more than 3 angles) electrode for BAW excitation.

[0044] Some disclosed embodiments may enable a border frame structure formed of dielectric underneath edges of electrode(s) to suppress spurious modes.

[0045] Some disclosed embodiments may enable periodic electrode strips (grating portions) with a pitch ranging from 0.3 micrometers to 2 micrometers. Periodic electrode strips may enable energy loss reduction.

[0046] It is noted that in this description, the word (or rather, verb) “to configure” or “configuring” may be used as a synonym to the word “to arrange” or “arranging” respectively. In other words, these words are to be treated as equivalent to each other unless otherwise stated. For example, a first layer may be configured or arranged to a second layer, or the like.

[0047] Fig. 1 is a diagram illustrating an acoustic resonator device 100 according to an embodiment of the disclosure comprising a first piezoelectric layer 102 and a second piezoelectric layer 104 wherein a first surface 150 of the first piezoelectric layer 102 is configured to a first surface 152 of the second piezoelectric layer 104. In other words, the ‘bottom’ of first piezoelectric layer 102 is configured to the ‘top’ of second piezoelectric layer 104 when referring to the orientation of acoustic resonator device 100 in Fig. 1. It is to be noted that the illustrated embodiment of Fig. 1 comprises a thin-film bulk acoustic resonator (FBAR) however, present disclosure enables embodiment(s) of a solidly mounted resonators (SMR).

[0048] Furthermore, first piezoelectric layer 102 and second piezoelectric layer 104 may comprise opposite phase wave excitation for a given wave polarization with same or similar acoustic impedances. An example of such two materials may comprise first piezoelectric layer 102 comprising aluminum scandium nitride (AlScN) and second piezoelectric layer 104 comprising 36°Y LiNbO3 (Lithium Niobate) or its counterpart (36oY-180°)Y LiNbO3. It is to be noted that material choice for the two piezoelectric layers are not limited to the given example. In some embodiments, first piezoelectric layer 102 may comprise 36°Y LiNbO3 and second piezoelectric layer 104 may comprise AlScN.

[0049] Even furthermore, first piezoelectric layer 120 and second piezoelectric layer 104 may be selected from one or more crystal symmetry groups, i.e., first piezoelectric layer 102 and second piezoelectric layer 104 may belong to the same or different crystal symmetry groups. In some embodiments, at least one of the first piezoelectric layer 102 and second piezoelectric layer 104 is from a 3m point group. The 3m point group includes e.g., LiNbO3 and Lithium Tantalate (LiTaO3). If only one of first piezoelectric layer 102 and second piezoelectric layer 104 is from the 3 m point group, the other one of first piezoelectric layer 102 and second piezoelectric layer 104 may be from a 6mm group including Aluminum Scandium Nitride (AlScN) and Sc doped AIN.

[0050] In some embodiments where first piezoelectric layer 102 and second piezoelectric layer 104 are from different crystal symmetry groups, first piezoelectric layer 102 may be a compression negative C-axis AlScN layer and second piezoelectric layer 104 may be a LiNbO3 layer having a rotated Y-cut in the range of -134° to -154°, or vice versa. First piezoelectric layer 102 may further be a compression positive C-axis AlScN layer and second piezoelectric layer 104 may be a LiNbO3 layer having a rotated Y -cut in the range of 26° to 46°, or vice versa. In this way, first piezoelectric layer 102 and second piezoelectric layer 104 have different crystal orientation and combinations between compression positive and compression negative excitations in each layer is achieved. The compression positive C-axis AlScN layer and the compression negative C-axis AlScN layer may be an Al(l-x)ScxN layer, where x > 0.2. The AlScN layer may be grown on the LiNbO3 layer, and the LiNbO3 layer may be a single crystalline layer. The AlScN layer may e.g., be grown using a deposition or a spluttering technique on a single crystalline layer LiNbO3 layer fabricated e.g., by means of piezoelectric on insulator (POI) techniques. In some embodiments, first piezoelectric layer 102 and second piezoelectric layer 104 are both from the 3m point group. For example, first piezoelectric layer 102 may be a first LiNbO3 layer and second piezoelectric layer 104 may be a second LiNbO3 layer, or vice versa. The first LiNbO3 layer and the second LiNbO3 layer may have a rotated Y-cut in any of the ranges of 153° to 173° or -7° to -27°, and the first LiNbO3 layer may have a 180° rotated X-axis in relation to an X-axis of the second LiNbO3 layer. These configurations make the phase excitation in one of the piezoelectric layer opposite to the phase excitation in the other piezoelectric layer and is valid for shear wave polarization only hence the mentioned cuts.

[0051] Furthermore, first piezoelectric layer 102 may be a first LiNbO3 layer having a first rotated Y-cut and second piezoelectric layer 104 maybe a second LiNbO3 layer having a second rotated Y-cut, or vice versa, where the first rotated Y-cut is rotated 180° around an X-axis of the LiNbO3 layer crystal in relation to the second rotated Y -cut, or vice versa. For example, the first LiNbO3 layer may have a rotated Y-cut in the range of 26° to 46° and the second LiNbO3 layer may have a rotated Y-cut in the range of -134° to -154°. Alternatively, the first LiNbO3 layer may have a rotated Y-cut in the range of 153° to 173° and the second LiNbO3 layer may have a rotated Y-cut in the range of -7° to -27°. The first LiNbO3 layer may further have a 0°, 60°, 90°, 120° or 180° rotated X-axis in relation to the X-axis of the second LiNbO3 layer. These configurations make the phases of excitation in the two piezoelectric layers opposite to each other for either the longitudinal wave, the shear wave or both. The electromechanical coupling will be strong for a desired wave polarization at its second thickness resonance while minimizing the coupling of the remaining polarizations.

[0052] The first LiNbO3 layer and the second LiNbO3 layer may be single crystalline layers and may e.g., be fabricated by means of ion-slicing techniques on carrier substrates such as POI substrates. The first LiNbO3 layer may then be attached to the second LiNbO3 layer, or vice versa, by bonding.

[0053] In some embodiments, a ratio between the acoustic impedance of first piezoelectric layer 102 and acoustic impedance of second piezoelectric layer 104 is in the range of 0.8 - 1.2. Thus, an even energy distribution between the first 102 and second 104 piezoelectric layers can be achieved. First piezoelectric layer 102 and second piezoelectric layer 104 further have opposite phase wave excitation for a given wave polarization. The given wave polarizations may be of the type longitudinal or shear with respect to wave propagation. One given wave polarization at a time, i.e., either longitudinal or shear, is of interest and the other should be sufficiently suppressed.

[0054] Utilizing two piezoelectric layers may enable better power handling capabilities of the acoustic resonator device 100, as the static capacitance (CO) per unit electrode area increases with frequency scaling due to thickness reduction of the piezoelectric. First piezoelectric layer 102 and second piezoelectric 104 may comprise thicknesses of half the wavelength of the resonant frequency of acoustic resonator device 100 i.e., half the wavelength of the target design frequency. In some embodiments, for example, thickness of first piezoelectric layer 102 and second piezoelectric layer 104 may be in range of 0.3 / . to 0.7 , where is the acoustic wavelength at resonance in each material. Furthermore, the thickness of first piezoelectric layer 102 and the thickness of second piezoelectric layer 104 may be in range of 100 to 1100. The thickness of the two piezoelectric layers may be considered as design parameters and may depend on asymmetry of chosen electrodes.

[0055] Acoustic resonator device 100 may comprise at least four electrodes 110, 120, 130, 140. A first electrode 110 may be configured on a second surface 154 of first piezoelectric layer 102. A second electrode 120 may be configured on a second surface 156 of second piezoelectric layer 104. A third electrode 130 may be configured on second surface 154 of first piezoelectric layer 102. Finally, a fourth electrode 140 may be configured in a portion of a boundary between first surface 150 of first piezoelectric layer 102 and first surface 152 of second piezoelectric layer 104. ‘In a portion of the boundary between first surface 150 of first piezoelectric layer 102 and first surface 152 of second piezoelectric layer 104’ may comprise fourth electrode 140 configured somewhere in an area between the two piezoelectric layers or rather, somewhere in an interface between the piezoelectric layers, or substantially in the interface between the two piezoelectric layers.

[0056] For example, fourth electrode 140 may lie partially in a portion of first piezoelectric layer 102 and partially in a portion of second piezoelectric layer 104.

[0057] In other words, fourth electrode 140 is enclosed by the two different piezoelectric layers or enclosed only by one of first piezoelectric layer 102 or second piezoelectric layer 104.

[0058] Alternatively, fourth electrode 140 may lie in full in either of the two piezoelectric layers. E.g., fourth electrode 140 may he completely in second piezoelectric layer 104 and no portion of fourth electrode 102 lies in first piezoelectric layer 102 and vice versa.

[0059] Fourth electrode 140 may be arranged, for example, on the first surface 150 of first piezoelectric layer 102 during early stages of a manufacturing process. Example of manufacturing steps are presented later in reference to Figs. 6A-6D.

[0060] Fourth electrode 140 may be configured substantially on a vertical direction (Y-axis in Fig. 1) extending from third electrode 130 towards second electrode 120.

[0061] It is to be noted that combination of first piezoelectric layer 102 and second piezoelectric layer 104 may be referred to as a ‘piezoelectric stack’, a ‘piezo stack’ ora ‘stack layer’.

[0062] Acoustic resonator device 100 is configured to enable two different resonators with a common electrode and where the common electrode may comprise second electrode 120. As such, in the example embodiment illustrated in FIG. 1, first electrode 110, the stack layer and second electrode 120 comprises a first acoustic resonator and third electrode 130, the stack layer, second electrode 120 and fourth electrode 140 comprises a second acoustic resonator.

[0063] Embodiments of acoustic resonator device 100 may be referred to as ‘BAW resonator’, ‘BAW resonator device’, or the like. In other words, acoustic resonator device 100 generally comprises a BAW resonator. Some embodiments may comprise FBAR devices, and some embodiments may comprise SMR devices.

[0064] The two different resonators may be configured in, for example, an RF filter apparatus or the like in a ladder filter configuration. Fourth electrode 140 may enable a significant mass loading effect on a resonant frequency of acoustic resonator device 100. For example, a 10% resonant frequency downshift compared to a resonator without fourth electrode 140, while retaining and even improving the electromechanical factor.

[0065] In acoustic resonators, it may be beneficial to inhibit spurious modes generated during excitation.

[0066] Fig. 2 illustrates a border frame structure 200 arranged underneath at least a portion of one of first electrode 110 or third electrode 130, to inhibit spurious modes. Border frame structure 200 may be frame-like, ring-like, peripherical or circumferential in reference to the electrode it is arranged underneath of. The word ‘frame ’ in border frame structure 200 is not to imply only a frame structure that would enclose the electrode it is arranged underneath of, but rather, border frame structure 200 may be intended to circumvent underneath edges of the electrode it is arranged underneath of. Therefore, border frame structure 200 may comprise a rectangular structure that circumvents around the edges of the respective electrode, for example. Orborderframe structure 200 may comprise a multi -angle asymmetrical shape that circumvents around underneath the edges of the respective electrode. In some embodiments, border frame structure 200 may comprise a circular structure.

[0067] On the left of FIG. 2, a top-down view of one of first electrode 110 or third electrode 130 is illustrated and on the right of FIG. 2, a side-view of acoustic resonator device 100 is illustrated, wherein border frame structure 200 is arranged underneath a portion of edges of first electrode 110 or third electrode 130. E.g., border frame structure 200 may be used to break even properties of the electrode it is arranged underneath of.

[0068] While the perspective in Fig. 2. illustrates border frame structure 200 not covering the front face facing the view, border frame structure 200 may be arranged to cover each side of the corresponding electrode.

[0069] In some embodiments of acoustic resonator device 100, a separate border frame structure 120 may be arranged underneath both first electrode 110 and third electrode 130, for example.

[0070] Border frame structure 200 may comprise a dielectric material, such as SiO2, or variations of SiO2.

[0071] Fig. 3 A illustrates various different shapes and / or arrangements of the at least four electrodes. At 310, an electrode may comprise a rectangularly shaped electrode, with a 0° rotation with respect to crystal axis of LiNbO3. At 320, an electrode may comprise a rectangularly shaped electrode with a 45° rotation with respect to crystal axis of LiNbO3. At 330, an electrode may comprise a multi -angle asymmetrically shaped electrode. A multi -angle asymmetrically shaped electrode may be beneficial for inhibiting spurious modes.

[0072] It is understood that the disclosed shapes of electrodes are not limited to the given examples. In some embodiments, an electrode may comprise a rectangular electrode with edges under -45, 45, 135, 225 degrees with respect to OX crystal axis of LN.

[0073] In some embodiments, an electrode may comprise a rectangular electrode with edges under -90, 0 ,180, 270 degrees with respect to OX crystal axis of LN.

[0074] Fig. 3B illustrates an example embodiment of an electrode 340, wherein three physically separate grated portions 350 are arranged to at least one side of at least one of electrode 340. In some embodiments, more than three grated portions 350 may be arranged to at least one side. In some embodiments, three physically separate grated portions 350 may be arranged to more than one sides of electrode 340. Three physically separate grated portions 350 may comprise a ‘reflective grating’, and it may be beneficial for increasing energy confinement of acoustic resonator device 100. For example, a transverse mode with respect to a wave traveling through the bulk (i.e., vertically) of acoustic resonator device 100 may be reflected back on electrode 340 on the interface of one the at least three grated portions 350. Consequently, each grated portion in the reflective grating may increase energy confinement at the cost of area.

[0075] The reflective grating may comprise same material than the respective electrode it is associated with. The ‘pitch’ or, rather, the separation distance between the grated portions may vary. In some embodiments, the separation distance may be any value between 0.3 micrometers to 2 micrometers. Separation distance is illustrated at 360 in Fig. 3B. Separation between electrode 340 may be the same as the separation distance 360 between the grated portions. Fig. 4 illustrates an example embodiment of acoustic resonator device 100 comprising a removed portion 400. In the example, a portion of second piezoelectric layer 104 is removed. Removing a portion may be beneficial for energy confinement of acoustic resonator device 100, similarly to the reflective grating illustrated in Fig. 3B.

[0076] A portion may be removed by, for example, etching. Removed portion 400 may be formed substantially for the whole thickness of one of first piezoelectric layer 102 or second piezoelectric layer 104. Or removed portion 400 may be formed through the whole thickness of for example, first piezoelectric layer 102 and then extended partially to second piezoelectric layer 104. Removed portion 400 is generally formed substantially near an edge of one of the at least four electrodes. In the example of Fig. 4, removed portion 400 is formed substantially near an edge of second electrode 120. Removed portion 400 may be referred to as ‘trench’. The distance between an edge of an electrode and removed portion 400 is illustrated by letter ‘d’ in Fig. 4. In some embodiments, the distance d may be, for example, 1-5 micrometers.

[0077] Fig. 5 illustrates a ladder filter 500 comprising a plurality of series impedance components 510 (Zs) and a plurality of shunt impedance components 520 (Zp). Embodiments of acoustic resonator device 100 may be used to comprise two of any of these components. For example, acoustic resonator device 100 may comprise one series impedance component 510 and one shunt impedance components 520 by having first electrode 110 comprising terminal 530, second electrode 120 comprising T-point 550 and third electrode 130 comprising a ground / common connection. Therefore, connecting one of first electrode 110 or third electrode 130 of an additional acoustic resonator device 110 to T-point 550 enables constructing ladder filter 500.

[0078] In some embodiments, acoustic resonator device 100 may comprise two series impedance components. E.g., third electrode 130 comprises one terminal (input), second electrode 120 comprises a series connection point and first electrode 110 comprises second terminal (output). In such an embodiment, the order of first electrode 110 and third electrode 130 is of no consequence i.e., it does not necessarily affect the operation of acoustic resonator device 110 in a ladder filter.

[0079] In other words, any combination of first electrode 110, second electrode 120, third electrode 130 and fourth electrode 140 may comprise any combination of two impedance elements on a ladder filter, such as an RF filter.

[0080] In some embodiments, a ladder filter, such as example ladder filter 550, may be manufactured on a single die of a substrate (e.g., Silicon substrate). It may be beneficial for, e.g., designing multiple acoustic resonator devices 100 side-by-side on a single die. Any suitable configuration designed by a layout engineer may be possible.

[0081] Fig. 6A illustrates a method 600A according to an example embodiment of the disclosure for manufacturing an embodiment of acoustic resonator device 100. The illustration comprises a drawn illustration, and an accompanying text with a reference number, which briefly summarizes one step of method 600 A.

[0082] At operation 602, first piezoelectric layer 102 may be arranged on top of a base substrate 620. Base substrate 620 may comprise, for example, SiO2 or Si.

[0083] At operation 604, fourth electrode 140 may be configured on the first piezoelectric layer 102. In other words, fourth electrode 140 may be configured to a first surface 150 of first piezoelectric layer 102.

[0084] At operation 606, second piezoelectric layer 104 may be configured on first piezoelectric layer 102, enclosing fourth electrode 104. In other words, first surface 150 of first piezoelectric layer 102 is configured to a first surface 152 of second piezoelectric layer. Refer to FIG. 1 for the illustration of surfaces. At operation 608, second electrode 120 may be arranged on second piezoelectric layer 104. In other words, second electrode 120 may be configured to second surface 154 of second piezoelectric layer 104.

[0085] At operation 610, base substrate 650 may be removed. Base substrate 650 may be removed by, for example, etching.

[0086] And at operation 612, first electrode 110 and third electrode 130 may be configured on the first piezoelectric layer 102 after removing base substrate 650. In other words, first electrode 110 and third electrode 130 may be configured on second surface 154 of first piezoelectric layer 102.

[0087] Fig. 6B illustrates an example embodiment of a method 600B for manufacturing an embodiment of acoustic resonator device 100. Method 600B comprises common steps with method 600 A, illustrated as text boxes 602 to 608. Additional steps are then illustrated both as a drawing and an accompanying text with a reference number.

[0088] At operation 614, after configuring second electrode 120 (operation 608 in FIG. 6A), at least two bonding pedestals 652 may configured to the second piezoelectric layer 104. In other words, two bonding pedestals may be configured to second surface 156 of second piezoelectric layer 104.

[0089] At operation 616, a carrier substrate 654 may be configured to the at least two bonding pedestals 652. Carrier substrate 654 may enable structural support to the device.

[0090] At operation 618, base substrate 650 may be removed, similarly to operation 610 in FIG. 6A.

[0091] At operation 620, first electrode 110 and third electrode 130 may be configured to first piezoelectric layer 102, similarly to operation 612 in FIG. 6 A.

[0092] And at operation 622, final device is illustrated. The final device comprises a FBAR device i.e., method 600B enables manufacturing of a FBAR embodiment of acoustic resonator device 100.

[0093] Fig. 6C illustrates an example embodiment of a method 600C for manufacturing an embodiment of acoustic resonator device 100. Method 600C comprises common steps with method 600A, illustrated as text boxes 602 to 608. Additional steps are then illustrated both as a drawing and an accompanying text with a reference number.

[0094] At operation 624, a pooled substrate 656 may be configured to second piezoelectric layer 104. In other words, a pooled substrate 656 may be configured to second surface 156 of second piezoelectric layer 104. Pooled substrate 656 may comprise a cavity that encloses second electrode 120.

[0095] At operation 626, base substrate 650 may be removed, similarly to operation 610 in FIG. 6A.

[0096] At operation 628, first electrode 110 and third electrode 130 may be configured to first piezoelectric layer 102, similarly to operation 612 in FIG. 6 A.

[0097] And at operation 630, final device is illustrated. The final device comprises a FBAR device, in other words, method 600C enables manufacturing of a FBAR embodiment of acoustic resonator device 100. Fig. 6D illustrates an example embodiment of a method 600D for manufacturing an embodiment of acoustic resonator device 100. Method 600D comprises common steps with method 600 A, illustrated as text boxes 602 to 608. Additional steps are then illustrated both as a drawing and an accompanying text with a reference number.

[0098] At operation 632, a Bragg stack 658 may be configured to second piezoelectric layer 104. In other words, Bragg stack 658 may be configured to second surface 156 of second piezoelectric layer 104. Bragg stack 658 may comprise a plurality of alternating layers having different acoustic impedances. Each layer on Bragg stack 658 from the plurality of alternating layers may be approximately a quarter wavelength thick, and the reflectivity from each layer will be larger if the difference between the acoustic impedances of the layers is larger. Typically, materials with large acoustic impedance differences may be used such as W / SiO2, Mo / SiO2 and SiN / SiO2.

[0099] At operation 634, a carrier substrate 660 may be configured to face of Bragg stack 658 not facing second piezoelectric layer 104. Carrier substrate 660 may enable structural support for Bragg stack 658 and / or to the whole device.

[0100] At operation 636, base substrate 650 may be removed, similarly to operation 610 in FIG. 6A.

[0101] At operation 638, first electrode 110 and third electrode 130 may be configured to first piezoelectric layer 102, similarly to operation 612 in FIG. 6 A.

[0102] And at operation 640, final device is illustrated. The final device comprises a SMR device, in other words, method 600D enables manufacturing of a SMR embodiment of acoustic resonator device 100.

[0103] Further features of methods 600 A-600D directly resulting from the functionalities and parameters of acoustic resonator device 100 are not repeated here.

[0104] Fig. 7 is a block diagram illustrating an electronic apparatus 700 according to an embodiment of the disclosure. The electronic apparatus 700 may comprise acoustic resonator device 100 disclosed above. Electronic apparatus 700 may further comprise a radio frequency (RF) filter 702. More specifically, at least in some embodiments, one or more of the acoustic resonator devices 100 comprised in the RF filter 702.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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. 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.

[0109] 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. An acoustic resonator device (100) comprising: a first piezoelectric layer (102) and a second piezoelectric layer (104), wherein a first surface (150) of the first piezoelectric layer is configured to a first surface (152) of the second piezoelectric layer and the first piezoelectric layer and the second piezoelectric layer comprises opposite phase wave excitation for a given wave polarization; and at least four electrodes, wherein: a first electrode (110) is configured on a second surface (154) of the first piezoelectric layer; a second electrode (120) is configured on a second surface (156) of the second piezoelectric layer; a third electrode (130) is configured on the second surface of the first piezoelectric layer; and a fourth electrode ( 140) is configured in a portion of a boundary between the first surface of the first piezoelectric layer and the first surface of the second piezoelectric layer.

2. The acoustic resonator device (100) according to claim 1, wherein one or more border frame structures (200) are configured at least partially underneath one or more electrodes (110,130) of the at least four electrodes, such that the border frame structure extends along edges of a corresponding electrode.

3. The acoustic resonator device (100) according to claim 1 or 2, wherein the first piezoelectric layer (102) and the second piezoelectric layer (104) each comprises a stack layer, and a portion of the stack layer is removed (400) substantially near at least one of the electrodes.

4. The acoustic resonator device (100) according to any of claims 1 to 3, wherein the first piezoelectric layer (102) and the second piezoelectric layer (104) comprise alternatively Aluminium Scandium Nitride (AlScN) and Lithium Niobate (LiNbO3).

5. The acoustic resonator device (100) according to claim 4, wherein the AlScN comprises compression negative or compression positive C-Axis AlScN (c -AlScN), and the LiNbO3 comprises 36°Y LiNbO3 or (36°-180°)Y LiNbO3.

6. The acoustic resonator device (100) according to any of claims 1 to 5, wherein at least one of the first electrode (110) and the third electrode (130) is substantially rectangularly shaped and is configured in 0° rotation with respect to the OX crystal axis of the first piezoelectric layer (310).

7. The acoustic resonator device (100) according to any of claims 1 to 5, wherein at least one of the first electrode (110) and the third electrode (130) is substantially rectangularly shaped and is configured in 45° rotation with respect to the OX crystal axis of the first piezoelectric layer (320).

8. The acoustic resonator device (100) according to any of claims 1 to 5, wherein at least one of the first electrode (110) and the third electrode (130) is multi-angle asymmetrically shaped (330).

9. The acoustic resonator device (100) according to any of claims 6 to 8, wherein at least three physically separate grated portions (350) are configured to at least one side of at least one of the first electrode (110) and the third electrode (130).

10. The acoustic resonator device (100) according to claim 9, wherein the at least three physically separate grated portions (350) are of the same material than the first electrode (110) or the third electrode (130).

11. The acoustic resonator device (100) according to claim 9 or 10, wherein the physical separation of each grated portion from the at least three physically separate grated portions (350) is between 0.3 micrometers and 2 micrometers.

12. The acoustic resonator device (100) according to any of claims 1 to 11, wherein a Bragg reflector stack (658) is configured to the second surface (156) of second piezoelectric layer (104).

13. An electronic apparatus (700) comprising the acoustic resonator device (100) according to any of claims 1 to 12.

14. A method (600 A) of manufacturing the acoustic resonator device (100) according to any of claims 1 to 12 comprising: configuring the first piezoelectric layer (102) to a first surface of a base substrate (650); configuring the fourth electrode (140) to the first surface (150) of the first piezoelectric layer (102); configuring the second piezoelectric layer (104) to the first surface (150) of the first piezoelectric layer; configuring the second electrode (120) to the second surface (156) of the second piezoelectric layer; removing the base substrate; and configuring the first electrode (110) and the third electrode (130) on the second surface (154) of the first piezoelectric layer.

15. The method (600B) according to claim 14, wherein after the configuring of the second electrode (120) to the second surface (156) of the second piezoelectric layer (104), the method further comprises: configuring two or more bonding pedestals (652) to the second surface (156) of the second piezoelectric layer (104); and configuring a carrier substrate (654) to the two or more bonding pedestals.

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