Electroacoustic resonator and RF filter

Abstract

An electroacoustic resonator is provided that is compatible with a thin piezoelectric film and provides additional degrees of freedom. The resonator includes an IDT section with two busbars (ES, BB) and electrode fingers (ES, EF). The IDT section is tilted at an angle α by shear and is rotated as a whole by an angle β with respect to the piezoelectric axis (PA).

Description

[0001] The present invention relates to electroacoustic resonators that can be combined to build RF filters that can be used in wireless communication devices.

[0002] The electroacoustic resonators can be electrically combined, for example in the form of a ladder circuit topology or a lattice circuit topology, to build RF filters such as bandpass filters or bandstop filters. Such filters can be used in wireless communication devices. The trend towards miniaturization requires smaller spatial dimensions. The trend towards an increasing number of wireless functions leads to the necessity to comply with more stringent specifications. Thus, there is a general problem of providing resonators for filters that have good electrical and acoustic properties that comply with the specifications.

[0003] Conventional electroacoustic resonators can include acoustic tracks in which acoustic waves can propagate. Electrode structures are arranged on piezoelectric materials and convert between electromagnetic RF signals and acoustic RF signals propagating in the acoustic tracks due to the piezoelectric effect. Generally, it is desirable to have a single acoustic wave mode. However, in practical transducers, spurious modes may be excited, which deteriorate the acoustic and electrical properties of the resonator and the corresponding RF filter.

[0004] From US 2013 / 0051588 A1, electroacoustic transducers and corresponding resonators are known that have reduced losses and reduced lateral emission of acoustic energy and improved performance and improved lateral mode suppression.

[0005] However, it has been found that the technical measures disclosed therein may be ineffective in novel electroacoustic resonators using piezoelectric materials configured as thin films.

[0006] Therefore, there is a desire for an improved electroacoustic resonator that provides an RF filter having good electrical and acoustic properties and that is compatible with thin film piezoelectric materials.

[0007] Furthermore, the corresponding transducer should have spurious modes suppressed or eliminated, reduced acoustic losses, and improved dielectric strength to prevent electrostatic discharge and improved power durability.

[0008] In addition, there is a desire for additional degrees of freedom in designing the resonators and filters. Specifically, it is desirable to obtain steeper passband or rejection band flanks.

[0009] To this end, electroacoustic resonators according to the independent claims are provided. The dependent claims provide preferred embodiments and preferred filters.

[0010] The electroacoustic resonator includes a piezoelectric material having a piezoelectric axis, a propagation direction, and an electrode structure. The electrode structure has an IDT portion (IDT = interdigital transducer), and the IDT portion has two bus bars and electrode fingers. The electrode fingers extend in a direction perpendicular to the propagation direction. The IDT portion is inclined. In addition, the inclined IDT portion is rotated with respect to the piezoelectric axis.

[0011] In this resonator, the piezoelectric material and the electrode structure establish an acoustic track. The acoustic track is the area of the resonator provided for the propagation of sound waves. The propagation direction of the sound waves establishes the acoustic track and the longitudinal direction x of the resonator. The inclination of the IDT portion means that, compared with a non-inclined resonator, the resonator is subject to shear such that the electrode fingers maintain their direction of extension. However, the lateral position of the electrode fingers depends on the longitudinal position of the electrode fingers. In contrast, the bus bars have an extension direction rotated with respect to the longitudinal direction x. The bus bars can be arranged at the lateral flanks of the acoustic track. In a plane substantially defined by the surface of the piezoelectric material, the lateral direction is substantially orthogonal to the longitudinal direction.

[0012] Note that "x" represents the position along the longitudinal direction. "y" represents the position along the lateral direction orthogonal to the longitudinal direction.

[0013] In addition to the rotation of the extension of the bus bars caused by the inclination, the corresponding inclined IDT portion is additionally rotated by an angle β with respect to the piezoelectric axis.

[0014] The normal direction of the electrode fingers remains to define the propagation direction x along the longitudinal direction, because this direction is defined by the orientation of the finger as the direction perpendicular to the extension of the finger. However, the rotation with respect to the piezoelectric axis results in a non-orthogonal relationship between the finger and the piezoelectric axis.

[0015] This rotation has the potential to reduce the electroacoustic coupling coefficient.

[0016] The reduced electroacoustic coupling coefficient may reduce the zero-pole distance of the resonator.

[0017] If such a resonator is connected to respectively establish a band-pass filter or a band-stop filter, the reduction of the zero-pole distance will result in a reduced bandwidth or a reduced width of the stop band.

[0018] In addition, the reduced zero-pole distance will result in steep flanks of the pass band or the stop band.

[0019] Therefore, new degrees of freedom can be obtained for shaping the flanks of the band-pass filter or the band-stop filter.

[0020] The rotation angle β can be equal to or between -45° and -5°, or equal to or between -5° and 5°, or equal to or between 5° and 45°: -45° ≤ β ≤ -5°, or -5° ≤ β ≤ 5°, or 5° ≤ β ≤ 45°.

[0021] The bus bar can extend along an inclined direction that is rotated by an angle α1 with respect to the propagation direction. The inclined direction can be rotated by an angle greater than or equal to -15° and less than or equal to 15°: -15° ≤ α1 ≤ 15°.

[0022] The resonator can also include a second IDT section having two bus bars and electrode fingers, and / or more IDT sections having their corresponding electrode fingers and bus bars.

[0023] It should be noted that in the case of a resonator having more than one IDT section, the bus bars of different sections can be electrically connected or not. A one-port resonator can have a first set of connected bus bars and a second set of connected bus bars. These two sets are electrically corresponding to the electrical connections of the resonator.

[0024] If it is a two-port resonator or a multi-port resonator (such as a DMS resonator), then there can be more than two sets of electrically isolated bus bars.

[0025] The bus bar of the second IDT section can extend along an inclined direction that is rotated by an angle α2 with respect to the propagation direction. The inclined direction can be rotated by an angle greater than or equal to -15° and less than or equal to 15°: -15° ≤ α1 ≤ 15°. Thus, the rotation direction of the second section can be opposite to that of the first IDT section.

[0026] The bus bar of the second IDT section can extend parallel to the propagation direction.

[0027] Then, the second IDT section is a non-inclined section, and the bus bar of this non-inclined section is rotated with respect to the piezoelectric axis. The rotation angle is β.

[0028] A resonator including 2 inclined sections (usually having different inclination angles) is represented as a broken inclined resonator.

[0029] The resonator can be a rotating zigzag inclined resonator.

[0030] The zigzag inclined transducer includes iteratively repeated segments having substantially different inclination angles, and these inclination angles can have alternating signs (positive and negative inclination angles).

[0031] The resonator can have a symmetric zigzag pattern.

[0032] The symmetry of the resonator can be translational symmetry, reflection symmetry with respect to a mirror plane, or point symmetry.

[0033] The resonator can include two inclined IDT sections and an impedance element, and the impedance element is arranged beside the IDT section in the lateral direction.

[0034] Tilting generally requires additional area consumption of the piezoelectric material. However, if a location (e.g., in a "V" - shaped area next to a resonator having at least two segments) is used to place additional circuit elements, filter elements with small spatial dimensions can be obtained. Such circuit elements can be passive elements (such as inductive elements, impedance elements, resistive elements, signal lines, phase lines, etc.) and circuits including such elements. For example, an impedance - matching circuit can be composed of or include such elements.

[0035] The electro - acoustic resonator can be selected from SAW resonators (SAW = Surface Acoustic Wave), TC - SAW resonators (TC = Temperature Compensated), GBAW resonators (GBAW = Guided Bulk Acoustic Wave), and TF - SAW resonators (TF = Thin Film).

[0036] The TC - SAW resonator includes temperature - compensating material above or below the electrode structure. The stiffness parameter of the material of the temperature - compensating structure is selected such that the temperature - induced drift of the characteristic frequency of the resonator can be reduced or eliminated. The corresponding temperature - compensating structure can include oxides, such as silicon oxide, such as SiO 2 .

[0037] The GBAW resonator includes a waveguide structure that is arranged above and / or below the electrode structure such that the propagating wave propagates at the interface between the piezoelectric material and the corresponding waveguide layer.

[0038] The TF - SAW resonator utilizes a piezoelectric material provided as a thin film. The thin film is provided using thin - film layer deposition techniques, such as CVD (Chemical Vapor Deposition), PVD (Physical Vapor Deposition), sputtering, MBE (Molecular Beam Epitaxy), etc.

[0039] The thin - film piezoelectric material can be arranged on a carrier substrate.

[0040] The electrode structure can be selected from unweighted transducers, apodized transducers, tilted transducers, broken - tilted transducers, and zigzag - tilted transducers. In an unweighted transducer, each pair of electrode fingers contributes substantially the same amount to the conversion between the electromagnetic RF signal and the acoustic RF signal. To this end, along the longitudinal direction of the acoustic track, the overlap in the transverse direction of adjacent electrode fingers of opposite polarities can be equal.

[0041] Conversely, for different pairs of adjacent electrode fingers of different polarities, a weighted transducer provides different contributions to the total excitation of the acoustic wave. To this end, the transverse overlap of adjacent electrode fingers can be different along the longitudinal direction. Such a weighted transducer can be an apodized transducer. The apodized transducer can be a sine - weighted transducer or a cosine - weighted transducer.

[0042] The angle between the extension direction of the bus bar and the electrode fingers of the tilted transducer deviates from 90°. Generally, the direction of the electrode fingers is orthogonal to the piezoelectric axis of the piezoelectric material. The electrode fingers are usually also orthogonal to the propagation direction of the acoustic wave of the required main acoustic mode. Therefore, the extension of the bus bar in the tilted transducer is not parallel to the propagation direction of the acoustic wave, i.e., not parallel to the longitudinal direction.

[0043] It has been found that even in TF-SAW resonators, tilted or apodized resonators can effectively reduce unwanted transverse modes.

[0044] In addition, it has also been found that the diffraction effect in the gap region of the resonator has a more serious impact on the resonator performance compared to the unweighted resonator, because the interaction between the acoustic wave and the gap region is enhanced in the corresponding geometry. Therefore, providing a counterintuitive method that can correspond to a uniform transverse velocity distribution of uniform acoustic impedance even in the gap region minimizes the unwanted acoustic effects in the gap region.

[0045] Therefore, an improved electroacoustic resonator compatible with thin-film piezoelectric materials can be obtained by the above measures.

[0046] The broken tilted transducer has segments with different tilt angles along the acoustic track. Therefore, the broken tilted transducer has at least two segments. In one segment, the tilt angle can be 0°. Such a segment corresponds to the segment of a conventional non-tilted resonator.

[0047] The zigzag tilted transducer includes iteratively repeated segments with substantially different tilt angles and with possibly alternating signs. Both positive and negative tilt angles are possible.

[0048] The electroacoustic resonator can be selected from a single-port resonator, a two-port resonator, a multi-port resonator, and a DMS resonator (DMS = dual-mode SAW).

[0049] The single-port resonator has only one port to be connected to the external circuit environment. The two-port resonator has two ports to be connected to the external circuit environment. One of the two ports can be an input port for receiving an electromagnetic RF signal. The corresponding other port can be an output port for providing an electromagnetic RF signal to the external circuit environment.

[0050] The DMS resonator can be established as a single-port resonator or a two-port resonator. In the DMS resonator, more than one acoustic main mode can propagate. The DMS resonator can include a first IDT (IDT = interdigital transducer) and a second IDT.

[0051] The resonator can have a single transducer or multiple transducers. One or more transducers of the resonator can be arranged between the elements of the acoustic reflector (e.g., the elements of the Bragg reflector).

[0052] One or more transducers may be weighted, apodized, tilted, broken tilted or zigzag tilted. However, several transducers may also be tilted such that a plurality of transducers in a sound track establish a broken tilted or zigzag tilted excitation structure.

[0053] The IDT of the resonator may be disposed between reflector structures of the resonator.

[0054] The described resonator may be used in an RF filter.

[0055] Correspondingly, the RF filter may include an electroacoustic resonator as described above.

[0056] The RF filter may be a bandpass filter or a bandstop filter and may be used in a front-end circuit of a wireless communication device. The RF filter may have a ladder topology or a lattice topology.

[0057] In a ladder filter topology, one or more series resonators are serially electrically connected in a signal line between an input port and an output port. One or more parallel resonators may be disposed in one or more shunt paths that electrically ground the signal line.

[0058] The lattice filter topology may have an input port and an output port. The input port may include a first input terminal and a second input terminal. The output port may include a first output terminal and a second output terminal. If one resonator electrically connects the first input terminal to the second output terminal, the lattice filter topology will be obtained. Obtain a signal crossover of signals propagating via a first resonator and a second resonator.

[0059] The RF filter may further include non-tilted and / or non-rotated resonators with respect to a piezoelectric axis.

[0060] Then, by combining a conventional resonator (having a non-rotated and tilted IDT portion) that allows a wide bandwidth with the resonator as described above, frequency-dependent attenuation can be obtained, thereby locally increasing the flank steepness.

[0061] The RF filter may be a transmit filter or a receive filter of a duplexer (e.g., a multiplexer).

[0062] The above-described resonator reduces unwanted acoustic modes and provides additional degrees of freedom to the designer, thereby obtaining a resonator that is compatible with good electrical and acoustic characteristics and thin-film piezoelectric materials.

[0063] The accompanying schematic diagrams illustrate and explain the main aspects of the provided resonator and the details of the preferred embodiments. For simplicity, some of the drawings do not show the acoustic reflectors or other elements necessary to form the resonator.

[0064] Figure 1 Shows an inclined IDT section rotated with respect to the piezoelectric axis.

[0065] Figure 2 Shows a rotated fractured inclined resonator.

[0066] Figure 3 Shows a rotated zigzag inclined IDT.

[0067] Figure 4 Shows a schematic diagram of a first embodiment of an electroacoustic resonator having two IDT sections enclosing different angles with the x-axis.

[0068] Figure 5 Shows only Figure 4 more details of the IDT section schematically shown in

[0069] Figure 6 Shows another embodiment of two IDT sections enclosing different angles with the x-axis.

[0070] Figure 7 Shows four subsequent IDT sections forming a zigzag arrangement.

[0071] Figures 8 to 11 Schematically shows different ways of circuit connection of two subsequent IDT sections inclined with respect to each other.

[0072] Figure 12 and Figure 13 Shows two subsequent IDT sections connected via different passive elements.

[0073] Figure 14 Shows an inclined IDT section where the bus bars are oriented parallel to the wave propagation direction (x-axis) and generate stub fingers of different lengths.

[0074] Figure 15 Shows an arrangement of two IDT sections inclined at different angles to the x-axis but with two common bus bars, which are oriented parallel to the wave propagation direction (x-axis), and the stub fingers have different lengths.

[0075] Figure 16 Shows two inclined IDT sections of a single-port resonator arranged between two reflectors.

[0076] Figure 17 Schematically shows two longitudinally acoustically coupled subsequent IDT sections inclined at the same inclination angle.

[0077] Figure 18 Schematically shows two longitudinally acoustically coupled subsequent IDT sections inclined at different inclination angles.

[0078] Figure 19 Shows a possible layout of a DMS resonator.

[0079] Figure 20 Shows another embodiment of a DMS filter having three IDTs, where each IDT includes a plurality of different tilted IDT sections within the same IDT.

[0080] Figure 21 Shows a possible ladder circuit topology connected to a DMS resonator.

[0081] Figure 1 Shows a tilted interdigital transducer IDT rotated with respect to the piezoelectric axis PA. The transducer IDT can be arranged on a piezoelectric material. The material has a piezoelectric axis PA.

[0082] The extension direction y of the electrode fingers EF is represented as the transverse direction. The longitudinal direction x is within the plane in which the electrode structure is oriented and is orthogonal to the transverse direction. When the resonator is effective, the longitudinal direction is also the propagation direction of the acoustic wave.

[0083] Even if the resonator is a TF-SAW resonator, the tilt of the resonator reduces unwanted wave modes. It should be noted that the tilt does not change the direction of the electrode fingers or the propagation direction.

[0084] The rotation of the resonator with respect to the piezoelectric axis results in a rotated electrode finger direction, a rotated propagation direction, and a reduced electroacoustic coupling factor.

[0085] Generally, the angle represented by α refers to the tilt angle caused by the shear of the IDT section. The angle labeled β refers to the rotation of the electrode structure of the entire IDT section.

[0086] Figure 2 Shows the combination of two tilted IDT sections IS1, IS2, called a broken tilted IDT. These two IDT sections have different tilt angles defined by their tilt directions SD1, SD2 or different tilt directions. However, all the electrode fingers are parallel, and these two sections are rotated with the same rotation angle β with respect to the piezoelectric axis PA.

[0087] These two sections IS1, IS2 are symmetric with respect to a t mirror plane parallel to the electrode finger direction.

[0088] Figure 3 Shows a rotated zigzag tilted interdigital transducer. There are two sets of tilted sections. These two sets have translational symmetry. Within each set, these sections have mirror plane symmetry. Each section is tilted according to one of two tilt directions. The entire resonator rotates together with a rotation angle β. A sound reflector LL with reflector fingers FI is shown.

[0089] Figure 4 A simple embodiment of the present invention including two adjacent IDT portions IS1 and IS2 is shown in a simplified illustration. The first IDT portion IS1 extends along a first inclined direction SD1, which includes an angle α1 relative to the x-axis, where the x-axis is the propagation direction of the acoustic wave. The directly adjacent second IDT portion IS2 includes an inclination angle α2 relative to the x-axis, where α1 is not equal to α2. The second IDT portion IS2 extends parallel to a second inclined direction SD2. For clarity, each inclined direction is adjacent to the corresponding resonator portion IS. The inclination angle α can have an absolute value between 0 degrees and 30 degrees. The optimized inclination angle α is selected depending on the piezoelectric material and the desired characteristics of the SAW device of which the shown arrangement is a part.

[0090] Figure 5 An exemplary IDT portion IS is shown, which shows its most important parts. The IDT portion IS includes two bus bars BB, BB', and electrode fingers EF extend from these two bus bars BB, BB' to alternately cross each other. The electrode fingers EF are oriented perpendicular to the x-axis and form an overlapping region extending parallel to the inclined direction SD. The inclination angle α is measured between the x-axis and the inclined direction SD. The bus bar BB can be oriented parallel to the inclined direction or, alternatively, deviate from this parallel orientation. Not shown are the stub fingers present in the non-overlapping region arranged between the overlapping region and the corresponding bus bar in a preferred IDT portion design. If the orientation of the bus bar BB deviates from the orientation of the inclined direction, the non-overlapping region produces a triangular shape (e.g., as Figure 14 or Figure 15 shown). Preferably, the overlap between two adjacent electrode fingers EF is the same along the entire length of the IDT portion IS and, more preferably, is the same in all IDT portions IS.

[0091] Figure 6 Another embodiment showing how two adjacent IDT portions IS1, IS2 are arranged relative to each other is shown. In this broken inclined resonator, the first IDT portion IS1 includes an inclination angle α1 relative to the x-axis, while the second IDT portion IS2 extends parallel to the x-axis, such that the inclination angle α of the second IDT portion IS2 is 0. In addition, the lengths of the two shown IDT portions are different, but they can also be the same.

[0092] Figure 7A zigzag arrangement of subsequent IDT portions IS is shown. Four IDT portions IS1 to IS4 are shown, but the zigzag arrangement can generally be achieved by three or more IDT portions. Each IDT portion IS includes an inclination angle α enclosed between the inclination direction of the corresponding IDT portion and the x-axis. Each IDT portion can have a different inclination angle. The length of each IDT portion can be equal for all IDT portions. Moreover, the length can be different for two adjacent IDT portions, or can be different for all IDT portions.

[0093] Each IDT section comprises a tilt angle α relative to the x-axis, wherein the tilt angles of two subsequent IDT sections IS are different. Figure 7 As shown, the zigzag arrangement of the IDT sections can extend parallel to the x-axis as a whole, but the zigzag topology can also extend at an angle relative to the x-axis. This means that not only the IDT sections are tilted, but the entire zigzag arrangement can also be tilted relative to the x-axis.

[0094] Furthermore, although a symmetrical arrangement of the IDT portions is preferred, the arrangement may not have symmetrical elements.

[0095] As already explained, different IDT sections IS may or may not be electrically connected. In all cases, however, different IDT sections within one track belong to the same resonator.

[0096] Figures 8 to 11 Four different possibilities for electrically connecting two adjacent IDT parts IS arranged in an acoustic track between two reflectors LL are exemplarily shown in the corresponding block diagram. The figure is drawn only schematically and does not show any geometrical details such as the tilt angle of at least one of the IDT parts IS1, IS2.

[0097] Figure 8 Two adjacent IDT sections IS1, IS2 within one sound track are shown. The two IDT sections share one bus bar. The other bus bar is split so that each IDT section has its own bus bar section that is separate from the bus bar section of the other IDT section. The resulting structure is an electrical series connection of the first and second IDT sections IS1, IS2 between the first and second terminals TE1, TE2.

[0098] Figure 9 shows two IDT sections, which have Figure 8 The same busbar arrangement is shown, but the circuit is different. Each busbar or busbar section of an IDT section has its own electrical terminal TE which can connect the IDT sections IS1 , IS2 in parallel or in series circuit.

[0099] Figure 10Shows an arrangement in which each of the two shown IDT sections IS1, IS2 has its own bus bar on both sides of the interdigital transducer, such that there is no current contact between the two IDT sections. Nevertheless, the four terminals of the two IDT sections allow any mutual circuit connection of the two IDT sections.

[0100] Figure 11 Shows the simplest arrangement of two adjacent IDT sections sharing two bus bars. The two IDT sections IS1, IS2 share the first and second bus bars. Each bus bar is coupled to a corresponding terminal TE on the respective side of the arrangement.

[0101] Figures 8 to 11 The shown arrangement can represent a single-port resonator, while Figure 10 It can also be circuit-connected as a two-port resonator.

[0102] Each two subsequent IDT sections IS1, IS2 with different tilt angles α form a V-shaped arrangement. There is some space between the inner branches of the V-shaped arrangement for arranging components such as passive components PE therein.

[0103] Figure 12 Shows a very general depiction of such an arrangement that uses the free space between the two branches of the V-shaped arrangement. The passive component PE can be interconnected to one or both of the IDT sections, or to any other component of the SAW device or the circuit in which the SAW device is arranged. The passive component can be, for example, a capacitor or an inductor or a combination thereof, for example to form a matching circuit.

[0104] Figure 13 Shows an arrangement of two IDT sections with a series circuit connection between the first and second terminals TE1, TE2. Here, the passive component (or more generally: component or circuit, for example, a matching circuit) interconnects the first bus bar connected to terminal TE1 and the opposite bus bar. But as described above, any other interconnection to any component of the SAW device is also possible. The passive component PE can be used as a matching component of the SAW device. Such a connection of the matching circuit component is also possible for all circuits (for example, Figures 9 to 11 in the variants).

[0105] An arrangement that uses the free space between the two branches of the V-shaped arrangement by placing any component of the SAW device or the circuit results in a better utilization of the available space. Then, since the space for additional components (for example, the passive component PE) is saved at another location on the substrate surface, the area of the SAW device can be reduced.

[0106] Figure 14Shows an IDT section IS including an interdigital transducer. The transducer includes first and second bus bars BB1, BB2. Electrode fingers EF extend from each bus bar to cross each other in an overlapping region OR. Between the tips of the electrode fingers EF and the bus bar not connected to that electrode finger EF, stub fingers ST are arranged. Thus, the non-overlapping regions between the overlapping region and the corresponding bus bar BB are filled with stub fingers or non-overlapping portions of the electrode fingers EF.

[0107] Another feature of the shown interdigital transducer is the orientation of the overlapping region OR, which is parallel to the tilt direction of the IDT section. Contrary to the previously described arrangement, the bus bars are not parallel to the tilt direction. Thus, the overlapping region OR is oriented along the tilt direction LA, and LA is inclined with respect to the linearly extending bus bars. This means that each non-overlapping region of the IDT section is trapezoidal or triangular. Then, the stub fingers ST must have various lengths to completely fill the non-overlapping region GU. However, one of the central axes can be oriented parallel to the x-axis such that, except for inevitable lateral gaps and optional stub fingers ST, the non-overlapping region GU is not formed adjacent to the IDT section IS.

[0108] Figure 15 Shows an arrangement of two such IDT sections IS1, IS2, each IDT section having a different tilt angle α with respect to the x-axis. These two adjacent IDT sections share their bus bars BB1, BB2 such that each common bus bar has a linear and straight extension, which can be arranged parallel to the x-axis but not parallel to the tilt direction of either of the two IDT sections. Here, the schematically shown non-overlapping region GU between the overlapping region OR and the opposite bus bar BB is also filled with stub fingers ST.

[0109] According to a variant, the non-overlapping region GU can be covered by a continuous metal layer, which can be formed by correspondingly constructing one or more bus bars. Then, the corresponding bus bar portions have a triangular shape.

[0110] The resonator formed by at least one IDT section is within the acoustic track between two reflectors LL. Since there is only one tilted resonator in the acoustic track, the SAW device forms a single-port SAW resonator.

[0111] Figure 16 Is another depiction of a single-port resonator having two tilted IDT sections to form a V-shaped arrangement. Again, here, each bus bar BB1, BB2 is shared by two IDT sections IS2, IS2 and extends linearly and can be arranged parallel to the x-axis or not parallel to the x-axis. This means that trapezoidal (e.g., triangular) non-overlapping regions are formed between the overlapping regions OR1, OR2 and the adjacent bus bar BB. In Figure 16In [the figure], the overlapping region OR is shown as the region between two dashed lines. Meanwhile, the dashed lines are at the positions of the finger gaps between the tips of the overlapping electrode fingers and the opposing stubs. Preferably, the lateral gap is as small as possible. Using currently available techniques, a small gap of 100 nm to 500 nm can be achieved.

[0112] On both sides of the shown resonator, corresponding acoustic reflectors LL1, LL2 are placed to enclose the acoustic energy between them. The dashed lines extend into a part of the corresponding reflectors, which indicates that although there is an electrical short, the reflector fingers of each acoustic reflector LL still partially cross each other. Alternatively, the gap does not have to extend into the reflector such that each reflector finger is connected to two reflector busbars.

[0113] From Figure 16 It can also be seen that the holes defined by the lateral lengths of the finger overlap portions are offset or vary in the y direction between fingers along the x-axis. However, this offset is small enough such that when viewed parallel to the x-axis, the holes with the maximum offset or variation relative to the outermost holes at the start or end of the resonator still overlap each other. This indicates that the coupling between different ends of the IDT portion is still high enough to allow the resonator to operate properly.

[0114] Figure 17 and Figure 18 Two adjacent IDT portions IS1, IS2 that can form part of a DMS filter are shown. Although Figure 17 the IDT portions are inclined at the same inclination angle such that they share the same inclination direction SD in Figure 18 , in the broken inclination design according to the present invention, these two IDT portions are arranged at different inclination angles. The shown arrows indicate the longitudinal acoustic coupling between the two IDT portions. Depending on Figure 18 the inclination angles in

[0115] In all embodiments, every two subsequent IDT portions IS1, IS2 with different inclination angles α form a V-shaped arrangement. Therefore, some free space between the inner branches of the V-shaped arrangement is reserved, thereby allowing circuit elements such as passive elements PE to be arranged therein.

[0116] Figure 19 A schematic block diagram of a DMS filter including three interdigital transducers IDT1 to IDT3 is shown, and each interdigital transducer IDT includes an IDT portion IS as described above, such that the DMS filter has a broken inclination design. Each inclination angle of the IDT portion can be different. The inclination angles α1 and α2 can alternately vary according to the relationship α1 = -α2 to form a regular symmetric zigzag arrangement of the IDT portions. Each reflector LL is arranged at two side (longitudinal) ends of the acoustic track of the DMS filter.

[0117] However, the interdigital transducers of the resonators forming the DMS structure are not limited to each including only one IDT section. Thus, each resonator can include two or more IDT sections tilted at corresponding tilt angles, where different IDT sections can have different tilt angles.

[0118] The DMS filter can have more than three interdigital transducers that are typically alternately connected to the first and second terminals.

[0119] The passive element can be interconnected to one or two IDT sections, or to any other element of the SAW device or any other element of the circuit in which the SAW device is arranged. The passive element can be, for example, a capacitor or an inductor. Similarly, it can be an element having an inductance value and an ac capacitance value. Specifically, it can be a combination of elements, such as a circuit, such as a matching circuit. It can be formed by structuring metallization over the idle substrate surface. Alternatively, discrete passive elements can be arranged between every two branches of the V on the substrate. The passive element can be connected to one branch, two branches, or only arranged between the branches to use only the idle space without connecting to the bus bar of the V or another IDT section. If connected to the resonator, the passive element can be used as a matching element of the SAW device.

[0120] The arrangement of using the idle space between the two branches of the V-shaped arrangement by placing any element of the SAW device or the circuit results in a better utilization of the available chip area. Then, since the space for additional elements (e.g., passive elements) is saved at another location on the substrate surface, the area of the SAW device can be reduced.

[0121] Figure 20 Another embodiment of a DMS filter including at least three interdigital transducers IDT1, IDT2, and IDT3 is shown. The first interdigital transducer IDT1 includes two IDT sections IS1, IS2, each IDT section having a tilt angle α1, α2 with respect to the longitudinal direction (which can be equal to zero, and thus its representation in the figure is omitted). In this embodiment, the first tilt angle α1 is greater than 0 and greater than the second tilt angle α2, and the second tilt angle α2 can be zero as shown, or can be non-zero.

[0122] The second interdigital transducer IDT2 includes three IDT sections IS3 to IS5, and each IDT section IS includes a respective tilt angle with respect to the longitudinal direction. Like the second IDT section IS2, the third IDT section IS3 is arranged at a low tilt angle, preferably zero. This allows for maximum longitudinal acoustic coupling between the second and third IDT sections and thus maximum coupling between the first and second interdigital transducers IDT1 and IDT2. The tilt angle α4 of the fourth IDT section IS4, which is the second IDT section of the second transducer IDT2 and is arranged in the middle of the second interdigital transducer IDT2, is greater than the tilt angle of the third IDT section IS3 (not explicitly shown either) and greater than the tilt angle of the fifth IDT section IS5.

[0123] The third interdigital transducer IDT3 on the right side of the figure includes two IDT sections IS6 and IS7, and each IDT section includes a respective tilt angle α6, α7 (not explicitly shown either) with respect to the longitudinal direction. The tilt angle α7 of the rightmost IDT section IS7 is greater than the tilt angle α6 of the sixth IDT section IS6.

[0124] As a result, the outermost IDT sections of each pair of facing interdigital transducers IDT can have a small tilt angle or a zero tilt angle. The tilt angles of two directly adjacent outermost IDT sections can also be equal but non - zero. Thus, the two adjacent outermost IDT sections between the first and second or second and third interdigital transducers IDT extend parallel or almost parallel to each other. In the figure, the tilt angles of the outermost IDT sections IS2, IS3, IS5, and IS6 are shown as zero, but this is not an essential feature of the present invention as described above.

[0125] With this arrangement, the longitudinal acoustic coupling between adjacent interdigital transducers is maximized, as shown by the double - sided arrows in the figure.

[0126] If two adjacent outermost IDT sections are tilted with respect to each other, the coupling will be reduced. Thus, Figure 20 The arrangement of the shown DMS filter combines the advantages of the tilted orientation for transverse mode suppression and the high longitudinal acoustic coupling between the outermost IDT sections of two adjacent resonators. In this embodiment, each current tilt angle α can be different from other used tilt angles. However, it is preferred to design a DMS filter with high symmetry with respect to the middle transducer or the middle IDT section. If the absolute values of the tilt angles of IDT sections with the same symmetric elements are equal and the lengths are equal, a symmetric arrangement of the transducers can be achieved.

[0127] For example, as Figure 20As shown, the IDT part of the DMS filter can have different lengths. Preferably, the length of the outermost IDT part with the smallest tilt angle is less than the lengths of the other IDT parts, but they need to be long enough to ensure optimal longitudinal acoustic coupling between adjacent IDTs. Additionally, the resonator can be divided into more IDT parts compared to the two or three IDT parts shown, such that the corresponding interdigital transducer can include four or more IDT parts. A short IDT can have only one IDT part.

[0128] When designing a specific DMS filter, all possible variations can be used to increase the degrees of freedom. The filter can be optimized to obtain better filter performance or to better utilize the chip area. Usually, a trade-off must be made, which can be optimized through the possible variations.

[0129] Further variations of the SAW filter are possible, which are known in the art per se and can advantageously improve the SAW device. By adding mode-forming features in the design of the electrode fingers, the mode propagating in the acoustic track of the SAW filter can be formed into a pure piston mode. Such features can include additional mass loading at the finger tips or a greater finger width at their tips. Different gap lengths can reduce unnecessary lateral modes. Preferably, the lateral gap is as small as possible. Using currently available technology, small gaps of 100 nm to 500 nm can be achieved.

[0130] In the tilted IDT part, the holes defined by the lateral length of the electrical finger overlap portions are offset in the y direction between the electrode fingers along the longitudinal direction. However, the offset is small enough such that when viewed with respect to the longitudinal direction, the holes having the maximum offset or variation with respect to the outermost holes at the start or end of the resonator still overlap each other. This means that the coupling between different ends of the IDT part is still high enough to allow the resonator to operate properly.

[0131] Figure 21 A possible ladder circuit topology of the RF filter is shown. The RF filter has a first port P1 and a second port P2. The first port P1 can be an input port for receiving an RF signal from an external circuit environment. The second port can be an output port for providing the filtered RF signal to the external circuit environment.

[0132] In the signal path between the two ports P1, P2, the DMS resonator DMS, the first series resonator SR1, and the second series resonator SR2 are connected in series electrically. Two parallel shunt paths ground the signal path. In one shunt path, a parallel resonator PR is connected. In the other parallel path, an impedance element IE is connected. The impedance element can include an acoustically inactive IDT structure to establish a capacitive element. The capacitive element can be used to improve the passband flanks.

[0133] The DMS resonator DMS includes four tilted and rotated IDT sections.

[0134] The first series SR1 resonator includes a conventional (i.e., non-rotated, non-tilted) IDT section.

[0135] The second series resonator SR2 includes a cascaded (2×2) rotated and tilted IDT section.

[0136] The parallel resonator PR includes a cascaded (2×3) rotated and tilted IDT section. The degree of cascading is two. The degree of parallel cascading is three. Thus, there are 2×3 = 6 IDT sections included in the parallel resonator PR.

[0137] List of reference numerals

[0138] β: Rotation angle with respect to the piezoelectric axis

[0139] BB, BBl, BB2: Bus bars

[0140] SD, SD1, SD2: Tilt directions

[0141] IDT, IDT1, ……: Interdigital transducers

[0142] IS, IS1, IS2, ……: IDT sections

[0143] P1, P2: First, second filter ports

[0144] α: Angle between the x-axis and the tilt direction

[0145] LL: Acoustic reflector

[0146] ES: Electrode structure

[0147] GU: Non-overlapping region

[0148] TE: Terminals of the IDT section

[0149] ST: Stub fingers

[0150] EF: Electrode fingers

[0151] FI: Reflector fingers

[0152] DMS: Dual-mode SAW filter

[0153] OR: Overlapping region

[0154] P: Filter port

[0155] PA: Piezoelectric axis

[0156] PE: Passive component

[0157] x: longitudinal direction, propagation direction of SAW

[0158] y: transverse direction

Claims

1. An electroacoustic resonator, comprising a piezoelectric material having a piezoelectric axis and a propagation direction, an electrode structure having an IDT portion, the IDT portion including a first IDT portion and a second IDT portion, the first IDT portion and the second IDT portion each having two bus bars and electrode fingers, wherein: the electrode fingers extend perpendicular to the propagation direction, the first IDT portion and the second IDT portion are each inclined with respect to the piezoelectric axis, and the first IDT portion and the second IDT portion are arranged in a V shape; an impedance element at least partially disposed in the space between the first IDT portion and the second IDT portion formed by the V-shaped arrangement.

2. The electroacoustic resonator according to claim 1, wherein · the bus bar of the first IDT portion extends along an inclined direction rotated by an angle α1 with respect to the propagation direction, where -15° ≤ α1 ≤ 15°.

3. The electroacoustic resonator according to any one of claims 1-2, wherein the bus bar of the second IDT portion extends along an inclined direction rotated by an angle α2 with respect to the propagation direction, and -15° ≤ α2 ≤ 155°.

4. The electroacoustic resonator according to any one of claims 1-2, wherein the electrode structure includes a third IDT portion, and the third IDT portion forms a zigzag pattern with the first IDT portion and the second IDT portion.

5. The electroacoustic resonator according to any one of claims 1-2, wherein the electrode structure forms a symmetric zigzag pattern.

6. The electroacoustic resonator according to any one of claims 1-2, wherein the impedance element is arranged in the lateral direction.

7. The electroacoustic resonator according to any one of claims 1-2, wherein the electroacoustic resonator includes a SAW resonator, a TC-SAW resonator, a GBAW resonator, or a TF-SAW resonator.

8. The electroacoustic resonator according to any one of claims 1-2, wherein the electrode structure is selected from at least one of the following: an unweighted transducer, a tapered transducer, an inclined transducer, a broken inclined transducer, or a zigzag inclined transducer.

9. The electroacoustic resonator according to any one of claims 1-2, wherein the electroacoustic resonator includes a single-port resonator, a two-port resonator, or a DMS resonator.

10. The electroacoustic resonator according to any one of claims 1-2, wherein the electroacoustic resonator is part of an electroacoustic filter.

11. The electroacoustic resonator according to claim 10, wherein the electroacoustic filter includes a ladder topology or a lattice topology.

12. The electroacoustic resonator according to claim 10, wherein the electroacoustic filter includes non-inclined and / or non-rotated resonators with respect to the piezoelectric axis.

13. The electroacoustic resonator according to claim 1, further comprising a substrate, wherein the piezoelectric material is positioned between the substrate and the electrode structure.

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