TUNERABLE RESONATOR ELEMENT, FILTER CIRCUIT AND METHOD

Abstract

Resonator element for a filter, comprising the following: a first resonator comprising a first electrode (30) coupled to a first terminal, a second electrode (32) coupled to a second terminal, and a first piezoelectric material (31) arranged between the first electrode (30) and the second electrode (32), wherein the first terminal and the second terminal are configured for coupling to a filter structure, a second resonator with a third electrode (34) coupled to a third terminal, a fourth electrode (36) coupled to a fourth terminal, and a second piezoelectric material (35) arranged between the third electrode (34) and the fourth electrode (36), wherein the second resonator is acoustically coupled to the first resonator via at least one electrically insulating layer (33) between the second electrode (32) and the third electrode (34), and a tuning circuit (15) which is coupled to the third and fourth terminals.

Description

Technical field

[0001] The present invention relates to tunable resonator elements, filters that use such tunable resonator elements, and corresponding methods. background

[0002] Filters are used in a variety of electronic circuits to filter out specific frequency components of a signal while allowing other frequency components to pass through. For example, filters can be used in communication circuits to block frequency components outside of a frequency band, or outside of a portion of a frequency band, used for communication and to be processed by other circuits.

[0003] To increase bandwidth, communication standards, such as wireless communication standards (e.g., LTE, Long-Term Evolution) or wired communication standards, continuously increase the frequency range and number of frequency bands used. Communication devices implementing such standards often require highly selective filters adapted to the respective frequency bands. The frequency bands used can vary from country to country. Therefore, multiple filters with different filter characteristics (for example, different passbands) are needed. Furthermore, the technique known as "carrier aggregation" uses several frequency bands simultaneously. This requires specific filter designs for precisely these combinations.With a specific filter provided for every possible combination, the number of physical filters is actually much higher than the number of available bands. To reduce the number of different filters (two-port to n-port filters) actually needed in a communication device, tunable filters are highly desirable.

[0004] Surface Acoustic Wave (SAW) or Bulk Acoustic Wave (BAW) technologies are widely used in communication circuits and devices as highly selective bandpass filters. Conventional filters of this type are designed for fixed resonant or center frequencies. Consequently, many filters must serve individual frequency bands or aggregated combinations of some frequency bands used in current communication standards such as LTE, including Wi-Fi. Radio frequency (RF) switches are then used to select individual filters from among multiple filters, for example, for a desired signal path between an antenna and a low-noise amplifier or a power amplifier.Therefore, such conventional approaches require a large number of primarily discrete components, increasing circuit complexity, high-frequency losses, manufacturing complexity, and the space required for high-frequency front ends in communication devices. Space is limited in mobile devices such as smartphones, making tunable solutions highly desirable for saving space.

[0005] Several approaches have been pursued to make such SAW or BAW filters tunable in order to reduce the overall number of filters required. However, conventional tuning techniques can have drawbacks regarding their tuning range, selectivity, and / or losses introduced by the ability to tune the filter. Therefore, providing improved filter tuning capabilities is a key objective.

[0006] German patent DE 102 25 201 A1 discloses a structure in which a GDE (Giant Delta E) layer is arranged adjacent to a resonator. The GDE layer is mechanically braced, the bracing being adjustable by a piezoelectric tuning layer.

[0007] A. Frederick et al., “Frequency Tuning of Film Bulk Acoustic Resonators”, Proceedings of SPIE, Vol. 6172, 2006, reveals a method for tuning a resonator using a piezoelectric layer. Brief description

[0008] A resonator element according to claim 1, a filter device according to claim 15, and a method according to claim 18 are provided. The dependent claims define further embodiments. Brief description of the drawings Fig. Figure 1 is a schematic block diagram of a resonator element according to one embodiment. Fig. Figure 2 is a schematic cross-sectional view illustrating an implementation of a resonator. Fig. Figure 3 is a schematic cross-sectional view of a resonator stack that can be used in embodiments. Fig. 4 is an equivalent example circuit of the resonator stack from Fig. 3. Fig. Figure 5 is an example filter structure that can be implemented using resonator elements, according to embodiments. Fig. Figure 6 is a circuit diagram of a resonator element according to an embodiment that can be used as a shunt resonator element. Fig. Figure 7 is a circuit diagram of a resonator element according to an embodiment that can be used as a series resonator element. Fig. 8, Fig. 9, Fig. 10, Fig. 11, Fig. 12 to Fig. 13 illustrate simulation results to demonstrate the operation of embodiments. Fig. Figure 14 is a flowchart illustrating a procedure according to one embodiment. Detailed description

[0009] Various embodiments are described in detail below with reference to the attached drawings. It should be noted that these embodiments serve only illustrative purposes and are not to be considered limiting. While embodiments are comprehensively described as including several features, elements, or details, in other embodiments, for example, some of these features, elements, or details may be omitted and / or replaced by alternative features, elements, or details. In addition to the explicitly described features, elements, or details, other features, elements, or details, such as components commonly used in acoustic volume wave (BAW)-based filters, may be provided.

[0010] Unless otherwise stated, features from different embodiments may be combined to form further embodiments. Variations and modifications described with respect to one embodiment may also be applicable to other embodiments unless otherwise stated.

[0011] The embodiments discussed below relate to acoustic volume wave (BAW) resonator elements that can be used to construct a BAW-based filter. To form BAW resonators, a piezoelectric layer is generally provided between two electrodes. Applying an electric field between the two electrodes generates a mechanical stress that is propagated as an acoustic wave through the volume of the structure. A resonance condition is established when the acoustic path and a thickness direction of the structure correspond to integer multiples of half the acoustic wavelength.

[0012] In these embodiments, at least two resonators are used, acoustically coupled to form a single resonator element. A first resonator has connections for integration into a filter structure. A second resonator is coupled to a tuning circuit. The tuning circuit allows modification of the resonator element's resonance position.

[0013] Furthermore, in some embodiments, the first resonator can be connected to another tuning circuit.

[0014] Fig. Figure 1 schematically illustrates such a resonator element according to one embodiment. The resonator element of the embodiment from Fig. The apparatus comprises a first resonator 10, which is coupled to a second resonator 14 via an acoustic coupling 13. In this context, acoustic coupling means that acoustic waves from the first resonator 10 can propagate at least partially to the second resonator 14 and vice versa. Such acoustic coupling between resonators can be implemented, for example, using a dielectric material.

[0015] The first resonator 10 has a first terminal 11 and a second terminal 12. Using the first and second terminals 11, 12, which can, for example, correspond to electrodes of the first resonator 10 or be coupled to them, the resonator element can be constructed from Fig. 1. be integrated into a filter structure, such as a branch filter structure or a cross-link filter structure.

[0016] Furthermore, a tuning circuit 15 is coupled to a second resonator 14. The tuning circuit 15 can include an impedance network, which may comprise variable elements such as variable impedances, for example a variable capacitor, or switches such as RF switches. By changing the value of one or more of the variable element(s) of the tuning circuit 15, resonances of the resonator element can be set. Fig. 1 can be moved. This can be used to build a tunable filter using one or more as in Fig. The 1 shown resonator elements are used.

[0017] It should be noted that, unlike some conventional approaches, the tuning circuit 15 is electrically decoupled from the first resonator 10 and only acts on the first resonator 10 via the second resonator 14 and the acoustic coupling 13. In some embodiments, this avoids adverse effects compared to tuning circuits that are directly coupled to the first resonator 10.

[0018] In some embodiments, the first resonator 10 and the second resonator 14 can be similar resonator structures using similar materials. In other embodiments, different materials can be used. For example, in one embodiment, a material with comparatively weak piezoelectric coupling, such as aluminum nitride (AlN), can be used for the first resonator 10. This makes it possible to build filters with a narrow bandwidth. On the other hand, in embodiments based on a material with comparatively strong piezoelectric coupling, such as lithium niobate (LiNbO3), potassium niobate (KNbO3), or Sc-doped aluminum nitride or aluminum scandium nitride (AlScN), the second resonator 14 can be built. In some embodiments, this allows for a wide tuning range. In some embodiments, the piezoelectric coupling constant k can be T 2for the piezoelectric material of the first resonator below 30%, for example below 20% or below 10%, while the piezoelectric coupling constant k T 2 The piezoelectric (electromechanical) coupling constant k of the second resonator can be above 10%, for example above 20%, above 30%, or above 40%. T 2 k can be calculated from the tensor properties of the respective piezoelectric material, i.e., from elastic stiffness or compliance coefficients, dielectric coefficients, and piezoelectric coefficients. T 2 is also referred to as the piezoelectric coupling constant for a transversely clamped material. k T 2 can be considered k T 2 =K 2 / (1+K 2 ) are defined, where the piezoelectric coupling constant K 2 as K2 =e 2 / (ε S c E ) is defined. e is the piezoelectric material coefficient, ε S the dielectric material coefficient and c E the elastic material coefficient of the respective piezoelectric material used.

[0019] The piezoelectric coupling constant k T 2The bandwidth is a measure of the relative bandwidth of an (ideal) piezoelectric resonator. Therefore, combinations of different materials for the first resonator 10 and the second resonator 14 in various embodiments allow, on the one hand, a narrow bandwidth, as required for some communication applications, and on the other hand, a comparatively wide tuning range. The use of an aluminum nitride-based resonator as the first resonator 10 in some embodiments also provides good thermal conductivity, which is capable of heat dissipation. This can be important for some applications to prevent overheating. However, the materials mentioned above are merely examples, and other materials can also be used.

[0020] The first resonator 10 can also be called a filter resonator, since it can be integrated into a filter structure using the first and second connections 11, 12. The second resonator 14 can also be called a frequency-tuning resonator, since it is used to tune the resonant frequencies of the resonator element. Fig. 1 is used using the tuning circuit 15.

[0021] The first resonator 10, the acoustic coupling 13 and the second resonator 14 can be implemented in a single stack of material using existing process flows.

[0022] Corresponding stacking structures will be described next with reference to Fig. 2 and Fig. 3 discussed. As an introduction, it shows Fig. 2. A resonator element with a single resonator for explanatory purposes. Then a resonator stack, comprising a first and a second resonator (for example, resonators 10 and 14 from...) Fig. 1) includes, with reference to Fig. 3 explained.

[0023] Fig. Figure 2 illustrates a cross-sectional view of an acoustic volume wave (BAW) resonator. The resonator itself comprises a piezoelectric material 21 located between an upper electrode 20 and a lower electrode 22. The upper electrode 20 and the lower electrode 22 can each be formed from one or more metal layers.

[0024] Instead of a single resonator, as in Fig. As illustrated in Figure 2, in some embodiments a resonator stack comprising a first resonator and a second resonator is provided, as shown below. Fig. 3 is explained.

[0025] In the embodiment from Fig. 2. For acoustic isolation of the resonator, a so-called acoustic mirror is placed below the resonator. The acoustic mirror is made of Fig. 2 comprises a series of layers with alternating low and high acoustic impedances. For example, number 23 in Fig. 2 denotes a material with a comparatively low acoustic impedance, while 24A to 24C denote layers with a comparatively high acoustic impedance, resulting in alternating layers of low and high acoustic impedance below the resonator 20, 21, 22. In embodiments, each individual layer (parts of the material 23 between layers 24A, 24B, 24C, the electrode 22 and a substrate 25, as well as the layers 24A to 24C themselves) has a thickness of approximately λ / 4, where λ is the acoustic wavelength of a longitudinal wave within the layer. It should be noted that λ depends on the specific layer material. This acoustic mirror structure acoustically decouples the resonator from the supporting substrate 25. In other embodiments, a cavity may be provided instead of such an acoustic mirror.The cavity can be located directly below the lower electrode 22 or below a thin membrane that supports the resonator structure 20 / 21 / 22.

[0026] The resonant frequencies of a system like in Fig. The resonator 2 illustrated, comprising an upper electrode 20, a piezoelectric material 21, and a lower electrode 22, depends on the thicknesses of all these layers discussed, with the thickness of the piezoelectric layer having the greatest influence, followed by the electrode thicknesses. Therefore, in this case, Fig. 2 In the absence of other circuits that influence the frequency, the resonant frequencies of the resonator are fixed for a specific combination of materials and layer thicknesses and can only be changed by physically altering the structure, for example by using processing steps such as deposition or etching (as global measures or as local measures defined by lithography).

[0027] Fig. Figure 3 illustrates a resonator stack that can be used in embodiments. The resonator stack consists of Fig. 3 can, for example, show the resonator 20-22 in cross-sectional view in embodiments. Fig. Replace 2.

[0028] The resonator stack made of Fig. The resonator stack 3 comprises a first resonator formed by a first piezoelectric material 31 located between a first upper electrode 30 and a first lower electrode 32. The resonator stack 3 further comprises a second resonator formed by a second piezoelectric material 35 located between a second upper electrode 34 and a second lower electrode 36. The first and second resonators are separated by one or more layers 33, which provide acoustic coupling and, in some embodiments, also electrical insulation. The layers 33 can be formed from one or more dielectric layers. The layers 33 can also comprise a combination of dielectric and conductive (e.g., metal) layers.In embodiments where electrical insulation is required between the lower electrode 32 and the upper electrode 34 (as is the case for series resonator elements), the one or more layers 33 comprise at least one dielectric (electrically non-conductive) layer. Regardless of whether they are electrically insulating or not, the one or more layers (e.g., a stack of layers) 33 always provide acoustic coupling between the first and the second resonator.

[0029] The electrodes 30, 32, 34, and 36 can each comprise, for example, one or more metal layers, such as aluminum, copper, or tungsten layers, but are not limited to this. The first piezoelectric material 31 and the second piezoelectric material 35 can be the same material in some embodiments. However, different materials can also be used in some embodiments. As already mentioned with reference to Fig. As explained in section 1, the first piezoelectric material 31 can, for example, be a material with a comparatively weak piezoelectric coupling, such as aluminum nitride, and the first resonator can serve as a filter resonator, as explained above, to construct a filter with a comparatively narrow bandwidth. A piezoelectric aluminum nitride layer, such as layer 31, can, for example, be produced by reactive sputtering of an Al target. The second piezoelectric material 35 can comprise a material with a comparatively strong piezoelectric coupling, such as lithium niobate, potassium niobate, or Sc-doped aluminum nitride, to provide a wide tuning range. Note that Sc-doped AlN layers can also be formed as so-called AlScN layers, which can contain a significant amount of Sc.In other embodiments, both piezoelectric layers 31, 35 can be aluminium nitride-based, but with different dopants and / or dopant concentrations, for example different scandium(Sc) concentrations.

[0030] It should be noted that, in order for the first and second resonators to be properly coupled, the piezoelectric materials of both resonators must, in certain embodiments, couple piezoelectrically with the same type (polarization) of acoustic waves. Piezoelectric coupling generally depends on the material, but also on the crystal orientation used. In certain embodiments, the tuning circuit of the second resonator can only influence the frequency response of the first resonator if both piezoelectric layers couple with the same type / polarization of acoustic waves. For example, if sputtered piezoelectric aluminum nitride materials are used, the piezoelectric layer 35 is used in a cut (crystal orientation) that provides strong piezoelectric coupling with the same polarization as the piezoelectric layer 31.

[0031] For example, in embodiments where aluminum nitride is used in the first piezoelectric layer 31 or the second piezoelectric layer 35, aluminum nitride can be deposited on the substrate material in a c-axis orientation. The substrate material (for example, substrate 25 made of Fig. 2) a silicon wafer or a lithium niobate (LiNbO3) or a lithium tantalate (LiTaO3) crystal can be used.

[0032] Fig. Figure 4 illustrates an equivalent circuit of the layer stack made of Fig. 3. The number 40 designates the first resonator, which is in Fig. 3 is formed by layers 30, 31 and 32, and 41 designates the second resonator, which is in Fig. 3 is formed by layers 34, 35 and 36. A terminal 43 contacts the first upper electrode (30 from Fig. 3, in Fig. 4 (also labelled t1), a terminal 44 contacts the first lower electrode (32 in Fig. 3, also labelled b1) electrically, one terminal 45 contacts the second upper electrode (34 in Fig. 3, also labelled t2) and a connection 46 contacts the second lower electrode (36 in Fig. 3, also labelled b2) electrical.

[0033] A parasitic capacitor 42 with a capacitance C 12 is associated with the dielectric layer (stack) 33 between the lower electrode of the first resonator and the upper electrode of the second resonator. It should be noted that, although the first lower electrode 32 in the embodiments is made of Fig. 3 and Fig. 4 is electrically separated from the second upper electrode 34. In other embodiments, if no separate connections are required, a single electrode can be provided that serves both as the second upper electrode and as the first lower electrode, and the acoustic coupling of the resonators then takes place via this common electrode. In this case, no dielectric layer is required for electrical separation.

[0034] In embodiments, terminals 43 and 44 then serve to connect the resonator element from Fig. 4 to be incorporated into a filter structure. To provide frequency tuning, a tuning circuit can be coupled to terminals 45 and 46. Examples are given next with reference to Fig. 5 and Fig. 7 discussed.

[0035] Fig. Figure 5 illustrates an example topology of a tap filter, in this case a 3.5-stage tap filter. Digit 50 denotes a signal input, digit 51 denotes a signal output, and digit 52 denotes a ground line. The tap filter consists of Fig. Section 5 comprises four series resonators 53A to 53D and three shunt resonators 54A to 54C. Typically, all series resonators 53A to 53D have the same resonant frequency, and all shunt resonators 54A to 54C have the same resonant frequencies, but the resonant frequencies of the series and shunt resonators are detuned relative to each other. The degree of detuning roughly corresponds to the bandwidth of the resulting filters. The resonant frequencies of the shunt resonators 54A to 54C are typically lower than the resonant frequencies of the series resonators 53A to 53D.

[0036] Each resonator 53A to 53D, 54A to 54C can be a first resonator of a resonator element, as previously referred to Fig. 1, Fig. 3 and Fig. As discussed in section 4, the filter can be frequency-tuned using a tuning circuit coupled to the respective second resonator of the resonator elements. The branch filter structure consists of Fig. Figure 5 serves only as an example, and any conventional branch or cross-link filter structures used in BAW resonator engineering can be used and modified by replacing commonly used resonators with resonator elements that function as the first and second resonators, as described in Figure 5. Fig. 1, Fig. 3 and Fig. Section 4 explains that several such filters can be combined to form an n-port filter structure, for example, to filter multiple frequency bands used in communication applications.

[0037] Fig. Figure 6 illustrates a resonator element according to one embodiment, which includes a tuning circuit and which can be used as a shunt resonator element, for example to connect the shunt resonators 54A to 54C of the branch filter structure. Fig. 5 to implement.

[0038] The resonator element made of Fig. Figure 6 comprises a first resonator 62 with a first upper electrode t1 and a first lower electrode b1, and a second resonator 65 with a second upper electrode t2 and a second lower electrode b2. The first resonator 62 and the second resonator 65 are electrically isolated (but not acoustically decoupled), e.g., by a dielectric material represented by a parasitic capacitance 64. This dielectric material provides acoustic coupling between the resonators 62 and 65, as indicated by an arrow 63. The implementation of the first resonator 62 and the second resonator 65 can be as described previously with reference to Figure 6. Fig. 1, Fig. 3 and Fig. 4 discussed.

[0039] The first upper electrode t1 of the first resonator 62 is connected to a first terminal 60 (also labeled "3") and a second terminal 61 (also labeled "4"). Terminals 60 and 61 are used to connect to other resonators or signal input / output terminals to build filter structures. For example, if the shunt resonator element is made of Fig. 6 to implement the shunt resonator 54A from Fig. When 5 is used, the first terminal 60 is connected to the series resonator 53A and the second terminal 61 is connected to the series resonator 53B.

[0040] The first lower electrode b1 of the first resonator 62 is coupled to ground via a terminal 68, which is also labeled "0". In the example filter structure from Fig. 5 corresponds to the coupling of any one of the shunt resonators 54A to 54C with the ground line 52.

[0041] The second upper electrode t2 of the second resonator 65 is coupled to ground via a connection 69, which is also labelled "0".

[0042] Furthermore, a tuning circuit is coupled between the second upper electrode t2 and the second lower electrode b2 of the second resonator 65. In the example from Fig. The tuning circuit comprises a variable capacitor 67 connected in parallel with an inductor 66. In some embodiments, the inductor 66 can be implemented as a high-Q (quality-factor) inductive element or another reactance, e.g., with a Q factor greater than 10, 50, or 100. The inductance L1 of the inductive element can be, for example, between 0.5 and 200 nH, or below 50 nH, e.g., between 1 and 10 nH. The variable capacitor 67 can be implemented in any conventional way, for example, using varactors or switched capacitors. By changing the capacitance value of the variable capacitor 67, resonances (series resonance and parallel resonance) of the resonator element can be produced. Fig. 6 will be voted on. The voting circuit consists of Fig. Figure 6 is only one example, and various combinations of capacitors, inductors, and / or resistors can be used, with one or more of these capacitors, inductors, and / or resistors being variable to provide tuning. In some embodiments, the tuning circuit may also include switches, such as high-frequency (HF) switches, which can be selectively opened and closed to tune the resonator element. In such tuning circuits, capacitors or inductors may be connected in series or parallel with the switch(es) (e.g., an HF switch or switches).

[0043] As will be discussed in more detail later using simulation results, an inductance 66, e.g. an inductive element, can increase a tuning range compared to a case where only a variable capacitor is used.

[0044] Fig. 7 is a circuit diagram of a resonator element, which is used as a series resonator in filter structures, such as the filter structure from Fig. 5, for example, is suitable for implementing series resonators 53A to 53D. The resonator element made of Fig. 7 comprises a first resonator 72 and a second resonator 75, which are electrically separated as by a (parasitic) capacitance 73 with a capacitance value C 12 The capacitor 73 is associated with one or more dielectric layers that acoustically couple the first resonator 72 and the second resonator 75, as indicated by an arrow 74. The first resonator 72 has a first upper electrode t1 and a first lower electrode b1, and the second resonator 75 has a second upper electrode t2 and a second lower electrode b2. The first and second resonators 72, 75 can be implemented as previously described with reference to Fig. 1, Fig. 3 and Fig. 4 explained.

[0045] The first upper electrode t1 is coupled to a first terminal 70, also labeled "5", and the first lower electrode b1 is coupled to a second terminal 71, also labeled "6". The resonator element can be connected via the first and second terminals 70 and 71. Fig. 7 can be integrated into a filter structure. For example, to use the series resonator 53A from Fig. To implement version 5, the first terminal 70 would be coupled to the signal input 50, and the second terminal 71 would be coupled to resonators 54A and 53B. If resonator 54A is configured as shown in... Fig. If 6 is implemented, for example the second connection 71 would be Fig. 7 with the first connection 60 from Fig. 6 coupled and then the second connection 61 would be from Fig. 6 coupled with a corresponding connection of the resonator 53B.

[0046] The second upper electrode t2 is coupled to ground via terminal 78, which is also labeled "0". The designations 3, 4, 5 and 6 of terminals 60, 61, 70, 71 from Fig. 6 and Fig. 7 will be discussed later in a discussion of simulations with reference to Fig. 8, Fig. 9, Fig. 10, Fig. 11 to Fig. 12 is used, while the terminals that are coupled to ground are in Fig. 6 and Fig. 7 are also labelled with "0".

[0047] Furthermore, a tuning circuit is coupled to the second upper electrode t2 and the second lower electrode b2, which includes, for example, an inductor 76 and a variable capacitor 77. The impedance 76 and the variable capacitance 77 can be implemented in a similar way to the inductor 66 and the variable capacitance 67, respectively. Fig. 6 discussed. Furthermore, the inductance 76 and the capacitance 77 are merely an example of a tuning circuit coupled to a second resonator 75, and, as also discussed for Fig. As explained in section 6, other tuning circuit configurations are also possible.

[0048] With the shunt resonator element made of Fig. 6 and the series resonator element from Fig. 7. Different filter structures can be used, such as cross-link filters and branch filters, for example the branch filter structure from Fig. 5, are formed.

[0049] To further illustrate the functionality of the resonator elements discussed above, simulation results or various configurations are presented with reference to Fig. 8, Fig. 9, Fig. 10, Fig. 11 to Fig. 12 discussed.

[0050] For the simulation from Fig. 8, Fig. 9, Fig. 10, Fig. 11 to Fig. 12. A first resonator (filter resonator) made of doped aluminum nitride (for example scandium-doped or doped with another material) with a piezoelectric coupling constant k was developed. T 2 a coefficient of 7.1% was assumed, and a LiNbO3 crystal-based resonator with a piezoelectric coupling constant k was used for the second resonator (frequency tuning resonator). T 2 = 25% assumed.

[0051] Fig. Figures 8(a) to 8(d) show the S-parameter (scattering parameter, which represents insertion loss) versus frequency for different configurations. Fig. 8(a) and Fig. Figure 8(b) shows the S-parameter for a resonator element where the first resonator is coupled in a shunt configuration, as in Fig. 6 illustrates. Fig. 8(c) and Fig. 8(d) illustrate curves for a series coupling of a first resonator, as for example in Fig. 7 illustrates. Fig. 8(a) and Fig. Figure 8(b) illustrates the same curves, with the y-axis in Fig. 8(b) is larger compared to 8(a), and likewise the y-axis is in Fig. 8(d) compared to Fig. 8(c) enlarged. In Fig. 8(a) and Fig. Figure 8(b) shows a curve 80 representing the S-parameter for a tuning circuit, which has an impedance, such as the impedance 66 from Fig. Section 6 comprises the following. The impedance in the simulation exhibited an inductance of 1 nH with a very high quality factor. Furthermore, a small capacitance 67 of 1 pF was assumed. Curve 81 illustrates the S-parameter with an additional capacitance of 10 pF in parallel with the impedance of curve 80. A significant shift of the shown resonance on the order of 300 MHz is observed.

[0052] A curve 82 in Fig. 8(c) and Fig. Figure 8(d) illustrates, similar to curve 80 from Fig. Figures 8(a) and (b) show the S-parameter for the series resonator case for a tuning circuit comprising an impedance formed by a 1 nH inductor with a very high quality factor, plus a small 1 pF capacitor. A curve 83 illustrates the behavior with an additional 10 pF capacitor connected in parallel with the impedance. A frequency shift of the resonance on the order of 300 MHz is also observed here.

[0053] Then, with reference to Fig. 9, Fig. 10, Fig. 11 to Fig. 12 the influence of the inductance of the impedance 66 or 76 from Fig. 6 and Fig. 7 explained. Similar to Fig. Figure 8 illustrates graphs (a) and (b) in Fig. 9, Fig. 10, Fig. 11 to Fig. 12 curves for a like in Fig. Figure 6 illustrates a shunt resonator arrangement, and graphs (c) and (d) show the S-parameter for a shunt resonator arrangement as shown in Figure 6. Fig. 7 illustrated series resonator configuration. Similar to Fig. 8 is the y-axis in graph (b) from Fig. 9, Fig. 10, Fig. 11 to Fig. 12. The y-axis is also enlarged compared to graph (a), and in graph (d), it is enlarged compared to graph (c). In each of the graphs from Fig. 9, Fig. 10, Fig. 11 to Fig. Figure 12 shows a curve (or set of curves) for a capacitance of 1 pF and a curve or set of curves for a capacitance of 10 pF, similar to what is shown for Fig. 8 was explained.

[0054] In Fig. Figure 9 shows that impedances 66 and 76 of the tuning circuit each have a value of 100 nH. Curves 90 and 92 show the S-parameter for a capacitance of 1 pF, and curves 91 and 93 show the S-parameter for a capacitance of 10 pF. The resonances shown are shifted by less than 100 MHz for both the shunt resonator and series resonator cases.

[0055] Fig. Figure 10 shows the case for an inductance of 3 nH. Curves 100 and 102 illustrate the S-parameter for a capacitance of 1 pF, and curves 101 and 103 illustrate the S-parameter for a capacitance of 10 pF. Each of curves 100 to 103 comprises several curves, which are particularly visible in the enlarged versions of graphs (b) and (d) for curves 91 and 93, respectively. These curves represent the behavior for different Q-factors (quality factors) of the inductance for a Q-factor range of 42 to 100. In general, higher Q-factors lead to more pronounced resonances and reduced insertion loss. The resonances are shifted by approximately 150 MHz in this case.

[0056] Fig. Figure 11 illustrates curves for an inductance value of 1.7 nH. Curves 110 and 112 illustrate the S-parameter for a capacitance of 1 pF, and curves 111 and 113 illustrate the S-parameter for a capacitance of 10 pF. Individual curves of curves 110 to 113, which are particularly visible in the enlarged views from Fig. Figures 11(b) and (d) illustrate different Q-factors for the inductance, again in the range of 42 to 200. The change in capacitance shifts the resonance by slightly less than 300 MHz.

[0057] Finally, it illustrates Fig. Figure 12 shows a case with an inductance of 1.3 nH. Curves 120 and 122 illustrate the S-parameter for a capacitance of 1 pF, and curves 121 and 123 illustrate the S-parameter for a capacitance of 10 pF. Individual curves from 120 to 123 illustrate the behavior for different Q-factors. Here, the resonances are shifted by almost 400 MHz. As can be seen, a larger frequency tuning range can therefore be obtained by reducing the inductance with the same capacitance values. However, the difference between different Q-factors becomes more pronounced with reduced inductances, so that in embodiments using low inductances below 5 nH, high Q-factors above 100, for example above 150, can be selected to implement the inductance.

[0058] Fig. Figure 13 illustrates the acoustic phase of a resonator stack, as in Fig. Figure 6 illustrates the configuration (shunt resonator configuration) with adapted intrinsic acoustic port terminations for the acoustic path illustrated by arrow 63. Curve 130 shows the phase with tuning impedance 66, while curve 131 shows the phase when capacitance 67 is additionally introduced. Changing the capacitance, for example, shifts point 132 to point 133, resulting in a tuning region as indicated by arrow 134.

[0059] Fig. Figure 14 illustrates a method according to one embodiment. Although the method is made up of Fig. 14. Since the procedure is described as a series of actions or events, the order in which these actions or events are described and shown is not to be considered restrictive. The procedure from Fig. Procedure 14 can be implemented using the resonator elements discussed above, and features, elements, variations, and modifications described with respect to those resonator elements are also applicable to this procedure. For ease of reference, the procedure is derived from Fig. 14 with reference to the previous description of the resonator elements. However, the procedure can be derived from Fig. 14 can also be implemented independently of the resonator elements described above.

[0060] At 140 in Fig. 14. A resonator stack is provided. Providing the resonator stack can, for example, involve forming two stacked resonators on a substrate, such as stacked resonators as described in section 14. Fig. 3 discussed and described, include. Providing the resonator stack may also include providing an acoustic mirror or cavity below the resonators, as referred to in Fig. 2 discussed, include.

[0061] In Evidence 141, the method involves integrating a first resonator of the resonator stack, for example, the first resonator (filter resonator) of the previously discussed embodiments, into a filter structure. For example, the first resonator can be incorporated into the filter structure as a shunt resonator or as a series resonator.

[0062] At 142, a tuning circuit is provided for a second resonator of the resonator stack, for example a tuning circuit that includes an inductive element and a variable capacitor, as in Fig. 6 and Fig.Figure 7 illustrates the process. The tuning circuit allows the resonator stack to be tuned to a desired frequency for use in the filter structure. For example, the filter structure can be adapted to different frequency bands used in a communication device by means of the tuning circuit.

[0063] It should be noted that, although a tuning circuit is provided only for the second resonator of the respective resonator elements in the embodiments discussed above, a further tuning circuit can be provided for the first resonator element in other embodiments of resonator elements and methods. The further tuning circuit can be implemented in a similar manner to that described above for the tuning circuit, e.g., as an impedance network.

[0064] Although filters that use resonator elements as described above can be used particularly in communication devices such as mobile communication devices, and such communication devices that use corresponding filter structures can form embodiments, the filters can also be used in other devices where signals, especially high-frequency signals in the GHz range, need to be filtered.

Claims

[1] Resonator element for a filter comprising: a first resonator comprising a first electrode (30) coupled to a first terminal, a second electrode (32) coupled to a second terminal, and a first piezoelectric material (31) arranged between the first electrode (30) and the second electrode (32), wherein the first terminal and the second terminal are configured for coupling to a filter structure, a second resonator with a third electrode (34) coupled to a third terminal, a fourth electrode (36) coupled to a fourth terminal, and a second piezoelectric material (35) arranged between the third electrode (34) and the fourth electrode (36), wherein the second resonator is acoustically coupled to the first resonator via at least one electrically insulating layer (33) between the second electrode (32) and the third electrode (34), and a tuning circuit (15) which is coupled to the third and fourth terminals. [2] Resonator element according to claim 1, wherein the first resonator and the second resonator are implemented as a resonator stack. [3] Resonator element according to claim 2, wherein one of the first resonator and the second resonator is formed on a substrate and the other of the first resonator and the second resonator is formed on one of the first resonator and the second resonator. [4] Resonator element according to one of claims 1-3, wherein a piezoelectric coupling of the first piezoelectric material (31) is weaker than a piezoelectric coupling of the second piezoelectric material (35). [5] Device according to one of claims 1-4, wherein a piezoelectric coupling constant k T 2 of the first piezoelectric material (31) is less than 10%. [6] Resonator element according to one of claims 1-5, wherein the piezoelectric coupling constant k T 2 of the second piezoelectric material (35) is greater than 10%. [7] Resonator element according to one of claims 1-6, wherein the first piezoelectric material (31) comprises aluminium nitride and / or scandium-doped aluminium nitride. [8] Resonator element according to one of claims 1-7, wherein the second piezoelectric material (35) comprises lithium niobate and / or potassium niobate and / or scandium-doped aluminum nitride. [9] Resonator element according to one of claims 1-8, wherein the tuning circuit (15) comprises an impedance network. [10] Resonator element according to claim 9, wherein the impedance network comprises a variable capacitance (67; 77) and / or a switch and / or a switch with a fixed capacitance and / or a switch in parallel with a fixed capacitance. [11] Resonator element according to one of claims 9 or 10, wherein the impedance network comprises at least one inductive element (66; 76). [12] Resonator element according to claim 11, wherein the inductive element has an inductance below 50 nH. [13] Resonator element according to claim 11 or 12, wherein the inductive element has a Q-factor of at least 10. [14] Resonator element according to one of claims 1-13, comprising a further tuning circuit coupled to the first and second terminals. [15] Filter device comprising a signal input, a signal output and at least one resonator element according to any one of claims 1-14, coupled between the signal input and the signal output. [16] Filter device according to claim 15, wherein a first resonator of at least one resonator element of the at least one resonator element is coupled as a series resonator in the filter structure in a series connection between the signal input and the signal output. [17] Filter device according to claim 15 or 16, wherein a first resonator of a resonator element of the at least one resonator is coupled as a shunt resonator between a signal path between the signal input and the signal output and ground. [18] Method for manufacturing a filter device according to any one of claims 15-17, comprising the following: Providing a stack of resonators including the first resonator and the resonator, Incorporating the first resonator stack of the resonator into a filter structure, and Providing the tuning circuit for the second resonator of the resonator stack. [19] Method according to claim 18, wherein providing the tuning circuit comprises providing an inductive element in parallel with a variable capacitor. [20] Method according to one of claims 18 or 19, further comprising providing a further tuning circuit for the first resonator.

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