Tunable resonant element, filter circuit and method

Abstract

Embodiments of the present disclosure relate to tunable resonant elements, filter circuits, and methods. A resonator element for a filter is provided. The resonator element includes a first resonator acoustically coupled to a second resonator or a third resonator or both. The first resonator has a terminal for incorporating into a filter structure. A tuning circuit is coupled to the second resonator or the third resonator or both to enable tuning of the resonator element. The tuning circuit includes a variable capacitor and an inductor.

Description

Technical Field

[0001] The present application relates to a tunable resonator element, a filter using such a tunable resonator element and a corresponding method. Background Art

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

[0003] In order to increase the bandwidth, communication standards such as wireless communication standards (e.g., LTE, Long Term Evolution) or wire-based communication standards are constantly increasing the frequency range used and the number of frequency bands used. In communication equipment that implements such standards, highly selective filters that match the corresponding frequency bands are usually required. The frequency bands used may vary from country to country. Therefore, multiple filters with different filter characteristics (e.g., different passbands) are required. Moreover, in so-called carrier aggregation, several frequency bands work simultaneously. This requires specific filter designs for exactly these combinations. With specific filters provided for each possible combination, the number of physical filters is actually much higher than the number of available frequency bands. In order to reduce the number of different filters (dual-port filters to n-port filters) actually required in communication equipment, tunable filters are very desirable.

[0004] As highly selective bandpass filters in communication circuits and devices, surface acoustic wave (SAW) or bulk acoustic wave (BAW) technology is usually used. Conventional filters of this type are designed for fixed resonance or center frequency. Therefore, many filters are needed to serve individual frequency bands or aggregated combinations of several frequency bands used in current communication standards such as LTE (including WiFi). Then, a radio frequency (RF) switch is used to select a single filter from multiple filters, for example, for the desired signal path between the antenna and the low noise amplifier or power amplifier. Therefore, in this conventional approach, a large number of main discrete components are required, thereby increasing circuit complexity, RF losses, manufacturing complexity, and the space required for the RF front end in the communication device. The space in mobile devices such as smartphones is limited, and therefore a tunable solution is highly desired to save area.

[0005] Some methods have been proposed to manufacture such SAW or BAW tunable filters to reduce the total number of filters required. However, conventional tuning techniques may be deficient in their tuning range, their selectivity and / or in terms of the losses caused by the possibility of tuning the filter. Therefore, an object is to provide improved possibilities for filter tuning. Summary of the invention

[0006] According to one embodiment, a resonator element for a filter includes: a first resonator having a first terminal and a second terminal for coupling to a filter structure; a second resonator having a third terminal and a fourth terminal, wherein the second resonator is acoustically coupled to the first resonator; and a tuning circuit coupled to the third and fourth terminals. In one embodiment, the third resonator is coupled to the first resonator. In one embodiment, the tuning circuit includes at least one of a variable capacitor and an inductor.

[0007] According to another embodiment, an RF filtering device includes: a signal input; a signal output; a plurality of series resonator elements coupled between the signal input and the signal output, wherein each series resonator element includes: a first resonator having a first terminal and a second terminal, a second resonator having a third terminal and a fourth terminal, wherein the second resonator is acoustically coupled to the first resonator, and a tuning circuit coupled to the third and fourth terminals; and a plurality of parallel resonator elements coupled to the plurality of series resonator elements, wherein each parallel resonator element includes: a first resonator having a first terminal and a second terminal, a second resonator having a third terminal and a fourth terminal, wherein the second resonator is acoustically coupled to the first resonator, and a tuning circuit coupled to the third and fourth terminals.

[0008] According to another embodiment, an RF integrated circuit filter includes: a substrate; an insulating layer arranged on the substrate; a plurality of filter resonators arranged in the insulating layer, the insulating layer including a patterned top electrode layer, a patterned piezoelectric layer and a patterned bottom electrode layer, wherein at least two of the plurality of filter resonators are coupled together using the patterned top electrode layer; an acoustic coupling layer arranged on the plurality of filter resonators; and a plurality of tuning resonators arranged on the acoustic coupling layer and correspondingly located above each of the plurality of filter resonators.

[0009] According to another embodiment, an RF filtering device includes: a signal input; a signal output; and a resonator element coupled between the signal input and the signal output, wherein the resonator element includes: a first resonator, a second resonator above the first resonator, wherein the second resonator is acoustically coupled to the first resonator, a third resonator below the first resonator, wherein the third resonator is acoustically coupled to the first resonator, a first tuning circuit coupled to the second resonator, and a second tuning circuit coupled to the third resonator.

[0010] According to another embodiment, an RF filter includes: a substrate; an insulating layer on the substrate; a plurality of filter resonators in the insulating layer, the insulating layer including a patterned top electrode layer, a patterned piezoelectric layer and a patterned bottom electrode layer, wherein at least two of the plurality of filter resonators are coupled together using the patterned top electrode layer, and at least two of the plurality of filter resonators are coupled together using the patterned bottom electrode layer; an acoustic coupling layer on the plurality of filter resonators; a plurality of tuning resonators correspondingly located above each of the plurality of filter resonators on the acoustic coupling layer; and a plurality of tuning circuits coupled to the plurality of tuning resonators, wherein each tuning circuit includes a variable capacitor and an inductor. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] For a more complete understanding of the present invention and its advantages, reference is now made to the following description in conjunction with the accompanying drawings, in which:

[0012] Figure 1 is a schematic block diagram of a resonator element according to one embodiment;

[0013] Figure 2 is a cross-sectional schematic diagram illustrating an implementation of a resonator;

[0014] Figure 3 is a schematic cross-sectional view of a resonator stack that may be used in an embodiment;

[0015] Figure 4 yes Figure 3 An exemplary equivalent circuit of a resonator;

[0016] Figure 5 is an exemplary filter structure that can be implemented using resonator elements according to an embodiment;

[0017] Figure 6 is a circuit diagram of a resonator element that may be used as a parallel resonator element according to one embodiment;

[0018] Figure 7 is a circuit diagram of a resonator element that may be used as a series resonator element according to one embodiment;

[0019] Figures 8 to 13 Figures are used to illustrate simulation results for explaining the operation of the embodiment;

[0020] Fig.14 is a flow chart illustrating a method according to one embodiment;

[0021] Fig.15 is a cross-sectional view of a resonator element including a filter resonator at a top position in a layer stack and a tuning resonator at a bottom position in the layer stack, and a tuning circuit coupled to the tuning resonator;

[0022] Fig.16 Serves 2 1 A schematic diagram of a 2-stage ladder filter, wherein each resonator element comprises a filter resonator and a corresponding tuning resonator coupled to a tuning circuit;

[0023] Fig.17 is a cross-sectional view of a resonator element including a filter resonator at a bottom position in a layer stack and a tuning resonator at a top position in the layer stack, and a tuning circuit coupled to the tuning resonator;

[0024] Fig.18A Serves 1 1 A cross-sectional view of a 2-stage ladder filter integrated circuit, wherein each resonator element includes a filter resonator and a corresponding tuning resonator coupled to a tuning circuit, and a deep via for providing grounding;

[0025] Fig.18B is with Fig.18A Schematic diagram corresponding to the ladder filter;

[0026] Fig.19 is a cross-sectional view of a resonator element in a layer stack, the resonator element comprising a first tuning resonator in a top position coupled to a first tuning circuit, a filter resonator in a middle position, and a second tuning resonator in a bottom position coupled to a second tuning circuit;

[0027] Fig. 20 [A] and [B] show cross-sectional views of a resonator element layer stack including a tuned resonator in top and bottom positions, the tuned resonator being coupled to a corresponding tuning network Zt;

[0028] Fig.21 [A] to [D] are circuit diagrams including parallel and series resonator elements of a tuned resonator in a top position or a bottom position, the tuned resonator being coupled to a corresponding tuning network Zt including a variable capacitor and an inductor;

[0029] Fig. 22 Serves 1 1 A schematic diagram of a 1 / 2 stage ladder filter, wherein each filter resonator comprises a corresponding tuned resonator coupled to a tuning circuit comprising a variable capacitor and an inductor; and

[0030] Figure 23 to Figure 26 Show Fig. 22 Various integrated circuit implementations of ladder filters. DETAILED DESCRIPTION

[0031] In the following, each embodiment will be described in detail with reference to the accompanying drawings. It should be noted that these embodiments are for illustrative purposes only and are not to be construed as limiting. For example, although an embodiment may be described as including a plurality of features, elements or details, in other embodiments, some of these features, elements or details may be omitted and / or may be replaced with alternative features, elements or details. In addition to the features, elements or details explicitly described, other features, elements or details may be provided, for example, components conventionally used in filters based on bulk acoustic waves (BAW).

[0032] Unless otherwise stated, features from different embodiments may be combined to form further embodiments. Unless otherwise stated, changes or modifications described with respect to one of the embodiments may also apply to other embodiments.

[0033] The embodiments discussed below relate to bulk acoustic wave (BAW) resonator elements that can be used to construct BAW-based filters. To form a BAW resonator, a piezoelectric layer is typically provided between two electrodes. Applying an electric field between the two electrodes generates mechanical stresses that further propagate through the bulk of the structure as acoustic waves. A resonant condition is established when the acoustic path and thickness direction of the structure correspond to an integer multiple of half the length of the acoustic wave.

[0034] In an embodiment, at least two resonators are used, which are acoustically coupled to each other to form a resonator element. A first resonator of the two resonators has a terminal for being incorporated into a filter structure. The second resonator is coupled to a tuning circuit. The resonant position of the resonator element can be changed via the tuning circuit.

[0035] Additionally, in some embodiments, the first resonator may be coupled to another tuning circuit. Figure 1 Such a resonator element according to one embodiment is schematically illustrated. Figure 1 The resonator element of the illustrated embodiment comprises a first resonator 10 coupled to a second resonator 14 via an acoustic coupling 13. In this context, acoustic coupling means that an acoustic wave of the first resonator 10 can at least partially propagate to the second resonator 14 and vice versa. For example, such acoustic coupling between resonators can be achieved using a dielectric material.

[0036] The first resonator 10 has a first terminal 11 and a second terminal 12. By using the first and second terminals 11, 12 (for example, which may correspond to or be coupled to electrodes of the first resonator 10), Figure 1 The resonator elements are incorporated into a filter structure (such as a ladder filter structure or a lattice filter structure).

[0037] Furthermore, a tuning circuit 15 is coupled to the second resonator 14. The tuning circuit 15 may include an impedance network. The impedance network may include a variable element such as a variable impedance, for example a variable capacitor, or a switch such as a radio frequency (RF) switch. By changing the value of the variable element of the tuning circuit 15, the Figure 1 This can be used to construct a resonator using Figure 1 A tunable filter having one or more resonator elements is shown.

[0038] It should be noted that, in contrast to some conventional approaches, the tuning circuit 15 is electrically decoupled from the first resonator 10 and acts on the first resonator 10 only via the second resonator 14 and the acoustic coupling 13. In certain embodiments, this avoids adverse effects compared to a tuning circuit directly coupled to the first resonator 10.

[0039] 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 an embodiment of the first resonator 10, a material with lower piezoelectric coupling can be used, such as aluminum nitride (AlN). This allows the construction of a filter with a small bandwidth. On the other hand, in an embodiment, the second resonator 14 can be constructed based on a material with higher electrical coupling, such as lithium niobate (LiNbO3) or potassium niobate (KNbO3) or Sc-doped aluminum nitride or aluminum scandium nitride (AlScN). In some embodiments, this allows a high tuning range. In some embodiments, the piezoelectric coupling constant k of the piezoelectric material of the first resonator is T 2 It can be lower than 30%, for example, lower than 20% or lower than 10%; and the piezoelectric coupling coefficient k of the second resonator T 2 It may be higher than 10%, for example higher than 20%, for example higher than 30% or higher than 40%. The piezoelectric (electromechanical) coupling constant k T 2 It can be calculated from the tensor properties of the corresponding piezoelectric material, for example, from the elastic stiffness or compliance coefficient, the dielectric constant and the piezoelectric coefficient. T 2 It can also be called the piezoelectric coupling constant of the lateral clamping material; k T 2 It can be defined as k T 2 =K 2 / (1+K 2 ), where the piezoelectric coupling constant K 2 Defined as K 2 =e 2 / (ε S c E), e is the piezoelectric material coefficient, ε S is the dielectric material coefficient, c E is the elastic material coefficient of the corresponding piezoelectric material used.

[0040] Piezoelectric coupling constant k T 2 is a measure of the relative bandwidth of a (ideal) piezoelectric resonator. Thus, in embodiments, a combination of different materials for the first resonator 10 and the second resonator 14 allows, on the one hand, a small bandwidth as required for some communication applications, and, on the other hand, a relatively wide tuning range. The use of an aluminum nitride-based resonator as the first resonator 10 in embodiments additionally provides a good thermal conductivity capable of transferring heat, which is important for certain applications to prevent overheating. However, the above materials are only examples and other materials may also be used.

[0041] When the first resonator 10 is to be incorporated into a filter structure by using the first and second terminals 11, 12, the first resonator may also be referred to as a filter resonator. When the second resonator 14 is to be tuned by using the tuning circuit 15 Figure 1 When the resonant frequency of the resonator element is φt, the second resonator 14 may also be referred to as a frequency-tuned resonator.

[0042] The first resonator 10, the acoustic coupling 13 and the second resonator 14 may be realized in a single material stack by using existing process flows.

[0043] Next, we will refer to Figure 2 and Figure 3 Discuss the corresponding stacking structure. As an introduction, Figure 2 A resonator element having a single resonator is shown for illustration purposes. Figure 3 , will include the first and second resonators (eg, Figure 1 A resonator stack of resonators 10, 14) is described.

[0044] Figure 2 A cross-sectional view of a bulk acoustic wave (BAW) resonator is shown. The resonator itself comprises a piezoelectric material 21 sandwiched between a top electrode 20 and a bottom electrode 22. The top electrode 20 and the bottom electrode 22 may each be formed of one or more metal layers.

[0045] and Figure 2 Unlike the single resonator shown, in some embodiments a resonator stack including a first resonator and a second resonator is provided, as described below in Figure 3 As shown in .

[0046] exist Figure 2 In an embodiment of the present invention, for acoustic isolation of the resonator, a so-called acoustic mirror is placed below the resonator. Figure 2 The acoustic mirror of comprises a series of layers with alternating low and high acoustic impedances. Figure 2 In the figure, reference numeral 23 refers to a material with a lower acoustic impedance, while reference numerals 24A to 24C refer to layers with a higher acoustic impedance, thereby producing alternating layers of low and high acoustic impedance below the top electrode 20, piezoelectric material 21, and bottom electrode 22 of the resonator. In an embodiment, the thickness of each individual layer (the portion of material 23 between layers 24A, 24B, 24C, the electrode 22 and the substrate 25, and the layers 24A to 24C themselves) is approximately λ / 4, λ being the acoustic wavelength of the longitudinal waves in the layer. In this regard, it should be noted that λ depends on the corresponding layer material. The acoustic mirror structure acoustically decouples the resonator from the supporting substrate 25. Unlike this acoustic mirror, in other embodiments, a cavity can also be provided. The cavity can be directly below the bottom electrode 22 or below the membrane supporting the resonator structure 21 / 21 / 22.

[0047] like Figure 2 The resonant frequency of the resonator shown, which includes the top electrode 20, the piezoelectric material 21, and the bottom electrode 22, depends on the thickness of all of these layers discussed, with the thickness of the piezoelectric layer having the greatest influence, followed by the thickness of the electrodes. Figure 2 The resonant frequency of a resonator is fixed for a specific material combination and layer thicknesses, and can be changed only by physically changing the structure, for example using processing steps such as deposition or etching (either as a comprehensive measurement or as a local measurement defined by lithography), in the absence of other circuits in the device that influence the frequency.

[0048] Figure 3 A resonator stack that can be used in an embodiment is shown. In an embodiment, for example, Figure 3 The resonator stack can replace Figure 2 A cross-sectional view of the resonator.

[0049] Figure 3The resonator stack includes a first resonator formed by a first piezoelectric layer 31, which is sandwiched between a first top electrode layer 30 and a first bottom electrode layer 32. In addition, the resonator stack includes a second resonator formed by a second piezoelectric layer 35, which is sandwiched between a second top electrode layer 34 and a second bottom electrode layer 36. The first and second resonators are separated by one or more layers 33 that provide acoustic coupling (and in some embodiments, electrical isolation). The layer 33 can be formed by one or more dielectric layers. The layer 33 can also include a combination of a dielectric layer and a conductive layer (e.g., a metal layer). In embodiments where electrical isolation is required between the first bottom electrode layer 32 and the second top electrode 34 (such as in the case of a series resonator element), the one or more layers 33 include at least one dielectric (non-conductive) layer. Regardless of whether there is electrical isolation, the one or more layers (e.g., a layer stack) 33 always provide acoustic coupling between the first and second resonators.

[0050] For example, the first top electrode layer 30, the first bottom electrode layer 32, the second top electrode layer 34, and the second bottom electrode layer 36 may each include one or more metal layers, such as an aluminum layer, a copper layer, or a tungsten layer, but are not limited thereto. In some embodiments, the material of the first piezoelectric layer 31 and the material of the second piezoelectric layer 35 may be the same material. However, in other embodiments, different materials may be used. For example, as already mentioned with reference to Figure 1 As described above, the material of the first piezoelectric layer 31 can be a material with lower piezoelectric coupling, such as aluminum nitride, and the first resonator can be used as a filter resonator as described above to construct a filter with a narrower bandwidth. For example, an aluminum nitride piezoelectric layer (such as the first piezoelectric layer 31) can be produced by a reactive sputtering method from an Al target. The material of the second piezoelectric layer 35 can include a material with higher piezoelectric coupling, such as lithium niobate, potassium niobate or Sc-doped aluminum nitride, to provide a large tuning range. It should be noted that the Sc-doped AlN layer can also be formed as a so-called AlScN layer that can contain a large amount of Sc. In other embodiments, the first piezoelectric layer 31 and the second piezoelectric layer 35 can both be based on aluminum nitride, but they have different dopants and / or doping concentrations, for example, different scandium (Sc) concentrations.

[0051] It should be noted that in order to properly couple the first resonator and the second resonator, in an embodiment, the piezoelectric materials of both resonators are made to piezoelectrically couple the same type (polarization) of acoustic waves. Piezoelectric coupling generally depends on the materials, but also on the crystal orientation used. In an embodiment, the tuning circuit of the second resonator can only affect the frequency behavior of the first resonator if both piezoelectric layers couple the same acoustic wave type / polarization. For example, when using sputtered aluminum nitride piezoelectric material, the second piezoelectric layer 35 is used in the cut (crystal orientation) to provide strong piezoelectric coupling of the same polarization as the first piezoelectric layer 31.

[0052] For example, in an embodiment where aluminum nitride is used for the first piezoelectric layer 31 or the second piezoelectric layer 35, the aluminum nitride may be deposited on the substrate material in a c-axis orientation. Figure 2 As the substrate 25), a silicon wafer or a lithium niobate (LiNbO3) or lithium tantalate (LiTaO3) crystal can be used.

[0053] Figure 4 Picture shows Figure 3 Reference numeral 40 denotes an equivalent circuit of a stack of layers. Figure 3 The first resonator formed by the layers 30, 32 and the first piezoelectric layer 31, and reference numeral 41 denotes a first resonator composed of Figure 3 The second resonator is formed by layers 34, 35 and 36 in the embodiment. Terminal 43 contacts the first top electrode ( Figure 3 30 of them, in Figure 4 Terminal 44 is also marked as t1 in FIG. 1 , and terminal 44 is electrically contacted with the first bottom electrode ( Figure 3 32, also marked as b1), terminal 45 contacts the second top electrode ( Figure 3 34, also labeled t2), and terminal 46 electrically contacts the second bottom electrode ( Figure 3 36 in (also marked as b2).

[0054] With capacitance C 12 A parasitic capacitor 42 is associated with the dielectric layer (stack) 33 between the bottom electrode of the first resonator and the top electrode of the second resonator.

[0055] It should be noted that although Figure 3 and Figure 4 In the embodiment of the present invention, the first bottom electrode 32 is electrically separated from the second top electrode 34, but in other embodiments, when separate terminals are not required, a single electrode can also be provided as the second top electrode and the first bottom electrode, and then the acoustic coupling of the resonator is achieved via the common electrode. In this case, a dielectric layer for electrical separation is not required.

[0056] In the embodiment, terminals 43 and 44 are used to connect Figure 4 The resonator element is incorporated into the filter structure. To provide frequency tuning, a tuning circuit can be coupled to terminals 45 and 46. Figures 5 to 7 Discuss the examples.

[0057] Figure 5 An exemplary topology of a ladder filter is shown, which in this case is a 3 1 / 2 stage ladder type filter. Reference numeral 50 denotes a signal input, reference numeral 51 denotes a signal output, and reference numeral 52 denotes a ground line. Figure 5The ladder filter includes four series resonators 53A to 53D and three parallel resonators 54A to 54C. Typically, all series resonators 53A to 53D have the same resonant frequency, and all parallel resonators 54A to 54C have the same resonant frequency; however, the resonant frequencies of the series resonators and the parallel resonators are detuned relative to each other. The amount of detuning roughly corresponds to the bandwidth of the resulting filter. In general, the resonant frequency of the parallel resonators 54A to 54C is lower than the resonant frequency of the series resonators 53A to 53D.

[0058] Each of the resonators 53A to 53D, 54A to 54C may be a first resonator of a resonator element, as previously described with respect to Figure 1 , Figure 3 and Figure 4 Frequency tuning of the filter may be performed via a tuning circuit coupled to a respective second resonator of the resonator element. Figure 5 The ladder filter structure is used only as an example and can be referred to by Figure 1 , Figure 3 and Figure 4 The resonator element comprising the first resonator and the second resonator replaces the conventionally used resonators to use and modify any conventional ladder or lattice filter structure used with BAW resonators in the art. A plurality of such filters can be combined to form an n-port filter structure, for example, to filter multiple frequency bands used in communication applications.

[0059] Figure 6 A resonator element according to one embodiment is illustrated, which includes a tuning circuit and can be used as a parallel resonator element, for example, to achieve Figure 5 The parallel resonators 54A to 54C of the ladder type filter.

[0060] Figure 6 The resonator element of includes a first resonator 62 having a first top electrode t1 and a first bottom electrode b1, and a second resonator 65 having a second top electrode t2 and a second bottom electrode b2. The first resonator 62 is electrically isolated (but not acoustically decoupled) from the second resonator 65, for example, by a dielectric material represented by a parasitic capacitor 64. The dielectric material provides acoustic coupling between the resonators 62, 65, as indicated by arrow 63. The implementation of the first resonator 62 and the second resonator 65 can be as previously described with respect to Figure 1 , Figure 3 and Figure 4 as described.

[0061] The first top electrode t1 of the first resonator 62 is coupled to a first terminal 60 (also labeled "3") and a second terminal 61 (also labeled "4"). The terminals 60 and 61 are used to connect with other resonators or signal input / output terminals to construct a filter structure. For example, when Figure 6 The parallel resonator elements are used to realize Figure 5 When the parallel resonator 54A is connected, the first terminal 60 is coupled with the series resonator 53A, and the second terminal 61 is coupled with the series resonator 53B.

[0062] The first bottom electrode b1 of the first resonator 62 is coupled to ground via a terminal 68 (also labeled "0"). Figure 5 In the exemplary filter structure of , this corresponds to coupling of any one of the parallel resonators 54A to 54C to the ground line 52.

[0063] The second top electrode t2 of the second resonator 65 is coupled to ground via a terminal 69 (also labeled “0”).

[0064] In addition, the tuning circuit is coupled between the second top electrode t2 and the second bottom electrode b2 of the second resonator 65. Figure 6 In the example of FIG. 6 , the tuning circuit includes a variable capacitor 67 coupled in parallel to an inductor 66. In some embodiments, the inductor 66 may be implemented as a high-Q (quality factor) inductor or other reactance having, for example, a Q factor greater than 10, greater than 50, or greater than 100. The inductance L1 of the inductor may be, for example, between 0.5 and 200 nH, for example, less than 50 nH, for example, between 1 and 10 nH. The variable capacitor 67 may be implemented in any conventional manner, for example, using a varactor or a switched capacitor. By varying the capacitance of the variable capacitor 67, the Figure 6 The resonance (series resonance and parallel resonance) of the resonator elements are tuned. Figure 6 The tuning circuits of are examples only, and various combinations of capacitors, inductors, and / or resistors may be used, one or more of which may be variable to provide tuning. In some embodiments, the tuning circuit may also include switches such as radio frequency (RF) switches that may be selectively opened and closed to tune the resonator element. In such a tuning circuit, a capacitor or inductor may be coupled in series or in parallel to one or more switches (e.g., one or more RF switches).

[0065] As will be described in more detail later using simulation results, the inductance 66 (eg, an inductor) may increase the tuning range compared to when only a variable capacitor is used.

[0066] Figure 7 is a circuit diagram of a resonator element suitable for use as Figure 5 A series resonator in a filter structure such as a filter structure of FIG. 5A , for example, is used to implement the series resonators 53A to 53D. Figure 7 The resonator element includes a first resonator 72 and a second resonator 75, wherein the first resonator 72 and the second resonator 75 are connected by a capacitor having a capacitance value C as shown in the figure. 12 The (parasitic) capacitance 73 is electrically separated from the first resonator 72 and the second resonator 75. The capacitance 73 is associated with the dielectric layer(s) that acoustically couples the first resonator 72 and the second resonator 75, as indicated by arrow 74. The first resonator 72 has a first top electrode t1 and a first bottom electrode b1, and the second resonator 75 has a second top electrode t2 and a second bottom electrode b2. The first and second resonators 72, 75 can be as described above with reference to Figure 1 , Figure 3 and Figure 4 to be implemented as described.

[0067] The first top electrode t1 is coupled to the first terminal 70 (also labeled as "5"), and the first bottom electrode b1 is coupled to the second terminal 71 (also labeled as "6"). Figure 7 resonator elements are incorporated into the filter structure. For example, to achieve Figure 5 In the case of a series resonator 53A, the first terminal 70 will be coupled to the signal input 50, and the second terminal 71 will be coupled to the resonators 54A and 53B. Figure 6 When the resonator 54A is implemented in this way, for example, Figure 7 The second terminal 71 will be connected to Figure 6 The first terminal 60 is coupled, and Figure 6 The second terminal 61 of will be coupled to the corresponding terminal of the resonator 53B.

[0068] The second top electrode t2 is coupled to ground via terminal 78 (also labeled "0"). Figure 6 and Figure 7 The terminal numbers 3, 4, 5 and 6 will be referred to below. Figures 8 to 12 The terminals coupled to ground are used in the simulation discussion. Figure 6 and Figure 7 It can also be marked as "0".

[0069] In addition, a tuning circuit is coupled to the second top electrode t2 and the second bottom electrode b2, which includes, for example, an inductor 76 and a variable capacitor 77. The inductor 76 and the variable capacitor 77 can be respectively Figure 6 The inductor 66 and the variable capacitor 67 are implemented in a similar manner as described above. In addition, the inductor 76 and the variable capacitor 77 are only an example of a tuning circuit coupled to the second resonator 75; Figure 6As described, other tuning circuit configurations are possible.

[0070] use Figure 6 The parallel resonator elements and Figure 7 A variety of filter structures can be constructed by using series resonator elements, such as lattice filters and ladder filters. Figure 5 Ladder filter structure.

[0071] To further explain the function of the above resonator element, reference will be made to Figures 8 to 12 Discuss the simulation results or various configurations.

[0072] for Figures 8 to 12 In the simulation, it is assumed that the first resonator (filter resonator) consists of a piezoelectric coupling constant k T 2 7.1% doped aluminum nitride (e.g., doped with scandium or another material), and assuming that the second resonator (the frequency-tuned resonator) is a piezoelectric coupling constant k T 2 =25% of the resonator based on LiNbO3 crystal.

[0073] Figure 8 (a) to Figure 8 (d) shows the S parameters (scattering parameters, representing insertion loss) as a function of frequency for various configurations. Figure 8 (a) and Figure 8 (b) shows the S parameters of the resonator elements in which the first resonator is coupled in a parallel configuration, for example, Figure 6 shown. Figure 8 (c) and Figure 8 (d) illustrates the curve of the series coupling of the first resonator, for example, Figure 7 shown. Figure 8 (a) and Figure 8 (b) shows the same curve with the y-axis at Figure 8 (b) and Figure 8 (a) is enlarged, and the y-axis is Figure 8 (d) Figure 8 The (c) is also enlarged. Figure 8 (a) and Figure 8 In (b), curve 80 shows the impedance (such as Figure 6 The S parameters of the tuned circuit of the impedance 66 of curve 80 are shown. The impedance in the simulation is an inductance of 1 nH, with a very high quality factor. In addition, a small capacitor 67 of 1 pF is assumed. Curve 81 illustrates the S parameters of another capacitance in parallel with the impedance of curve 80. It is observed that the resonance shown has a large shift of the order of 300 MHz.

[0074] Figure 8 (c) and Figure 8 Curve 82 in (d) illustrates the S parameters for the case of a series resonator for a tuned circuit comprising an impedance formed by the addition of a 1 nH inductance having a very high quality factor and a small 1 pF capacitance as a capacitor, Figure 8 (a) and Figure 8 The curve 80 in (b) is similar, and the curve 83 illustrates the behavior with an additional capacitance of 10 pF coupled in parallel with the impedance. Here too a frequency shift of the resonance of the order of 300 MHz is observed.

[0075] Next, we will refer to Figures 9 to 12 right Figure 6 and Figure 7 The effect of the inductance of the impedance 66 or 76 is explained. Figure 8 Similar, in Figures 9 to 12 In the figure, graphs (a) and (b) illustrate the Figure 6 The curves for the parallel resonator arrangement shown in FIG. 1 and the curves (c) and (d) show that Figure 7 The S parameters of the series resonator configuration are shown in Figure 2. Figure 8 Similarly, the y-axis is Fig. 9 The graph (b) is enlarged compared to the graph (a), and the y-axis is enlarged in the graph (d) compared to the graph (c). Figures 9 to 12 In each of the graphs, a curve (or a group of curves) for a capacitance of 1 pF and a curve or a group of curves for a capacitance of 10 pF are shown, and Figure 8 Similar to what is described in .

[0076] exist Fig. 9 , the impedances 66 and 76 of the tuned circuit have values ​​of 100 nH respectively. Curves 90 and 92 show the S parameters of a 1 pF capacitor, and curves 91 and 93 show the S parameters of a 10 pF capacitor. The resonances shown are shifted by less than 100 MHz for both the parallel resonator case and the series resonator case.

[0077] Fig.10 The case where the inductance is 3nH is shown. Curves 100 and 102 illustrate the S parameters of a 1pF capacitor, and curves 101 and 103 illustrate the S parameters of a 10pF capacitor. Each of curves 100 to 103 includes multiple curves, which can be seen in the enlarged versions of the curve graphs (b) and (d) of curves 91 and 93, respectively. These curves represent the behavior of different Q factors (quality factors) of the inductance, with the Q factor ranging from 42 to 100. In general, a higher Q factor results in a more pronounced resonance and less insertion loss. In this case, the resonance is shifted by approximately 150MHz.

[0078] Fig.11 1.7 nH is a graph showing an inductance value. Curves 110 and 112 show S parameters for a 1 pF capacitor, and curves 111 and 113 show S parameters for a 10 pF capacitor. Each of curves 110 to 113 (in Fig.11 (b) and Fig.11 The enlarged view of (d) shows that the inductance is again varied over a range of Q factors from 42 to 200. By varying the capacitance, the resonance is shifted by slightly less than 300 MHz.

[0079] at last, Fig.12 The case with an inductance of 1.3 nH is illustrated. Curves 120 and 122 illustrate the S parameters of a 1 pF capacitor, and curves 121, 123 illustrate the S parameters of a 10 pF capacitor. Individual curves from curves 120 to 123 illustrate the behavior of different Q factors. Here, the resonance is shifted by nearly 400 MHz. It can therefore be seen that a larger frequency tuning range can be obtained with the same capacitance variant by reducing the inductance. However, the difference between the different Q factors becomes more pronounced as the inductance decreases, so that in embodiments using small inductances below 5 nH, a high Q factor above 100 (e.g., above 150) can be selected to achieve the inductance.

[0080] Fig.13 The diagram shows Figure 6 (Parallel resonator configuration) with matching intrinsic acoustic port terminations for the acoustic path as indicated by arrow 63. Curve 130 shows the phase with tuning inductance 66, while curve 131 shows the phase when capacitor 67 is additionally introduced. Thus, by varying the capacitance, for example, point 132 is shifted to point 133, resulting in a tuning range as indicated by arrow 134.

[0081] Fig.14 A method according to one embodiment is illustrated. Fig.14 The methods are described as a series of acts or events, but the order in which these acts or events are described and illustrated is not to be construed as limiting. Fig.14 The method can be implemented using the resonator elements described above, and the features, elements, variations and modifications described with respect to these resonator elements are equally applicable to the method. For ease of reference, reference will be made to the previous description of the resonator elements. Fig.14 However, Fig.14 The method can also be implemented independently of the resonator element described previously.

[0082] exist Fig.14At 140, a resonator stack is provided. For example, providing a resonator stack may include forming two stacked resonators on a substrate, for example, relative to Figure 3 Providing a stack of resonators may also include providing an acoustic mirror or chamber below the resonator, as described with reference to Figure 2 described.

[0083] At 141, the method includes incorporating a first resonator of the resonator stack (eg, the first resonator (filter resonator) of the above-described embodiment) into a filter structure. For example, the first resonator may be included in the filter structure as a parallel resonator or a series resonator.

[0084] At 142, a tuning circuit is provided to a second resonator of the resonator stack, for example, a tuning circuit including an inductor and a variable capacitor, such as Figure 6 and Figure 7 As shown. Then, by means of a tuning circuit, the resonator stack can be tuned to a desired frequency for use in a filter structure. For example, the filter structure can be adapted to different frequency bands used in a communication device via the tuning circuit.

[0085] Frequency tunable RF filters using circuit topologies with frequency tunable bulk acoustic wave (BAW) resonators have been described herein. For example, possible filter circuit topologies are ladder filters or lattice filters. The individual resonators of any filter topology differ in their respective impedance levels or equivalent resonator areas. In order to construct a tunable filter from tunable resonators, all resonators are ideally tunable (or programmable) in a similar manner, to enable, for example, Figure 8 (a) to Fig.13 Consistent tuning / shifting of the filter curve shown in . Ideally, each tunable BAW resonator has a corresponding individual tuning network comprising tunable or programmable capacitors and / or inductors. Such passive components ideally provide a high quality factor in order to minimize losses and maximize the resulting (bandpass) filter performance. Consistent frequency tuning / shifting of individual resonators in a filter configuration is achieved by corresponding tuning networks scaled according to the associated resonator impedance. The capacitors in the tuning network are scaled proportionally to the static capacitance of the corresponding resonator, while the inductors in the tuning network are scaled inversely proportional to the static capacitance of the corresponding resonator.

[0086] While any conventional RF filter with a topology based on fixed frequency (BAW) resonators can be converted into a tunable filter with the same topology, tunable / programmable (BAW) resonators are used in place of the fixed frequency (BAW) resonators of the conventional RF filter. Each tunable / programmable BAW resonator is controlled by a separate tuning network. The impedance of each tuning network is scaled proportionally to the impedance of the tuned resonator (within limits based on manufacturing tolerances and parasitics). The shunt resonator can be tuned differently than the series resonator to allow adjustment of the bandwidth of the frequency-shifted filter curve.

[0087] Generally speaking, a tunable RF ladder filter has N half-stages, where N ≥ 2 and is usually between 4 (e.g., 2 stages) and 7 (e.g., 3 stages). 1 / 2 stages) or 8 (e.g., 4 stages). A single ladder filter stage includes a series resonator and a parallel resonator. A half stage can be a series resonator or a parallel resonator. 1 The / 2-stage ladder filter can be implemented with 4 parallel resonators and 3 series resonators, or 3 parallel resonators and 4 series resonators. Fig.16 Shown 2 1 / 2 level ladder filter example. It should be noted that a series or parallel resonator (half level) may include more than one resonator, for example, to increase power handling capability. Typically, all series resonators provide the same (series) layer stack, and all parallel resonators provide the same (parallel) layer stack. Therefore, all series resonators provide similar resonant and anti-resonant frequencies. The same applies to all parallel resonators. For a bandpass filter, the resonant frequency of the parallel resonator is less than the corresponding resonant frequency of the series resonator. (A band-stop filter will be produced instead). However, the areas of the individual resonators of the filter are different. The static capacitance of the resonator is proportional to its area, while the impedance function of the resonator is inversely proportional to its area. For a given layer stack, as described herein, tunable / programmable BAW resonators of different areas provide the same frequency shift when the impedance of the corresponding tuning network is proportional to the impedance of the tuning resonator. This scaling of the impedance of the tuning network with the static capacitance (or area) of the corresponding tuning resonator is an element for realizing a frequency tunable (programmable) filter by a separate frequency tunable (programmable) resonator.

[0088] Fig.15 An example of a tunable BAW resonator 1500 is shown having a filter resonator 1502, a tuning resonator 1506, and an acoustic coupling layer(s) 1504 between the filter resonator 1502 and the tuning resonator 1506. A variable tuning circuit 1508 is coupled to Fig.15The exemplary tunable BAW resonator of the tuning resonator 1506. The filter resonator 1502 includes a piezoelectric layer Piezo 1, and the tuning resonator 1506 includes a piezoelectric layer Piezo 2. Fig.15 Also depicted is a substrate layer 1512, and an acoustic decoupling layer 1510 for acoustically decoupling the tunable BAW resonator 1500 from the substrate 1512. Different piezoelectric materials can be used for the two resonators. The piezoelectric layers can have different thicknesses. The individual electrodes can be made of different materials and can have different thicknesses.

[0089] Fig.16 Shows a 2 1 / 2-stage ladder filter 1600, the 2 1 1600 of the ladder type of / 2 level has three series resonators 1602, 1606 and 1610 and two parallel resonators 1604 and 1608. Each resonator includes three elements: a filter resonator, a tuning resonator acoustically coupled to the filter resonator, and a tuning circuit further described below that is electrically coupled to the tuning resonator. Therefore, the filter 1600 includes three series filter resonators 1602A, 1606A, 1610A, two parallel filter resonators 1604A, 1608A, an RF input 1612 and an RF output 1614. Each filter resonator is coupled to its own tuning network. The series filter resonator 1602A has a corresponding tuning network including a tuning resonator 1602B coupled to a tuning circuit 1602C. The parallel filter resonator 1604A has a corresponding tuning network including a tuned resonator 1604B coupled to a tuning circuit 1604C. The series filter resonator 1606A has a corresponding tuning network including a tuned resonator 1606B coupled to a tuning circuit 1606C. The parallel filter resonator 1608A has a corresponding tuning network including a tuned resonator 1608B coupled to a tuning circuit 1608C. The series filter resonator 1610A has a corresponding tuning network including a tuned resonator 1610B coupled to a tuning circuit 1610C. The impedance of each tuning network is scaled with the impedance (or area) of the corresponding resonator to ensure that all individual resonators exhibit the same (or similar) frequency tuning behavior. Impedance scaling ensures, for example, that Figure 8 (a) to Fig.13 The resulting bandpass filter is shown to have a consistent frequency shift.

[0090] It is worth noting that the notation used for the tunable resonator is chosen to simplify Fig.16The “side-by-side” tunable resonator symbol is used to represent the acoustic coupling between the filter resonator and the tuning resonator. For a tunable BAW resonator, such as tunable resonator 1602, for example, in Fig.15 In the embodiment shown, the filter resonator and the tuning resonator are combined on top of each other and acoustically coupled into one layer stack.

[0091] According to an embodiment, a frequency tunable RF filter is implemented using a circuit topology of a frequency tunable bulk acoustic wave (BAW) resonator with minimal parasitic effects. In order to achieve optimal resonator performance, i.e., the highest quality factor for tunable resonance, it is important to minimize the parasitic effects of the tuning network and the interconnection lines between the tuning network and the tuning resonator (electrode). Although the metallization layer of its electrode can be used to interconnect individual filter resonators, all tuned resonators require their own tuning networks. For example, the tuning network can be implemented as a programmable IC in CMOS technology. Ideally, the interconnection of the corresponding port (terminal) of the tuning network with the corresponding port (electrode) of the tuning resonator should be achieved with minimal parasitic effects (i.e., within the minimum resistance loss). Therefore, the port (electrode) of the tuning resonator should be close to the surface of the BAW chip. Therefore, the filter resonator should be positioned (made) close to the substrate (using an acoustic mirror or membrane / chamber for acoustic decoupling) and directly connected to their (buried) electrode metallization layer. Then, the tuning resonator is positioned (made) on top of the corresponding filter resonator at / near the substrate surface. Thus, the interconnects between the tuned resonators and their tuning networks are as short and low ohmic as possible, since no deep vias are needed in the case of a tunable BAW resonator with a filter resonator on top of its respective tuned resonator. The embodiments to be discussed below are particularly suitable for filter implementations where each BAW resonator requires its own tuning network. Thus, for example, a ladder filter with N resonators requires 2*N interconnects to the tuning circuits, but only one interconnect (via) for the filter input and one interconnect (via) for the filter output (plus ground connection).

[0092] The embodiments discussed in further detail below use at least some of the following construction aspects to implement a tunable (or programmable) RF filter based on a tunable (or programmable) BAW (bulk acoustic wave) resonator: each tunable BAW resonator is characterized by a layer stack, wherein the tuning resonator is positioned on top of the filter resonator; the individual tunable BAW filter resonators are coupled to each other within their respective electrode layers (some vias may be required between the two electrode layers to implement a specific filter topology, but the length of these vias is determined by the thickness of the piezoelectric layer of the filter resonator, so these vias are very short / shallow, typically about 1 μm); only the filter input and filter output are coupled to the surface of the BAW filter chip through deep vias, which minimizes the number of deep vias required to combine the filter resonators into the filter circuit; and the tuning resonators of the individual tunable BAW resonators are all implemented on top of their respective filter resonators. Therefore, the interconnection lines of the tuning resonator to its respective tuning network are as short as possible (at or near the chip surface), with only shallow vias for contacting the bottom electrodes of the tuning resonators. This configuration greatly aids the tunable resonator performance and thus the overall filter performance.

[0093] Fig.17 An example of a tunable BAW resonator 1700 is shown having a tuning resonator 1702 located on top of a filter tuner 1706 according to one embodiment. Fig.17 Also shown in FIG. 1704 are acoustic coupling layers and tuning circuits 1708. Different piezoelectric materials can be used for the two resonators. The piezoelectric layers can have different thicknesses. The individual electrodes can be made of different materials and can have different thicknesses. Fig.17 The stacked layer configuration shown is superior in some respects to Fig.15 The standard stacked layer construction of the filter can be easily realized, such as the interconnection between the tuning network and the tuned resonator, and provides the additional advantage of smaller parasitic effects (especially ohmic losses). Depending on the filter topology to be realized, the filter resonators can be easily coupled to each other by utilizing their electrode metallization layers (optionally, in some embodiments, combining some shallow vias between these electrode layers), thereby minimizing the total number of vias, as will be described below with respect to Fig.18A Further details are given in Fig.18A In an embodiment, each tuned resonator is coupled to its own tuning network.

[0094] Fig.18AA cross-sectional schematic diagram of an integrated circuit filter 1800 having tunable resonators 1812, 1814, and 1816 is illustrated. As described above, each tunable resonator includes a filter resonator, a tuning resonator, and a tuning circuit coupled in the manner described above. Thus, tunable resonator 1812 includes filter resonator 1812A, tuning resonator 1812B, and tuning circuit 1812C. Tunable resonator 1814 includes filter resonator 1814A, tuning resonator 1814B, and tuning circuit 1814C. Tunable resonator 1816 includes filter resonator 1816A, tuning resonator 1816B, and tuning circuit 1816C.

[0095] Fig.18A The specific filter configuration shown is 1 1 / 2 stage ladder filter. Filter resonator 1812A is a parallel resonator coupled between ground (through bottom electrode 1832 and deep via 1828A) and RF IN (through top electrode 1834 and shallow via 1826'). Top electrode 1834 of filter resonator 1812A is coupled to top electrode 1834 of filter resonator 1814A as shown. Filter resonator 1814A is a series resonator coupled between filter resonator 1812A (in a parallel configuration with top electrode 1834 coupled to RF In port 1808) and filter resonator 1816A (in a parallel configuration with bottom electrode 1824 coupled to ground through deep via 1828B and top electrode 1822 coupled to RF Out port 1810 through shallow via 1826). The top electrode 1822 of the parallel filter resonator 1816A is coupled to the bottom electrode 1820 of the series resonator 1814A. The connection uses a via 1830 between the respective bottom electrode 1820 and the top electrode 1822. It should be noted that in addition to the via 1830, the electrical coupling between the electrodes of the individual filter resonators can also be achieved by appropriately constructing the respective metallization layers for these electrodes. Thus, by using several shallow vias and only two deep vias shown, the coupling of the series filter resonator and the parallel filter resonator can be achieved to realize the filter circuit.

[0096] exist Fig.18A Also shown are acoustic decoupling layers 1836A, 1836B, and 1836C. Decoupling layer 1836A is used to decouple resonator 1812 from substrate 1802. Decoupling layer 1836B is used to decouple resonator 1814 from substrate 1802. Decoupling layer 1836C is used to decouple resonator 1816 from substrate 1802.

[0097] The tuning resonators 1812B, 1814B, and 1816B are placed on top of the stack of corresponding filter resonators 1812A, 1814A, and 1816A, which results in a short and low-ohmic interconnect to the tuning circuits 1812C, 1814C, and 1816C. The filter resonators 1812A, 1814A, 1816A are located in the deeper region of the resonator layer stack, closer to the substrate 1802 and the acoustic decoupling provided by the chamber or acoustic mirror (in one embodiment, in Fig.18A 1836A, 1836B, and 1836C as described above). The filter resonators are interconnected to each other according to the filter circuit topology. Filter resonators 1812A and 1814A are coupled together by top electrode 1834, and filter resonators 1814A and 1816A are coupled together by bottom electrode 1820, top electrode 1822, and shallow vias 1830. These interconnects can be implemented within the electrode metallization layers of the filter resonators, without requiring any vias or only a small number of (shallow) vias between the two electrode metallization layers (depending on the filter topology). In some embodiments, only deeper vias 1828A and 1828B are required for contacting RF In and RF Out; and for Fig.18A The embodiment shown requires only a deeper via for the ground connection.

[0098] exist Fig.18A 1800. In the embodiment of the present invention, filter resonators 1812A, 1814A, 1816A are shown as being formed (or embedded) in an insulating layer 1804. For example, the insulating layer may include silicon dioxide or other known insulating materials. An acoustic coupling layer is shown as a common acoustic coupling layer 1806 for acoustically coupling the filter resonator and the tuning resonator. There may also be more than one layer and more than one material for acoustic decoupling. Tuning circuits 1812C, 1814C, and 1816C may be implemented at least in part using the same fabrication process as integrated circuit filter 1800. Alternatively, the tuning circuits may be implemented using different fabrication processes, as will be described in further detail below.

[0099] Fig.18B (1 1 / 2-stage ladder filter) reproduces Fig.18A FIG. 1 is a filter circuit of FIG. 1 , in which the filter resonators 1812A, 1814A, and 1816A are highlighted by corresponding circular symbols ①, ②, and ③. 11814A and 1816A are connected in parallel and in series. The filter circuit is composed of electrically connected filter resonators. The independent filter resonator is acoustically coupled to its corresponding tuned resonator (the tunability produced is indicated by the small arrow in the resonator symbol here). The corresponding electrical schematic diagram is also shown, wherein the left schematic diagram retains the physical orientation of filter resonators 1812A, 1814A and 1816A, and the right schematic diagram is shown in a more conventional method. The filter resonators 1812A and 1816A in parallel and the filter resonator 1814A in series are clearly shown as being coupled between the RF IN port 1808 and the RFOUT port 1810 in the ladder filter configuration.

[0100] Examples of frequency tunable bulk acoustic wave (BAW) resonators with enhanced tuning range are Fig.19 As shown and will be explained below. As mentioned earlier, the tunable BAW resonator can be implemented as a pair of coupled BAW resonators. One of the resonators is a filter resonator, i.e., a resonator for being built into a filter circuit topology. The other acoustically coupled BAW resonator is a tuned resonator. The tuned resonator is coupled to a tuning network. The tuned resonator combined with the tuning network actually acts as a tuning layer in the filter resonator layer stack. The tuning layer provides tunable mechanical stiffness. The tunable mechanical stiffness depends on the tuning network setting and affects the acoustic velocity and the acoustic impedance of the tuning layer.

[0101] Refer again Fig.19 , the composite BAW resonator includes two (rather than just one, e.g., see Fig.15 and Fig.17 ) tuning resonators 1902 and 1912. The two tuning resonators 1902 and 1912 are placed on both sides of the filter resonator, i.e., one tuning resonator (top tuning resonator 1902) is above the filter resonator 1908 and the second tuning resonator (bottom tuning resonator 1912) is below the filter resonator. Thus, in effect, a tuning layer with tunable mechanical stiffness is placed on both sides (top and bottom) of the filter resonator.

[0102] exist Fig.191904. Filter resonator 1908 includes piezoelectric layer Piezo 2. Bottom tuning resonator includes piezoelectric layer Piezo 3 and is coupled to tuning circuit 1914. Acoustic coupling layer 1906 acoustically couples top tuning resonator 1902 and filter resonator 1908. Acoustic coupling layer 1910 acoustically couples bottom tuning resonator 1912 to filter resonator 1908. Specifically, acoustic coupling layer 1906 is coupled between a bottom electrode of top tuning resonator 1902 and a top electrode of filter resonator 1908. Similarly, acoustic coupling layer 1910 is coupled between a bottom electrode of filter resonator 1908 and a top electrode of bottom tuning resonator 1912. The areas of the top tuning resonator 1902, the filter resonator 1908, and the bottom tuning resonator 1912 are matched. The static capacitance of the filter resonator 1908 and the top tuning resonator 1902 and the bottom tuning resonator 1912 depends not only on the area, but also on the thickness and dielectric constant of the corresponding materials of the independent piezoelectric layers, and are generally different. As in the previous embodiment, the filter signal terminal is associated with the top electrode and the bottom electrode of the filter resonator. The resonator 1900 can be used in a ladder filter as described above as needed.

[0103] exist Fig.19 Also shown is a substrate layer 1918 and an acoustic decoupling layer 1916 for acoustically decoupling the resonator 1900 from the substrate 1918.

[0104] In with Fig.15 and Fig.17 Compared to the single tuned resonator embodiment shown, the embodiment provides an enhanced tuning range. Fig.19 The composite resonator 1900 is a stack of layers.

[0105] Now refer to Figure 20 to Figure 26 , embodiments of tuning circuits with enhanced tuning ranges including inductors are described. Adding an inductor to a tuning circuit provides an improvement in the tuning range of a tuning circuit that includes only a variable capacitor. An inductor with a high Q (quality factor) can be integrated on a piezoelectric die with a corresponding resonator, interposer material, RF filter control chip, or IPD (integrated passive device) according to any available manufacturing process that provides an optimal metal layer for the inductor. A metal layer with low resistivity can be used to design a high-Q inductor. For example, a thick or aluminum metal layer can be patterned into a high-Q inductor suitable for a tuning circuit.

[0106] The higher the Q value of the inductor used, the higher the frequency the resonator can extend its tuning range without significant losses. For example, an inductor Q value of 30 to 50 can increase the total tuning range by a factor of 1.5.

[0107] The tuning network is equipped with a piezoelectric die ( Fig.23 ) or interposer material ( Fig.24 ) or RF filter control chip ( Fig.25 or Fig.26 ) or IPD( Fig.25 or Fig.26 ) on a high-Q inductor, as described in further detail below.

[0108] Fig. 20 [A] of FIG. 2 illustrates a tunable BAW resonator 2000A having a filter resonator 2002, a tuning resonator 2004, and an acoustic coupling layer 2006 located between the filter resonator and the tuning resonator. The filter resonator 2002 includes a top electrode t1, a piezoelectric layer Piezo1, and a bottom electrode b1, and is located above the acoustic coupling layer 2006 in the layer stack. The tuning resonator 2004 includes a top electrode t2, a piezoelectric layer Piezo 2, and a bottom electrode b2, and is located below the acoustic coupling layer 2006 in the layer stack. A tuning network (having a tunable / programmable impedance) Zt is coupled to the tuning resonator 2004. In one embodiment, the tuning network Zt includes an inductor and a variable capacitor.

[0109] Fig. 20 [B] illustrates a tunable BAW resonator 2000B having a filter resonator 2002, a tuning resonator 2004, and an acoustic coupling layer 2006 located between the filter resonator and the tuning resonator. The filter resonator 2002 includes a top electrode t2, a piezoelectric layer Piezo2, and a bottom electrode b2, and is located below the acoustic coupling layer 2006 in the layer stack. The tuning resonator 2004 includes a top electrode t1, a piezoelectric layer Piezo 1, and a bottom electrode b1, and is located above the acoustic coupling layer 2006 in the layer stack. A tuning network Zt is coupled to the tuning resonator 2004. In one embodiment, the tuning network Zt includes an inductor and a variable capacitor.

[0110] Fig.21 [A] to Fig.21 [D] shows that acoustically coupled resonator devices can be in parallel or series configuration. Fig.21 [A] and Fig.21 [B] shows a parallel configuration (one electrode of the filter resonator is grounded), while Fig.21 [C] and Fig.21[D] shows a series configuration. The electrical ports are denoted by reference numerals 1 and 2. Zt is the impedance of the two electrodes coupled in parallel to the tuned resonator. In practice, Zt may include a high-Q inductor Lt, and the variable capacitor Ct may be implemented by a programmable capacitor, such as a C tuner available from Infineon Technologies. Fig.21 [A] to Fig.21 In [D], the acoustic coupling layer is shown as having a static capacitance C12 and an acoustic coupling component ka12. Each tuned resonator is shown as being coupled to a corresponding tuning circuit Zt.

[0111] Fig.21 [A] shows a parallel resonator 2100A with a filter resonator 2002 positioned at the top and a tuning resonator 2004 positioned at the bottom in the layer stack. Fig.21 [B] shows a series resonator 2100B having a filter resonator 2002 positioned at the top and a tuning resonator 2004 positioned at the bottom in the layer stack. Fig.21 [C] shows a parallel resonator 2100C having a filter resonator 2002 positioned at the bottom and a tuning resonator 2004 positioned at the top in the layer stack. Fig.21 [D] shows a series resonator 2100D having a filter resonator 2002 positioned at the bottom and a tuning resonator 2004 positioned at the top in the layer stack.

[0112] Fig. 22 Figure 1 1 An example of a / 2-stage ladder filter 2200, the 1 1 The / 2-stage ladder filter 2200 has a series tunable resonator 2208 (filter resonator 2208A, tuning resonator 2208B, variable capacitor 2208C and inductor 2208D) and two parallel tunable resonators 2206 (filter resonator 2206A, tuning resonator 2206B, variable capacitor 2206C and inductor 2206D) and 2210 (filter resonator 2210A, tuning resonator 2210B, variable capacitor 2210C and inductor 2210D). Each tunable resonator includes a filter resonator and a tuning resonator coupled to a tuning circuit, which includes a variable capacitor and an inductor. Fig. 22 Also shown is an RF In port 2202 and an RF Out port 2204.

[0113] The impedance of each tuning network is inversely scaled with the static capacitance (or area) of the corresponding tuned resonator to ensure that all individual resonators exhibit the same (or similar) frequency tuning behavior. Matched tuning frequencies ensure consistent frequency shifts of the resulting bandpass filter curves. By coupling a high-Q inductor in parallel to the tuning capacitor, the tuning range of the equivalent filter can be significantly increased. It is worth noting that the symbols used for the tunable resonators are selected to simplify the filter circuit diagram. For tunable BAW resonators, the filter resonator and the tuning resonator are combined on top of each other and acoustically coupled in a layer stack, as has been described in this article.

[0114] Fig.23 Figure 1 1 / 2 stage ladder filter 2300, the 1 1 The / 2-stage ladder filter 2300 has a series tunable resonator 2312 (filter resonator 2312A, tuning resonator 2312B, variable capacitor 2312C and inductor 2312D) and two parallel tunable resonators 2310 (filter resonator 2310A, tuning resonator 2310B, variable capacitor 2310C and inductor 2310D) and 2314 (filter resonator 2314A, tuning resonator 2314B, variable capacitor 2314C and inductor 2314D). The inductive part of the tuning inductance Zt, Lt is preferably integrated on the piezoelectric acoustic tube core using a thick metal layer with very low resistance to achieve a very high Q inductor (Ql>15, where Ql is the loaded quality factor). The capacitive part of the tuning inductance Zt, Ct is preferably integrated on the piezoelectric acoustic tube core using a thick metal layer with very low resistance. Fig.23 The middle figure shows a varactor.

[0115] Fig.23 The upper portion of illustrates a cross-sectional view of a piezoelectric acoustic die including a substrate layer 2302, an insulating layer 2304 including filter resonators 2310A, 2312A, 2314A, an acoustic coupling layer 2306, and an insulating layer including tuning resonators 2310B, 2312B, 2314B. Metallized via 2316 is configured to provide an RF input and to contact the top electrodes of filter resonators 2310A and 2312A. Metallized via 2318 is configured to provide an RF output and to contact the bottom electrodes of filter resonators 2312A and 2314A. Metallized vias 2310E and 2310F are configured to electrically contact tuning resonator 2310B with variable capacitor 2310C and inductor 2310D. Metallized vias 2312E and 2312F are configured to electrically contact the tuned resonator 2312B with the variable capacitor 2312C and the inductor 2312D. Metallized vias 2314E and 2314F are configured to electrically contact the tuned resonator 2314B with the variable capacitor 2314C and the inductor 2314D.

[0116] Fig.23 The bottom portion of the 2320 shows the implementation of variable capacitors 2310C, 2312C, 2314C and inductors 2310D, 2312D, 2314D on the upper surface 2320 of the integrated circuit filter. In the relevant part, the inductors 2310D, 2312D, 2314D are illustrated as patterned metal traces using metal layers that are available in the piezoelectric acoustic integrated circuit process used to make the lower layer of the chip. The inductors 2310D, 2312D, 2314D include corresponding cross-sections 2310G, 2312G, 2314G so that the innermost coils of the inductors can be electrically contacted. Typically, the variable capacitors 2310C, 2312C and 2314C are made on different chips and electrically coupled to 2310E / 2310F, 2312E / F and 2314E / F, respectively. In one embodiment, variable capacitors 2310C, 2312C, and 2314C may be fabricated as varactors using capacitor-connected transistors.

[0117] Fig.24 The diagram shows a piezoelectric acoustic chip made of 1 1 / 2-stage ladder filter 2400, the piezoelectric acoustic chip includes the previously Fig.23 The layers 2302, 2304, 2306 and 2308 are described above, but wherein the inductor portions Zt, Lt are integrated on the interposer metal layer (e.g., laminate material) 2324. Fig.24 In the figure, the inductor metal layer may not be available on the piezoelectric acoustic chip, but may be available on the interposer 2324. For the inductor metal, a thick metal layer with very low resistance is preferred to achieve a high Q inductor (Ql>15). The capacitive portions Zt, Ct are illustrated in the block diagram only as varactors. In one embodiment, metallized vias 2330 are used to provide an RF In port. In one embodiment, metallized vias 2328 are used to provide an RF Out port. The interposer 2324 includes a plurality of additional metallized vias for contacting the varactors 2310C, 2312C, 2314C and the inductors 2310D, 2312D, 2314D, as shown in the plan view below. The interposer 2314 includes a top surface 2326 for making inductors and connecting variable capacitors. In the Fig.24 Also shown in the upper portion of FIG. 2 is a ball grid array 2322 for electrically contacting corresponding through holes in the interposer 2324 .

[0118] Fig.24The lower portion of the diagram shows the top surface 2326 of the interposer 2324, including the mounted / attached / coupled variable capacitors 2310C, 2312C, 2314C, and the corresponding coupled inductors 2310D, 2312D, and 2314D, respectively, which are made as part of the interposer 2324. The inductors include corresponding cross-sections 2310G, 2312G, 2314G, which function as described above with respect to Fig.23 described.

[0119] Fig.25 FIG1 shows a circuit having one series tunable resonator and two parallel tunable resonators. 1 An example of a / 2-stage ladder filter 2500. The inductor parts Zt, Lt are integrated on a filter control chip with very low circuit or a thick metal layer with a high Q IPD with very low resistance through an interposer material (e.g., two layers of laminated material) to achieve a very high Q inductor (Ql>15). The capacitor parts Zt, Ct are Fig.25 The middle figure shows a varactor.

[0120] Fig.25 The upper portion of the cross-sectional view of the construction of the ladder filter 2500 according to one embodiment is shown. A piezoelectric acoustic chip including layers 2302, 2304, 2306 and 2308 interconnected as described above, and a ball grid array 2322 is described. Interposer 2324 includes a plurality of through holes for coupling the piezoelectric acoustic chip to IPD 2334. IPD 2334 includes variable capacitors 2310C, 2312C, 2314C and inductors 2310D, 2312D, 2314D, and a ball grid array 2332. Depending on the IPD process used, the inductors and variable capacitors in IPD 2334 can be made inside the IPD or on top of the IPD.

[0121] Fig.25 The lower portion of shows a plan view of an IPD 2334 including variable capacitors 2310C, 2312C, and 2314C and inductors 2310D, 2312D, and 2314D.

[0122] Fig.26 Figure 1 1 / 2 ladder filter 2600 example, basically as compared to Fig.25 However, in Fig.26 , it should be noted that IPD 2334 is coupled directly to ball grid array 2332, as shown, and interposer 2324 is removed. Fig.26 The upper portion is a cross-sectional view of the ladder filter 2600, and Fig.26 The lower portion is a plan view of the above-mentioned IPD2334.

[0123] It should be noted that although in the above embodiments the tuning circuit is only provided to the second or third resonator of the respective resonator element, in other embodiments of the resonator element and the method, another tuning circuit may be provided to the first resonator element. The other tuning circuit may be implemented in a manner similar to that described above for the tuning circuit, for example, as an impedance network.

[0124] Although the above-mentioned filters using resonator elements can be specifically used in communication devices such as mobile communication devices, and these communication devices using corresponding filter structures can constitute embodiments, the filters can also be used in other devices that need to filter signals (especially high-frequency signals in the GHz range).

[0125] The above-described methods are intended only as examples and are not to be construed as limiting, as other implementation possibilities exist besides the one explicitly illustrated and described.

Claims

1. An RF integrated circuit filter, comprising: substrate; an insulating layer disposed on the substrate; a plurality of filter resonators arranged in the insulating layer, the insulating layer comprising a patterned top electrode layer, a patterned piezoelectric layer, and a patterned bottom electrode layer, wherein at least two filter resonators of the plurality of filter resonators are coupled together using the patterned top electrode layer; an acoustic coupling layer disposed on the plurality of filter resonators; as well as A plurality of tuning resonators are arranged on the acoustic coupling layer and correspondingly located above each of the plurality of filter resonators.

2. The RF integrated circuit filter according to claim 1, further comprising: A through-hole passes through the acoustic coupling layer to provide at least one of RF input access or RF output access to at least one filter resonator of the plurality of filter resonators.

3. The RF integrated circuit filter of claim 1 , further comprising: A via passes through the acoustic coupling layer and the insulating layer to provide ground access to at least one filter resonator of the plurality of filter resonators.

4. The RF integrated circuit filter of claim 1, wherein a top electrode of at least one of the tuned resonators is configured to provide access to a tuning circuit.

5. The RF integrated circuit filter of claim 4, wherein the tuning circuit comprises a tunable or programmable variable capacitor.

6. The RF integrated circuit filter of claim 1, wherein a bottom electrode of at least one of the tuned resonators is configured to provide access to a tuning circuit.

7. The RF integrated circuit filter of claim 6, wherein the tuning circuit comprises a tunable or programmable variable capacitor.

8. The RF integrated circuit filter of claim 1 , further comprising: A plurality of tuning circuits are respectively coupled to the plurality of tuned resonators.

9. The RF integrated circuit filter of claim 1 , further comprising: A plurality of tuning circuits are coupled to the plurality of tuned resonators, wherein each tuning circuit includes a variable capacitor and an inductor.

10. The RF integrated circuit filter of claim 1, wherein the top electrode and the bottom electrode of at least one of the tuned resonators are configured to provide corresponding access to the first node and the second node of the tuning circuit.

11. An RF filter device, comprising: Signal input; Signal output; as well as a resonator element coupled between the signal input and the signal output, wherein the resonator element comprises: A filter resonator comprising an intermediate piezoelectric layer, a first tuned resonator comprising an upper piezoelectric layer above the filter resonator, wherein the first tuned resonator is acoustically coupled to the filter resonator, a second tuned resonator comprising a lower piezoelectric layer below the filter resonator, wherein the second tuned resonator is acoustically coupled to the filter resonator, a first tuning circuit coupled to the first tuned resonator; as well as A second tuning circuit is coupled to the second tuned resonator.

12. The RF filter arrangement of claim 11, wherein impedances of the filter resonator, the first tuning resonator, and the second tuning resonator are matched. 13 . The RF filter device of claim 11 , wherein the RF filter device comprises a layer stack, and areas of the filter resonator, the first tuning resonator, and the second tuning resonator in the layer stack are matched.

14. An RF filter, comprising: substrate; an insulating layer on the substrate; a plurality of filter resonators in the insulating layer, the insulating layer comprising a patterned top electrode layer, a patterned piezoelectric layer, and a patterned bottom electrode layer, wherein at least two of the plurality of filter resonators are coupled together using the patterned top electrode layer, and at least two of the plurality of filter resonators are coupled together using the patterned bottom electrode layer; an acoustic coupling layer on the plurality of filter resonators; a plurality of tuned resonators on the acoustic coupling layer, the plurality of tuned resonators correspondingly located above each of the plurality of filter resonators; as well as A plurality of tuning circuits are coupled to the plurality of tuned resonators, wherein each tuning circuit includes a variable capacitor and an inductor.

15. The RF filter according to claim 14, wherein the RF filter comprises: a single piezoelectric acoustic integrated circuit in addition to the variable capacitors in the plurality of tuning circuits.

16. The RF filter according to claim 14, wherein the RF filter comprises: a piezoelectric acoustic integrated circuit comprising the plurality of filter resonators, the acoustic coupling layer, and the plurality of tuned resonators; as well as An interposer is coupled to the piezoelectric acoustic integrated circuit, the interposer including the plurality of tuning circuits.

17. The RF filter of claim 16, wherein the piezoelectric acoustic integrated circuit is fabricated using a first metal process and the interposer is fabricated using a second metal process different from the first metal process.

18. The RF filter according to claim 14, wherein the RF filter comprises: a piezoelectric acoustic integrated circuit comprising the plurality of filter resonators, the acoustic coupling layer, and the plurality of tuned resonators; an interposer coupled to the piezoelectric acoustic integrated circuit, the interposer comprising a plurality of through holes; as well as An IPD or control chip is coupled to the interposer, the IPD or control chip including the plurality of tuning circuits.

19. The RF filter of claim 18, wherein the piezoelectric acoustic integrated circuit is coupled with the interposer via a ball grid array.

20. The RF filter of claim 18, wherein the IPD or control chip is coupled with the interposer via a ball grid array. 21 . The RF filter of claim 18 , wherein the piezoelectric acoustic integrated circuit is fabricated using a first metal process, and the IPD or control chip is fabricated using a second metal process different from the first metal process.

22. The RF filter of claim 14, wherein the RF filter comprises: a piezoelectric acoustic integrated circuit comprising the plurality of filter resonators, the acoustic coupling layer, and the plurality of tuned resonators; as well as An IPD or control chip is coupled to the piezoelectric acoustic integrated circuit, and the IPD or control chip includes the plurality of tuning circuits. 23 . The RF filter of claim 22 , wherein the piezoelectric acoustic integrated circuit is fabricated using a first metal process, and the IPD or control chip is fabricated using a second metal process different from the first metal process.

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