Hybrid bulk acoustic wave filter

Abstract

To provide radio frequency filtering circuitry having a better balance between performance parameters such as electromechanical coupling (and thus bandwidth) and a quality factor.SOLUTION: Radio frequency filtering circuitry includes a first node 26, a second node 28, and a series signal path 30 between the first node and the second node. A number of acoustic resonators are coupled to one or more of the first node and the second node via the series signal path. A first acoustic resonator R1 out of the acoustic resonators is associated with a first quality factor and a first electromechanical coupling coefficient. A second acoustic resonator R2 out of the acoustic resonators is associated with a second quality factor and a second electromechanical coupling coefficient. The first quality factor is different from the second quality factor and the first electromechanical coupling coefficient is different from the second electromechanical coupling coefficient.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a filtering circuit for radio frequency (RF) signals, specifically, a filtering circuit for RF signals including bulk acoustic wave (BAW) resonators.

Background Art

[0002] Acoustic wave devices are widely used in modern electronic devices. At a high level, an acoustic wave device includes a piezoelectric material in contact with one or more electrodes. Piezoelectric materials acquire electric charge when compressed, twisted, or distorted, and similarly compress, twist, or distort when an electric charge is applied to them. Thus, when an alternating electrical signal is applied to one or more electrodes in contact with a piezoelectric material, a corresponding mechanical signal (i.e., a rocking or vibration) is transmitted therein. Based on other factors such as the characteristics of the one or more electrodes on the piezoelectric material, the properties of the piezoelectric material, and the shape of the acoustic wave device and other structures provided on the device, the mechanical signal converted within the piezoelectric material exhibits frequency dependence on the alternating electrical signal. Acoustic wave devices utilize this frequency dependence to provide one or more functions such as filtering.

[0003] Exemplary acoustic wave devices include BAW resonators, which are increasingly used to form filters used in the transmission and reception of RF signals for communication. Due to the stringent requirements for filters in modern RF communication systems such as the specifications of fifth-generation (5G) wireless networks, acoustic wave devices for these applications need to provide a high quality factor and high bandwidth (which can be achieved by high electro-mechanical coupling).

Summary of the Invention

[0004] In one embodiment, the RF filtering circuit comprises a first node, a second node, and a series signal path between the first and second nodes. Several acoustic resonators are coupled to the first and second nodes via the series signal path. The first acoustic resonator among the acoustic resonators is associated with a first quality factor and a first electromechanical coupling coefficient. The second acoustic resonator among the acoustic resonators is associated with a second quality factor and a second electromechanical coupling coefficient. The first quality factor is different from the second quality factor, and the first electromechanical coupling coefficient is different from the second electromechanical coupling coefficient. A better balance between performance parameters such as electromechanical coupling (and therefore bandwidth) and quality factors can be achieved for the RF filtering circuit by providing some acoustic resonators to satisfy a first set of performance criteria and others to satisfy a second set of performance criteria.

[0005] Each of the acoustic resonators may include a first electrode, a piezoelectric layer on the first electrode, and a second electrode on the piezoelectric layer such that the piezoelectric layer is between the first electrode and the second electrode.

[0006] The piezoelectric material of the first acoustic resonator among the acoustic resonators may be different from the piezoelectric material of the second acoustic resonator among the acoustic resonators. In particular, the first acoustic resonator among the acoustic resonators may include a piezoelectric layer containing the first piezoelectric material, and the second acoustic resonator among the acoustic resonators may include a piezoelectric layer containing the second piezoelectric material.

[0007] In one embodiment, the first piezoelectric material comprises intrinsic aluminum nitride, and the second piezoelectric material comprises scandium-doped aluminum nitride.

[0008] In another embodiment, the first piezoelectric material comprises aluminum nitride doped with scandium at a first doping concentration, and the second piezoelectric material comprises aluminum nitride doped with scandium at a second doping concentration greater than the first doping concentration.

[0009] Those skilled in the art will understand the scope of this disclosure and realize additional embodiments thereof after reading the following detailed description of preferred embodiments associated with the accompanying drawings. [Brief explanation of the drawing]

[0010] The accompanying drawings incorporated herein and forming part of herein illustrate several aspects of this disclosure and serve to illustrate the principles of this disclosure together with the description.

[0011] [Figure 1A] Cross-sectional views of acoustic resonators according to various embodiments of this disclosure are shown. [Figure 1B] Cross-sectional views of acoustic resonators according to various embodiments of this disclosure are shown. [Figure 2] This graph shows the relationship between quality factors, electromechanical coupling, and doping concentration in a piezoelectric layer. [Figure 3] This is a schematic diagram showing an RF filtering circuit according to one embodiment of the present disclosure. [Figure 4A] This graph shows the relationship between quality factors, input impedance, and frequency in various embodiments of the present disclosure of an RF filtering circuit. [Figure 4B] This graph shows the relationship between quality factors, input impedance, and frequency in various embodiments of the present disclosure of an RF filtering circuit. [Figure 5A] This is a graph showing the relationship between input impedance, S21, and the frequency of the RF filtering circuit in various embodiments of the present disclosure. [Figure 5B] This is a graph showing the relationship between input impedance, S21, and the frequency of the RF filtering circuit in various embodiments of the present disclosure. [Figure 6A] This graph shows the filter response of an RF filtering circuit according to various embodiments of the present disclosure. [Figure 6B] This graph shows the filter response of an RF filtering circuit according to various embodiments of the present disclosure. [Figure 7] This is a schematic diagram showing an RF filtering circuit according to one embodiment of the present disclosure. [Modes for carrying out the invention]

[0012] The embodiments described below provide the information necessary to enable those skilled in the art to carry out the embodiments and illustrate the best mode of carrying out the embodiments. By reading the following description in reference to the accompanying drawings, those skilled in the art will understand the concepts of this disclosure and recognize the uses of these concepts not specifically addressed herein. It should be understood that these concepts and uses fall within the scope of this disclosure and the accompanying claims.

[0013] In this specification, various elements may be described using terms such as "first," "second," etc., but it should be understood that these elements should not be limited by these terms. These terms are used solely to distinguish one element from another. For example, without departing from the scope of this disclosure, a first element may be called a second element, and similarly, a second element may be called a first element. Where used herein, the term "and / or" includes one or more of the associated enumerated items, and all of them, in combination.

[0014] When an element such as a layer, region, or substrate is referred to as being "on top of" another element, or extending "on top of" another element, it should be understood that the element is directly on the other element, can extend directly onto it, or may have an intervening element. In contrast, when an element is referred to as being "directly on top of" another element, or extending "directly onto" another element, there is no intervening element. Similarly, when an element such as a layer, region, or substrate is referred to as being "across" another element, or extending "across" it, it should be understood that the element is directly across another element, can extend directly onto it, or may have an intervening element. In contrast, when an element is referred to as being "directly across" another element, or extending "directly across" another element, there is no intervening element. When an element is described as being "connected" or "joined" to another element, it should be understood that it may be directly connected to, joined to, or have an intermediary element. In contrast, when an element is described as being "directly connected" or "directly joined" to another element, there is no intermediary element.

[0015] In this specification, relative terms such as “downward” or “upward” or “upper side” or “lower side” or “horizontal” or “vertical” may be used to describe the relationship between one element, layer, or region and another, as shown in the figure. It will be understood that these terms and the terms considered above are intended to encompass different orientations of the device in addition to the orientation shown in the figure.

[0016] The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the disclosure. Where used herein, the singular forms “a,” “an,” and “the” are intended to include the plural form unless the context clearly indicates otherwise. Where used herein, the terms “comprises,” “comprising,” “includes,” and / or “including” specify the presence of the described features, integers, steps, actions, elements, and / or components, but should be further understood not to exclude the presence or addition of one or more other features, integers, steps, actions, elements, components, and / or groups thereof.

[0017] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as those generally understood by those skilled in the art to which this disclosure belongs. It should be further understood that terms used herein should be construed to have meanings consistent with their meanings in the context of this specification and related art, and not to be construed in an idealized or overly formal sense unless expressly defined herein.

[0018] Figure 1A shows an acoustic resonator 10 according to one embodiment of the present disclosure. The acoustic resonator 10 includes a substrate 12, a reflector 14 on the substrate, the reflector 14 comprising several reflector layers 16 having alternating material properties (indicated as reflector layers 16A and 16B) to provide a Bragg reflector, a first electrode 18 on the reflector 14, a piezoelectric layer 20 on the first electrode 18, and a second electrode 22 on the piezoelectric layer 20 such that the piezoelectric layer 20 is between the first electrode 18 and the second electrode 22.

[0019] In one embodiment, the substrate 12 includes silicon. The reflector 14 may include alternating layers of silicon oxide (e.g., layer 16A may include silicon oxide) and tungsten (e.g., layer 16B may include tungsten). The first electrode 18 and the second electrode 22 may include molybdenum. In particular, the materials described above for the substrate 12, the reflector 14, the first electrode 18, and the second electrode 22 are merely exemplary, and those skilled in the art will readily understand that many different materials may be used for these layers without departing from the principles described herein.

[0020] The piezoelectric layer 20 may include aluminum nitride. As discussed above, to meet the high requirements of modern wireless communication standards such as those proposed for 5G networks, an increase in the electromechanical coupling, and thus the bandwidth, for acoustic resonators forming RF filtering circuits is desired. To increase the electromechanical coupling of the acoustic resonator 10, the piezoelectric layer 20 may be provided as scandium-doped aluminum nitride. Providing the piezoelectric layer 20 as scandium-doped aluminum nitride increases the electromechanical coupling and thus increases the bandwidth of the acoustic resonator 10. However, the increase in electromechanical coupling comes at the expense of a reduction in the quality factor. Since the same modern wireless communication standards discussed above also require a high quality factor, it is difficult to provide an RF filtering circuit that meets both the requirements of electromechanical coupling (and thus bandwidth) and the quality factor.

[0021] FIG. 1B shows an acoustic resonator 10 according to an additional embodiment of the present disclosure. The acoustic resonator 10 shown in FIG. 1B is substantially the same as that discussed above with respect to FIG. 1A, except that the reflector 14 is removed and an air cavity 23 is provided under the first electrode 18 such that the acoustic resonator is a thin film bulk acoustic resonator rather than a resonator firmly mounted as shown in FIG. 1A. As will be readily understood by those skilled in the art, the principles of the present disclosure apply to any type of acoustic resonator.

[0022] Figure 2 is a graph showing the relationship between the scandium doping percentage in the aluminum nitride of the piezoelectric layer 20, the quality factor, and the electromechanical coupling of the acoustic resonator 10. Specifically, Figure 2 shows the solid vertical axis and line representing the quality factor, the dashed vertical axis and line representing the electromechanical coupling, and the horizontal axis representing the doping concentration. As shown, as the scandium doping concentration increases from left to right, the electromechanical coupling increases while the quality factor decreases. As discussed above, it is desirable to have both high electromechanical coupling and a high quality factor for acoustic resonators used in modern RF filtering circuits.

[0023] Figure 3 is a schematic diagram showing an RF filtering circuit 24 according to one embodiment of the present disclosure. The RF filtering circuit 24 includes a first node 26, a second node 28, a series signal path 30 between the first node 26 and the second node 28, and several shunt signal paths 32 between the series signal path 30 and ground. A first acoustic resonator R1 is coupled between the first node 26 and a first intermediate node 34A. A second acoustic resonator R2 and a first inductor L1 are coupled in series between the first intermediate node 34A and ground to provide a first shunt signal path 32A. A third acoustic resonator R3 is coupled between the first intermediate node 34A and a second intermediate node 34B. A fourth acoustic resonator R4 and a second inductor L2 are coupled in series between the second intermediate node 34B and ground to provide a second shunt signal path 32B. The fifth acoustic resonator R5 is coupled between the second intermediate node 34B and the third intermediate node 34C. The sixth acoustic resonator R6 and the third inductor L3 are coupled between the third intermediate node 34C and ground to provide the third shunt signal path 32C. The seventh acoustic resonator R7 is coupled between the third intermediate node 34C and the fourth intermediate node 34D. The eighth acoustic resonator R8 and the fourth inductor L4 are coupled in series between the fourth intermediate node 34D and ground to provide the fourth shunt signal path 32D. The ninth acoustic resonator R9 is coupled between the fourth intermediate node 34D and the fifth intermediate node 34E. The tenth acoustic resonator R10 and the fifth inductor L5 are coupled in series between the fifth intermediate node 34E and ground to provide the fifth shunt signal path 32E. The eleventh acoustic resonator R11 is coupled between the fifth intermediate node 34E and the second node 28. The twelfth acoustic resonator R12 and the sixth inductor L6 are coupled in series between the second node 28 and ground to provide the sixth shunt signal path 32F.

[0024] It should be noted that the RF filtering circuit 24 shown in Figure 3 is merely illustrative. Those skilled in the art will understand that the number of acoustic resonators and inductors, as well as their arrangement between the first node 26 and the second node 28 and ground, will vary based on the specific specifications of the RF filtering circuit 24. The concepts described herein also apply to all topologies of RF filtering circuits, including ladder topology, grid topology, cross topology, or any other type of topology.

[0025] In general, the acoustic resonators (R1-R12) within the RF filtering circuit 24 are uniform in terms of their performance characteristics, such as electromechanical coupling (and therefore bandwidth) and quality factors. This is because all acoustic resonators (R1-R12) utilize the same material for their piezoelectric layer 20. For example, all acoustic resonators (R1-R12) have a piezoelectric layer 20 which is either a unique aluminum nitride or aluminum nitride doped with scandium. Due to the trade-off between quality factors and electromechanical coupling discussed above with respect to these materials, this results in suboptimal performance of the RF filtering circuit 24 with respect to either electromechanical coupling (and therefore bandwidth) or quality factors.

[0026] To achieve a better trade-off between electromechanical coupling and quality factors, it is proposed herein to provide some acoustic resonators (R1-R12) having a first electromechanical coupling coefficient and a first quality factor, and the remaining acoustic resonators (R1-R12) having a second electromechanical coupling coefficient and a second quality factor. The first electromechanical coupling coefficient is different from the second coupling coefficient, and the first quality factor is different from the second quality factor. In particular, the first electromechanical coupling coefficient may be smaller than the second electromechanical coupling coefficient, and the first quality factor may be larger than the second quality factor. This approach, in which some of the acoustic resonators (R1-R12) are configured to meet the first set of performance criteria and the remaining acoustic resonators (R1-R12) are configured to meet the second set of performance criteria, is called a hybrid approach.

[0027] One way to achieve a hybrid approach is to provide piezoelectric layers 20 for some of the acoustic resonators (R1-R12) containing a first piezoelectric material (providing a first quality factor and a first electromechanical coupling coefficient), and piezoelectric layers 20 for the remaining acoustic resonators (R1-R12) containing a second piezoelectric material different from the first piezoelectric material (providing a second quality factor and a second electromechanical coupling coefficient). In the exemplary RF filtering circuit 24 described above, the second acoustic resonator R2 and the twelfth acoustic resonator R12 may have piezoelectric layers 20 containing the first piezoelectric material, while the remaining acoustic resonators (R1 and R3-R11) may have piezoelectric layers 20 containing the second piezoelectric material. In one embodiment, the first piezoelectric material is intrinsic aluminum nitride, and the second piezoelectric material is scandium-doped aluminum nitride. This configuration can also be reversed so that the first piezoelectric material is scandium-doped aluminum nitride and the second piezoelectric material is intrinsic aluminum nitride. In another embodiment, the first piezoelectric material is aluminum nitride doped with scandium at a first concentration, and the second piezoelectric material is aluminum nitride doped with scandium at a second doping concentration greater than the first doping concentration. In one embodiment, the second doping concentration is at least 1% higher than the first doping concentration. The disclosure also envisions embodiments in which the second doping concentration is more than 1% higher than the first doping concentration. In various embodiments, the second doping concentration may be at least 2%, at least 3%, at least 4%, at least 5%, etc., higher than the first doping concentration. It should be noted that the disclosure is not limited to aluminum nitride for the first and second piezoelectric materials. In various embodiments, the first and second piezoelectric materials may be any combination of lithium tantalate, zinc oxide, and lead zirconate titanate. Furthermore, the disclosure is not limited to scandium as a dopant. In various embodiments, the dopant may be any combination of co-dopes of multiple elements such as gallium, yttrium, chromium, or magnesium and zirconium, as well as magnesium and titanium.Those skilled in the art will understand that the materials described above are merely examples and that the principles of this disclosure apply to any piezoelectric material and / or dopant.

[0028] Notably, the embodiments discussed above describe a second acoustic resonator R2 and a twelfth acoustic resonator R12 having a piezoelectric layer 20 containing a first piezoelectric material, as well as the remaining acoustic resonators (R1 and R3-R11) having a piezoelectric layer 20 containing a second piezoelectric material, but any one of the acoustic resonators (R1-R12) may have a piezoelectric layer 20 containing a different piezoelectric material than any other one of the acoustic resonators (R1-R12). In some embodiments, one of the acoustic resonators (R1-R12) having a piezoelectric layer 20 containing a first piezoelectric material is provided to one or more of the shunt signal paths 32. In other embodiments, one of the acoustic resonators (R1-R12) having a piezoelectric layer 20 containing a first piezoelectric material is provided to the series signal path 30. In yet another embodiment, one of the acoustic resonators (R1-R25) having a piezoelectric layer 20 containing a first piezoelectric material is provided to both the series signal path 30 and one or more of the shunt signal paths 32. Generally, a person skilled in the art may use a piezoelectric layer 20 having a material that provides higher electromechanical coupling within the acoustic resonators (R1-R12) involved in providing the passband of the filter response of the RF filtering circuit 24, or conversely, a piezoelectric layer 20 having a material that provides higher quality factors within the acoustic resonators (R1-R12) involved in providing the edge of the filter response of the RF filtering circuit 24.

[0029] As discussed above, in conventional designs, the acoustic resonators (R1-R12) of the RF filtering circuit 24 would be provided to have a uniform piezoelectric layer 20. Therefore, the acoustic resonators (R1-R12) of the RF filtering circuit 24 would generally be provided on a single acoustic die. In some embodiments, all acoustic resonators (R1-R12) in the RF filtering circuit 24 are provided on the same acoustic die. Such an approach may require more advanced die forming techniques due to differences in the material and / or doping of the piezoelectric layer 20 of the acoustic resonators (R1-R12). In other embodiments, to simplify the forming of the RF filtering circuit 24, the acoustic resonators (R1-R12) may be provided on separate dies based on the material used for their piezoelectric layer 20. For example, the first acoustic die may be used for one of the acoustic resonators (R1 to R12) having a piezoelectric layer 20 containing a first piezoelectric material, while the second acoustic die may be used for one of the acoustic resonators (R1 to R12) having a piezoelectric layer 20 containing a second piezoelectric material.

[0030] The above embodiments envision a first subset of acoustic resonators having a piezoelectric layer 20 containing a first piezoelectric material and a second subset of acoustic resonators having a piezoelectric layer 20 containing a second piezoelectric material. However, the disclosure also applies to RF filtering circuits in which these acoustic resonators are divided into any number of subsets, each having a different piezoelectric material. For example, the disclosure applies to RF filtering circuits having a first subset of acoustic resonators in which the piezoelectric layer 20 is intrinsic aluminum nitride, a second subset of acoustic resonators in which the piezoelectric layer 20 is aluminum nitride doped with scandium at a first doping concentration, and a third subset of acoustic resonators in which the piezoelectric layer 20 is aluminum nitride doped with scandium at a second doping concentration higher than the first doping concentration. Those skilled in the art will recognize that the disclosure generally envisions the use of different piezoelectric materials for different subsets of acoustic resonators in RF filtering circuits to improve their performance.

[0031] Figures 4A and 4B are graphs showing the input impedance and quality factors of acoustic resonators having a uniquely doped piezoelectric layer (e.g., aluminum nitride) and a doped piezoelectric layer (e.g., scandium-doped aluminum nitride), respectively. In particular, the solid lines in the graphs shown in Figures 4A and 4B illustrate the input impedance, while the dashed lines illustrate the Bode plot of the quality factor. As shown, the distance between the resonant frequency and anti-resonant frequency of the acoustic resonator with the uniquely doped piezoelectric layer is relatively small compared to the acoustic resonator with the doped piezoelectric layer. This indicates that the acoustic resonator with the doped piezoelectric layer has higher electromechanical coupling and bandwidth than the acoustic resonator with the unique piezoelectric layer. The graphs also show a significantly higher quality factor for the acoustic resonator with the unique piezoelectric layer, thus illustrating the trade-off between electromechanical coupling (and therefore bandwidth) and the quality factor discussed above.

[0032] Figures 5A and 5B are graphs showing the input impedance and S-parameter (|S21|) of a pair of acoustic resonators, where in Figure 5A, both acoustic resonators contain a doped piezoelectric layer (e.g., scandium-doped aluminum nitride), and in Figure 5B, one of the pair of acoustic resonators contains a unique piezoelectric layer, while the other acoustic resonator contains a doped piezoelectric layer (e.g., aluminum nitride). In Figures 5A and 5B, the solid line represents |S21|, the dashed line represents the input impedance of the first acoustic resonator of the pair, and the dotted and dashed lines represent the input impedance of the second acoustic resonator of the pair (in Figure 5B, the first acoustic resonator of the pair contains a unique piezoelectric layer, while the second acoustic resonator of the pair contains a doped piezoelectric layer). Comparing Figure 5A with Figure 5B, Figure 5B shows a greater slope at the lower band edge and therefore lower losses.

[0033] Figure 6A is a graph showing the rejection of the RF filtering circuit 24 around the industrial, scientific, and medical (ISM) bands. In Figure 6A, the dashed line represents the performance of the RF filtering circuit 24 when all of its acoustic resonators have a piezoelectric layer made of the same material (e.g., intrinsic aluminum nitride), and the solid line represents the performance of the RF filtering circuit 24 when some of the acoustic resonators have piezoelectric layers containing different materials from the rest of the acoustic resonators (e.g., intrinsic aluminum nitride and scandium-doped aluminum nitride), as discussed above. The hatched boxes in the graph indicate the desired rejection of the ISM band. As shown, the slope and therefore rejection of the ISM band is improved when a hybrid approach is used in which some of the acoustic resonators have piezoelectric layers containing different materials from the others to provide high electromechanical coupling to some of the acoustic resonators and a high quality factor to one of the other acoustic resonators.

[0034] Figure 6B is a graph showing the insertion loss of the RF filtering circuit 24 within the band of interest. As shown in Figure 6A, the dashed line represents the performance of the RF filtering circuit 24 when all of its acoustic resonators have a piezoelectric layer made of the same material (e.g., intrinsic aluminum nitride), while the solid line represents the performance of the RF filtering circuit 24 when some of the acoustic resonators have different piezoelectric materials than the rest (e.g., intrinsic aluminum nitride and scandium-doped aluminum nitride), as discussed above. The hatched boxes in the graph indicate the band of interest. As shown, the hybrid approach, in which some of the acoustic resonators have different piezoelectric materials than the others, results in a higher bandwidth and therefore lower losses at the bottom of the band of interest.

[0035] In short, the graphs in Figures 5A, 5B, 6A, and 6B show that a subset of acoustic resonators, by using a hybrid approach in which the piezoelectric layer has a different material from the rest of the acoustic resonator, such as those discussed above, results in a better trade-off between electromechanical coupling (and therefore bandwidth) and quality factors than an approach in which all acoustic resonators in the RF filtering circuit have a uniform piezoelectric layer and therefore the same relationship between electromechanical coupling, bandwidth, and quality factors.

[0036] As discussed above, the RF filtering circuit 24 shown in Figure 3 is merely illustrative. The principles of this disclosure can be applied to any topology of RF filtering circuits, including single-band filters, diplexers, triplexers, and the like. Accordingly, Figure 7 shows an RF filtering circuit 24 configured as a diplexer. The RF filtering circuit 24 includes a first node 26, a second node 28, a series signal path 30 between the first node 26 and the second node 28, and several shunt signal paths 32 between the series signal path 30 and ground. The configuration of the series signal path 30 and the shunt signal paths 32 coupled to it is similar to the configuration shown in Figure 2. In particular, the first input output inductor LIO1 is coupled between the first node 26 and ground. The first acoustic resonator R1 is coupled between the first node 26 and the first intermediate node 34A. The second acoustic resonator R2 and the first inductor L1 are coupled in series between the first intermediate node 34A and ground to provide the first shunt signal path 32A. The third acoustic resonator R3 is coupled between the first intermediate node 34A and the second intermediate node 34B. The fourth acoustic resonator R4 and the second inductor L2 are coupled in series between the second intermediate node 34B and ground to provide the second shunt signal path 32B. The fifth acoustic resonator R5 is coupled between the second intermediate node 34B and the third intermediate node 34C. The sixth acoustic resonator R6 and the third inductor L3 are coupled between the third intermediate node 34C and ground to provide the third shunt signal path 32C. The seventh acoustic resonator R7 is coupled between the third intermediate node 34C and the fourth intermediate node 34D. The eighth acoustic resonator R8 and the fourth inductor L4 are coupled in series between the fourth intermediate node 34D and ground to provide the fourth shunt signal path 32D. The ninth acoustic resonator R9 is coupled between the fourth intermediate node 34D and the fifth intermediate node 34E. The tenth acoustic resonator R10 and the fifth inductor L5 are coupled in series between the fifth intermediate node 34E and ground to provide the fifth shunt signal path 32E. The eleventh acoustic resonator R11 is coupled between the fifth intermediate node 34E and the sixth intermediate node 34F.The 12th acoustic resonator R12 and the 6th inductor L6 are coupled in series between the 6th intermediate node 34F and ground to provide the 6th shunt signal path 32F. The 2nd input output inductor LIO2 is coupled between the 6th intermediate node 34F and the 2nd node 28.

[0037] The RF filtering circuit 24 further includes a third node 38, an additional series signal path 40 coupled between the first node 26 and the third node 38, and several additional shunt signal paths 42 coupled between the additional series signal path 40 and ground. A 13th acoustic resonator R13 is coupled between the first node 26 and the 7th intermediate node 34G. A 14th acoustic resonator R14 and the 7th inductor L7 are coupled in series between the 7th intermediate node 34G and ground to provide a first additional shunt signal path 42A. A 15th acoustic resonator R15 is coupled between the 7th intermediate node 34G and the 8th intermediate node 34H. A 16th acoustic resonator R16 and the 8th inductor L8 are coupled in series between the 8th intermediate node 34H and ground to provide a second additional shunt signal path 42B. The 17th acoustic resonator R17 is coupled between the 8th intermediate node 34H and the 9th intermediate node 34I. The 18th acoustic resonator R18 and the 9th inductor L9 are coupled in series between the 9th intermediate node 34I and ground to provide a third additional shunt signal path 42C. The 19th acoustic resonator R19 is coupled between the 9th intermediate node 34I and the 10th intermediate node 34J. The 20th acoustic resonator R20 and the 10th inductor L10 are coupled in series between the 10th intermediate node 34J and ground to provide a fourth additional shunt signal path 42D. The 21st acoustic resonator R21 is coupled between the 10th intermediate node 34J and the 11th intermediate node 34K. The 22nd acoustic resonator R22 and the 11th inductor L11 are coupled in series between the 11th intermediate node 34K and ground to provide a fifth additional shunt signal path 42E. The 23rd acoustic resonator R23 is coupled between the 11th intermediate node 34K and the 12th intermediate node 34L. The 24th acoustic resonator R24 ​​is coupled in series with the 12th inductor L12 between the 12th intermediate node 34L and ground to provide a sixth additional shunt signal path 42F. The third input output inductor LIO3 is coupled between the 12th intermediate node 34L and the third node 38.

[0038] Those skilled in the art will understand that the RF filtering circuit 24 shown in Figure 7 is merely illustrative. The number of acoustic resonators, as well as their arrangement between the first node 26, the second node 28, the third node 38 and ground, will vary based on the specific specifications of the RF filtering circuit 24. The concepts described herein apply equally to all topologies of RF filtering circuits, including grid and modified grid topologies.

[0039] The RF filtering circuit 24 shown in Figure 7 may provide a diplexer function such that signals in the first RF band are separated and passed between the first node 26 and the second node 28, and RF signals in the second RF band are separated and passed between the first node 26 and the third node 38. Using a hybrid approach as considered above may involve providing piezoelectric layers 20 containing the first piezoelectric material to the second acoustic resonator R2, the twelfth acoustic resonator R12, the thirteenth acoustic resonator R13, the fifteenth acoustic resonator R15, the twenty-first acoustic resonator R21, and the twenty-third acoustic resonator R23, and providing piezoelectric layers 20 containing a second piezoelectric material different from the first piezoelectric material to the remaining acoustic resonators (R1, R3-R11, R14, R16-R20, R22, and R24). In one embodiment, the first piezoelectric material is intrinsic aluminum nitride, and the second piezoelectric material is scandium-doped aluminum nitride. In another embodiment, the first piezoelectric material is scandium-doped aluminum nitride at a first concentration, and the second piezoelectric material is scandium-doped aluminum nitride at a second doping concentration greater than the first doping concentration. In one embodiment, the second doping concentration is 1% higher than the first doping concentration. The disclosure also envisions embodiments in which the second doping concentration is more than 1% higher than the first doping concentration. In various embodiments, the second doping concentration may be at least 2%, at least 3%, at least 4%, at least 5%, etc., higher than the first doping concentration.

[0040] In particular, any one of the acoustic resonators (R1-R24) may have a piezoelectric layer 20 containing a different material than any other of the acoustic resonators (R1-R24). Generally, a person skilled in the art may use a piezoelectric layer 20 having a material that provides higher electromechanical coupling within the acoustic resonators (R1-R24) involved in providing the passband of the filter response, while using a piezoelectric layer 20 having a material that provides a higher quality factor within the acoustic resonators (R1-R24) involved in providing the edge of the filter response of the RF filtering circuit 24.

[0041] As discussed above, in conventional designs, the acoustic resonators (R1-R24) of the RF filtering circuit 24 would be provided to have a uniform piezoelectric layer 20. Therefore, the acoustic resonators (R1-R24) of the RF filtering circuit 24 would generally be provided on a single acoustic die. In some embodiments, all acoustic resonators (R1-R24) are similarly provided on the same acoustic die. Such an approach may require more advanced die forming techniques due to differences in the materials and / or doping in the piezoelectric layer 20 of the acoustic resonators (R1-R24). In other embodiments, to simplify the forming of the RF filtering circuit 24, the acoustic resonators (R1-R24) may be separated onto separate dies based on the material used for their piezoelectric layer 20. For example, the first acoustic die may be used for one of the acoustic resonators (R1 to R24) having a piezoelectric layer 20 containing a first piezoelectric material, while the second acoustic die may be used for one of the acoustic resonators (R1 to R24) having a piezoelectric layer 20 containing a second piezoelectric material.

[0042] The above embodiments envision a first subset of acoustic resonators having a piezoelectric layer 20 containing a first piezoelectric material, and a second subset of acoustic resonators having a piezoelectric layer 20 containing a second piezoelectric material. However, the disclosure also applies to RF filtering circuits in which these acoustic resonators are divided into any number of subsets, each having a different piezoelectric material. For example, the disclosure applies to RF filtering circuits having a first subset of acoustic resonators in which the piezoelectric layer 20 is intrinsic aluminum nitride, a second subset of acoustic resonators in which the piezoelectric layer 20 is aluminum nitride doped with scandium at a first doping concentration, and a third subset of acoustic resonators in which the piezoelectric layer 20 is aluminum nitride doped with scandium at a second doping concentration higher than the first doping concentration. Those skilled in the art will recognize that the disclosure generally envisions the use of different piezoelectric materials for different subsets of acoustic resonators in RF filtering circuits to improve their performance.

[0043] Those skilled in the art will recognize improvements and modifications to preferred embodiments of this disclosure. All such improvements and modifications are considered within the concepts disclosed herein and the claims that follow.

Claims

1. 1. A high frequency filtering circuit, comprising: a first node and a second node; a series signal path between the first node and the second node; a plurality of acoustic resonators, each coupled to one or more of the first node and the second node via the series signal path; a first acoustic resonator of the plurality of acoustic resonators includes a first piezoelectric layer including an intrinsic piezoelectric material, the first acoustic resonator of the plurality of acoustic resonators being associated with a first quality factor and a first electromechanical coupling coefficient; a plurality of acoustic resonators, the second of the plurality of acoustic resonators including a second piezoelectric layer including a doped piezoelectric material, the second of the plurality of acoustic resonators being associated with a second quality factor and a second electromechanical coupling coefficient such that the first quality factor is different from the second quality factor and such that the first electromechanical coupling coefficient is different from the second electromechanical coupling coefficient.

2. the first piezoelectric layer is disposed between a first electrode and a second electrode of the first acoustic resonator of the plurality of acoustic resonators; The high frequency filtering circuit of claim 1 , wherein the second piezoelectric layer is disposed between a first electrode and a second electrode of the second acoustic resonator of the plurality of acoustic resonators.

3. The high frequency filtering circuit of claim 1 , further comprising one or more shunt signal paths coupled between the series signal path and ground.

4. the first acoustic resonator of the plurality of acoustic resonators is coupled in the series signal path; The high frequency filtering circuit of claim 3 , wherein the second acoustic resonator of the plurality of acoustic resonators is coupled within one of the one or more shunt signal paths.

5. the first acoustic resonator of the plurality of acoustic resonators is coupled within one of the one or more shunt signal paths; The high frequency filtering circuit of claim 3 , wherein the second acoustic resonator of the plurality of acoustic resonators is coupled in the series signal path.

6. The high frequency filtering circuit of claim 1 , wherein an acoustic resonator of the plurality of acoustic resonators is a bulk acoustic wave resonator.

7. the intrinsic piezoelectric material is intrinsic aluminum nitride; 4. A high frequency filtering circuit as claimed in claim 1, wherein said doped piezoelectric material is scandium doped aluminum nitride.

8. 2. The high frequency filtering circuit of claim 1, further comprising a first acoustic die and a second acoustic die, wherein the first acoustic resonator of the plurality of acoustic resonators is provided on the first acoustic die and the second acoustic resonator of the plurality of acoustic resonators is provided on the second acoustic die.

9. The high frequency filtering circuit of claim 1 , wherein the first acoustic resonator of the plurality of acoustic resonators and the second acoustic resonator of the plurality of acoustic resonators are provided on a same acoustic die.

10. 1. A high frequency filtering circuit, comprising: a first node and a second node; a series signal path between the first node and the second node; a plurality of acoustic resonators, each coupled to one or more of the first node and the second node via the series signal path; a first acoustic resonator of the plurality of acoustic resonators includes a first piezoelectric layer including a piezoelectric material including a dopant at a first doping concentration, the first acoustic resonator of the plurality of acoustic resonators being associated with a first quality factor and a first electromechanical coupling coefficient; a plurality of acoustic resonators, wherein a second acoustic resonator of the plurality of acoustic resonators includes a second piezoelectric layer including a piezoelectric material including a dopant at a second doping concentration greater than the first doping concentration, and the second acoustic resonator of the plurality of acoustic resonators is associated with a second quality factor and a second electromechanical coupling coefficient, the second electromechanical coupling coefficient being different from the first electromechanical coupling coefficient.

11. 11. The high frequency filtering circuit of claim 10, wherein the piezoelectric material is aluminum nitride and the dopant is scandium.

12. The high frequency filtering circuit of claim 10 , further comprising one or more shunt signal paths coupled between the series signal path and ground.

13. the first acoustic resonator of the plurality of acoustic resonators is coupled in the series signal path; The high frequency filtering circuit of claim 12 , wherein the second acoustic resonator of the plurality of acoustic resonators is coupled within one of the one or more shunt signal paths.

14. the first acoustic resonator of the plurality of acoustic resonators is coupled within one of the one or more shunt signal paths; The high frequency filtering circuit of claim 12 , wherein the second acoustic resonator of the plurality of acoustic resonators is coupled in the series signal path.

15. The high frequency filtering circuit of claim 10 , wherein an acoustic resonator of the plurality of acoustic resonators is a bulk acoustic wave resonator.

16. 11. The high frequency filtering circuit of claim 10, wherein the piezoelectric material of the first and second piezoelectric layers comprises scandium doped aluminum nitride.

17. 11. The high frequency filtering circuit of claim 10, further comprising a first acoustic die and a second acoustic die, the first acoustic resonator of the plurality of acoustic resonators being provided on the first acoustic die and the second acoustic resonator of the plurality of acoustic resonators being provided on the second acoustic die.

18. The high frequency filtering circuit of claim 10 , wherein the first acoustic resonator of the plurality of acoustic resonators and the second acoustic resonator of the plurality of acoustic resonators are provided on a same acoustic die.

19. 11. The high frequency filtering circuit of claim 10, wherein the second doping concentration is 1% higher than the first doping concentration.

20. the first piezoelectric layer is disposed between a first electrode and a second electrode of the first acoustic resonator of the plurality of acoustic resonators; The high frequency filtering circuit of claim 10 , wherein the second piezoelectric layer is disposed between a first electrode and a second electrode of the second acoustic resonator of the plurality of acoustic resonators.

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