Bulk acoustic wave filter circuits of adjustable inductive impedance
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- QORVO US INC
- Filing Date
- 2026-01-20
- Publication Date
- 2026-08-06
Smart Images
Figure US2026011797_06082026_PF_FP_ABST
Abstract
Description
Attorney Docket No. 62306.114WO01BULK ACOUSTIC WAVE FILTER CIRCUITS OF ADJUSTABLE INDUCTIVE IMPEDANCE RELATED APPLICATIONS
[0001] The present application claims the benefit of U.S. Provisional Application No. 63 / 752,283, filed January 31, 2025, which is incorporated herein by reference in its entiretyFIELD OF THE INVENTION
[0002] This disclosure relates to bulk acoustic wave (BAW) structures. In particular, this disclosure relates to BAW filter circuits of adjustable inductive impedance.BACKGROUND
[0003] Acoustic wave devices are widely used in modem electronics. At a high level, acoustic wave devices include a piezoelectric material in contact with one or more electrodes. Piezoelectric materials acquire a charge when compressed, twisted, or distorted, and similarly compress, twist, or distort when a charge is applied to them. Accordingly, when an alternating electrical signal is applied to the one or more electrodes in contact with the piezoelectric material, a corresponding mechanical signal (i.e., an oscillation or vibration) is transduced therein. Based on the characteristics of the one or more electrodes on the piezoelectric material, the properties of the piezoelectric material, and other factors such as the shape of the acoustic wave device and other structures provided on the device, the mechanical signal transduced in the piezoelectric material exhibits a frequency dependence on the alternating electrical signal. Acoustic wave devices leverage this frequency dependence to provide one or more functions, such as filtering.
[0004] A Radio Frequency (RF) front-end module (FEM) is an important component in modem wireless communication systems, responsible for processing signal transmission and reception between the antenna and the transmitter (TX) / receiver (RX). These modules are integral to ensuring seamless wireless connectivity in applications such as smartphones, loT (Internet of Things) devices, automotive systems, and satellite communications. A RF FEM typically integrates multiple components, including low-noise amplifiers (LNAs), power amplifiers (PAs), filters, etc. Filters in RF FEMs are used to select specific frequency bands to pass through, reduce interference, supportAttorney Docket No. 62306.114WO01 multi-band operations, etc. The inductive impedances between the TX / RX and LNA / PA need to match to reduce omega loss in a RF FEM.
[0005] Therefore, there is a need to reduce the inductive impedance mismatch between the TX / RX and LNA / PA in a RF FEM.SUMMARY
[0006] Aspects of the present disclosure provide a radio frequency (RF) filter structure. The RF filter structure includes a first terminal and a second terminal communicatively coupled to the first terminal; a first series resonator structure directly communicatively coupled to the first terminal; a second series resonator structure directly communicatively coupled to the second terminal; and a third series resonator structure located between and communicatively coupled to the first series resonator structure and the second series resonator structure. A doping concentration of the first series resonator structure is higher than a doping concentration of the third series resonator structure. A doping concentration of the second series resonator structure is higher than the doping concentration of the third series resonator structure.
[0007] In some embodiments, the doping concentrations of the first series resonator structure and the second series resonator structure are in a range of about 1 * 1020cm’3and about 1 * 1040crn’3; and the doping concentration of the third series resonator structure is in a range of about 1 * 10°cm’3and about 1 * 106cm’3.
[0008] In some embodiments, the doping concentration of the first series resonator structure includes a doping concentration of a piezoelectric layer in the first series resonator structure; the doping concentration of the second series resonator structure includes a doping concentration of a piezoelectric layer in the second series resonator structure; and the doping concentration of the third series resonator structure includes a doping concentration of a piezoelectric layer in the third series resonator structure.
[0009] In some embodiments, the first series resonator structure includes a plurality of bulk acoustic wave (BAW) resonators communicatively coupled in parallel.
[0010] In some embodiments, the second series resonator structure includes a plurality of BAW resonators connected in series.
[0011] In some embodiments, the third series resonator structure includes at least one set of BAW resonators connected in series.
[0012] In some embodiment, dopants in the first series resonator structure, the second series resonator structure, and the third series resonator structure include scandium (Sc).Attorney Docket No. 62306.114WO01
[0013] In some embodiments, the RF filter structure further includes a first shunt resonator structure and a second shunt resonator structure. The third series resonator structure is communicatively coupled between the first shunt resonator structure and the second shunt resonator structure.
[0014] In some embodiments, the RF filter structure further includes a third shunt resonator structure directly and communicatively coupled to the first terminal. The first series resonator structure is communicatively coupled between the first shunt resonator structure and the third shunt resonator structure; and the second series resonator structure is communicatively coupled between the second shunt resonator structure and the second terminal.
[0015] In some embodiments, the first shunt resonator structure, the second shunt resonator structure, and the third shunt resonator structure each includes one or more BAW resonators communicatively coupled in parallel.
[0016] Aspects of the present disclosure provide a RF filter structure. The RF filter structure includes a first terminal and a second terminal; a series signal path communicatively coupled to the first terminal and the second terminal; a first series resonator structure directly communicatively coupled to the first terminal via the series signal path; a second series resonator structure directly communicatively coupled to the second terminal via the series signal path; and a third series resonator structure located between and communicatively coupled to the first series resonator structure and the second series resonator structure via the series signal path. A doping concentration of the first series resonator structure is higher than a doping concentration of the third series resonator structure. A doping concentration of the second series resonator structure is higher than the doping concentration of the third series resonator structure.
[0017] In some embodiments, the doping concentrations of the first series resonator structure and the second series resonator structure are in a range of about 1 x 1020cm-3 and about 1 x 1030cm-3; and the doping concentration of the third series resonator structure is in a range of about 1 x 100cm-3 and about lx!06cm-3.
[0018] In some embodiments, the doping concentration of the first series resonator structure includes a doping concentration of a piezoelectric layer in the first series resonator structure; the doping concentration of the second series resonator structure includes a doping concentration of a piezoelectric layer in the second series resonator structure; and the doping concentration of the third series resonator structure includes a doping concentration of a piezoelectric layer in the third series resonator structure.Attorney Docket No. 62306.114WO01
[0019] In some embodiments, the first series resonator structure includes a plurality of bulk acoustic wave (B AW) resonators communicatively coupled in parallel along the series signal path.
[0020] In some embodiments, the second series resonator structure includes a plurality of BAW resonators connected in series along the series signal path.
[0021] In some embodiments, the third series resonator structure includes at least one set of BAW resonators connected in series.
[0022] In some embodiments, dopants in the first series resonator structure, the second series resonator structure, and the third series resonator structure include scandium (Sc).
[0023] In some embodiments, the RF filter structure further includes a first shunt signal path and a second shunt signal path each communicatively coupled to the series signal path. The third series resonator structure is communicatively coupled between the first shunt signal path and the second shunt signal path.
[0024] In some embodiments, the RF filter structure further includes a third shunt signal path directly and communicatively coupled to the first terminal. The first series resonator structure is communicatively coupled between the first shunt signal path and the third shunt signal path; and the second series resonator structure is communicatively coupled between the second shunt signal path and the second terminal.
[0025] In some embodiments, the first shunt signal path, the second shunt signal path, and the third shunt signal path each includes one or more BAW resonators communicatively coupled in parallel.BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 illustrates an block diagram of an exemplary RF FEM, according to embodiments of the present disclosure.
[0027] FIG. 2A illustrates a block diagram of an exemplary filter circuit, according to embodiments of the present disclosure.
[0028] FIG. 2B illustrates a simplified cross-sectional view of an exemplary BAW resonator in a filter circuit in a RF FEM, according to embodiments of the present disclosure.
[0029] FIG. 3 illustrates an exemplary filter circuit , according to embodiments of the present disclosure.
[0030] FIG. 4A shows examples of input impedances of certain series resonators and a corresponding filter response, according to some embodiments.Attorney Docket No. 62306.114WO01
[0031] FIG. 4B illustrates performance of an exemplary filter circuit with the series resonators in FIG.4A, according to embodiments of the present disclosure.DETAILED DESCRIPTION
[0032] The following detailed description is illustrative in nature and is not intended to limit the scope, applicability, or configuration of inventive embodiments disclosed herein in any way. Rather, the following description provides practical examples, and those skilled in the art will recognize that some of the examples may have suitable alternatives. Embodiments will hereinafter be described in conjunction with the appended drawings, which are not to scale (unless so stated), wherein like numerals / letters denote like elements. However, it will be understood that the use of a number to refer to a component in a given drawing is not intended to limit the component in another drawing labeled with the same number. In addition, the use of different numbers to refer to components in different drawings is not intended to indicate that the different numbered components cannot be the same or similar to other numbered components. Examples of constructions, materials, dimensions and fabrication processes are provided for select elements and all other elements employ that which is known by those skilled in the art.
[0033] As used herein, the term "about" refers to a given amount of value that may vary based on the particular technology node associated with the semiconductor device. Based on a particular technology node, the term "about" can refer to a given amount of value that varies, for example, within 10-30% of the value (e.g., ± 10%, ± 20%, or ± 20% of that value, or ± 30%).
[0034] As used herein, the term “coupling” refers to combining or joining via electricity, and may be interchangeable with “electrically coupling,” “electrically connected,” “connected,” “conductively coupled,” “communicatively coupling”, and / or “conductively connected.”
[0035] Reference will now be made in greater detail to various embodiments of the subject matter of the present disclosure, some embodiments of which are illustrated in the accompanying drawings.
[0036] In a RF FEM, B AW filters with a single doping concentration of scandium (Sc)-doped BAW resonators are often communicatively coupled to TX / RX of high capacitive impedance. Besides that, the Tx / Rx routing trace can add more capacitive impedance on the Tx / Rx impedance due to module environment, such as metal shielding. Therefore, a matching component, such as an inductor, is often used to raise the imaginary part of TX / RX impedance before connecting the BAW filter to the PA / LNA in the RF FEM. However, a large mismatch (typically 0.2-1.0 dB) can occur between routing trace and the matching component. In addition, large capacitive impedanceAttorney Docket No. 62306.114WO01 requires large inductors to raise the imaginary impedance, which also leads more omega loss inside the inductor. In an existing RF FEM, such mismatch and omega loss are hard to avoid.
[0037] Embodiments of the present disclosure provide a BAW filter circuit with adjustable inductive impedance. The inductive impedance of the BAW filter circuit can vary by changing the doping concentration in the BAW resonators in the BAW filter circuit. Specifically, the inductive impedance of the BAW filter circuit can be increased by increasing the doping concentrations in the series BAW resonators that are closest to the terminals (e.g., input terminal and output terminal) of the BAW filter circuit. The BAW resonators further away from the terminals have lower doping concentrations. The dopants in the BAW resonators include scandium (Sc). In various embodiments, the doping concentrations can be varied for the BAW filter circuit to achieve different, e.g., desirable, inductive impedances. The BAW filter circuit can thus compensate the impedance mismatch between TX / RX and the LNA / PA. Mismatch loss can be reduced. In some embodiments, a smaller matching component or no matching component is needed for the RF FEM module, potentially reducing omega loss, size, and / or cost of the RF FEM.
[0038] In the disclosure, by using the BAW filter circuit with resonators of two different Sc doping concentrations and certain filter topology, more inductive impedance can be achieved by the BAW filter circuit itself without trade-off loss. The mismatch loss mentioned above in the TX / RX chain can be reduced. Also, as the needed inductor becomes smaller, the omega loss from the inductor can also be reduced. In general, the proposed technique improve the loss performance, by reducing chain mismatching and omega loss with inductive filter impedance.
[0039] FIG. 1 shows schematics of an exemplary RF FEM 100, according to embodiments of the present disclosure. RF FEM 100 may include a power amplifier (PA) 102, a band select switch (BSSW) 106, a filter A 108a, a filter B 108b, a multiplexer (Mux) 110, an antenna switch (ASW) 112, and an antenna (Ant) 118. An element may be communicatively connected to another element, as shown in FIG. 1, by the lines. In various embodiments, RF FEM may or may not include surface mounted devices (SMDs) 106a and 106b communicatively coupled respectively to filter A 108a and filter B 108b. RF FEM 100 may be part of or connected to a receiver (RX) and / or a transmitter (TX). It should be noted that, RF FEM 100 is merely an example to illustrate an operation environment of a filter of the present disclosure, and is not meant to limit the scope of present disclosure. In various embodiments, a RF FEM may include other components, e.g., more filters, and the number, types, and / or functions of elements should not be limited by the embodiments of the present disclosure.Attorney Docket No. 62306.114WO01
[0040] PA 102 may increase the power of a signal (e.g., an electrical signal or a RF signal). Depending on the application of RF FEM 100, the signal may be transmitted towards Ant 118 or from Ant 118. BSSW 104 may include a switch component close to PA 102 that can disconnect or connect a certain frequency band in an electrical circuit. LNA 114 may include an electrical component that amplifies an incoming signal without significantly degrading its signal-to-noise ratio (SNR). Mux 110 may combine two or more signals to provide a match between the filters and ASW 112. ASW 112 may include a switch component close to Ant 118 to select a frequency for Ant 118. Ant 118 may receive or transmit a signal.
[0041] At least one of filter A 108a and filter B 108b may have adjustable impedance, e.g., increased inductive impedance compared to an existing BAW filter. In some embodiments, filter A 108a and / or filter 108b may include a BAW filter, and the details of the BAW filter is further illustrated in view of FIGS. 2 A, 2B and 3. SMDs 106a and 106b may each include an inductor and / or a capacitor directly mounted on the surface of a die. SMDs 106a and / or 106b may be configured to provide additional inductive impedance between the RX / TX and Ant 118. Compared to an existing RF FEM, because filter A 108a and / or filter B 108b may have higher inductive impedance, SMDs 106a and / or 106b may be smaller or may not be needed, reducing space and cost required to form RF FEM 100.
[0042] In some embodiments, RF FEM 100 may be part of or connected to a TX. Two signals may respectively be transmitted towards Ant 118. For example, a first RF signal may be amplified by PA 102. One or more frequencies in the first signal may be selected by BSSW 104. The frequencies may further be filtered by filter A 108. A second RF signal may be amplified by LNA 114 and filtered by filter B 108b. The filtered first RF signal and filtered second RF signal may be multiplexed in Mux 110. ASW 112 may be switched on or off to select a desired frequency from the multiplexed signal. The selected frequency is then transmitted by Ant 118.
[0043] FIG. 2 A shows a simplified block diagram of a BAW filter circuit 201, according to embodiments of the present disclosure. BAW filters 201 may be an example of filter A 108a and / or filter B 108b. BAW filter circuit 201 may include a first terminal 208 and an second terminal 210, communicatively coupled to each other. In some embodiments, first terminal 208 may be an input terminal and second terminal 210 may be an output terminal; while in some other embodiments, first terminal 208 may be an output terminal and second terminal 210 may be an input terminal. BAW filter circuit 201 may include a series signal path 220 from first terminal 208 to second terminal 210. BAW filter circuit 201 may include a plurality of series resonator structures 212, 214, ... , 2M, and 2N through series signal path 220, M and N being positive integers. BAW filter circuitAttorney Docket No. 62306.114WO01 201 may also include a plurality of shunt resonator structures 222, 224, ..., 2P, and 2Q, P and Q being positive integers. Each shunt resonator structure 222, 224, ..., 2P, 2Q may be communicatively coupled to series signal path 220 and ground (GND). For ease of illustration, the connection / coupling between a shunt resonator structure and series resonator series 220 is shown as a dot. The inductive impedance of BAW filter circuit 210 may be computed as the inductive impedance between first terminal 208 and second terminal 210. In some embodiments, the inductive impedance of BAW filter circuit 210 is adjustable by changing the doping concentrations in series resonator structures 212, 214, ..., 2M, and 2N.
[0044] The doping concentrations of series resonator structures in BAW filter circuit 201 may be manipulated to change, e.g., increase, the inductive impedance between the terminals (e.g., 208 and 210) until the omega loss between the terminal is optimized (e.g., minimized or is below a predetermined threshold level). In some embodiments, the doping concentrations of series resonator structures closer to one of the terminals (e.g., 208 and 210) may be higher than the doping concentrations of series resonator structures farther away from both terminals to increase the inductive impedance between the terminals. For example, the doping concentrations of series resonator structures that are closest and in direct electrical connection with a terminal may be higher than the other series resonator structures. As shown in FIG. 2A, the doping concentration of series resonator structure 212 may be higher than the doping concentrations of series resonator structures 214, ..., 2M; and the doping concentration of series resonator structure 2N may be higher than the doping concentrations of series resonator structures 214, ..., 2M. The doping concentrations of series resonator structures 212 and 2N may be the same or may be different. The doping concentrations of shunt resonator structures 222, ... , 2Q have little or no impact on the inductive impedance (or inductive impedance change).
[0045] In various embodiments, a series resonator structure may include more than one resonators. If the series resonator structure is closer to a terminal (e.g., 212 or 2N), the doping concentration of the series resonator structure may refer to the lowest doping concentration in the series resonator structure. For example, if the serries resonator structure includes a first resonator with a higher doping concentration and a second resonator with a lower doping concentration, the doping concentration of the series resonator structure may refer to the lower doping concentration. If the series resonator structure is further away from both terminals (e.g., 214, ..., 2M, or 2N), the doping concentration of the series resonator structure may refer to the highest doping concentration in the series resonator structure. For example, if the serries resonator structure includes a first resonator with a higher doping concentration and a second resonator with a lower dopingAttorney Docket No. 62306.114WO01 concentration, the doping concentration of the series resonator structure may refer to the higher doping concentration. In other words, the lowest doping concentration in a series resonator structure closest to (e.g., in direct electrical connection with) a terminal is higher than the highest doping concentration in a series resonator structure farther away from (e.g., not in direct electrical connection with) both terminals.
[0046] FIG. 2B shows a simplified cross-sectional view of a BAW resonator 200 in a series resonator structure, according to embodiments of the present disclosure. BAW resonator 200 may include a piezoelectric layer 202, a first electrode 204, and a second electrode 206. Piezoelectric layer 202 may be disposed between first electrode 204 and second electrode 206. Piezoelectric layer 202 may include a suitable piezoelectric material such as one or more of aluminum nitride (AIN), scandium-doped aluminum nitride (ScAlN), magnesium hydrofluoric acid aluminum nitride (MgHfAlN), magnesium zirconium aluminum nitride (MgZrAlN), and magnesium titanium aluminum nitride (MgTiAlN), zinc oxide (ZnO). In various embodiments, first electrode 204 and second electrode 206 include one or more of tungsten (W), molybdenum (Mo), platinum (Pt), titanium tungsten (TiW), titanium (Ti), copper (Cu), aluminum copper (AICu). In operation, a voltage may be applied across piezoelectric layer 202 through first electrode 204 and second electrode 206. An acoustic wave may propagate in the piezoelectric layer 202 in the z-direction. The frequency of the acoustic wave may contribute to the filtering frequency of BAW filter circuit 201. In some embodiments, BAW resonator 200 may be an example of the BAW resonator disclosed in International Publication Number: WO 2024 / 044106 Al.
[0047] In some embodiments, piezoelectric layer 202 may be doped with scandium (Sc), and the doping concentration in this disclosure may refer to the doping concentration of Sc in a piezoelectric layer. In some embodiments, piezoelectric layer 202 include AIN or ScAlN. The doping concentration of Sc may range from about 1 * 10°cm’3to about 1 x 1030cm'3.
[0048] FIG. 3 shows a BAW filter circuit 300 with adjustable inductive impedance, according to some embodiments. BAW filter circuit 300 may be an example of BAW filter circuit 201, and may have a 4s4p ladder topology. As an example, BAW resonators in BAW filter circuit 300 may be doped with Sc, and have a first doping concentration Sc-1 and a second doping concentration Sc-2, shown as different patterns. In some embodiments, first doping concentration Sc-1 is higher than second doping concentration Sc-2. In describing FIG. 3, the doping concentration may refer to the Sc doping concentration in the piezoelectric layer of a BAW resonator.
[0049] As shown in FIG. 3, BAW filter circuit 300 may include a first terminal 302 and a second terminal 304. In some embodiments, first terminal 302 includes a transmitter (“TX”) terminal (e.g.,Attorney Docket No. 62306.114WO01 similar to the signal line entering filter A 108a or filter B 108b from PA 102 or LNA, respectively), and second terminal 304 includes an antenna (“ANT,” similar to Ant 118). BAW filter circuit 300 may include a plurality of series resonator structures 306, 308, 310, and 312 electrically coupled between first terminal 302 and second terminal 304. In some embodiments, a series signal path 322 is formed, e.g., through series resonator structures 306-312, between first terminal 302 and second terminal 304. In some embodiments, series resonator structures refer to those coupled between first terminal 302 and 304 and along series signal path 322. BAW filter circuit 300 may also include a plurality of shunt resonator structures 314, 316, 318, and 320 each being electrically coupled to series signal path 322 and GND. In some embodiments, shunt resonator structures refer to those coupled between series signal path 322 and GND.
[0050] Series resonator structure 306 may be directly coupled to first terminal 302 such that no other series resonator structure is coupled between first terminal 302 and series resonator structure 306. Series resonator structure 312 may be directly coupled to second terminal 304 such that no other series resonator structure is coupled between second terminal 304 and series resonator structure 312. Series resonator structures 308 and 310 may be coupled between series resonator structures 306 and 312. Series resonator structures 306 and 312 may each have a higher doping concentration than those of series resonator structures 308 and 310.
[0051] Series resonator structure 306 may include a BAW resonator 306a (“Ser4a”) and a BAW resonator 306b (“Ser4b”) coupled in parallel. Series resonator structure 308 may include a BAW resonator 308a (“Ser3a”) and a BAW resonator 308b (“Ser3b”) coupled in parallel. Series resonator structure 310 may include a BAW resonator 310a (“Ser2a”) and a BAW resonator 310b (“Ser2b”) coupled in parallel. Series resonator structure 312 may include a BAW resonator 312a (“Serla”) and a BAW resonator 312b (“Serlb”) coupled in series. In some embodiments, BAW resonators in the same series resonator structure may have the same doping concentration.
[0052] To vary the inductive impedance of BAW filter structure 300, doping concentrations in series resonator structures 306, 308, 310, and 312 may be manipulated, e.g., until a desired inductive impedance is reached. In an example, to increase the inductive impedance between first terminal 302 and second terminal 304, BAW resonators in series resonator structures 306 and 312 may have first doping concentration Sc-1, and BAW resonators in series resonator structures 308 and 310 may have second doping concentration Sc-2. That is, series resonator structures closest (e.g., directly coupled to) to the terminals may have higher Sc doping concentrations than those further away (e.g., indirectly coupled to) the terminals. In some embodiments, the difference in the doping concentrations (e.g., between Sc-1 and Sc-2) contributes to the inductive impedance change. InAttorney Docket No. 62306.114WO01 some embodiments, the difference in the doping concentrations may be at least about 1 * 10°cm’3to about 1 / IO2Ocm’3to reach a loss reduction of about 0.1 dB to about 0.4 dB in the corresponding FEM (e.g., similar to 100). In various embodiments, Sc-1 may be in the range of about 1 * 1020cm’3and | / IO4Ocrrr and Sc-2 may be in the range of about lxl0°cm'3and | / IO6crrT3. In some embodiments, Sc-1 may be about lxl020cm'3and Sc-2 may be about lxl0°cm'3. In some embodiments, Sc-1 may be about lxl020cm'3and Sc-2 may be about lxl06cm'3. In some embodiments, Sc-1 may be about lxl030cm'3and Sc-2 may be about lxl06cm'3. In some embodiments, if -3dB is considered as the common loss across band, and 0.3dB is the loss reduction. The FEM may have a 50% mismatch power loss with single doping concentration for all series resonator structures compared to 46% mismatch power loss with series resonator structures closest to the terminals having higher doping concentrations, reaching about 10% less loss power.
[0053] In some embodiments, BAW resonators in the same series resonator structure may have different doping concentrations. For example, BAW resonators 306a and 306b may have different doping concentrations, BAW resonators 308a and 308b may have different doping concentrations, BAW resonators 310a and 310b may have different doping concentrations, and / or BAW resonators 312a and 312b may have different doping concentrations. The doping concentration of a series resonator structure closest to a terminal (e.g., 302 or 304) may refer to the lowest doping concentration in the BAW resonator(s) of the series resonator structure, and the doping concentration of a series resonator structure further away from both terminals (e.g., 302 and 304) may refer to the highest doping concentration in the BAW resonator(s) of the series resonator structure. That is, in some embodiments, the lowest doping concentration in each of BAW resonators 306a, 306b, 312a, and 312b is higher than the highest doping concentration in each of BAW resonators 308a, 308b, 310a, and 310b.
[0054] Shunt resonator structures 314, 316, 318, and 320 may each include at least one BAW electrically coupled between series signal path 322 and GND. As shown in FIG. 3, Shunt resonator structure 314 may include a single BAW resonator (“Shu4”), and may be coupled to a connection point between first terminal 302 and series resonator structure 306, and an inductor “LGND4,” which is further coupled to GND. Shunt resonator structure 316 may include a BAW resonator 316a (“ Shu3 a”) and a BAW resonator 316b (“ Shu3b”) coupled in parallel . Shunt resonator structure 316 may be coupled to a connection point between series resonators 306 and 308, and an inductor “LGND23,” which is further coupled to GND. Shunt resonator structure 318 may include a BAW resonator 318a (“Shu2a”) and a BAW resonator 318b (“Shu2b”) coupled in parallel. Shunt resonator structure 318 may be coupled to a connection point between series resonators 308 andAttorney Docket No. 62306.114WO01 310, and inductor “LGND23”. Shunt resonator structure 320 may include a BAW resonator 320a (“Shula”) and a BAW resonator 320b (“Shulb”) coupled in parallel. Shunt resonator structure 320 may be coupled to a connection point between series resonators 310 and 312, and an inductor “LGND1,” which is further coupled to GND. In some embodiments, the doping concentrations in the BAW resonators in shunt resonator structures 314, 316, 318, and 320 may be Sc-1. In various embodiments, the doping concentrations in the BAW resonators in shunt resonator structures 314, 316, 318, and 320 may be any other suitable values, and should not be limited by the embodiments of the present disclosure.
[0055] In some embodiments, by adjusting doping concentrations in the series resonator structures in BAW filter circuit 300 (and / or 201), the inductive impedance of BAW filter circuit 300 (and / or 201) can be increased to a desired value. The surface mounted device (SMD, e.g., an inductor) coupled to first terminal 302 in the corresponding FEM, to increase / compensate the imaginary impedance of the BAW filter circuit, may not be needed. In some embodiments, a smaller SMD is used instead. In some embodiments, the inductive impedance of the BAW filter circuit is sufficiently high that no SMD. Less space is needed for the FEM, and lower cost can be achieved.
[0056] FIG. 4A shows certain characteristics of BAW filter circuit 300, according to some embodiments. As an example, series resonator structures 306 and 312 may have doping concentration of about U I02°crrr\ and series resonator structures 308 and 310 may have doping concentration of about 1 * 1 Oocm’3. FIG. 4A shows the filter response, e.g., pass-band characteristics, of BAW filter circuit with the described doping concentrations.
[0057] FIG. 4B shows comparisons of upper band edge (UBE) loss (a), real impedance (b), and imaginary impedance (c) between two BAW filter circuits, according to some embodiments. BAW filter circuit 1 (1, represented by the solid line) may be BAW filter circuit 300 with the doping concentrations described in FIG. 4A. BAW filter circuit 2 (2, represented by the dotted line) may be another BAW filter circuit with the same topology as BAW filter circuit 300 but with a single doping concentration of 1 * 1020cm’3for all series resonator structures.
[0058] As shown in (a), in the frequency range [ / i,^], UBE loss of BAW filter circuit 1 may be about 0.27 dB lower than the UBE loss of BAW filter 2. The real impedances of BAW filter circuits 1 and 2 may be comparable, as shown in (b). However, the imaginary impedance of BAW filter circuit 1 may be about 0, as shown in (c). The total inductive impedance of BAW filter circuit 1 may be higher than that of BAW filter circuit 2, with lower loss.Attorney Docket No. 62306.114WO01
[0059] Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.
Claims
Attorney Docket No. 62306.114WO01 CLAIMS:
1. A radio frequency (RF) filter structure, comprising:a first terminal and a second terminal communicatively coupled to the first terminal; a first series resonator structure directly communicatively coupled to the first terminal; a second series resonator structure directly communicatively coupled to the second terminal; anda third series resonator structure located between and communicatively coupled to the first series resonator structure and the second series resonator structure, whereina doping concentration of the first series resonator structure is higher than a doping concentration of the third series resonator structure; anda doping concentration of the second series resonator structure is higher than the doping concentration of the third series resonator structure.
2. The RF filter structure of claim 1, wherein:the doping concentrations of the first series resonator structure and the second series resonator structure are in a range of about 1 x 1020cm'3and about 1 x 1040cm'3; andthe doping concentration of the third series resonator structure is in a range of about lxlO°cm'3and about lxl06cm'3.
3. The RF filter structure of claim 1, wherein:the doping concentration of the first series resonator structure comprises a doping concentration of a piezoelectric layer in the first series resonator structure;the doping concentration of the second series resonator structure comprises a doping concentration of a piezoelectric layer in the second series resonator structure; andthe doping concentration of the third series resonator structure comprises a doping concentration of a piezoelectric layer in the third series resonator structure.
4. The RF filter structure of claim 1, wherein the first series resonator structure comprises a plurality of bulk acoustic wave (BAW) resonators communicatively coupled in parallel.
5. The RF filter structure of claim 1, wherein the second series resonator structure comprises a plurality of BAW resonators connected in series.Attorney Docket No. 62306.114WO016. The RF filter structure of claim 1, wherein the third series resonator structure comprises at least one set of BAW resonators connected in series.
7. The RF filter structure of claim 2, wherein dopants in the first series resonator structure, the second series resonator structure, and the third series resonator structure comprise scandium (Sc).
8. The RF filter structure of claim 1, further comprising a first shunt resonator structure and a second shunt resonator structure, wherein the third series resonator structure is communicatively coupled between the first shunt resonator structure and the second shunt resonator structure.
9. The RF filter structure of claim 8, further comprising a third shunt resonator structure directly and communicatively coupled to the first terminal, wherein:the first series resonator structure is communicatively coupled between the first shunt resonator structure and the third shunt resonator structure; andthe second series resonator structure is communicatively coupled between the second shunt resonator structure and the second terminal.
10. The RF filter structure of claim 9, wherein the first shunt resonator structure, the second shunt resonator structure, and the third shunt resonator structure each comprises one or more BAW resonators communicatively coupled in parallel.
11. A radio frequency (RF) filter structure, comprising:a first terminal and a second terminal;a series signal path communicatively coupled to the first terminal and the second terminal;a first series resonator structure directly communicatively coupled to the first terminal via the series signal path;a second series resonator structure directly communicatively coupled to the second terminal via the series signal path; anda third series resonator structure located between and communicatively coupled to theAttorney Docket No. 62306.114WO01 first series resonator structure and the second series resonator structure via the series signal path, wherein:a doping concentration of the first series resonator structure is higher than a doping concentration of the third series resonator structure; anda doping concentration of the second series resonator structure is higher than the doping concentration of the third series resonator structure.
12. The RF filter structure of claim 11, wherein:the doping concentrations of the first series resonator structure and the second series resonator structure are in a range of about 1 x 1020cm'3and about 1 x 1030cm'3; andthe doping concentration of the third series resonator structure is in a range of about lxlO°cm'3and about lxl06cm'3.
13. The RF filter structure of claim 11, wherein:the doping concentration of the first series resonator structure comprises a doping concentration of a piezoelectric layer in the first series resonator structure;the doping concentration of the second series resonator structure comprises a doping concentration of a piezoelectric layer in the second series resonator structure; andthe doping concentration of the third series resonator structure comprises a doping concentration of a piezoelectric layer in the third series resonator structure.
14. The RF filter structure of claim 11, wherein the first series resonator structure comprises a plurality of bulk acoustic wave (BAW) resonators communicatively coupled in parallel along the series signal path.
15. The RF filter structure of claim 11, wherein the second series resonator structure comprises a plurality of BAW resonators connected in series along the series signal path.
16. The RF filter structure of claim 11, wherein the third series resonator structure comprises at least one set of BAW resonators connected in series.
17. The RF filter structure of claim 12, wherein dopants in the first series resonator structure, the second series resonator structure, and the third series resonator structure compriseAttorney Docket No. 62306.114WO01 scandium (Sc).
18. The RF filter structure of claim 11, further comprising a first shunt signal path and a second shunt signal path each communicatively coupled to the series signal path, wherein the third series resonator structure is communicatively coupled between the first shunt signal path and the second shunt signal path.
19. The RF filter structure of claim 18, further comprising a third shunt signal path directly and communicatively coupled to the first terminal, wherein:the first series resonator structure is communicatively coupled between the first shunt signal path and the third shunt signal path; andthe second series resonator structure is communicatively coupled between the second shunt signal path and the second terminal.
20. The RF filter structure of claim 19, wherein the first shunt signal path, the second shunt signal path, and the third shunt signal path each comprises one or more BAW resonators communicatively coupled in parallel.