Microacoustic filter structure including symmetric metal shielding structures and method of manufacture

Abstract

Coupling resonators in series provides a solution for achieving a low effective static capacitance, as needed in a high frequency filter, while maintaining a high quality factor. As the number of resonators in the series increases, so does vulnerability of the series to external noise that can reduce signal stability. A microacoustic filter structure includes bulk acoustic wave, BAW, resonators (404(1),...404(8)) coupled in series in a mirror symmetrical arrangement with respect to axis A1 and metal shielding structures (406A, 406B) symmetrically spaced around the arrangement of BAW resonators to reduce or avoid dips or spikes in an output signal. Inclusion of the metal shielding structures generally reduces environmental parasitic impacts, and the symmetrical spacing between the metal shielding structures and the arrangement of BAW resonators minimizes deviations of those parasitics among the respective BAW resonators and also reduces the level of harmonic frequencies for improved signal stability.

Description

Qualcomm Ref No. 2500433 1MICROACOUSTIC FILTER STRUCTURE INCLUDING SYMMETRIC METAL SHIELDING STRUCTURES AND METHOD OF MANUFACTURETECHNICAL FIELD

[0001] This disclosure relates generally to wireless transceivers and other electronic components that employ radio-frequency filters and, more specifically, to microacoustic filters comprising multiple acoustic resonators.BACKGROUND

[0002] Electronic devices use radio-frequency (RF) signals to communicate information. To transmit or receive the RF signals within a given frequency band, an electronic device may use filters to pass signals within the frequency band and to suppress (e g., attenuate) frequencies outside of the frequency band, such as jamming signals or noise. It can be challenging, however, to design a filter that provides filtering for RF applications, including those that utilize frequencies above 3 gigahertz (GHz), such as for the 5th-generation (5G) and higher generations of cellular network technology. This challenge is due, in part, to the decreasing geometries of features in acoustic filters to accommodate the increasing frequencies of operation.SUMMARY

[0003] Aspects disclosed in the detailed description include a microacoustic filter structure including symmetric metal shielding structures. Related methods of manufacturing a microacoustic filter structure including symmetric metal shielding structures are also disclosed Coupling resonators in series provides a solution for achieving a low effective static capacitance, as needed in a high frequency filter, while maintaining a high quality factor (Q factor). As the number of resonators in the series increases, so does vulnerability of the series to external noise that can reduce signal stability. An exemplary microacoustic filter structure includes bulk acoustic wave (BAW) resonators coupled in series in a symmetrical arrangement and metal shielding structures symmetrically spaced around the arrangement or BAW resonators to reduce or avoid dips or spikes in an output signal. Inclusion of the metal shielding structures generally reduces environmental parasitic impacts, and the symmetrical spacing between the metal shielding structures and the arrangement of BAW resonators minimizesWT Ref No. 1173-967Qualcomm Ref No. 2500433 2deviations of those parasitics among the respective BAW resonators and also reduces the level of harmonic frequencies for improved signal stability.

[0004] In this regard, in one aspect, a die is disclosed The die includes a substrate and an acoustic filter on the substrate. The acoustic filter comprises an arrangement of BAW resonators coupled in series, wherein each of the BAW resonators comprises a first electrode in a first section of a first metal layer, a second electrode in a second section of a second metal layer, and a piezoelectric slab disposed between the first electrode and the second electrode; and wherein the arrangement of BAW resonators is symmetrical with respect to a first axis extending in a first direction. The die also includes a first metal shielding structure disposed around the arrangement of BAW resonators on a first side of the first axis; and a second metal shielding structure disposed around the arrangement of BAW resonators on a second side of the first axis

[0005] In another aspect, a method of manufacturing a microacoustic filter is disclosed. The method comprises forming a substrate and forming an acoustic filter on the substrate. The acoustic filter comprises an arrangement of BAW resonators coupled in series, wherein each of the BAW resonators comprises a first electrode formed in a first metal layer, a second electrode formed in a second metal layer, and a piezoelectric slab disposed between the first electrode and the second electrode, and the arrangement of BAW resonators is symmetrical with respect to a first axis extending in a first direction. The method also comprises forming a first metal shielding structure disposed around the arrangement of BAW resonators on a first side of the first axis, and forming a second metal shielding structure disposed around the arrangement of BAW resonators on a second side of the first axis; wherein a first space separating the first metal shielding structure from the arrangement of BAW resonators on the first side of the first axis is symmetrical to a second space separating the second metal shielding structure from the arrangement of BAW resonators on the second side of the first axis.

[0006] In another aspect, an acoustic filter structure is disclosed. The acoustic filter comprises an arrangement of BAW resonators coupled in series, wherein each of the BAW resonators comprises a first electrode formed in a first metal layer, a second electrode formed in a second metal layer, and a piezoelectric slab disposed between the first electrode and the second electrode The acoustic filter also comprises a first metal shielding structure disposed around the arrangement of BAW resonators and on a first side of a first axis extending through the arrangement of BAW resonators in a firstWT Ref No. 1173-967Qualcomm Ref No. 2500433 3direction, and a second metal shielding structure disposed around the arrangement of BAW resonators on a second side of the first axis.BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 illustrates an exemplary operating environment for operating an electronic device including a microacoustic filter including a microacoustic filter structure with symmetrical metal shielding structures around an arrangement of acoustic resonators coupled in series;

[0008] Figure 2 illustrates an exemplary wireless transceiver including at least one microacoustic filter including a microacoustic filter structure with symmetrical metal shielding structures around an arrangement of acoustic resonators coupled in series,

[0009] Figure 3 is an illustration of a microacoustic filter for high frequency signals comprising a plurality of microacoustic resonators coupled in series for low capacitance and high quality factor (Q factor);

[0010] Figure 4 is an exemplary microacoustic filter including a microacoustic filter structure including a symmetrical arrangement of serially-coupled acoustic resonators and metal shielding structures providing symmetrical spacing around the resonator arrangement;

[0011] Figure 5 is a cross-sectional side view of a portion of the arrangement of serially-coupled resonators in Figure 4;

[0012] Figure 6 is a microacoustic filter including a microacoustic filter structure including an arrangement of serially-coupled acoustic resonators and non-symmetrical metal shielding structures;

[0013] Figure 7 is a flowchart illustrating a process of fabricating a microacoustic filter including a microacoustic filter structure including a symmetrical arrangement of serially-coupled resonators and metal shielding structures, as shown in Figure 4;

[0014] Figure 8 is a block diagram of an exemplary wireless communication device that includes a microacoustic filter including a microacoustic filter structure including a symmetrical arrangement of serially-coupled resonators and metal shielding structures, as shown in Figure 4; and

[0015] Figure 9 is a block diagram of an exemplary processor-based system that can include a microacoustic filter including a microacoustic filter structure including a symmetrical arrangement of serially-coupled resonators and metal shielding structures, as shown in Figure 4.WT Ref No. 1173-967Qualcomm Ref No. 2500433 4DETAILED DESCRIPTION

[0016] Aspects disclosed in the detailed description include a microacoustic filter structure including symmetric metal shielding structures. Related methods of manufacturing a microacoustic filter structure including symmetric metal shielding structures are also disclosed Coupling resonators in series provides a solution for achieving a low effective static capacitance, as needed in a high frequency filter, while maintaining a high quality factor (Q factor). As the number of resonators in the series increases, so does vulnerability of the series to external noise that can reduce signal stability. An exemplary microacoustic filter structure includes bulk acoustic wave (BAW) resonators coupled in series in a symmetrical arrangement and metal shielding structures symmetrically spaced around the arrangement or BAW resonators to reduce or avoid dips or spikes in an output signal. Inclusion of the metal shielding structures generally reduces environmental parasitic impacts, and the symmetrical spacing between the metal shielding structures and the arrangement of BAW resonators minimizes deviations of those parasitics among the respective BAW resonators and also reduces the level of harmonic frequencies for improved signal stability.

[0017] An electronic device may use filters to pass radio-frequency signals transmitted or received within a given frequency and to suppress (e.g., attenuate) jammers or noise-having frequencies outside of the frequency band Electroacoustic devices (e.g., “microacoustic filters”) can be used to filter high-frequency signals in many applications, such as those with frequencies that are greater than 100 megahertz (MHz). A microacoustic filter is tuned to pass certain frequencies (e.g., frequencies within its passband) and attenuate other frequencies (e.g., frequencies that are outside of its passband). Using a piezoelectric material, the microacoustic filter operates by transforming an electrical signal wave that is applied to an electrical conductor into an acoustic wave (e.g., an acoustic signal wave) that forms across the piezoelectric material. The acoustic wave is then converted back into an electrical filtered signal. The microacoustic filter can include an electrode structure that transforms or converts between the electromagnetic and acoustic waves.

[0018] The acoustic wave features a velocity having a magnitude that is significantly less than that of a velocity of the electromagnetic wave. Generally, the magnitude of the propagation velocity of a wave is proportional to a size of a wavelength of the wave. Consequently, after conversion of the electrical signal wave into the acoustic signal wave, the wavelength of the acoustic signal wave is significantly smaller than the wavelength WT Ref No. 1173-967Qualcomm Ref No. 2500433 5of the electrical signal wave. The resulting smaller wavelength of the acoustic signal wave enables filtering to be performed using a smaller filter device. This permits acoustic filters to be used in space-constrained devices, including portable electronic devices such as cellular phones. These acoustic filters can be referred to as microacoustic filters.

[0019] It can be challenging to design a microacoustic filter that can provide filtering for higher frequencies, such as those used with Wi-Fi® at 2.4 gigahertz (GHz) and higher, approximately 3 GHz to 7 GHz frequencies (e.g., 5GNR), and frequencies between 7 and 18 GHz and higher. In particular, it can be challenging to design a filter that is affordable; can realize a target level of performance in terms of resonance quality factors, electromechanical coupling, temperature coefficient of frequency (TCF), power durability, insertion loss, and spurious-mode suppression; and operate at the frequencies employed in cell phones and other types of communications now and in the future

[0020] To address these challenges, some techniques implement coupling multiple BAW resonators in series for a lower effective capacitance in a microacoustic filter, as needed for higher frequencies. In this manner, BAW resonators having larger geometries, which are easier to manufacture and provide higher resonance quality factors (Q factors) can be used. Another advantage of coupling multiple BAW resonators in series is to improve the power durability of the filter in the way of distribution of applied voltage over several resonators which will result in smaller voltages applied to each individual resonator. Furthermore, the cascading of resonators also improves the non-linear performance of microacoustic filters (such as level of harmonics, intermodulation products etc.) However, as discussed further below, increasing the number of BAW resonators in the microacoustic filter may lead to increased exposure to environmental parasitics

[0021] Figure 1 illustrates an exemplary environment 100 for operating a microacoustic filter including a symmetrical arrangement of multiple BAW resonators coupled in series and symmetrically spaced metal shielding structures to provide signal stability. In the environment 100, a computing device 102 communicates with a base station 104 through a wireless communication link 106 (wireless link 106). In this example, the computing device 102 is depicted as a smartphone. However, the computing device 102 can be implemented as any suitable computing or electronic device, such as a modem, a cellular base station, a broadband router, an access point, a cellular phone, a gaming device, a navigation device, a media device, a laptop computer, a desktop computer, a tablet computer, a wearable computer, a server, a network-attached storage WT Ref No. 1173-967Qualcomm Ref No. 2500433 6(NAS) device, a smart appliance or other internet of things (loT) device, a medical device, a vehicle-based communication system, a radar, a radio apparatus, and so forth. Use of a microacoustic resonator is not limited to microacoustic filters for wireless communication as a microacoustic filter can be applied in any technological field where such filtering is useful .

[0022] The base station 104 communicates with the computing device 102 via the wireless link 106, which can be implemented as any suitable type of wireless link. Although depicted as a tower of a cellular network, the base station 104 can represent or be implemented as another device, such as a satellite, a server device, a terrestrial television broadcast tower, an access point, a peer-to-peer device, a mesh network node, and so forth. Therefore, the computing device 102 may communicate with the base station 104 or another device via a wireless connection.

[0023] The wireless link 106 can include a downlink of data or control information communicated from the base station 104 to the computing device 102, an uplink of other data or control information communicated from the computing device 102 to the base station 104, or both a downlink and an uplink. The wireless link 106 can be implemented using any suitable communication protocol or standard, such as 2nd-generation (2G), 3rd-generation (3G), 4th-generation (4G), 5th-generation (5G), or 6th-generation (6G) cellular; IEEE 802.11 (e g., Wi-Fi®); IEEE 802.15 (e.g., Bluetooth®); IEEE 802.16 (e.g., WiMAX®); and so forth. In some implementations, the wireless link 106 may wirelessly provide power and the base station 104 or the computing device 102 may comprise a power source.

[0024] As shown in Figure 1, the computing device 102 includes an application processor 108 and a computer-readable storage medium 110 (CRM 110). The application processor 108 can include any type of processor, such as a multi-core processor, that executes processor-executable code stored by the CRM 110. The CRM 110 can include any suitable type of data storage media, such as volatile memory (e.g., random access memory (RAM)), non-volatile memory (e.g., Flash memory), optical media, magnetic media (e.g., disk), and so forth. In the context of this disclosure, the CRM 110 is implemented to store instructions 112, data 114, and other information of the computing device 102, and thus does not include transitory propagating signals or carrier waves

[0025] The computing device 102 can also include input / output ports 116 (I / O ports 116) and a display 118 The I / O ports 116 enable data exchanges or interaction with other devices, networks, users, or the environment. The I / O ports 116 can include serial WT Ref No. 1173-967Qualcomm Ref No. 2500433 7ports (e.g., universal serial bus (USB) ports), parallel ports, audio ports, infrared (IR) ports, user interface ports such as a touchscreen, and so forth. The display 118 presents graphics of the computing device 102, such as a user interface associated with an operating system, program, or application. Alternatively or additionally, the display 118 can be implemented as a display port or virtual interface through which graphical content of the computing device 102 is presented.100261 A wireless transceiver 120 of the computing device 102 provides connectivity to respective networks and other electronic devices connected therewith. The wireless transceiver 120 can facilitate communication over any suitable type of wireless network, such as a wireless local area network (WLAN), peer-to-peer (P2P) network, mesh network, cellular network, ultra-wideband (UWB) network, wireless wide-area-network (WWAN), and / or wireless personal-area-network (WP AN) Tn the context of the example environment 100, the wireless transceiver 120 enables the computing device 102 to communicate with the base station 104 and networks connected therewith. However, the wireless transceiver 120 can also enable the computing device 102 to communicate “directly” with other devices or networks.

[0027] The wireless transceiver 120 includes circuitry and logic for transmitting and receiving communication signals via an antenna 122. Components of the wireless transceiver 120 can include amplifiers, switches, mixers, analog-to-digital converters, filters, and so forth for conditioning the communication signals (e.g., for generating or processing signals). The wireless transceiver 120 can also include logic to perform in-phase / quadrature (I / Q) operations, such as synthesis, encoding, modulation, decoding, demodulation, and so forth. In some cases, components of the wireless transceiver 120 are implemented as separate transmitter and receiver entities Additionally or alternatively, the wireless transceiver 120 can be realized using multiple or different sections to implement respective transmitting and receiving operations (e.g., separate transmit and receive chains). In general, the wireless transceiver 120 processes data and / or signals associated with communicating data of the computing device 102 over the antenna 122.

[0028] In the example shown in Figure 1, the wireless transceiver 120 includes at least one microacoustic filter 124 including at least one microacoustic resonator structure 126. In some implementations, the wireless transceiver 120 includes multiple microacoustic filters 124, in which the microacoustic resonator structures 126 can be formed from multiple microacoustic BAW resonators 128 arranged in series. The BAW WT Ref No. 1173-967Qualcomm Ref No. 2500433 8resonators 128 each include a top electrode structure 130, a piezoelectric layer 132, and a bottom electrode structure 134. The microacoustic resonator structure 126 also includes metal shielding structures 136 to shield the BAW resonators 128 from parasitic environmental influences.

[0029] With the above improvements, the microacoustic filter 124 can be designed to support frequency ranges above 3 GHz, including frequencies between approximately 3 and 20 GHz. For example, the microacoustic resonator structure 126 can be designed to have a resonance frequency between approximately 4 and 18 GHz, between approximately 4.5 and 7.5 GHz, or equal to approximately 4, 5, 6, 7, 8, 10, 13, 15, 17, or 20 GHz. In general, the term “approximately” can mean that any of the frequencies can be within ± 10% of a specified value or less (e.g., within ± 5%, ± 3%, or ± 2% of a specified value). The microacoustic filter 124 is further described with respect to Figure 2.

[0030] Figure 2 illustrates an exemplary wireless transceiver 120. In the depicted configuration, the wireless transceiver 120 includes a transmitter 202 and a receiver 204, which are respectively coupled to a first antenna 122-1 and a second antenna 122-2. In other implementations, the transmitter 202 and the receiver 204 can be connected to a same antenna through a duplexer (not shown). The transmitter 202 is shown to include at least one digital-to-analog converter 206 (DAC 206), at least one first mixer 208-1 , at least one amplifier 210 (e.g., a power amplifier), and at least one first microacoustic filter 124-1. The receiver 204 includes at least one second microacoustic filter 124-2, at least one amplifier 212 (e.g., a low-noise amplifier), at least one second mixer 208-2, and at least one analog-to-digital converter 214 (ADC 214). The first mixer 208-1 and the second mixer 208-2 are coupled to a local oscillator 216. Although not explicitly shown, the DAC converter 206 of the transmitter 202 and the ADC converter 214 of the receiver 204 can be coupled to the application processor 108 (of Figure 1) or another processor associated with the wireless transceiver 120 (e.g., a modem).

[0031] In some implementations, the wireless transceiver 120 is implemented using multiple circuits (e.g., multiple integrated circuits), such as a transceiver circuit 236 and a radio-frequency front-end (RFFE) circuit 238. As such, the components that form the transmitter 202 and the receiver 204 are distributed across these circuits. As shown in Figure 2, the transceiver circuit 236 includes the DAC converter 206 of the transmitter 202, the mixer 208-1 of the transmitter 202, the mixer 208-2 of the receiver 204, and the ADC converter 214 of the receiver 204. In other implementations, the DAC converter WT Ref No. 1173-967Qualcomm Ref No. 2500433 9206 and the ADC converter 214 can be implemented on another separate circuit that includes the application processor 108 or the modem. The RFFE circuit 238 includes the amplifier 210 of the transmitter 202, the microacoustic filter 124-1 of the transmitter 202, the microacoustic filter 124-2 of the receiver 204, and the amplifier 212 of the receiver 204.

[0032] During transmission, the transmitter 202 generates a radio-frequency transmit signal 218, which is transmitted using the antenna 122-1. To generate the radio-frequency transmit signal 218, the DAC converter 206 provides a pre-upconversion transmit signal 220 to the first mixer 208-1. The pre-upconversion transmit signal 220 can be a baseband signal or an intermediate-frequency signal. The first mixer 208-1 upconverts the pre-upconversion transmit signal 220 using a local oscillator (LO) signal 222 provided by the local oscillator 216. The first mixer 208-1 generates an upconverted signal, which is referred to as a pre-filter transmit signal 224. The pre-filter transmit signal 224 can be a radio-frequency signal and include some noise or unwanted frequencies, such as a harmonic frequency. The amplifier 210 amplifies the pre-filter transmit signal 224 and passes the amplified pre-filter transmit signal 224 to the first microacoustic filter 124-1.

[0033] The first microacoustic filter 124-1 filters the amplified pre-filter transmit signal 224 to generate a filtered transmit signal 226. As part of the filtering process, the first microacoustic filter 124-1 attenuates the noise or unwanted frequencies within the pre-filter transmit signal 224. The transmitter 202 provides the filtered transmit signal 226 to the antenna 122-1 for transmission. The transmitted filtered transmit signal 226 is represented by the radio-frequency transmit signal 218.

[0034] During reception, the antenna 122-2 receives a radio-frequency receive signal 228 and passes the radio-frequency receive signal 228 to the receiver 204. The second microacoustic filter 124-2 accepts the received radio-frequency receive signal 228, which is represented by a pre-filter receive signal 230. The second microacoustic filter 124-2 filters any noise or unwanted frequencies within the pre-filter receive signal 230 to generate a filtered receive signal 232.

[0035] The amplifier 212 of the receiver 204 amplifies the filtered receive signal 232 and passes the amplified filtered receive signal 232 to the second mixer 208-2. The second mixer 208-2 downconverts the amplified filtered receive signal 232 using the LO signal 222 to generate the downconverted receive signal 234. The ADC converter 214 converts the downconverted receive signal 234 into a digital signal, which can beWT Ref No. 1173-967Qualcomm Ref No. 2500433 10processed by the application processor 108 or another processor associated with the wireless transceiver 120 (e.g., the modem).

[0036] Figure 2 illustrates one exemplary configuration of the wireless transceiver 120. Other configurations of the wireless transceiver 120 can support multiple frequency bands and share an antenna 122 across multiple transceivers. One of ordinary skill in the art can appreciate the variety of other configurations for which microacoustic filters 124 may be included. For example, the microacoustic filters 124 can be integrated within duplexers or diplexers of the wireless transceiver 120.

[0037] Figure 3 is an illustration of one example of a microacoustic filter 300 comprising a plurality of microacoustic BAW resonators 302 coupled in series The microacoustic filter 300 also includes capacitors 304 coupled in series, as well as a capacitor 306 and an inductor 308 coupled to a reference voltage GND (e g., ground) The microacoustic filter 300 provides a high-pass filter of an incoming signal SIG FN to generate a filtered output signal S1G OUT. The microacoustic filter 300 may also include other components (not shown) or more or less capacitors and inductors in different configurations.

[0038] As the frequencies of telecommunication signals increase, lower capacitance is needed in signal filters. To achieve lower capacitance, the physical features of microacoustic filters have been reduced in size to a degree that reliable manufacturability is difficult or impossible. However, coupling multiple, higher-capacitance BAW resonators in series produces an effective capacitance less than the capacitance of any one of the BAW resonators and high Q factor may be achieved. However, increasing the number of BAW resonators in the series increases the susceptibility of the microacoustic filter 300 to environmental parasitic effects. Operation of the microacoustic filter 300 is optimized by identical performance of each of the serially-coupled BAW resonators 302. This may be referred to as symmetrical performance of the BAW resonators 302. Therefore, parasitic capacitive coupling affecting one of the BAW resonators 302 can change its performance, making such performance non-symmetrical with respect to the other BAW resonators 302 in the microacoustic filter 300, which degrades the overall performance of the microacoustic filter 300.

[0039] Environmental parasitic capacitance affecting the BAW resonators 302 may be significantly reduced by metal shielding. One important aspect of such shielding is a space or distance separating the metal shielding from the BAW resonators, which is discussed further with reference to Figure 4.WT Ref No. 1173-967Qualcomm Ref No. 2500433 11

[0040] Figure 4 is an illustration of a plan view of an exemplary microacoustic filter 400 on a die 401 including a microacoustic filter structure 402 formed on a substrate 403. The microacoustic filter structure 402 (“filter structure 402”) includes an arrangement of serially-coupled BAW resonators 404(l)-404(R) (where R=8 in this example) and symmetrical metal shielding structures 406A and 406B. The BAW resonators 404(1)-404(R) in the filter structure 402 are one example implementation of the serially-coupled BAW resonators 302 in Figure 3. Capacitors of the microacoustic filter 400, corresponding to the capacitors 304 in Figure 3, are not shown in Figure 4. The BAW resonators 404(l)-404(R) are positioned in an arrangement 412 that is symmetrical with respect to an axis Al that extends in a first, Y-axis direction. The arrangement 412 extends in the Y-axis direction and a second, X-axis direction. As shown in Figure 4, a first portion 408A of the arrangement 412 includes BAW resonators 404(1 )-404(4) on a first side SA, in a second, X-axis direction, of the axis Al and a second portion 408B of the arrangement 412, including BAW resonators 404(5)-404(8) is on a second side SB of the axis Al in the second direction. The first portion 408A and the second portion 408B of the arrangement 412 are symmetrical with (e.g., mirror images of) each other in the X-axis direction relative to the axis Al. The term “mirror image” or “symmetrical” with respect to the axis Al refers to having identical or substantially similar shapes that are oppositely oriented and each at a same distance from, but on opposite sides (SA and SB) of, the axis Al. More specifically, the BAW resonators 404(4) and 404(5) are symmetrical (mirror images) relative to the axis Al, the BAW resonators 404(3) and 404(6) are symmetrical, the BAW resonators 404(2) and 404(7) are symmetrical, and the BAW resonators 404(1) and 404(8) are symmetrical relative to the axis Al.

[0041] The BAW resonators 404(l)-404(8) are formed of piezoelectric slabs (e g., layers) 410(l)-410(8) between sections 414(l)-414(5) of a first metal layer 416 and sections 418(1)-418(4) of a second metal layer 420. The piezoelectric slabs 410(1)-410(8) may comprise a piezoelectric material such as aluminum nitride (AIN), zinc oxide (ZnO), or lead zirconate titanate (PZT), for example. As an example, the BAW resonator 404(1) includes a first electrode 422(1) in the section 414(1) of the first metal layer 416 and a second electrode 424(1) in the section 418(1) of the second metal layer 420. Similarly, the BAW resonators 404(2)-404(8) include first electrodes 422(2)-422(8) in sections 414(l)-414(5) of the first metal layer 416 and second electrodes 424(2)-424(8) in sections 418(1)-418(4) of the second metal layer 420. Thus, each of the BAW resonators 404(l)-404(8) includes one of the piezoelectric slabs 410(l)-410(8) disposed WT Ref No. 1173-967Qualcomm Ref No. 2500433 12between one of the first electrodes 422(l)-422(8) and one of the second electrodes 424(1)-424(8) (more clearly shown in Figure 5).

[0042] With reference also to Figure 5, an illustration of a side view in the Y-axis direction of a cross-section 500 from A’ to A” of the arrangement 412 in Figure 4 is shown. The cross-section 500 includes the BAW resonators 404(1 )-404(4) in Figure 4, and shows the sections 414(l)-414(3) of the first metal layer 416, the sections 418(1) and 418(2) of the second metal layer 420, and the piezoelectric slabs 410(l)-410(4) of the BAW resonators 404(l)-404(4). The piezoelectric slabs 410(l)-410(4) may each be formed of a same piezoelectric material having a thickness T410 in the Z-axis direction. Although not shown in Figure 5, the piezoelectric slabs 410(5)-410(8) also have the thickness T410 in the Z-axis direction. In addition to having the same thickness T410, the piezoelectric slabs 410(1 )-410(4) may each have a same shape in a plane P500 extending in the X-axis and Y-axis directions.

[0043] With continued reference to Figures 4 and 5, each of the piezoelectric slabs 410(l)-410(8) may occupy a same area having a same shape (in various orientations) extending in the X-axis and Y-axis directions, between sections of the first metal layer 416 and the second metal layer 420. As one example, the piezoelectric slabs 410(1)-410(8) each have a perimeter P410 including five (5) sides. For example, the piezoelectric slab 410(3) includes sides SS1-SS5, which are representative of sides of each of the piezoelectric slabs 410(l)-410(8).

[0044] Capacitances C1-C8 are capacitances of the BAW resonators 404(1 )-404(8) between the sections 414(1) and 418(1), the sections 418(1) and 414(2), the sections 414(2) and 418(2), and so on to the sections 418(4) and 414(5), respectively. A total capacitance of the microacoustic filter 400 depends on the capacitances Cl- C8 of the BAW resonators 404(l)-404(8). Due to having the same thickness T410 (Fig. 5) and the same shapes (Fig. 4), the capacitances C1-C8 may be the same (e.g., identical) or very similar to each other. Accordingly, a total capacitance CT of the series of BAW resonators 404(l)-404(8) may be approximated as:

[0045] 1 / CT = 1 / C 1 + 1 / C2 + 1 / C3 +1 / C4 + 1 / C5 + 1 / C6 + 1 / C7 +1 / C8

[0046] and, where C1=C2=C3=C4=C5=C6=C7=C8, CT = Cl / 8.

[0047] Thus, the microacoustic filter 400 can achieve a lower capacitance for high frequency operation with the BAW resonators 404(l)-404(8) that are large enough to be reliably manufactured. Because the total capacitance CT according to such approximation may be very low, even parasitic capacitances to environmental structures WT Ref No. 1173-967Qualcomm Ref No. 2500433 13or components external to the microacoustic filter structure 402 can have a significant influence on the total capacitance. In addition, environmental capacitance may affect one or two of the BAW resonators 404(l)-404(8), for example, more than the others, thereby creating an imbalance in the symmetry of operation that can cause instability in the output signal SIG OUT. Such instability may produce dips or spikes in the output signal SIG OUT.|0048| The filter structure 402 includes the metal shielding structures 406A and 406B disposed around (in the X-axis and Y-axis directions) the arrangement 412 to provide electromagnetic shielding of the BAW resonators 404(l)-404(8) to minimize exposure to environmental influences. The metal shielding structure 406A is disposed around the first portion 408A of the arrangement 412 of BAW resonators 404(l)-404(4) on the first side SA of the axis A1, and the metal shielding structure 406B is disposed around the second portion 408B of the arrangement 412 of BAW resonators 404(5)-404(8) on the second side SB of the axis Al. In this regard, the metal shielding structures 406 A and 406B are separated from the arrangement 412 by spaces SPA and SPB on the opposite sides SA and SB of the axis Al. A first space SPA being symmetrical to a second space SPB provides symmetrical isolation of the first portion 408A and the second portion 408B from the environment. In some examples, the protection provided by the metal shielding structures 406A and 406B may be dependent, in part, on the size (e g., width) of the spaces SPA and SPB as determined by distances separating the metal shielding structures 406A and 406B from the filter structure 402 (i.e., the BAW resonators 404(l)-404(8)). Symmetrical isolation may be achieved by having the distances D1A-D5A of separation between the first portion 408A and the metal shielding structure 406A on the first side SA of the axis Al reflected (e g., across the axis Al) by the distances D1B-D5B of separation between the second portion 408B and the metal shielding structure 406B on the second side SB of the axis Al. In some examples, the metal shielding structures 406A and 406B are disposed around the arrangement 412 of BAW resonators such that the metal shielding structure 406A is on a first side of the first axis Al in the first, Y-axis direction, and the metal shielding structure 406B is disposed on a second side of the first axis A l in the first direction.

[0049] As shown in the cross-sectional side view in Figure 5, the metal shielding structure 406A and the metal shielding structure 406B may include multiple metal layers 426, which may include regions of the first metal layer 416 and / or the second metal layer 420 as well as a via layer 428 extending (e.g., in the Z-axis direction) between the first WT Ref No. 1173-967Qualcomm Ref No. 2500433 14metal layer 416 and the second metal layer 420. The via layer 428 may be formed of a metal, which may or may not be a same metal as the metal layers 426. In addition, a shield extension layer 431 may extend further (e.g., in the Z-axis direction) above the metal shielding structures 406A and 406B, effectively forming higher walls to increase the protection of the BAW resonators 404(1 )-404(4) from external sources of parasitic capacitance. The shield extension layer 431 may comprise one or more layers of one or more types of metal disposed on the first metal layer 416, where the one or more types of metal may or may not be a same metal as the first metal layer 416.

[0050] In some examples, the optional one or more metal layers may be above the first metal layer 416 or below the second metal layer 420. Thus, the distances DI A-D5A are measured in the X-axis and Y-axis directions from the BAW resonators 404(l)-404(4) to edges of the first metal shielding structure 406A on the first side SA, and the distances D1B-D5B are measured in the X-axis and Y-axis directions from the BAW resonators 404(5)-404(8) to edges of the second metal shielding structure 406B on the second side SB.

[0051] In some examples, symmetrical spaces may be achieved where distances DI A-D5A between each of the BAW resonators 404(l)-404(4) and edges of metal layers in the first metal shielding structure 406A on the first side SA are the same as (mirrorimage) distances D1B-D5B between each of the BAW resonators 404(5)-404(8) and edges of metal layers in the second metal shielding structure 406B on the second side SB. For example, symmetry may be achieved on a first side 412U of the arrangement 412 with distances D1A and D2A in the Y-axis direction from the BAW resonators 404(2) and 404(3) to the metal shielding structure 406A that are the same as (e.g., mirror-image) distances DIB and D2B in the Y-axis direction from the BAW resonators 404(6)-404(7) to the metal shielding structure 406B. In addition, symmetrical spacing may be provided on a first end 430A and a second end 430B on of the arrangement 412 with a distance D3A in the X-axis direction from the BAW resonators 404(l)-404(4) to the metal shielding structure 406A that is symmetrical to the distance D3B in the X-axis direction from the BAW resonator 404(5)-404(8) to the metal shielding structure 406B. Symmetrical spacing is provided on a second side 412L with distances D4A and D5A in the Y-axis direction on the first side SA of the axis Al that are the same as distances D4B and D5B in the Y-axis direction on the second side SB of the axis Al.

[0052] In this regard, a first space SPA separating the first metal shielding structure 406A from the arrangement 412 of BAW resonators 404(l)-404(4) on the first side SA WT Ref No. 1173-967Qualcomm Ref No. 2500433 15of the first axis Al is symmetrical to a second space SPB separating the second metal shielding structure 406B from the arrangement 412 of BAW resonators 404(5)-404(8) on the second side SB of the first axis Al. More specifically, first space SPA includes an area 432A on the first side 412U of the arrangement 412 of BAW resonators 404(1)-404(8), an area 434A on the first end 430A of the arrangement 412, and an area 436A on the second side 412L of the arrangement 412. The second space SPB includes an area 432B on the first side 412U of the arrangement 412 of BAW resonators 404(l)-404(8), an area 434B on the second end 43 OB of the arrangement 412, and an area 436B on the second side 412L of the arrangement 412.

[0053] Figure 6 is an illustration of a plan view of a microacoustic filter 600 including a microacoustic filter structure 602 formed on a substrate 603. The microacoustic filter structure 602 (“filter structure 602”) includes a symmetrical arrangement 612 of serially-coupled BAW resonators 604(l)-604(8) that corresponds to the arrangement 412 in Figure 4. The arrangement 612 is symmetrical in the second, X-axis direction with respect to an axis A2 in the first, Y-axis direction, like the arrangement 412 in Figure 4. However, the filter structure 602 is an example including non-symmetrical metal shielding structures 606A, 606B, 606C, and 606D. In Figure 6, the metal shielding structures 606A, 606B, 606C, and 606D are not shaped and positioned to provide symmetrical spaces around the arrangement 612 on both sides of the axis A2. For example, the filter structure 602 does not include a metal shielding structure on the first side SA of the axis A2 that provides a spacing to the arrangement 612 symmetrical to a spacing between the arrangement 612 and the metal shielding structure 606D on the second side SB. Accordingly, the BAW resonators 604(l)-604(4) on the first side SA may be exposed to parasitic capacitance or noise from other features 608 of the microacoustic filter 600. As discussed above, the environment of the arrangement 612 may cause non-symmetrical operation of the BAW resonators 604(l)-604(4) compared to the BAW resonators 604(5)-604(8), which may lead to dips or spikes in an output signal S1G OUT generated by the microacoustic filter 600. The exemplary microacoustic filter 400 in Figure 4 includes symmetrical metal shielding structures for improved performance.

[0054] Figure 7 is a flowchart of a method 700 of fabricating a microacoustic filter 400, the method comprising: forming a substrate 403 (block 702), and forming an acoustic filter on the substrate 403 and comprising an arrangement 412 of bulk acoustic wave (BAW) resonators 404(l)-404(8) coupled in series, wherein: each of the BAW resonators WT Ref No. 1173-967Qualcomm Ref No. 2500433 16404(l)-404(8) comprises: a first electrode 422(l)-422(8) in a first metal layer 416; a second electrode 424(l)-424(8) in a second metal layer 420; and a piezoelectric slab 410(l)-410(8) disposed between the first electrode 422(l)-422(8) and the second electrode 424(1 )-424(8); and the arrangement 412 of BAW resonators 404(l)-404(8) is symmetrical with respect to a first axis Al extending in a first direction (block 704). The method 700 includes forming a first metal shielding structure 406A disposed around the arrangement 412 of BAW resonators 404(l)-404(4) on a first side SA of the axis Al (block 706); and forming a second metal shielding structure 406B disposed around the arrangement 412 of BAW resonators 404(5)-404(8) on a second side SB of the axis Al (block 708).

[0055] Microacoustic filters may include microacoustic filter structures including a symmetrical arrangement of serially-coupled acoustic resonators and metal shielding structures providing symmetrical spacing around the resonator arrangement, as shown in Figure 4. Examples of such microacoustic filters, without limitation, include a set top box, an entertainment unit, a navigation device, a communications device, a fixed location data unit, a mobile location data unit, a global positioning system (GPS) device, a mobile phone, a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a tablet, a phablet, a server, a computer, a portable computer, a mobile computing device, laptop computer, a wearable computing device (e.g., a smart watch, a health or fitness tracker, eyewear, etc.), a desktop computer, a personal digital assistant (PDA), a monitor, a computer monitor, a television, a tuner, a radio, a satellite radio, a music player, a digital music player, a portable music player, a digital video player, a video player, a digital video disc (DVD) player, a portable digital video player, an automobile, a vehicle component, an avionics system, a drone, and a multicopter.

[0056] Figure 8 illustrates an exemplary wireless communications device 800 that includes radio-frequency (RF) components formed from one or more dies 802, wherein any of the dies 802 may include a microacoustic filter including a microacoustic filter structure including a symmetrical arrangement of serially-coupled acoustic resonators and metal shielding structures providing symmetrical spacing around the resonator arrangement, as shown in Figure 4. The wireless communications device 800 may include or be provided in any of the above-referenced devices, as examples. As shown in Figure 8, the wireless communications device 800 includes a transceiver 804 and a data processor 806 The data processor 806 may include a memory to store data and program codes. The transceiver 804 includes a transmitter 808 and a receiver 810 that support bi- WT Ref No. 1173-967Qualcomm Ref No. 2500433 17directional communications. In general, the wireless communications device 800 may include any number of transmitters 808 and / or receivers 810 for any number of communication systems and frequency bands. All or a portion of the transceiver 804 may be implemented on one or more analog ICs, RF ICs (RFICs), mixed-signal ICs, etc.

[0057] The transmitter 808 or the receiver 810 may be implemented with a superheterodyne architecture or a direct-conversion architecture. In the super-heterodyne architecture, a signal is frequency-converted between RF and baseband in multiple stages, for example, from RF to an intermediate frequency (IF) in one stage and then from IF to baseband in another stage for the receiver 810. In the direct-conversion architecture, a signal is frequency-converted between RF and baseband in one stage The superheterodyne and direct-conversion architectures may use different circuit blocks and / or have different requirements. In the wireless communications device 800 in Figure 8, the transmitter 808 and the receiver 810 are implemented with the direct-conversion architecture.

[0058] In the transmit path, the data processor 806 processes data to be transmitted and provides I and Q analog output signals to the transmitter 808. In the exemplary wireless communications device 800, the data processor 806 includes digital-to-analog converters (DACs) 812(1), 812(2) for converting digital signals generated by the data processor 806 into the I and Q analog output signals (e g , I and Q output currents) for further processing.

[0059] Within the transmitter 808, lowpass filters 814(1), 814(2) filter the I and Q analog output signals, respectively, to remove undesired signals caused by the prior digital-to-analog conversion. Amplifiers (AMPs) 816(1), 816(2) amplify the signals from the lowpass filters 814(1), 814(2), respectively, and provide I and Q baseband signals. An upconverter 818 upconverts the I and Q baseband signals with I and Q transmit (TX) local oscillator (LO) signals through mixers 820(1), 820(2) from a TX LO signal generator 822 to provide an upconverted signal 824. A filter 826 filters the upconverted signal 824 to remove undesired signals caused by the frequency up-conversion as well as noise in a receive frequency band. A power amplifier (PA) 828 amplifies the upconverted signal 824 from the filter 826 to obtain the desired output power level and provides a transmit RF signal. The transmit RF signal is routed through a duplexer or switch 830 and transmitted via an antenna 832.

[0060] In the receive path, the antenna 832 receives signals transmitted by base stations and provides a received RF signal, which is routed through the duplexer or switch WT Ref No. 1173-967Qualcomm Ref No. 2500433 18830 and provided to a low noise amplifier (LNA) 834. The duplexer or switch 830 is designed to operate with a specific receive (RX)-to-TX duplexer frequency separation, such that RX signals are isolated from TX signals. The received RF signal is amplified by the LNA 834 and filtered by a filter 836 to obtain a desired RF input signal. Downconversion mixers 838(1), 838(2) mix the output of the filter 836 with I and Q RX LO signals (i.e., LO_I and LO_Q) from an RX LO signal generator 840 to generate I and Q baseband signals. The 1 and Q baseband signals are amplified by AMPs 842(1), 842(2) and further filtered by lowpass filters 844(1), 844(2) to obtain I and Q analog input signals, which are provided to the data processor 806. In this example, the data processor 806 includes analog-to-digital converters (ADCs) 846(1), 846(2) for converting the analog input signals into digital signals to be further processed by the data processor 806.

[0061] In the wireless communications device 800 of Figure 8, the TX LO signal generator 822 generates the I and Q TX LO signals used for frequency up-conversion, while the RX LO signal generator 840 generates the I and Q RX LO signals used for frequency down-conversion. Each LO signal is a periodic signal with a particular fundamental frequency. A TX phase-locked loop (PLL) circuit 848 receives timing information from the data processor 806 and generates a control signal used to adjust the frequency and / or phase of the TX LO signals from the TX LO signal generator 822. Similarly, an RX PLL circuit 850 receives timing information from the data processor 806 and generates a control signal used to adjust the frequency and / or phase of the RX LO signals from the RX LO signal generator 840. The microacoustic filter 400 may be employed in one or both of the filters 852 and 854 in Figure 8.

[0062] In this regard, Figure 9 illustrates an example of a processor-based system 900 that can include a microacoustic filter including a microacoustic filter structure including a symmetrical arrangement of serially-coupled acoustic resonators and metal shielding structures providing symmetrical spacing around the resonator arrangement, as shown in Figure 4. The processor-based system 900 also includes an IC 904 including a central processing unit (CPU) 908 that includes one or more processors 910, which may also be referred to as CPU cores or processor cores. The CPU 908 may have cache memory 912 coupled to the CPU 908 for rapid access to temporarily stored data. The CPU 908 is coupled to a system bus 914 and can intercouple master and slave devices included in the processor-based system 900. As is well known, the CPU 908 communicates with these other devices by exchanging address, control, and data information over the system bus 914. For example, the CPU 908 can communicate bus transaction requests to a memory WT Ref No. 1173-967Qualcomm Ref No. 2500433 19controller 916, as an example of a slave device. Although not illustrated in Figure 9, multiple system buses 914 could be provided, wherein each system bus 914 constitutes a different fabric.

[0063] Other master and slave devices can be connected to the system bus 914. As illustrated in Figure 9, these devices can include a memory system 920 that includes the memory controller 916 and a memory array(s) 918, one or more input devices 922, one or more output devices 924, one or more network interface devices 926, and one or more display controllers 928, as examples. The input device(s) 922 can include any type of input device, including, but not limited to, input keys, switches, voice processors, etc. The output device(s) 924 can include any type of output device, including, but not limited to, audio, video, other visual indicators, etc. The network interface device(s) 926 can be any device configured to allow an exchange of data to and from a network 930. The network 930 can be any type of network, including, but not limited to, a wired or wireless network, a private or public network, a local area network (LAN), a wireless local area network (WLAN), a wide area network (WAN), a BLUETOOTH™ network, and the Internet. The network interface device(s) 926 can be configured to support any type of communications protocol desired.

[0064] The CPU 908 may also be configured to access the display controller(s) 928 over the system bus 914 to control information sent to one or more displays 932. The display controlled s) 928 sends information to the display(s) 932 to be displayed via one or more video processed s) 934, which processes the information to be displayed into a fonnat suitable for the display(s) 932. The display(s) 932 can include any type of display, including, but not limited to, a cathode ray tube (CRT), a liquid crystal display (LCD), a plasma display, a light emitting diode (LED) display, etc.

[0065] Those of skill in the art will further appreciate that the various illustrative logical blocks, modules, circuits, and algorithms described in connection with the aspects disclosed herein may be implemented as electronic hardware, instructions stored in memory or in another computer-readable medium wherein any such instructions are executed by a processor or other processing device, or combinations of both. The devices and components described herein may be employed in any circuit, hardware component, integrated circuit (TC), or IC chip, as examples. Memory disclosed herein may be any type and size of memory and may be configured to store any type of information desired. To clearly illustrate this interchangeability, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their WT Ref No. 1173-967Qualcomm Ref No. 2500433 20functionality. How such functionality is implemented depends upon the particular application, design choices, and / or design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

[0066] The various illustrative logical blocks, modules, and circuits described in connection with the aspects disclosed herein may be implemented or performed with a processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration).

[0067] The aspects disclosed herein may be embodied in hardware and in instructions that are stored in hardware and may reside, for example, in Random Access Memory (RAM), flash memory, Read Only Memory (ROM), Electrically Programmable ROM (EPROM), Electrically Erasable Programmable ROM (EEPROM), registers, a hard disk, a removable disk, a CD-ROM, or any other form of computer readable medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from and write information to the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a remote station. In the alternative, the processor and the storage medium may reside as discrete components in a remote station, base station, or server.

[0068] It is also noted that the operational steps described in any of the exemplary aspects herein are described to provide examples and discussion. The operations described may be performed in numerous different sequences other than the illustrated sequences. Furthermore, operations described in a single operational step may actually be performed in a number of different steps. Additionally, one or more operational steps discussed in the exemplary aspects may be combined It is to be understood that the operational steps illustrated in the flowchart diagrams may be subject to numerous WT Ref No. 1173-967Qualcomm Ref No. 2500433 21different modifications as will be readily apparent to one of skill in the art. Those of skill in the art will also understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0069] The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0070] Implementation examples are described in the following numbered clauses: 1. A die, comprising:a substrate;an acoustic filter on the substrate and comprising an arrangement of bulk acoustic wave (BAW) resonators coupled in series, wherein:each of the BAW resonators comprises:a first electrode in a first section of a first metal layer;a second electrode in a second section of a second metal layer; and a piezoelectric slab disposed between the first electrode and the second electrode; andthe arrangement of BAW resonators is symmetrical with respect to a first axis extending in a first direction;a first metal shielding structure disposed around the arrangement of BAW resonators on a first side of the first axis; anda second metal shielding structure disposed around the arrangement of BAW resonators on a second side of the first axis.2. The die of clause 1, wherein a first space separating the first metal shielding structure from the arrangement of BAW resonators on the first side of the first axis isWT Ref No. 1173-967Qualcomm Ref No. 2500433 22symmetrical to a second space separating the second metal shielding structure from the arrangement of BAW resonators on the second side of the first axis.3. The die of clause 2, wherein the arrangement of BAW resonators extends in the first direction and in a second direction orthogonal to the first direction4. The die of clause 3, wherein:the first space comprises:a first area on a first side of the arrangement of BAW resonators in the first direction; andthe second space comprises:a second area on the first side of the arrangement of BAW resonators in the second direction.5. The die of clause 4, wherein:the first space comprises:a third area on a first end of the arrangement of BAW resonators in the second direction; anda fourth area on a second side of the arrangement of BAW resonators in the first direction; andthe second space comprises:a fifth area on a second end of the arrangement of BAW resonators in the second direction; anda sixth area on the second side of the arrangement of BAW resonators in the first direction.6. The die of any of clause 1 to clause 5, wherein each of the first metal shielding structure and the second metal shielding structure comprises a first plurality of metal layers comprising at least one of the first metal layer and the second metal layer.7. The die of any of clause 1 to clause 6, wherein each of the first metal shielding structure and the second metal shielding structure extend in a third direction, orthogonal to the first direction and the second direction, between the first metal layer and the second metal layer.WT Ref No. 1173-967Qualcomm Ref No. 2500433 238. The die of any of clause 1 to clause 7, wherein each of the BAW resonators in the series has a same first capacitance.9. The die of any of clause 3 to clause 8, wherein each of the piezoelectric slabs comprises a same first shape in a plane extending in the first direction and the second direction.10. The die of any of clause 3 to clause 9, wherein a perimeter of each of the piezoelectric slabs in a plane extending in the first direction and the second direction comprises five (5) sides.11. The die of any of clause 1 to clause 10, wherein:a first BAW resonator in the arrangement of BAW resonators at a first end of the series is configured to couple to a signal input; anda second BAW resonator in the arrangement of BAW resonators at a second end of the series is coupled to a signal output.12. The die of any of clause 1 to clause 11, wherein:the first metal shielding structure is disposed exclusively on the first side of the first axis; andthe second metal shielding structure is disposed exclusively on the second side of the first axis.13. The die of any of clause 1 to clause 12 integrated into a device selected from the group consisting of: a set-top box; an entertainment unit, a navigation device, a communications device; a fixed location data unit; a mobile location data unit; a global positioning system (GPS) device; a mobile phone; a cellular phone; a smartphone; a session initiation protocol (SIP) phone; a tablet; a phablet; a server; a computer; a portable computer; a mobile computing device; a wearable computing device; a desktop computer; a personal digital assistant (PDA); a monitor; a computer monitor; a television; a tuner; a radio; a satellite radio; a music player; a digital music player; a portable music player; a digital video player; a video player; a digital video disc (DVD) player, a portable digital video player; an automobile; a vehicle component; an avionics system; a drone; and a multicopter.WT Ref No. 1173-967Qualcomm Ref No. 2500433 2414. A method of manufacturing a microacoustic filter, comprising:forming a substrate;forming an acoustic filter on the substrate and comprising an arrangement of bulk acoustic wave (BAW) resonators coupled in series, wherein: each of the BAW resonators comprises:a first electrode formed in a first metal layer;a second electrode formed in a second metal layer; and a piezoelectric slab disposed between the first electrode and the second electrode; andthe arrangement of BAW resonators is symmetrical with respect to a first axis extending in a first direction;forming a first metal shielding structure disposed around the arrangement of BAW resonators on a first side of the first axis; andforming a second metal shielding structure disposed around the arrangement of BAW resonators on a second side of the first axis;wherein a first space separating the first metal shielding structure from the arrangement of BAW resonators on the first side of the first axis is symmetrical to a second space separating the second metal shielding structure from the arrangement of BAW resonators on the second side of the first axis.15. An acoustic filter structure, comprising:an arrangement of bulk acoustic wave (BAW) resonators coupled in series, wherein:each of the BAW resonators comprises:a first electrode formed in a first metal layer;a second electrode formed in a second metal layer; and a piezoelectric slab disposed between the first electrode and the second electrode;a first metal shielding structure disposed around the arrangement of BAW resonators and on a first side of a first axis extending through the arrangement of BAW resonators in a first direction, anda second metal shielding structure disposed around the arrangement of BAW resonators on a second side of the first axis.WT Ref No. 1173-967Qualcomm Ref No. 2500433 2516. The acoustic filter structure of clause 15, wherein the arrangement of BAW resonators is symmetrical with respect to the first axis.17. The acoustic filter structure of clause 15, wherein a first space separating the first metal shielding structure from the arrangement of BAW resonators on the first side of the first axis is symmetrical to a second space separating the second metal shielding structure from the arrangement of BAW resonators on the second side of the first axis.18. The acoustic filter structure of any of clause 15 to clause 17, wherein the arrangement of BAW resonators extends in the first direction and in a second direction orthogonal to the first direction.19. The acoustic filter structure of clause 17 or clause 18, wherein:the first space comprises:a first area on a first side of the arrangement of BAW resonators in the first direction; andthe second space comprises:a second area on the first side of the arrangement of BAW resonators in the second direction.20. The acoustic filter structure of any of clause 17 to clause 19, wherein each of the first metal shielding structure and the second metal shielding structure comprises a first plurality of metal layers comprising at least one of the first metal layer and the second metal layer and extends in a third direction, orthogonal to the first direction and the second direction, between the first metal layer and the second metal layer.WTRef. No. 1173-967

Claims

Qualcomm Ref No. 2500433 26What is claimed is:

1. A die, comprising:a substrate,an acoustic filter on the substrate and comprising an arrangement of bulk acoustic wave (BAW) resonators coupled in series, wherein:each of the BAW resonators comprises:a first electrode in a first section of a first metal layer;a second electrode in a second section of a second metal layer; and a piezoelectric slab disposed between the first electrode and the second electrode; andthe arrangement of BAW resonators is symmetrical with respect to a first axis extending in a first direction;a first metal shielding structure disposed around the arrangement of BAW resonators on a first side of the first axis; anda second metal shielding structure disposed around the arrangement of BAW resonators on a second side of the first axis.

2. The die of claim 1, wherein a first space separating the first metal shielding structure from the arrangement of BAW resonators on the first side of the first axis is symmetrical to a second space separating the second metal shielding structure from the arrangement of BAW resonators on the second side of the first axis.

3. The die of claim 2, wherein the arrangement of BAW resonators extends in the first direction and in a second direction orthogonal to the first direction.

4. The die of claim 3, wherein:the first space comprises:a first area on a first side of the arrangement of BAW resonators in the first direction; andthe second space comprises:a second area on the first side of the arrangement of BAW resonators in the second direction.WT Ref No. 1173-967Qualcomm Ref No. 2500433 275. The die of claim 4, wherein:the first space comprises:a third area on a first end of the arrangement of BAW resonators in the second direction; anda fourth area on a second side of the arrangement of BAW resonators in the first direction; andthe second space comprises:a fifth area on a second end of the arrangement of BAW resonators in the second direction; anda sixth area on the second side of the arrangement of BAW resonators in the first direction.

6. The die of claim 1, wherein each of the first metal shielding structure and the second metal shielding structure comprises a first plurality of metal layers comprising at least one of the first metal layer and the second metal layer.

7. The die of claim 1, wherein each of the first metal shielding structure and the second metal shielding structure extend in a third direction, orthogonal to the first direction and the second direction, between the first metal layer and the second metal layer.

8. The die of claim 1, wherein each of the BAW resonators in the series has a same first capacitance.

9. The die of claim 3, wherein each of the piezoelectric slabs comprises a same first shape in a plane extending in the first direction and the second direction.

10. The die of claim 3, wherein a perimeter of each of the piezoelectric slabs in a plane extending in the first direction and the second direction comprises five (5) sides.

11. The die of claim 1, wherein:a first BAW resonator in the arrangement of BAW resonators at a first end of the series is configured to couple to a signal input; andWT Ref No. 1173-967Qualcomm Ref No. 2500433 28a second B AW resonator in the arrangement of BAW resonators at a second end of the series is coupled to a signal output.

12. The die of claim 1, wherein:the first metal shielding structure is disposed exclusively on the first side of the first axis; andthe second metal shielding structure is disposed exclusively on the second side of the first axis.

13. The die of claim 1 integrated into a device selected from the group consisting of: a set-top box; an entertainment unit; a navigation device; a communications device, a fixed location data unit; a mobile location data unit; a global positioning system (GPS) device; a mobile phone; a cellular phone; a smartphone; a session initiation protocol (SIP) phone; a tablet; a phablet; a server; a computer; a portable computer; a mobile computing device; a wearable computing device; a desktop computer; a personal digital assistant (PDA); a monitor; a computer monitor; a television; a tuner; a radio; a satellite radio; a music player; a digital music player; a portable music player; a digital video player; a video player; a digital video disc (DVD) player, a portable digital video player; an automobile; a vehicle component; an avionics system; a drone; and a multicopter.

14. A method of manufacturing a microacoustic filter, comprising:forming a substrate;forming an acoustic filter on the substrate and comprising an arrangement of bulk acoustic wave (BAW) resonators coupled in series, wherein: each of the BAW resonators comprises:a first electrode formed in a first metal layer;a second electrode formed in a second metal layer; and a piezoelectric slab disposed between the first electrode and the second electrode; andthe arrangement of BAW resonators is symmetrical with respect to a first axis extending in a first direction;forming a first metal shielding structure disposed around the arrangement of BAW resonators on a first side of the first axis; andWT Ref No. 1173-967Qualcomm Ref No. 2500433 29forming a second metal shielding structure disposed around the arrangement of BAW resonators on a second side of the first axis;wherein a first space separating the first metal shielding structure from the arrangement of BAW resonators on the first side of the first axis is symmetrical to a second space separating the second metal shielding structure from the arrangement of BAW resonators on the second side of the first axis.

15. An acoustic filter structure, comprising:an arrangement of bulk acoustic wave (BAW) resonators coupled in series, wherein:each of the BAW resonators comprises:a first electrode formed in a first metal layer;a second electrode formed in a second metal layer; and a piezoelectric slab disposed between the first electrode and the second electrode;a first metal shielding structure disposed around the arrangement of BAW resonators and on a first side of a first axis extending through the arrangement of BAW resonators in a first direction; anda second metal shielding structure disposed around the arrangement of BAW resonators on a second side of the first axis.

16. The acoustic filter structure of claim 15, wherein the arrangement of BAW resonators is symmetrical with respect to the first axis.

17. The acoustic filter structure of claim 15, wherein a first space separating the first metal shielding structure from the arrangement of BAW resonators on the first side of the first axis is symmetrical to a second space separating the second metal shielding structure from the arrangement of BAW resonators on the second side of the first axis.

18. The acoustic filter structure of claim 15, wherein the arrangement of BAW resonators extends in the first direction and in a second direction orthogonal to the first direction.WT Ref No. 1173-967Qualcomm Ref No. 2500433 3019. The acoustic filter structure of claim 17, wherein:the first space comprises:a first area on a first side of the arrangement of BAW resonators in the first direction; andthe second space comprises:a second area on the first side of the arrangement of BAW resonators in the second direction.

20. The acoustic filter structure of claim 17, wherein each of the first metal shielding structure and the second metal shielding structure comprises a first plurality of metal layers comprising at least one of the first metal layer and the second metal layer and extends in a third direction, orthogonal to the first direction and the second direction, between the first metal layer and the second metal layer.WT Ref No. 1173-967

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