Separation ladder wave filter

Abstract

A filter device and a method of manufacturing the filter device. The filter device includes a first chip and a second chip. The first chip has a first material stack and includes one or more series resonators of a stepped filter circuit. The second chip has a second material stack and includes one or more parallel resonators of a stepped filter circuit. The first material stack and the second material stack are different.

Description

[0001] This application is a divisional application of Chinese invention patent application No. 202080044128.1, filed on June 17, 2020, entitled "Separated Stepped Acoustic Filter". Technical Field

[0002] This disclosure relates to radio frequency filters using acoustic resonators, and more particularly to filters used in communication devices. Background Technology

[0003] Radio frequency (RF) filters are two-ended devices configured to allow some frequencies to pass while blocking others. "Passing" means transmitting with relatively low insertion loss, while "blocking" means blocking or essentially attenuating. The range of frequencies a filter can pass through is called its "passband." The range of frequencies blocked by such a filter is called its "stopband." A typical RF filter has at least one passband and at least one stopband. The specific requirements for the passband or stopband depend on the application. For example, a "passband" can be defined as a frequency range where the filter's insertion loss is less than a defined value such as 1 dB, 2 dB, or 3 dB. A "stopband" can be defined as a frequency range where the filter's insertion loss is greater than a defined value, such as 20 dB, 30 dB, 40 dB, or larger, depending on the application.

[0004] RF filters are used in communication systems that transmit information over wireless links. For example, RF filters can be found in base stations, mobile phones and computing devices, satellite transceivers and ground stations, Internet of Things (IoT) devices, laptops and tablets, fixed-point radio links, and the RF front end of other communication systems. RF filters are also used in radar and electronic and information warfare systems.

[0005] RF filters typically require numerous design trade-offs to achieve the optimal balance between performance parameters such as insertion loss, suppression, isolation, power handling, linearity, size, and cost for each specific application. Specific design and manufacturing approaches and enhancements can simultaneously benefit one or more of these requirements.

[0006] Enhancements to the performance of RF filters in wireless systems can have a wide-ranging impact on system performance. Improvements to RF filters can lead to improvements such as larger cell size, longer battery life, higher data rates, greater network capacity, lower cost, enhanced security, and higher reliability. These improvements can be implemented individually or in combination at various levels of the wireless system, such as at the RF module, RF transceiver, mobile or fixed subsystem, or network level. Summary of the Invention

[0007] The present invention discloses a filter device, comprising: a first chip having a first material stack, the first chip including one or more series resonators of a stepped filter circuit; and a second chip having a second material stack, the second chip including one or more parallel resonators of a stepped filter circuit, wherein the first material stack and the second material stack are different.

[0008] The first chip contains all the series resonators of the stepped filter circuit, and the second chip contains all the parallel resonators of the stepped filter circuit.

[0009] The first chip and the second chip are attached to a circuit card, which includes at least one conductor for making an electrical connection between one of the series resonators of one or more series resonators and one of the parallel resonators of one or more parallel resonators.

[0010] Wherein, the first material stack includes a first piezoelectric element, the second material stack includes a second piezoelectric element, and the first piezoelectric element and the second piezoelectric element differ in at least one aspect of material, thickness, and orientation of the crystal axis of the material.

[0011] Wherein, the one or more series resonators and the one or more parallel resonators are unbonded SAW (surface acoustic wave) resonators, and the first material stack and the second material stack differ in one or more of the following aspects: the material of the piezoelectric plate, the thickness of the piezoelectric plate, the orientation of the crystal axis of the piezoelectric plate, the material of the conductor pattern formed above the piezoelectric plate, the thickness of the conductor pattern, the material of the dielectric layer formed above the conductor pattern, and the thickness of the dielectric layer.

[0012] Wherein, the one or more series resonators and the one or more parallel resonators are combined wafer resonators, and the first material stack and the second material stack differ in one or more of the following aspects: the material of the base, the thickness of the base, the dielectric layer material between the base and the piezoelectric wafer, the thickness of the dielectric layer between the base and the piezoelectric wafer, the material of the piezoelectric wafer, the thickness of the piezoelectric wafer, the orientation of the crystal axis of the piezoelectric wafer, the material of the conductor pattern formed above the piezoelectric wafer, the thickness of the conductor pattern, the material of the dielectric layer formed above the conductor pattern, and the thickness of the dielectric layer formed above the conductor pattern.

[0013] Wherein, the one or more series resonators and the one or more parallel resonators are floating diaphragm resonators, and the first material stack and the second material stack differ in one or more of the following aspects: the material of the base, the thickness of the base, the dielectric layer material between the base and the piezoelectric wafer, the thickness of the dielectric layer between the base and the piezoelectric wafer, the material of the piezoelectric wafer, the thickness of the piezoelectric wafer, the orientation of the crystal axis of the piezoelectric wafer, the material of the conductor pattern formed above the piezoelectric wafer, the thickness of the conductor pattern, the material of the dielectric layer formed above the conductor pattern, and the thickness of the dielectric layer formed above the conductor pattern.

[0014] Wherein, the one or more series resonators and the one or more parallel resonators are solid-state assembled diaphragm resonators, and the first material stack and the second material stack differ in one or more of the following aspects: the material of the base, the thickness of the base, the number of layers of the acoustic Bragg reflector disposed between the base and the piezoelectric wafer, and the material and thickness of each layer, the thickness of the dielectric layer between the base and the piezoelectric wafer, the material of the piezoelectric wafer, the thickness of the piezoelectric wafer, the orientation of the crystal axis of the piezoelectric wafer, the material of the conductor pattern formed above the piezoelectric wafer, the thickness of the conductor pattern, the material of the dielectric layer formed above the conductor pattern, and the thickness of the dielectric layer formed above the conductor pattern.

[0015] Wherein, the one or more series resonators and the one or more parallel resonators are thin-film bulk acoustic wave resonators, and the first material stack and the second material stack differ in one or more of the following aspects: the material of the base, the thickness of the base, the material of the lower conductor pattern, the lower conductor pattern being disposed between the base and the piezoelectric element, the thickness of the lower conductor pattern, the material of the piezoelectric element, the thickness of the piezoelectric element, the crystal axis orientation of the piezoelectric element, the material of the upper conductor pattern formed above the piezoelectric element, the thickness of the upper conductor pattern, the material of the dielectric layer formed above the upper conductor pattern, and the thickness of the dielectric layer.

[0016] Wherein, the one or more series resonators and the one or more parallel resonators are solid-state assembled thin-film bulk acoustic resonators, and the first material stack and the second material stack differ in one or more of the following aspects: the material of the base, the thickness of the base, the number of layers of the acoustic Bragg reflector disposed between the base and the lower conductor pattern, and the material and thickness of each layer, the material of the lower conductor pattern disposed between the acoustic Bragg reflector and the piezoelectric element, the thickness of the lower conductor pattern, the material of the piezoelectric element, the thickness of the piezoelectric element, the crystal axis orientation of the piezoelectric element, the material of the upper conductor pattern formed above the piezoelectric element, the thickness of the upper conductor pattern, the material of the dielectric layer formed above the upper conductor pattern, and the thickness of the dielectric layer.

[0017] Wherein, the one or more series resonators and the one or more parallel resonators are combined wafer resonators, the first material stack includes a 46-degree Y-cut lithium tantalate piezoelectric wafer, and the second material stack includes a 42-degree Y-cut lithium tantalate piezoelectric wafer.

[0018] Wherein, the one or more series resonators are bonded wafer resonators, and the one or more parallel resonators are unbonded SAW resonators.

[0019] The present invention also discloses a duplexer, including a transmit staircase filter circuit and a receive staircase filter circuit, comprising: a first chip having a first material stack, the first chip including one or more series resonators of the transmit staircase filter circuit; and a second chip having a second material stack, the second chip including one or more parallel resonators of the receive filter circuit, wherein the first material stack and the second material stack are different.

[0020] The first chip includes a series resonator of the transmitting ladder filter circuit and the receiving ladder filter circuit, and the second chip includes a parallel resonator of the transmitting ladder filter circuit and the receiving ladder filter circuit.

[0021] The first chip contains all the series resonators of the transmitting ladder filter circuit and the receiving ladder filter circuit, and the second chip contains all the parallel resonators of the transmitting ladder filter circuit and the receiving ladder filter circuit.

[0022] The first chip includes a series resonator of the transmitting ladder filter circuit, and the second chip includes a parallel resonator of the transmitting ladder filter circuit and all the resonators of the receiving filter circuit.

[0023] The series resonator of the transmitting ladder filter circuit is a combined wafer resonator, and the parallel resonator of the transmitting ladder filter circuit and all the resonators of the receiving filter circuit are uncombined SAW resonators.

[0024] The present invention further discloses a method for manufacturing a filter device, comprising: fabricating a first chip having a first material stack, the first chip including one or more series resonators of a stepped filter circuit; and

[0025] A second chip is manufactured having a second material stack, the second chip containing one or more parallel resonators of the stepped filter circuit, wherein the first material stack and the second material stack are different.

[0026] The first chip contains all the series resonators of the stepped filter circuit, and the second chip contains all the parallel resonators of the stepped filter circuit.

[0027] The first chip and the second chip are attached to a circuit card, which includes at least one conductor for making an electrical connection between one of the series resonators of the one or more series resonators and one of the parallel resonators of the one or more parallel resonators.

[0028] Wherein, the first material stack includes a first piezoelectric element, the second material stack includes a second piezoelectric element, and the first piezoelectric element and the second piezoelectric element differ in at least one aspect of the material, thickness, and orientation of the crystal axis of the material. Attached Figure Description

[0029] Figure 1A This is a schematic diagram of an exemplary RF ladder filter circuit that includes an acoustic resonator.

[0030] Figure 1B This is a schematic diagram of an alternative embodiment of an RF ladder filter circuit that includes an acoustic resonator.

[0031] Figure 2A This is a simplified schematic cross-sectional view of the first acoustic resonator.

[0032] Figure 2B This is a simplified schematic cross-sectional view of the second acoustic resonator.

[0033] Figure 3A This is a simplified schematic cross-sectional view of the third acoustic resonator.

[0034] Figure 3B This is a simplified schematic cross-sectional view of the fourth acoustic resonator.

[0035] Figure 4AThis is a simplified schematic cross-sectional view of the fifth acoustic resonator.

[0036] Figure 4B This is a simplified schematic cross-sectional view of the sixth acoustic resonator.

[0037] Figure 5 This is a simplified schematic diagram of a traditional stepped filter.

[0038] Figure 6 This is a simplified schematic plan view of a separation ladder implementation of a bandpass filter.

[0039] Figure 7 yes Figure 6 A simplified schematic cross-sectional view of an exemplary bandpass filter separation ladder implementation.

[0040] Figure 8 This is a diagram of S12 comparing two exemplary implementations of a bandpass filter.

[0041] Figure 9 This is a diagram of S12 of an exemplary implementation of a separated ladder of a bandpass filter.

[0042] Figure 10A This is a simplified schematic diagram of a two-chip duplexer.

[0043] Figure 10B This is a simplified schematic plan view of the separation step implementation of a duplexer.

[0044] Figure 11 This is a simplified schematic plan view of another separate step implementation of a duplexer.

[0045] Figure 12 This is a flowchart of the manufacturing method of a discrete step filter device.

[0046] in, Figure 1A , Figure 1B , Figure 2A , Figure 2B , Figure 3A , Figure 3B , Figure 4A , Figure 4B , Figure 5 and Figure 10A The figures illustrate prior art. Throughout the specification, elements appearing in the figures are assigned three-digit reference numerals, where the two least significant bits are unique to that element, and one or two most significant bits are the figure number in which the element was first shown. It can be assumed that elements not described in conjunction with the figures have the same characteristics and functions as previously described elements having the same reference numerals. Detailed Implementation

[0047] Device Description

[0048] Figure 1A A simplified schematic circuit diagram of an exemplary RF filter circuit 100 is shown, which incorporates six acoustic resonators, labeled X1 to X6, arranged in a configuration commonly referred to as a “ladder”. This type of ladder filter is typically used in bandpass filters in communication equipment. Filter circuit 100 can be, for example, used in conjunction with a transmit or receive filter in a communication device. Filter circuit 100 is a two-port network, where one terminal of each port is typically connected to signal ground. Filter circuit 100 includes three series resonators (X1, X3, and X5) connected in series between a first port (port 1) and a second port (port 2). Either port can be the input of the filter, and the other port can be the output. Filter circuit 100 also includes three parallel resonators (X2, X4, and X6). Each parallel resonator is connected between ground and the node or input / output port of the adjacent series resonator. Figure 1A The simplified diagram omits passive components, such as the inductance inherent in the conductors of interconnecting resonators. The use of six acoustic resonators, three series resonators, and three parallel resonators is exemplary. Bandpass filter circuits may include more or fewer than six resonators, and more or fewer than three series resonators and three parallel resonators.

[0049] Figure 1B A simplified schematic diagram of an alternative RF filter circuit 150 is shown. The filter circuit 150 is a two-port network where the signals at each port are balanced, meaning the signals at the two terminals of each port are nominally equal in amplitude and 180 degrees out of phase. For the purposes of this patent, the RF filter circuit 150 is considered a stepped filter. Resonators X1a, X1b, X3a, X3b, X5a, and X5b are considered series resonators, while resonators X2, X4, and X6 are considered parallel resonators. The stepped filter circuit 150 is not commonly used, and all subsequent examples in this patent employ this method. Figure 1A The stepped filter configuration.

[0050] Each acoustic resonator X1 to X6 can be a bulk acoustic wave (BAW) resonator, a thin-film bulk acoustic wave (FBAW) resonator, a surface acoustic wave (SAW) resonator, a temperature-compensated surface acoustic wave resonator (TC-SAW), a wafer-mounted acoustic resonator, a laterally excited thin-film bulk acoustic wave resonator (XBAR) as described in application 16 / 230,443, a solid-state assembled laterally excited thin-film bulk acoustic wave resonator (SM-XBAR) as described in application 16 / 438,141, or other types of acoustic resonators. In current filters, the acoustic resonators are typically of the same type.

[0051] Each acoustic resonator exhibits very high admittance at its resonant frequency and very low admittance at its anti-resonant frequency, which is higher than the resonant frequency. In short, each resonator is approximately short-circuited at its resonant frequency and approximately open-circuited at its anti-resonant frequency. Therefore, the transmission between Port 1 and Port 2 of bandpass filter circuits 100 and 150 is very low at the resonant frequencies of the parallel resonators and the anti-resonant frequencies of the series resonators. In a typical stepped bandpass filter, the resonant frequency of the parallel resonators is lower than the lower edge of the filter's passband to create a stopband at frequencies below the passband. The anti-resonant frequency of the parallel resonators is typically within the filter's passband. Conversely, the anti-resonant frequency of the series resonators is higher than the upper edge of the passband to create a stopband at frequencies above the passband. The resonant frequency of the series resonators typically falls within the filter's passband. In some designs, the resonant frequencies of one or more parallel resonators may be higher than the upper edge of the passband.

[0052] Filter devices, such as bandpass filter circuits 100 and 150, including acoustic resonators, are conventionally implemented using multilayer materials, wherein multiple layers of material are deposited on, bonded to, or otherwise formed on a substrate. The substrate and sequence of material layers are often referred to as a “stack” for forming the acoustic resonator and filter device. In this patent, the term “material stack” refers to an ordered sequence of material layers formed on a substrate, wherein the substrate is considered part of the material stack. The term “element” refers to one of the layers in the substrate or material stack. At least one element (i.e., the substrate or layer) in the material stack is a piezoelectric material, such as quartz, lithium niobate, lithium tantalate, lanthanum gallium silicate, gallium nitride, or aluminum nitride. When the piezoelectric material is a single crystal, the orientation of the X, Y, Z crystal axes is known and consistent. One or more layers in the material stack, such as one or more conductor layers and / or dielectric layers, can be patterned using photolithography methods such that not all elements of the material stack are present at every point on the acoustic device.

[0053] Figure 2A This is a schematic cross-sectional view of a first exemplary acoustic resonator 200. The first acoustic resonator 200 will be referred to herein as an "unbonded SAW resonator" (as opposed to a bonded SAW resonator). Figure 2BThe term "bonded wafer resonator" is used in contrast to "unbonded SAW resonator." An "unbonded SAW resonator" is characterized by a conductor pattern 210 formed on a piezoelectric plate 205, which is not bonded to a thicker base or substrate. This term encompasses both temperature-compensated and non-temperature-compensated SAW resonators. The conductor pattern 210 comprises interdigital transducers (IDTs) formed on the surface of a plate 205 of a single-crystal piezoelectric material. Dimension p is the spacing between the IDT fingers or the conductor-to-conductor spacing. Dimension λ = 2p is the wavelength of the acoustic wave propagating across the surface of the piezoelectric plate 205. When multiple unbonded SAW resonators 200 are combined to form a filter device, the resonant frequency of each resonator is set by selecting the spacing of each resonator. Dimension h is the thickness of the conductor pattern. A dielectric layer 215 of thickness td1 can be deposited over and between the conductors of the conductor pattern. The dielectric layer 215 can be, for example, a thin passivation layer to seal and protect the electrode pattern and the surface of the piezoelectric plate 205. In a TC-SAW resonator, the dielectric layer 215 can be a relatively thick layer, such as a SiO2 layer, to reduce the frequency temperature coefficient of the resonator.

[0054] The material stack for an unbonded SAW resonator (e.g., the first exemplary acoustic resonator 200) includes a piezoelectric plate 205, a conductor pattern 210, and a dielectric layer 215. The piezoelectric plate 205 is defined by the material type, thickness, and crystal axis orientation of the piezoelectric material. The conductor pattern 210 is defined by a thickness h and a material, which may be, for example, aluminum, copper, gold, molybdenum, tungsten, alloys, or combinations thereof. The dielectric layer 215 is defined by a thickness td1 and a material, which may be, for example, silicon dioxide or silicon nitride. When multiple unbonded SAW resonators 200 are incorporated into a filter device, the material stack may include... Figure 2A Additional layers not shown. For example, filter devices typically include a second metal layer to increase the conductivity of the conductors of interconnect resonators, and may include an additional dielectric layer and / or a third metal layer of thick gold or solder to form bumps to interconnect the filter with an external circuit card.

[0055] Figure 2B This is a schematic cross-sectional view of a second exemplary acoustic resonator 220. The second acoustic resonator 220 will be referred to herein as a “bonded wafer resonator.” A “bonded wafer resonator” is characterized by a thin wafer or plate 225 of a single-crystal piezoelectric material bonded to a non-piezoelectric substrate 230. The thin wafer or plate 225 of the single-crystal piezoelectric material may be directly bonded to the non-piezoelectric substrate 230, or bonded to the non-piezoelectric substrate 230 through one or more intermediate dielectric layers 240. The second acoustic resonator 220 may be, for example, a bonded wafer SAW resonator, an IHP (Incredible High Performance) SAW resonator, or a plate-wave resonator. The second acoustic resonator 220 includes a conductor pattern 235 comprising an IDT formed on the surface of the thin wafer 225 of the single-crystal piezoelectric material. The thickness of the conductor pattern is dimension h (see…). Figure 2A ). Dimension tp is the thickness of the piezoelectric material wafer 225. Dimension p is the spacing between the IDT fingers or the conductor-to-conductor spacing. Dimension λ = 2p is the wavelength of the sound wave propagating across the surface of the piezoelectric wafer 225 or within the piezoelectric wafer 225. When multiple combined wafer resonators 220 are combined to form a filter device, the resonant frequencies of various resonators are set by selecting the IDT spacing of each resonator. Thickness td1 (see...) Figure 2A The dielectric layer 245 can be deposited on and between the conductors of the conductor pattern as described above. A second dielectric layer 240 with a thickness of td2 can be disposed between the wafer 225 and the substrate 230. In some cases, two dielectric layers can be disposed between the wafer 225 and the substrate 230.

[0056] The material stack used to incorporate a wafer resonator, such as the second exemplary acoustic resonator 220, includes a base 230, one or more underlying dielectric layers 240 (if present), a piezoelectric wafer 225, a conductor pattern 235, and dielectric layers 245. The base 230 is defined by material and thickness. The underlying dielectric layers 240 are defined by the material type and thickness td2 of each layer. The piezoelectric wafer 225 is defined by the material type, thickness tp, and crystal axis orientation of the piezoelectric material. The conductor pattern 235 is defined by thickness h (see [reference]). Figure 2A The dielectric layer 245 is defined by its thickness td1 and material. When multiple bonded wafer resonators 220 are bonded to a filter, the material stack may include additional layers as described above.

[0057] Figure 3A This is a schematic cross-sectional view of a third exemplary acoustic resonator 300. The third acoustic resonator 300 will be referred to herein as a "floating diaphragm resonator". The floating diaphragm resonator is characterized in that a thin diaphragm 335 of monocrystalline piezoelectric material floats above a cavity 330 formed in a non-piezoelectric substrate 315. The third acoustic resonator 300 may be, for example, an XBAR resonator as described in application 16 / 230,443 or other types of acoustic resonators. The third acoustic resonator 300 includes a conductor pattern 305 comprising an IDT formed on the surface of a thin wafer 310 of monocrystalline piezoelectric material, which is attached or bonded to the non-piezoelectric substrate 315. When the third acoustic resonator is a plate wave resonator, the conductor pattern may include a Bragg reflector (…). Figure 3A (Not shown in the image). One or more dielectric layers 320 may be present between wafer 310 and substrate 315. Cavity 330 is formed in substrate 315 and one or more dielectric layers 320 (if present), such that a portion of wafer 310 forms a diaphragm 335 spanning cavity 330. IDT fingers are disposed on diaphragm 335. Dielectric layer 325 may be deposited on and between the fingers of conductor pattern 305.

[0058] The material stack for a floating diaphragm resonator, such as the third exemplary acoustic resonator 300, includes a base 315, one or more underlying dielectric layers 320 (if present), a piezoelectric wafer 310, a conductor pattern 305, and a dielectric layer 325. The base 315 is defined by its material and thickness. The underlying dielectric layers 320 are defined by the material type and thickness td2 of each layer. The piezoelectric wafer 310 is defined by the material type, thickness tp, and crystal axis orientation of the piezoelectric material. The conductor pattern 305 is defined by its thickness and material. The dielectric layer 325 is defined by its thickness td1 and material. When multiple acoustic resonators 300 are incorporated into a filter, the material stack may include additional layers as described above.

[0059] Figure 3B This is a schematic cross-sectional view of a fourth exemplary acoustic resonator 350. The fourth acoustic resonator 350 will be referred to herein as a "solid-state assembled membrane resonator". The solid-state assembled membrane resonator is characterized by a conductor pattern 355 comprising an IDT formed on the surface of a thin film 360 of a single-crystal piezoelectric material supported by a non-piezoelectric substrate 365, with an acoustic Bragg reflector 370 sandwiched between the film 360 and the substrate 365. The acoustic Bragg reflector 370 comprises multiple layers alternating between a first material having high acoustic impedance and a second material having low acoustic impedance. The acoustic Bragg reflector 370 is configured to reflect and confine acoustic waves generated by the film 360. A dielectric layer 375 may be deposited on and between the fingers of the conductor pattern 355.

[0060] The material stack for the solid-state assembled membrane resonator 350 includes a base 365, an acoustic Bragg reflector 370, a piezoelectric film 360, a conductor pattern 355, and a dielectric layer 375. The base 365 is defined by its material and thickness. The acoustic Bragg reflector 370 is defined by the first and second material types of each layer, the number of layers, and the thickness of each layer. The piezoelectric film 360 is defined by the material type, thickness tp, and crystal axis orientation of the piezoelectric material. The conductor pattern 355 is defined by its thickness and material. The dielectric layer 375 is defined by its thickness td1 and material. When multiple solid-state assembled membrane resonators are incorporated into a filtering device, the material stack may include additional layers as described above.

[0061] Figure 4A This is a schematic cross-sectional view of a fifth exemplary acoustic resonator 400. The fifth acoustic resonator 400 is a thin-film bulk acoustic resonator (FBAR). The fifth acoustic resonator 400 includes a thin wafer or film 405 of a single-crystal piezoelectric material sandwiched between an upper conductor 420 and a lower conductor 415. This sandwich structure is supported by a non-piezoelectric base 410. A cavity 425 is formed in the base 410 such that a portion of the sandwich structure 415 / 405 / 420 forms a diaphragm across the cavity 425.

[0062] The material stack of the FBAR 400 includes a substrate 410, a lower conductor layer 415, a piezoelectric wafer or thin film 405, and an upper conductor layer 420. The substrate 410 is defined by its material and thickness. The lower conductor layer 415 is defined by its material type and thickness. The piezoelectric wafer or film 405 is defined by the material type, thickness, and crystal axis orientation of the piezoelectric material. The upper conductor layer 420 is defined by its thickness and material. When multiple FBARs 400 are incorporated into a filter, the material stack may include additional layers as described above.

[0063] Figure 4B This is a schematic cross-sectional view of the sixth exemplary acoustic resonator 450. The sixth acoustic resonator will be referred to herein as a "solid-state assembled thin-film bulk acoustic resonator" (SM-FBAR). The sixth acoustic resonator 450 includes a thin wafer or film 455 of a single-crystal piezoelectric material sandwiched between an upper conductor 470 and a lower conductor 465. This sandwich structure is supported by a non-piezoelectric base 460. An acoustic Bragg reflector 475 is sandwiched between the sandwich structure 470 / 455 / 465 and the base 460. The acoustic Bragg reflector 475 includes multiple layers, alternating between a first material with high acoustic impedance and a second material with low acoustic impedance. The acoustic Bragg reflector 475 is configured to reflect and confine acoustic waves generated by the sandwich structure 470 / 455 / 465.

[0064] The material stack for the SM-FBAR 450 includes a base 460, an acoustic Bragg reflector 475, a lower conductor layer 465, a piezoelectric wafer or film 455, and an upper conductor layer 470. The base 460 is defined by its material and thickness. The acoustic Bragg reflector 475 is defined by first and second material types, the number of layers, and the thickness of each layer. The lower conductor layer 465 is defined by its material type and thickness. The piezoelectric wafer or film 455 is defined by the material type, thickness, and crystal axis orientation of the piezoelectric material. The upper conductor layer 470 is defined by its thickness and material. When multiple SM-FBAR 450s are incorporated into a filter, the material stack may include additional layers as described above.

[0065] Figures 2A to 4B The acoustic resonators shown are not a list encompassing all types of acoustic resonators. Other types of acoustic resonators with different material stacks can be used in filters. Furthermore, Figures 2A to 4B A cross-sectional view may not necessarily show all layers in the corresponding material stack. For example, additional layers may exist to promote adhesion between other layers, prevent chemical interactions between other layers, or passivate and protect other layers.

[0066] Figure 5This is an exemplary schematic plan view of a conventional implementation of a bandpass filter 500, having the same schematic diagram as the bandpass filter circuit 100 shown in the figure. In the filter 500, all six acoustic resonators X1-X6 are formed on a common chip 510. All acoustic resonators X1-X6 can be unbonded SAW resonators, bonded wafer resonators, floating diaphragm resonators, solid-state assembled membrane resonators, FBARs, SM-FBARs, or some other type of acoustic resonator. All acoustic resonators X1 to X6 are typically of the same type. For ease of illustration, Figure 5 All resonators X1-X6 in the filter have the same dimensions. This is almost never seen in practical filters.

[0067] Acoustic resonators X1-X6 are interconnected via conductors (e.g., conductor 530) formed on substrate 510. Filter 500 is electrically connected to a system outside the filter via pads (e.g., pad 520). For example, each pad may be or be coupled with solder or gold bumps for connection to a circuit board (not shown). In addition to establishing electrical connections, pads and bumps are typically the primary means of removing heat from filter 500.

[0068] When multiple acoustic resonators are formed on the same chip, the fabrication process and material stacking of all resonators are essentially the same. In particular, the piezoelectric elements (i.e., plates, wafers, or thin films of piezoelectric material) within the material stack are identical for all resonators. However, the requirements for parallel and series resonators typically differ, as shown in the table below:

[0069]

[0070] It may be impossible to select the most suitable or even sufficient material stack for all resonators in the filter.

[0071] Figure 6 This is an exemplary schematic plan view of a stepped separation filter 600, which has the same characteristics as... Figure 1A The schematic diagram is the same as that of the stepped filter circuit 100. (Similar to...) Figure 5 Unlike the conventional filter 500 shown, the series resonators X1, X3, and X5 of the separated stepped filter 600 are fabricated on the first chip 610, and the parallel resonators X2, X4, and X6 of the separated stepped filter 600 are fabricated on the second chip 640. Within each chip 610, 640, the acoustic resonators are interconnected by conductors formed on the respective chips, such as conductor 630. The chips 610, 640 are electrically connected to each other and to a system external to the filter via pads such as pads 620. Each pad may be, for example, solder or gold bump, or interact with solder or gold bumps to connect to a circuit board (not shown).

[0072] The electrical connection 650 between the series resonator on the first chip 610 and the parallel resonator on the second chip 640 is shown as a thick dashed line. Connection 650 is made, for example, by conductors on a circuit card on which the first and second chips are mounted. In this context, the term "circuit card" refers to a basic planar structure containing conductors for connecting the first and second chips to each other and connecting them to the outside of the bandpass filter 600. The circuit card can be, for example, a single-layer or multi-layer printed circuit board, a low-temperature co-fired ceramic (LTCC) card, or other types of circuit cards. The traces on the circuit card may have very low resistance, so losses in the traces are negligible. The inductance of the electrical connection 650 between the series and parallel resonators can be compensated for in the design of the acoustic resonator.

[0073] In some cases, the performance of a filter can be improved by using an inductor with an electrical connection of 650, for example by increasing the filter bandwidth by lowering the resonant frequency of one or more parallel resonators.

[0074] In the exemplary separated ladder filter 600, all series resonators are on the first chip and all parallel resonators are on the second chip. However, this is not always the case. In some filters, the first chip may contain fewer than all series resonators and / or the second chip may contain fewer than all parallel resonators.

[0075] Figure 7 This is a schematic cross-sectional view of a discrete step filter 700, which may be a discrete step filter 600. The discrete step filter 700 includes a first chip 710 and a second chip 740 attached to and interconnected with a circuit card 770. In this example, the first and second chips 710, 740 are mounted to the circuit card 770 in a "flip-chip" manner. The electrical connection between the first and second chips 710, 740 and the circuit card 770 is made by solder or gold bumps, such as bump 720. The electrical connection between the first chip 710 and the second chip 740 is made by conductors, such as conductor 750, on or inside the circuit card 770. The first and second chips 710, 740 may be mounted on and / or connected to the circuit card 770 in some other way.

[0076] The advantage of separate stepped filters (such as separate stepped filters 600 and 700) is that stacks of different materials can be used for both series and parallel resonators. A first material stack can be used for a first chip containing some or all of the series resonators, while a second material stack can be used for a second chip containing some or all of the parallel resonators. The first and second material stacks can be different. This allows for separate optimization of the first and second material stacks for both series and parallel resonators.

[0077] Two material stacks are considered different if at least one aspect of at least one element within the stack differs. Differences between material stacks can be, for example, the order of the elements or different material types, thicknesses, or other parameters of at least one element in the stack. Typically, a first material stack includes a first piezoelectric element and a second material stack includes a second piezoelectric element that differs from the first piezoelectric element in at least one aspect of material, thickness, and orientation of the crystal axes of the materials.

[0078] like Figure 2A As shown, when the separate stepped filters 600 / 700 are incorporated into the unbonded SAW resonator, the first material stack and the second material stack may differ in one or more of the following characteristics: the material type, thickness and crystal axis orientation of the piezoelectric plate 205; the material and / or thickness h of the conductor pattern 210; and the thickness td1 and material of the dielectric layer 215.

[0079] When the 600 / 700 split-step filter is combined as follows: Figure 2B When the combined wafer resonator is shown, the first material stack and the second material stack may differ in one or more of the following characteristics: the material and thickness of the base 230; the number of underlying dielectric layers 240 (if any) and the material and thickness td2 of each layer; the material type, thickness tp and crystal axis orientation of the piezoelectric wafer 225; the thickness h and material of the conductor pattern 235; and the thickness td1 and material of the dielectric layer 245.

[0080] When the separate stepped filter 600 / 700 is combined as follows Figure 3A When the floating diaphragm resonator is shown, the first material stack and the second material stack may differ in one or more of the following characteristics: the material and thickness of the base 315; the number of underlying dielectric layers 320 (if any) and the material and thickness td2 of each layer; the material type, thickness tp and crystal axis orientation of the piezoelectric wafer 310; the thickness h and material of the conductor pattern 305; and the thickness td1 and material of the dielectric layer 325.

[0081] When the separate stepped filter 600 / 700 is combined as follows Figure 3B In the solid-state assembled film resonator shown, the first material stack and the second material stack may differ in one or more of the following characteristics: the material and thickness of the base 365; the number of layers in the acoustic Bragg reflector 370 and the material and thickness of each layer; the material type, thickness tp and crystal axis orientation of the piezoelectric wafer 360; the thickness h and material of the conductor pattern 365; and the thickness td1 and material of the dielectric layer 375.

[0082] When the separate step filter 600 / 700 is incorporated as follows Figure 4AIn the FBAR shown, the first material stack and the second material stack may differ in one or more of the following characteristics: the material and thickness of the base 410; the material and thickness of the lower conductor 415; the material type, thickness tp and crystal axis orientation of the piezoelectric wafer 405; and the thickness and material of the upper conductor 420.

[0083] When the separate step filter 600 / 700 is incorporated as follows Figure 4B In the SM-FBAR shown, the first and second material stacks may differ in one or more of the following characteristics: the material and thickness of the base 460; the number of layers in the acoustic Bragg reflector 475 and the material and thickness of each layer; the material and thickness of the lower conductor 465; the material type, thickness tp, and crystal axis orientation of the piezoelectric wafer 455; and the thickness and material of the upper conductor 470.

[0084] The preceding six paragraphs do not necessarily define the difference between the first and second material stacks of the separated stepped filter. In addition to the parameters identified herein, the first and second material stacks may differ on one or more parameters, or on one or more parameters not identified herein. The type of resonator is not limited to... Figures 2A to 4B The types shown. Furthermore, series resonators and parallel resonators do not necessarily have to be the same type of resonator.

[0085] Example 1

[0086] A desirable characteristic for filters used in portable devices is the stability of the filter passband over a wide temperature range. A technique that at least partially achieves this goal is to fabricate filters with resonators that incorporate a bonded wafer using thin wafers of piezoelectric material. The piezoelectric material is bonded to a substrate (e.g., a silicon substrate) having a low coefficient of thermal expansion and high thermal conductivity. Compared to filters using unbonded SAW resonators, bonded wafer SAW filters exhibit lower temperature rise at a given power input and reduced temperature sensitivity of the passband frequency.

[0087] One drawback of in-chip SAW resonators is the presence of parasitic acoustic modes that can propagate within the piezoelectric material or into the silicon wafer or other substrates. A key element in designing bandpass filters using in-chip resonators is ensuring that these parasitic modes appear at frequencies far from the filter's passband. The cross-sectional structure and material stacking of in-chip SAW resonators are similar to... Figure 2B The resonator is 250.

[0088] Figure 8This is diagram 800 showing the S12 amplitude of two bonded wafer SAW filters fabricated using lithium tantalate (LT) wafers bonded to a silicon substrate. S12 is the transmission between the first and second ports of the filter. The dashed line 810 is the S12 diagram of a filter fabricated on a 42-degree Y-cut LT wafer. The dashed line 820 is the S12 diagram of a filter fabricated on a 46-degree Y-cut LT wafer. The thick line 830 defines the requirements for LTE (Long Term Evolution) Band 2 transmission filters (insertion loss less than 2 dB in the transmission band from 1850 MHz to 1910 MHz).

[0089] When the filter is manufactured on a 42-degree LT (dotted line 810), parasitic modes appear at frequencies near the anti-resonant frequency of the series resonators in the filter. These parasitic modes reduce S12 near the upper edge of the filter passband between 1902 MHz and 1915 MHz (and correspondingly increase insertion loss).

[0090] When the filters are manufactured on 46-degree LT (dashed 820), parasitic modes appear at frequencies near the resonant frequency of the parallel resonator. These parasitic modes reduce S12 between 1845 MHz and 855 MHz (and correspondingly increase insertion loss). None of these filters meet the requirement of less than 2 dB insertion loss in the LTE Band 2 transmission band.

[0091] Figure 9 This is illustration 900 (curve 910) of the amplitude of S12 of a separate stepped LTE Band 2 transmit filter fabricated on two chips, each having a lithium tantalate (LT) wafer bonded to a silicon substrate. The first chip contains a series resonator fabricated on a 46-degree LT. The second chip contains a parallel resonator fabricated on a 42-degree LT. The material stacking for the first and second chips differs at least in the orientation of the crystal axes of their respective LT wafers, and in many other respects.

[0092] Using a 46-degree trailing edge (LT) for series resonators avoids losses at the upper edge of the passband due to parasitic modes prominent in curve 810. Using a 42-degree LT for parallel resonators avoids losses at the lower edge of the passband due to parasitic modes prominent in curve 820. Figure 8 Compared to the performance of any conventional (i.e., single-chip) step filter in the above, such as Figure 9 As shown, the separated stepped filter meets the insertion loss requirement (thick line 930) of the LTE band 2 transmission filter.

[0093] Example 2

[0094] For most acoustic resonators, increased temperature causes both the resonant and anti-resonant frequencies to shift to lower frequencies. The decrease in the resonant frequency of a parallel resonator increases the margin between the lower edge of the filter passband and the lower edge of the actual frequency band. Therefore, the effect of temperature on a parallel resonator may be small. Conversely, the decrease in the anti-resonant frequency of a series resonator reduces the margin between the upper edge of the filter passband and the upper edge of the actual frequency band. This effect is accompanied by an increase in power losses in the series resonator. Therefore, the advantages of combined-chip resonators (lower frequency temperature coefficient and higher thermal conductivity to limit temperature rise) are more important for series resonators than for parallel resonators. A discrete stepped filter, comprising a first chip with a combined-chip series resonator and a second chip with a non-combined SAW parallel resonator, offers a lower cost than the previous Example 1 while retaining the benefits of using a combined-chip series resonator.

[0095] Example 3

[0096] Many frequency bands used by portable communication devices are "Frequency Division Duplex" (FDD) bands, meaning that a separate frequency range or band is used for signals transmitted from and received by the device. A duplexer is a filter subsystem used to separate the transmit band from the receive band. Typically, a duplexer includes a transmit filter and a receive filter. The transmit filter receives the transmitted signal from the transmitter and sends the filtered transmitted signal to the antenna, while the receive filter receives the received signal from the antenna and sends the filtered received signal to the receiver.

[0097] A duplexer can be implemented as two filters on a common chip, where the transmit and receive filters use the same material stack. Alternatively, the duplexer 1000 can be implemented with transmit and receive filters on separate chips, such as... Figure 10A As shown. The first chip 1010 contains a transmit filter and the second chip 1020 contains a receive filter. The pads on chips 1010 and 1020 are connected to the circuit card as described above. The pad labeled "Tx" is the input from the transmitter. The pad labeled "Rx" is the output of the receiver. The pad labeled "A" is connected to the antenna. The pad labeled "G" is grounded. Figure 10A The concept of a two-chip duplexer is shown, but a specific duplexer design is not illustrated. For ease of manufacture, the emitter filter on the first chip 1010 and... Figure 5 The filters shown are the same, but the receiving filter on the second chip 1020 is... Figure 5 The mirror image of the filter.

[0098] Implementing a duplexer with transmit and receive filters on separate chips allows for different material stackings for the two filters. A two-chip implementation may be suitable for frequency division duplex bands where the transmit and receive bands are significantly separated. For example, LTE Band 4 has a 400 MHz gap between its transmit (1710 MHz to 1755 MHz) and receive (2110 MHz to 2155 MHz) bands. By implementing an LTE Band 4 duplexer with transmit and receive filters on separate chips, the material stacking of the two filters can be optimized for their respective frequency ranges.

[0099] Figure 10B This is an exemplary schematic plan view of a split-step duplexer 1050 including a transmit filter and a receive filter, each filter having a... Figure 1A The schematic diagram is the same as that of the bandpass filter circuit 100. The transmitting filter includes series resonators XT1, XT3, and XT5 and parallel resonators XT2, XT4, and XT6. The receiving filter includes series resonators XR1, XR3, and XR5 and parallel resonators XR2, XR4, and XR6. Figure 10A Compared to the dual-chip duplexer 1000 shown, series resonators XT1, XT3, XT5, XR1, XR3, and XR5 for transmitting and receiving filters are fabricated on the first chip 1060. Parallel resonators XT2, XT4, XT6, XR2, XR4, and XR6 for transmitting and receiving filters are fabricated on the second chip 1070. Chips 1060 and 1070 are electrically connected to each other and connected to a system external to the filters via pads and as a circuit card as described above. For example, each pad may be solder or a gold bump or interact with it to connect to a circuit card (not shown). The electrical connection 650 between the series resonators on the first chip 1060 and the parallel resonators on the second chip 1070 is shown in bold dashed lines. Connection 650 is formed, for example, by conductors on the circuit card on which the first and second chips 1060 and 1070 are mounted.

[0100] The transmit filter can be, for example, combined with Figure 8 and Figure 9 The described LTE band 2 transmit discrete step filter. The receive filter may be similar to a discrete step filter with a passband from 1930 MHz to 1990 MHz.

[0101] Example 4

[0102] Figure 11 This is an exemplary schematic plan view of another separate ladder duplexer 1100 including a transmit filter and a receive filter, each filter having a... Figure 1AThe same schematic diagram as the bandpass filter circuit 100 is used. The transmitting filter includes series resonators XT1, XT3, and XT5 and parallel resonators XT2, XT4, and XT6. The receiving filter includes series resonators XR1, XR3, and XR5 and parallel resonators XR2, XR4, and XR6. The series resonators XT1, XT3, and XT5 of the transmitting filter are fabricated on a first chip 1060. The parallel resonators XT2, XT4, and XT6 of the transmitting filter and all the resonators XR1, XR2, XR3, XR4, XR5, and XR6 of the receiving filter are fabricated on a second chip 1070. Chips 1060 and 1070 are electrically connected to each other and connected to an external system via pads and as circuit cards as described above.

[0103] Compared to the resonators on the second chip 1120, the series resonators XT1, XT3, and XT5 of the emitter filter on the first chip 1160 have higher power consumption. Therefore, the first chip can have a material stack that allows for effective heat dissipation of the resonators. The series resonators XT1, XT3, and XT5 of the emitter filter can be, for example, bonded wafer resonators or solid-state assembled film resonators. The second chip, where heat dissipation is less critical, can be fabricated using different types of resonators. The resonators on the second chip can be, for example, unbonded SAW resonators.

[0104] Method Description

[0105] Figure 12 This is a flowchart of method 1200 for manufacturing a discrete step filter device, which can be discrete step filter device 600, 700, or 1050. Method 1200 begins at 1210 and ends at 1290, at which point the filter device is manufactured.

[0106] At 1220, a first chip is fabricated using a first material stack. The first chip contains one, some, or all of the series resonators of a filter device. The first chip may be part of a first multi-chip wafer, such that multiple copies of the first chip are produced each time step 1220 is repeated. In this case, individual chips can be cut from the wafer and tested as part of the operation at 1220.

[0107] At 1230, a second chip is fabricated using a second material stack different from the first material stack. The second chip contains one, some, or all of the parallel resonators of the filter device. The second chip can be part of a second multi-chip wafer, such that multiple copies of the second chip are produced each time step 1230 is repeated. In this case, individual chips can be cut from the wafer and tested as part of the operation at 1230.

[0108] At 1240, a circuit card is manufactured. The circuit card can be, for example, a printed circuit board, an LTCC card, or some other form of circuit card. The circuit card may include one or more conductors for at least one electrical connection between a series resonator on the first chip and a parallel resonator on the second chip. The circuit may be part of a large substrate, such that multiple copies of the circuit card are produced during each repetition of step 1240. In this case, individual circuit cards can be cut from the substrate and tested as part of the operation at 1240. Alternatively, after attaching the chip to the circuit card at 1250, or after packaging the device at 1260, individual circuit cards can be cut from the substrate.

[0109] At 1250, separate first and second chips are assembled onto the circuit card using known processes (which may or may not be part of a larger substrate). For example, the first and second chips can be mounted onto the circuit card in a "flip-chip" manner using solder or gold bumps or balls to establish electrical, mechanical, and thermal connections between the chips and the circuit card. The first and second chips can also be assembled onto the circuit card in some other way.

[0110] The filter assembly is completed at 1260. Completing the filter assembly at 1260 includes packaging and testing. Completing the filter assembly at 1260 may include cutting individual circuit cards / chip assemblies from a larger substrate before or after packaging.

[0111] Conclusion

[0112] Throughout this specification, the embodiments and examples shown should be considered as examples and not as limitations on the disclosed or claimed devices and processes. While many of the examples provided herein relate to specific combinations of method actions or system elements, it should be understood that those actions and elements can be combined in other ways to achieve the same objective. Regarding the flowcharts, additional or fewer steps may be taken, and the steps shown may be combined or further refined to implement the methods described herein. Actions, elements, and features discussed in connection with only one embodiment are not intended to exclude their similarity in other embodiments.

[0113] As used herein, “multiple” means two or more. As used herein, a “group” of items may include one or more such items. As used herein, whether in the written description or in the claims, the terms “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” etc., shall be understood as open-ended, i.e., referring to including but not limited to. Only the transitional phrases “consisting of…” and “substantially consisting of…” are closed or semi-closed transitional phrases relative to the claims. Ordinal numbers used in the claims, such as “first,” “second,” “third,” etc., are used to modify claim elements. This does not in itself indicate the priority, order, or sequence of action of one claim element over another, but is merely used to distinguish one claim element with the same name from another element with the same name (but with ordinal numbers), thereby differentiating claim elements. As used herein, “and / or” means that the listed items are alternatives, but alternatives also include any combination of the listed items.

Claims

1. A filter device, comprising: The first chip includes a first interdigital transducer of a first acoustic resonator on a first piezoelectric plate, the first interdigital transducer being disposed on a portion of the first piezoelectric plate above a first cavity of the first acoustic resonator. as well as The second chip includes a second interdigital transducer of a second acoustic resonator on a second piezoelectric plate, the second interdigital transducer being disposed on a portion of the second piezoelectric plate above a second cavity of the second acoustic resonator; as well as A planar structure, coupled to the first chip and the second chip. The thickness of the first piezoelectric plate is greater than the thickness of the second piezoelectric plate.

2. The filter device according to claim 1, wherein: The first chip includes a series resonator of a stepped filter circuit, and The second chip includes a parallel resonator of the stepped filter circuit.

3. The filter device according to claim 1, wherein, The planar structure includes at least one electrical connection between the first acoustic resonator of the first chip and the second acoustic resonator of the second chip.

4. The filter device according to claim 1, wherein, The first piezoelectric plate and the second piezoelectric plate differ in at least one aspect of the material and the orientation of the crystal axis of the material.

5. The filter device according to claim 1, wherein, The thickness of the first interdigital transducer of the first acoustic resonator is different from the thickness of the second interdigital transducer of the second acoustic resonator.

6. The filter device according to claim 1, wherein, The material of the first interdigital transducer of the first acoustic resonator is different from the material of the second interdigital transducer of the second acoustic resonator.

7. The filter device according to claim 1, wherein, The first interdigital transducer of the first acoustic resonator is covered by a dielectric layer, the thickness of which is different from the thickness of the dielectric layer covering the second interdigital transducer of the second acoustic resonator.

8. The filter device according to claim 1, wherein, The first interdigital transducer of the first acoustic resonator is covered by a dielectric layer, the material of which is different from the material of the dielectric layer covering the second interdigital transducer of the second acoustic resonator.

9. The filter device according to claim 1, wherein, The thickness of the dielectric layer formed between the first interdigital transducer and the first piezoelectric plate in the first acoustic resonator is different from the thickness of the dielectric layer between the second interdigital transducer and the second piezoelectric plate in the second acoustic resonator.

10. The filter device according to claim 1, wherein, The first chip further includes a first base and a first dielectric layer located above the first base, wherein the first cavity is formed in the first dielectric layer.

11. The filter device according to claim 10, wherein, The second chip includes a second base and a second dielectric layer located above the second base, wherein the second cavity is formed in the second dielectric layer.

12. The filter device according to claim 11, wherein, The first acoustic resonator and the second acoustic resonator differ in one or more of the following aspects: the material of the first base is different from the material of the second base, or the thickness of the first base is different from the thickness of the second base.

13. The filter device according to claim 11, wherein, The first base includes a non-piezoelectric base.

14. The filter device according to claim 13, wherein, The second base includes a non-piezoelectric base.

15. The filter device according to claim 1, wherein, The first acoustic resonator is a floating diaphragm resonator.

16. The filter device according to claim 1, wherein, The second acoustic resonator is a floating diaphragm resonator.

17. The filter device according to claim 1, wherein, The first acoustic resonator is a transversely excited thin-film bulk acoustic resonator.

18. The filter device according to claim 1, wherein, The second acoustic resonator is a transversely excited thin-film bulk acoustic resonator.

19. The filter device according to claim 1, wherein, The planar structure electrically connects the first acoustic resonator of the first chip and the second acoustic resonator of the second chip via gold bumps and traces.

20. The filter device according to claim 1, wherein, The first chip and the second chip are connected to form a stepped filter circuit, wherein, in the stepped filter circuit, the first acoustic resonator is a series resonator and the second acoustic resonator is a parallel resonator.

21. The filter device according to claim 20, wherein, The series resonator is one of a plurality of series resonators located on the first chip.

22. The filter device according to claim 20, wherein, The parallel resonator is one of a plurality of parallel resonators located on the second chip.

23. The filter device according to claim 1, wherein, The planar structure electrically connects the first acoustic resonator of the first chip and the second acoustic resonator of the second chip through metal through-holes to interconnect the first acoustic resonator and the second acoustic resonator.

24. The filter device according to claim 1, wherein, The planar structure is a circuit card.

25. The filter device according to claim 2, wherein: The first chip includes all the series resonators of the stepped filter circuit, and The second chip includes all the parallel resonators of the stepped filter circuit.

26. A filter device, comprising: The first chip includes at least one first bulk acoustic wave resonator, the first bulk acoustic wave resonator including a first piezoelectric material located between a first upper conductor and a first lower conductor; The second chip includes at least one second bulk acoustic resonator, the second bulk acoustic resonator including a second piezoelectric material located between a second upper conductor and a second lower conductor; as well as A planar structure, coupled to the first chip and the second chip. The thickness of the first piezoelectric material is greater than the thickness of the second piezoelectric material.

27. The filter device according to claim 26, wherein: The first chip includes a series resonator of a stepped filter circuit, and The second chip includes a parallel resonator of the stepped filter circuit.

28. The filter device according to claim 26, wherein, The planar structure includes at least one electrical connection between the first bulk acoustic wave resonator of the first chip and the second bulk acoustic wave resonator of the second chip.

29. The filter device according to claim 26, wherein, The first piezoelectric material and the second piezoelectric material differ in at least one aspect of the orientation of the material and the crystal axis of the material.

30. The filter device according to claim 26, wherein, The first upper conductor and the second upper conductor differ in one or more of the following aspects: the first upper conductor and the second upper conductor have different thicknesses, or the first upper conductor and the second upper conductor are made of different materials.

31. The filter device according to claim 26, wherein, The first lower conductor and the second lower conductor differ in one or more of the following aspects: the first lower conductor and the second lower conductor have different thicknesses, or the first lower conductor and the second lower conductor are made of different materials.

32. The filter device according to claim 26, in, The at least one first bulk acoustic resonator is covered by a first dielectric layer, and the at least one second bulk acoustic resonator is covered by a second dielectric layer; and The first dielectric layer and the second dielectric layer differ in one or more of the following aspects: the first dielectric layer and the second dielectric layer have different thicknesses, or the first dielectric layer and the second dielectric layer are made of different materials.

33. The filter device according to claim 26, wherein, The first chip further includes a first base and a first cavity located in the first base, wherein at least a portion of each of the first upper conductor, the first piezoelectric material and the first lower conductor forms a diaphragm over the first cavity.

34. The filter device according to claim 33, wherein, The second chip includes a second base and a second cavity located in the second base, wherein at least a portion of each of the second upper conductor, the second piezoelectric material and the second lower conductor forms a diaphragm over the second cavity.

35. The filter device according to claim 34, wherein, The at least one first bulk acoustic resonator and the at least one second bulk acoustic resonator differ in one or more of the following aspects: the materials of the first base and the second base are different, or the thickness of the first base and the thickness of the second base are different.

36. The filter device according to claim 26, wherein, The first chip also includes a first base and a first acoustic Bragg reflector located between the first lower conductor and the first base.

37. The filter device according to claim 36, wherein, The second chip also includes a second base and a second acoustic Bragg reflector located between the second lower conductor and the second base.

38. The filter device according to claim 37, wherein, The at least one first bulk acoustic resonator and the at least one second bulk acoustic resonator differ in one or more of the following aspects: the materials of the first base and the second base are different, or the thickness of the first base and the thickness of the second base are different.

39. The filter device according to claim 26, wherein, The planar structure is a circuit card.

40. The filter device according to claim 27, wherein: The first chip includes all the series resonators of the stepped filter circuit; and The second chip includes all the parallel resonators of the stepped filter circuit.

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