Ladder filter device and filter device

Abstract

To increase the filter bandwidth.SOLUTION: A split ladder filter 600 which is a filter device includes a first chip 610 and a second chip 640. The first chip has a first material stack and includes one or more series resonators X1, X3, X5 of a ladder filter circuit. The second chip has a second material stack and includes one or more shunt resonators X2, X4, X6 of the ladder filter circuit. The first material stack and the second material stack are different. The first chip and the second chip are mounted on a circuit card that includes at least one conductor for forming an electrical connection between one of the one or more series resonators and one of the one or more shunt resonators.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present disclosure relates to radio frequency filters that use acoustic wave resonators, and in particular to filters for use in communications equipment. [Background technology]

[0002] A radio frequency (RF) filter is a two-port device configured to pass some frequencies and stop others, where "pass" means to transmit with relatively low insertion loss, and "stop" means to block or substantially attenuate. The range of frequencies that pass through a filter is called the filter's "passband." The range of frequencies that do not pass through such a filter is called the filter's "stopband." A typical RF filter has at least one passband and at least one stopband. The specific requirements for a passband or stopband depend on the particular application. For example, a "passband" can be defined as the frequency range over which 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 the frequency range over which the filter's insertion loss is greater than a defined value, such as 20 dB, 30 dB, 40 dB, or more, depending on the application.

[0003] RF filters are used in communication systems where information is transmitted 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, laptop computers and tablets, fixed-point radio links, and the RF front ends of other communication systems. RF filters are also used in radar and electronic information warfare systems.

[0004] RF filters typically require many design tradeoffs to achieve the best compromise between performance parameters such as insertion loss, rejection, isolation, power handling, linearity, size, and cost for each specific application. Specific design and manufacturing methods and enhancements can simultaneously benefit one or more of these requirements.

[0005] Improving the performance of RF filters in wireless systems can have a wide impact on system performance. RF filter improvements can be leveraged to provide system performance improvements such as larger cell sizes, longer battery life, higher data rates, increased network capacity, reduced costs, enhanced security, and improved reliability. These improvements can be realized at many levels of a wireless system, either individually or in combination, for example, at the RF module, RF transceiver, mobile or fixed subsystem, or network level. [Brief explanation of the drawings]

[0006] [Figure 1A] FIG. 1 is a schematic diagram of an exemplary RF ladder filter circuit incorporating acoustic wave resonators. [Figure 1B] FIG. 1 is a schematic diagram of an alternative implementation of an RF ladder filter circuit incorporating acoustic wave resonators. [Figure 2A] FIG. 2 is a simplified schematic cross-sectional view of a first acoustic wave resonator. [Figure 2B] FIG. 2 is a simplified schematic cross-sectional view of a second acoustic wave resonator. [Figure 3A] FIG. 10 is a simplified schematic cross-sectional view of a third acoustic wave resonator. [Figure 3B] FIG. 10 is a simplified schematic cross-sectional view of a fourth acoustic wave resonator. [Figure 4A] FIG. 10 is a simplified schematic cross-sectional view of a fifth acoustic wave resonator. [Figure 4B] FIG. 10 is a simplified schematic cross-sectional view of a sixth acoustic wave resonator. [Figure 5] FIG. 1 is a simplified schematic plan view of a conventional ladder filter. [Figure 6]FIG. 1 is a simplified schematic plan view of a split ladder implementation of a bandpass filter. [Figure 7] FIG. 7 is a simplified schematic cross-sectional view of a split ladder implementation of the exemplary bandpass filter of FIG. [Figure 8] 10 is a chart comparing S12 of two implementations of an exemplary bandpass filter. [Figure 9] 10 is a chart of S12 for a split ladder implementation of an exemplary bandpass filter. [Figure 10A] FIG. 1 is a simplified schematic plan view of a two-chip duplexer. [Figure 10B] FIG. 1 is a simplified schematic plan view of a split ladder implementation of a duplexer. [Figure 11] FIG. 10 is a simplified schematic plan view of another split-ladder implementation of a duplexer. [Figure 12] 1 is a flowchart of a method for manufacturing a segmented ladder filter device.

[0007] Throughout this description, elements depicted in the drawings are assigned three-digit reference numbers, the last two of which are unique to the element and the first one or two digits of which are the drawing number in which the element is first introduced. An element not described in connection with a drawing may be presumed to have the same properties and functionality as an element previously described with the same reference number. DETAILED DESCRIPTION OF THE INVENTION

[0008] FIG. 1A shows a simplified schematic diagram of an exemplary RF filter circuit 100 incorporating six acoustic wave resonators, labeled X1 through X6, arranged in what is commonly referred to as a "ladder" configuration. Ladder filters of this configuration are commonly used for bandpass filters in communication devices. The filter circuit 100 can be, for example, a transmit or receive filter for incorporation into a communication device. The filter circuit 100 is a two-port network, with one terminal of each port typically connected to signal ground. The 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 to the filter, and the other port can be the output. The filter circuit 100 also includes three shunt resonators (X2, X4, and X6). Each shunt resonator is connected between ground and either the junction of the adjacent series resonator or the input or output port. The schematic diagram of Figure 1A is simplified and does not show passive components such as inductance inherent in the conductors interconnecting the resonators. The use of six acoustic wave resonators (three series resonators and three shunt resonators) is exemplary. A bandpass filter circuit may include more or less than six resonators (more or less than three series resonators and more or less than three shunt resonators).

[0009] FIG. 1B shows a simplified schematic diagram of an alternative RF filter circuit 150. Filter circuit 150 is a two-port network in which the signals at each port are balanced, i.e., the signals at the two terminals of each port are nominally equal in amplitude and 180 degrees apart in phase. For the purposes of this patent, RF filter circuit 150 is considered a ladder filter. Resonators X1a, X1b, X3a, X3b, X5a, and X5b are considered series resonators, and resonators X2, X4, and X6 are considered shunt resonators. Ladder filter circuit 150 is not commonly used, and all subsequent examples in this patent assume the ladder filter configuration of FIG. 1A.

[0010] Each acoustic wave resonator X1-X6 may be a bulk acoustic wave (BAW) resonator, a film bulk acoustic wave (FBAW) resonator, a surface acoustic wave (SAW) resonator, a temperature-compensated surface acoustic wave (TC-SAW) resonator, a bonded wafer acoustic resonator, a transversely excited film bulk acoustic resonator (XBAR) as described in U.S. patent application Ser. No. 16 / 230,443, a solid-mounted transversely excited film bulk acoustic resonator (SM-XBAR) as described in U.S. patent application Ser. No. 16 / 438,141, or some other type of acoustic wave resonator. Acoustic wave resonator current filters typically have the same type of resonator.

[0011] Each acoustic wave resonator exhibits very high admittance at its resonant frequency and very low admittance at an anti-resonant frequency higher than the resonant frequency. Simply put, each resonator is nearly a short circuit at its resonant frequency and an open circuit at its anti-resonant frequency. This results in very low transmission between Port 1 and Port 2 of the bandpass filter circuit 100, 150 at the resonant frequency of the shunt resonator and the anti-resonant frequency of the series resonator. In a typical ladder bandpass filter, the resonant frequency of the shunt resonator is less than the lower edge of the filter passband to create a stopband at frequencies below the passband. The anti-resonant frequency of the shunt resonator typically falls within the passband of the filter. Conversely, the anti-resonant frequency of the series resonator is greater than the upper edge of the passband to create a stopband at frequencies above the passband. The resonant frequency of the series resonator typically falls within the passband of the filter. In some designs, one or more shunt resonators can have a resonant frequency higher than the upper edge of the passband.

[0012] Filter devices, such as the bandpass filter circuits 100 and 150, that include acoustic wave resonators are conventionally realized using multiple layers of material deposited on, bonded to, or formed on a substrate. The sequence of substrates and material layers is typically referred to as the "stack" used to form the acoustic wave resonators and filter devices. In this patent, the term "material stack" refers to an ordered sequence of material layers formed on a substrate, and the substrate is considered to be part of the material stack. The term "element" refers to either the substrate or one of the layers in the material stack. At least one element in the material stack (i.e., either the substrate or a layer) is a piezoelectric material, such as quartz, lithium niobate, lithium tantalate, lanthanum gallium silicate, gallium nitride, or aluminum nitride. If the piezoelectric material is single crystalline, the orientation of the X, Y, and Z crystal axes is known and consistent. One or more layers in the material stack, such as one or more conductor and / or dielectric layers, can be patterned using photolithography techniques so that not all elements of the material stack are present at all points on the acoustic wave device.

[0013] FIG. 2A is a schematic cross-sectional view of a first exemplary acoustic wave resonator 200. The first acoustic wave resonator 200 is referred to herein as a "bonded SAW resonator" (as opposed to a "bonded wafer resonator" described in conjunction with FIG. 2B). The "bonded SAW resonator" is characterized by a conductor pattern 210 formed on a piezoelectric plate 205 that 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 includes an interdigital transducer (IDT) formed on the surface of the plate 205 of single-crystal piezoelectric material. Dimension p is the pitch of the IDT fingers, i.e., the spacing between the conductors. Dimension λ=2p is the wavelength of an acoustic wave propagating across the surface of the piezoelectric plate 205. When multiple bonded SAW resonators 200 are combined to form a filter device, the resonant frequencies of the various resonators are set by selecting the pitch of each resonator. Dimension h is the thickness of the conductor pattern. A dielectric layer 215 having a thickness td1 may be deposited on or between the conductors of the conductor pattern. The dielectric layer 215 may be, for example, a thin passivation layer to seal and protect the surface of the electrode pattern and the piezoelectric plate 205. In a TC-SAW resonator, the dielectric layer 215 may be a relatively thick layer of, for example, SiO2, used to reduce the temperature coefficient of the frequency of the resonator.

[0014] The material stack for a bonded SAW resonator, such as the first exemplary acoustic wave 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, and 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 bonded SAW resonators 200 are incorporated into a filter device, the material stack can include additional layers not shown in FIG. 2A . For example, a filter device typically includes a second metal layer to increase the conductivity of the conductors interconnecting the resonators, and an additional dielectric layer and / or a third metal layer of thick gold or solder to interconnect the filter to an external circuit card and form bumps.

[0015] FIG. 2B is a schematic cross-sectional view of a second exemplary acoustic wave resonator 220. The second acoustic wave resonator 220 is referred to herein as a “bonded wafer resonator.” The “bonded wafer resonator” is characterized by a thin wafer or plate 225 of single crystal piezoelectric material bonded to a non-piezoelectric base 230. The thin wafer or plate 225 of single crystal piezoelectric material may be directly bonded to the non-piezoelectric base 230 or indirectly bonded via one or more intermediate dielectric layers 240. The second acoustic wave resonator 220 may be, for example, a bonded wafer SAW resonator, an IHP (Incredibly High Performance) SAW resonator, or a plate wave resonator. The second acoustic wave resonator 220 includes a conductor pattern 235 including an IDT formed on a surface of the thin wafer 225 of single crystal piezoelectric material. The thickness of the conductor pattern is dimension h (see FIG. 2A ). Dimension tp is the thickness of the wafer 225 of piezoelectric material. The dimension p is the pitch of the IDT fingers, i.e., the spacing between the conductors. The dimension λ=2p is the wavelength of the acoustic wave propagating across or within the surface of the piezoelectric wafer 225. When multiple bonded wafer resonators 220 are combined to form a filter device, the resonant frequencies of the various resonators are set by selecting the IDT pitch of each resonator. A dielectric layer 245 of thickness td1 (see FIG. 2A) may be deposited on or between the conductors of the conductor pattern, as previously described. A second dielectric layer 240 having a thickness td2 may be disposed between the wafer 225 and the base 230. In some cases, two dielectric layers may be disposed between the wafer 225 and the base 230.

[0016] The material stack for a bonded wafer resonator, such as the second exemplary acoustic wave resonator 220, includes a base 230, one or more underlying dielectric layers 240 (if present), a piezoelectric wafer 225, a conductor pattern 235, and a dielectric layer 245. The base 230 is defined by a material and a 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 a thickness h (see FIG. 2A ) and a material. The dielectric layer 245 is defined by a thickness td1 and a material. When multiple bonded wafer resonators 220 are incorporated into a filter, the material stack can include additional layers, as previously described.

[0017] FIG. 3A is a schematic cross-sectional view of a third exemplary acoustic wave resonator 300. The third acoustic wave resonator 300 is referred to herein as a "floating diaphragm resonator." A floating diaphragm resonator is characterized by a thin diaphragm 335 of single-crystal piezoelectric material floating above a cavity 330 formed in a non-piezoelectric base 315. The third acoustic wave resonator 300 may be, for example, an XBAR resonator as described in U.S. Patent Application No. 16 / 230,443, or some other type of acoustic resonator. The third acoustic wave resonator 300 includes a conductor pattern 305 including an IDT formed on the surface of a thin wafer 310 of single-crystal piezoelectric material, which is attached or bonded to a non-piezoelectric base 315. If the third acoustic wave resonator is a plate wave resonator, the conductor pattern may include a Bragg reflector (not shown in FIG. 3A). One or more dielectric layers 320 may be present between the wafer 310 and the base 315. A cavity 330 is formed in the base 315 and the dielectric layer 320 such that, when the cavity is present, a portion of the wafer 310 forms a diaphragm 335 that spans the cavity 330. The fingers of the IDT are disposed on the diaphragm 335. The dielectric layer 325 may be deposited on or between the fingers of the conductor pattern 305.

[0018] A material stack for a floating diaphragm resonator such as the third exemplary acoustic wave resonator 300 includes a base 315, one or more lower 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 lower 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 wave resonators 300 are incorporated into a filter, the material stack may include additional layers, as described above.

[0019] FIG. 3B is a schematic cross-sectional view of a fourth exemplary acoustic wave resonator 350. The fourth acoustic wave resonator 350 is referred to herein as a “solid-mounted membrane resonator.” The solid-mounted membrane resonator is characterized by a conductor pattern 355 including an IDT formed on the surface of a thin film 360 of single-crystal piezoelectric material supported by a non-piezoelectric base 365, with an acoustic Bragg reflector 370 sandwiched between the film 360 and the base 365. The acoustic Bragg reflector 370 includes multiple layers alternating between a first material having a high acoustic impedance and a second material having a low acoustic impedance. The acoustic Bragg reflector 370 is configured to reflect and confine acoustic waves generated with the membrane 360. A dielectric layer 375 may be deposited on or between the fingers of the conductor pattern 355.

[0020] The material stack for the solid-mounted membrane resonator 350 includes a base 365, an acoustic Bragg reflector 370, a piezoelectric membrane 360, a conductor pattern 355, and a dielectric layer 375. The base 365 is defined by a material and a thickness. The acoustic Bragg reflector 370 is defined by first and second material types, the number of layers, and the thickness of each layer. The piezoelectric membrane 360 ​​is defined by a material type, a thickness tp, and the orientation of the crystal axis of the piezoelectric material. The conductor pattern 355 is defined by its thickness and material. The dielectric layer 375 is defined by a thickness td1 and a material. When multiple solid-mounted membrane resonators are incorporated into a filter device, the material stack can include additional layers, as described above.

[0021] 4A is a schematic cross-sectional view of a fifth exemplary acoustic wave resonator 400. The fifth acoustic wave resonator 400 is a film bulk acoustic resonator (FBAR). The fifth acoustic wave resonator 400 includes a thin wafer or film 405 of single-crystal piezoelectric material sandwiched between an upper conductor 420 and a lower conductor 415, respectively. This sandwich is supported by a non-piezoelectric base 410. A cavity 425 is formed in the base 410 such that a portion of the sandwich 415 / 405 / 420 forms a diaphragm spanning the cavity 425.

[0022] The material stack for FBAR 400 includes a base 410, a lower conductor layer 415, a piezoelectric wafer or film 405, and an upper conductor layer 420. The base 410 is defined by a material and a thickness. The lower conductor layer 415 is defined by a material type and a 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. If multiple FBARs 400 are incorporated into a filter, the material stack can include additional layers, as previously described.

[0023] FIG. 4B is a schematic cross-sectional view of a sixth exemplary acoustic wave resonator 450. The sixth acoustic wave resonator is referred to herein as a “solid-mounted film bulk acoustic resonator” (SM-FBAR). The sixth acoustic wave resonator 450 includes a thin wafer or film 455 of single-crystal piezoelectric material sandwiched between an upper conductor 470 and a lower conductor 465, respectively. This sandwich is supported by a non-piezoelectric base 460. An acoustic Bragg reflector 475 is sandwiched between sandwiches 470 / 455 / 465 and base 460. Acoustic Bragg reflector 475 includes multiple layers alternating between a first material having a high acoustic impedance and a second material having a low acoustic impedance. Acoustic Bragg reflector 475 is configured to reflect and confine acoustic waves generated in sandwiches 470 / 455 / 465.

[0024] The material stack for 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. Base 460 is defined by a material and a thickness. Acoustic Bragg reflector 475 is defined by first and second material types, the number of layers, and the thickness of each layer. Lower conductor layer 465 is defined by a material type and a thickness. Piezoelectric wafer or film 455 is defined by the material type, thickness, and crystal axis orientation of the piezoelectric material. Upper conductor layer 470 is defined by its thickness and material. When multiple SM-FBARs 450 are incorporated into a filter, the material stack can include additional layers, as described above.

[0025] The acoustic resonators shown in Figures 2A-4B are not an all-inclusive list of acoustic resonator types. Other types of acoustic resonators with other material stacks may be used in the filters. Additionally, the cross-sectional views of Figures 2A-4B do not necessarily show all layers within each material stack. For example, additional layers may be present to promote adhesion between other layers, prevent chemical interaction between other layers, or passivate and protect other layers.

[0026] FIG. 5 is an exemplary schematic plan view of a conventional implementation of a bandpass filter 500, having a similar schematic diagram to the bandpass filter circuit 100 shown. In filter 500, six acoustic wave resonators X1-X6 are all formed on a common chip 510. All of acoustic wave resonators X1-X6 may be unbonded SAW resonators, bonded wafer resonators, floating diaphragm resonators, solid-mounted membrane resonators, FBARs, SM-FBARs, or some other type of acoustic wave resonator. All of acoustic wave resonators X1-X6 are typically the same type of resonator. For ease of illustration, resonators X1-X6 are all shown in FIG. 5 as the same size. This would almost certainly not be the case in an actual filter.

[0027] Acoustic wave resonators X1-X6 are interconnected by conductors, such as conductor 530, formed on substrate 510. Filter 500 is electrically connected to systems external to the filter by pads, such as pad 520. Each pad may be, for example, a solder or gold bump for connection to or interface with a circuit board (not shown). In addition to establishing electrical connections, the pads and bumps are typically the primary means for removing heat from filter 500.

[0028] When multiple acoustic wave resonators are formed on the same chip, the manufacturing process and material stack are essentially the same for all of the multiple resonators. In particular, the piezoelectric elements (i.e., plates, wafers, or films of piezoelectric material) within the material stack are the same for all resonators. However, the requirements for shunt and series resonators are typically different, as summarized in the table below. [Table 1]

[0029] It may not be possible to select an optimal or even sufficient material stack for all resonators in a filter.

[0030] FIG. 6 is an exemplary schematic plan view of a split ladder filter 600, which has the same schematic diagram as the ladder filter circuit 100 of FIG. 1A. In contrast to the conventional filter 500 shown in FIG. 5, the series resonators X1, X3, and X5 of split ladder filter 600 are fabricated on a first chip 610, and the shunt resonators X2, X4, and X6 of split ladder filter 600 are fabricated on a second chip 640. Within each chip 610, 640, the acoustic wave resonators are interconnected by conductors, such as conductor 630, formed on the respective chips. Chips 610, 640 are electrically connected to each other and to systems external to the filter by pads, such as pad 620. Each pad may be, for example, a solder or gold bump for connection to or interface with a circuit card (not shown).

[0031] The electrical connection 650 between the series resonator on the first chip 610 and the shunt resonator on the second chip 640 is shown as a thick dashed line. The connection 650 is made, for example, from conductors on a circuit card on which the first and second chips are mounted. In this context, the term “circuit card” refers to an essentially planar structure that includes conductors for connecting the first and second chips to each other and to systems external to the bandpass filter 600. The circuit card can be, for example, a single-layer or multi-layer printed wiring board, a low-temperature co-fired ceramic (LTCC) card, or some other type of circuit card. The resistance of the traces on the circuit card is very low, so losses in the traces can be negligible. The inductance of the electrical connection 650 between the series resonator and the shunt resonator can be compensated for in the design of the acoustic wave resonator. In some cases, the inductance of the electrical connection 650 can be used to improve filter performance, for example, to lower the resonant frequency of one or more shunt resonators and widen the filter bandwidth.

[0032] In the exemplary split ladder filter 600, all of the series resonators are on a first chip and all of the shunt resonators are on a second chip. However, in practice, this is not necessarily the case. In some filters, the first chip may include fewer than all of the series resonators and / or the second chip may include fewer than all of the shunt resonators.

[0033] FIG. 7 is a schematic cross-sectional view of split ladder filter 700, which may be split ladder filter 600. Split ladder filter 700 includes a first chip 710 and a second chip 740, both of which are attached to and interconnected by a circuit card 770. In this example, first chip 710 and second chip 740 are "flip-chip" mounted to circuit card 770. Electrical connections between first chip 710 and second chip 740 and circuit card 770 are made by solder or gold bumps, such as bump 720. Electrical connections between first chip 710 and second chip 740 are made by conductors, such as conductor 750, on or within circuit card 770. First chip 710 and second chip 740 may also be mounted and / or connected to circuit card 770 in some other manner.

[0034] An advantage of split ladder filters such as split ladder filters 600 and 700 is that different material stacks can be used for the series resonators and the shunt resonators. A first material stack can be used for a first chip that contains some or all of the series resonators, and a second material stack can be used for a second chip that contains some or all of the shunt resonators. The first and second material stacks can be different. This allows for separate optimization of the first and second material stacks for the series and shunt resonators.

[0035] Two material stacks are considered different if they differ in at least one aspect of at least one element in the stack. The difference between the material stacks can be, for example, the sequence of the elements, or a different material type, thickness, or other parameter for at least one element in the stack. Generally, 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 of the material, thickness, and orientation of the crystal axis of the material.

[0036] When the split ladder filter 600 / 700 incorporates unbonded SAW resonators, as shown in FIG. 2A, the first and second material stacks may differ in one or more of the following characteristics: material type, thickness, and crystal axis orientation of the piezoelectric plate 205; material and / or thickness h of the conductor pattern 210; and thickness td1 and material of the dielectric layer 215.

[0037] When the split ladder filter 600 / 700 incorporates bonded wafer resonators, as shown in FIG. 2B, the first and second material stacks may differ in one or more of the following characteristics: material and thickness of the base 230; the number of underlying dielectric layers 240 (if present); 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.

[0038] When the split ladder filter 600 / 700 incorporates a floating diaphragm resonator, as shown in FIG. 3A, the first and second material stacks may differ in one or more of the following characteristics: material and thickness of the base 315; the number of underlying dielectric layers 320 (if present); 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.

[0039] When the split ladder filter 600 / 700 incorporates solid-mounted membrane resonators, as shown in FIG. 3B, the first and second material stacks may differ in one or more of the following characteristics: material and thickness of the base 365; the number of layers in the acoustic Bragg reflector 370, 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.

[0040] When split ladder filter 600 / 700 incorporates FBARs, as shown in FIG. 4A, the first and second material stacks may differ in one or more of the following characteristics: base 410 material and thickness; lower conductor 415 material and thickness; piezoelectric wafer 405 material type, thickness tp and crystal axis orientation; and upper conductor 420 thickness and material.

[0041] When split ladder filter 600 / 700 incorporates SM-FBARs as shown in FIG. 4B, the first and second material stacks may differ in one or more of the following characteristics: material and thickness of base 460; number of layers in acoustic Bragg reflector 475, material and thickness of each layer; material and thickness of lower conductor 465; material type, thickness tp and crystal axis orientation of piezoelectric wafer 455; and thickness and material of upper conductor 470.

[0042] The differences between the first and second material stacks of the split ladder filter are not necessarily those identified in the previous six paragraphs. The first and second material stacks may differ in one or more parameters in addition to or instead of the parameters identified herein. The types of resonators are not limited to those shown in Figures 2A-4B. Also, the series resonators and shunt resonators need not be the same type of resonators. [Example]

[0043] Example 1 A desirable characteristic of filters for use in portable devices is stability of the filter passband over a wide temperature range. One technique that at least partially achieves this goal is to fabricate filters with bonded-wafer resonators, using a thin wafer of piezoelectric material bonded to a base, such as a silicon substrate, that has a low coefficient of thermal expansion and high thermal conductivity. Bonded-wafer SAW filters exhibit lower temperature rise for a given power input and lower temperature sensitivity of the passband frequency compared to filters that use unbonded SAW resonators.

[0044] A drawback of bonded-wafer SAW resonators is the presence of spurious acoustic modes that can propagate within the piezoelectric material or into the silicon wafer or other base. A key element in the design of bandpass filters using bonded-wafer resonators is ensuring that spurious modes occur at frequencies away from the filter passband. The cross-sectional structure and material stack for a bonded-wafer SAW resonator is similar to resonator 250 of FIG. 2B.

[0045] FIG. 8 is a graph 800 of the magnitude of S12 for two bonded-wafer SAW filters fabricated using lithium tantalate (LT) wafers bonded to a silicon base. S12 is the transmission between the first and second ports of the filter. The dashed-dotted line 810 is a plot of S12 for a filter fabricated on a 42-degree Y-cut LT wafer. The dashed line 820 is a plot of S12 for a filter fabricated on a 46-degree Y-cut LT wafer. The thick line 830 defines the requirements for an LTE (Long Term Evolution) Band 2 transmit filter (less than 2 dB insertion loss across the 1850 MHz to 1910 MHz transmission band).

[0046] When the filter is fabricated on 42° LT (dash-dotted line 810), spurious modes occur at frequencies around the anti-resonance frequency of the series resonator in the filter. These spurious modes cause a decrease in S12 (and a corresponding increase in insertion loss) near the top edge of the filter passband between 1902 MHz and 1915 MHz. When the filter is fabricated on 46° LT (dashed line 820), spurious modes occur at frequencies around the resonant frequency of the shunt resonator. These spurious modes cause a decrease in S12 (and a corresponding increase in insertion loss) between 1845 MHz and 1855 MHz. Neither of these filters meets the requirement for less than 2 dB of insertion loss across the LTE Band 2 transmission band.

[0047] 9 is a graph 900 of the S12 magnitude (curve 910) for a split-ladder LTE Band 2 transmit filter fabricated on two chips, each having a lithium tantalate (LT) wafer bonded to a silicon base. The first chip includes a series resonator fabricated on a 46-degree LT. The second chip includes a shunt resonator fabricated on a 42-degree LT. The material stacks for the first and second chips differ at least by the orientation of the crystal axes of the respective LT wafers and may differ in other ways.

[0048] The use of a 46 degree LT for the series resonators avoids the loss at the upper end of the passband due to spurious modes that were evident in curve 810. The use of a 42 degree LT for the shunt resonators avoids the loss at the lower end of the passband due to spurious modes that were evident in curve 820. As shown in Figure 9, the split ladder filter meets the LTE Band 2 transmit filter insertion loss requirement (bold line 930) in contrast to the performance of either of the conventional (i.e., single-chip) ladder filters shown in Figure 8.

[0049] Example 2 In most acoustic wave resonators, increasing the temperature shifts both the resonant frequency and the antiresonant frequency to lower frequencies. Lowering the resonant frequency of a shunt resonator increases the margin between the lower end of the filter passband and the lower end of the actual frequency band. Therefore, the temperature effect on shunt resonators may be small. Conversely, lowering the antiresonant frequency of a series resonator decreases the margin between the upper end of the filter passband and the upper end of the actual frequency band. This effect may be accompanied by increased power dissipation in the series resonator. Thus, the advantages of bonded wafer resonators (low temperature coefficient of frequency, high thermal conductivity, and reduced temperature rise) are greater for series resonators than for shunt resonators. A split-ladder filter including a first chip with a bonded wafer series resonator and a second chip with an unbonded SAW shunt resonator can be achieved at a lower cost than Example 1 while maintaining the advantages of using bonded wafer series resonators.

[0050] Example 3 Many of the frequency bands used by mobile communication devices are "frequency division duplex" (FDD) bands, i.e., separate frequency ranges or bands are used for signals transmitted from and received by the device. A duplexer is a filter subsystem for separating the transmit frequency band from the receive frequency band. Typically, a duplexer includes a transmit filter that receives the transmit signal from the transmitter and sends a filtered transmit signal to the antenna, and a receive filter that receives the receive signal from the antenna and sends a filtered receive signal to the receiver.

[0051] The duplexer may be implemented as two filters on a common chip, using the same material stack for both the transmit and receive filters. Alternatively, the duplexer 1000 may be implemented with the transmit and receive filters on separate chips, as shown in FIG. 10A. The first chip 1010 contains the transmit filter, and the second chip 1020 contains the receive filter. The pads on the chips 1010 and 1020 connect to the circuit card as described above. The pad labeled "Tx" is the input from the transmitter. The pad labeled "Rx" is the output to the receiver. The pad labeled "A" connects to the antenna. The pad labeled "G" connects to ground. FIG. 10A illustrates the concept of a two-chip duplexer, rather than a specific duplexer design. For ease of illustration, the transmit filter on the first chip 1010 is the same as the filter shown in FIG. 5, and the receive filter on the second chip 1020 is a mirror image of the filter in FIG. 5.

[0052] By implementing a duplexer with the transmit and receive filters on different chips, the material stacks of the two filters can be different. A two-chip implementation is suitable for frequency division duplex bands where the transmit and receive frequency bands are widely separated. For example, LTE Band 4 has a 400 MHz separation between the transmit band (1710 MHz to 1755 MHz) and the receive band (2110 MHz to 2155 MHz). By implementing an LTE Band 4 duplexer with the transmit and receive filters on different chips, the material stacks of the two filters can be optimized for their respective frequency ranges.

[0053] FIG. 10B is an exemplary schematic plan view of a split-ladder duplexer 1050 including a transmit filter and a receive filter, each of which has the same schematic diagram as the bandpass filter circuit 100 of FIG. 1. The transmit filter includes series resonators XT1, XT3, and XT5 and shunt resonators XT2, XT4, and XT6. The receive filter includes series resonators XR1, XR3, and XR5 and shunt resonators XR2, XR4, and XR6. In contrast to the two-chip duplexer 1000 shown in FIG. 10A, the series resonators XT1, XT3, XT5, XR1, XR3, and XR5 of both the transmit filter and the receive filter are fabricated on a first chip 1060. The shunt resonators XT2, XT4, XT6, XR2, XR4, and XR6 of both the transmit filter and the receive filter are fabricated on a second chip 1070. The chips 1060, 1070 are electrically connected to each other and to systems external to the filter, such as the circuit card, by pads. Each pad may be, for example, a solder or gold bump for connection on, or interface with, a circuit card (not shown). The electrical connection 650 between the series resonator on the first chip 1060 and the shunt resonator on the second chip 1070 is shown as a thick dashed line. The connection 650 may be made, for example, from conductors on the circuit card to which the first chip 1060 and the second chip 1070 are mounted.

[0054] The transmit filter may be, for example, the LTE Band 2 transmit split ladder filter described in relation to Figures 8 and 9. The receive filter may be similar to a split ladder filter with a passband of 1930 MHz to 1990 MHz.

[0055] Example 4 11 is an exemplary schematic plan view of another split ladder duplexer 1100 including a transmit filter and a receive filter, each of which has the same schematic diagram as the bandpass filter circuit 100 of FIG. 1. The transmit filter includes series resonators XT1, XT3, and XT5 and shunt resonators XT2, XT4, and XT6. The receive filter includes series resonators XR1, XR3, and XR5 and shunt resonators XR2, XR4, and XR6. The series resonators XT1, XT3, and XT5 of the transmit filter are fabricated on a first chip 1060. The shunt resonators XT2, XT4, and XT6 of the transmit filter and the resonators XR1, XR2, XR3, XR4, XR5, and XR6 of the receive filter are all fabricated on a second chip 1070. The chips 1060, 1070 are electrically connected to each other and to systems external to the filter by pads and to the circuit card as described above.

[0056] The series resonators XT1, XT3, and XT5 of the transmit filter on the first chip 1160 have higher power dissipation than the resonators on the second chip 1120. Therefore, the first chip may have a material stack that provides efficient heat removal from the resonators. The series resonators XT1, XT3, and XT5 of the transmit filter may be, for example, bonded wafer resonators or solid-mounted membrane resonators. The second chip, where heat removal is less important, may be fabricated using a different type of resonator. The resonators on the second chip may be, for example, unbonded SAW resonators.

[0057] (Method description) 12 is a flowchart of a method 1200 of manufacturing a split ladder filter device, which may be split ladder filter device 600, 700, or 1050. Method 1200 begins at 1210 and ends at 1290 with a completed filter device.

[0058] At 1220, the first stack of material is used to fabricate a first chip. The first chip includes one, some, or all of the series resonators of the filter device. The first chip may be part of a first larger multi-chip wafer, such that multiple copies of the first chip are produced during each iteration of step 1220. In this case, individual chips can be cut from the wafer and tested as part of the action at 1220.

[0059] At 1230, a second chip is fabricated using a second stack of material different from the first stack of material. The second chip includes one, some, or all of the shunt resonators of the filter device. The second chip may be part of a second, larger, multi-chip wafer, such that multiple copies of the second chip are produced during each iteration of step 1230. In this case, individual chips can be cut from the wafer and tested as part of the action at 1230.

[0060] At 1240, a circuit card is manufactured. The circuit card may be, for example, a printed wiring board, or an LTCC card, or some other form of circuit card. The circuit card may include one or more conductors for forming at least one electrical connection between a series resonator on the first chip and a shunt resonator on the second chip. The circuit may be a portion of a larger substrate, such that multiple copies of the circuit card are generated during each iteration of step 1240. In this case, individual circuit cards may be cut from the substrate and tested as part of the actions at 1240. Alternatively, individual circuit cards may be cut from the substrate after the chips are attached to the circuit card at 1250 or after the device is packaged at 1260.

[0061] At 1250, the individual first and second chips are assembled into a circuit card (which may or may not be part of a larger substrate) using known processes. For example, the first and second chips may be "flip-chip" mounted to the circuit card using solder or gold bumps or balls to provide electrical, mechanical, and thermal connections between the chips and the circuit card. The first and second chips may be assembled into the circuit card in some other manner.

[0062] The filter device is completed at 1260. Completing the filter device at 1260 includes packaging and testing. Completing the filter device at 1260 may also include cutting individual circuit card / chip assemblies from a larger substrate, either before or after packaging.

[0063] Throughout this description, the embodiments and examples shown should be considered as exemplars, not limitations on the disclosed or claimed apparatus and procedures. While many of the examples presented herein include specific combinations of method operations or system elements, it should be understood that these operations and these elements can be combined in other ways to achieve the same purpose. With respect to flowcharts, there may be additional steps or fewer steps, and the steps shown may be combined or further refined to achieve the methods described herein. Acts, elements, and features discussed only in connection with one embodiment are not intended to be excluded from a similar role in other embodiments.

[0064] As used herein, "plurality" means two or more. As used herein, a "set" of items can include one or more of such items. As used herein, whether in the written description or the claims, the terms "comprising," "including," "carrying," "having," "containing," "involving," and the like, shall be understood to mean open-ended, i.e., including, but not limited to. Only the transitional phrases "consisting of" and "consisting essentially of" shall be closed or semi-closed transitional phrases, respectively. The use of ordinal numbers such as "first," "second," and "third" in the claims to modify claim elements does not, by itself, imply a priority, precedence, or ordering of one claim element over another claim element, or a temporal order in which method actions are performed, but is merely used as a label to distinguish one claim element having a certain name from another element having the same name (but for the purposes of using ordinal numbers) to distinguish between 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 first chip having a first material stack, the first chip including at least one series resonator formed by an interdigital transducer (IDT) having a plurality of interleaved fingers disposed on a first piezoelectric plate with a first dielectric layer disposed on and between the interleaved fingers; a second chip having a second material stack, the second chip including at least one shunt resonator formed by an IDT having a plurality of interleaved fingers disposed on a second piezoelectric plate with a second dielectric layer disposed over and between the interleaved fingers; Equipped with the first chip and the second chip each include a base, and the first material stack differs from the second material stack in that a combined thickness of the first piezoelectric plate and the first dielectric layer differs from a combined thickness of the second piezoelectric plate and the second dielectric layer; Ladder filter device.

2. A ladder filter device as described in claim 1, wherein the first chip includes a plurality of series resonators of the ladder filter device including the at least one series resonator, and the second chip includes a plurality of shunt resonators of the ladder filter device including the at least one shunt resonator.

3. A ladder filter device as described in claim 1, wherein the first chip and the second chip are electrically connected.

4. A ladder filter device as described in claim 1, wherein the first material stack differs from the second material stack in that the first piezoelectric plate has a crystal axis orientation of the piezoelectric material that is different from the crystal axis orientation of the piezoelectric material of the second piezoelectric plate.

5. A ladder filter device as described in claim 1, wherein the at least one series resonator and the at least one shunt resonator are each floating diaphragm resonators.

6. A ladder filter device as described in claim 1, wherein the first chip and the second chip each include a substrate having at least one cavity extending through a non-piezoelectric layer.

7. A ladder filter device as described in claim 6, wherein the first piezoelectric plate has a diaphragm spanning the at least one cavity of the first chip, and the second piezoelectric plate has a diaphragm spanning the at least one cavity of the second chip.

8. A ladder filter device as described in Claim 7, wherein each IDT of each of the first and second chips is arranged on a surface of each diaphragm opposite each of the cavities.

9. A ladder filter device as described in Claim 7, wherein the first dielectric layer is arranged between the substrate and the first piezoelectric plate of the first chip, and the second dielectric layer is arranged between the substrate and the second piezoelectric plate of the second chip.

10. The at least one series resonator and the at least one shunt resonator are each a floating diaphragm resonator. and the first piezoelectric plate of the first material stack comprises a 46 degree Y-cut lithium tantalate piezoelectric wafer; the second piezoelectric plate of the second material stack comprises a 42 degree Y-cut lithium tantalate piezoelectric wafer; The ladder filter device according to claim 1 .

11. A ladder filter device as described in claim 1, wherein the at least one series resonator including a plurality of series resonators is connected in series between a first port and a second port of the ladder filter device, and the at least one shunt resonator including a plurality of shunt resonators is connected between a ground connection and a junction of an adjacent series resonator, or the first port, or the second port.

12. A ladder filter device as described in claim 1, wherein the first material stack differs from the second material stack in that the first dielectric layer includes at least one dielectric layer and the second dielectric layer includes a plurality of dielectric layers that is greater in number than the at least one dielectric layer of the first material stack.

13. The at least one series resonator is a floating diaphragm resonator; the at least one shunt resonator is a floating diaphragm resonator. The ladder filter device according to claim 1 .

14. A ladder filter device as described in claim 1, wherein the first chip and the second chip each have a substrate.

15. A ladder filter device as described in Claim 14, wherein the first chip has a Bragg reflector between each of the substrates and the first piezoelectric plate, and the second chip has a Bragg reflector between each of the substrates and the second piezoelectric plate.

16. A piezoelectric element comprising: a first non-piezoelectric base; a first dielectric layer on the first non-piezoelectric base; a first piezoelectric plate on the first dielectric layer; a first interdigital transducer (IDT) on the first piezoelectric plate; a first bulk acoustic resonator provided on a first chip, the first bulk acoustic resonator comprising: a second non-piezoelectric base; and a second dielectric layer on the second non-piezoelectric base; and a second piezoelectric plate on the second dielectric layer; a second interdigital transducer (IDT) on the second piezoelectric plate; and a second bulk acoustic resonator provided on a second chip, the second bulk acoustic resonator comprising: a circuit card that electrically couples the first chip and the second chip; Equipped with The filter device, wherein the thickness of the first piezoelectric plate is greater than the thickness of the second piezoelectric plate.

17. The method of claim 16, wherein the first bulk acoustic resonator is a series resonator in a ladder filter circuit, 17. The filter apparatus of claim 16, wherein the second bulk acoustic resonator is a shunt resonator of a ladder filter circuit.

18. A filter device as described in claim 16, wherein the circuit card has at least one electrical connection between the first bulk acoustic resonator of the first chip and the second bulk acoustic resonator of the second chip.

19. A filter device as described in claim 16, wherein the first piezoelectric plate and the second piezoelectric plate differ in at least one of the material and the orientation of the crystal axis of the material.

20. A filter device as described in claim 16, wherein the thickness of the first IDT is different from the thickness of the second IDT.

21. A filter device as described in claim 16, wherein the first IDT is covered with a third dielectric layer having a thickness different from that of a fourth dielectric layer covering the second IDT.

22. A filter device as described in Claim 16, wherein a third dielectric layer formed between the first IDTs has a thickness different from the thickness of a fourth dielectric layer formed between the second IDTs.

23. The filter device described in claim 16, wherein the first bulk acoustic resonator and the second bulk acoustic resonator differ in one or more of the following: the first non-piezoelectric base and the second non-piezoelectric base are made of different materials; and the first non-piezoelectric base and the second non-piezoelectric base are made of different thicknesses.

24. The filter device of claim 16, wherein at least one of the first bulk acoustic resonator and the second bulk acoustic resonator is a floating diaphragm resonator.

25. The filter device of claim 16, wherein at least one of the first bulk acoustic resonator and the second bulk acoustic resonator is a solid-mounted laterally excited film bulk acoustic resonator.

26. The filter device of claim 16, wherein at least one of the first bulk acoustic resonator and the second bulk acoustic resonator is a laterally excited film bulk acoustic resonator.

27. ​​A filter device as described in claim 16, wherein the circuit card electrically connects the first bulk acoustic resonator of the first chip and the second bulk acoustic resonator of the second chip via gold bumps and traces.

28. A filter device as described in claim 16, wherein the circuit card is an essentially planar structure including conductors for connecting the first chip and the second chip to each other.

29. A filter device as described in claim 16, wherein the first chip and the second chip are connected by a ladder filter circuit, and in the ladder filter circuit, the first bulk acoustic resonator is a series resonator and the second bulk acoustic resonator is a shunt resonator.

30. The filter device of claim 29, wherein the series resonator is one of a plurality of series resonators all located on the first chip.

31. The filter device of claim 29, wherein the shunt resonator is one of a plurality of shunt resonators all located on the second chip.

32. A filter device as described in claim 16, wherein the circuit card electrically connects the first bulk acoustic resonator of the first chip and the second bulk acoustic resonator of the second chip via a metal layer for interconnecting the first and second bulk acoustic resonators.

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