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] This 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 a 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 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 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-end of other communication systems. RF filters are also used in radar and electronic information warfare systems.

[0004] RF filters typically require many design trade-offs 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 benefit one or more of these requirements simultaneously.

[0005] Improved 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 size, longer battery life, higher data rates, greater network capacity, reduced cost, enhanced security, and improved reliability. These improvements can be realized at many levels of the wireless system, either individually or in combination, for example, at the RF module, RF transceiver, mobile or fixed subsystem, or network level. [Brief description of the drawings]

[0006] [Figure 1A] FIG. 1 is a schematic diagram of an example 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] 2 is a simplified schematic cross-sectional view of a first acoustic wave resonator. FIG. [Figure 2B] FIG. 2 is a simplified schematic cross-sectional view of a second acoustic wave resonator. [Figure 3A] FIG. 11 is a simplified schematic cross-sectional view of a third acoustic wave resonator. [Figure 3B] FIG. 11 is a simplified schematic cross-sectional view of a fourth acoustic wave resonator. [Figure 4A] FIG. 13 is a simplified schematic cross-sectional view of a fifth acoustic wave resonator. [Figure 4B] FIG. 13 is a simplified schematic cross-sectional view of a sixth acoustic wave resonator. [Diagram 5] FIG. 1 is a simplified schematic plan view of a conventional ladder filter. [Figure 6]FIG. 2 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 example bandpass filter of FIG. [Figure 8] 1 is a chart comparing S12 of two implementations of an exemplary bandpass filter. [Figure 9] 13 is a chart of S12 for a split ladder implementation of an exemplary bandpass filter. [Figure 10A] FIG. 2 is a simplified schematic plan view of a two-chip duplexer. [Figure 10B] FIG. 2 is a simplified schematic plan view of a split ladder implementation of a duplexer. [Figure 11] FIG. 2 is a simplified schematic plan view of another split ladder implementation of a duplexer. [Figure 12] 1 is a flow chart of a method for manufacturing a split 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 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 having the same reference number. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] FIG. 1A shows a simplified schematic circuit diagram of an exemplary RF filter circuit 100 incorporating six acoustic wave resonators, labeled X1-X6, arranged in what is commonly referred to as a "ladder" configuration. Ladder filters in this configuration are commonly used for bandpass filters in communication devices. The filter circuit 100 may be, for example, a transmit filter or a 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 may be an input to the filter and the other port may be an output. The filter circuit 100 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 FIG. 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. The bandpass filter circuit can 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 circuit 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 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 laterally excited film bulk acoustic resonator (XBAR) as described in U.S. patent application Ser. No. 16 / 230,443, a solidly-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 resonator. In an acoustic resonator current filter, the resonators are typically of the same type.

[0011] Each acoustic resonator exhibits very high admittance at its resonant frequency and very low admittance at an anti-resonant frequency that is 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 end 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 end 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 of the shunt resonators can have a resonant frequency that is higher than the upper end of the passband.

[0012] Filter devices such as bandpass filter circuits 100 and 150 including acoustic 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 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 one of the layers in the substrate or material stack. At least one element in the substrate 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 crystal, the orientation of the X, Y, and Z crystal axes is known and consistent. One or more layers in the substrate stack, such as one or more conductor layers and / or dielectric layers, can be patterned using photolithographic techniques such that not all elements of the substrate stack are present at all points on the acoustic 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 "non-bonded SAW resonator" (as opposed to a "bonded wafer resonator" described in conjunction with FIG. 2B). The "non-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. The term encompasses both temperature-compensated and non-temperature-compensated SAW resonators. The conductor pattern 210 includes an interdigital transducer (IDT) formed on a surface of a plate 205 of single crystal piezoelectric material. Dimension p is the pitch of the fingers of the IDT, 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 non-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 an unbonded 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 unbonded 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 with an external circuit card to 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 by 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 fingers of the IDT, i.e., the spacing between the conductors. The dimension λ=2p is the wavelength of the acoustic waves 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 placed between the wafer 225 and the base 230. In some cases, two dielectric layers may be placed 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 layer 240 is 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 Serial 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 a 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 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 a material and a thickness. The underlying dielectric layer 320 is 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 a thickness td1 and a 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 a surface of a thin film 360 of single crystal piezoelectric material supported by a non-piezoelectric base 365, and an acoustic Bragg reflector 370 is sandwiched between the membrane 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 a first and second material type, 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 previously described.

[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. The 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 that spans the cavity 425.

[0022] The material stack for the 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 to be incorporated into a filter, the material stack can include additional layers, as previously described.

[0023] 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. The sandwich is supported by a non-piezoelectric base 460. An acoustic Bragg reflector 475 is sandwiched between the sandwich 470 / 455 / 465 and the base 460. The 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. The acoustic Bragg reflector 475 is configured to reflect and confine acoustic waves generated in the sandwich 470 / 455 / 465.

[0024] 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 a material and a thickness. The acoustic Bragg reflector 475 is defined by a first and second material type, a number of layers, and a thickness of each layer. The lower conductor layer 465 is defined by a material type and a 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. If multiple SM-FBARs 450 are incorporated into the filter, the material stack can include additional layers, as previously described.

[0025] The acoustic resonators shown in Figures 2A-4B are not an all-inclusive list of types of acoustic resonators. Other types of acoustic resonators having other material stacks may be used in the filters. Additionally, the cross-sectional views of Figures 2A-4B do not necessarily show all layers in each material stack. Additional layers may be present, for example, to promote adhesion between other layers, to prevent chemical interaction between other layers, or to 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 as the bandpass filter circuit 100 of the figure. In the filter 500, six acoustic wave resonators X1-X6 are all formed on a common chip 510. All of the 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 the acoustic wave resonators X1-X6 are typically the same type of resonator. For ease of preparation of the figure, the resonators X1-X6 are all the same size in FIG. 5. This will 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 a system 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 of 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) in the material stack are the same for all of the 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 a material stack that is optimal, or even sufficient, 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, X5 of the split ladder filter 600 are fabricated on a first chip 610, and the shunt resonators X2, X4, X6 of the 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. The chips 610, 640 are electrically connected to each other and to a system 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 a system 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 the performance of the filter, for example, to lower the resonant frequency of one or more shunt resonators to 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. In practice, however, this may not be the case. In some filters, the first chip may include less than all of the series resonators and / or the second chip may include less than all of the shunt resonators.

[0033] 7 is a schematic cross-sectional view of a 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 be mounted and / or connected on 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, a sequence of elements, or a different material type, thickness, or other parameter for at least one element in the stack. In general, the first material stack includes a first piezoelectric element and the 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 the 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 the split ladder filter 600 / 700 incorporates an SM-FBAR 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 the base 460, the number of layers in the acoustic Bragg reflector 475, 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.

[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. EXAMPLES

[0043] Example 1 A desired characteristic of filters for use in portable devices is stability of the filter passband over a wide range of temperatures. A technique that at least partially achieves this objective 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 a lower temperature rise for a given power input and a lower sensitivity of the passband frequency to temperature 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 to ensure that the 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 and 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 bold line 830 defines the requirements for a Long Term Evolution (LTE) Band 2 transmit filter (insertion loss less than 2 dB over the transmission band from 1850 MHz to 1910 MHz).

[0046] When the filter is fabricated on 42 degrees LT (dash-dotted line 810), spurious modes occur at frequencies around the anti-resonant frequency of the series resonator in the filter. These spurious modes cause a reduction in S12 (and a corresponding increase in insertion loss) near the top of the filter passband between 1902 MHz and 1915 MHz. When the filter is fabricated on 46 degrees LT (dashed line 820), spurious modes occur at frequencies around the resonant frequency of the shunt resonator. These spurious modes cause a reduction in S12 (and a corresponding increase in insertion loss) between 1845 MHz and 1855 MHz. None of these filters meet the requirement of less than 2 dB insertion loss across the LTE Band 2 transmission band.

[0047] 9 is a graph 900 of 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 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 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 requirements (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 and anti-resonant frequencies to lower frequencies. Reducing the resonant frequency of the shunt resonator increases the margin between the lower end of the filter passband and the lower end of the actual frequency band. Thus, the effect of temperature on the shunt resonator may be small. Conversely, reducing the anti-resonant frequency of the 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, 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 a non-bonded SAW shunt resonator is less expensive than the previous 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, 1020 are connected to the circuit card as previously described. The pads labeled "Tx" are the inputs from the transmitter. The pads labeled "Rx" are the outputs to the receiver. The pads labeled "A" are connected to the antenna. The pads labeled "G" are connected to ground. FIG. 10A illustrates the concept of a two-chip duplexer, rather than a specific duplexer design. For ease of preparation, 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 transmit and receive filters on different chips, the material stacks of the two filters can be different. The 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 - 1755 MHz) and the receive band (2110 MHz - 2155 MHz). By implementing an LTE Band 4 duplexer with transmit and receive filters on different chips, the material stacks of the two filters can be optimized for each frequency range.

[0053] 10B is an exemplary schematic plan view of a split ladder duplexer 1050 including transmit and receive filters, 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 and receive filters are fabricated on a first chip 1060. The shunt resonators XT2, XT4, XT6, XR2, XR4, and XR6 of both the transmit and receive filters 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 and to the aforementioned circuit card. 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 a conductor 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 as previously described circuit cards.

[0056] The series resonators XT1, XT3, XT5 of the transmit filter on the first chip 1160 have a high power dissipation compared to 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, 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 manufactured 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 flow chart of a method 1200 of manufacturing a split ladder filter device, which may be split ladder filter device 600, 700, or 1050. The method 1200 begins at 1210 and ends at 1290 with a completed filter device.

[0058] At 1220, the first material stack 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 may 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 material stack different from the first material stack. 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 may 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 action 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 to 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 to 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 illustrated embodiments and examples should be considered as illustrations, not limitations on the disclosed or claimed apparatus and procedures. Many of the examples presented herein include specific combinations of method operations or system elements, but it should be understood that these operations and these elements can be combined in other ways to achieve the same purpose. With respect to flow charts, 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 an item can include one or more of such items. As used herein, whether in the written description or claims, the terms "comprising," "including," "carrying," "having," "containing," "involving," and the like, should 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," "third," etc. 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 operations 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 the alternatives also include any combination of the listed items.

Claims

1. a first chip having a first material stack, the first chip including one or more series resonators of a ladder filter circuit; a second chip having a second material stack, the second chip including one or more shunt resonators of the ladder filter circuit; A filter device comprising: The first stack of material and the second stack of material are different.

2. the first chip includes all of the series resonators of the ladder filter circuit; the second chip includes all of the shunt resonators of the ladder filter circuit; The filter device of claim 1 .

3. 2. The filter apparatus of claim 1 , wherein the first chip and the second chip are mounted on a circuit card including 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.

4. the first stack of materials includes a first piezoelectric element; the second stack of material includes a second piezoelectric element; the first and second piezoelectric elements differ in at least one of material, thickness, and orientation of the crystal axes of the material; The filter device according to claim 1 .

5. the one or more series resonators and the one or more shunt resonators are non-bonded SAW (surface acoustic wave) resonators; The first material stack and the second material stack are A material for the piezoelectric plate; a thickness of the piezoelectric plate; and an orientation of the crystal axes of the piezoelectric plate; and A material for a conductor pattern formed on the piezoelectric plate; A thickness of the conductor pattern; and a material for a dielectric layer formed on the conductor pattern; and the thickness of the dielectric layer; The filter device of claim 1 , wherein one or more of:

6. the one or more series resonators and the one or more shunt resonators are bonded-wafer resonators; The first material stack and the second material stack are The base material and A thickness of the base; and a material for a dielectric layer between the base and the piezoelectric wafer; a thickness of the dielectric layer between the base and the piezoelectric wafer; and A material of the piezoelectric wafer; a thickness of the piezoelectric wafer; and the orientation of the crystal axes of the piezoelectric wafer; A material for a conductor pattern formed on the piezoelectric wafer; A thickness of the conductor pattern; and a material for a dielectric layer formed on the conductor pattern; and a thickness of the dielectric layer formed on the conductor pattern; and The filter device of claim 1 , wherein one or more of:

7. the one or more series resonators and the one or more shunt resonators are floating diaphragm resonators; The first material stack and the second material stack are The base material and A thickness of the base; and a material for a dielectric layer between the base and the piezoelectric wafer; a thickness of the dielectric layer between the base and the piezoelectric; and A material of the piezoelectric wafer; a thickness of the piezoelectric wafer; and the orientation of the crystal axes of the piezoelectric wafer; A material for a conductor pattern formed on the piezoelectric wafer; A thickness of the conductor pattern; and a material for a dielectric layer formed on the conductor pattern; and a material of the dielectric layer formed on the conductor pattern; and The filter device of claim 1 , wherein one or more of:

8. the one or more series resonators and the one or more shunt resonators are solid mounted diaphragm resonators; The first material stack and the second material stack are The base material and A thickness of the base; and the number of layers in an acoustic Bragg reflector disposed between the base and the piezoelectric wafer, and the material and thickness of each layer; a thickness of a dielectric layer between the base and the piezoelectric; and A material of the piezoelectric wafer; a thickness of the piezoelectric wafer; and the orientation of the crystal axes of the piezoelectric wafer; A material for a conductor pattern formed on the piezoelectric wafer; A thickness of the conductor pattern; and a material for a dielectric layer formed on the conductor pattern; and a thickness of the dielectric layer formed on the conductor pattern; and The filter device of claim 1 , wherein one or more of:

9. the one or more series resonators and the one or more shunt resonators are film bulk acoustic resonators; The first material stack and the second material stack are The base material and A thickness of the base; and a lower conductor pattern material disposed between the base and the piezoelectric element; a thickness of the lower conductor pattern; and a material for the piezoelectric element; and a thickness of the piezoelectric element; and an orientation of the crystal axes of the piezoelectric element; and a material of an upper conductor pattern formed on the piezoelectric element; a thickness of the upper conductor pattern; and a material for a dielectric layer formed on the upper conductor pattern; the thickness of the dielectric layer; The filter device of claim 1 , wherein one or more of:

10. the one or more series resonators and the one or more shunt resonators are solid mounted film bulk acoustic resonators; The first material stack and the second material stack are The base material and A thickness of the base; and the number of layers of an acoustic Bragg reflector disposed between the base and the lower conductor pattern, the material and thickness of each layer; a material of the lower conductor pattern disposed between the acoustic Bragg reflector and a piezoelectric element; a thickness of the lower conductor pattern; and a material for the piezoelectric element; and a thickness of the piezoelectric element; and an orientation of the crystal axes of the piezoelectric element; and a material of an upper conductor pattern formed on the piezoelectric element; a thickness of the upper conductor pattern; and a material for a dielectric layer formed on the upper conductor pattern; the thickness of the dielectric layer; The filter device of claim 1 , wherein one or more of:

11. the one or more series resonators and the one or more shunt resonators are bonded-wafer resonators; the first stack of materials includes a 46 degree Y-cut lithium tantalate piezoelectric wafer; the second material stack includes a 42 degree Y-cut lithium tantalate piezoelectric wafer; The filter device according to claim 1 .

12. the one or more series resonators are bonded wafer resonators; the one or more shunt resonators are unbonded SAW resonators; The filter device according to claim 1 .

13. A duplexer including a transmission ladder filter circuit and a reception ladder filter circuit, a first chip having a first material stack, the first chip including one or more series resonators of the transmit ladder filter circuit; a second chip having a second material stack, the second chip including one or more shunt resonators of the receive ladder filter circuit; Equipped with The first and second stacks of material are different.

14. the first chip includes series resonators in both the transmit ladder filter circuit and the receive ladder filter circuit; the second chip includes shunt resonators in both the transmit ladder filter circuit and the receive ladder filter circuit; The duplexer according to claim 13.

15. the first chip includes all of the series resonators of the transmission ladder filter circuit and the reception ladder filter circuit, the second chip includes all of the shunt resonators of the transmitting ladder filter circuit and the receiving ladder filter circuit; The duplexer of claim 14.

16. the first chip includes a series resonator of the transmission ladder filter circuit; the second chip includes shunt resonators of the transmission ladder filter circuit and all resonators of the reception ladder filter circuit; The duplexer according to claim 13.

17. the series resonator of the transmit ladder filter circuit is a bonded-wafer resonator; 17. The duplexer of claim 16, wherein the shunt resonators of the transmit ladder filter circuit and all resonators of the receive filter circuit are non-bonded SAW resonators.

18. A method for manufacturing a filter device, comprising the steps of: fabricating a first chip having a first material stack, the first chip including one or more series resonators of a ladder filter circuit; fabricating a second chip having a second material stack, the second chip including one or more shunt resonators of a ladder filter circuit; Including, A method for manufacturing a filter device, wherein the first layer of material and the second layer of material are different.

19. the first chip includes all of the series resonators of the ladder filter circuit; the second chip includes all of the shunt resonators of the ladder filter circuit; A method for manufacturing the filter device according to claim 18.

20. mounting the first chip and the second chip on a circuit card including 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; The method of claim 18 further comprising:

21. the first stack of materials includes a first piezoelectric element; the second stack of material includes a second piezoelectric element; 20. The method of claim 18, wherein the first and second piezoelectric elements differ in at least one of material, thickness, and orientation of a crystal axis of the material.

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