Electro-acoustic filter, multiplexer, and method of manufacturing electro-acoustic filter
By designing independent stacked first and second resonator layers in the electroacoustic filter, utilizing decoupling techniques and specific materials, the electrical and acoustic properties of the electroacoustic filter are optimized, solving the problems of compatibility and performance improvement, and achieving wide bandwidth and improved frequency temperature coefficient.
Patent Information
- Application Number
- CN202610058570.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2018-04-25
- Filing Date
- 2019-03-21
- Publication Date
- 2026-05-05
AI Technical Summary
Existing electroacoustic filters struggle to simultaneously optimize multiple electrical and acoustic properties, such as the temperature coefficient of frequency (TCF), electroacoustic coupling coefficient K2, and spurious modes, while maintaining compatibility with next-generation mobile communication system specifications.
The first and second resonators are designed separately in the first and second layers of the stack, respectively, and are optimized independently through decoupling technology. By utilizing different layer structures and material properties, including piezoelectric materials, electrode structures and temperature compensation layers, acoustic decoupling and electrical optimization are achieved.
Improvements were made to the electroacoustic filter in terms of bandwidth and frequency temperature coefficient, spurious modes were reduced, and compatibility with carrier aggregation systems was enhanced.
Smart Images
Figure CN121984475A_ABST
Abstract
Description
Technical Field
[0001] This application is a divisional application of Chinese patent application No. 201980027686.4, filed on March 21, 2019, entitled "Electroacoustic Filter, Multiplexer and Method of Manufacturing Electroacoustic Filter".
[0002] This invention relates to electroacoustic filters that can be used in mobile communication devices, and to multiplexers including such filters. Furthermore, this invention relates to an improved method for manufacturing electroacoustic filters. Background Technology
[0003] An electroacoustic filter is an RF filter that utilizes sound waves from an electroacoustic resonator. This resonator includes an electrode structure and a piezoelectric material for converting between RF signals and sound waves. Electroacoustic filters can be bandpass filters or bandstop filters that provide steep side edges.
[0004] What is desired is an improved electroacoustic filter that is compatible with the specifications of next-generation mobile communication systems. Specifically, good electrical and acoustic properties are desired. For example, a small temperature coefficient of frequency (TCF) and a high electroacoustic coupling coefficient K providing wide bandwidth are preferred. 2 Electroacoustic filters that reduce spurious modes in the critical frequency range are desirable. Furthermore, the electroacoustic filters should be compatible with carrier aggregation (CA) systems.
[0005] Conventional electroacoustic filters may include SAW resonators (SAW = Surface Acoustic Wave) or BAW resonators (BAW = Bulk Acoustic Wave). In RF filters employing SAW resonators, a TCF layer can be provided to reduce temperature-induced variations in characteristic frequencies.
[0006] However, conventional RF filters are optimized for only one parameter or a small number of parameters. Therefore, what is needed is an electroacoustic filter that provides improved electrical and acoustic properties for a variety of parameters. Summary of the Invention
[0007] For this purpose, an electroacoustic filter according to the independent claim, a method for manufacturing the electroacoustic filter, and a multiplexer are provided. The dependent claims provide preferred embodiments.
[0008] The electroacoustic filter includes a first resonator implemented in a first layer stack and a second resonator implemented in a second layer stack. The second layer stack differs from the first layer stack in that at least one parameter is selected from the number of layers, the thickness of the layers, and the material of the layers.
[0009] The first resonator can be an electroacoustic resonator, and the second resonator can also be an electroacoustic resonator. For this purpose, the corresponding layer stack includes piezoelectric materials and electrode structures to utilize the piezoelectric effect to convert between RF signals and sound waves when an RF signal is applied to the electrode structures.
[0010] The first and second stacks can have similar constructions. In particular, it is possible that for each or more layers of the first stack, there are related layers in the second stack that serve the same purpose as the related layers in the first stack.
[0011] The difference between the first stack and the second stack, or several differences between the first stack and the second stack, corresponds to the decoupling of the first resonator and the second resonator.
[0012] Decoupling can be acoustic decoupling of the corresponding resonator, or decoupling of at least one process step in the corresponding process step of the method of manufacturing the resonator.
[0013] Decoupling between the first and second resonators allows for independent optimization for the first and second resonators.
[0014] Conventional RF filters consist of a structure with a first resonator and a second resonator arranged adjacent to each other on a common carrier. Due to the similarity in the construction of the first and second resonators in conventional filters, the manufacturing method is greatly simplified by using the same processing steps to create corresponding layers for both the first and second resonators.
[0015] However, this simplification in the processing leads to coupled resonators and / or coupled processing steps that prevent the second resonator from being independent of the first resonator, and that prevents the corresponding electroacoustic filter from having good electrical and acoustic properties for multiple parameters.
[0016] Therefore, the proposed decoupling of the first and second resonators provides the possibility of optimizing the first resonator with respect to a first parameter and optimizing the second resonator with respect to a second parameter, thereby optimizing the overall electroacoustic filter with respect to two or more parameters. It is possible that the first and second resonators are SAW resonators or BAW resonators. In the case of a SAW resonator, the resonator may include an electrode structure within the electrode layer. In the case of a BAW resonator, the resonator may include a bottom electrode in a bottom electrode layer, a top electrode in a top electrode layer above the bottom electrode layer, and a cavity or acoustic mirror below the bottom electrode.
[0017] SAW resonators can have an electrode structure as an interdigitated comb-like electrode structure disposed on or above a piezoelectric material. The piezoelectric material can be a piezoelectric thin layer or a piezoelectric single crystal. The resonator may include additional structures, such as acoustic reflectors, at the distal end of the acoustic track to confine the acoustic energy within the active region of the resonator. Additional materials can be deposited above the electrode structure and above the piezoelectric material between the electrode structures. For example, the dielectric material of a TCF layer and / or the dielectric material of a passivation layer can be disposed there.
[0018] The TCF layer preferably comprises a material having a temperature dependence of a characteristic frequency that is opposite to the temperature characteristics of the electrode structure and / or the piezoelectric material.
[0019] Typically, temperature changes alter the elastic properties of the materials used and cause thermally induced expansion. As a result, wave velocity and electrode pitch cause frequency drift in the characteristic frequencies of the resonator, such as resonant or anti-resonant frequencies. By providing a TCF layer comprising a material that has the opposite effect to temperature changes, the overall frequency drift can be reduced or even eliminated.
[0020] The TCF layer may include, for example, silicon oxide, such as silicon dioxide.
[0021] A BAW resonator has its piezoelectric material sandwiched between a bottom electrode and a top electrode. To confine the acoustic energy to the resonator's region, the resonator may include an acoustic mirror or a cavity below the bottom electrode. An electroacoustic BAW resonator with an acoustic mirror below the bottom electrode is an SMR type resonator (SMR = Solid-State Assembly Resonator). A resonator with a cavity below its bottom electrode is an FBAR type resonator (FBAR = Thin Film Bulk Acoustic Resonator).
[0022] BAW resonators may include a trimming layer above the top electrode. Additionally, additional structures (e.g., a frame structure above the top electrode) may be arranged to suppress unwanted acoustic modes.
[0023] Preferably, if the first resonator is a SAW resonator, then the second resonator is a SAW resonator. Furthermore, preferably, if the first resonator is a BAW resonator, then the second resonator is a BAW resonator.
[0024] Residual similarity in construction leads to less complex manufacturing methods, while the possibility of optimizing different parameters is obtained.
[0025] It is possible that the electroacoustic filter has a trapezoidal filter topology. The first resonator can be a series resonator, and the second resonator can be a parallel resonator.
[0026] A trapezoidal filter topology has two or more series resonators electrically connected in series in the signal path between the input and output ports. Furthermore, this topology has two or more parallel paths electrically connecting the signal path to ground. In each of the two or more parallel paths, at least one electroacoustic parallel resonator is connected between the signal path and ground.
[0027] Bandpass and bandstop filters can be readily implemented using this trapezoidal filter topology. Electroacoustic resonators have a resonant frequency and an anti-resonant frequency higher than the resonant frequency. A bandpass filter is obtained when the resonant frequency of the series resonator essentially corresponds to the anti-resonant frequency of the parallel resonator. In this case, the series path is transparent to RF signals within the frequency range of the series resonator's resonant frequency, and RF power cannot be shunted to ground because the parallel resonator essentially provides open-circuit impedance. For RF frequencies within the resonant frequency range of the parallel resonator, the corresponding RF power can be shunted to ground. For RF signals within the anti-resonant frequency range of the series resonator, the series resonator provides open-circuit impedance, and RF power cannot pass through the series resonator. Therefore, a bandpass filter is obtained such that its lower edge is positioned at the resonant frequency of the parallel resonator, and its upper edge is positioned at the anti-resonant frequency of the series resonator.
[0028] By swapping the series resonator and the parallel resonator, the corresponding band-stop filter or notch filter can be obtained.
[0029] Therefore, resonators with different frequency responses are needed for series resonators and for parallel resonators. The decoupling mentioned above between the first and second resonators makes it easy to provide different first and second resonators respectively for series and parallel resonators.
[0030] It is possible that the first and second layer stacks include one or more layers selected from piezoelectric layers, TCF layers, trimming layers, and passivation layers.
[0031] Correspondingly, it is possible that both layer stacks include a piezoelectric layer, a TCF layer, a trimming layer, and / or a passivation layer. In this case, the piezoelectric layer of the first stack will be the associated layer of the piezoelectric layer of the second stack. The TCF layer of the first stack will be the associated layer of the corresponding TCF layer of the second stack. The trimming layer of the first stack will be the associated layer of the corresponding trimming layer of the second stack, and the passivation layer of the first stack will be the associated layer of the corresponding passivation layer of the second stack.
[0032] Due to the similar but different correspondences, layer constructions with different optimized parameters can be obtained.
[0033] It is possible that the first and second resonators are acoustically decoupled.
[0034] Acoustic decoupling can be achieved by providing a piezoelectric material or by providing an interface between the piezoelectric material and the electrode structure at different vertical positions. This is possible by selectively adding an additional layer beneath only one of the two resonators.
[0035] However, it is also possible to have the same number of layers, but provide a layer with a different thickness compared to the corresponding layer in another stack.
[0036] Alternatively or as an alternative, acoustic decoupling may be achieved by including a groove between the first resonator and the second resonator.
[0037] The trench physically separates the stacked layers of the resonator and results in acoustic isolation of the resonator structure due to the large difference in acoustic impedance between the material and vacuum or air.
[0038] It is possible that the first and second resonators are arranged on a common carrier.
[0039] The common carrier can be a carrier substrate on which structures for BAW resonators and / or SAW resonators are arranged. Acoustic mirrors for SMR resonators can be arranged on the carrier. Cavities for providing FBAR resonators can be arranged within the carrier.
[0040] In addition, it is possible to establish a common single-crystal piezoelectric material on a common carrier, on which the electrode structures of the first resonator and the second resonator are arranged.
[0041] It is also possible that the first and / or second layer stack has a piezoelectric material provided as a thin layer or as a bulk material, for example, as a thin bulk material.
[0042] In particular, it is possible that two stacked piezoelectric materials are provided as thin layers or as bulk materials, for example, as thin bulk materials.
[0043] When provided as a bulk material, piezoelectric materials can be provided as single-crystal materials with appropriate crystal cutting.
[0044] In addition, the two stacked piezoelectric materials can be provided as thin layers, i.e., through wafer bonding and thin film processing, such as mechanical polishing or "smart cutting", or by using thin film deposition techniques such as sputtering, physical vapor deposition, chemical vapor deposition, molecular beam epitaxy, etc.
[0045] The piezoelectric material can be arranged on or above a carrier, such as a different carrier or a common carrier, such as a common carrier substrate for two stacked layers.
[0046] The carrier substrate used for the two-layer stack can comprise or consist of materials selected from or composed of the following: silicon, alumina, sapphire, crystalline carbon (diamond), silicon carbide (SiC), quartz, and similar materials doped with the aforementioned carrier substrate materials. In particular, carrier substrates made of materials with good thermal conductivity are preferred.
[0047] It is possible that the SAW resonator includes a sagittal acoustic waveguide. Piezoelectric material can be placed on or above this waveguide.
[0048] Waveguides can consist of a single layer. However, it is possible for a waveguide to comprise two or more layers. Preferably, the waveguide has layers comprising materials having an acoustic impedance different from that of the layers above or below the waveguide layer. Correspondingly, it is possible for the waveguide to have two or more layers with different acoustic impedances. The interface between the two materials with different acoustic impedances reflects sound waves. Therefore, sound waves from the surface of the resonator are reflected, and acoustic energy is prevented from dissipating in the underlying layer system. Thus, the waveguide helps to confine acoustic energy to the surface of the resonator, which improves the quality factor. The high acoustic impedance layer of the waveguide may include aluminum nitride, silicon carbide, crystalline carbon (diamond), or polycrystalline silicon.
[0049] The waveguide layer with low acoustic impedance may include silicon dioxide, doped silicon dioxide, or germanium dioxide. Silicon dioxide may be doped with fluorine, phosphorus, or boron.
[0050] If the SAW resonator has a waveguide and a carrier substrate, it is preferable that the waveguide is arranged between the carrier substrate and the piezoelectric material.
[0051] Furthermore, it is possible that an intermediate layer is provided as a temperature compensation layer. The temperature compensation layer may include silicon oxide, such as SiO2, ...
[0052] It is possible that the SAW resonator has a passivation layer arranged above the electrode structure.
[0053] The passivation layer may include oxides, such as metal oxides or silicon oxides. The metal oxide may be an oxide of the metal of the electrode structure.
[0054] It is possible to use this type of electroacoustic filter to build a multiplexer.
[0055] Therefore, it is possible that the multiplexer includes one or more electroacoustic filters as described above.
[0056] Then, the electroacoustic filter has a first sub-filter and a second sub-filter. The first sub-filter can be a TX (transmit) filter. The second sub-filter can be an RX (receive) filter. The first resonator can be the resonator of the TX sub-filter, and the second resonator can be the resonator of the RX sub-filter.
[0057] In a multiplexer that includes TX and RX filters, the filters are used to separate desired signals from unwanted signals, specifically guiding the transmitted signal from the transmit port to the common port and the received signal from the common port to the receive port, while blocking high-power transmitted signals from entering the receive port. For this purpose, the TX and RX filters can be bandpass filters with different center frequencies. To obtain bandpass filters with different center frequencies, a difference between the first resonator and the second resonator can be employed.
[0058] It is possible that it is a multiplexer, a quadruple, or a higher-order multiplexer.
[0059] It is possible that the above optimizations are used to shift the characteristic frequency of the bulk acoustic mode of the resonator out of the characteristic frequency band, such as band 40, to meet carrier aggregation requirements.
[0060] A method for manufacturing an electroacoustic filter includes the following steps:
[0061] - Provide the first layer of stack for the first resonator,
[0062] - Provide a second layer of stack for the second resonator,
[0063] - Decouple the first layer stack from the second layer stack, or decouple at least one processing step for providing the first layer stack from the processing for providing the second layer stack. Attached Figure Description
[0064] The schematic drawings explain and illustrate the main aspects of the electroacoustic filter and details of preferred embodiments.
[0065] In the attached diagram:
[0066] Figure 1 The possible arrangement of the stacked layers of an RF filter employing a SAW structure is shown;
[0067] Figure 2 The possible details of the layer stacking of the filter employing a BAW resonator are shown;
[0068] Figure 3 This demonstrates its potential use in the electroacoustic resonator of a duplexer; and
[0069] Figure 4 The diagram illustrates the possible frequency shifts of the spurious modes. Detailed Implementation
[0070] Figure 1 Possible layers of a layer stack for an RF filter as discussed above are shown. The filter has a first layer stack LS1, in which elements of a first resonator R1 are implemented. Furthermore, elements of a second resonator R2 are implemented in a second layer stack LS2. The first layer stack LS1 and the second layer stack are arranged adjacent to each other. Both the first layer stack LS1 and the second layer stack LS2 include an electrode structure ELS, which is disposed on a piezoelectric material PM within a piezoelectric layer PL. On and above the electrode structure ELS, a TCF layer TCFL material is disposed to compensate for temperature-induced frequency drift.
[0071] A passivation layer PAL is disposed on the TCF layer material. The first layer stack LS1 and the second layer stack LS2 are acoustically isolated and separated by the trench TR between the layer stacks.
[0072] Figure 1 The SAW assembly is constructed by stacking layers LS1 and LS2. The electrode structure ELS includes interdigitated comb-shaped electrode structures and / or reflector fingers at the distal end of the sound track to convert RF signals into acoustic waves that propagate at the surface of the piezoelectric material PM and at the interfaces between the piezoelectric material and the materials of the electrode structure ELS and the TCF layer TCFL, respectively.
[0073] Different layer stacks are obtained by reducing the thickness of the TCF layer TCFL of the second layer stack LS2 accordingly, compared to the thickness of the corresponding TCF layer of the first layer stack LS1.
[0074] By providing differently constructed layer stacks for the first and second resonators, the fabrication method is more complex than the fabrication steps used to build conventional RF filters. However, the achievable gains in the electrical and acoustic properties of the overall filter make the additional effort in the fabrication steps worthwhile.
[0075] Figure 2 The diagram illustrates the concept of a current electroacoustic filter applied to a BAW resonator. Therefore, Figure 2 The diagram illustrates a first-layer stack LS1 that implements the first resonator R1 as a BAW resonator and a second-layer stack LS2 that implements the second resonator R2 as a BAW resonator. The corresponding BAW resonator includes a bottom electrode BE in the bottom electrode layer BEL, a corresponding top electrode TE in the corresponding top electrode layer TEL, and piezoelectric material in a piezoelectric layer PL sandwiched between the bottom and top electrode layers. A trimming layer TRL is disposed on top of the top electrode TE in the top electrode layer TEL within the two resonators R1 and R2.
[0076] The difference in the layer construction is achieved by providing a piezoelectric layer PL for the second resonator R2 with a reduced thickness, compared to the piezoelectric layer PL in the first resonator R1.
[0077] Below the corresponding bottom electrode layer, an electroacoustic mirror (EAM) is provided to confine acoustic energy to the resonant structure. The EAM comprises adjacent layers with different acoustic impedances (not shown in the figure) to create a Bragg mirror for the propagation of sound waves (longitudinal) in the vertical direction.
[0078] Figure 3 The diagram illustrates a ladder-shaped topology for a multiplexer MUL (duplexer, DU type) with a transmit filter TXF and a receive filter RXF. The transmit filter TXF is positioned between the transmit port and the antenna port connected to the antenna AN. The receive filter RXF is positioned between the antenna port and the receive port. Additional circuitry is arranged between the antenna port and the receive filter RXF to establish an impedance matching circuit connected to the antenna port.
[0079] In a trapezoidal topology, series resonators SR are electrically connected in series in the signal path. Parallel resonators PR are electrically connected in parallel paths, which connect the signal path to ground.
[0080] Figure 4 The diagram illustrates the potential beneficial effects of the proposed electroacoustic filter. In particular, Figure 4 Frequency-dependent insertion loss is shown for the resonator described above and for conventional resonators, for series resonators and for parallel resonators.
[0081] Resonators with lower resonant frequencies can be used to construct parallel resonators in bandpass filters and series resonators in bandstop filters. Resonators with higher resonant frequencies can be used to construct series resonators in bandpass filters and parallel resonators in bandstop filters.
[0082] The resonant and anti-resonant frequencies of conventional and improved resonators are essentially equal. However, the improved resonator causes spurious modes present in the critical frequency range indicated by the rectangles in the figure, as indicated by the arrows, to be shifted to lower frequencies and outside the critical frequency range.
[0083] Electroacoustic filters and corresponding multiplexers, as well as methods for constructing filters and multiplexers, are not limited to the technical features described above and the embodiments shown in the accompanying drawings. Electroacoustic filters may include additional resonators and additional sub-filters to establish additional basic elements of a ladder-like topology. These additional basic elements are cascaded with respect to other basic elements and can be used in additional signal paths, such as in higher-order multiplexers. Furthermore, resonators may include additional layers and electrode structures, such as for establishing waveguides, and additional components for preventing the dissipation of electrical or acoustic energy.
[0084] Reference Symbol List
[0085] AN: Antenna
[0086] BE: Bottom Electrode
[0087] BEL: Bottom Electrode Layer
[0088] DU: Duplexer
[0089] EAF: Electroacoustic Filter
[0090] EAM: Electroacoustic Mirror
[0091] ELS: Electrode Structure
[0092] LS1, LS2: First and second layer stacking
[0093] MUL: Multiplexer
[0094] PAL: Passivation layer
[0095] PL: Piezoelectric layer
[0096] PM: Piezoelectric materials
[0097] PR: Parallel Resonator
[0098] R1, R2: First and second resonators
[0099] RXF: Receiver filter
[0100] SR: Series resonator
[0101] TCFL: TCF layer
[0102] TE: Top electrode
[0103] TEL: Top Electrode Layer
[0104] TR: Trench
[0105] TXF: Transmit Filter
Claims
1. An electroacoustic filter, comprising: The first surface acoustic wave (SAW) resonator is implemented in the first layer stack. The second SAW resonator is implemented in the second layer stack, and The trench between the first SAW resonator and the second SAW resonator The first SAW resonator and the second SAW resonator include electrode structures in the electrode layer. The second layer stack differs from the first layer stack in that it selects at least one parameter from the following: the number of layers, the layer thickness, and the layer material. The first and second layer stacks include piezoelectric layers.
2. The electroacoustic filter according to claim 1, wherein: The electroacoustic filter has a trapezoidal topology. The first SAW resonator is a series resonator, and The second SAW resonator is a parallel resonator.
3. The electroacoustic filter according to claim 1 or 2, wherein the first layer stack and the second layer stack comprise layers selected from a frequency temperature coefficient (TCF) layer, a trimming layer, and a passivation layer.
4. The electroacoustic filter according to claim 1 or 2, wherein the first layer stack and the second layer stack include a frequency temperature coefficient (TCF) layer, and the thickness of the TCF layer of the first layer stack is different from the thickness of the TCF layer of the second layer stack.
5. The electroacoustic filter according to claim 1 or 2, wherein the trench is arranged above the piezoelectric layer of the first and second layer stacks.
6. The electroacoustic filter according to claim 1 or 2, wherein the first SAW resonator and the second SAW resonator are acoustically decoupled.
7. The electroacoustic filter according to claim 1 or 2, wherein the first SAW resonator and the second SAW resonator are arranged on a common carrier.
8. The electroacoustic filter according to claim 1 or 2, wherein the first layer stack and / or the second layer stack has a piezoelectric material, the piezoelectric material being provided as a thin layer or as a bulk material.
9. A multiplexer comprising an electroacoustic filter according to any one of the preceding claims, wherein: The electroacoustic filter has a TX sub-filter and an RX sub-filter. The first SAW resonator is in the TX sub-filter, and the second SAW resonator is in the RX sub-filter.
10. The multiplexer according to claim 9, wherein the multiplexer is a duplexer, quadplexer, or a higher-order multiplexer.
11. A method for manufacturing an electroacoustic filter, comprising the following steps: A first layer stack is provided for a first surface acoustic wave (SAW) resonator, the first layer stack including a piezoelectric layer. A second layer stack is provided for the second SAW resonator, the second layer stack including a piezoelectric layer. Provide a trench between the first layer stack and the second layer stack. Decouple the first layer stack from the second layer stack, or decouple at least one processing step for providing the first layer stack from the processing step for providing the second layer stack.
12. The method according to claim 11, wherein: The electroacoustic filter has a trapezoidal topology. The first SAW resonator is a series resonator, and The second SAW resonator is a parallel resonator.
13. The method of claim 11 or 12, wherein the first layer stack and the second layer stack are provided with a layer selected from a frequency temperature coefficient (TCF) layer, a trimming layer, and a passivation layer.
14. The method of claim 11 or 12, wherein the first stack and the second stack are provided with a frequency temperature coefficient (TCF) layer, and the thickness of the TCF layer of the first stack is different from the thickness of the TCF layer of the second stack.
15. The method of claim 11 or 12, wherein the trench is disposed over the piezoelectric layer of the first and second layer stacks.
16. The method of claim 11 or 12, wherein the first SAW resonator and the second SAW resonator are acoustically decoupled.
17. The method according to claim 11 or 12, wherein the first SAW resonator and the second SAW resonator are arranged on a common carrier.
18. The method of claim 11 or 12, wherein the first layer stack and / or the second layer stack has a piezoelectric material, the piezoelectric material being provided as a thin layer or as a bulk material.