WO2019206533A1 - Electroacoustic filter, multiplexer and method of manufacturing an electroacoustic filter - Google Patents

Electroacoustic filter, multiplexer and method of manufacturing an electroacoustic filter Download PDF

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Publication number
WO2019206533A1
WO2019206533A1 PCT/EP2019/057085 EP2019057085W WO2019206533A1 WO 2019206533 A1 WO2019206533 A1 WO 2019206533A1 EP 2019057085 W EP2019057085 W EP 2019057085W WO 2019206533 A1 WO2019206533 A1 WO 2019206533A1
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Prior art keywords
layer
resonator
layer stack
filter
electroacoustic
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PCT/EP2019/057085
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French (fr)
Inventor
Matthias Knapp
Franz Kubat
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RF360 Europe GmbH
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Priority to CN201980027686.4A priority Critical patent/CN112042119A/en
Priority to EP19712759.0A priority patent/EP3785368A1/en
Publication of WO2019206533A1 publication Critical patent/WO2019206533A1/en

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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
    • H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
    • H03H3/02—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks
    • H03H3/04—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks for obtaining desired frequency or temperature coefficient
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
    • H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
    • H03H3/08—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of resonators or networks using surface acoustic waves
    • H03H3/10—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of resonators or networks using surface acoustic waves for obtaining desired frequency or temperature coefficient
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02007—Details of bulk acoustic wave devices
    • H03H9/02157—Dimensional parameters, e.g. ratio between two dimension parameters, length, width or thickness
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02535—Details of surface acoustic wave devices
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/15—Constructional features of resonators consisting of piezoelectric or electrostrictive material
    • H03H9/17—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator
    • H03H9/171—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator implemented with thin-film techniques, i.e. of the film bulk acoustic resonator [FBAR] type
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/70—Multiple-port networks for connecting several sources or loads, working on different frequencies or frequency bands, to a common load or source
    • H03H9/703—Networks using bulk acoustic wave devices
    • H03H9/706—Duplexers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/70—Multiple-port networks for connecting several sources or loads, working on different frequencies or frequency bands, to a common load or source
    • H03H9/72—Networks using surface acoustic waves
    • H03H9/725—Duplexers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
    • H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
    • H03H3/02—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks
    • H03H3/04—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks for obtaining desired frequency or temperature coefficient
    • H03H2003/0414—Resonance frequency
    • H03H2003/0421—Modification of the thickness of an element
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
    • H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
    • H03H3/02—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks
    • H03H3/04—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks for obtaining desired frequency or temperature coefficient
    • H03H2003/0414—Resonance frequency
    • H03H2003/0471—Resonance frequency of a plurality of resonators at different frequencies
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
    • H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
    • H03H3/02—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks
    • H03H3/04—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks for obtaining desired frequency or temperature coefficient
    • H03H2003/0414—Resonance frequency
    • H03H2003/0478—Resonance frequency in a process for mass production
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02228—Guided bulk acoustic wave devices or Lamb wave devices having interdigital transducers situated in parallel planes on either side of a piezoelectric layer

Definitions

  • the present invention refers to electroacoustic filters that may be used in mobile communication devices and to
  • multiplexers comprising such filters.
  • the present invention refers to improved methods of manufacturing an electroacoustic filter.
  • Electroacoustic filters are RF filters that utilize acoustic waves in electroacoustic resonators.
  • Such resonators comprise electrode structures and a piezoelectric material for converting between RF signals and acoustic waves.
  • Electroacoustic filters can be bandpass filters or band rejection filters providing steep flanks.
  • electroacoustic filter that is compatible with specifications of next generation mobile communication systems.
  • good electric and acoustic properties are wanted.
  • electroacoustic filters having small temperature coefficients of frequency (TCF) , a high electroacoustic coupling coefficient K 2
  • electroacoustic filters should be compatible with carrier aggregation (CA) systems.
  • CA carrier aggregation
  • Conventional electroacoustic filters can comprise SAW
  • SAW surface acoustic wave
  • BAW bulk acoustic wave
  • an electroacoustic filter and a method of manufacturing an electroacoustic filter according to the independent claims and a multiplexer are provided.
  • Dependent claims provide preferred embodiments.
  • the electroacoustic filter comprises a first resonator realized in a first layer stack and a second resonator realized in a second layer stack.
  • the second layer stack is different from the first layer stack in at least one
  • the first resonator can be an electroacoustic resonator and the second resonator can be an electroacoustic resonator.
  • the corresponding layer stack comprises a
  • piezoelectric material and an electrode structure to employ the piezoelectric effect to convert between RF signals and acoustic waves when an RF signal is applied to the electrode structure .
  • the first layer stack and the second layer stack can have a similar construction.
  • the difference between the first layer stack and the second layer stack or several differences between the first layer stack and the second layer stack correspond to a decoupling of the first resonator and the second resonator.
  • the decoupling can be an acoustic decoupling of the
  • the decoupling between the first resonator and the second resonator allows independent optimizations directed to the first resonator and directed to the second resonator.
  • Conventional RF filters comprise structures of a first resonator and structures of a second resonator arranged one next to another on a common carrier. Due to similarities in construction of first and second resonators in conventional filters manufacturing methods are substantially simplified by creating corresponding layers for the first resonator and for the second resonator together utilizing same processing steps .
  • the suggested decoupling of the first resonator and of the second resonator provides the possibility of optimizing the first resonator with respect to a first parameter and the second resonator with respect to a second parameter such that the overall electroacoustic filter is optimized with respect to two or more parameters.
  • the first resonator and the second resonator are SAW resonators or BAW resonators.
  • the resonators can comprise electrode structures in an electrode layer.
  • the resonators can comprise a bottom electrode in a bottom electrode layer, top electrode in a top electrode layer above the bottom electrode layer and a cavity or an acoustic mirror below the bottom electrode.
  • SAW resonators can have the electrode structures as
  • the piezoelectric material may be a piezoelectric thin layer or a piezoelectric single crystal.
  • the resonator can comprise further structures such as acoustic reflectors at the distal ends of an acoustic track to confine acoustic energy in the resonator' s active area. Further material can be deposited above the electrode structure and above the piezoelectric material between the electrode structure. For example dielectric material of a TCF layer and/or dielectric material of a passivation layer can be arranged there.
  • a TCF layer preferably comprises a material that has a temperature dependence of characteristic frequencies opposite to temperature characteristics of the electrode structure and/or the piezoelectric material. Usually, a change in temperature changes elastic properties of the used materials and causes a thermally induced
  • the wave velocity and the pitch of the electrode structures result in a frequency drift of characteristic frequencies such as resonance frequencies or anti-resonance frequencies of the resonator.
  • a TCF layer can comprise, for example, a silicon oxide such as silicon dioxide.
  • a BAW resonator has its piezoelectric material sandwiched between the bottom electrode and the top electrode. To confine acoustic energy to the resonator' s area, the
  • resonator can comprise an acoustic mirror below the bottom electrode or a cavity below the bottom electrode.
  • SMR solidly mounted resonator
  • FBAR film bulk acoustic resonator
  • BAW resonators can comprise a trimming layer above the top electrode.
  • additional structures e.g. frame
  • structures above the top electrode can be arranged in order to suppress unwanted acoustic modes.
  • the first resonator is a SAW
  • the second resonator is a SAW resonator. Further, it is preferred that if the first resonator is a BAW resonator, then the second resonator is a BAW resonator.
  • the electroacoustic filter has a ladder- type like filter topology.
  • the first resonator can be a series resonator and the second resonator can be a parallel resonator .
  • a ladder-type like filter topology has two or more series resonators electrically connected in series in a signal path between an input port and an output port. Further, such a topology has two or more parallel paths electrically
  • each of the two or more parallel paths at least one electroacoustic parallel resonator is connected between the signal path and ground.
  • Bandpass filters and band rejections filters can easily be implemented with such ladder-type like filter topologies.
  • An electroacoustic resonator has a resonance frequency and an anti-resonance frequency above the resonance frequency.
  • a bandpass filter is obtained when the resonance frequency of series resonators essentially corresponds to the anti
  • the series path is transparent for RF signals in the frequency range of the resonance frequency of the series resonators and the RF power cannot be shunted to ground because the parallel resonators essentially provide an open circuit impedance.
  • the parallel resonators For RF frequencies in the range of the resonance frequency of the parallel resonators the corresponding RF power can be shunted to ground.
  • the series resonators For RF signals in the range of the anti-resonance frequency of the series resonators, the series resonators provide an open circuit impedance and the RF power cannot pass the series resonators.
  • a bandpass filter having its lower flank arranged at the resonance frequency of the parallel resonators and having its upper flank arranged at the anti-resonance frequency of the series resonators is obtained .
  • the first layer stack and the second layer stack comprise one or more layers selected from a piezoelectric layer, a TCF layer, a trimming layer, and a passivation layer.
  • both layer stacks comprise a piezoelectric layer, a TCF layer, a trimming layer and/or a passivation layer.
  • the piezoelectric layer of the first layer stack would be an associated layer of a piezoelectric layer of the second layer stack.
  • a TCF layer of the first layer stack would be an associated layer of a corresponding TCF layer of the second layer stack.
  • a trimming layer of the first layer stack would be an associated layer of the corresponding trimming layer of the second layer stack and a passivation layer of the first layer stack would be an associated layer of the corresponding passivation layer of the second layer stack.
  • first resonator and the second resonator are acoustically decoupled.
  • An acoustic decoupling can be obtained by providing the piezoelectric material or providing an interface between the piezoelectric material and an electrode structure at
  • an acoustic decoupling by comprising a trench between the first resonator and the second resonator.
  • the trench physically separates the layer stacks of the resonators and leads to - due to the large difference in acoustic impedance of material and vacuum or air - an
  • first resonator and the second resonator are arranged on a common carrier.
  • the common carrier can be a carrier substrate on which the structures for BAW and/or SAW resonators are arranged. On the carrier acoustic mirrors of SMR-type resonators can be arranged. In the carrier cavities for providing FBAR-type resonators can be arranged.
  • a common carrier establishes a common single crystal piezoelectric material on which
  • electrode structures of the first resonator and electrode structures of the second resonator are arranged.
  • first and/or second layer stack have a piezoelectric material provided as a thin layer or as a bulk material, e.g. as a thin bulk material.
  • the piezoelectric material of both layer stacks is provided as a thin layer or as a bulk material, e.g. as a thin bulk material.
  • the piezoelectric material When provided as a bulk material the piezoelectric material can be provided as a monocrystalline material that has an appropriate crystal cut.
  • the piezoelectric material of both layer stacks can be provided as a thin layer, i.e. by wafer bonding with thin film processing, e.g. mechanical grinding or "smart cut", or employing thin-film layer deposition techniques such as sputtering, physical vapour deposition, chemical vapour deposition, molecular beam epitaxy and the like.
  • the piezoelectric material can be arranged on or above a carrier, e.g. different carriers or a common carrier, e.g. a common carrier substrate for both layer stacks.
  • the carrier substrate for both layer stacks can comprise or consist of a material selected from silicon, aluminium oxide, sapphire, crystalline carbon (diamond) , silicon carbide SiC, quartz and similar materials including doping of the
  • carrier substrate materials In particular, carrier substrates having a material with a good thermal conductance are preferred.
  • the SAW resonators comprise a sagittal acoustic wave guide.
  • the piezoelectric material can be arranged on or above this wave guide.
  • the wave guide can consist of a single layer. However, it is possible that the wave guide comprises two or more layers. It is preferred that the wave guide has a layer comprising a material that has an acoustic impedance different from the acoustic impedance of a layer above or below the wave guide's layer. Correspondingly, it is possible that the wave guide has two or more layers of different acoustic impedances. An interface between two materials of different acoustic
  • a layer of high acoustic impedance of the wave guide can comprise aluminium nitride, silicon carbide, crystalline carbon (diamond) or polycrystalline silicon.
  • a layer of the wave guide having a low acoustic impedance can comprise silicon dioxide, a doped silicon dioxide or
  • Silicon dioxide can be doped by fluorine or phosphorous or boron.
  • the SAW resonator has a wave guide and a carrier substrate then it is preferred that the wave guide is arranged between the carrier substrate and the piezoelectric material.
  • the temperature compensation layer may comprise a silicon oxide, e.g. Si02, ...
  • the SAW resonator has a passivation layer arranged above the electrode structure.
  • the passivation layer can comprise an oxide, e.g. a metal oxide or a silicon oxide.
  • the metal oxide can be an oxide of the metal of the electrode structure.
  • a multiplexer comprises one or more electroacoustic filters as described above.
  • the electroacoustic filter has a first subfilter and a second subfilter.
  • the first subfilter can be a TX
  • the second subfilter can be an RX (reception) filter.
  • the first resonator can be a resonator of the TX subfilter and the second resonator can be a resonator of the RX subfilter.
  • the filters are employed to separate wanted signals from unwanted signals, in particular to conduct transmission signals from a transmission port to a common port and to conduct reception signals from a common port to a reception port and to prevent a high power transmission signal from entering the reception port.
  • the TX filter and the RX filter can be bandpass filters that have different center frequencies. To obtain bandpass filters with different center frequencies the differences between the first resonator and the second resonator can be employed.
  • the multiplexer a quadplexer or a multiplexer of a higher order.
  • a method of manufacturing an electroacoustic filter comprises the steps of:
  • Fig. 1 shows a possible arrangement of layer stacks of an
  • Fig. 2 shows possible details of layer stacks of filters employing BAW resonators
  • Fig. 3 shows a possible use in electroacoustic resonators of a duplexer
  • Fig. 4 illustrates a possible frequency shift of a
  • Figure 1 shows possible layers of layer stacks of an RF filter as discussed above.
  • the filter has a first layer stack LSI in which elements of a first resonator R1 are realized. Further, in a second layer stack LS2 elements of the second resonator R2 are realized.
  • the first layer stack LSI and the second layer stack are arranged one next to another.
  • the first layer stack LSI and the second layer stack LS2 comprise electrode structures ELS arranged on a piezoelectric material PM in a piezoelectric layer PL. On and above the electrode structures ELS material of a TCF layer TCFL is arranged to compensate for temperature induced frequency drifts.
  • the first layer stack LSI and the second layer stack LS2 are acoustically isolated and separated by a trench TR between the layer stacks.
  • the layer stacks LSI, LS2 in Figure 1 establish SAW components.
  • the electrode structures ELS comprise
  • a different layer stack is obtained by reducing the thickness of the TCF layer TCFL of the second layer stack LS2 compared to the thickness of the corresponding TCF layer of the first layer stack LSI, respectively.
  • Figure 2 illustrates a first layer stack LSI realizing a first resonator R1 as a BAW resonator and a second layer stack LS2 realizing a second resonator R2 as a BAW resonator.
  • the corresponding BAW resonators comprise a bottom electrode BE in a bottom electrode layer BEL, a corresponding top electrode TE in a corresponding top electrode layer TEL and a piezoelectric material in a piezoelectric layer PL sandwiched between the bottom electrode layer and the top electrode layer.
  • a trim layer TRL is arranged in both resonators Rl, R2.
  • electroacoustic mirrors EAM are provided to confine acoustic energy to the resonating structure.
  • the electroacoustic mirrors EAM comprise adjacent layers of different acoustic impedance (not shown in the figure) to establish a Bragg mirror for acoustic (longitudinal) waves propagating in the vertical direction.
  • Figure 3 illustrates a ladder-type like topology used for a transmission filter TXF and for a reception filter RXF of a multiplexer MUL in the form of a duplexer DU.
  • transmission filter TXF is arranged between a transmission port and an antenna port connected to an antenna AN.
  • the reception filter RXF is arranged between the antenna port and a reception port.
  • a further circuit is arranged that may establish an impedance matching circuit connected to the antenna port.
  • series resonators SR are electrically connected in series in the signal path.
  • Parallel resonators PR are electrically connected in parallel paths that electrically connect the signal path to ground.
  • Figure 4 illustrates a possible beneficial effect of the suggested electroacoustic filter.
  • Figure 4 shows the frequency-dependent insertion losses for series and for parallel resonators according to the above-described resonators and according to conventional resonators.
  • the resonators having the lower resonance frequency can be used to establish parallel resonators in bandpass filters and series resonators in band rejection filters.
  • the resonators having the higher resonance frequency can be used to
  • the resonance frequencies and the anti-resonance frequencies of the conventional and of the improved resonators are essentially equal.
  • the improved resonators have a spurious mode that is present in a critical frequency range denoted by the rectangle in the figure moved to a lower frequency and outside the critical frequency range as
  • electroacoustic filter and corresponding multiplexers and methods for establishing filters and multiplexers are not limited to the technical features described above and
  • Electroacoustic filters can comprise further resonators and further subfilters to
  • resonators can comprise additional layers and electrode structures, e.g. for establishing a waveguide and for further means for preventing electrical or acoustical energy dissipation.
  • EAF electroacoustic filter
  • LSI, LS2 first, second layer stack MUL: multiplexer
  • TEL top electrode layer

Abstract

An improved electroacoustic SAW or BAW filter (EAF) with improved electric and/or acoustic properties is provided. The filter has a first resonator (Rl) in a first layer stack (LSI) and a second resonator (R2) in a second layer stack (LS2). The second layer stack is different from the first layer stack in at least one parameter selected from the number of layers, the thickness of a layer and the material of a layer.

Description

Description
Electroacoustic filter, multiplexer and method of
manufacturing an electroacoustic filter
The present invention refers to electroacoustic filters that may be used in mobile communication devices and to
multiplexers comprising such filters. Further, the present invention refers to improved methods of manufacturing an electroacoustic filter.
Electroacoustic filters are RF filters that utilize acoustic waves in electroacoustic resonators. Such resonators comprise electrode structures and a piezoelectric material for converting between RF signals and acoustic waves.
Electroacoustic filters can be bandpass filters or band rejection filters providing steep flanks.
What is wanted is an improved electroacoustic filter that is compatible with specifications of next generation mobile communication systems. In particular, good electric and acoustic properties are wanted. For example, electroacoustic filters having small temperature coefficients of frequency (TCF) , a high electroacoustic coupling coefficient K2
providing wide bandwidths, and reduced spurious modes in critical frequency ranges are wanted. Further,
electroacoustic filters should be compatible with carrier aggregation (CA) systems.
Conventional electroacoustic filters can comprise SAW
resonators (SAW = surface acoustic wave) or BAW resonators (BAW = bulk acoustic wave) . In RF filters employing SAW resonators a TCF layer may be provided for reducing
temperature induced changes of characteristic frequencies.
However, conventional RF filters are optimized with respect to one parameter or small numbers of parameters only. Thus, what is needed is an electroacoustic filter that provides improved electric and acoustic properties for a variety of parameters .
To that end, an electroacoustic filter and a method of manufacturing an electroacoustic filter according to the independent claims and a multiplexer are provided. Dependent claims provide preferred embodiments.
The electroacoustic filter comprises a first resonator realized in a first layer stack and a second resonator realized in a second layer stack. The second layer stack is different from the first layer stack in at least one
parameter selected from the number of layers, the thickness of a layer and the material of a layer.
The first resonator can be an electroacoustic resonator and the second resonator can be an electroacoustic resonator. To that end, the corresponding layer stack comprises a
piezoelectric material and an electrode structure to employ the piezoelectric effect to convert between RF signals and acoustic waves when an RF signal is applied to the electrode structure .
The first layer stack and the second layer stack can have a similar construction. In particular, it is possible that for each layer or for a plurality of layers of the first layer stack there is an associated layer in the second layer stack that has the same purpose as the associated layer of the first stack.
The difference between the first layer stack and the second layer stack or several differences between the first layer stack and the second layer stack correspond to a decoupling of the first resonator and the second resonator.
The decoupling can be an acoustic decoupling of the
corresponding resonators or a decoupling of at least one process step in the corresponding process steps of methods of manufacturing the resonators.
The decoupling between the first resonator and the second resonator allows independent optimizations directed to the first resonator and directed to the second resonator.
Conventional RF filters comprise structures of a first resonator and structures of a second resonator arranged one next to another on a common carrier. Due to similarities in construction of first and second resonators in conventional filters manufacturing methods are substantially simplified by creating corresponding layers for the first resonator and for the second resonator together utilizing same processing steps .
Such simplifications in processing, however, lead to coupled resonators and/or to coupled processing steps that prevent the second resonator being independent from the first
resonator and that prevent a corresponding electroacoustic filter from having good electric and acoustic properties for a plurality of parameters. Thus, the suggested decoupling of the first resonator and of the second resonator provides the possibility of optimizing the first resonator with respect to a first parameter and the second resonator with respect to a second parameter such that the overall electroacoustic filter is optimized with respect to two or more parameters. It is possible that the first resonator and the second resonator are SAW resonators or BAW resonators. In the case of SAW resonators the resonators can comprise electrode structures in an electrode layer. In the case of BAW resonators the resonators can comprise a bottom electrode in a bottom electrode layer, top electrode in a top electrode layer above the bottom electrode layer and a cavity or an acoustic mirror below the bottom electrode.
SAW resonators can have the electrode structures as
interdigitated comb-like electrode structures arranged on or above a piezoelectric material. The piezoelectric material may be a piezoelectric thin layer or a piezoelectric single crystal. The resonator can comprise further structures such as acoustic reflectors at the distal ends of an acoustic track to confine acoustic energy in the resonator' s active area. Further material can be deposited above the electrode structure and above the piezoelectric material between the electrode structure. For example dielectric material of a TCF layer and/or dielectric material of a passivation layer can be arranged there.
A TCF layer preferably comprises a material that has a temperature dependence of characteristic frequencies opposite to temperature characteristics of the electrode structure and/or the piezoelectric material. Usually, a change in temperature changes elastic properties of the used materials and causes a thermally induced
expansion of the materials. As a consequence thereof, the wave velocity and the pitch of the electrode structures result in a frequency drift of characteristic frequencies such as resonance frequencies or anti-resonance frequencies of the resonator. By providing the TCF layer comprising a material that has the opposite effect to temperature changes, the overall frequency drift can be reduced or even
eliminated .
A TCF layer can comprise, for example, a silicon oxide such as silicon dioxide.
A BAW resonator has its piezoelectric material sandwiched between the bottom electrode and the top electrode. To confine acoustic energy to the resonator' s area, the
resonator can comprise an acoustic mirror below the bottom electrode or a cavity below the bottom electrode. An
electroacoustic BAW resonator comprising an acoustic mirror below the bottom electrode is an SMR-type resonator (SMR = solidly mounted resonator) . A resonator having a cavity below its bottom electrode is a FBAR-type resonator (FBAR = film bulk acoustic resonator) .
BAW resonators can comprise a trimming layer above the top electrode. Further, additional structures, e.g. frame
structures above the top electrode, can be arranged in order to suppress unwanted acoustic modes.
It is preferred that if the first resonator is a SAW
resonator then the second resonator is a SAW resonator. Further, it is preferred that if the first resonator is a BAW resonator, then the second resonator is a BAW resonator.
Remaining similarities in construction lead to less complex manufacturing methods while the possibility to optimize different parameters is obtained.
It is possible that the electroacoustic filter has a ladder- type like filter topology. The first resonator can be a series resonator and the second resonator can be a parallel resonator .
A ladder-type like filter topology has two or more series resonators electrically connected in series in a signal path between an input port and an output port. Further, such a 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.
Bandpass filters and band rejections filters can easily be implemented with such ladder-type like filter topologies. An electroacoustic resonator has a resonance frequency and an anti-resonance frequency above the resonance frequency. A bandpass filter is obtained when the resonance frequency of series resonators essentially corresponds to the anti
resonance frequency of the parallel resonators. Then, the series path is transparent for RF signals in the frequency range of the resonance frequency of the series resonators and the RF power cannot be shunted to ground because the parallel resonators essentially provide an open circuit impedance. For RF frequencies in the range of the resonance frequency of the parallel resonators the corresponding RF power can be shunted to ground. For RF signals in the range of the anti-resonance frequency of the series resonators, the series resonators provide an open circuit impedance and the RF power cannot pass the series resonators. Thus, a bandpass filter having its lower flank arranged at the resonance frequency of the parallel resonators and having its upper flank arranged at the anti-resonance frequency of the series resonators is obtained .
By exchanging series and parallel resonators, corresponding band rejection filters or notch filters can be obtained.
Thus, resonators having different frequency responses for series resonators and for parallel resonators are needed. The above-mentioned decoupling between the first resonator and the second resonator makes it easily possible to provide correspondingly different first and second resonators for series and parallel resonators, respectively.
It is possible that the first layer stack and the second layer stack comprise one or more layers selected from a piezoelectric layer, a TCF layer, a trimming layer, and a passivation layer.
Correspondingly, it is possible that both layer stacks comprise a piezoelectric layer, a TCF layer, a trimming layer and/or a passivation layer. Then, the piezoelectric layer of the first layer stack would be an associated layer of a piezoelectric layer of the second layer stack. A TCF layer of the first layer stack would be an associated layer of a corresponding TCF layer of the second layer stack. A trimming layer of the first layer stack would be an associated layer of the corresponding trimming layer of the second layer stack and a passivation layer of the first layer stack would be an associated layer of the corresponding passivation layer of the second layer stack.
Due to the correspondences similar but - in detail - different layer constructions can be obtained that are optimized with respect to different parameters.
It is possible that the first resonator and the second resonator are acoustically decoupled.
An acoustic decoupling can be obtained by providing the piezoelectric material or providing an interface between the piezoelectric material and an electrode structure at
different vertical positions. This is possible by adding one additional layer there below selectively only for one of the two resonators.
However, it is also possible to have the same number of layers but to provide one layer with a different thickness compared to the associated layer of the corresponding other layer stack.
Additionally or as an alternative it is possible to obtain an acoustic decoupling by comprising a trench between the first resonator and the second resonator.
The trench physically separates the layer stacks of the resonators and leads to - due to the large difference in acoustic impedance of material and vacuum or air - an
acoustic isolation of the resonator's structures. It is possible that the first resonator and the second resonator are arranged on a common carrier.
The common carrier can be a carrier substrate on which the structures for BAW and/or SAW resonators are arranged. On the carrier acoustic mirrors of SMR-type resonators can be arranged. In the carrier cavities for providing FBAR-type resonators can be arranged.
Further, it is possible that a common carrier establishes a common single crystal piezoelectric material on which
electrode structures of the first resonator and electrode structures of the second resonator are arranged.
It is also possible that the first and/or second layer stack have a piezoelectric material provided as a thin layer or as a bulk material, e.g. as a thin bulk material.
In particular, it is possible that the piezoelectric material of both layer stacks is provided as a thin layer or as a bulk material, e.g. as a thin bulk material.
When provided as a bulk material the piezoelectric material can be provided as a monocrystalline material that has an appropriate crystal cut.
Further, the piezoelectric material of both layer stacks can be provided as a thin layer, i.e. by wafer bonding with thin film processing, e.g. mechanical grinding or "smart cut", or employing thin-film layer deposition techniques such as sputtering, physical vapour deposition, chemical vapour deposition, molecular beam epitaxy and the like. The piezoelectric material can be arranged on or above a carrier, e.g. different carriers or a common carrier, e.g. a common carrier substrate for both layer stacks.
The carrier substrate for both layer stacks can comprise or consist of a material selected from silicon, aluminium oxide, sapphire, crystalline carbon (diamond) , silicon carbide SiC, quartz and similar materials including doping of the
mentioned carrier substrate materials. In particular, carrier substrates having a material with a good thermal conductance are preferred.
It is possible that the SAW resonators comprise a sagittal acoustic wave guide. The piezoelectric material can be arranged on or above this wave guide.
The wave guide can consist of a single layer. However, it is possible that the wave guide comprises two or more layers. It is preferred that the wave guide has a layer comprising a material that has an acoustic impedance different from the acoustic impedance of a layer above or below the wave guide's layer. Correspondingly, it is possible that the wave guide has two or more layers of different acoustic impedances. An interface between two materials of different acoustic
impedance reflects acoustic waves. Thus, acoustic waves from the surface of the resonator are reflected and acoustic energy is prevented from dissipating in the layer system below. Thus, the wave guide helps to confine the acoustic energy to the surface of the resonator, which improves the quality factor. A layer of high acoustic impedance of the wave guide can comprise aluminium nitride, silicon carbide, crystalline carbon (diamond) or polycrystalline silicon. A layer of the wave guide having a low acoustic impedance can comprise silicon dioxide, a doped silicon dioxide or
germanium dioxide. Silicon dioxide can be doped by fluorine or phosphorous or boron.
If the SAW resonator has a wave guide and a carrier substrate then it is preferred that the wave guide is arranged between the carrier substrate and the piezoelectric material.
Further, it is possible that an intermediate layer is
provided as a temperature compensation layer. The temperature compensation layer may comprise a silicon oxide, e.g. Si02, ...
It is possible that the SAW resonator has a passivation layer arranged above the electrode structure.
The passivation layer can comprise an oxide, e.g. a metal oxide or a silicon oxide. The metal oxide can be an oxide of the metal of the electrode structure.
It is possible to utilize such electroacoustic filters to establish multiplexers.
Consequently, it is possible that a multiplexer comprises one or more electroacoustic filters as described above.
Then, the electroacoustic filter has a first subfilter and a second subfilter. The first subfilter can be a TX
(transmission) filter. The second subfilter can be an RX (reception) filter. The first resonator can be a resonator of the TX subfilter and the second resonator can be a resonator of the RX subfilter. In multiplexers comprising a TX filter and an RX filters the filters are employed to separate wanted signals from unwanted signals, in particular to conduct transmission signals from a transmission port to a common port and to conduct reception signals from a common port to a reception port and to prevent a high power transmission signal from entering the reception port. To that end, the TX filter and the RX filter can be bandpass filters that have different center frequencies. To obtain bandpass filters with different center frequencies the differences between the first resonator and the second resonator can be employed.
It is possible that the multiplexer, a quadplexer or a multiplexer of a higher order.
It is possible that the above optimizations are used to shift the characteristic frequency of a bulk acoustic wave mode of a resonator out of a characteristic frequency band, e.g. band 40, to comply with carrier aggregation requirements.
A method of manufacturing an electroacoustic filter comprises the steps of:
- providing a first layer stack for a first resonator,
- providing a second layer stack for a second resonator,
- decoupling the first layer stack from the second layer stack or decoupling at least one processing step for
providing the first layer stack from a processing for
providing the second layer stack.
Central aspects of the electroacoustic filter and details of preferred embodiments are explained and shown in the
schematic accompanying figures. In the figures:
Fig. 1 shows a possible arrangement of layer stacks of an
RF filter employing SAW structures;
Fig. 2 shows possible details of layer stacks of filters employing BAW resonators;
Fig. 3 shows a possible use in electroacoustic resonators of a duplexer; and
Fig. 4 illustrates a possible frequency shift of a
spurious mode.
Figure 1 shows possible layers of layer stacks of an RF filter as discussed above. The filter has a first layer stack LSI in which elements of a first resonator R1 are realized. Further, in a second layer stack LS2 elements of the second resonator R2 are realized. The first layer stack LSI and the second layer stack are arranged one next to another. The first layer stack LSI and the second layer stack LS2 comprise electrode structures ELS arranged on a piezoelectric material PM in a piezoelectric layer PL. On and above the electrode structures ELS material of a TCF layer TCFL is arranged to compensate for temperature induced frequency drifts.
On the material of the TCF layer a passivation layer PAL is arranged. The first layer stack LSI and the second layer stack LS2 are acoustically isolated and separated by a trench TR between the layer stacks. The layer stacks LSI, LS2 in Figure 1 establish SAW components. The electrode structures ELS comprise
interdigitated comb-like electrode structures and/or
reflector fingers at the distal ends of the acoustic track to convert between RF signals and acoustic waves propagating at the surface of the piezoelectric material PM and at the interface between the piezoelectric material and the
electrode structures ELS and the material of the TCF layer TCFL, respectively.
A different layer stack is obtained by reducing the thickness of the TCF layer TCFL of the second layer stack LS2 compared to the thickness of the corresponding TCF layer of the first layer stack LSI, respectively.
By providing differently constructed layer stacks for the first and for the second resonator manufacturing methods are more complex compared to manufacturing steps for establishing conventional RF filters. However, the obtainable gain in electric and acoustic properties of the whole filter may render the additional efforts in manufacturing steps
worthwhile .
Figure 2 illustrates the concept of the present
electroacoustic filter applied to BAW resonators. Thus,
Figure 2 illustrates a first layer stack LSI realizing a first resonator R1 as a BAW resonator and a second layer stack LS2 realizing a second resonator R2 as a BAW resonator. The corresponding BAW resonators comprise a bottom electrode BE in a bottom electrode layer BEL, a corresponding top electrode TE in a corresponding top electrode layer TEL and a piezoelectric material in a piezoelectric layer PL sandwiched between the bottom electrode layer and the top electrode layer. On top of the top electrode TE in the top electrode layer TEL a trim layer TRL is arranged in both resonators Rl, R2.
Differences in the layer construction are obtained by
providing the piezoelectric layer PL of the second resonator R2 with a reduced thickness compared to the piezoelectric layer PL in the first resonator Rl .
Below the corresponding bottom electrode layers
electroacoustic mirrors EAM are provided to confine acoustic energy to the resonating structure. The electroacoustic mirrors EAM comprise adjacent layers of different acoustic impedance (not shown in the figure) to establish a Bragg mirror for acoustic (longitudinal) waves propagating in the vertical direction.
Figure 3 illustrates a ladder-type like topology used for a transmission filter TXF and for a reception filter RXF of a multiplexer MUL in the form of a duplexer DU. The
transmission filter TXF is arranged between a transmission port and an antenna port connected to an antenna AN. The reception filter RXF is arranged between the antenna port and a reception port. Between the antenna port and the reception filter RXF a further circuit is arranged that may establish an impedance matching circuit connected to the antenna port.
In the ladder-type like topologies series resonators SR are electrically connected in series in the signal path. Parallel resonators PR are electrically connected in parallel paths that electrically connect the signal path to ground. Figure 4 illustrates a possible beneficial effect of the suggested electroacoustic filter. In particular, Figure 4 shows the frequency-dependent insertion losses for series and for parallel resonators according to the above-described resonators and according to conventional resonators.
The resonators having the lower resonance frequency can be used to establish parallel resonators in bandpass filters and series resonators in band rejection filters. The resonators having the higher resonance frequency can be used to
establish series resonators in bandpass filters and parallel resonators in band rejection filters.
The resonance frequencies and the anti-resonance frequencies of the conventional and of the improved resonators are essentially equal. However, the improved resonators have a spurious mode that is present in a critical frequency range denoted by the rectangle in the figure moved to a lower frequency and outside the critical frequency range as
indicated by the arrow.
The electroacoustic filter and corresponding multiplexers and methods for establishing filters and multiplexers are not limited to the technical features described above and
embodiments shown in the figures. Electroacoustic filters can comprise further resonators and further subfilters to
establish further basic elements of ladder-type like
topologies that are cascaded with respect to other basic elements and that can be used in additional signal paths, e.g. in multiplexers of higher orders. Further, resonators can comprise additional layers and electrode structures, e.g. for establishing a waveguide and for further means for preventing electrical or acoustical energy dissipation. List of Reference Signs
AN: antenna
BE : bottom electrode
BEL: bottom electrode layer
DU: duplexer
EAF: electroacoustic filter
EAM : electroacoustic mirror
ELS : electrode structures
LSI, LS2 : first, second layer stack MUL: multiplexer
PAL: passivation layer
PL: piezoelectric layer
PM: piezoelectric material
PR: parallel resonator
Rl, R2 : first, second resonator RXF : reception filter
SR: series resonator
TCFL : TCF-layer
TE : top electrode
TEL: top electrode layer
TR: trench
TXF : transmission filter

Claims

Claims
1. An electroacoustic filter, comprising
- a first resonator realized in a first layer stack,
- a second resonator realized in a second layer stack, wherein
- the second layer stack is different from the first layer stack in at least one parameter selected from the number of layers , the thickness of a layer and the material of a layer.
2. The electroacoustic filter of the previous claim, wherein the first and second resonator are
- SAW resonators comprising electrode structures in an electrode layer or
- BAW resonators comprising 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 an acoustic mirror below the bottom electrode layer.
3. The electroacoustic filter of one of the previous claims , wherein
- the filter has a ladder type like topology,
- the first resonator is a series resonator and
- the second resonator is a parallel resonator.
4. The electroacoustic filter of one of the previous claims, wherein the first layer stack and the second layer stack compri se a layer selected from a piezoelectric layer, a TCF layer, a trimming layer, a passivation layer.
5. The electroacoustic filter of one of the previous claims , wherein the first resonator and the second resonator are acoustically decoupled.
6. The electroacoustic filter of one of the previous claims, comprising a trench between the first resonator and the second resonator.
7. The electroacoustic filter of one of the previous claims, wherein the first resonator and the second resonator are arranged on a common carrier.
8. The electroacoustic filter of one of the previous claims, wherein the first layer stack and/or the second layer stack have a piezoelectric material provided as a thin layer or as a bulk material.
9. A Multiplexer, comprising an electroacoustic filter of one of the previous claims, wherein
- the filter has a TX subfilter and an RX subfilter
- the first resonator is in the TX subfilter and the second resonator is in the RX subfilter.
10. The Multiplexer of the previous claim being a duplexer, a quadplexer or a multiplexer of a higher order.
11. A Method of manufacturing an electroacoustic filter, comprising the steps of
- providing a first layer stack for a first resonator,
- providing a second layer stack for a second resonator,
- decoupling
the first layer stack from the second layer stack or at least one processing step for providing the first layer stack from a processing step for providing the second layer stack .
PCT/EP2019/057085 2018-04-25 2019-03-21 Electroacoustic filter, multiplexer and method of manufacturing an electroacoustic filter WO2019206533A1 (en)

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