WO2019185248A1 - Baw resonator with improved coupling, rf filter comprising a baw resonator and method of manufacturing a baw resonator - Google Patents

Baw resonator with improved coupling, rf filter comprising a baw resonator and method of manufacturing a baw resonator Download PDF

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Publication number
WO2019185248A1
WO2019185248A1 PCT/EP2019/054317 EP2019054317W WO2019185248A1 WO 2019185248 A1 WO2019185248 A1 WO 2019185248A1 EP 2019054317 W EP2019054317 W EP 2019054317W WO 2019185248 A1 WO2019185248 A1 WO 2019185248A1
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layer
baw resonator
bottom electrode
piezoelectric
resonator
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PCT/EP2019/054317
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French (fr)
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Maximilian SCHIEK
Ulrike RÖSLER
Willi Aigner
Giuseppe Toscano
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RF360 Europe GmbH
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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
    • 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
    • H03H9/02015—Characteristics of piezoelectric layers, e.g. cutting angles
    • H03H9/02023—Characteristics of piezoelectric layers, e.g. cutting angles consisting of quartz
    • 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
    • H03H9/15—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
    • H03H9/19—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator consisting of quartz
    • 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
    • H03H2003/021—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 the resonators or networks being of the air-gap type
    • 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
    • H03H2003/023—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 the resonators or networks being of the membrane type
    • 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
    • H03H2003/025—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 the resonators or networks comprising an acoustic mirror
    • 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
    • H03H2003/028—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 values of other parameters
    • 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
    • H03H9/02086—Means for compensation or elimination of undesirable effects
    • H03H9/02094—Means for compensation or elimination of undesirable effects of adherence
    • 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
    • H03H9/172—Means for mounting on a substrate, i.e. means constituting the material interface confining the waves to a volume
    • H03H9/173—Air-gaps
    • 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
    • H03H9/172—Means for mounting on a substrate, i.e. means constituting the material interface confining the waves to a volume
    • H03H9/174—Membranes
    • 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
    • H03H9/172—Means for mounting on a substrate, i.e. means constituting the material interface confining the waves to a volume
    • H03H9/175—Acoustic mirrors

Definitions

  • BAW resonator with improved coupling, RF filter comprising a BAW resonator and method of manufacturing a BAW resonator
  • BAW bulk acoustic wave
  • BAW resonators can be used in RF filters, e.g. of mobile com munication devices, where they convert between RF signals and acoustic waves in order to select wanted RF signals from un wanted RF signals.
  • bandpass filters or band rejection filters having steep bandpass skirts can be real ized with BAW resonators.
  • a BAW resonator typically has a piezoelectric material sand wiched between a bottom electrode and a top electrode.
  • the thickness of the piezoelectric material usually equals half the wavelength l/2 of the corresponding acoustic wave propa gating in the sandwich construction.
  • the piezoelectric mate rial is provided as a thin-film deposited onto the bottom electrode via thin film deposition techniques, typically via sputtering .
  • the thickness of the corresponding piezoelectric layer and the homogeneity of the thickness becomes important. What is wanted is a high layer uniformity and thickness uni formity and a uniformity of the material properties of the piezoelectric material over the whole area of the wafer. According to the current trend in mobile communication de vices, the range of used frequencies is expanded to lower frequencies and in particular to higher frequencies. Higher frequencies demand for thinner piezoelectric layers. Thinner piezoelectric layers have higher relative variations of the layer thickness. Thus, the trend towards high frequencies be comes problematic with typical BAW resonators.
  • piezoelectric material of a BAW resonator Another typical characteristic of a piezoelectric material of a BAW resonator is its piezoelectric property.
  • the piezoelec tric property of the piezoelectric material depends on the crystalline quality.
  • the achievable bandwidth of an RF filter comprising BAW resonators depends on the electroacoustic cou pling factor. Thus, with an improved crystalline quality the bandwidth of the corresponding RF filter could be increased.
  • a BAW resonator an RF filter comprising a BAW resonator and a method of manufacturing a BAW resonator ac cording to the independent claims are provided.
  • Dependent claims provide preferred embodiments.
  • the BAW resonator comprises a bottom electrode in a bottom electrode layer and a top electrode in a top electrode layer. Further, the BAW resonator comprises a piezoelectric material in a piezoelectric layer between the bottom electrode layer and the top electrode layer.
  • the piezoelectric material is a monocrystalline piezoelectric material. The use of a monocrystalline piezoelectric material provides a plurality of advantages. The crystallinity of a
  • monocrystalline piezoelectric material is higher than the quality of conventional piezoelectric materials that consist of deposited layers of polycrystalline piezoelectric domains.
  • the material's piezoelectric axis is much more precisely defined and the direction of orientation of the pi ezoelectric axis can be adjusted by choosing the correspond ing cut angles.
  • the use of a monocrystalline piezoelectric material provides an improved precision in layer thickness. Thickness variations are reduced compared to the piezoelectric layers comprising a deposited material.
  • BAW resonators are obtained, the electric and acoustic properties of which are better and more reproducibly con trolled.
  • RF filters such as bandpass filters or band rejection filters having a wider bandwidth, steeper filter skirts and a reduced insertion attenuation in a pass- band can be provided.
  • RF filters can be estab lished that utilize bulk acoustic waves, e.g. instead of SAW resonators employing surface acoustic waves.
  • RF filters having an improved power handling and a higher quality factor, especially at high frequencies, can be provided .
  • the piezoelectric material is selected from LiTaCy (lithium tantalate) , LiNbCy (lithium niobate) and quartz .
  • the piezoelectric properties of lithium tantalate, lithium niobate and quartz are well known.
  • material properties of monocrys talline lithium tantalate, lithium niobate and quartz are well known.
  • preferred cut angles e.g. defined by Euler angles
  • the BAW resonator is provided to work with a longitudinal acoustic wave mode.
  • BAW resonators Due to different working principles and different construc tions of BAW resonators and SAW resonators, the possibility of working with longitudinal acoustic wave modes is unique to BAW resonators. In such acoustic wave modes the displacement of atoms or ions of the piezoelectric material is parallel and anti-parallel to the direction of propagation of the cor responding wave mode.
  • the corresponding wave is reflected in a vertical direction between the bottom electrode and an acoustic mirror, respec tively, at the bottom side of the piezoelectric material and the top electrode at the top side of the piezoelectric mate rial .
  • the piezoelectric material i.e. the monocrystalline piezoelectric material, has a cut angle se lected from (0°, 0° £ m ⁇ 360°, 0°), (0°, 90°, 0°) and (0°,
  • the Euler angles (l, m, Q) are defined as fol lows: a set of axes x, y, z, which are the crystallographic axes of the substrate, are firstly taken as a basis.
  • the first angle, l specifies the amount by which the x-axis and the y-axis are rotated about the z-axis, the x-axis being rotated in the direction of the y-axis.
  • the z' -axis and the y' -axis are ro tated about the x' -axis by the angle m.
  • the y' -axis is rotated in the direction of the z'-axis.
  • the c' ' -axis and the y' ' -axis are ro tated about the z" -axis by the angle Q.
  • the c' ' -axis is rotated in the direction of the y' '-axis.
  • the x' ' ' -axis and the y' ' ' -axis are parallel to the surface of the substrate.
  • the z' " -axis is the normal to the surface of the substrate.
  • the x' ' ' -axis specifies the propagation direction of the acoustic waves.
  • the given angles l, m, and Q can have tolerances of ⁇ 5° or ⁇ 10°: (0° ⁇ 5°, m, 0° ⁇ 5°), (0° ⁇ 5°, 90° ⁇ 5°, 0° ⁇ 5°), (0° ⁇ 5°, 300 ° ⁇ 5°, 0° ⁇ 5°), and (0° ⁇ 5°, 120° ⁇ 5°, 0° ⁇ 5°) or (0° ⁇ 10°, m, 0 ° ⁇ 10°), ( 0 ° ⁇ 10°, 90 ° ⁇ 10°, 0° ⁇ 10°), (0° ⁇ 10°, 300 ° ⁇ 10°, 0 ° ⁇ 10°), and (0° ⁇ 10°, 120° ⁇ 10°, 0° ⁇ 10°) .
  • the BAW resonator further comprises an acoustic mirror below the bottom electrode or a cavity below the bottom electrode.
  • either the acoustic mirror or the cavity acous tically decouple the resonator area from the carrier sub strate on which the resonator area is arranged. Without de coupling acoustic energy would dissipate into the substrate and a resonance with a quality factor needed for RF filters would not be possible.
  • the BAW resonator fur ther comprises a carrier substrate below the bottom elec trode.
  • the carrier substrate can be attached directly below the bottom electrode layer, e.g. in the case of a FBAR type resonator.
  • an acoustic mirror in the case of an SMR type resonator, is arranged between the bottom electrode and the carrier substrate.
  • the acoustic mirror comprises a layer stack where layers with a low acoustic impedance and layers with a high acoustic im pedance are alternately arranged on one another. Such a con figuration establishes a Bragg mirror for the characteristic resonance frequency of the BAW resonator.
  • Layers comprising a high acoustic impedance can comprise tungsten.
  • Layers of a low acoustic impedance can comprise a silicon oxide, e.g. a silicon dioxide.
  • the BAW resonator com prises a carrier substrate, a first Ti (titanium) layer on the carrier substrate, a first W (tungsten) layer on the first titanium layer, a first silicon dioxide layer on the first tungsten layer.
  • the resonator can comprise a second titanium layer on the first tungsten layer, a second tungsten layer on the second titanium layer and a second silicon dioxide on the second tungsten layer.
  • the silicon dioxide layers establish layers of a low acoustic impedance.
  • the tungsten layers establish layers of a high acoustic impedance.
  • the titanium layers establish intermedi ate layers that provide a good adhesion between the layers and that allow a good crystalline quality of the correspond ing layers above the titanium layers.
  • the BAW resonator comprises an AIN (alu minium nitride) layer.
  • the bottom electrode layer can be ar ranged on the aluminium layer.
  • the piezoelectric layer can be arranged on the bottom electrode layer and the top electrode layer can be arranged on the piezoelectric layer.
  • the aluminium nitride layer can be used as a base to provide a good crystalline quality of the bottom electrode layer.
  • the aluminium nitride layer can be arranged on an acoustic mirror, e.g. on a top layer comprising tungsten.
  • the aluminium nitride layer is arranged on a carrier substrate, e.g. in a BAW resonator of the FBAR type.
  • the aluminium nitride layer can be preferred as a seed layer for bottom electrodes comprising or consisting of tungsten.
  • a carrier substrate can have a thickness of 150 pm.
  • a first titanium layer can have a thickness of 32 nm.
  • a first tung sten layer can have a thickness of 510 nm.
  • a first layer of low acoustic impedance can have a thickness of 620 nm.
  • a sec ond titanium layer can have a thickness of 32 nm.
  • a second tungsten layer can have a thickness of 490 nm.
  • a second layer of low acoustic impedance can have a thickness of 680 nm.
  • An aluminium nitride layer can have a thickness of 30 nm.
  • a bot tom electrode can comprise or consist of molybdenum and have a thickness of 300 nm.
  • the piezoelectric material can have a thickness of 610 nm and the top electrode can comprise or consist of molybdenum and have a thickness of 300 nm.
  • the thick ness of the piezoelectric material can be 600 nm.
  • the Euler angles can be 0°, 300°, 0°.
  • Such a layer stack has a resonance frequency of approximately 2 GHz.
  • an RF filter comprises a BAW resonator or several BAW resonators as described above.
  • the resonators can be electrically connected in a ladder-type like topology or in a lattice-type like topology.
  • two or more series resonators are electrically connected in series in a signal path between an input port and an output port.
  • Two or more parallel paths electrically connect the signal path to ground and comprise one or several resonators.
  • BAW resonators having a high electroacoustic cou pling factor K 2 allows to create RF filters having a wide bandwidth which is also beneficial for complying with the trend towards more and more frequencies used in modern mobile communication devices.
  • the resonators can be electrically connected to impedance elements.
  • the RF filter further comprises one or more impedance elements.
  • electrode structures of impedance elements are combined with a glass material to benefit from the elec trical properties of the glass material.
  • the one or more impedance elements can be selected from resistance elements, inductance elements and capacitance elements. It is possible to use silicon or a doped silicon as a mate rial for the carrier substrate. However, it is also possible to use a glass material for the carrier substrate. Then, PoG elements can be arranged on or above the carrier substrate next to the layer construction establishing the BAW resonator or several BAW resonators. Thus, the integration density of electroacoustic and electrical circuit elements can be in creased and smaller components can be provided.
  • the carrier substrate can be provided on the form of a car rier wafer.
  • a plurality of resonators can be manufactured simultaneously by processing a single wafer or by processing a plurality of wafers.
  • a method of manufacturing a BAW resonator comprises the steps :
  • the carrier wafer can be provided with a certain thickness, e.g. between 700 pm and 750 pm, e. g. with a thickness of 725 pm.
  • the thickness can be reduced to a thickness between 100 pm and 200 pm, e.g. to 150 pm.
  • the thickness reduction can be realized by thinning.
  • the carrier substrate can also comprise stacked layers for the acoustic mirror.
  • the further steps for establishing the cavity can comprise a deep reactive ion etching.
  • a layer below the bottom elec trode e.g. an aluminium nitride layer, can act as an etch stop layer.
  • the implanted ions weaken the structural stability of the crystal lattice.
  • Temperature changes e.g. by heating the crystal, can be used to mechanically separate the slice from the crystal. Also, it is possible to use a mechanical sheer force to sepa rate the slice from the crystal.
  • thermal means and mechanical means for separating the slice from the crystal are used.
  • Fig. 1 shows a basic layer stack of a resonator of the FBAR type
  • Fig. 2 shows a basic layer construction of a BAW resonator of the SMR type
  • Fig. 3 to 11 show possible steps for manufacturing a BAW res onator
  • Fig. 12 to 20 show possible steps for manufacturing a BAW resonator
  • Fig. 21 and 22 show a simulation of the resonance
  • Fig. 23 shows the comparison between two different simula tions .
  • Fig. 24 and 25 show simulated dispersions
  • Fig. 26 and 27 show simulated resonances of a freestanding resonator
  • Fig. 28 and 29 show simulated dispersions of a freestanding resonator .
  • FIG. 1 shows details of a basic construction of a BAW reso nator BAWR.
  • the resonator comprises a bottom electrode BE in a bottom electrode layer and a top electrode TE in a top electrode layer. Between the bottom electrode layer and the top electrode layer the piezoelectric material is arranged.
  • the piezoelectric material is provided as a monocrystalline piezoelectric material MCPM in contrast to the polycrystal line piezoelectric material provided utilizing deposition techniques in conventional BAW resonators.
  • the BAW resonator BAWR shown in Figure 1 is a FBAR type resonator .
  • FIG. 2 illustrates a possible embodiment of a BAW resonator BAWR of the SMR type.
  • the resonator has the monocrystalline piezoelectric material MCPM between the bottom electrode BE and a bottom electrode layer and the top electrode TE and the top electrode layer.
  • the bottom electrode BE is ar- ranged on an acoustic mirror located below the bottom elec trode BE.
  • the acoustic mirror comprises layers of a low acoustic impedance LAI and layers of a high acoustic imped ance HAI .
  • the acoustic mirror is arranged on a carrier sub strate CS .
  • the acoustic mirror acoustically decouples the electroacoustically active region comprising the electrodes and the piezoelectric material from the carrier substrate CS .
  • no further structuring steps applicable to the carrier substrate CS are necessary.
  • Adhesive layers ADL can be provided between the layers of low acoustic impedance and high acoustic impedance. Further, an interface layer INL between a second layer of low acoustic impedance and the bottom electrode BE can be provided. The interface layer INL can be used to improve the crystalline quality of the material of the bottom electrode BE.
  • Figures 3 to 11 show steps for manufacturing a BAW resonator with Figure 11 showing the result of the manufacturing.
  • a monocrystalline piezoelectric material MCPM is provided.
  • the material can consist of a single crystal.
  • the single crystal can have a preferred cut angle.
  • the surface of the crystal is arranged in a preferred orien tation with respect to the piezoelectric axis of the crystal.
  • Figure 4 shows a bottom electrode BE structured on the top side of the monocrystalline piezoelectric material MCPM. It is to be noted that the side shown in Figure 4 as the top side of the material MCPM will become the bottom side of the later resonator.
  • Figure 5 shows that an intermediate layer IML is deposited onto the surface of the crystalline material on which the bottom electrode is arranged and on the bottom electrode.
  • Figure 6 shows that the intermediate layer IML is planarized. Thus, a planar surface is provided and the material at the bottom electrode has a defined layer thickness.
  • Figure 7 shows the implantation process. Ions that should weaken the crystal lattice of the piezoelectric material in a defined depth are implanted
  • Figure 8 shows the provision of the carrier substrate CS on which an acoustic mirror AM has already been structured.
  • Figure 9 shows that the intermediate layer IML of the layer construction shown in Figure 7 is wafer-bonded to a corre sponding intermediate layer IML establishing the material of a low acoustic impedance of the acoustic mirror AM
  • Typical wafer bonding methods can be utilized to mechanically connect the two layer constructions to obtain a single layer con struction .
  • Figure 10 further shows the step of removing the ex cess material of the monocrystalline piezoelectric material.
  • the region in the specific depth in which the ions have been implanted has weakened the crystal lattice structure and thermal or mechanical means can be used to separate the slice of the monocrystalline piezoelectric material MCPM that should remain on the acoustic mirror.
  • Figure 11 shows the result after depositing a top electrode TE on the monocrystalline piezoelectric material MCPM in the area above the bottom electrode BE.
  • Figures 3 to 11 show manufacturing steps for establishing an SMR type resonator.
  • Figures 12 to 20 show steps for estab lishing a BAW resonator of the FBAR type, respectively.
  • Figure 12 shows the step of providing the monocrystalline pi ezoelectric material MCPM.
  • Figure 13 shows the step of structuring the bottom electrode BE on the side of the piezoelectric material that will become the bottom side of the piezoelectric material.
  • Figure 14 shows the corresponding step of depositing material of an intermediate layer IML that can be used later to wafer bond the part comprising the piezoelectric material to the carrier substrate.
  • Figure 15 shows the corresponding part after a planarization step to provide a planar surface and a predefined thickness of the intermediate layer IML.
  • Figure 16 shows the step of implanting ions to provide a predetermined breaking point at a predefined depth within the monocrystalline piezoelectric material.
  • the bottom part of Figure 16 shows the provision of the carrier sub strate CS on which further material of an intermediate layer IML can be arranged to perform the wafer bonding step.
  • the wafer bonding step is shown in Figure 17 where material of the intermediate layer IML is used to wafer bond the part comprising the piezoelectric material to the part comprising the carrier substrate.
  • Figure 18 shows the step of removing the excess piezoelectric material .
  • Figure 19 shows the top electrode TE structured on the piezo electric material in the range of the bottom electrode BE.
  • Figure 20 shows the resonator after a step for establishing the cavity CV below the bottom electrode BE.
  • an etch stop layer (not shown in the fig ures) can be provided.
  • Figure 21 shows the resonance according to a simulation in the resonator area.
  • a resonance frequency of 2000 MHz and an anti-resonance frequency of approximately 2250 MHz is ob tained .
  • Figure 22 shows a corresponding simulation of the resonance in the horizontal vicinity of the resonator area.
  • the reso nance frequency is sufficiently far away from the resonance in the resonator area to allow the creation of RF filters without disturbances in the passband or a rejection band caused by resonating parts of the outer area of the resona tor .
  • Figure 23 shows the result of different simulations with re spect to a specific layer construction indicating a good agreement between different simulations.
  • Figures 24 and 25 show simulated dispersions in the resonator area (Figure 24) and in the outer area adjacent to the reso nator area ( Figure 25) , respectively.
  • the figures clearly show that no mode propagation in the outer area at the reso nance frequency FS of the resonator area is present.
  • Figures 26 and 27 show a corresponding resonance (Figure 26) and the absence of a resonance (Figure 27) of a simulated freestanding resonator.
  • Figures 28 and 29 show the corresponding dispersions for the resonator area and the outer area, respectively, of a free standing resonator.
  • resonator the RF filter and the method of manufacturing a resonator are not limited by the technical details and em bodiments shown in the figures and described above.
  • Resona tors can comprise further layers or structured elements.
  • RF filters can comprise further circuit elements.
  • Manufacturing methods can comprise further steps. List of Reference Signs
  • AM acoustic mirror
  • HAI layer of high acoustic impedance
  • MCPM monocrystalline piezoelectric material
  • S21 transfer matrix element

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  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)

Abstract

An improved BAW resonator with an increased electroacoustic coupling is provided. The resonator has a monocrystalline piezoelectric material (MCPM) obtained by layer transfer of LN, LT or quartz between a bottom electrode (BE) and a top electrode (TE).

Description

Description
BAW resonator with improved coupling, RF filter comprising a BAW resonator and method of manufacturing a BAW resonator
The present invention refers to BAW resonators (BAW = bulk acoustic wave) having an improved electroacoustic coupling, to RF filters comprising such resonators and to methods of manufacturing such resonators.
BAW resonators can be used in RF filters, e.g. of mobile com munication devices, where they convert between RF signals and acoustic waves in order to select wanted RF signals from un wanted RF signals. In particular, bandpass filters or band rejection filters having steep bandpass skirts can be real ized with BAW resonators.
A BAW resonator typically has a piezoelectric material sand wiched between a bottom electrode and a top electrode. The thickness of the piezoelectric material usually equals half the wavelength l/2 of the corresponding acoustic wave propa gating in the sandwich construction. The piezoelectric mate rial is provided as a thin-film deposited onto the bottom electrode via thin film deposition techniques, typically via sputtering .
However, especially on large wafers and with respect to BAW resonators that should be used in RF filters for higher fre quencies, the thickness of the corresponding piezoelectric layer and the homogeneity of the thickness becomes important. What is wanted is a high layer uniformity and thickness uni formity and a uniformity of the material properties of the piezoelectric material over the whole area of the wafer. According to the current trend in mobile communication de vices, the range of used frequencies is expanded to lower frequencies and in particular to higher frequencies. Higher frequencies demand for thinner piezoelectric layers. Thinner piezoelectric layers have higher relative variations of the layer thickness. Thus, the trend towards high frequencies be comes problematic with typical BAW resonators.
Another typical characteristic of a piezoelectric material of a BAW resonator is its piezoelectric property. The piezoelec tric property of the piezoelectric material depends on the crystalline quality. The achievable bandwidth of an RF filter comprising BAW resonators depends on the electroacoustic cou pling factor. Thus, with an improved crystalline quality the bandwidth of the corresponding RF filter could be increased.
Thus, what is wanted is a BAW resonator that allows an in creased bandwidth when comprised in RF filters and that com plies with the trend towards higher frequency ranges.
To that end, a BAW resonator, an RF filter comprising a BAW resonator and a method of manufacturing a BAW resonator ac cording to the independent claims are provided. Dependent claims provide preferred embodiments.
The BAW resonator comprises a bottom electrode in a bottom electrode layer and a top electrode in a top electrode layer. Further, the BAW resonator comprises a piezoelectric material in a piezoelectric layer between the bottom electrode layer and the top electrode layer. The piezoelectric material is a monocrystalline piezoelectric material. The use of a monocrystalline piezoelectric material provides a plurality of advantages. The crystallinity of a
monocrystalline piezoelectric material is higher than the quality of conventional piezoelectric materials that consist of deposited layers of polycrystalline piezoelectric domains.
As a consequence of the use of a monocrystalline piezoelec tric material the material's piezoelectric axis is much more precisely defined and the direction of orientation of the pi ezoelectric axis can be adjusted by choosing the correspond ing cut angles.
Also, the use of a monocrystalline piezoelectric material provides an improved precision in layer thickness. Thickness variations are reduced compared to the piezoelectric layers comprising a deposited material.
Thus, BAW resonators are obtained, the electric and acoustic properties of which are better and more reproducibly con trolled. Correspondingly, RF filters such as bandpass filters or band rejection filters having a wider bandwidth, steeper filter skirts and a reduced insertion attenuation in a pass- band can be provided.
With such improved BAW resonators RF filters can be estab lished that utilize bulk acoustic waves, e.g. instead of SAW resonators employing surface acoustic waves. As a consequence thereof, RF filters having an improved power handling and a higher quality factor, especially at high frequencies, can be provided . It is possible that the piezoelectric material is selected from LiTaCy (lithium tantalate) , LiNbCy (lithium niobate) and quartz .
The piezoelectric properties of lithium tantalate, lithium niobate and quartz are well known. In particular from the field of SAW resonators (compared to BAW resonators, SAW res onators employ a different type of transducer and utilize a different working principle) material properties of monocrys talline lithium tantalate, lithium niobate and quartz are well known. In particular, preferred cut angles (e.g. defined by Euler angles) are known.
It is possible that the BAW resonator is provided to work with a longitudinal acoustic wave mode.
Due to different working principles and different construc tions of BAW resonators and SAW resonators, the possibility of working with longitudinal acoustic wave modes is unique to BAW resonators. In such acoustic wave modes the displacement of atoms or ions of the piezoelectric material is parallel and anti-parallel to the direction of propagation of the cor responding wave mode.
The corresponding wave is reflected in a vertical direction between the bottom electrode and an acoustic mirror, respec tively, at the bottom side of the piezoelectric material and the top electrode at the top side of the piezoelectric mate rial . It is possible that the piezoelectric material, i.e. the monocrystalline piezoelectric material, has a cut angle se lected from (0°, 0° £ m < 360°, 0°), (0°, 90°, 0°) and (0°,
300°, 0°) .
In this case, the Euler angles (l, m, Q) are defined as fol lows: a set of axes x, y, z, which are the crystallographic axes of the substrate, are firstly taken as a basis.
The first angle, l, specifies the amount by which the x-axis and the y-axis are rotated about the z-axis, the x-axis being rotated in the direction of the y-axis. A new set of axes c' , y' , z' accordingly arises, where z = z' .
In a further rotation, the z' -axis and the y' -axis are ro tated about the x' -axis by the angle m. In this case, the y' -axis is rotated in the direction of the z'-axis. A new set of axes x' ' , y' ' , z' ' accordingly arises, where x' = x' ' .
In a third rotation, the c' ' -axis and the y' ' -axis are ro tated about the z" -axis by the angle Q. In this case, the c' ' -axis is rotated in the direction of the y' '-axis. A third set of axes x' ' ' , y' ' ' , z' ' ' thus arises, where z' ' = z' ' ' .
In this case, the x' ' ' -axis and the y' ' ' -axis are parallel to the surface of the substrate. The z' " -axis is the normal to the surface of the substrate. The x' ' ' -axis specifies the propagation direction of the acoustic waves.
The definition is in accordance with the international stand ard IEC 62276, 2005-05, Annex A1.
The given angles l, m, and Q can have tolerances of ± 5° or ± 10°: (0°± 5°, m, 0°± 5°), (0°± 5°, 90°± 5°, 0°± 5°), (0°± 5°, 300 °± 5°, 0°± 5°), and (0°± 5°, 120°± 5°, 0°± 5°) or (0°± 10°, m, 0 ° ± 10°), ( 0 ° ± 10°, 90 ° ± 10°, 0°± 10°), (0°± 10°, 300 °± 10°, 0 ° ± 10°), and (0°± 10°, 120°± 10°, 0°± 10°) .
It is possible that the BAW resonator further comprises an acoustic mirror below the bottom electrode or a cavity below the bottom electrode.
BAW resonators having an acoustic mirror below the bottom electrode are BAW resonators of the SMR type (SMR = solidly mounted resonator) . Resonators having a cavity below the bot tom electrode are resonators of the FBAR type (FBAR = film bulk acoustic resonator) .
In both cases either the acoustic mirror or the cavity acous tically decouple the resonator area from the carrier sub strate on which the resonator area is arranged. Without de coupling acoustic energy would dissipate into the substrate and a resonance with a quality factor needed for RF filters would not be possible.
It is possible that above the top electrode no further mat ter, except a gas for example, is present to acoustically de couple the resonating area at the top side.
Correspondingly, it is possible that the BAW resonator fur ther comprises a carrier substrate below the bottom elec trode. The carrier substrate can be attached directly below the bottom electrode layer, e.g. in the case of a FBAR type resonator. Further, it is possible that an acoustic mirror, in the case of an SMR type resonator, is arranged between the bottom electrode and the carrier substrate. The acoustic mirror comprises a layer stack where layers with a low acoustic impedance and layers with a high acoustic im pedance are alternately arranged on one another. Such a con figuration establishes a Bragg mirror for the characteristic resonance frequency of the BAW resonator.
Layers comprising a high acoustic impedance can comprise tungsten. Layers of a low acoustic impedance can comprise a silicon oxide, e.g. a silicon dioxide.
It is correspondingly possible that the BAW resonator com prises a carrier substrate, a first Ti (titanium) layer on the carrier substrate, a first W (tungsten) layer on the first titanium layer, a first silicon dioxide layer on the first tungsten layer. Further, the resonator can comprise a second titanium layer on the first tungsten layer, a second tungsten layer on the second titanium layer and a second silicon dioxide on the second tungsten layer.
The silicon dioxide layers establish layers of a low acoustic impedance. The tungsten layers establish layers of a high acoustic impedance. The titanium layers establish intermedi ate layers that provide a good adhesion between the layers and that allow a good crystalline quality of the correspond ing layers above the titanium layers.
It is possible that the BAW resonator comprises an AIN (alu minium nitride) layer. The bottom electrode layer can be ar ranged on the aluminium layer. The piezoelectric layer can be arranged on the bottom electrode layer and the top electrode layer can be arranged on the piezoelectric layer. The aluminium nitride layer can be used as a base to provide a good crystalline quality of the bottom electrode layer.
The aluminium nitride layer can be arranged on an acoustic mirror, e.g. on a top layer comprising tungsten. However, it is possible that the aluminium nitride layer is arranged on a carrier substrate, e.g. in a BAW resonator of the FBAR type.
The aluminium nitride layer can be preferred as a seed layer for bottom electrodes comprising or consisting of tungsten.
A carrier substrate can have a thickness of 150 pm. A first titanium layer can have a thickness of 32 nm. A first tung sten layer can have a thickness of 510 nm. A first layer of low acoustic impedance can have a thickness of 620 nm. A sec ond titanium layer can have a thickness of 32 nm. A second tungsten layer can have a thickness of 490 nm. A second layer of low acoustic impedance can have a thickness of 680 nm. An aluminium nitride layer can have a thickness of 30 nm. A bot tom electrode can comprise or consist of molybdenum and have a thickness of 300 nm. The piezoelectric material can have a thickness of 610 nm and the top electrode can comprise or consist of molybdenum and have a thickness of 300 nm.
In the case of a BAW resonator of the FBAR type, the thick ness of the piezoelectric material can be 600 nm.
In such a BAW resonator the Euler angles can be 0°, 300°, 0°. Such a layer stack has a resonance frequency of approximately 2 GHz.
It is possible that the BAW resonator or several such BAW resonators are used to establish an RF filter. Correspondingly, it is possible that an RF filter comprises a BAW resonator or several BAW resonators as described above.
The resonators can be electrically connected in a ladder-type like topology or in a lattice-type like topology.
In a ladder-type like topology two or more series resonators are electrically connected in series in a signal path between an input port and an output port. Two or more parallel paths electrically connect the signal path to ground and comprise one or several resonators.
The use of BAW resonators having a high electroacoustic cou pling factor K2 allows to create RF filters having a wide bandwidth which is also beneficial for complying with the trend towards more and more frequencies used in modern mobile communication devices.
In the RF filter the resonators can be electrically connected to impedance elements.
Thus, it is possible that the RF filter further comprises one or more impedance elements. The impedance elements can be re alized as PoG (PoG = passives on glass) .
In PoG elements electrode structures of impedance elements are combined with a glass material to benefit from the elec trical properties of the glass material.
Correspondingly, the one or more impedance elements can be selected from resistance elements, inductance elements and capacitance elements. It is possible to use silicon or a doped silicon as a mate rial for the carrier substrate. However, it is also possible to use a glass material for the carrier substrate. Then, PoG elements can be arranged on or above the carrier substrate next to the layer construction establishing the BAW resonator or several BAW resonators. Thus, the integration density of electroacoustic and electrical circuit elements can be in creased and smaller components can be provided.
The carrier substrate can be provided on the form of a car rier wafer. A plurality of resonators can be manufactured simultaneously by processing a single wafer or by processing a plurality of wafers.
A method of manufacturing a BAW resonator comprises the steps :
- providing a piezoelectric monocrystalline substrate with a structured bottom electrode,
- providing a carrier substrate,
- separating a slice from the piezoelectric monocrystalline substrate, the slice having the structured bottom electrode at a first side,
- connecting the slice to the carrier substrate via a wafer bonding method,
- structuring a top electrode at the second side of the slice .
It is possible that for separating the slice from the piezoe lectric monocrystalline substrate the method further com prises the steps:
- implanting ions below the piezoelectric monocrystalline substrate surface or - grinding the piezoelectric monocrystalline substrate at its side opposite to the side with the bottom electrode.
The carrier wafer can be provided with a certain thickness, e.g. between 700 pm and 750 pm, e. g. with a thickness of 725 pm. During manufacturing the thickness can be reduced to a thickness between 100 pm and 200 pm, e.g. to 150 pm. The thickness reduction can be realized by thinning.
In the case of establishing a BAW resonator of the SMR type, the carrier substrate can also comprise stacked layers for the acoustic mirror.
In the case of a BAW resonator of the FBAR type, further con struction steps for structuring the cavity below the bottom electrode are possible
The further steps for establishing the cavity can comprise a deep reactive ion etching. A layer below the bottom elec trode, e.g. an aluminium nitride layer, can act as an etch stop layer.
Also a Bosch process for passivating electrode structures at the flanks of the electrodes is possible.
When ions are implanted into the monocrystalline piezoelec tric material such that the material of the later piezoelec tric material of the resonator is arranged between the bottom electrode and the area in which the ions are implanted, then the implanted ions weaken the structural stability of the crystal lattice. Temperature changes, e.g. by heating the crystal, can be used to mechanically separate the slice from the crystal. Also, it is possible to use a mechanical sheer force to sepa rate the slice from the crystal.
Also, it is possible to use thermal means and mechanical means for separating the slice from the crystal.
Central aspects of the BAW resonator, of the RF filter and of the method of manufacturing a BAW resonator and details of preferred embodiments are shown in the accompanying schematic figures .
In the figures:
Fig. 1 shows a basic layer stack of a resonator of the FBAR type;
Fig. 2 shows a basic layer construction of a BAW resonator of the SMR type;
Fig. 3 to 11 show possible steps for manufacturing a BAW res onator;
Fig. 12 to 20 show possible steps for manufacturing a BAW resonator;
Fig. 21 and 22 show a simulation of the resonance;
Fig. 23 shows the comparison between two different simula tions ;
Fig. 24 and 25 show simulated dispersions; Fig. 26 and 27 show simulated resonances of a freestanding resonator; and
Fig. 28 and 29 show simulated dispersions of a freestanding resonator .
Figure 1 shows details of a basic construction of a BAW reso nator BAWR. The resonator comprises a bottom electrode BE in a bottom electrode layer and a top electrode TE in a top electrode layer. Between the bottom electrode layer and the top electrode layer the piezoelectric material is arranged. The piezoelectric material is provided as a monocrystalline piezoelectric material MCPM in contrast to the polycrystal line piezoelectric material provided utilizing deposition techniques in conventional BAW resonators.
The use of a monocrystalline piezoelectric material provides the above-described advantages although the method for manu facturing a corresponding BAW resonator is more complex than resonators utilizing sputtered piezoelectric material between the electrodes.
Below the bottom electrode BE a cavity CV is provided to acoustically decouple the resonator from its environment. Thus, the BAW resonator BAWR shown in Figure 1 is a FBAR type resonator .
Figure 2 illustrates a possible embodiment of a BAW resonator BAWR of the SMR type. The resonator has the monocrystalline piezoelectric material MCPM between the bottom electrode BE and a bottom electrode layer and the top electrode TE and the top electrode layer. However, the bottom electrode BE is ar- ranged on an acoustic mirror located below the bottom elec trode BE. The acoustic mirror comprises layers of a low acoustic impedance LAI and layers of a high acoustic imped ance HAI . The acoustic mirror is arranged on a carrier sub strate CS . The acoustic mirror acoustically decouples the electroacoustically active region comprising the electrodes and the piezoelectric material from the carrier substrate CS . Thus, no further structuring steps applicable to the carrier substrate CS are necessary.
Adhesive layers ADL can be provided between the layers of low acoustic impedance and high acoustic impedance. Further, an interface layer INL between a second layer of low acoustic impedance and the bottom electrode BE can be provided. The interface layer INL can be used to improve the crystalline quality of the material of the bottom electrode BE.
Figures 3 to 11 show steps for manufacturing a BAW resonator with Figure 11 showing the result of the manufacturing.
In Figure 3 a monocrystalline piezoelectric material MCPM is provided. The material can consist of a single crystal. The single crystal can have a preferred cut angle. For example the surface of the crystal is arranged in a preferred orien tation with respect to the piezoelectric axis of the crystal.
Figure 4 shows a bottom electrode BE structured on the top side of the monocrystalline piezoelectric material MCPM. It is to be noted that the side shown in Figure 4 as the top side of the material MCPM will become the bottom side of the later resonator. Figure 5 shows that an intermediate layer IML is deposited onto the surface of the crystalline material on which the bottom electrode is arranged and on the bottom electrode.
Figure 6 shows that the intermediate layer IML is planarized. Thus, a planar surface is provided and the material at the bottom electrode has a defined layer thickness.
Figure 7 shows the implantation process. Ions that should weaken the crystal lattice of the piezoelectric material in a defined depth are implanted
Figure 8 shows the provision of the carrier substrate CS on which an acoustic mirror AM has already been structured.
Figure 9 shows that the intermediate layer IML of the layer construction shown in Figure 7 is wafer-bonded to a corre sponding intermediate layer IML establishing the material of a low acoustic impedance of the acoustic mirror AM Typical wafer bonding methods can be utilized to mechanically connect the two layer constructions to obtain a single layer con struction .
The corresponding single layer construction is shown in Fig ure 10. Figure 10 further shows the step of removing the ex cess material of the monocrystalline piezoelectric material. The region in the specific depth in which the ions have been implanted has weakened the crystal lattice structure and thermal or mechanical means can be used to separate the slice of the monocrystalline piezoelectric material MCPM that should remain on the acoustic mirror. Finally, Figure 11 shows the result after depositing a top electrode TE on the monocrystalline piezoelectric material MCPM in the area above the bottom electrode BE.
In the rim area of the electrodes highlighted by rectangles, further manufacturing steps can be performed, e.g. to passiv ate the flanks.
Figures 3 to 11 show manufacturing steps for establishing an SMR type resonator. Figures 12 to 20 show steps for estab lishing a BAW resonator of the FBAR type, respectively.
Figure 12 shows the step of providing the monocrystalline pi ezoelectric material MCPM.
Figure 13 shows the step of structuring the bottom electrode BE on the side of the piezoelectric material that will become the bottom side of the piezoelectric material.
Figure 14 shows the corresponding step of depositing material of an intermediate layer IML that can be used later to wafer bond the part comprising the piezoelectric material to the carrier substrate.
Figure 15 shows the corresponding part after a planarization step to provide a planar surface and a predefined thickness of the intermediate layer IML.
Figure 16 (top part) shows the step of implanting ions to provide a predetermined breaking point at a predefined depth within the monocrystalline piezoelectric material. The bottom part of Figure 16 shows the provision of the carrier sub strate CS on which further material of an intermediate layer IML can be arranged to perform the wafer bonding step.
The wafer bonding step is shown in Figure 17 where material of the intermediate layer IML is used to wafer bond the part comprising the piezoelectric material to the part comprising the carrier substrate.
Figure 18 shows the step of removing the excess piezoelectric material .
Figure 19 shows the top electrode TE structured on the piezo electric material in the range of the bottom electrode BE.
Figure 20 shows the resonator after a step for establishing the cavity CV below the bottom electrode BE.
To enhance the step of creating the cavity CV below the bot tom electrode BE, an etch stop layer (not shown in the fig ures) can be provided.
Figure 21 shows the resonance according to a simulation in the resonator area. A resonance frequency of 2000 MHz and an anti-resonance frequency of approximately 2250 MHz is ob tained .
Figure 22 shows a corresponding simulation of the resonance in the horizontal vicinity of the resonator area. The reso nance frequency is sufficiently far away from the resonance in the resonator area to allow the creation of RF filters without disturbances in the passband or a rejection band caused by resonating parts of the outer area of the resona tor .
Figure 23 shows the result of different simulations with re spect to a specific layer construction indicating a good agreement between different simulations.
Figures 24 and 25 show simulated dispersions in the resonator area (Figure 24) and in the outer area adjacent to the reso nator area (Figure 25) , respectively. The figures clearly show that no mode propagation in the outer area at the reso nance frequency FS of the resonator area is present.
Figures 26 and 27 show a corresponding resonance (Figure 26) and the absence of a resonance (Figure 27) of a simulated freestanding resonator.
Figures 28 and 29 show the corresponding dispersions for the resonator area and the outer area, respectively, of a free standing resonator.
The resonator, the RF filter and the method of manufacturing a resonator are not limited by the technical details and em bodiments shown in the figures and described above. Resona tors can comprise further layers or structured elements. RF filters can comprise further circuit elements. Manufacturing methods can comprise further steps. List of Reference Signs
ADL: adhesion layer
AM: acoustic mirror
BAWR : BAW resonator
BE : bottom electrode
CS : carrier substrate
CV: cavity
f : frequency
FO: anti-resonance frequency
FS : resonance frequency
HAI : layer of high acoustic impedance
IML : intermediate layer
INL: interface layer
kx: longitudinal wave vector component LAI : layer of low acoustic impedance
MCPM : monocrystalline piezoelectric material S21 : transfer matrix element
TE : top electrode

Claims

Claims
1. A BAW resonator, comprising
- a bottom electrode in a bottom electrode layer, a top electrode in a top electrode layer, and a piezoelectric material in a piezoelectric layer between the bottom
electrode layer and the top electrode layer,
wherein
- the piezoelectric material is a monocrystalline
piezoelectric material.
2. The BAW resonator of the previous claim, wherein the piezoelectric material is selected from LiTaCg, LiNbCg,
Quartz .
3. The BAW resonator of one of the previous claims, provided to work with a longitudinal acoustic wave mode.
4. The BAW resonator of one of the previous claims, wherein the piezoelectric monocrystalline piezoelectric material has a cut angle selected from (0°, 0° £ m < 360°, 0°), (0°, 90°,
0°) and (0°, 300°, 0°) .
5. The BAW resonator of one of the previous claims, further comprising
- an acoustic mirror below the bottom electrode or
- a cavity below the bottom electrode.
6. The BAW resonator of one of the previous claims, further comprising a carrier substrate below the bottom electrode.
7. The BAW resonator of one of the previous claims,
compr srng - a carrier substrate,
- a first Ti layer on the carrier substrate,
- a first W layer on the first Ti layer,
- a first Si02 layer on the first W layer,
- a second Ti layer on the first W,
- a second W layer on the second Ti layer,
- a second SiCy layer on the second W layer.
8. The BAW resonator of one of the previous claims,
comprising
- an AIN layer,
- the bottom electrode layer on the AIN layer,
- the piezoelectric layer on the bottom electrode layer,
- the top electrode layer on the piezoelectric layer.
9. An RF filter comprising a BAW resonator of one of the previous claims.
10. The RF filter of the previous claim, further comprising an impedance element realized as a POG element.
11. A method of manufacturing a BAW resonator, comprising the steps :
- providing a piezoelectric monocrystalline substrate with a structured bottom electrode,
- providing a carrier substrate,
- separating a slice from the piezoelectric monocrystalline substrate, the slice having the structured bottom electrode at a first side,
- connecting the slice to the carrier substrate via a wafer bonding method,
- structuring a top electrode at the second side of the slice .
12. The method of the previous claim, wherein for separating the slice from the piezoelectric monocrystalline substrate the method further comprises
- implanting ions below the piezoelectric monocrystalline substrate's surface or
- grinding the piezoelectric monocrystalline substrate at its side opposite to the side with the bottom electrode.
PCT/EP2019/054317 2018-03-28 2019-02-21 Baw resonator with improved coupling, rf filter comprising a baw resonator and method of manufacturing a baw resonator WO2019185248A1 (en)

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