WO2019101391A1 - Electroacoustic filter with reduced acoustic coupling, method of reducing acoustic coupling and multiplexer - Google Patents

Electroacoustic filter with reduced acoustic coupling, method of reducing acoustic coupling and multiplexer Download PDF

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Publication number
WO2019101391A1
WO2019101391A1 PCT/EP2018/075524 EP2018075524W WO2019101391A1 WO 2019101391 A1 WO2019101391 A1 WO 2019101391A1 EP 2018075524 W EP2018075524 W EP 2018075524W WO 2019101391 A1 WO2019101391 A1 WO 2019101391A1
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resonator
electroacoustic
resonators
filter
acoustic
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PCT/EP2018/075524
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French (fr)
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Gholamreza Dadgar Javid
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RF360 Europe GmbH
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    • 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
    • H03H9/02818—Means for compensation or elimination of undesirable effects
    • 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
    • H03H9/02818—Means for compensation or elimination of undesirable effects
    • H03H9/02905—Measures for separating propagation paths on substrate
    • 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
    • H03H9/125—Driving means, e.g. electrodes, coils
    • H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
    • H03H9/14544—Transducers of particular shape or position
    • H03H9/14558—Slanted, tapered or fan shaped transducers
    • 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
    • H03H9/125—Driving means, e.g. electrodes, coils
    • H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
    • H03H9/14544—Transducers of particular shape or position
    • H03H9/14594—Plan-rotated or plan-tilted transducers
    • 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
    • H03H9/205—Constructional features of resonators consisting of piezoelectric or electrostrictive material having multiple resonators
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/54—Filters comprising resonators of piezo-electric or electrostrictive material
    • H03H9/58—Multiple crystal filters
    • H03H9/582—Multiple crystal filters implemented with thin-film techniques
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/64—Filters using surface acoustic waves
    • H03H9/6423—Means for obtaining a particular transfer characteristic
    • H03H9/6433—Coupled resonator filters
    • H03H9/6483—Ladder SAW filters
    • 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
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/54—Filters comprising resonators of piezo-electric or electrostrictive material
    • H03H9/56—Monolithic crystal filters
    • H03H9/566—Electric coupling means therefor
    • H03H9/568—Electric coupling means therefor consisting of a ladder configuration
    • 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

Definitions

  • the present invention refers to the reduction of acoustic coupling between electroacoustic resonators that may be used in electroacoustic filters or multiplexers.
  • Electroacoustic filters can be used in wireless communication systems.
  • electroacoustic resonators are arranged in a filter topology.
  • Electroacoustic resonators employ the piezoelectric effect to convert between RF signals and acoustic waves.
  • SAW surface acoustic wave
  • BAW bulk acoustic wave
  • GBAW guided bulk acoustic wave
  • interdigitating electrode fingers are arranged on a
  • piezoelectric material Excited acoustic waves propagate at a surface of the piezoelectric material.
  • BAW resonators a piezoelectric material is sandwiched between a bottom
  • This sandwich construction can be arranged on a cavity or on an acoustic mirror.
  • the filter topology comprises two or more
  • electroacoustic resonators arranged in the vicinity of each other.
  • desired acoustic wave modes and non-desired spurious acoustic wave modes may leave an electroacoustic resonator and enter into another electroacoustic resonator of the filter.
  • Such an acoustic coupling between the resonators deteriorates the overall performance of the filter.
  • interference between intrinsic acoustic wave modes of an electroacoustic resonator and received acoustic waves from another electroacoustic resonator deteriorates the performance of the electroacoustic resonator.
  • an electroacoustic filter with reduced acoustic coupling a method of reducing acoustic coupling and a multiplexer are provided according to the independent claims.
  • the dependent claims provide preferred embodiments.
  • An electroacoustic filter with reduced acoustic coupling comprises a first electroacoustic resonator and a second electroacoustic resonator.
  • the resonator has a first side.
  • the second electroacoustic resonator has a second side.
  • the first side of the first electroacoustic resonator and the first side of the second electroacoustic resonator are aligned non-parallel.
  • the acoustic coupling between the resonators can be decreased, i.e. the acoustic decoupling between the resonators can be improved.
  • side of an electroacoustic resonator denotes the area of the resonator from which acoustic waves can be emitted.
  • electroacoustic resonator allows a reduction of acoustic coupling although it contradicts the trend towards
  • one part of the first electroacoustic waves can hit a first position of the first side of the second electroacoustic resonator and a part of the second acoustic waves from the first electroacoustic resonator can enter the second electroacoustic resonator at a second position of the second electroacoustic resonator' s first side.
  • electroacoustic waves can have a phase difference that allows a full or a partial destructive interference at the second electroacoustic resonator.
  • interference of acoustic waves propagating from the first electroacoustic resonator to the second electroacoustic resonator can be used to decrease the acoustic effect of the first resonator on the second resonator. This is in contrast to a parallel alignment of respective sides of resonators where all partial waves would constructively interfere and cause a maximum effect on the second resonator's electric output signal.
  • electroacoustic resonator is arranged between the first electroacoustic resonator and the second electroacoustic resonator.
  • the first side of the second electroacoustic resonator is arranged between the first electroacoustic resonator and the second electroacoustic resonator.
  • electroacoustic resonators are the sides of the resonators that point to each other. These sides have the closest distance between the resonators and their direction of propagation of acoustic waves usually lead to the highest degree of unwanted coupling that is reduced as described above .
  • electroacoustic resonator and the second electroacoustic resonator is free from another electroacoustic resonator.
  • the angle between the first side of the first electroacoustic resonator and the first side of the second electroacoustic resonator is larger than or equal to 10° and smaller than or equal to 40°.
  • the above-mentioned angle interval provides a good trademark between decoupling and package size.
  • the angle is 15°, 20°, 25°, 30° or 35° .
  • the electroacoustic filter can have further electroacoustic resonators and different angles with respect to the alignment of respective sides of different resonators are possible.
  • the second electroacoustic resonator is selected from a SAW resonator, a TFSAW resonator, a BAW resonator and a GBAW resonator .
  • the resonator can comprise two oppositely arranged bus bars and finger electrodes arranged and
  • a resonator working with surface waves can comprise reflector structures arranged at the distal ends of the acoustic track.
  • Resonators working with bulk acoustic waves can comprise an electroacoustic mirror arranged below the bottom electrode to confine acoustic energy to the resonator and to prevent energy dissipation. Also, it is possible that a cavity is arranged below the bottom electrode.
  • Resonators working with surface waves can be arranged on a common surface of the piezoelectric material, e.g. a
  • the resonators are arranged on opposite sides of such a substrate and unwanted acoustic coupling between the resonators takes place via a conversion to bulk waves propagating through the substrate.
  • Resonators working with bulk waves can be arranged on a common carrier substrate.
  • An electrically conducting or a dielectric material can be arranged between the stacked structures of the individual resonators.
  • resonator structures of bulk acoustic wave resonators are arranged one above the other.
  • the electroacoustic filter further comprises one or more additional resonator.
  • Each additional resonator has a side. The side can emit acoustic waves. Two or more neighbored sides of neighbored resonators are aligned non-parallel .
  • every side of every resonator with respect to sides of other resonators are arranged non-parallel
  • first electroacoustic resonator and/or the second electroacoustic resonator is a SAW
  • electroacoustic resonator is flat. Further, it is possible that the first side of the second electroacoustic resonator is flat.
  • Resonators with flat sides simplify the process of finding an appropriate angle according to which the sides are aligned. The angle can be chosen such that a smallest distance between the opposite sides of the two resonators and a corresponding maximum distance of opposing positions of the sides are mainly equal to l/2 or an integer multiple of l/2 where l is the wavelength of the acoustic waves propagating in one of the resonators.
  • Such an angle usually provides the highest degree of destructive interference resulting in a maximum effectiveness of acoustically decoupling the resonators.
  • electroacoustic resonators have electrode structures with a preferred alignment with respect to the piezoelectric axis of the piezoelectric material.
  • the piezoelectric axis of the piezoelectric material is the direction in which deformations of the piezoelectric material cause the highest degree of piezoelectric effect.
  • the alignment of the sides of the resonators are chosen such that the
  • piezoelectric effect can be maintained at a high level. This can be obtained by maintaining the electrodes' alignment with respect to the piezoelectric axis. In particular, it is possible to maintain a perpendicular alignment between the direction of extension of the electrode and the piezoelectric axis .
  • a slanted resonator is a resonator with the shape of a parallelogram - at least in a horizontal or vertical cross-section of the resonator .
  • electroacoustic resonator according to the above cited has the shape of a parallelogram. This is valid for resonators working with bulk waves and for resonators working with surface waves.
  • resonators working with bulk waves can have the shape of a prism with a parallelogram as its base area.
  • the electrode fingers can have the footprint of a parallelogram.
  • a multiplexer e.g. a duplexer, a triplexer or a multiplexer of a higher degree, is used for separating RF signals of different frequency ranges into separate signal paths or to combine RF signals of different frequency ranges obtained from different signal paths in one or more common signal paths.
  • a multiplexer comprises an electroacoustic filter as described above as a first and/or as a second filter .
  • one filter is a transmission filter while the other filter is a reception filter.
  • an impedance-matching circuit can be electrically connected between the transmission filter and the reception filter.
  • the electroacoustic filter has a ladder- type like filter topology.
  • a ladder-type like filter topology one or more serial resonators are electrically connected in series in a signal path.
  • One or more shunt resonators is arranged in one or more shunt paths and
  • electroacoustic resonators can comprise the following steps:
  • the time difference t2-tl is half the period or an odd integer multiple of the period of the corresponding RF signal.
  • the slanting can be performed with an angle such that the aperture experienced by the acoustic waves is such that unwanted spurious modes but not wanted acoustic modes are suppressed or reduced in intensity.
  • the slanting causes an effective aperture that deviates from the width of the resonator in a direction orthogonal to the direction of the main mode.
  • the effective aperture generally an reduced effective aperture, can lead to interference effects within the resonator that is destructive for unwanted spurious modes.
  • Figure 1 shows a possible alignment of two resonators.
  • Figure 2 shows a configuration where the angle is obtained by a rotation.
  • Figure 3 shows a configuration where the angle is obtained by slanting one resonator.
  • Figure 4 shows a configuration where the alignment is obtained by slanting two resonators.
  • Figure 5 shows one possibility of obtaining a slanted
  • Figure 6 shows a possibility of obtaining a rotated
  • Figure 7 shows another possibility of obtaining a slanted resonator .
  • Figure 8 shows the principle of destructive interference.
  • Figure 10 illustrates the possibilities of arranging non parallel aligned BAW resonator structures one next to
  • Figure 11 shows a layout of resonators on a piezoelectric substrate .
  • Figure 12 shows a ladder-type like filter topology.
  • Figure 13 shows resonator arrangements allowing a higher package density.
  • Figure 1 shows a first resonator R1 and a second resonator R2 located close together.
  • the first resonator R1 has a first side SI.
  • the second resonator R2 also has a first side SI.
  • the first side SI of the first resonator R1 and the first side SI of the second resonator R2 are aligned to be non parallel .
  • Each position on each side of each electroacoustic resonator could, generally, be the source of unwanted acoustic wave emission.
  • the reception of such unwanted acoustic waves in another resonator leads to an acoustic interaction between the two resonators and a degradation of the acoustic and electric properties of the resonators and especially of the electric response of the corresponding filter.
  • received acoustic waves have
  • Figure 2 illustrates at least one possible way of providing angle a. At least one resonator is rotated by or both resonators are rotated such that an effective relative rotation angle is obtained.
  • Figure 3 illustrates another possibility of obtaining a non-parallel alignment of opposite sides of the first and second resonator without deviating the electrode fingers' alignment with respect to the preferred
  • each electrode finger maintains its direction of extension. However, each electrode finger is dislocated. The amount of dislocation depends on the longitudinal
  • bus bars can be slanted. However, it is possible to just rotate the bus bars.
  • Figure 5 illustrates the possibility of obtaining a slanted resonator structure by rotating the bus bars BB and just dislocating the electrode fingers EF.
  • Figure 6 illustrates the possibility of rotating the whole structures including rotating the bus bars BB and the electrode fingers EF.
  • Figure 7 illustrates an additional possibility:
  • the bus bars BB are rotated.
  • the electrode fingers are dislocated and slanted. This allows to maintain a constant distance between a distal end of the electrode finger EF and the opposing bus bar BB while the non-slanted electrode fingers EF have at their distal end positions which are closer to the other bus bar than other positions at the distal end of the electrode finger .
  • slanted resonators may be regarded as having a reduced aperture.
  • the width of the resonator in the direction of the extension of the electrode fingers can, thus, be chosen such that the effective aperture of the resonator equals the desired aperture of a non-slanted resonator .
  • Figure 8 illustrates the principle of destructive interference. In principle each position DPI, PI, P2, DP2 of a side of an active electroacoustic resonator can be the source of emitted acoustic waves. Acoustic waves, for
  • acoustic waves emitted at position PI of the first resonator Rl hit the second resonator R2 at a corresponding first position PI.
  • acoustic waves emitted from a second position P2 of the first resonator Rl hit the second resonator R2 at a second position P2. It is preferred that for every possible PI there is a position P2 such that the phase difference between the received acoustic waves at the side of the second resonator is an odd integer multiple of 180°. Then, acoustic waves completely interfere destructively and the effects of acoustic interaction would be prevented. However, even a partial destructive interference improves the acoustic response of the corresponding RF filter.
  • the high degree of destructive interference can be obtained if the phase difference obtained at first, closest distal points DPI is 180° more or less, the phase difference at respective second distal points DP2 at the respective other end of the resonator that has the high possible distance. Further, odd integer multiples of 180° are also possible.
  • FIG. 9 illustrates the possibility of having a non-parallel alignment of BAW resonator structures arranged one above the other.
  • Each structure has a first electrode ELI and a second electrode EL2.
  • the first electrode can be the bottom
  • electrode and the second electrode can be the top electrode.
  • FIG. 10 shows the possibility of providing two BAW resonator stacks one next to the other, e.g. on a common carrier substrate. The opposing sides are arranged non parallel .
  • Figure 11 shows an exemplary layout of resonators R on a piezoelectric substrate PSU. Arrows indicate sides of the resonators opposing corresponding sides of other resonators such that non-parallel alignments are obtained. Further, it is to be noted that on the piezoelectric substrate PSU further space is needed for providing electrical connections such as bump connections BC or electrical connections, e.g. signal lines between the resonators (omitted for improved clarity) .
  • Figure 12 shows a possible resonator configuration of an electroacoustic filter EAF:
  • SP resonators R are electrically connected in series. The two parallel paths shunt the signal path SP to ground. Each parallel branch has one further resonator R.
  • Such filter topologies can provide bandpass filters or band rejection filters.
  • the combination of two or more bandpass filters allows the creation of duplexers or multiplexers of a higher degree .
  • Figure 13 shows conventionally arranged resonators R that are aligned relative to each other such that a high package density can be obtained.
  • Electroacoustic filters can comprise further filter
  • circuit elements such as inductance elements, resistance elements and/or capacitance elements and matching circuits.
  • EAF electroacoustic filter

Abstract

An electroacoustic filter with reduced acoustic coupling is provided. The filter comprises two electroacoustic resonators (Rl, R2). Two opposing sides (SI) of the electroacoustic resonators are aligned non-parallel (angle alpha). It is preferred that the phase difference between the received acoustic waves at the side of the second resonator is an odd integer multiple of 180°. Then, acoustic waves completely interfere destructively and the effects of acoustic interaction would be prevented. However, even a partial destructive interference improves the acoustic response of the corresponding RF filter.

Description

Description
Electroacoustic filter with reduced acoustic coupling, method of reducing acoustic coupling and multiplexer
The present invention refers to the reduction of acoustic coupling between electroacoustic resonators that may be used in electroacoustic filters or multiplexers.
Electroacoustic filters, e.g. multiplexers, can be used in wireless communication systems. In electroacoustic filters, electroacoustic resonators are arranged in a filter topology. Electroacoustic resonators employ the piezoelectric effect to convert between RF signals and acoustic waves. Typical electroacoustic resonators are SAW resonators (SAW = surface acoustic wave) , BAW resonators (BAW = bulk acoustic wave) and GBAW resonators (GBAW = guided bulk acoustic wave) . In SAW resonators comb-shaped electrode structures with
interdigitating electrode fingers are arranged on a
piezoelectric material. Excited acoustic waves propagate at a surface of the piezoelectric material. In BAW resonators a piezoelectric material is sandwiched between a bottom
electrode and a top electrode. This sandwich construction can be arranged on a cavity or on an acoustic mirror.
Usually, the filter topology comprises two or more
electroacoustic resonators arranged in the vicinity of each other. However, desired acoustic wave modes and non-desired spurious acoustic wave modes may leave an electroacoustic resonator and enter into another electroacoustic resonator of the filter. Such an acoustic coupling between the resonators deteriorates the overall performance of the filter. In particular, interference between intrinsic acoustic wave modes of an electroacoustic resonator and received acoustic waves from another electroacoustic resonator deteriorates the performance of the electroacoustic resonator.
The ongoing trend towards miniaturization demands for smaller resonator structures, usually resulting in smaller distances between the resonators. However, smaller distances between resonators lead to an increased coupling between the
resonators .
Thus, what is wanted is an electroacoustic RF filter with reduced acoustic coupling between the filter's resonators.
To that end, an electroacoustic filter with reduced acoustic coupling, a method of reducing acoustic coupling and a multiplexer are provided according to the independent claims. The dependent claims provide preferred embodiments.
An electroacoustic filter with reduced acoustic coupling comprises a first electroacoustic resonator and a second electroacoustic resonator. The first electroacoustic
resonator has a first side. The second electroacoustic resonator has a second side. The first side of the first electroacoustic resonator and the first side of the second electroacoustic resonator are aligned non-parallel.
In such an electroacoustic filter the acoustic coupling between the resonators can be decreased, i.e. the acoustic decoupling between the resonators can be improved.
The term "side" of an electroacoustic resonator denotes the area of the resonator from which acoustic waves can be emitted. A non-parallel alignment of a side of the first electroacoustic resonator and of a side of the second
electroacoustic resonator allows a reduction of acoustic coupling although it contradicts the trend towards
miniaturization because it does not comply with the concept of a highest possible density of resonator structures of an electroacoustic filter.
If acoustic waves leave a first position of the first side of the first electroacoustic resonator and if second acoustic waves leave a second position of the first side of the first electroacoustic resonator then the first acoustic waves and the second acoustic waves can enter the second
electroacoustic resonator. In particular, one part of the first electroacoustic waves can hit a first position of the first side of the second electroacoustic resonator and a part of the second acoustic waves from the first electroacoustic resonator can enter the second electroacoustic resonator at a second position of the second electroacoustic resonator' s first side. By the non-parallel alignment of the
electroacoustic resonator's sides, the two received
electroacoustic waves can have a phase difference that allows a full or a partial destructive interference at the second electroacoustic resonator. Thus, interference of acoustic waves propagating from the first electroacoustic resonator to the second electroacoustic resonator can be used to decrease the acoustic effect of the first resonator on the second resonator. This is in contrast to a parallel alignment of respective sides of resonators where all partial waves would constructively interfere and cause a maximum effect on the second resonator's electric output signal.
It is possible that the first side of the first
electroacoustic resonator is arranged between the first electroacoustic resonator and the second electroacoustic resonator. The first side of the second electroacoustic resonator is arranged between the first electroacoustic resonator and the second electroacoustic resonator.
Thus, in other words, the mentioned sides of the
electroacoustic resonators are the sides of the resonators that point to each other. These sides have the closest distance between the resonators and their direction of propagation of acoustic waves usually lead to the highest degree of unwanted coupling that is reduced as described above .
It is possible that the space between the first
electroacoustic resonator and the second electroacoustic resonator is free from another electroacoustic resonator.
Thus, in other words, the above principle is applied to neighboring electroacoustic resonators with no further electroacoustic resonator in between.
It is possible that the angle between the first side of the first electroacoustic resonator and the first side of the second electroacoustic resonator is larger than or equal to 10° and smaller than or equal to 40°.
Although a higher value for the angle supports an
increasing amount of decoupling, a reduced angle simplifies the combination of resonator structures to obtain a compact package. Correspondingly, the above-mentioned angle interval provides a good trademark between decoupling and package size. In particular, it is possible that the angle is 15°, 20°, 25°, 30° or 35° . Of course, the electroacoustic filter can have further electroacoustic resonators and different angles with respect to the alignment of respective sides of different resonators are possible.
It is possible that the first electroacoustic resonator is selected from a SAW resonator, a TFSAW resonator (TFSAW = thin film SAW), a BAW resonator and a GBAW resonator. Also, the second electroacoustic resonator is selected from a SAW resonator, a TFSAW resonator, a BAW resonator and a GBAW resonator .
In the case of an electroacoustic resonator working with surface waves such as a SAW resonator, a GBAW resonator or a TFSAW resonator, the resonator can comprise two oppositely arranged bus bars and finger electrodes arranged and
electrically configured in an interdigitated pattern.
Further, a resonator working with surface waves can comprise reflector structures arranged at the distal ends of the acoustic track.
Resonators working with bulk acoustic waves can comprise an electroacoustic mirror arranged below the bottom electrode to confine acoustic energy to the resonator and to prevent energy dissipation. Also, it is possible that a cavity is arranged below the bottom electrode.
Resonators working with surface waves can be arranged on a common surface of the piezoelectric material, e.g. a
piezoelectric monocrystalline substrate. However, it is possible that the resonators are arranged on opposite sides of such a substrate and unwanted acoustic coupling between the resonators takes place via a conversion to bulk waves propagating through the substrate.
Resonators working with bulk waves can be arranged on a common carrier substrate. An electrically conducting or a dielectric material can be arranged between the stacked structures of the individual resonators. However, it is also possible that resonator structures of bulk acoustic wave resonators are arranged one above the other.
It is possible that the electroacoustic filter further comprises one or more additional resonator. Each additional resonator has a side. The side can emit acoustic waves. Two or more neighbored sides of neighbored resonators are aligned non-parallel .
In a preferred embodiment as many as possible opposing sides of different resonators are arranged non-parallel. In
particular, it is preferred that the arrangement of every side of every resonator with respect to sides of other resonators are arranged non-parallel
It is possible that the first electroacoustic resonator and/or the second electroacoustic resonator is a SAW
resonator, a TFSAW resonator or a GBAW resonator and
comprises slanted electrode fingers.
It is possible that the first side of the first
electroacoustic resonator is flat. Further, it is possible that the first side of the second electroacoustic resonator is flat. Resonators with flat sides simplify the process of finding an appropriate angle according to which the sides are aligned. The angle can be chosen such that a smallest distance between the opposite sides of the two resonators and a corresponding maximum distance of opposing positions of the sides are mainly equal to l/2 or an integer multiple of l/2 where l is the wavelength of the acoustic waves propagating in one of the resonators.
Such an angle usually provides the highest degree of destructive interference resulting in a maximum effectiveness of acoustically decoupling the resonators.
It is to be noted that electroacoustic resonators have electrode structures with a preferred alignment with respect to the piezoelectric axis of the piezoelectric material. The piezoelectric axis of the piezoelectric material is the direction in which deformations of the piezoelectric material cause the highest degree of piezoelectric effect.
Consequently, it should be avoided to arbitrarily rotate resonator structures to acoustically decouple the structures from the structures of other resonators. Instead, it must be considered that a certain degree of piezoelectric coupling must be maintained.
Correspondingly, it is preferred if the alignment of the sides of the resonators are chosen such that the
piezoelectric effect can be maintained at a high level. This can be obtained by maintaining the electrodes' alignment with respect to the piezoelectric axis. In particular, it is possible to maintain a perpendicular alignment between the direction of extension of the electrode and the piezoelectric axis .
One way of obtaining good values for and a high degree of coupling is the use of slanted resonators and/or the use of slanted electrode fingers within a resonator. A slanted resonator is a resonator with the shape of a parallelogram - at least in a horizontal or vertical cross-section of the resonator .
Thus, it is preferred that the footprint of an
electroacoustic resonator according to the above cited has the shape of a parallelogram. This is valid for resonators working with bulk waves and for resonators working with surface waves. In particular, resonators working with bulk waves can have the shape of a prism with a parallelogram as its base area.
The same holds true for the shape of the electrode fingers in the case of resonators working with surface waves: the electrode fingers can have the footprint of a parallelogram.
Further, it is possible to use one or more of such
electroacoustic filters in a multiplexer. A multiplexer, e.g. a duplexer, a triplexer or a multiplexer of a higher degree, is used for separating RF signals of different frequency ranges into separate signal paths or to combine RF signals of different frequency ranges obtained from different signal paths in one or more common signal paths.
Correspondingly, a multiplexer comprises an electroacoustic filter as described above as a first and/or as a second filter . In the case off a duplexer one filter is a transmission filter while the other filter is a reception filter. Further, an impedance-matching circuit can be electrically connected between the transmission filter and the reception filter.
It is possible that the electroacoustic filter has a ladder- type like filter topology. In a ladder-type like filter topology one or more serial resonators are electrically connected in series in a signal path. One or more shunt resonators is arranged in one or more shunt paths and
electrically connect the signal path to ground.
A method for reducing acoustic coupling between
electroacoustic resonators can comprise the following steps:
- emitting a first acoustic wave from a first position of a side of a first electroacoustic resonator,
- emitting a second acoustic wave from a second position of the side of the first electroacoustic resonator,
- receiving the first acoustic wave at a first position of a side of a second electroacoustic resonator at a first time tl
- receiving the second acoustic wave at a second position of the side of the second electroacoustic resonator at a second time t2 different from tl .
In particular, it is preferred that the time difference t2-tl is half the period or an odd integer multiple of the period of the corresponding RF signal.
Basic principles and details of preferred embodiments are described in the accompanying schematic figures. It is possible that the rotation or slanting (especially the slanting) of one or more resonators also improves the
reduction of unwanted spurious modes. The rotation or
slanting can be performed with an angle such that the aperture experienced by the acoustic waves is such that unwanted spurious modes but not wanted acoustic modes are suppressed or reduced in intensity. In particular, the slanting causes an effective aperture that deviates from the width of the resonator in a direction orthogonal to the direction of the main mode. The effective aperture, generally an reduced effective aperture, can lead to interference effects within the resonator that is destructive for unwanted spurious modes.
In the figures:
Figure 1 shows a possible alignment of two resonators.
Figure 2 shows a configuration where the angle is obtained by a rotation.
Figure 3 shows a configuration where the angle is obtained by slanting one resonator.
Figure 4 shows a configuration where the alignment is obtained by slanting two resonators.
Figure 5 shows one possibility of obtaining a slanted
resonator .
Figure 6 shows a possibility of obtaining a rotated
resonator . Figure 7 shows another possibility of obtaining a slanted resonator .
Figure 8 shows the principle of destructive interference.
Figure 9 illustrates a possible non-alignment of BAW
resonator elements arranged one above another.
Figure 10 illustrates the possibilities of arranging non parallel aligned BAW resonator structures one next to
another .
Figure 11 shows a layout of resonators on a piezoelectric substrate .
Figure 12 shows a ladder-type like filter topology.
Figure 13 shows resonator arrangements allowing a higher package density.
Figure 1 shows a first resonator R1 and a second resonator R2 located close together. The first resonator R1 has a first side SI. The second resonator R2 also has a first side SI.
The first side SI of the first resonator R1 and the first side SI of the second resonator R2 are aligned to be non parallel .
Each position on each side of each electroacoustic resonator could, generally, be the source of unwanted acoustic wave emission. The reception of such unwanted acoustic waves in another resonator leads to an acoustic interaction between the two resonators and a degradation of the acoustic and electric properties of the resonators and especially of the electric response of the corresponding filter. By providing a non-zero angle with respect to the alignments of opposing sides of the resonators, received acoustic waves have
different phases with respect to each other and allow the possibility of destructive interference. Thus, the effects of acoustic coupling are reduced and a deterioration of the filter performance is reduced.
However, providing non-zero angles with respect to the alignment of sides of the resonators deteriorates the
possibilities of stacking the resonators close together which results in a lower possible package density and
correspondingly higher area consumptions, a higher need for piezoelectric material, higher weight and higher production costs .
Figure 2 illustrates at least one possible way of providing angle a. At least one resonator is rotated by or both resonators are rotated such that an effective relative rotation angle is obtained.
However, such a rotation is generally unwanted because the rotation causes a misalignment of the electrode structures with respect to the piezoelectric axis and the coupling factor would be deteriorated.
Consequently, Figure 3 illustrates another possibility of obtaining a non-parallel alignment of opposite sides of the first and second resonator without deviating the electrode fingers' alignment with respect to the preferred
piezoelectric axis. The non-parallel alignment is obtained by slanting at least one resonator (in this example the first resonator Rl) . Each electrode finger maintains its direction of extension. However, each electrode finger is dislocated. The amount of dislocation depends on the longitudinal
position within the acoustic track. Also, the bus bars can be slanted. However, it is possible to just rotate the bus bars.
Figure 4 illustrates the possibility of slanting both
resonators with respect to the preferred orientation of the extension of the electrode fingers such that effective angle is obtained.
Figure 5 illustrates the possibility of obtaining a slanted resonator structure by rotating the bus bars BB and just dislocating the electrode fingers EF.
In contrast, Figure 6 illustrates the possibility of rotating the whole structures including rotating the bus bars BB and the electrode fingers EF.
Figure 7 illustrates an additional possibility: The bus bars BB are rotated. The electrode fingers are dislocated and slanted. This allows to maintain a constant distance between a distal end of the electrode finger EF and the opposing bus bar BB while the non-slanted electrode fingers EF have at their distal end positions which are closer to the other bus bar than other positions at the distal end of the electrode finger .
It is to be noted that slanted resonators may be regarded as having a reduced aperture. The width of the resonator in the direction of the extension of the electrode fingers can, thus, be chosen such that the effective aperture of the resonator equals the desired aperture of a non-slanted resonator . Figure 8 illustrates the principle of destructive interference. In principle each position DPI, PI, P2, DP2 of a side of an active electroacoustic resonator can be the source of emitted acoustic waves. Acoustic waves, for
example, emitted at position PI of the first resonator Rl, hit the second resonator R2 at a corresponding first position PI. Further, acoustic waves emitted from a second position P2 of the first resonator Rl hit the second resonator R2 at a second position P2. It is preferred that for every possible PI there is a position P2 such that the phase difference between the received acoustic waves at the side of the second resonator is an odd integer multiple of 180°. Then, acoustic waves completely interfere destructively and the effects of acoustic interaction would be prevented. However, even a partial destructive interference improves the acoustic response of the corresponding RF filter.
The high degree of destructive interference can be obtained if the phase difference obtained at first, closest distal points DPI is 180° more or less, the phase difference at respective second distal points DP2 at the respective other end of the resonator that has the high possible distance. Further, odd integer multiples of 180° are also possible.
Figure 9 illustrates the possibility of having a non-parallel alignment of BAW resonator structures arranged one above the other. Each structure has a first electrode ELI and a second electrode EL2. The first electrode can be the bottom
electrode and the second electrode can be the top electrode.
A piezoelectric material PM is sandwiched between the two electrodes . Similarly, Figure 10 shows the possibility of providing two BAW resonator stacks one next to the other, e.g. on a common carrier substrate. The opposing sides are arranged non parallel .
Figure 11 shows an exemplary layout of resonators R on a piezoelectric substrate PSU. Arrows indicate sides of the resonators opposing corresponding sides of other resonators such that non-parallel alignments are obtained. Further, it is to be noted that on the piezoelectric substrate PSU further space is needed for providing electrical connections such as bump connections BC or electrical connections, e.g. signal lines between the resonators (omitted for improved clarity) .
The disadvantage of such an arrangement and alignment of resonators is obviously clear: the area consumption is strongly increased compared to parallel arrangements as shown in Figure 13.
Figure 12 shows a possible resonator configuration of an electroacoustic filter EAF: In a signal path SP resonators R are electrically connected in series. The two parallel paths shunt the signal path SP to ground. Each parallel branch has one further resonator R.
Depending on the selection of resonance and anti-resonance frequencies of series and parallel resonators, such filter topologies can provide bandpass filters or band rejection filters. The combination of two or more bandpass filters allows the creation of duplexers or multiplexers of a higher degree . In contrast to the arrangement shown in Figure 11, Figure 13 shows conventionally arranged resonators R that are aligned relative to each other such that a high package density can be obtained.
The electroacoustic filter, the multiplexer and the method for reducing acoustic coupling are not limited to the technical features shown in the figures and explained above. Electroacoustic filters can comprise further filter
structures such as further resonators, further circuit elements such as inductance elements, resistance elements and/or capacitance elements and matching circuits.
List of Reference Signs : angle between opposing sides of neighbored resonators
BB: bus bar
BC: bump connection
DPI, DP2 : first, second distal position
EAF: electroacoustic filter
EF: electrode finger
ELI: first, bottom electrode
EL2 : second, top electrode
PI, P2 : first, second position
PM: piezoelectric material
PSU : piezoelectric substrate
Rl, R2 , R: electroacoustic resonator
SI : first side
SP: signal path

Claims

Claims
1. An electroacoustic filter (EAF) with reduced acoustic coupling, comprising
- a first electroacoustic resonator (Rl) having a first side (SI) ,
- a second electroacoustic resonator (R2) having a first side (SI) ,
wherein
- the first side (SI) of the first electroacoustic resonator (Rl) and the first side (SI) of the second electroacoustic resonator (R2) are aligned non-parallel.
2. The electroacoustic filter of the previous claim, wherein
- the first side (SI) of the first electroacoustic resonator (Rl) is arranged between the first electroacoustic resonator (Rl) and the second electroacouStic resonator (R2) and
- the first side (SI) of the second electroacoustic resonator (R2) is arranged between the first electroacoustic resonator (Rl) and the second electroacouStic resonator (R2).
3. The electroacoustic filter of one of the previous claims, wherein the space between the first electroacoustic resonator (Rl) and the second electroacoustic resonator (R2) is free from another electroacoustic resonator.
4. The electroacoustic filter of one of the previous claims, wherein the angle between the first side (SI) of the first electroacoustic resonator (Rl) and the first side (SI) of the second electroacoustic resonator (R2) is 10° < £ 40°.
5. The electroacoustic filter of one of the previous claims, wherein the first electroacoustic resonator (Rl) and the second electroacoustic resonator (R2) are selected from a SAW resonator, a TFSAW resonator, a BAW resonator, a GBAW
resonator .
6. The electroacoustic filter of one of the previous claims, further comprising one or more additional resonators (R) , each additional resonator (R) having a side, wherein two or more neighbored sides of neighbored resonators (R) are aligned non-parallel.
7. The electroacoustic filter of one of the previous claims, wherein the first electroacoustic resonator (Rl) and/or the second electroacoustic resonator (R2) is a SAW resonator, a TFSAW resonator or a GBAW resonator and comprises slanted electrode fingers (EF) .
8. The electroacoustic filter of one of the previous claims, wherein the first side (SI) of the first electroacoustic resonator (Rl) is flat and the first side of the second electroacoustic resonator (R2) is flat.
9. A multiplexer comprising an electroacoustic filter (EAF) of one of the previous claims as a first and/or as a second filter .
10. A method for reducing acoustic coupling between
electroacoustic resonators (Rl, R2), comprising the steps:
- emitting a first acoustic wave from a first position (PI) of a side (SI) of a first electroacoustic resonator (Rl),
- emitting a second acoustic wave from a second position (P2) of the side (SI) of the first electroacoustic resonator (Rl), - receiving the first acoustic wave at a first position (PI) of a side (SI) of a second electroacoustic resonator (R2) at a first time tl,
- receiving the second acoustic wave at
Figure imgf000021_0001
second position (P2) of the side (SI) of the second electroacoustic resonator
(R2) at a second time t2 <> tl.
PCT/EP2018/075524 2017-11-23 2018-09-20 Electroacoustic filter with reduced acoustic coupling, method of reducing acoustic coupling and multiplexer WO2019101391A1 (en)

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Citations (6)

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EP2264891A1 (en) * 2008-04-11 2010-12-22 Nihon Dempa Kogyo Co., Ltd. Duplexer
US20130099875A1 (en) * 2011-04-12 2013-04-25 Hidehito Shimizu Acoustic wave device and antenna duplexer employing the same
US20160261038A1 (en) * 2013-10-31 2016-09-08 Kyocera Corporation Acoustic wave element, filter element, and communication device
US20160294361A1 (en) * 2013-12-26 2016-10-06 Murata Manufacturing Co., Ltd. Elastic wave device and filter device

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Publication number Priority date Publication date Assignee Title
US4193045A (en) * 1977-05-25 1980-03-11 Nippon Telegraph And Telephone Public Corporation Temperature compensated surface acoustic wave oscillators
US20090224852A1 (en) * 2005-07-13 2009-09-10 Murata Manufacturing Co., Ltd. Acoustic wave filter device
EP2264891A1 (en) * 2008-04-11 2010-12-22 Nihon Dempa Kogyo Co., Ltd. Duplexer
US20130099875A1 (en) * 2011-04-12 2013-04-25 Hidehito Shimizu Acoustic wave device and antenna duplexer employing the same
US20160261038A1 (en) * 2013-10-31 2016-09-08 Kyocera Corporation Acoustic wave element, filter element, and communication device
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