WO2020069794A1 - Saw device designed for high frequencies - Google Patents

Saw device designed for high frequencies

Info

Publication number
WO2020069794A1
WO2020069794A1 PCT/EP2019/071850 EP2019071850W WO2020069794A1 WO 2020069794 A1 WO2020069794 A1 WO 2020069794A1 EP 2019071850 W EP2019071850 W EP 2019071850W WO 2020069794 A1 WO2020069794 A1 WO 2020069794A1
Authority
WO
WIPO (PCT)
Prior art keywords
mode
filter
resonators
resonance frequency
plate mode
Prior art date
Application number
PCT/EP2019/071850
Other languages
French (fr)
Inventor
Gholamreza Dadgar Javid
Original Assignee
RF360 Europe GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by RF360 Europe GmbH filed Critical RF360 Europe GmbH
Publication of WO2020069794A1 publication Critical patent/WO2020069794A1/en

Links

Classifications

    • 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
    • H03H9/02—Details
    • H03H9/02535—Details of surface acoustic wave devices
    • H03H9/02543—Characteristics of substrate, e.g. cutting angles
    • H03H9/02559—Characteristics of substrate, e.g. cutting angles of lithium niobate or lithium-tantalate substrates
    • 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
    • H03H9/6406—Filters characterised by a particular frequency characteristic
    • H03H9/6409—SAW notch 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
    • H03H9/46—Filters
    • H03H9/64—Filters using surface acoustic waves
    • H03H9/6423—Means for obtaining a particular transfer characteristic
    • H03H9/6426—Combinations of the characteristics of different 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
    • H03H9/46—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
    • H03H9/46—Filters
    • H03H9/64—Filters using surface acoustic waves
    • H03H9/6489—Compensation of undesirable effects
    • H03H9/6493—Side lobe suppression
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H2250/00—Indexing scheme relating to dual- or multi-band 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
    • H03H9/02535—Details of surface acoustic wave devices
    • H03H9/02818—Means for compensation or elimination of undesirable effects
    • H03H9/02834—Means for compensation or elimination of undesirable effects of temperature influence

Definitions

  • a typical maximum frequency is around 3-4 GHz.
  • Up to now higher frequencies can only be operated with devices other than SAW that is with BAW devices. With SAW devices it is not possible to build up pass band at frequencies that substantially exceed a limit around 5 GHz
  • the general idea is to use a higher mode like the plate mode PM of a SAW resonator to build a passband/rej ect-band filter, functioning at higher frequencies, which may not be
  • the passband range of a typical SAW filters is dominantly dependent on the pitch or finger distance of its built-in IDT's and hence is bounded at the higher frequency side due to photo-lithography limitations on fabrication of such
  • IDT's typically around 4-5 GHz.
  • resonators using certain layer stacks containing metal, SiCy and SiN on LiNbCy Substrates possess, beside the main mode, also a second mode, called z-mode or plate-mode.
  • the resonance frequency and the amplitude of the PM depends on geometric parameters of the resonator like pitch and metallization ratio as well as on the heights of single layers in the stack. In particular, the resonance frequency of the PM is mostly much higher than that of MM, typically around 20-30% above the main mode.
  • the amplitude of PM mainly depends on the height of SiCy and SiN layer. Depending on the underlying substrate and layer stack, the resonance frequency of PM may have even a higher Q factor than that of MM.
  • filters utilizing the plate mode PM of a resonator are expected to have a higher power-durability, since PM is mainly located within the dielectric layer above the IDT. Hence, wave energy does not affect the IDT as much as the main mode that propagates mainly within the piezo layer and directly in the plane of the IDT.
  • the new SAW device has a layer stack comprising a substrate with a piezoelectric layer on top or consists of a
  • An interdigital transducer - IDT - is arranged on top of the substrate and a SiCy layer covers the surface of the IDT and the connecting pads.
  • the height of the SiCy layer and optionally the height of further layers that are part of the stack like the above mentioned SiN layer is/are set to a value that facilitates exciting of a
  • the SAW device is construed to make use of the resonance frequency of the plate mode for filtering purpose.
  • the substrate may be a monocrystalline piezoelectric chip of a suitable cut angle.
  • the substrate may comprise a carrier and a thin film of a piezoelectric applied on the carrier.
  • An SiCy layer is often used for compensating the temperature drift of frequency or the TCF.
  • TCF compensated SAW filter are usually formed on a LiNbCy substrate - LN - due to the better coupling of this piezo material.
  • a SAW device formed on a LN material with a cut angle of e.g. ROT 128 a plate mode is excited and can propagate.
  • any or all dielectric layers that are present in the layer stack can be varied to shift the frequencies of main mode MM, plate mode PM and the relative signal amplitudes thereof.
  • design variations it is possible to make the plate mode become a dominant mode. Any stages between excitation of only a main mode, a main mode and a plate mode at the same time and only plate mode are possible and be set dependent on the desired use of plate mode and/or main mode.
  • the resonance frequency of the plate mode is used for forming a pass band of a filter.
  • the SAW device comprises at least one resonator that is designed such that the plate mode has substantial amount, is dominating or is even the mode that can mainly propagate in the layer stack.
  • the SAW device is construed as a ladder type filter comprising resonators that are designed to allow excitation of main mode and plate mode at the same time.
  • the resonance frequencies of both existing modes that is plate mode and main mode are used for forming a dual pass band filter.
  • Such a band pass filter works optimally if the amplitudes of both modes are set to be comparable or equal. Shifting one or both resonance frequencies of the two modes as mentioned above can provide a SAW filter with two pass bands of a wide range of possible distances in frequencies.
  • the new SAW device is not restricted to band pass filter but can also be embodied as a band reject filter.
  • a filter can be construed as a ladder type filter comprising series and or parallel resonators that are designed to allow
  • the resonance frequencies of plate mode and main mode are used for forming a dual reject band filter.
  • the SAW device is a ladder type filter construed out of SAW resonators comprising series and parallel resonators. At least one of the resonators is designed to allow excitation of the plate mode. While the resonance frequency of the main mode is used for forming the pass band of the filter the resonance frequency of the plate mode is used for improving the selectivity of the filter. Setting the main mode at the pass band frequency and shifting the resonance of the plate mode of at least one parallel resonator that enables exciting a plate mode to a frequency where additional attenuation is required results in a filter with improved selectivity above the passband.
  • the selectivity below the pass band may be improved.
  • the SAW device is a ladder type filter construed out of SAW resonators comprising series and parallel resonators. At least one of the series resonators is designed to allow excitation of the plate mode the resonance frequency of the plate mode is used for forming the pass band. At the same time the resonance frequency of the main mode is used for improving the selectivity of the filter at the resonance frequency of the main mode that is usually below the pass band frequencies.
  • the SAW filter may be construed as a band reject filter.
  • SAW resonators are arranged in a ladder type arrangement of series and parallel resonators thereby
  • a resonator showing a main mode and a plate mode as well.
  • the resonance frequency of the plate mode of this resonator is used to create a notch by circuiting the resonator as a parallel resonator in in a common ladder type filter circuit.
  • the resonance frequency of the plate mode can be set just at or near a frequency where a higher suppression of a parasitic signal is required.
  • the main advantage that can be achieved with most of the embodiments is that the resonance frequency of the plate mode is much higher than that of the main mode.
  • the plate mode excited with this minimal pitch lies at a frequency well above the main mode that is usually excited in such a filter.
  • Such high operating frequencies have up to now not been achieved with known filters.
  • the proposed SAW resonator can hence be used for construing a pass band filter or a band reject filter with a passband/rej ect band frequency higher than a maximum frequency up to now achieved with a SAW device.
  • the maximum frequency is the resonance frequency of a resonator using its main mode which is optimized for the highest possible frequency that can be safely reproduced with a given structuring method.
  • the plate mode producing SAW device can be used not only for construing complete filters but can only be used to improve the selectivity of any other filter circuit.
  • a SAW resonator with a substantial amount of plate mode can be used in a circuit comprising a DMS filter as a main filter component.
  • the plate mode of the resonator is used to improve the selectivity of the DMS filter at a frequency above the pass band.
  • Figures 1A to 1C show the admittance of a SAW resonator comprising a layer stack depicted threefold as real part, imaginary part and magnitude wherein the height of a layer of the layer stack is varied.
  • Figures 2A to 2C show the P-matrix elements S21, Sll and S22 and respective Smith charts of a SAW filter with two
  • Figures 3A to 3C show the P-matrix elements S21, Sll and S22 and respective Smith charts of a SAW band reject filter with two comparable reject-bands.
  • Figures 4A to 4C show the P-matrix elements S21, Sll and S22 and respective Smith charts of a SAW passband with improved selectivity below the passband.
  • Figures 1A to 1C show the admittance of a SAW resonator with a similar layer structure comprising a layer stack with a piezo layer, an IDT, a SiCy layer and a SiN layer as trimming and/or passivation layer depicted threefold as real part, imaginary part and magnitude wherein the height of a layer of the layer stack is varied.
  • the real part of the admittance of this resonator is
  • Figures IB and 1C show respective imaginary part and magnitude thereof.
  • Each diagram shows three curves a to c that are measured with a different height of the Si02 layer. The height is varied between 460 and 520 nm.
  • the figures clearly show that signal amplitude and frequency of the plate mode can be set by suitably setting the height of the Si02 layer.
  • For each curve a to c two admittance maxima are present.
  • the peak on the low frequency side at about 2700 MHz is assigned to the respective main mode while the plate mode arises at frequencies between about 3200 and 3400MHz.
  • FIGS 2A to 2C show the P-matrix elements S21, Sll and S22 and respective Smith charts of a SAW bandpass filter showing two comparable passbands.
  • the filter is construed in a common manner as a ladder type arrangement of series and parallel SAW resonators.
  • the used resonators are configured according to the proposed idea and show two comparable signal amplitudes that are assigned to a main mode and a plate mode. Accordingly the resulting ladder type filter shows two passbands of nearly the same amplitude.
  • Such dual passband filters can be used as duplexer or multiplexer having a much simpler topology as no separate resonators for Tx and Rx are required .
  • Figures 3A to 3C show the P-matrix elements S21, Sll and S22 and respective Smith charts of a SAW band reject filter showing two comparable reject bands.
  • the filter is construed in a common manner as a ladder type arrangement of series and parallel SAW resonators.
  • the used resonators are configured according to the proposed idea and respectively show two comparable signal amplitudes that are assigned to a main mode and a plate mode.
  • filters utilizing PM are expected to have a higher power-durability, since PM is mainly located within the dielectric layer above the IDT.
  • the PM can also be combined with the main-mode simultaneously, to create a dual passband filter or a dual notch-filter, or to improve the selectivity on the right or left side of the passband/rej ect-band of a filter .
  • Figures 4A to 4C show the P-matrix elements S21, Sll and S22 and respective Smith charts of a SAW bandpass filter with improved selectivity below the passband.
  • the plate mode of the SAW resonators is used to form the passband.
  • the main mode of some resonators is used to further improve the lower stop band by using the resonance frequency of the respective main mode of some resonators that are mainly circuited as parallel resonators in respective shunt arms of the ladder type filter circuit.
  • the main mode of a DMS filter's resonators can be used for creating the passband and the plate mode of the resonators for improving the selectivity.
  • matching elements such as inductors and capacitors can be connected to the resonators (in series or parallel) to shift the resonance or anti-resonance of the main mode to set it to the desired frequencies.
  • the invention has been shown by reference of a limited number of embodiments but is not restricted to specific features of any embodiment. Additionally the invention can generally be applied to BAW filters as well. The embodiments are only illustrative and the scope of the invention is only defined by the claims.

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  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)

Abstract

It is proposed to use a higher mode like the plate mode PM of a SAW resonator to build a bandpass/reject-band filter, functioning at higher frequencies, which may not be realizable with SAW devices that are using only the main mode MM of the resonator. The SAW device may be a ladder type filter constructed out of SAW resonators comprising series and parallel resonators wherein at least one of the resonators is designed to allow excitation of the plate mode wherein the resonance frequency of the main mode is used for forming the pass band and wherein the resonance frequency of the plate mode is used for improving the selectivity of the filter at the resonance frequency of the plate mode.

Description

Description
SAW device designed for high frequencies
The passband frequency of a typical SAW filters is primarily dependent on the pitch (finger-finger distance) of its built- in IDT's (IDT = interdigital transducer) and hence is limited to not exceed a maximum frequency due to photo-lithography limitations while fabricating such IDT's. A typical maximum frequency is around 3-4 GHz. Up to now higher frequencies can only be operated with devices other than SAW that is with BAW devices. With SAW devices it is not possible to build up pass band at frequencies that substantially exceed a limit around 5 GHz
It is hence an object to provide a SAW device that is not bound to this upper frequency limit and can operate at higher frequencies .
This and other objects are met by a SAW device according to claim 1. Specific further features of the new SAW device as well as advantageous embodiments can be taken from the dependent claims.
The general idea is to use a higher mode like the plate mode PM of a SAW resonator to build a passband/rej ect-band filter, functioning at higher frequencies, which may not be
realizable with SAW devices that are using only the main mode MM of the resonator.
The passband range of a typical SAW filters is dominantly dependent on the pitch or finger distance of its built-in IDT's and hence is bounded at the higher frequency side due to photo-lithography limitations on fabrication of such
IDT's, typically around 4-5 GHz.
However, resonators using certain layer stacks containing metal, SiCy and SiN on LiNbCy Substrates possess, beside the main mode, also a second mode, called z-mode or plate-mode. The resonance frequency and the amplitude of the PM depends on geometric parameters of the resonator like pitch and metallization ratio as well as on the heights of single layers in the stack. In particular, the resonance frequency of the PM is mostly much higher than that of MM, typically around 20-30% above the main mode. The amplitude of PM mainly depends on the height of SiCy and SiN layer. Depending on the underlying substrate and layer stack, the resonance frequency of PM may have even a higher Q factor than that of MM.
On the other hand, filters utilizing the plate mode PM of a resonator are expected to have a higher power-durability, since PM is mainly located within the dielectric layer above the IDT. Hence, wave energy does not affect the IDT as much as the main mode that propagates mainly within the piezo layer and directly in the plane of the IDT.
The new SAW device has a layer stack comprising a substrate with a piezoelectric layer on top or consists of a
piezoelectric bulk material. An interdigital transducer - IDT - is arranged on top of the substrate and a SiCy layer covers the surface of the IDT and the connecting pads. The height of the SiCy layer and optionally the height of further layers that are part of the stack like the above mentioned SiN layer is/are set to a value that facilitates exciting of a
substantial amount of a respective plate mode that can propagate in the layer stack system. The SAW device is construed to make use of the resonance frequency of the plate mode for filtering purpose.
The substrate may be a monocrystalline piezoelectric chip of a suitable cut angle. Alternatively, the substrate may comprise a carrier and a thin film of a piezoelectric applied on the carrier.
An SiCy layer is often used for compensating the temperature drift of frequency or the TCF. Such TCF compensated SAW filter are usually formed on a LiNbCy substrate - LN - due to the better coupling of this piezo material. In a SAW device formed on a LN material with a cut angle of e.g. ROT 128 a plate mode is excited and can propagate.
Starting from a given SAW device on such a piezo material design parameter like metallization ratio, pitch, and heights of any or all dielectric layers that are present in the layer stack can be varied to shift the frequencies of main mode MM, plate mode PM and the relative signal amplitudes thereof. By doing such design variations it is possible to make the plate mode become a dominant mode. Any stages between excitation of only a main mode, a main mode and a plate mode at the same time and only plate mode are possible and be set dependent on the desired use of plate mode and/or main mode.
According to an embodiment of the SAW device the resonance frequency of the plate mode is used for forming a pass band of a filter. Hence, the SAW device comprises at least one resonator that is designed such that the plate mode has substantial amount, is dominating or is even the mode that can mainly propagate in the layer stack. In another embodiment the SAW device is construed as a ladder type filter comprising resonators that are designed to allow excitation of main mode and plate mode at the same time. The resonance frequencies of both existing modes that is plate mode and main mode are used for forming a dual pass band filter. Such a band pass filter works optimally if the amplitudes of both modes are set to be comparable or equal. Shifting one or both resonance frequencies of the two modes as mentioned above can provide a SAW filter with two pass bands of a wide range of possible distances in frequencies.
The new SAW device is not restricted to band pass filter but can also be embodied as a band reject filter. Such a filter can be construed as a ladder type filter comprising series and or parallel resonators that are designed to allow
excitation of a main mode and a plate mode at the same time. In this embodiment the resonance frequencies of plate mode and main mode are used for forming a dual reject band filter.
But even if the plate mode is not the dominant mode of a filter nevertheless it can be used along with the main mode. According to an embodiment the SAW device is a ladder type filter construed out of SAW resonators comprising series and parallel resonators. At least one of the resonators is designed to allow excitation of the plate mode. While the resonance frequency of the main mode is used for forming the pass band of the filter the resonance frequency of the plate mode is used for improving the selectivity of the filter. Setting the main mode at the pass band frequency and shifting the resonance of the plate mode of at least one parallel resonator that enables exciting a plate mode to a frequency where additional attenuation is required results in a filter with improved selectivity above the passband. Alternatively the selectivity below the pass band may be improved. According to an embodiment the SAW device is a ladder type filter construed out of SAW resonators comprising series and parallel resonators. At least one of the series resonators is designed to allow excitation of the plate mode the resonance frequency of the plate mode is used for forming the pass band. At the same time the resonance frequency of the main mode is used for improving the selectivity of the filter at the resonance frequency of the main mode that is usually below the pass band frequencies.
The SAW filter may be construed as a band reject filter. In such a filter SAW resonators are arranged in a ladder type arrangement of series and parallel resonators thereby
respecting a suitable resonance frequency position of series and parallel resonators.
Further it is possible use a resonator showing a main mode and a plate mode as well. The resonance frequency of the plate mode of this resonator is used to create a notch by circuiting the resonator as a parallel resonator in in a common ladder type filter circuit. By suitably shifting the resonance frequency of the plate mode the plate mode can be set just at or near a frequency where a higher suppression of a parasitic signal is required.
The main advantage that can be achieved with most of the embodiments is that the resonance frequency of the plate mode is much higher than that of the main mode. When a SAW device is construed with an IDT of minimum pitch that is a pitch that can still safely reproduced in a manufacturing process, the plate mode excited with this minimal pitch lies at a frequency well above the main mode that is usually excited in such a filter. Such high operating frequencies have up to now not been achieved with known filters. The proposed SAW resonator can hence be used for construing a pass band filter or a band reject filter with a passband/rej ect band frequency higher than a maximum frequency up to now achieved with a SAW device. The maximum frequency is the resonance frequency of a resonator using its main mode which is optimized for the highest possible frequency that can be safely reproduced with a given structuring method.
According to a further embodiment the plate mode producing SAW device can be used not only for construing complete filters but can only be used to improve the selectivity of any other filter circuit. Hence, a SAW resonator with a substantial amount of plate mode can be used in a circuit comprising a DMS filter as a main filter component. The plate mode of the resonator is used to improve the selectivity of the DMS filter at a frequency above the pass band.
In the following the invention will be explained in more detail with respect to embodiment and the accompanied
figures .
Figures 1A to 1C show the admittance of a SAW resonator comprising a layer stack depicted threefold as real part, imaginary part and magnitude wherein the height of a layer of the layer stack is varied.
Figures 2A to 2C show the P-matrix elements S21, Sll and S22 and respective Smith charts of a SAW filter with two
comparable passbands. Figures 3A to 3C show the P-matrix elements S21, Sll and S22 and respective Smith charts of a SAW band reject filter with two comparable reject-bands.
Figures 4A to 4C show the P-matrix elements S21, Sll and S22 and respective Smith charts of a SAW passband with improved selectivity below the passband.
Figures 1A to 1C show the admittance of a SAW resonator with a similar layer structure comprising a layer stack with a piezo layer, an IDT, a SiCy layer and a SiN layer as trimming and/or passivation layer depicted threefold as real part, imaginary part and magnitude wherein the height of a layer of the layer stack is varied. In the upper part - Figure 1A - the real part of the admittance of this resonator is
depicted. Figures IB and 1C show respective imaginary part and magnitude thereof. Each diagram shows three curves a to c that are measured with a different height of the Si02 layer. The height is varied between 460 and 520 nm. The figures clearly show that signal amplitude and frequency of the plate mode can be set by suitably setting the height of the Si02 layer. For each curve a to c two admittance maxima are present. The peak on the low frequency side at about 2700 MHz is assigned to the respective main mode while the plate mode arises at frequencies between about 3200 and 3400MHz.
Figures 2A to 2C show the P-matrix elements S21, Sll and S22 and respective Smith charts of a SAW bandpass filter showing two comparable passbands. The filter is construed in a common manner as a ladder type arrangement of series and parallel SAW resonators. However, the used resonators are configured according to the proposed idea and show two comparable signal amplitudes that are assigned to a main mode and a plate mode. Accordingly the resulting ladder type filter shows two passbands of nearly the same amplitude. Such dual passband filters can be used as duplexer or multiplexer having a much simpler topology as no separate resonators for Tx and Rx are required .
Figures 3A to 3C show the P-matrix elements S21, Sll and S22 and respective Smith charts of a SAW band reject filter showing two comparable reject bands. The filter is construed in a common manner as a ladder type arrangement of series and parallel SAW resonators. However, the used resonators are configured according to the proposed idea and respectively show two comparable signal amplitudes that are assigned to a main mode and a plate mode.
On the other hand, filters utilizing PM are expected to have a higher power-durability, since PM is mainly located within the dielectric layer above the IDT.
Besides the main application, the PM can also be combined with the main-mode simultaneously, to create a dual passband filter or a dual notch-filter, or to improve the selectivity on the right or left side of the passband/rej ect-band of a filter .
Figures 4A to 4C show the P-matrix elements S21, Sll and S22 and respective Smith charts of a SAW bandpass filter with improved selectivity below the passband. Here the plate mode of the SAW resonators is used to form the passband. The main mode of some resonators is used to further improve the lower stop band by using the resonance frequency of the respective main mode of some resonators that are mainly circuited as parallel resonators in respective shunt arms of the ladder type filter circuit.
Deviating from the above examples it is possible to use the general idea for construing a bandpass filter of the DMS type by using the plate mode of the DMS transducers to achieve a pass band at a frequency higher that up to now possible with a SAW filter. Alternatively, the main mode of a DMS filter's resonators can be used for creating the passband and the plate mode of the resonators for improving the selectivity.
On the other hand, matching elements such as inductors and capacitors can be connected to the resonators (in series or parallel) to shift the resonance or anti-resonance of the main mode to set it to the desired frequencies. The invention has been shown by reference of a limited number of embodiments but is not restricted to specific features of any embodiment. Additionally the invention can generally be applied to BAW filters as well. The embodiments are only illustrative and the scope of the invention is only defined by the claims.

Claims

Claims
1. A SAW device comprising
- a substrate comprising piezoelectric layer on top or consisting of a piezoelectric bulk material
- an interdigital transducer - IDT - on top of the
substrate
- a SiCy layer on top of the IDT
wherein the height of the SiCy layer is set to a value that facilitates exciting of a substantial amount of a respective plate mode that can propagate in the layer system
wherein the SAW device is construed to make use of the resonance frequency of the plate mode for filtering purpose.
2. The SAW device of the foregoing claim,
making use of the resonance frequency of the plate mode for forming a pass band of a filter.
3. The SAW device of one of the foregoing claims,
construed as a ladder type filter
comprising resonators that are designed to allow excitation of main mode and plate mode at the same time
wherein the resonance frequencies of plate mode and main mode are used for forming a dual pass band filter.
4. The SAW device of one of the foregoing claims,
construed as a ladder type filter
comprising resonators that are designed to allow excitation of main mode and plate mode at the same time
wherein the resonance frequencies of plate mode and main mode are used for forming a dual reject band filter.
5. The SAW device of one of the foregoing claims, wherein the SAW device is a ladder type filter construed out of SAW resonators comprising series and parallel resonators wherein at least one of the resonators is designed to allow excitation of the plate mode
wherein the resonance frequency of the main mode is used for forming the pass band
wherein the resonance frequency of the plate mode is used for improving the selectivity of the filter at the resonance frequency of the plate mode.
6. The SAW device of one of the foregoing claims,
wherein the SAW device is a ladder type filter construed out of SAW resonators comprising series and parallel resonators wherein at least one of the resonators is designed to allow excitation of the plate mode
wherein the resonance frequency of the plate mode is used for forming the pass band
wherein the resonance frequency of the main mode is used for improving the selectivity of the filter at the resonance frequency of the main mode.
7. The SAW device of one of the foregoing claims,
wherein the SAW device is a reject band filter construed out of SAW resonators arranged in a ladder type arrangement of series and parallel resonators
wherein at least one of the resonators is designed to allow excitation of the plate mode
wherein the resonance frequency of the main mode is used for forming the reject band
wherein the resonance frequency of the plate mode is used for improving the selectivity of the filter at the resonance frequency of the plate mode.
8. The SAW device of one of the foregoing claims, wherein the SAW device is a reject band filter construed out of SAW resonators arranged in a ladder type arrangement of series and parallel resonators
wherein at least one of the resonators is designed to allow excitation of the plate mode
wherein the resonance frequency of the plate mode is used for forming the reject band
wherein the resonance frequency of the main mode is used for improving the selectivity of the filter at the resonance frequency of the main mode.
9. The SAW device of one of the foregoing claims,
comprising a resonator showing a main mode and a plate mode as well
wherein the resonance frequency of the plate mode of this resonator is used to create a notch by circuiting the
resonator as a parallel resonator in in a filter circuit wherein the plate mode is set at a frequency where a higher suppression of a parasitic signal is required.
10. The SAW device of one of the foregoing claims,
comprising resonators showing a main mode, a plate mode or both excitations at the same time
wherein the resonance frequency the main mode is used to create a notch by circuiting the resonator as a parallel resonator in in a filter circuit
wherein the main mode is set at a frequency where further suppression of a parasitic signal is required.
11. The SAW device of one of the foregoing claims,
wherein matching elements such as inductors and capacitors are connected to the resonators in series or parallel to shift the resonance or anti-resonance of the main mode to a desired frequency.
12. Using a SAW device of one of the foregoing claims for a pass band filter or a band reject filter with a
passband/rej ect band frequency higher than a maximum
frequency
wherein the maximum frequency is the resonance frequency of a resonator using main mode only optimized for the highest possible frequency that can be safely reproduced with a given structuring method.
13. Using a SAW resonator of one of the foregoing claims in a circuit comprising a DMS filter as a main filter component wherein the plate mode of the resonator is used to improve the selectivity of the DMS filter at a frequency above the pass band.
PCT/EP2019/071850 2018-10-01 2019-08-14 Saw device designed for high frequencies WO2020069794A1 (en)

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