Saw multiplexer with SWA filters having different bandwidths due to dielectric layer between IDT and piezoelectric layer adjusting acoupling factor
The SAW filter chip comprises a plurality of SAW filters ( 1, 2 ), wherein at least one of the several electric filters is a first-type electric filter ( 1 ) comprising at least one first-type SAW-resonator ( 10 ). The first-type SAW-resonator comprises a piezoelectric layer ( 11 ), an intermediate layer ( 12 ) on the piezoelectric layer ( 11 ) and an interdigital electrode structure ( 13 ) on the intermediate layer ( 12 ). The interdigital electrode structure is separated from the piezoelectric layer by the intermediate layer. The intermediate layer is made of a dielectric, non-piezoelectric material and adjusts the electromechanical coupling factor and the bandwidth of the respective filter. The plurality of SAW filters form an LTE multiplexer, wherein the thickness of the intermediate layer is chosen to adjust the required bandwidth to the desired bands. The intermediate layer may be absent for larger required bandwidths.
1. A filter chip comprising:
a first-type filter disposed on the filter chip and comprising a first-type surface acoustic wave (SAW)-resonator; and
a plurality of second-type filters disposed on the filter chip, each second-type filter comprising at least one second-type SAW-resonator;
wherein the first-type SAW-resonator comprises a piezoelectric layer, an intermediate layer on the piezoelectric layer, and an interdigital electrode structure on the intermediate layer, the interdigital electrode structure is separated from the piezoelectric layer by the intermediate layer, and the intermediate layer includes a dielectric, non-piezoelectric material; and
wherein the at least one second-type SAW-resonator comprises the piezoelectric layer and the interdigital electrode structure applied on top of the piezoelectric layer.
2. The filter chip according to claim 1 , wherein;
a main mode acoustic wave of the first-type SAW-resonator of the first-type filter has a wavelength λ; and
a thickness of the intermediate layer is between 0.001·λ and 0.05·λ inclusive.
3. The filter chip according to claim 1 , wherein the intermediate layer has a lower relative permittivity ε r than the piezoelectric layer.
4. The filter chip according to claim 1 , wherein the intermediate layer comprises at least one of Al 2 O 3 , MgO, or ZrO 2 .
5. The filter chip according to claim 1 , wherein each of the first-type filter and the plurality of second-type filters comprises a passband filter.
6. The filter chip according to claim 1 , wherein the first-type filter comprises a passband filter with a bandwidth of at most 20 MHz.
7. The filter chip according to claim 1 , wherein the filter chip comprises a multiplexer.
8. The filter chip according to claim 1 , wherein the intermediate layer is deposited by Atomic Layer Deposition.
9. The filter chip according to claim 1 , wherein:
each filter comprises at least one SAW-resonator;
each SAW-resonator comprises an interdigital electrode structure on top of a piezoelectric layer; and
piezoelectric layers of all SAW-resonators of all filters are formed by a contiguous piezoelectric layer.
10. The filter chip according to claim 1 , wherein the plurality of second-type filters each comprises a bandpass filter with a bandwidth of at least 30 MHz.
11. The filter chip according to claim 1 , wherein:
the filter chip comprises a pentaplexer for communications applications;
the filter chip comprises a single first-type filter and four second-type filters;
the first-type filter is an Rx-filter configured for a first frequency band;
two of the plurality of second-type filters are Tx-filters, one configured for a second frequency band and one configured for a third frequency band; and
two of the plurality of second-type filters are Rx-filters, one configured for the second frequency band and one configured for the third frequency band.
12. A first-type surface acoustic wave (SAW)-resonator comprising:
a piezoelectric layer,
an intermediate layer on the piezoelectric layer;
a substrate;
a temperature compensation layer between the piezoelectric layer and the substrate; and
an interdigital electrode structure on the intermediate layer, wherein
the interdigital electrode structure is separated from the piezoelectric layer by the intermediate layer, and
the intermediate layer is made of a dielectric, non-piezoelectric material.
13. The filter chip according to claim 1 , wherein the first-type SAW-resonator further comprises a temperature compensation layer between the piezoelectric layer and a substrate.
14. The filter chip according to claim 1 , wherein the temperature compensation layer comprises a dielectric material.
15. The first SAW-resonator according to claim 12 , wherein the temperature compensation layer comprises a dielectric material.