SAW MULTIPLEXER WITH SWA FILTERS HAVING DIFFERENT BANDWIDTHS DUE TO DIELECTRIC LAYER BETWEEN IDT AND PIEZOELECTRIC LAYER ADJUSTING ACOUPLING FACTOR

Abstract

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.

Claims

1. A filter chip comprising several electric filters, wherein at least one of the several electric filters is a first-type electric filter comprising at least one first-type SAW-resonator, 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 is made of a dielectric, non-piezoelectric material.

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, the thickness of the intermediate layer is between 0.001.Math.λ and 0.05.Math.λ inclusive.

3. The filter chip according to claim 1, wherein the intermediate layer has a lower relative permittivity ε.sub.r than the piezoelectric layer.

4. The filter chip according to claim 1, wherein the intermediate layer comprises or consists of: Al.sub.2O.sub.3, MgO, ZrO.sub.2.

5. The filter chip according to claim 1, wherein each filter is a passband filter.

6. The filter chip according to claim 1, wherein the at least one first-type filter is a passband filter with a bandwidth of at most 20 MHz.

7. The filter chip according to claim 1, wherein the filter chip is 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, the 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 at least one of the several filters is a second-type electric filter comprising at least one second-type SAW-resonator, the second-type SAW-resonator comprises a piezoelectric layer and an interdigital electrode structure applied directly on top of the piezoelectric layer.

11. The filter chip according to claim 10, wherein the at least one second-type filter is a bandpass filter with a bandwidth of at least 30 MHz.

12. The filter chip according to claim 10, wherein the filter chip is a pentaplexer for LTE applications, the filter chip comprises one first-type filter and four second-type filters, the first-type filter is an Rx-filter configured for the frequency band 30, two of the second-type filters are Tx-filters, one configured for the frequency band 25 and one configured for the frequency band 66, two of the second-type filters are Rx-filters, one configured for the frequency band 25 and one configured for the frequency band 66.

13. A first type SAW-resonator comprising: a piezoelectric layer, an intermediate layer on the piezoelectric layer 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.

Description

[0043] In the drawings:

[0044] FIG. 1 shows an exemplary embodiment of the filter chip,

[0045] FIG. 2 shows a section of an exemplary embodiment of the first-type filter in a cross-sectional view,

[0046] FIG. 3 shows a section of an example of a second-type filter in a cross-sectional view,

[0047] FIG. 4 shows a section of a further exemplary embodiment of a first-type filter in a cross-sectional view,

[0048] FIG. 5 shows the simulated admittance curves of different SAW-resonators.

[0049] FIG. 1 shows an exemplary embodiment of the filter chip. The filter chip comprises four filters 1, 2. One filter 1 is a first-type filter and four filters are each second-type filters. The filters 1, 2 are all connected to an antenna 3. The antenna 3 is not part of filter chip.

[0050] The filter chip of FIG. 1 is a pentaplexer suitable for communication applications. For example, the filter chip of FIG. 1 can be used in mobile phones. By way of example, the first-type filter 1 is an Rx-filter configured for the LTE frequency band 30, two of the second-type filters 2 are Tx-filters configured for the LTE frequency bands 25 and 66, respectively, and the two remaining second-type filters 2 are Rx-filters configured for the LTE frequency bands 25 and 66, respectively.

[0051] FIG. 2 shows a section of an exemplary embodiment of the first-type filter 1, for example of the first-type filter 1 used in the filter chip of FIG. 1. The first-type filter 1 comprises a carrier substrate 14, for example made of Si. The carrier substrate 14 is preferably self-supporting and mechanically carries all structures applied on the carrier substrate 14. A piezoelectric layer 11 is applied on a top side of the carrier substrate 14. The piezoelectric layer 11 is made, for example, of LiTaO.sub.3 or LiNbO.sub.3. On a side of the piezoelectric layer 11 facing away from the carrier substrate 14, an intermediate layer 12 is applied. The intermediate layer 12 is in direct contact with the piezoelectric layer 11. The intermediate layer 12 consists of a dielectric, non-piezoelectric material. By way of example, the intermediate layer 12 is made of Al.sub.2O.sub.3. For example, the intermediate layer 12 was deposited with the help of Atomic Layer Deposition (ALD).

[0052] On a side of the intermediate layer 12 facing away from the piezoelectric layer 11, interdigital electrode structures 13 are applied. The electrode structures 13 each comprise electrodes, which are preferably made of a metal, like Al and/or Cu. The electrodes are in direct contact with the intermediate layer 12. The electrodes comprise fingers, wherein the fingers of the different electrodes interdigitate with each other.

[0053] In FIG. 2, two electrode structures 13, each with interdigitating electrodes, are applied on the intermediate layer 12. Each of the electrode structures 13 together with the piezoelectric layer 11 and the intermediate layer 12 forms a first-type SAW-resonator 10. The two first-type SAW-resonators 10 of FIG. 2 are, for example, connected in series. The first-type filter 1 of FIG. 2 may comprise further first-type SAW-resonators 10, for example first-type SAW-resonators 10 connected in parallel to the shown first-type SAW-resonators 10. The first-type filter 1 of FIG. 1 is, for example, a ladder-type filter.

[0054] On top of the electrode structures 13, a TCF compensation layer 15, for example made of SiO.sub.2, is applied.

[0055] As can be seen in FIG. 2, the two first-type resonators 10 share the same piezoelectric layer 11, which extends contiguously over both first-type SAW-resonators 10. Likewise, the intermediate layer 12 extends contiguously over both first-type SAW-resonators 10.

[0056] The first-type SAW-resonators 10 of FIG. 1 are each configured for the excitation of a main mode acoustic wave with a wavelength A. Particularly, the pitch between two adjacent fingers of the electrode structures 13 is λ/2. The thickness of the intermediate layer 12 is preferably at least 0.001.Math.λ and at most 0.02.Math.λ. Such a thin intermediate layer 12 reduces the pole-zero distance in each of the first-type SAW-resonators 10. For example, the first-type filter 1 of FIG. 2 has a bandwidth of at most 20 MHz.

[0057] FIG. 3 shows a section of an example of a second-type filter 2. For example, the second-type filter 2 of FIG. 3 is one of the second-type filters 2 used in the filter chip of FIG. 1. The second-type filter 2 comprises two second-type SAW-resonators 20. The second-type SAW-resonators 20 are designed similarly to the first-type SAW-resonators 10 of FIG. 2, with the difference that no intermediate layer 12 is used. Instead, the electrodes of the electrode structures 13 are applied directly onto the piezoelectric layer 11.

[0058] In FIG. 1, a piezoelectric layer of the different filters 1, 2 preferably extends contiguously over all filters 1, 2.

[0059] FIG. 4 shows a further exemplary embodiment of the first-type filter 1. Also this first-type filter 1 could be the first-type filter 1 of FIG. 1. The first-type filter 1 of FIG. 4 is designed similarly to the first-type filter 1 of FIG. 2. However, in this case, no TCF compensation layer is applied on top of the electrode structures 13. Instead, a TCF compensation layer 16, for example formed of SiO.sub.2, is located between the carrier substrate 14 and the piezoelectric layer 11. The piezoelectric layer 11 of FIG. 4 is preferably a thin-film.

[0060] FIG. 5 shows the simulated admittance curves of different SAW-resonators. The x-axis represents the frequency in MHz.

[0061] The y-axis represents the imaginary part of the admittance in arbitrary units.

[0062] The curve C1 represents the simulation results for a second-type SAW-resonator, in which the interdigital electrode structure is applied directly on the piezoelectric layer without using a dielectric, non-piezoelectric intermediate layer in between. The pole-zero distance, i.e. the distance between the resonance and the anti-resonance, is comparatively large.

[0063] The curves C2 to C4 represent the simulation results for first-type SAW-resonators. The design of the first-type SAW-resonators is almost identical to that of the simulated second-type SAW-resonator used for curve C1. The only difference is that for the first-type SAW-resonators a dielectric, non-piezoelectric intermediate layer was used between the interdigital electrode structures and the piezoelectric layer. For curve C2, the thickness of the intermediate layer was simulated to be 2.5 nm. For curve C3 the thickness was simulated to be 5 nm. For curve C4, the thickness was simulated to be 10 nm. As can be seen, with increasing thickness of the intermediate layer, the pole-zero distance can be reduced significantly. Thus, a first-type SAW-resonator can be used in filters for which a small bandwidth is desired.

[0064] The invention described herein is not limited by the description in conjunction with the exemplary embodiments. Rather, the invention comprises any new feature as well as any combination of features, particularly including any combination of features in the patent claims, even if said feature or said combination per se is not explicitly stated in the patent claims or exemplary embodiments.

REFERENCE SIGN LIST

[0065] 1 first-type filter

[0066] 2 second-type filter

[0067] 3 antenna

[0068] 10 first-type SAW-resonator

[0069] 11 piezoelectric layer

[0070] 12 intermediate layer

[0071] 13 interdigital electrode structure

[0072] 14 carrier substrate

[0073] 15 TCF compensation layer

[0074] 16 TCF compensation layer

[0075] 20 second-type SAW-resonator

[0076] C1, C2, C3, C4 simulated admittance curves