ELECTROACOUSTIC RESONATOR AND RF FILTER COMPRISING AN ELECTROACOUSTIC RESONATOR

Abstract

An electroacoustic resonator (EAR) that allows an RF filter having a large bandwidth is provided. The resonator comprises a piezoelectric material (PM) and an electrode structure (ES, EF) on the piezoelectric material. The piezoelectric material is lithium niobate and has a crystal cut defined by the Euler angles (0°, 80° to 88°, 0°).

Claims

1. An electroacoustic resonator, comprising a piezoelectric material and an electrode structure on the piezoelectric material, wherein an acoustic main mode having the wavelength λ can propagate, the piezoelectric material is lithium niobate or doped lithium niobate and has a crystal cut defined by the Euler angles (0°, 80° to 88°, 0°).

2. The resonator of claim 1, wherein the piezoelectric material has a crystal cut defined by the Euler angles (0°, 80° to 83°, 0°).

3. The resonator of claim 1, further comprising a TCF layer arranged on or above the electrode structure and the piezoelectric material.

4. The resonator of claim 3, wherein the TCF layer comprises SiO.sub.2 or SiOF.

5. The resonator of claim 3, wherein the TCF layer has a thickness of 20% to 40% λ.

6. The resonator of claim 1, further comprising a passivation layer arranged on or above the TCF layer.

7. The resonator of claim 6, wherein the passivation layer comprises SiN.

8. The resonator of claim 6, wherein the passivation layer has a thickness of 1% to 4% λ.

9. The resonator of claim 1, wherein the electrode structure comprises a metal selected from Au, Cu, Pt and W.

10. The resonator of claim 1, wherein the electrode structure has a thickness of 6% to 15% λ.

11. The resonator of claim 1, wherein the main mode is a shear mode or a shear-like mode.

12. The resonator of claim 1, being a SAW resonator or a GBAW resonator.

13. An RF filter comprising a resonator of claim 1.

14. The RF filter of claim 13, being a band pass filter for band 28, 71, 41, 42 or 43.

15. The RF filter of claim 13, being a band pass filter for band 3, 8, 20 or 26.

16. The RF filter of claim 13, being a band pass filter for band 40, 48, 66 or 68.

Description

[0052] Central aspects of the present resonator and details of preferred embodiments are shown in the accompanying schematic figures.

[0053] In the figures:

[0054] FIG. 1 shows a basic construction of electrode structures on a piezoelectric material;

[0055] FIG. 2 shows a piezoelectric material arranged on a carrier substrate;

[0056] FIG. 3 shows the use of a TCF layer;

[0057] FIG. 4 shows the use of a passivation layer;

[0058] FIG. 5 shows an electrode structure comprising different sublayers;

[0059] FIG. 6 shows the meaning of the Euler angles λ′, μ, θ; and

[0060] FIG. 7 shows a ladder-type like circuit topology.

[0061] FIG. 1 shows a piezoelectric material PM on which an electrode structure ES is arranged. The piezoelectric material PM in combination with the electrode structure ES establish the essential elements of an electroacoustic resonator EAR working with surface acoustic waves. The electrode structure comprises electrode fingers EF arranged on the piezoelectric material PM. The electrode fingers EF extend in a direction orthogonal to the direction of propagation of the main surface acoustic mode. Thus, FIG. 1 shows a cross-section through the corresponding parts of the electroacoustic resonators EAR.

[0062] At the distal ends of the acoustic track reflector structures REF, e.g. provided as metallized fingers arranged on the piezoelectric material PM confine acoustic energy to the active area of the resonator.

[0063] In FIG. 1 the direction of propagation of the acoustic main mode is in a horizontal direction from left to right. The electrode fingers EF extend in a direction perpendicular to the plane provided by the cross-sectional view of FIG. 1.

[0064] It is possible that the piezoelectric material is provided as a monocrystalline material.

[0065] FIG. 2 illustrates the possibility of arranging the piezoelectric material PM on a carrier substrate CS.

[0066] FIG. 3 shows the possibility of arranging material of a temperature compensation layer TCFL on or above the piezoelectric material PM and the electrode structure ES. The thickness of the TCF layer is defined as the distance between the top side of the electrode structure ES and the top side of the material of the TCF layer TCFL, although also material of the TCF layer TCFL can be arranged between electrode fingers of the electrode structure ES.

[0067] FIG. 4 illustrates the possibility of having a passivation layer PL to protect the elements of the resonator arranged below the passivation layer PL. In the layer construction shown in FIG. 4 the passivation layer PL is arranged on the material of the TCF layer TCFL. The material of the TCF layer can comprise a silicon oxide, e.g. silicon dioxide and the passivation layer protects the material of the TCF layer from being contaminated from its environment. In particular, the passivation layer PL protects the material of the TCF layer from coming into contact with water contained in the surrounding air of the atmosphere.

[0068] FIG. 5 illustrates the possibility of the electrode structure or of electrode fingers having a layer construction. Thus, the electrode structures and electrode fingers can comprise a sublayer system comprising two or more sublayers. In particular, it is possible that an adhesion layer L1 is arranged between the piezoelectric material PM and other components of the electrode structure ES. The adhesion L1 augments a mechanical connection of the electrode structure to the piezoelectric material.

[0069] It is possible that the adhesion layer L1 comprises or consists of titanium.

[0070] Other sublayers L2 arranged above the adhesion layer L1 essentially comprise the “heavy” metals for providing the preferred waveguide.

[0071] FIG. 6 illustrates the meaning of the Euler angles λ′, μ, θ and their effects on the correspondingly rotated axes.

[0072] FIG. 7 illustrates the use of ladder-type like topologies to establish filters, e.g. for a duplexer DU. In a signal path series resonators SR are electrically connected in series between two ports. Parallel resonators PR are arranged in shunt paths between the signal path and ground. With such ladder-type like topologies transmission filters TXF and reception RXF can be provided. A duplexer DU comprises a transmission filter TXF and a reception filter RXF that are connected to a common port at which an antenna AN can be connected.

[0073] The electroacoustic resonator and the corresponding RF filter are not limited to the features stated above and the embodiments shown in the figures. A resonator can comprise further elements and layers, e.g. further functional layers or barrier layers, e.g. for establishing an acoustic waveguide. An RF filter can comprise further electroacoustic resonators.

LIST OF REFERENCE SIGNS

[0074] AN: antenna [0075] CS: carrier substrate [0076] EAR: electroacoustic resonator [0077] EF: electrode finger [0078] ES: electrode structure [0079] L1, L2: sublayers of the electrode structure [0080] PL: passivation layer [0081] PM: piezoelectric material [0082] PR: parallel resonator [0083] REF: reflecting structure [0084] RXF: reception filter [0085] SR: series resonator [0086] TCFL: temperature compensation layer, TCF layer [0087] TXF: transmission filter