ELECTROACOUSTIC RESONATOR, RF FILTER WITH INCREASED USABLE BANDWIDTH AND METHOD OF MANUFACTURING AN ELECTROACOUSTIC RESONATOR
An electroacoustic resonator (EAR) that allows RF filters in which transversal modes are suppressed in a wider frequency range and corresponding RF filters and methods are provided. The resonator has an electrode structure (BB,EF) on a piezoelectric material and a transversal acoustic wave guide. The wave guide has a central excitation area (CEA), trap stripes (TP) and barrier stripes (B). The difference in wave velocity (|VCEA−VB|) between the central excitation area and the barrier stripes determines the frequency range of suppressed transversal modes.
1 . An electroacoustic resonator for bandpass filters having an increased bandwidth, the resonator comprising
a piezoelectric material,
an electrode structure on the piezoelectric material,
a transversal acoustic wave guide having a central excitation area, trap stripes flanking the central excitation area and barrier stripes flanking the trap stripes,
wherein
the wave velocity is VCEA in the central excitation area,
the wave velocity is VTP in the in the trap stripes,
the wave velocity is VB in the in the barrier stripes,
and 0.5≤ΔV/(Δf*λ)≤1.5 for a desired band width Δf
and ΔV=abs (VB−VCEA).
2 . The resonator of claim 1 , where
0.9≤Δ V /(Δ f*λ )≤1.1 or
Δ V /(Δ f*λ )=1.
3 . The resonator of any one of the claims 1 - 2 where
in case of a convex slowness: VB>VCEA and
in case of a concave slowness: VB<VCEA.
4 . The resonator of any one of the claims 1 - 3 , wherein ηCEA is the metallization ratio in the central excitation area, ηTP is the metallization ration in the trap stripes and/or ηB is the metallization ratio in the barrier stripes and
the number of different values selected ηCEA, ηTP and/or ηB is 1, 2 or 3.
5 . The resonator of any one of the claims 1 - 4 , wherein ηCEA is the metallization ratio in the central excitation area, ηTP is the metallization ration in the trap stripes and ηTP≠ηCEA.
6 . The resonator of any one of the claims 1 - 5 further comprising a dielectric material deposited in the central excitation area, in the area of the trap stripes and/or in the area of the barrier stripes.
7 . The resonator of claim 6 , wherein the dielectric material comprises a silicon nitride such as Si 3 N 4 , a silicon oxide such as a silicon dioxide, such as SiO 2 , and/or an aluminium oxide, e.g. Al 2 O 3 , a hafnium oxide, e.g. HfO2, or doped versions thereof.
8 . The resonator of any one of the claims 1 - 7 , wherein
the height of the electrode structure is hCEA in the central excitation area, hTP in the area of the trap stripes and hB in the area of the barrier stripes, and
the number of different values selected from hCEA, hTP and hB is 1, 2 or 3.
9 . The resonator of any one of the claims 1 - 8 , wherein the height of the electrode structure is hCEA in the central excitation area, hTP in the area of the trap stripes and hB in the area of the barrier stripes,
wherein hCEA≠hTP, hCEA≠hB and/or hTP≠hB.
10 . The resonator of any one of the claims 1 - 9 , which can work with a piston mode.
11 . The resonator of any one of the claims 1 - 10 , wherein the piezoelectric material comprises LiTaO 3 , LiNbO 3 , Quartz or a Lanthanum gallium silicate.
12 . The resonator of any one of the claims 1 - 1 where the piezoelectric material is selected from a piezoelectric substrate, a piezoelectric monocrystalline substrate, a thin film.
13 . An RF filter comprising one or more resonators of any one of the claims 1 - 12 .
14 . A Method for manufacturing an electroacoustic resonator, comprising the steps:
defining a bandwidth Δf of transversal mode suppression,
providing a piezoelectric material,
depositing electrode structures on the piezoelectric material and forming a transversal acoustic wave guide for surface acoustic waves at the surface on the piezoelectric material, the wave guide having a central excitation area wherein
the wave guide provides a wave velocity VCEA in the central excitation area,
the wave guide provides a wave velocity VTP in trap stripes flanking the central excitation area,
the wave guide provides a wave velocity VB in barrier stripes flanking the trap stripes where
for the given frequency bandwidth Δf of transversal mode suppression, VB and VCES are chosen such that
0.5≤Δ V /(Δ f *λ)≤1.5,
and Δ V =abs( VB−VCEA ) and
λ is the wavelength of the resonator.