US 6,472,954 B1 · Controlled effective coupling coefficients for film bulk acoustic resonators

Abstract

In an array of acoustic resonators, the effective coupling coefficient of first and second filters are individually tailored in order to achieve desired frequency responses. In a duplexer embodiment, the effective coupling coefficient of a transmit band-pass filter is lower than the effective coupling coefficient of a receive band-pass filter of the same duplexer. In one embodiment, the tailoring of the coefficients is achieved by varying the ratio of the thickness of a piezoelectric layer to the total thickness of electrode layers. For example, the total thickness of the electrode layers of the transmit filter may be in the range of 1.2 to 2.8 times the total thickness of the electrode layers of the receive filter. In another embodiment, the coefficient tailoring is achieved by forming a capacitor in parallel with an acoustic resonator within the filter for which the effective coupling coefficient is to be degraded. Preferably, the capacitor is formed of the same materials used to fabricate a film bulk acoustic resonator (FBAR). The capacitor may be mass loaded to change its frequency by depositing a metal layer on the capacitor. Alternatively, the mass loading may be provided by forming the capacitor directly on a substrate.

Claims10

Dependent claims

A method of fabricating an array of acoustic resonators comprising the steps of:

selecting a first target frequency response and a first target effective coupling coefficient for operation of a first film bulk acoustic resonator (FBAR) filter;
selecting a second target frequency response and a second target effective coupling coefficient for operation of a second FBAR filter, said first target effective coupling coefficient being substantially degraded relative to said second target effective coupling coefficient;
determining thicknesses and materials of piezoelectric and electrode layers for forming said first and second FBAR filters so as to achieve said first and second target frequency responses and said first and second target effective coupling coefficients, including selecting an increased electrode layer thickness for at least one electrode layer of said first FBAR filter, said increased electrode layer thickness being greater than electrode layer thicknesses selected for said second FBAR filter such that said substantially degraded first target effective coupling coefficient is achieved;
and
forming said first and second FBAR filters based on said thicknesses and materials.

2 more elements

Dependencies are inferred from the claim text.

Controlled effective coupling coefficients for film bulk acoustic resonators

Life of this patent

Controlled effective coupling coefficients for film bulk acoustic resonators

Life of this patent

Abstract

Claims10