CONTROLLED EFFECTIVE COUPLING COEFFICIENTS FOR FILM BULK ACOUSTIC RESONATORS
First Claim
1. 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.
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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.
37 Citations
15 Claims
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1. A method of fabricating an array of acoustic resonators comprising the steps of:
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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. - View Dependent Claims (2, 3, 4, 5)
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6. The method of claim 6 wherein said selecting steps and said step of forming said first and second FBAR filters includes providing a first target frequency response having a center frequency that is within 100 MHz of a center frequency said second target frequency response.
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7. A method of fabricating an array of acoustic resonators comprising the steps of:
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selecting a filter arrangement of FBARs to achieve a target frequency response and a target effective coupling coefficient;
designing at least one FBAR in said filter arrangement as a power bar in which a target impedance of said FBAR is substantially maintained while significantly increasing a power density of said filter arrangement at said power bar, including configuring said power bar as a pair of large area FBARs that are connected in series to provide a combined impedance that corresponds to said target impedance;
selecting ratios of thicknesses of piezoelectric layers to thicknesses of electrode layers in the fabrication of said filter arrangement to achieve said target frequency response and said target effective coupling coefficient, including selecting at least one said ratio to ensure an effective coupling coefficient that is substantially below an intrinsic coupling coefficient; and
fabricating said filter arrangement, including forming said power bar and including forming electrode layers and piezoelectric layers having thicknesses that are based upon achieving said selected ratios.
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8. A duplexer comprising:
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a transmit film bulk acoustic resonator (FBAR) array having transmit series FBARs connected in series and having transmit shunt FBARs; and
a receive FBAR array having series FBARs connected in series and having receive shunt FBARs;
wherein said transmit FBAR array has an effective coupling coefficient that is substantially less than an effective coupling coefficient of said receive FBAR array, said substantially less effective coupling coefficient being realized by providing at least some FBARs of said transmit FBAR array with substantially thicker electrode layers and substantially thinner piezoelectric layers than said FBARs of said receive FBAR array. - View Dependent Claims (9, 10, 11, 13, 14, 15)
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12. A method of forming an array of acoustic resonators comprising the steps of:
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selecting a first target frequency response and a first target effective coupling coefficient for operation of a first 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;
forming said first FBAR filter to seek said first target frequency response and an effective coupling coefficient greater than said first target effective coupling coefficient;
forming said second FBAR filter to seek said second target frequency response and to seek said second effective coupling coefficient; and
forming a capacitor in parallel with said at least one FBAR of said first FBAR filter to degrade said effective coupling coefficient of said first FBAR filter, thereby achieving said first target effective coupling coefficient.
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Specification