Tunable bulk acoustic resonator device with improved insertion loss

A mobile communications device operating in an allocated channel of a predetermined frequency band having a plurality of channels, the mobile communication device comprising:

• (i) a band pass filter including a plurality of BAW resonators having a corresponding plurality of resonance frequencies, the band pass filter comprising:
• a substrate and a plurality of acoustic reflectors corresponding to the plurality of BAW resonators;
• a first metal layer formed over the substrate, the first metal layer providing a bottom electrode for each of the plurality of BAW resonators;
• a piezoelectric layer formed over the first metal layer;
• a second metal layer formed over the piezoelectric layer, the second metal layer providing a top electrode for each of the plurality of BAW resonators;
• and
• (ii) a high impedance voltage bias network comprising:
• a voltage source for providing a direct current (DC) bias voltage to the second metal layer;
• a high resistance layer formed between the first metal layer and the voltage source, and configured to provide a resistance between each of the plurality of BAW resonators and the voltage source,
• wherein the voltage source is activated when a location of the allocated channel within the predetermined frequency band is near an upper corner or a lower corner of the predetermined frequency band, thereby applying the DC bias voltage to the top electrode of each BAW resonator, which causes the resonance frequency of each BAW resonator to shift toward a center of the predetermined frequency band, improving insertion loss of the mobile communications device, wherein the upper corner corresponds to a high frequency edge of the predetermined frequency band and the lower corner corresponds to a low frequency edge of the predetermined frequency band.

A method of improving insertion loss of an acoustic band pass filter, comprising a plurality of bulk acoustic wave (BAW) acoustic resonators, operating in an allocated channel of a plurality of channels in a predetermined frequency band, the method comprising:

• detecting when a location of the allocated channel is near an upper corner or a lower corner of the predetermined frequency band;
• and
• activating a direct current (DC) voltage source when the location of the allocated channel is detected as being near the upper corner or the lower corner of the predetermined frequency band, the activated voltage source applying a non-zero DC bias voltage to an electrode of each BAW resonator via a resistor having a high resistance that substantially prevents current flow at RF frequencies where a filter passband is through the resistor,
• wherein application of the non-zero DC bias voltage shifts a resonance frequency of each BAW resonator toward a center of the predetermined frequency band, thereby improving the insertion loss of the acoustic band pass filter.