Bulk acoustic wave resonator (BAW)
oscillators are a recent introduction in
the field of fixed frequency oscillators.
The resonator, more commonly known
as FBAR, is a three-layer structure with
the top and bottom electrodes of
molybdenum sandwiching a middle
layer of oriented piezoelectric aluminum
nitride. These resonators are
practical for use in the frequency range
of 500 MHz to 5 GHz. An air interface
is used on both outer surfaces to provide
high Q reflectors at all frequencies.
When RF signals are applied near
the mechanical resonant frequency the
piezoelectric transducer excites the
fundamental bulk compression wave
traveling perpendicular to the films