- Technical References
The Aging of Bulk Acoustic
Wave Resonators, Filters and Oscillators
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Although the state-of-the-art in the long term aging of low-aging
resonators has been on a plateau for more than a generation, there is no
reason to believe that the factors responsible for limiting the achievable
long term aging are insurmountable. The definitive experiments, in which
all known aging mechanisms are minimized, are yet to be performed. It is
the authors' hope that the review in this paper will assist future researchers
in the design of experiments that result in significant improvements in
Even though several possible aging mechanisms are well understood,
the aging of resonators is still not well understood.
Aging performance, including variations with temperature
and drive level, depends on the resonator design and fabrication technology.
Many processing deviations can degrade aging performance.
High temperature processing seems necessary (but not sufficient)
for the production of low-aging resonators.
The SC-cut, and modern ultrahigh vacuum and high temperature
fabrication techniques have resulted in resonators which achieve low-aging
in a shorter period of time than the best resonators made a generation
ago, however, the aging of the best modern resonators after extended periods
is no better today than what was reported for the best resonators in the
Accelerated aging studies are useful for process control.
Using accelerated aging data for long term aging predictions is possible,
but considerable work and expense are required to reduce the risk of error
to acceptable confidence levels
The best reproducible long term aging rates seem to be a
few times 10-11 per day. Occasional resonators exhibit aging
rates of a few times 10-12 per day after extended periods.
Environmental changes can produce frequency changes that
appear to be aging. This apparent aging is now called "drift."