Department of Electrical Engineering
Title: Charge and Frequency Drift Control in Resonant Electrostatic MEMS
Research Advisor: Prof. Thomas W. Kenny
Date: Thursday, May 27, 2010
Time: 4:30 pm
Location: CIS-X 101 (Auditorium)
Abstract :
Dielectrics play an important role as structural and electronic
materials in many kinds of micro/nanoscale systems (such as CMOS and
MEMS). However, it is also well known that dielectrics are susceptible
to various charging phenomena. Charge build-up and charge motion can
vary floating voltages, discharge electrodes, or screen electrode
potentials, affecting the overall properties of these devices. In MEMS,
these effects can include unpredictable actuation forces, frequency
drifts, and deteriorated signal transduction.
In our group, recent work has shown that SiO2-coated silicon MEMS
resonators have very desirable frequency vs. temperature
characteristics, making them ideal as a lower cost, lower power
replacement for quartz resonators, for the purpose of clocks and
frequency references. However, as SiO2 is a dielectric, these resonators
are also susceptible to adverse effects due to dielectric charge.
In this talk I will present a model describing the effects of fixed and
mobile dielectric charge on the frequency of these resonators. Further,
I will show how purely AC polarization of these resonators improves
frequency stability by eliminating charge drift, and removes the first
order dependence on fixed charge-induced offsets. Finally, I will
discuss oscillator design with these AC polarized resonators, including
a number of interesting implications regarding these oscillators.
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