High-Q HF microelectromechanical filters
Bannon, F.D.; Clark, J.R.; Nguyen, C.T.-C.
Solid-State Circuits, IEEE Journal of
Volume 35, Issue 4, Apr 2000 Page(s):512 - 526
Digital Object Identifier 10.1109/4.839911
Summary:IC-compatible microelectromechanical intermediate frequency
filters using integrated resonators with Q's in the thousands to achieve
filter Q's in the hundreds have been demonstrated using a polysilicon
surface micromachining technology. These filters are composed of two
clamped-clamped beam micromechanical resonators coupled by a soft
flexural-mode mechanical spring. The center frequency of a given filter
is determined by the resonance frequency of the constituent resonators,
while the bandwidth is determined by the coupling spring dimensions and
its location between the resonators. Quarter-wavelength coupling is
required on this microscale to alleviate mass loading effects caused by
similar resonator and coupler dimensions. Despite constraints arising
from quarter-wavelength design, a range of percent bandwidths is still
attainable by taking advantage of low-velocity spring attachment
locations. A complete design procedure is presented in which
electromechanical analogies are used to model the mechanical device via
equivalent electrical circuits. Filter center frequencies around 8 MHz
with Q's from 40 to 450 (i.e., percent bandwidths from 0.23 to 2.5%),
associated insertion losses less than 2 dB, and spurious-free dynamic
ranges around 78 dB are demonstrated using low-velocity designs with
input and output termination resistances of the order of 12 kΩ
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