13 research outputs found
A thickness-shear MEMS resonator employing electromechanical transduction through a coplanar waveguide
The design, modeling, fabrication, and characterization
of a vibrationally trapped thickness-shear MEMS resonator
is presented. This device is intended to avoid various limitations
of flexural MEMS resonators, including nonlinearity, clamping
losses, thermoelastic damping, and high damping in liquid. It
includes a silicon bridge and a reference line on an SOI wafer,
a coupled Au/Cr coplanar waveguide, Lorentz-force coupling,
variations in waveguide thickness for vibrational trapping, and
circuitry for nulling the components of the signal that are
unrelated to the acoustic resonance. Finite-element vibrational
modeling shows the lowest thickness-shear mode with a bridge
thickness of 4.9 µm to be dominated by shear displacements,
with the magnitude of out-of-plane displacements decreasing with
increasing bridge width. Two-dimensional modeling of vibrational
trapping, with central regions of the waveguides having
43 nm greater thickness, indicates that amplitudes are reduced
by several orders of magnitude at the ends of the bridges for
the fundamental ~ 400 MHz thickness-shear resonance. Sweptfrequency
network-analyzer measurements of fabricated devices
reveal no evidence for an acoustic resonance, despite a calculated
prediction of levels of acoustic power absorption that are well
above the measured noise level. A possible explanation for this
result is stiction of the bridges to the substrate.Peer ReviewedPostprint (published version
A thickness-shear MEMS resonator employing electromechanical transduction through a coplanar waveguide
The design, modeling, fabrication, and characterization
of a vibrationally trapped thickness-shear MEMS resonator
is presented. This device is intended to avoid various limitations
of flexural MEMS resonators, including nonlinearity, clamping
losses, thermoelastic damping, and high damping in liquid. It
includes a silicon bridge and a reference line on an SOI wafer,
a coupled Au/Cr coplanar waveguide, Lorentz-force coupling,
variations in waveguide thickness for vibrational trapping, and
circuitry for nulling the components of the signal that are
unrelated to the acoustic resonance. Finite-element vibrational
modeling shows the lowest thickness-shear mode with a bridge
thickness of 4.9 µm to be dominated by shear displacements,
with the magnitude of out-of-plane displacements decreasing with
increasing bridge width. Two-dimensional modeling of vibrational
trapping, with central regions of the waveguides having
43 nm greater thickness, indicates that amplitudes are reduced
by several orders of magnitude at the ends of the bridges for
the fundamental ~ 400 MHz thickness-shear resonance. Sweptfrequency
network-analyzer measurements of fabricated devices
reveal no evidence for an acoustic resonance, despite a calculated
prediction of levels of acoustic power absorption that are well
above the measured noise level. A possible explanation for this
result is stiction of the bridges to the substrate.Peer Reviewe