Online proceedings - EDA Publishing Association

B. Dynamics of Energy Flows
For a layout designer of switching networks, figure 4
provides a quantitative prediction of the energy consumed
and released by the switch. Immediately after the driving
voltage is applied, a major part of energy is stored in the
electrical field of the variable capacitor. The energy dissipation
along the bias line resistor, caused by the induced
current, is around fifty times smaller than the energy dissipated
by the squeeze-film damping and therefore negligible.
During the transition from up-state to down-state, the
potential and kinetic energy increase with increasing cantilever
deflection and velocity. At the same time, energy is
dissipated by the squeeze-film damping.
int[Vext(t)*i(t)]dt [microWs ]
3
2
1
0
0 10 20 30 40 50 60 70
time [us]
Figure 4: Total energy delivered to the system and fed back.
From the mechanical point of view, the system can be
optimised either, to provide fast switching, to dissipate
minimal energy, to minimise the actuation voltage or to reduce
the stored energy in the on-state of the system. From
the electrical point of view, the electrical signal can be preprocessed
offering a desired wave-form in order to control
the re-feeded power level, or to minimize the oscillation
amplitudes and contact bouncing.
VII.
x 10 -4
MEASUREMENTS
The developed ohmic contact RF MEMS switch shows
high isolation in the off-state and a low insertion
loss in the on-state up to frequencies as high as
[12].
All processing was carried out in industrial fabrication
line. The measurement results validate the theoretical
11-13
May 2011, Aix-en-Provence, France
Figure 5: fabricated ohmic contact MEMS switch in CPW configuration.
model presented in the previous sections. All measurements
are performed with switches fabricated within the same
batch (figure 5).
In order to ensure the initial conditions and the assumptions
used in the model, concerning geometrical aspects,
scanning electron microscopy is used. Scanning electron
microscopy allows identifying cantilever bending and verifying
geometric dimensions.
The accessible electrical triggering characteristics are
described by the bias threshold voltage resulting in an electrical
through-connection of the signal path, and the restoring
voltage, disconnecting the signal path. When performing
the measurement in ambient environment, possible interaction
with humidity and contamination of organic compounds
on the contact surfaces can provoke an excess of
force to overcome the action of an adhering passivation
layer.
Finally, the model is validated by the dynamic system
response: the transition time, defined as the time passed between
the supply of the bias potential and the event of first
charge transferred by the electrical contacts, and the switching
time, defined as the time passed between the supply of
the bias potential and the event of continuous charge transfer
by the electrical contacts.
The test setup uses a Keithley 2400 voltage source, powering
the collector path of a 2SC2911 npn-transistor form
SANYO. The transistor gate is controlled by a HP 3312A
function generator, providing a frequency variable square
signal of positive half-waves with an amplitude set to
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