Online proceedings - EDA Publishing Association

MEMS DC/DC converter
11-13 May 2011, Aix-en-Provence, France
Driving plate displacement
ΔC
Figure 3: Schematic view of the whole DC/DC converter system in Virtuoso.
R load = 1 TΩ
R load = 100 GΩ
R load = 10 GΩ
R load = 1 GΩ
Figure 4: Transient response of the DC/DC converter for
different resistive loads.
This modeling approach also allows a geometrical analysis of
the mechanical part regarding the output voltage of the whole
system. Figure 5 shows the transient response of the converter
for different rotor to stator distance d RS on the pump capacitor.
The stationary output voltage increases when d RS decreases,
which is explained by a higher maximum voltage multiplication
factor (C max /C min ) when d RS is low. However a drastic increase in
charging rate appears for very low rotor to stator distances. This
is due to a the electrostatic spring which appears because of the
electrostatic force generated at the capacitor plate when a
voltage is present (pull-in effect) [9,10]. This added stiffness
shifts the resonant frequency of the system during the charging
cycles which increases the driving plate amplitude displacement.
Figure 6 shows the FFT of the driving plate displacement for
different values of d RS . We can see that for a small value of d RS
another oscillating mode is superimposed on the driving mode
frequency. This new oscillation mode corresponds to the new
resonant frequency of the mechanical structure (around 8.1 kHz)
C1_d RS = 8 µm
C1_d RS = 5 µm
C1_d RS = 5.5 µm
C1_d RS = 6 µm
C1_d RS = 5 µm
C1_d RS = 8 µm
Figure 5: Transient response of the DC/DC converter for
different finger spacings.
Figure 6: FFT of the x displacement signal of the driving plate
for different rotor to stator distance d RS .
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