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A novel structure combining normal uncooled focal plane array (UFPA) microbridge and RF MEMS switch is presented.
The MEMS switch is integrated into the microbridge without any modification of the microbridge structure and
fabrication process. The upper electrode of the switch is the IR absorbing layer of the microbridge, and the down
electrode is the reflecting mirror of the IR resonant chamber on the substrate. With the help of the MEMS switch, the
microbridge can be pulled down to the substrate, and be cooled to the substrate temperature T0. Correlated double
sampling(CDS) method is used to read out the difference between R(T0) and R(T1), where R(T0) is the value of
thermistor on the microbridge when the microbridge is pulled down to the substrate, and cooled to the substrate
temperature T0, and R(T1) is the value of thermistor when the microbridge is heated up to T1 by radiation after the
microbridge is released from the substrate for a certain short time. The difference between R(T0) and R(T1) is just
related to thermistor R itself, and no reference resistor is need. Match between the thermistor and its reference in normal
structure, which is the most difficult task in fabrication, is no longer existed. And the signal due to mismatch between the
thermistor and the reference resistor, which is very large compared with the signal due to the thermistor change, and
which often makes op saturated, also no long exists. In CDS read-out circuit, the difference between R(T0) and R(T1)
can be very small, which cannot approximate thermal equilibrium state. So it only needs a very short time for the
microbridge to absorb radiation. The simulation results show that this novel structure can work up to 10KHz without any
performance decrease, which is 100 times faster than the speed of the normal structure.
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