  Uncooled InfraRed (IR) detectors have enabled the rapid growth of thermal
imaging applications. These detectors are predominantly bolometers, where the
heating of pixel from incoming IR radiation is read out as a resistance change.
Another uncooled sensing method is to transduce the IR radiation into the
frequency shift of a mechanical resonator. We present here a highly sensitive,
simple to fabricate resonant IR sensor, based on thermo-responsive Shape Memory
Polymers (SMPs). By exploiting the phase-change polymer as the transduction
mechanism, our approach provides 2 orders of magnitude improvement of the
temperature coefficient of frequency (TCF). The SMP has very good absorption in
IR wavelengths, obviating the need for an absorber layer. A Noise Equivalent
Temperature Difference (NETD) of 22 mK in vacuum and 112 mK in air are obtained
using f/2 optics. Such high performance in air eliminates the need for vacuum
packaging, paving a path towards flexible IR sensors.
