  We report on a giant enhancement in the thermal responsivity of the
doubly-clamped GaAs microelectromechanical (MEMS) beam resonators by using the
internal mode coupling effect. This is achieved by coupling the fundamental
bending mode with the fundamental torsional mode of the MEMS beam resonators
through the cubic Duffing nonlinearity. In the mode coupling regime, we have
found that, when the input heat to the MEMS resonators is modulated at a
particular frequency, the resonance frequency shift caused by heating can be
enhanced by almost two orders of magnitude. The observed effect is promising
for realizing high-sensitivity thermal sensing by using MEMS resonators, such
as ultrasensitive terahertz detection at room temperature.
