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.
We have fabricated two-dimensional phononic crystal (PnC) structures on GaAs doublyclamped microelectromechanical system (MEMS) beam resonators to modulate their thermal properties. Owing to the reduction in the thermal conductance of the MEMS beams by introducing the PnC structures, the MEMS bolometers with the PnC structures show 2-3 times larger thermal sensitivities than the unpatterned reference sample. Furthermore, since the heat capacitance of the MEMS beams is also reduced by introducing the PnCs, the thermal decay time of the patterned MEMS beams is increased only by about 30-40 %, demonstrating the effectiveness of the PnCs for enhancing the thermal sensitivities of bolometers without significantly deteriorating their operation bandwidths. __________________ a) Electronic
We have fabricated GaAs-based microelectromechanical systems' (MEMSs) terahertz bolometers on high-resistivity Si substrates by using a wafer-bonding technique. In contrast to polar GaAs, nonpolar Si has very small absorption in the terahertz (THz) frequency range. The wafer-bonded MEMS bolometers show a large responsivity even in the Reststrahlen band of GaAs, where the responsivity vanishes in the conventional MEMS bolometers fabricated on GaAs substrates. Furthermore, we have observed two peaks in the responsivity spectrum near the TO and LO phonon frequencies of GaAs, which originate from an interplay between strong reflection in the Reststrahlen band and strong absorption at the TO phonon frequency in the GaAs MEMS beam. The present result demonstrates that the wafer-bonded MEMS bolometers are a very good candidate for the room-temperature, fast, and sensitive broadband THz detection.
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