A self-sustained nanomechanical thermal-piezoresistive oscillator with ultra-low power consumption

This work reports wing-type thermal-piezoresistive oscillators operating at around 840 kHz in vacuum with ultra-low power consumption of only 70 μW for the first time. The combination of N-type heavily doped silicon with negative piezoresistive coefficients and sub-micron cross-sectional dimensions of the thermally actuated beams is key to ensuring self-sustained oscillation under sub-100μW level. In particular, shrinking thermal beam cross-sections in 2D is a novel and effective approach to achieve better figure of merit (e.g., FOM defined by the ratio of transconductance g_m to dc power consumption P_DC) of the self-sustained oscillators. By using proper control of silicon etching (ICP) recipe, the sub-micron cross-sectional dimensions of the thermally actuated beams can be easily and reproducibly fabricated in one process step. The phase noise of the proposed wing-type oscillators is also investigated in this work with -93.41 dBc/Hz at 1-kHz offset and -97.95 dBc/Hz at 100-kHz offset in air, and -95.9 dBc/Hz at 1-kHz offset and -95.7 dBc/Hz at 100-kHz offset in vacuum, respectively.