Eliminate the transmission feedthrough of thermal‐piezoresistive I ² ‐BAR MEMS resonators based on reverse‐biased PN junction

The thermally driving and piezo‐resistive sensing I ² ‐BAR resonators have attracted substantial attentions due to its promising features which could be widely applied for radio frequency) applications. However, one major drawback of the I ² ‐BAR resonators is that the thermal driving and the piezoresistive sensing signals are highly coupled which results in an excessive transmission feedthrough floor, masking thus the real resonance behaviours. In this work, a simple and effective approach to eliminate the feedthrough effect using reverse‐biased PN junction is presented. The device was fabricated on a p‐type silicon‐on‐insulator wafer with locally doped n‐type regions. With proper bias voltages, the thermal driving current and the output piezoresistive current were confined inside the p‐type layer and the n‐type layer, respectively. With such design concept, an improvement of 50 dB feedthrough reduction was observed comparing with the conventional measurement. The resonance behaviour can thus be physically obtained without further post data processing. This research also shows that such measurement methods can be transferred to other domains where integrated thermal driving and piezoresistive sensing transductions are required.