Zero-Power Electrically Tunable Micromechanical Photoswitches

Micromechanical photoswitches (MPs) have shown orders of magnitude lower standby power consumption compared to their solid-state technology-based counterparts. In this paper, we demonstrate that the infrared detection threshold (i.e., the lowest detectable power of incident infrared radiation) of this new type of photoswitch can be effectively decreased by applying a bias voltage across the switch without compromising its key feature of near-zero standby power consumption and low false-alarm rate. We show that by exploiting the electrostatic pull-in effect (using bias voltage of ~7 V), a threshold as low as 76 nW can be achieved, which is the lowest threshold demonstrated to date for MPs. A mathematical model predicting the device threshold under a bias voltage is derived and verified by experiments. Furthermore, the effects of the bias on the device's stability are carefully studied suggesting the existence of a tradeoff between the detection threshold and the false-alarm rate when the bias is higher than 85% of the pull-in voltage. The source of the instability that causes false alarms is found to originate from charge accumulation over time in the dielectric substrate surrounding the bottom contact, which we believe can be mitigated by an improved contact design. Another effect associated with high bias is the contact stiction after infrared-triggered pull-in. To address this, a microheater is integrated into the switch to reopen the contacts while consuming only ~0.5 μJ per operation. This paper thus presents an effective solution for post-fabrication threshold adjustment of MPs, which is useful for applications requiring variable thresholds.