Spontaneous mechanical oscillation of a DC driven single crystal

TL;DR

This paper demonstrates that a single crystal silicon nanobeam can spontaneously oscillate under a constant DC current due to an electrothermomechanical feedback mechanism, enabling miniaturized and highly sensitive mechanical oscillators.

Contribution

It introduces a novel self-oscillation phenomenon in a DC-driven single crystal silicon resonator driven by electrothermal feedback, expanding potential applications in miniaturized sensors and timing devices.

Findings

Spontaneous oscillation occurs in a silicon nanobeam under DC current.

Oscillation is sustained by electrothermomechanical feedback.

Effective in nano-scale conducting beams.

Abstract

There is a large interest to decrease the size of mechanical oscillators since this can lead to miniaturization of timing and frequency referencing devices, but also because of the potential of small mechanical oscillators as extremely sensitive sensors. Here we show that a single crystal silicon resonator structure spontaneously starts to oscillate when driven by a constant direct current (DC). The mechanical oscillation is sustained by an electrothermomechanical feedback effect in a nanobeam, which operates as a mechanical displacement amplifier. The displacement of the resonator mass is amplified, because it modulates the resistive heating power in the nanobeam via the piezoresistive effect, which results in a temperature variation that causes a thermal expansion feedback-force from the nanobeam on the resonator mass. This self-amplification effect can occur in almost any conducting material, but is particularly effective when the current density and mechanical stress are concentrated in beams of nano-scale dimensions.