Paper MN+NS-MoA8
Silicon Carbide (SiC) Optical Interferometry for Ultrasensitive Motion Transduction of High Frequency Mechanical Resonators

Monday, October 28, 2013, 4:20 pm, Room 102 A

We report on the first experimental demonstration of an ultrasensitive laser optical interferometric technology based on thin-film silicon carbide (SiC) micromechanical and nanomechanical resonant systems, which offer motion transduction with displacement sensitivities down to the sub-10fm/rtHz level, at room temperature.

Position and motion detection with advanced optical techniques have been widely used for studying the static and dynamic motions of various systems, ranging from the classical scanning probe microscopes to the emerging resonant nano/microelectromechanical systems (NEMS/MEMS). In particular, in recent years significant efforts and advances [1,2] have been made in developing laser optical interferometric systems based on various NEMS/MEMS resonators, with constituting materials in Si, SiN, GaAs, AlN, and more recently two-dimensional (2D) crystals such as graphene and MoS₂. These advances have kept enabling very sensitive detection of motions in various NEMS/MEMS resonators, with ever improving displacement sensitivities, from ~nm/rtHz to ~pm/rtHz levels. In many of these systems, there are limitations intrinsic to the device structures and constituting materials. For instance, light absorption and parasitic heating effects can compromise these interferometric systems from achieving better sensitivities.

In this work, we explore new optical interferometric techniques by exploiting some unique properties of SiC thin films, particularly the high transparency and ultralow photon absorption (60 times lower than Si) in the wide visible range, as well as the excellent thermal conductivity. The SiC thin films are prepared by low-pressure chemical vapor deposition (LPCVD) on various substrates, which enables us to develop a novel SiC-on-SiO₂ material platform. The suspended MEMS/NEMS devices fabricated in this thin-film platform all share important features such as smooth surfaces and a uniform interferometric gap. These structural features, combined with SiC’s outstanding physical properties, have permitted us to demonstrate unprecedented displacement sensitivities at ~5-10fm/rtHz levels, better than other MEMS/NEMS-based optical interferometric techniques reported to date. We demonstrate such ultrasensitive techniques for motion detections in high frequency SiC microdisk resonators and nanocantilever resonators. In both systems, we have measured the undriven, intrinsic thermomechanical resonances up to high-order modes.