Towards an Integrated Graphene Nano-Opto-Electro-Mechanical System

Abstract

Micro-electromechanical systems (MEMS) have found extensive applications in micromechanical sensing. The scaling of MEMS into nano-electromechanical systems (NEMS) was spurred primarily by the expectation of higher sensitivity . NEMS resonators offer unique attributes like vibrating frequencies in the radio-frequency (RF) and microwave range and vibrating mass in femtograms. They hold promise for ultra-low mass-sensing, force-sensing, charge-sensing, and study of nonlinear dynamics. One of the most exciting materials for NEMS is graphene, the thinnest mechanical membrane till date. The interesting question is, how the mechanics would behave when the size is scaled to a one or two atomic layers? Characterising mechanical property of such materials becomes extremely challenging with the current techniques. While electrical transduction is quite favourable for MEMS, similar techniques are challenging to implement in case of high frequency NEMS devices. Optical transduction techniques are preferable for NEMS. However, most existing optical transduction techniques are based on free-space optics, where the entire system is bulky, susceptible to noise and precise alignment of optical components poses a challenge. A highly sensitive integrated scheme with ultra-low noise characteristics is essential to probe such a system. In this thesis, I shall discuss about the integration of graphene nano-mechanical resonator over integrated-optic platforms operating at near-IR to form an integrated nano-opto-electromechanical system (NOEMS). The interaction of graphene with near-IR, on-chip optical transduction schemes using optical cavities is rst discussed. A displacement-sensitivity of 28 fm= p Hz has been theoretically estimated using a sensitive integrated-optic device (a micro-ring resonator loaded onto a Mach-Zehnder interferometer). Optical actuation schemes are discussed along with possible applications and implementational challenges. The ability to tune and actuate the mechanical resonance as well as to manipulate mechanical nonlinearity are theoretically demonstrated. Furthermore, integration of transparent electrodes over waveguides for manipulation of the mechanical resonance as well as the optical cavity, for cavity-optomechanical experiments, is discussed. Finally, the complete structure of the system and its fabrication are discussed