Nanoelectromechanical Studies of Suspended Resonators using Graphene grown by Chemical Vapour Deposition

Abstract

Graphene is an ideal material for high quality nanoelectromechanical resonators due to its high Young's modulus, low mass to surface ratio, ability to sustain high in-plane strain, and unique electrical properties like high carrier mobility, ballistic transport and nonlinear modulation of conductance under the electric field effect. In this work, atmospheric pressure chemical vapour deposition (CVD) is employed to obtain monolayer graphene on copper. The effect of growth parameters such as gas concentration, growth temperature and growth time are studied and optimized such that predominantly monolayer graphene is obtained. Scanning electron microscopy and Raman analysis reveal the presence of high quality, monolayer graphene. The graphene is transferred to Si/SiO_{2} wafers and multiple step electron beam lithography, metal deposition, substrate etching, and critical point drying are used to fabricate suspended graphene doubly-clamped resonators. The present fabrication technique, thus combines top-down and bottom-up fabrication method and presents an important work in the development of batch-processing of large area graphene towards future industrial applications. Modeling the suspended devices as Duffing resonators near their fundamental flexural mode shows the presence of mechanical nonlinearity in response to an applied force even at moderate bias voltages. We discuss the implications of this nonlinearity for parametric amplification. Interesting parametric responses such as gain saturation and presence of multistability are obtained as a result of the complex interplay between the mechanical nonlinearities in graphene suspended resonators. As a final step, a measurement system is developed to electrostatically actuate the suspended devices and read out the motion using nonlinear mixing of graphene's electrical conductivity. The electromechanical data for one such device is analyzed to quantify the resonant frequency and quality factors of three detectable modes. Experimental data for resonance and frequency tunability of the fundamental mode illustrates the presence of mass loading and initial strain in the suspended device. The present work combining the fabrication, modeling and electromechanical measurements are important steps for the prospects of developing measurement techniques for future sensors and quantum-limited mechanical measurements of CVD-grown graphene.