Paper GR-TuP7
Chemical Vapor Deposited Graphene-Based NEMS Resonators

Tuesday, October 19, 2010, 6:00 pm, Room Southwest Exhibit Hall

Graphene is a superb structural material for NEMS resonators because of its unique electrical and mechanical properties. Excellent material properties of graphene such as good conductivity, single atomic thickness layers, large surface area, low mass density, and high Young’s modulus as compared to other materials allow optimization of the resonance response to approach the ultimate limit for two dimensional NEMSs. Single device resonator has been studied extensively in the past with very high Q-factor and resonant frequency. However, for device technology, arrays of resonators provide a wider range of applications which appear to be possible in graphene based resonators. Figure 1 summarizes the fabrication process of the graphene resonators and Figure 2 presents a 3D schematic of graphene resonator array, indicating key parts and the materials. We have grown the monolayer quality graphene using thermal chemical vapor deposition method on Ni coated substrates at 1000˚C using a mixture of argon, hydrogen and methane as precursor gases. It was observed that growth time and thickness of Ni films are key parameters for controlling the number of layers of graphene. Initial results suggest the formation of 1-5 layers of graphene which was estimated from AFM, TEM and 2D peak intensity of Raman spectra [Figure 3]. Hall Effect data show mobility ~ 1500 cm²/V and resistivity of 2X10⁻⁶ Ω·cm for 3 layer graphene. Graphene was released from Ni by wet chemical etching and the layers were transferred onto SiO₂/ Si substrate. In order to employ graphene as a major building block, NEMS resonator structures were created by transferring a patterned graphene layer onto a silicon-on-insulator (SOI) substrate to act as mechanical interconnects. The Si device layer in SOI substrate is patterned by deep reactive ion etching (DRIE) using SiO₂ as hard mask to create the resonator body. An ultra-thin layer of high-k dielectric material is uniformly deposited by atomic layer deposition (ALD) followed by deposition and doping of a poly-Si layer. A lithography process is done to create the shape of the double side electrodes. Thereafter, the graphene is transferred and attached to the resonator bodies to complete the array. Finally, the resonator array is released by removing the buried SiO₂ in the SOI substrate.