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Tunable Graphene Based Nanoelectromechanical Resonators

One of the major challenges in producing highly accurate graphene-based sensors and filters is the poor fabrication repeatability of graphene resonators due to small variations in the residual stress and initial tension of the graphene film. This has meant that graphene-based nanoelectromechanical resonators tend to have large variations in natural frequency and quality factor from device to device. This poor repeatability makes it impossible to use these resonators to make accurate, high-precision force and displacement sensors or electromechanical filters. However, by actively controlling the tension on the graphene resonator it is possible both to increase repeatability between devices and to increase the force/mass sensitivity of the nanoelectromechanical resonators produced. Such tension control makes it possible to produce electrometrical filters that can be precisely tuned over a frequency range of up to several orders-of-magnitude. In order to controllably strain the graphene resonator, a microelectromechanical system (MEMS) is be used to apply tension to the graphene. The MEMS device consists of a graphene resonator connected between a set of gold electrodes. Each gold electrode is located on a different MEMS stage. Each stage is connected to a set of flexural bearings which are used to guide the motion of the stage. The displacement stage is actuated using a thermal actuator that allows a uniform and constant tension to be applied to the graphene resonator. The displacement of the actuator and the tension applied to the graphene are measured using a pair of differential capacitive actuators. The resonator is actuated electrostatically using the electrical backgate, and the resonant frequency is measured from the change in conductance of the graphene as it approaches resonance. Using this setup, it is possible to tune the natural frequency of the graphene resonator with high precision and accuracy.