In this paper, we present comprehensive analysis of the nonlinearities in a micromechanical clamped-clamped beam resonator. A nonlinear model which incorporates both mechanical and electrostatic nonlinear effects is established for the resonator and verified by experimental results. Both the nonlinear model and experimental results show that the first-order cancellation between the mechanical and electrostatic nonlinear spring constants occurs at about 45 V dc polarization voltage for a 193 kHz resonator in vacuum pressure of 37.5 µTorr.Our study also reveals that the nonlinearity cancellation is helpful in optimizing the overall resonator performance. On top of improving the frequency stability of the resonator by reducing its amplitude-frequency coefficient to almost zero, the nonlinearity cancellation also boosts the critical vibration amplitude of the resonator (0.57 µm for the beam resonator with 2 µm nominal gap spacing), leading to better power handling capabilities. The results from the clamped-clamped beam resonator studied in this work can be easily generalized and applied to other types of resonators.

In this paper, we present a systematic characterization and modeling technique for the micromechanical free-free beam resonator to analyze its nonlinear vibration behavior. Different from the conventional FEM-based approach whose simulation accuracy is usually limited around 60-70%, the proposed modeling method is able to accurately identify both the mechanical and electrostatic nonlinear parameters from just a few preliminary experimental observations. The nonlinear equation of motion is then numerically solved, demonstrating both the spring hardening and softening effects in the system. The simulated nonlinear behavior of the resonator under different driving conditions is validated by comparing them with the experimental data. In addition, based on the verified nonlinear model, design guidelines such as the nonlinearity cancellation are also highlighted. Although this work focuses on the free-free beam resonators, the proposed modeling approach can be applied to any other electrostatically driven microresonator to reveal different intrinsic nonlinear properties of the device.

The piezoresistance and noise of n-type gate-all-around nanowire field-effect-transistor (NWFET) is investigated as a function of gate bias. With narrow gate bias span of 0.6 V near threshold region, the piezoresistive coefficient of NWFET enhances up to seven times from 29 × 10−11 Pa−1 to 207 × 10−11 Pa−1 under compressive and tensile strain conditions. Results reveal that the low frequency noise is reduced when operated in subthreshold region. The higher piezoresistive coefficient and reduced noise improve the sensor resolution (minimum detectable strain) by sixteen times. NWFET operates at low bias with higher piezoresistance and signal-to-noise ratio and offers promising applications in strain sensors.