Frequency response of a new kind of silicon nanoelectromechanical systems resonators

Diffraction effects will bring about more difficulties in actuating resonators, which are electrostatically actuated ones with sub-micrometer or nanometer dimensions, and in detecting the frequency of the resonator by optical detection. To avoid the effects of diffraction, a new type of nanoelectromechanical systems (NEMS) resonators is fabricated and actuated to oscillate. As a comparison, a doubly clamped silicon beam is also fabricated and studied. The smallest width and thickness of the resonators are 180 and 200 nm, respectively. The mechanical oscillation responses of these two kinds of resonators are studied experimentally. Results show that the resonant frequencies are from 6.8 to 20 MHz, much lower than the theoretical values. Based on the simulation, it is found that over-etching is one of the important factors which results in lower frequencies than the theoretical values. It is also found that the difference between resonance frequencies of two types of resonators decreases with the increase in beam length. The quality factor is improved greatly by lowering the pressure in the sample chamber at room temperature.