Study Of NEMS Resonator Based On Field Effect Transistor Detection

Nowadays, it is possible to produce NEMS resonators with dimensions well below 100nm, which show increased eigenfrequencies up to 1GHz. In this frequency range NEMS resonators could serve as filters for information processing applications. Another range of applications emerges from the sensitivity these devices could reach in sensor applications. Using sophisticated detection schemes this might even lead to the quantum limit where e.g. the uncertainty principle might be observed in the motion of a mechanical resonator. NEMS resonators have drawn lots of attention because of these applications. However, as the dimension is so small, it is difficult to develop fabrication and detection method for NEMS resonator. MEMS and NEMS resonators are suitable for aeronautical and astronautical application because of their small size and low power consumption. But there is radiation in the outer space, mechanical property of the resonator will change due to radiation. A little research work has been done on this area.This work has done some researches on fabrication and detection method for NEMS resonators, noise characteristic and mechanical radiation damage for MEMS/NEMS resonators.Crystal-silicon nano-beam, with one hundred nanometers thickness, is fabricated on the top silicon of N-type SOI wafer. PNP junction is formed on the beam. P-channel air-gap thin film transistor (TFT) is obtained after the oxide layer under the beam removed, with the PNP junction as drain, channel and source, and the substrate of the SOI wafer as gate. Such an air-gap TFT can be used for vibration detection of the silicon beam. The electric characteristic of the as-released air-gap TFT is very poor. After treated in O₂ and N₂ plasma for 5 minutes, the characteristic is significantly improved. Negative resistance phenomenon in the output curve because of the beam motion is observed.It is found that n-type area of pn junction can be selectively etched by BOE solution without illumination, with etching rate lower than 1nm/min. The possible mechanism of the etching phenomenon is discussed. A simple fabrication process for NEMS resonator is proposed according to the above phenomenon. In this process only traditional micro-electromechanical system technology is used. Dimension of the fabricated nano-wire can be controlled well. A 50nm wide and 50nm thick resonator has been formed using this method.Liu et al developed a fabrication process for NEMS resonator based on TMAH anisotropic etching. Si₃N₄ is used as the etching mask. Using SiO₂, instead of Si₃N₄, as the etching mask, a NEMS resonator, with a few hundreds nanometer width and a few tens nanometer thickness is successfully fabricated. The fabrication process is more simple and easier to control.A simple noise model for MEMS/NEMS resonator is established. Simulation results indicate that the noise near the eigenfrequencies is determined by the Brownian noise, but the noise far from the eigenfrequencies is determined by the temperature fluctuation noise, Johnson noise and the Brownian noise. The noise becomes small when the resonator works at high vacuum and low temperature.Changes in the eigenfrequencies and Q of the MEMS/NEMS resonator have been detected by the electron and gamma ray radiation experiment. A simple mechanical radiation damage theory is established based on these results. Disfigurement will be produced in the semiconductor material by radiation. The disfigurement is unabiding and it can be annealed at room temperature.