Study On Piezoresistive Double Clamped Silicon Nano-beam

There is a growing attention in using NEMS resonator as trace sensors for biological detection and other applications, and the resonance response measurement on the nanometer scale is becoming one key technologic concern. Among the mainstream methods for resonance detection of the silicon resonators, the piezoresistive method has been proved useful since it is easy to implement and can be integrated directly into related devices. However, once the thickness of the NEMS resonator is decreased to nanometer values, the fabrication of a well-confined sensing region on the surface becomes extremely difficult. In this dissertation, a simple method for the measure of piezoresistance in nanoscale thick silicon resonator is explored, which is helpful to accelerate the application of the NEMS resonator.We present a technologic scheme for fabricating piezoresistor in nano-sized double clamped silicon beam in a creative manner by selectively implanting Argon ion into the nanometer thick silicon beam. The principle of the method can be understood as follows. High energy Argon ion implantation destroys the atomic structure of the top side silicon beam and produces a buried amorphous layer in the implanted silicon, which hence posseses a high concentration of broken bonds, thus, reducing the conductivity, and achieving a conductivity gradient along the longitudial direction, since the unimplanted layer underneath could maintain its atomic structure and conductivity. Therefore, the silicon beam demonstrates its piezoresistivity.The noise mechanism and damping mechanism in the micron and nanometer devices have been summarily introduced. Subsequently, we also analyse and calculate the resonance frequence and the resonant mode of the double-clamped beams in principle, and achieve the structure design of the NEMS resonator. Based on the comparison of the drive methods in the micron and nanometer devices, we decide to employ an electrostatical drive in our experiments. Besides, the piezoresistive character of the silicon has been introduced, and the piezoresistive shift of the silicon beam on nanometer scale has been analyzed.We adopt the method based on the MEMS technology for the fabrication of the nanometer scale devices, and emphasize the character of the KOH anisotropic etch technique. The double clamped silicon nano-beam with a thickness of approx 200nm has been fabricated via KOH anisotropic etching as well as other conventional MEMS processes. Thereafter, piezoresistive sensors were fabricated in the double-clamped silicon beam by selective implanting Argon ion into the silicon beam.Both the electrostatical drive and the piezoresistive detection systems are established for detecting the piezoresistive excusion and the vibration of the double clamped silicon nano-beams. The measurement of the piezoresistive excusion shows that the piezoresistance changs 0.5% per voltage with the electrostatical drive. We achieve the detection of the resonant response of the double-clamped Si nano-beam in the atmosphere. The resonant frequency and Q-factor are obtained, which are 400KHz and 7.9 respectively. Not least, a much higher Q factor of 394 has been realized by an anneal experiment. Therefore, we confirm that the moderate anneal can partly repair the damage incluced by Argon ion implantation, and nonetheless reduce the energy dissipation, this is helpful for the application since the piezoresistive character remains and whereas Q-factor is improved meanwhile.