Study Of Electromechanical Coupling Properties In Silicon And Graphene NEMS

Nano electromechanical systems (NEMS) are devices integrating electrical and mechanical functionality on nanometer scale. They are scaled down from micro electromechanical systems (MEMS), while also have distinguished characteristics due to the nanoscale dimensions. NEMS have advantages including small sizes, light active masses, high resonant frequencies, high quality factors, etc., which draw plenty of interest from both scientific and industrial communities. These advantages make NEMS suitable for ultrafast sensors or actuators, signal processing components and chemical substances detectors. Moreover, NEMS are expected to explore phonon mediated mechanical processes and quantum behavior of mesoscopic mechanical systems experimentally. Among the most important challenges of NEMS technology are the actuation and detection methods which do not rely on critical temperature or pressure environment, avoid using expensive equipments, and facilitate batch manufacturing. The methods also need to detect nanoscale displacement in high frequency. Besides, due to the air damping, realization of high quality factor in atmosphere is challenging.Traditional NEMS utilize materials in semiconductor industry as the moving components, so that silicon becomes the natural selection. This paper studies detection method of silicon NEMS devices based on field effect. Suspended channel field effect transistor (FET) is fabricated and the processes are improved to enhance stability of devices and provide ways making silicon nanowires. Meanwhile, theory of strained-silicon FET is used to calculate carrier mobility in strained channels, and finite element analysis is used to calculate the displacement of suspended beam versus bias voltage. Combining these simulation results, accurate electromechanical model is built to describe the I-V curves of NEMS devices. This model is used to verify the experimental transfer and output characteristics, including the negative differential resistance effect discovered. Good consistency is obtained.Graphene is one monolayer of carbon atoms that packed into two-dimensional hexagonal honeycomb lattice. Graphene is suitable to fabricate NEMS devices due to its outstanding mechanical, electrical and thermal properties. Previous experimental and theoretical works have made much progress on graphene NEMS. while systematic study of the electromechanical properties is still lacking. This paper uses tight-binding and density functional theories which consider the quantum effect in nanoscale, to study the electromechanical properties which are common issues in grapheme NEMS applications. These issues include electronic properties of deformed graphene, transport properties of step-shaped graphene, mechanical buckling and consequent electronic properties of graphene under compressive strain. Furthermore, two typical graphene NEMS devices, namely microwave switch and pressure sensor, are studied to investigate the characteristics in practical applications. These results prove that graphene is suitable to make NEMS devices with high sensitivity, high on/off ratio and excellent flexibility, while also provide structural parameters as references for design and fabrication.In summary, this paper studies NEMS devices made of silicon or graphene, focusing on electromechanical coupling models to analyze electronic properties under mechanical deformations. Our simulation results reveal the characteristics and perspectives of the two types of materials in NEMS applications, providing references to device fabrications and theory basis for analyzing experimental results.