Flexible Micro/Nano Electromechanical Structures And Devices Based On Nanowire Morphology Engineering

Crystalline silicon semiconductor materials are the foundation of modern microelectronics and information society.Quasi-one-dimensional crystalline silicon nanowires(SiNWs)structure,with excellent optoelectronic properties,quantum confinement and interface properties,has proven beneficial building blocks for the development of a new generation of high-performance silicon-based optoelectronics,micro/nano electromechanical devices and new flexible wearable electronic applications.However,the traditional "top-down" etching process to obtain SiNWs require electron beam etching(EBL)process,which is costly,inefficient and low in yield.In addition,crystalline silicon cannot be directly applied in flexible devices due to its rigidity and brittleness,thus elastic-shape nanowire is necessary to achieve its high stretchability.In the traditional way of nanowire growth by vapor-liquid-solid(VLS)mode,the use of gaseous supply leads to the insufficient morphology control of the nanowires.Herein,we applied a new silicon nanowire growth mode "bottom-up"of in-plane solid-liquid-solid(IPSLS),which uses a lower melting point metal such as indium as the catalyst droplet.While absorbing the amorphous silicon film deposited on the surface of the substrate,the crystalline silicon nanowires are deposited and grown along the guiding steps.The IPSLS growth mode enables a programmable topography design of the ultra-long planar silicon nanowires by pre-designed surface guiding edge patterns.In this paper,the SiNW structures of different morphologies were defined by lithography.Suspended SiNW bridges,loops and nano-grippers were successfully prepared by using dry/wet etching technology and reliable transfer processing.Subsequently,structural characterization and theoretical simulation of the suspended silicon nanowire structure arrays were conducted.The electrical and mechanical properties of these structures were studied,and the movement of suspended nanowire structures under electromagnetic interaction was designed to realize new program of specific functionality of NEMS devices.In addition,the stretchable crystalline silicon nanowire channel is realized by elastic shape design of the nanowire.The major innovations of this thesis work can be summarized as the following four aspects:1.The morphology engineering and realization of suspended SiNW rings,as well as structural optimization and testing.By using a conventional plasma enhanced chemical vapor deposition(PECVD)system,the SiNWs were grown via a wellcontrolled IPSLS growth an effective approach to overcome the adverse effect of the surface tension of the solution during the silicon nanowires suspending,thus obtained the suspended annular silicon nanowires.The structure,mechanical simulation analysis and preliminary electrical and magnetic testing were systematically characterized.2.The array of suspended silicon nano-grippers were designed and fabricated,and its structural characterization and simulation were carried out.Based on the preparation of silicon nanowires in IPSLS growth mode,combined with wet etching technology,critical point drying technology and SU-8 lithography transfer technology,the fabrication of suspended silicon nano-grippers structure arrays was realized.The silicon nano-grippers is simulated to achieve "open" and "closed" operation under the opposite electric field,which provided a key foundation for the final realization of NEMS devices such as biological cell detection.3.A planar annular SiNWs array was designed.The synergistic effect of magnetic field and electric field on the vibration of planar SiNWs ring was explored by depositing the magnetic film material.The preliminary experiment was designed to realize the magnetic read and write function with the electric field manipulation through the electric manipulation of the magnetic medium and the impedance change generated by the silicon loop under the alternating current,thereby improving the recording density and the information storage resolution.4.A two-dimensional wavy SiNWs spring network was obtained.The stretchable SiNWs network was prepared by IPSLS growth mechanism and then transferred onto the flexible substrate.This study will break the technical bottlenecks that limited the application of crystalline silicon nanowires in flexible electronic devices.While considering the advantages of high performance and high stability of silicon nanowires,the avenue is expected to realize the application of flexible electronic devices on wearable electronic devices and biosensors.