Fabrication And Properties Of Carbon-Based Nanogap Triode

Though millimeter wave system has exceptional advantages such as large bandwidth,high data rates and low latency,it still suffers from high free-space path-loss which bringing higher performance requirement of power amplifier(PA)including output power,operating frequency and efficiency.Solid state devices and vacuum tube are two technology most used for radiofrequency(RF)devices,however,both solid-state PAs and vacuum tube PAs are faced with challenges,on one hand,the output power and efficiency of solid-state PAs decreases with increasing frequency because of material limitations.On the other hand,the applications of vacuum tube PAs are limited by their poor scalability.Vacuum field emission devices(VFED)are scalable and expected to be integratable,besides,electrons can move ballistically in typical vacuum field emission devices.Therefore,Nanogap triodes which are a typical VFED are expected to be optional devices for mm-wave communication system.Nevertheless,nanogap triodes are suffering from low operating frequency,small current and poor reliability,which impedes the development of nanogap triodes as power devices at mm-wavelength.In this paper,lateral carbon nanotube(CNT)nanogap triode is proposed to improve the performances of nanogap triodes.Small-signal model is employed to understand the specific requirements for the properties of nanogap triodes as power devices at mm-wave.The RF characteristics of back-gate,coplanar-gate and gate-all-around nanogap triode derived from small-signal model indicates that gate-all-around nanogap triode can achieve power amplification by increasing the number of emitter tips that are put parallelly to improve power gain although it is hard for single emitter tip to achieve unity power gain.Additionally,gate-all-around nanogap triode with cut-off frequency and the maximum frequency of oscillation can be in the range of frequencies of mmwave even larger than 300 GHz.These results imply that more than one CNT are probably needed to form emitter of gate-all-around nanogap triode to amplify mm-wave signal.In order to fabricate emitter with more than one CNTs in a lateral nanogap triode,Single wall carbon nanotube(SWCNT)and multiwall carbon nanotube(MWCNT)random networks and aligned CNTs are fabricated using solution-based deposition and dielectrophoresis(DEP)respectively.And the effects of these two methods on the quality of CNT random networks and aligned CNTs are investigated to provide design and fabricating guidance to lateral nanogap triodes based on CNT random networks and aligned CNTs.Lateral nanogap triodes based on random CNT networks and aligned CNTs are fabricated using processes based on solution-based deposition and DEP,the influences of processes and structures on performances of lateral CNT nanogap triodes are studied as well.Nanogap triodes based on aligned SWCNTs fabricated by DEP can avoid adverse effects on field emission property caused by the fabricating processes based on solution-based deposition.In this case,the lateral CNT nanogap triodes based on DEP are expected to achieve better performances by optimizing structure parameters.Processes based on DEP provide a basic and feasible method to fabricate arrays of gate-all-around nanogap triodes,therefore,it is helpful to realize potential of gate-all-around nanogap triodes as devices for mm-wave communication systems.