Preparation And Characterization Of Ferroelectric Field Effect Transistor With Regular And Aligned MWCNTs Stripe Arrays As Channel Layer

Ferroelectric field effect transistor (FeFET) has many advantages such asnon-volatility, anti-radiation, high access speed, high endurance, high density storageand low power consumption, which can be used as a unit structure of ferroelectricmemory. The conventional FeFET is top-gate type, while the problems such asinterface diffusion, the depolarization field and complex preparation technology existin this FeFET, which hinder its applications. In recent years, a new bottom-gate typeFeFET unit structure attracted much attention due to its simple fabrication process,none buffer layer needed, excellent interface properties and being easy to realize allepitaxial structure and flexible devices. Carbon nanotube (CNT) has become a newfavorite channel material because of its high conductivity and large carrier mobilityand has widely applied in conventional field-effect transistor (FET). In the researchesof conventional FET, it is found regular and aligned CNT micron-wide stripe arraysare more beneficial to be the channel of FET than single nanowire or nanowirenetwork CNT. In this thesis, we thus develop and prepare a new bottom-gate typeFeFET with regular and aligned micron-wide stripe arrays of multiwall carbonnanotubes (MWCNT) as channel layer and Bi3.15Nd0.85Ti3O12(BNT) as ferroelectric-gate insulator. The main research contents and obtained results are summarized asfollows.(1) Preparation and characterization of BNT thin filmsThe BNT thin films were prepared on the heavily doped n-Si of22cm2bysol-gel method, in which the n-Si was used as substrate and bottom gate electrodesimultaneously. The microstructure and electrical properties of the BNT thin filmwere characterized. The results suggest that the prepared BNT thin films exhibit goodthickness uniformity, excellent ferroelectricity and high dielectric constant, whichmeet the standards of insulation layer for FeFET.(2) Preparation and characterization of regular and aligned MWCNTmicron-wide stripe arraysThe MWCNT micron-wide stripe arrays were fabricated using evaporation-induced self-assembly technique. The influences of solution concentration (60-5mg/L), self-assembly temperature (40-90oC) and tilted angle of substrate (45-90°) onthe morphologies of the MWCNT stripe arrays were studied. The MWCNT stripesprepared with the solution concentration of8mg/L, self-assembly temperation of65oC and tilted substrate angle of80°display remarkable regularity, which is very useful for application of channel layer in FeFET.(3) Preparation and characterization of MWCNT/BNT/Si-FeFETBased on the above studies, the bottom-gate type MWCNT/BNT/Si-FeFET wasfabricated and its output and transfer characteristics were analyzed. The results showthe prepared MWCNT/BNT/Si–FeFET possesses large “on” current, high Ion/Ioffratio,high channel carrier mobility, wide memory window, low subthreshold swing and lowthreshold voltage, which are1.510-2A,103,94.47cm2V-1s-1,4.38V,0.37V/decadeand1.6V, respectively. The excellent electrical performances are mainly attributed tothe special structure of MWCNT stripe array channel as well as the large spontaneouspolarization and high dielectric constant of BNT thin film.