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Register a new userSelf-assembly of carbon-nanotube-based single electron memories
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We demonstrate wafer-scale integration of single electron memories based on carbon nanotube field effect transistors (cnfets) by a complete self assembly process. First, a dry self assembly based on a Hot Filament assisted Chemical Vapor Deposition technique allows both localized growth and in situ electrical connection of carbon nanotubes on predefined catalytic electrodes. The semiconducting carbon nanotubes integration yield can exceed 50% for a batch. Secondly, a wet self-assembly attaches single 30 nm-diameter gold bead in the nanotube vicinity via chemical functionalization. The bead acts as the memory storage node while the cnfet operated in the subthreshold regime is an electrometer having exponential gain. Below 50 K, the transfer characteristics of some functionalized cnfets show highly reproducible hysteretical steps whose height can reach one decade of current. Evaluation of the capacitance confirms these current steps originate from single electron transfers between the bead and the nanotubes with a time retention exceeding 550s at 1.5K.
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Junctionless transistors made of silicon have previously been demonstrated experimentally and by simulations. Junctionless devices do not require fabricating an abrupt source-drain junction and thus can be easier to implement in aggressive geometries. In this paper, we explore a similar architecture for aggressively scaled devices with the channel consisting of doped carbon nanotubes (CNTs). Gate all around (GAA) field effect transistor (FET) structures are investigated for n- and p-type doping. Current-voltage characteristics and sub-threshold characteristics for a CNTbased junctionless FET is compared with a junctionless silicon nanowire (SiNW) FET with comparable dimensions. Despite the higher on-current of the CNT channels, the device characteristics are poorer compared to the silicon devices due to the smaller CNT band gap.
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