We demonstrate the wafer-scale integration of single electron memories based on carbon nanotube field effect transistors (CNFETs) using a process based entirely on self assembly. First, a "dry" self assembly step based on chemical vapor deposition (CVD) allows the growth and connection of CNFETs. Next, a "wet" self-assembly step is used to attach a single 30 nmdiameter gold bead in the nanotube vicinity via chemical functionalization. The bead is used as the memory storage node while the CNFET operated in the subthreshold regime acts as an electrometer exhibiting exponential gain. Below 60 K, the transfer characteristics of goldCNFETs show highly reproducible hysteretic steps. Evaluation of the capacitance confirms that these current steps originate from the controlled storage of single electrons with a retention time that exceeds 550 s at 4 K.
We present a full process based on chemical vapour deposition that allows fabrication and integration at the wafer scale of carbon-nanotube-based field effect transistors. We make a statistical analysis of the integration yield that allows assessment of the parameter fluctuations of the titanium-nanotube contact obtained by self-assembly. This procedure is applied to raw devices without post-process. Statistics at the wafer scale reveal the respective role of semiconducting and metallic connected nanotubes and show that connection yields up to 86% can be reached. For large scale device integration, our process has to implement both wafer-scale self-assembly of the nanotubes and high transistor performances. In order to address this last issue, a gate engineering process has been investigated. We present the improvements obtained using low and high κ dielectrics for the gate oxide.
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