Experimental characterization and compact modeling of high-field effects in CNTFET channels

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Compared to conventional bulk semiconductors, semiconducting single-walled carbon nanotubes (CNTs) possess a number of advantageous properties. The latest experimental results of 120 nm CNT field-effect transistors (FETs) obtained in our lab yielded extrinsic cut-off frequencies in the range of 40 GHz. This is approaching the 70 GHz cut-off frequency typical for 130 nm CMOS, despite the just 40 CNTs per micrometer channel width and a drain current of just about 4 microampere per tube. Both values are far below the theoretically achievable density of 600 CNTs/micrometer and already measured drain currents of 20...70 microampere/CNT.For designing competitive high-frequency (HF) circuits based on multi-tube multi-finger CNTFETs, the actually "useable" operating range needs to be known. Studies performed so far have mostly focused on thermal breakdown (and destruction) of metallic CNTs and of CNTs in vacuum or exposed to air. Unfortunately, such studies are not applicable to practically useful planar FET structures, where the CNTs are always embedded within at least one oxide layer. Therefore, this proposal mainly addresses: (1) the experimental characterization of at wafer-scale fabricated planar CNTFETs using different (i) channel formation methods (CVD, dispersion), (ii) gate oxide and isolation materials, and (iii) contact materials and gate arrangements; (2) the investigation and detailed understanding of the various physical breakdown mechanisms (avalanche, tunneling, thermal) and their interplay during transistor operation in electronic circuits; (3) the development of a numerically stable compact model for investigating the impact of CNTFET breakdown on the performance of HF circuits.