Carbon-based electronics is an emerging field. Its present progress is largely dominated by the materials science community due to the many still existing materials-related obstacles for realizing practically competitive transistors. Compared to graphene, carbon nanotubes provide better properties for building field-effect transistors, and thus, have higher chances for eventually becoming a production technology. This paper provides an overview on the state-of-the-art of CNTFET technology from an electrical engineering and radio frequency analog applications point of view. Important material properties, resulting device structures, their fabrication, and the most relevant modeling concepts are briefly reviewed. Furthermore, recent results on device and circuit performance and the future prospects are presented in the context of practical requirements and applications.
A compact large-signal model, called Compact Carbon Nanotube Model (CCAM), is presented that accurately describes the shape of DC and small-signal characteristics of fabricated carbon nano-tube FETs (CNTFETs). The new model consists of computationally efficient and smooth current and charge formulations. The model allows, for a given gate length, geometry scaling from single-finger single-tube to multifinger multitube transistors. Ambipolar transport, temperature dependence with self-heating, noise, and a simple trap model have also been included. The new model shows excellent agreement with the data from both the Boltzmann transport equation and measurements of Schottky-barrier CNTFETs and has been implemented in Verilog-A, making it widely available across circuit simulators.
IndexTerms-Carbon nanotube field-effect transistor (CNTFET), compact transistor modeling, high-frequency circuit design.
Experimental results gained by various electrical characterization techniques are discussed and compared for a CNTFET technology, which suffers as almost all emerging technologies from traps in the gate oxide. Based on these results, it is highlighted that, contrary to common practice, a fast data acquisition technique is required to ensure a proper electrical device characterization in terms of (i) trap-free device characteristics, (ii) reproducible experimental results and (iii) a consistent set of DC and small-signal (AC) characteristics. It is argued that a reasonable technology comparison among emerging technologies must be based on data fulfilling these criteria since trap-affected measurements distort the device behavior which can lead to wrong conclusions about the performance of a device such as the apparent linearity. A trap model capturing the above mentioned issues is briefly introduced. Moreover, the challenges of the electrical characterization of high-impedance devices are explored.
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