Extraction of the Contact Resistance of Carbon Nanotube Field Effect Transistors Using the Bias Extrapolation Method and Statistical Measurements

Carbon nanotubes (CNTs) offer great potential for both high-integration digital and high-frequency applications due to their unique 1-D carrier transport properties. However, the typically large contact resistance between the source/drain metal and the metal-covered CNT prevents the advantages of CNTs from being exploited. For supporting process development toward lowering the contact resistance and also compact modeling of CNT field-effect transistors (CNTFETs), a method for extracting the contact resistance is proposed. By measuring at sufficiently high gate voltages and subsequent suitable extrapolation toward infinite gate voltage, the bias-dependent components of the total channel resistance can be eliminated to extract the contact resistance. The accuracy of the proposed method was first verified using device simulation and subsequently applied to fabricated CNTFETs. The proposed method is suitable for both single- and multitube CNTFETs as well as for capturing the statistical variation of the contact resistance across the wafer.