Enabling fabrication of clean electrical contacts to carbon nanotubes using oxygen plasma ashing

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A fabrication approach to preserve the clean metal‐SWNT interface in individual based carbon nanotube field‐effect transistors (CNFETs) from substrate‐bond tubes is presented. The occurrence of resist residues at these interfaces is avoided because they otherwise have a strong influence on the CNFET contact resistance and variability. In this work, enabling the use of oxygen plasma ashing to remove resist impurities originating from the lithographic process by using a sacrificial alumina layer is demonstrated. Direct application of oxygen plasma in the CNFET standard fabrication process flow is not possible due to damage of unprotected SWNTs, while an alumina layer thicker than ∼18 nm is sufficient to protect substrate‐bond individual carbon nanotubes from the impact of mild ashing treatment (100 W, 1 min). Using this approach, a clear improvement of the contact resistance of the devices compared to devices fabricated without plasma treatment is demonstrated. The median on‐resistance for alumina passivated, Pd/Au‐contacted CNFETs reached 190 kΩ which is 66% lower than the one of devices prepared without using sacrificial layer and oxygen plasma treatment. Importantly, the interquartile dispersions of the device on‐resistance and hysteresis width were largely narrowed from 2050 to 247 kΩ and 3.7 to 1.2 V, respectively.