Y-Contacted High-Performance n-Type Single-Walled Carbon Nanotube Field-Effect Transistors: Scaling and Comparison with Sc-Contacted Devices

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Abstract
While it has been shown that scandium (Sc) can be used for making high-quality Ohmic contact to the conduction band of a carbon nanotube (CNT) and thus for fabricating high-performance n-type CNT field effect transistors (FETs), the cost for metal Sc is currently five times more expensive than that for gold and one thousand times more expensive than for yttrium (Y) which in many ways resembles Sc. In this Letter we show that near perfect contacts can be fabricated on single-walled CNTs (SWCNTs) using Y, and the Y-contacted CNT FETs outperform the Sc-contacted CNT FETs in many important aspects. Low-temperature measurements on Y-contacted devices reveal that linear output characteristics persist down to 4.3 K, suggesting that Y makes a perfect Ohmic contact with the conduction band of the CNT. Self-aligned top-gate devices have been fabricated, showing high performance approaching the theoretical limit of CNT-based devices. In particular a room temperature conductance of about 0.55G0 (with G0 = 4e2/h being the quantum conductance limit of the SWCNT), threshold swing of 73 mV/decade, electron mobility of 5100 cm2/V·s, and mean free length of up to 0.639 μm have been achieved. Gate length scaling behavior of the Y-contacted CNT FETs is also investigated, revealing a more favorable energy consumption and faster intrinsic speed scaling than that of the Si-based devices.

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