Bandgap Extraction at 10 K to Enable Leakage Control in Carbon Nanotube MOSFETs

Abstract

Carbon nanotube (CNT) transistors exemplify the fundamental tradeoff between desirable high mobility and undesirable leakage current due to the small effective mass and bandgap. To understand leakage current limits in high-speed CNT transistors, electrical bandgaps are extracted on 12 single-CNT top-gate MOSFETs from the energy gap between thermionic emission and band-to-band tunneling (BTBT) at 10 K. At 300 K the minimum I_OFF at 0.5 V V_DS is analyzed as a function of bandgap between 0.96 eV and 0.43 eV with I_OFF-MINfrom 0.2 pA/CNT to 15 nA/CNT. NEGF simulation validates the bandgap extraction methodology and reproduces the experimental MOSFET I_OFF-MIN data. A TCAD model calibrated to this work&#x2019;s leakage data projects the accessible I_ON-I_OFF design space bounded by CNT bandgap, indicating E_G &#x003E; 0.65 eV (d_CNT &#x003C; 1.3 nm) is needed to achieve 100 nA/<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> at 0.5 V V_DD and 250 CNT/<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> for channel length above 20 nm. An E_G of 1.06 eV (d_CNT &#x003D; 0.8 nm) can deliver <inline-formula> <tex-math notation="LaTeX">$2750\times $ </tex-math></inline-formula> tunable range of I_OFF by adjusting V_T, which exceeds the <inline-formula> <tex-math notation="LaTeX">$400\times $ </tex-math></inline-formula> tunable range of I_OFF used in Si CMOS platform technologies.