Electrostatic Discharge and Failure Model of Carbon Nanotube Field-Effect Transistors

The electrostatic discharge (ESD) and failure mechanisms of carbon nanotube field-effect transistors (CNT FETs) were thoroughly investigated via transient current tests and numerical simulations. Experiments demonstrated that CNT FETs have a three-stage ESD process according to transmission-line pulse (TLP) and human-body model (HBM) measurements, vastly different from the snapback phenomenon in conventional Si CMOS transistors. As the drain bias (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\text {DS}}$ </tex-math></inline-formula>) increases from 2 to 12 V, the ESD mechanism of CNT FETs changes from thermionic emission (first stage) to band-to-band tunneling (second stage), which results in a dynamic discharge impedance. The soft breakdown of the drain-to-gate isolation dielectric contributes to the discharge current in the third stage when <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\text {DS}} \gt 12$ </tex-math></inline-formula> V. The breakdown current-induced heating of CNT FETs can cause critical damage to the drain-to-gate isolation dielectric and the metal contacts and eventually result in device failure. Therefore, the drain-to-gate isolation dielectric is identified as the weak spot, requiring optimization to enhance the reliability of CNT FETs.