Quantification and Mechanism Analysis of Total-Ionizing-Dose Effect in Top-Gate CNT FETs

Abstract

The total-ionizing-dose (TID) effect in p-type top-gate carbon nanotube field-effect transistor (CNT FET) under on, off, transmission gate (TG), and All-0 bias conditions is investigated through experiments and simulations. The continuous application of electrical stress incites degradation in the device characteristics of CNT FETs, which is further complicated by the superimposition of TID effects. This work distinguished between the electrical stress impact and the TID effect through comparative experiments and analyzed the underlying mechanisms of these two effects with technology computer-aided design (TCAD) simulations. The experimental results demonstrate that both effects on CNT FETs mainly result in a threshold voltage shift. Electrical stress results in a $\Delta V_{\text {th}}$ of −0.1 V (off state) to +0.2 V (on state), while the TID effect results in a $\Delta V_{\mathbf {th}}$ of −0.15 V (TG state) to −0.05 V (on and off states). The TG state is recognized as the worst case bias condition of the TID effect on CNT FETs. TCAD simulation results denote that electrical stress incites changes in the trap charge density ( $\sim 10^{12}$ cm−2) in the gate dielectric layer, while the TID effect augments positive fixed charges ( $\sim 10^{11}$ – $10^{12}$ cm−2) in the substrate oxide. This study explains the mechanisms of electrical stress and TID effects in CNT FETs, providing a reference for subsequent device process optimization and radiation hardening.