Investigation of Vacuum Pumping and Gate Bias Stress Effects on Electrical Performance and Trap Characteristics in Bottom-Gated CNT FETs

Carbon nanotube (CNT) field-effect transistor (FET) technology has achieved significant advancements but continues to face critical challenges related to performance stability and reliability. Systematic research on trap variations and their correlation with electrical properties is essential to comprehensively understand the mechanisms underlying device instability and degradation. In this study, we investigate the trap characteristics in bottom-gated CNT FETs by analyzing current transients associated with the trapping and detrapping of charge carriers. Traps with distinct time constants, activation energy, and dependence on trapping conditions are identified from the established time constant spectra. These traps are attributed to water molecules at the CNT/SiO2 interface and to oxide defects within the gate dielectric SiO2. By examining the evolution of trap behavior, we elucidate the relationship between changes in electrical performance and specific trap states in CNT FETs. Under vacuum pumping, hysteresis curves are suppressed over time, and the detrapping behavior of water-related traps decreases as revealed by the time constant spectra. This indicates the desorption of water molecules during the pumping process. Under negative gate bias stress, the transfer curves shift in the direction of the applied bias, accompanied by a reduction in water-related traps and an increase in oxide traps. It confirms that water at the CNT/SiO2 interface undergoes oxidation in the presence of holes, leading to the reduction of water molecules and the migration of protons into the SiO2 layer.