Observation of the Ambient Effect in BTI Characteristics of Back-Gated Single Layer Graphene Field Effect Transistors

In this paper, the ambient doping effect on negative/positive bias temperature instability (NBTI/PBTI) of single layer graphene field effect transistors (FETs) is investigated. In ambient air, the ΔV_th of NBTI is comparable with that of PBTI under the same stress voltage at room temperature. The ΔV_th of NBTI appears insensitive to temperature, while the ΔV_th of PBTI increases significantly with rising temperatures, due to the thermally activated charging of ambient doped defects at the graphene/SiO₂ interface. This effect also results in an abnormal recovery of NBTI. In an ambient vacuum, the ΔV_th is much less than that in ambient air. In addition, the ΔV_th of both NBTI and PBTI decreases substantially for higher temperatures in the vacuum. The adsorbed molecules are mainly responsible for the ΔV_th under BTI stress and the back-gated graphene FETs in the air.