Effect of vacuum thermal annealing to encapsulated graphene field effect transistors

Water vapor barriers used for graphene encapsulation can both exclude water from the environment and trap water in the device, preventing annealing from improving device performance. In this paper, the authors investigate the effects of vacuum annealing on encapsulated single layer graphene field effect transistors (SLG-FETs). The stability of GFETs is monitored for a period of up to six months, and different annealing times and atmospheres are tested to recover lost electronic performance. Fabricated encapsulated devices based on a parylene-C/aluminum passivation layers offer increased stability over exposed back-gated devices, but still suffer from a significant Dirac point shift over extended air exposure. Our results show that GFETs subjected to varying annealing times exhibit similar initial behavior, characterized by a substantial reduction of their doping profile due to desorption of oxygen/water molecules, but drastically different long term stability. This suggests that moderate vacuum annealing can dehydrate even encapsulated devices, whereas extended annealing times can damage the encapsulation layer. (C) 2016 American Vacuum Society.