Microwave Graphene FETs
In collaboration with the Philip Kim group at Harvard, I am working on fabricating edge-contacted hBN/Graphene/hBN microwave field effect transistors. In parallel with spending time in the cleanroom, I have written a suite of simulation code to model graphene-based FET's in order to better understand how they could be eventually useful to the astronomical instrumentation community. The devices are measured on a cryogenic probe station with a VNA and noise figure meter from 10MHz to 50GHz. Fits to DC I-V behavior are used to extract RF model parameters, which can then be compared to measurements. The graphene channel itself is modelled as a lossy non-linear transmission line of finite length, allowing for treatment of FET's which may not behave as lumped elements as high frequency. Noise modelling is done in a similar fashion, by calculating the drain noise correlation matrix for any given DC bias point.
Shown above are two example devices with gate length 1um (left) and 300nm (right) as fabricated in the Harvard Center for Nanoscale Systems clean room. The devices are entirely fabricated using electron beam lithography on an Elionix F125.