Fabrication and Characterization of Reconfigurable Field Effect Transistors

To complement scaling of field effect transistors, new device concepts were introduced recently. One such concept is the reconfigurable field effect transistor (RFET). These transistors are based on nickel silicide-Si-nickel silicide Schottky junctions and their polarity can be switched between p- and n- type at runtime by the application of an electrostatic potential [1]. Control over silicide length and phase is important for scaling and proper functioning of these devices [2]. NiSi2 is the desirable silicide phase as its metal work function aligns itself near mid bandgap of Si, which enables reconfigurability of the device [1, 3].
We report on fabrication and electrical characterization results of RFETs. Si nanowires (SiNWs) are fabricated on undoped silicon-on-insulator (SOI) substrates by a top-down process based on electron beam lithography and inductively coupled plasma etching. Then, Ni is placed at both ends of the SiNWs by metal evaporation and lift-off processes. Afterwards, flash lamp annealing (FLA) is performed for silicidation of the NWs.
FLA has enabled better control over silicidation length since flash times are much shorter (of the order of milli-seconds) than rapid thermal annealing (RTA) times. Transmission electron microscopy (TEM) shows the formation of the desired NiSi2 phase near the silicide-Si interface. Electrical characterization of the devices with back gating shows ambipolar behaviour. For unipolar behaviour, top gates need to be fabricated, results of which will be presented at the conference.