Development of III-V RF Nanowire MOSFETs

Abstract: The silicon MOSFET is one of the most important components used in modern electronics. The pursuit to continue fulfilling Moore’s law by scaling transistors to even smaller sizes have driven the development forward for CMOS technologies and new approaches have been necessary. These include changing the geometry of the devices for even higher performance, like creating 3D structures (finFETs or tri-gates) for better electrostatic control. With the aggressive scaling, power dissipation has become an increasing problem in CMOS applications. One way to combat this is by introducing a material in the channel with superior transport properties, like InGaAs. As the development of MOSFET technology for CMOS applications continue, devices with excellent high frequency performance have been demonstrated. Thus, the MOSFET has also emerged as a possible alternative to the HEMT in high frequency applications. The desirable properties of an RF transistor differs somewhat from CMOS transistors, as stability and high gain are more important than size and power dissipation. In this thesis, lateral InGaAs nanowire MOSFETs for RF applications with different geometries have been fabricated and characterised. The transistors exhibit a highest ft and fmax of 150 GHz and 280 GHz respectively. The devices were fabricated in a cleanroom environment and measured in both DC and RF. Small signal modelling was performed using Matlab. A model of the devices was also made in COMSOL multiphysics and simulations were performed to investigate the effect of different geometries on the gate-source and gate-drain capacitance. The results form the simulation showed similar values to the fabricated devices. This indicates that the model was accurate. The fabrication yielded very few working devices compared to what was fabricated. Some of the working devices showed performance compared to similar devices that have been demonstrated. Though a few devices show promising RF characteristics, the fabrication process needs to be refined.