Advances in nonlinear characterization of millimetre-wave devices for telecommunications

Field Effect Transistors exhibit a variety of complicated dynamic and nonlinear interactions that affect millimetre-wave devices used for telecommunications. The dynamics include self heating, bias dependent change in trapped charge, and variations due to impact ionization. These are feedback mechanisms that contribute to intermodulation as a memory effect does. A FET is better viewed as a nonlinear system with feedback, bias dependent rates, and high-order nonlinear conductance and charge storage with specific terminal to terminal interaction. Identifying and characterizing FET dynamics and linearity is a key step in the design process. Extraction of true intrinsic characteristics is an important first step to understanding the physics of trapping and heating within the device. Standard measurement techniques tend to derive access networks with an emphasis on scaling with layout geometry. The intrinsic device is then modelled as whatever is left after de-embedding the measurements. As such, the intrinsic model exhibits significant frequency dispersions and behaviour that is not easily related to the operation of the transistor. A correct determination of the access network reveals that the dispersions within the intrinsic data are related to physical process, such as heating and trapping. Recent work has been carried out to accurately implement trapping within a circuit simulator. This is key to correct prediction of intermodulation and bias dependence effects generated by a FET. It is shown that heating significantly affects trapping and is an important factor in the transient rate dependence of the characteristics. The implementation of trapping within a circuit model, and its consequences on linearity are explored.