Compact modeling of 0.35 μm SOI CMOS technology node for 4 K DC operation using Verilog-A

Compact modeling of MOSFETs from a 0.35 μm SOI technology node operating at 4 K is presented. The Verilog-A language is used to modify device equations for BSIM models and more accurately reproduce measured DC behavior, which is not possible with the standard BSIM model set. The model presented exhibits convergent behavior and is shown to be experimentally accurate at 4 K. No design tool currently in place exhibits convergence and/or accuracy over this range. The Verilog-A approach also allows the embedding of nonlinear length, width and bias effects into BSIM calculated curves beyond those that can be achieved by the use of different BSIM parameter sets. Nonlinear dependences are necessary to capture effects particular to 4 K behavior, such as current kinks. The 4 K DC behavior is reproduced well by the compact model and the model seamlessly evolves during simulation of circuits and systems as the simulator encounters SOI MOSFETs with different lengths and widths. The incorporation of various length/width and bias dependent effects into one Verilog-A/BSIM4 library, therefore, produces one model for all sets of devices called up in a given product design kit (PDK) for this technology node.