FinFET vs. GAAFET vs. Nanosheet FET: A TCAD Modeling and Behavioral Analysis

The relentless pursuit of Moore's Law has driven transistor architectures from planar MOSFETs to sophisticated 3D structures. FinFETs marked a significant advancement, but as scaling approaches sub-5nm nodes, Gate-All-Around FETs (GAAFETs), particularly Nanosheet FETs (NS-FETs or MBCFETs), have emerged as leading solutions. Technology Computer-Aided Design (TCAD) modeling is essential for optimizing their performance and addressing challenges. This article compares FinFETs, GAAFETs (including nanowires), and Nanosheet FETs, focusing on their TCAD representations and electrical characteristics.

The Evolutionary Drivers: Why Move Beyond FinFETs?
FinFETs addressed critical short-channel effects (SCEs) that plagued planar MOSFETs at sub-22nm nodes. By encasing the gate on three sides of a vertical silicon "fin," FinFETs improved electrostatic control, reducing Drain-Induced Barrier Lowering (DIBL) and subthreshold swing (SS), which minimized leakage and enhanced power efficiency. However, as scaling progressed to sub-7nm nodes, FinFET limitations became apparent:

Width Quantization: The effective device width (W_eff = 2*H_Fin + W_Fin) is constrained by the number and dimensions of fins, limiting design flexibility for logic cells, SRAM, and analog circuits.
Electrostatic Control Limits: At narrow fin widths (<~5nm), controlling the channel...