Multi segment compact terahertz SPICE/ADS model

M. Shur, X. Liu, T. Ytterdal
Rensselaer Polytechnic Institute,
United States

Keywords: THz technology, silicon, CMOS, SPICE, FETs, spectrometer

Summary:

Recent developments in Si plasmonics showed that Si CMOS in plasmonic regimes of operation could detect THz radiation up to at least 5 THz and could also operate as THz interferometers, spectrometers, frequency-to-digital converters (FDCs) and even THz modulators and sources. Modeling of such high frequency operation requires to account for the electron inertia and for non-uniform propagation of the plasmonic excitation along the transistor channel. We report on the development of compact Si MOS models suitable for circuit design in the THz range and based on the multi segment unified charge control model, which accounts for the electron inertia effect (by incorporating segmented Drude inductances) and for the ballistic field effect mobility, which is proportional to the channel length. The model also accounts for parasitic resistances and capacitances and for the leakages current. It is validated by comparison with experimental data and TCAD simulation results. We present three applications of this model: (1) simulation and optimization of sub-THz and THz Si MOS detectors; (2) simulation of Si MOS THz spectrometers and interferometers detecting and comparing the phase shifting THz signals at the source and drain and (3) Si MOS THz FDCs. Our simulations used up to 200 segments in the device channel. The results are also in good qualitative agreement with the analytical hydrodynamic theory and numerical simulations using hydrodynamic equations. However, accounting for parasitics and a more accurate modeling of the nonlinear distributive capacitive coupling between the gate and the transistor channel using our compact THz model introduces important quantitative corrections and is, therefore, required for the design optimization.