A SCALABLE GENERAL-PURPOSE MODEL FOR MICROWAVE FETS INCLUDING DC AC DISPERSION EFFECTS/

This paper addresses the issue of scalability in equivalent circuit-ba sed models for FET's, emphasizing for the first time the particularly difficult problems associated with the scalability of dc/ac dispersion phenomena. A study has been carried out on devices from both MESFET ( L-G = 0.5 mu m) and pseudomorphic high electron-mobility transistor (P HEMT) (L-G = 0.2 mu m) foundry processes, with total gatewidths betwee n 60-1200 mu m. Results are presented, showing that at least up to med ium-size devices, de characteristics, and most of the bias-dependent s mall-signal circuit elements scale in general, very well provided a re liable parameter extraction methodology is implemented, However, in th e case of dispersion phenomena, while the differential dc/ac transcond uctance obeys straightforward scaling rules, the output conductance do es not, The main features of a general-purpose scaleable microwave FET model-COBRA-are described, This includes an equivalent circuit-based solution to account for dispersion effects, The solution is compact, o beys the required conservation constraints, and can ''absorb'' the sca ling inconsistencies observed in the output conductance, The correspon ding modeling methodology is also described, Finally, a comprehensive set of measurement versus simulation scalability test results are pres ented. including de, small-signal, and large-signal tests.