RF MOSFET modeling accounting for distributed substrate and channel resistances with emphasis on the BSIM3v3 SPICE model

A r.f. MOSFET model generated for use in LIBRA simulation typically applies to only one bias point. The model and its parameters can be unphysical. It is desirable to establish a physical, scalable model capable of simulating both d.c. and r.f. characteristics and applicable to all the bias ranges. BSIM3 is a potential candidate, having demonstrated accuracy and scalability in the devices' d.c. characteristics. When it is applied to simulate the s-parameters at r.f., we find BSIM3 to be somewhat problematic and two modifications are necessary to obtain a good fit. The first modification involves the addition of a bulk resistive network, achievable with a simple circuit extension to the existing BSIM3 model. The second improvement accounts for the finite channel resistance, whose origin lies in a nonquasi-static analysis. Since BSIM3 employs a quasi-static assumption, this improvement, while important, involves some changes in the BSIM3 source code.