Modeling of Semiconductor Substrates for RF Applications: Part I—Static and Dynamic Physics of Carriers and Traps

This article aims to provide deep insight into the physics of substrates for RF applications under large-amplitude signal excitations. The impact of physical parameters on substrate-induced harmonic distortion is modeled and well understood, from a theoretical and quantitative standpoint. This article formulates the interplay between applied voltage signal (dc or RF), interface fixed charge, and trapped charge in a charge-balance analysis for high-resistivity and trap-rich (TR) substrates. A TCAD approach gives strong insight into the impact of such semiconductor material and interface properties on the RF substrate's effective resistivity and linearity. First, a static analysis reveals how TR interface passivation overcomes the parasitic surface conduction effect using the concept of deep Fermi-level pinning. Next, substrates are analyzed in response to dynamic excitation signals. Using step functions to pulse an MOS structure from strong negative to strong positive applied charge sheds light on carrier dynamics. The characteristic time constants associated with variations in trap occupancy and in free carrier densities are discussed. Finally, sinusoidal large-amplitude signals are considered to analyze harmonic distortion from several types of substrates at various RF frequencies.