A physically based investigation of the small-signal behaviour of bulk and fully-depleted silicon-on-insulator MOSFETs for microwave applications

摘要

We present a Monte Carlo investigation of the dynamic performance of bulk and FD SOI MOSFET devices with one-to-one comparable topologies. The features of the simulator allow us to provide a complete comprehension of the transport phenomena and the main internal quantities that are connected to the small-signal behaviour of the devices at RF and microwave frequencies. In this way, the effect of the buried oxide and the variation of the active layer thickness on the static and dynamic characteristics of FD SOI MOSFETs are readily evaluated, and an exhaustive investigation of the physical basis of the dynamic performance is realized, thus clarifying the underlying differences between bulk and FD SOI transistors that can be used for the optimization of the devices. The parameters of the small-signal equivalent circuit are carefully analysed: important issues, such as the high frequency capacitive coupling to the substrate, the physical meaning of non-quasistatic parameters or the behaviour of figures of merit such as g_m, f_T and f_(max) are studied in detail. Furthermore, when scattering parameters are evaluated the kink effect in the S_(22) parameter at high frequencies has been checked to be much more pronounced in the case of FD SOI devices.