HiSIM-SOTB: A Compact Model for SOI-MOSFET with Ultra-Thin Si-Layer and BOX

M. Miura-Mattausch, H. Kikuchihara, U. Feldmann, T. Nakagawa, M. Miyake, T. Iizuka, H.J. Mattausch
Hiroshima University, JP

Keywords: SOI-MOSFET, thin BOX, surface-potential model, Poisson equation

Summary:

The Silicon-On-Thin-Buried-Oxide (SOTB) transistor is a descendant of the conventional SOI MOSFET with thin Silicon and BOX layers. Many different structure and material variations are possible, where the choice of a thicker BOX may be used to suppress the influence of the bulk substrate. The SOTB-MOSFET with a very thin BOX and a high substrate impurity concentration comes even close to the properties of a double gate MOSFET. Our purpose is thus to develop a compact model for SOTB MOSFETs, which covers this wide structural range and is easily extendable to any other type of thin-film transistor. The SOI-MOSFET has three surfaces, and HiSIM-SOTB is developed by solving the Poisson equation iteratively. It has been verified that the model can indeed reflect structural size variations over a very large range. HiSIM-SOTB includes all possible charges at the three oxide surfaces in the SOI structure. The approach with simultaneous inclusion of the three surface charges can easily make the circuit simulation unstable. To overcome such stability problems we have developed a sophisticated method for reliably solving the Poisson equation. We address the development of solutions to the outlined challenges in our report.