Degradation of current drivability of Schottky barrier source/drain transistors induced by high-k gate dielectrics and possible measures to suppress the phenomenon

This paper reports on a study on current drivability of Schottky barrier source/drain transistors. It is shown that current drivability is significantly degraded when high-k gate dielectrics are adopted and that the degradation is much more serious than that of conventional metal insulator semiconductor field effect transistors (MISFETs). It is also shown that current drivability is degraded in the case that gate electrode and source/drain have both an offset and overlap. These phenomena can be understood in terms of the fringing-induced barrier shielding (FIBS). In order to suppress the degradation, certain structures are studied from the viewpoint of improvement of current drivability. It is shown that a structure with a low-k interfacial layer between high-k gate dielectric and substrate is quite effective for suppressing the degradation of current drivability due to FIBS without influencing off-state characteristics. Another structure with high-k gate sidewalls is also studied and it is shown that current drivability has a local maximum in the case that gate electrode and source/drain have an offset. This phenomenon can be understood in terms of a refraction of lines of electric force at interfaces of two materials with different dielectric constants. This structure is also shown to be quite effective for suppressing the degradation without influencing off-state characteristics.