Improvement of drain leakage current characteristics in metal-oxide-semiconductor-field-effect-transistor by asymmetric source-drain structure

Abstract

This paper is on the comparison of drain leakage current in asymmetric source-drain (ASD) MOSFET using only lightly doped drain (LDD) on drain side versus symmetric source-drain (SSD) MOSFET using LDD and deep diffusion doping on drain side. We used long-channel devices so as to avoid any leakage associated with short-channel effects. Therefore, junction leakage and gate-induced-drain-leakage (GIDL) current are only considered. The band-to-band tunneling model is used to fit the measured drain leakage currents. Measurement results show that the drain leakage current is less in ASD MOSFET. For the ASD MOSFET, junction leakage current is dominant. For the SSD MOSFET, junction leakage current is still dominant in the low drain-to-gate voltage region. However, GIDL current is dominant in the high drain-to-gate voltage region. The GIDL current is more sensitive for interface trap generated by hot-carrier injection than junction leakage current. The plotting curves of band-to-band tunneling are more different in SSD MOSFET than ASD MOSFET. Thus, ASD MOSFET is superior in leakage-side.