An effective channel length determination method for LDD MOSFETs

We propose a definition of MOSFET effective channel length (L_EFF), that provides a method of determining L_EFF as a constant, and external resistance (R_EXT) virtually as a constant, even for lightly doped drain (LDD) transistors. A unified relationship between this L_EFF and MOSFET drive current (linear and saturation) that is common to a wide range of drain structures was confirmed. Therefore, the L_EFF is useful, not only for compact analytical models, but also as an index of MOSFET performance applicable to both single drain and LDD devices. The dependence of the channel length on the source/drain structure was clarified by introducing the concept of local contribution to channel length. The L_EFF varies, even if the metallurgical channel length is fixed, depending on the design of the source/drain