Analysis of LDD transistor asymmetry susceptibility in VLSI circuits

This paper describes problems due to asymmetry of source and drain impurity profile caused by the shadowing of ion beams by gate electrodes. This asymmetry degrades the sensitivity of sense amplifiers especially when Lightly-Doped-Drain/Source (LDD) transistors are adopted. This effect is a serious obstacle to realize ultra high density DRAM´s. In order to reduce this effect, a sensing circuit suppressing the asymmetry effect is proposed and its sensitivity improvement is evaluated.