A comparative study of threshold variations in symmetric and asymmetric undoped double-gate MOSFETs

For the purpose of giga-scale integration with double-gate (DG) MOSFET technology, it is imperative to consider parameter variations. In this paper, analytical long-channel and short-channel threshold voltage (V_TH) models for undoped asymmetric DG (ADG) MOSFETs are developed to reveal V_TH dependencies on device dimensions. Using the quantitative scaling theory, V_TH variations of ADG MOSFETs are then comprehensively investigated and compared to those of symmetric DG (SDG) MOSFETs recently studied by Chen (2002). ADG MOSFETs with p+/n+ poly or equivalent gates are used for case studies. It is found that threshold variations in nearly ideal, long-channel ADG devices are 10× as large as those in SDG devices.