Punchthrough currents in sub-micron short channel MOS transistors

The punchthrough current in sub-micron MOS transistors is essentially initiated at the surface near the edge of source junction. A surface diffusion current (I-sdif) originates from the injection of minority carriers from the source junction due to the combined effect of drain-induced-barrier-lowering (DIBL) and surface-band-bending (Delta phi(50)). The DIBL effect increases with decreasing channel length. In addition, the extracted Delta phi(50) from the punchthrough current indicates that surface space charges at the source edge shift from the accumulation/depletion mode for long sub-micron devices (approximate to 0.62 mu m) to the strong-inversion mode for deep sub-micron devices (approximate to 0.12 mu m). For intermediate sub-micron devices (approximate to 0.37 mu m), I-sdif eventually converts to the bulk space-charge-limited current (I-scl) as the connected source/drain depletion region expands with increasing drain bias. For long sub-micron devices only I-sdif dominates, while for deep sub-micron devices it converts rapidly to I-scl in the bulk depletion regions over the drain bias range investigated. (C) 1997 Elsevier Science Ltd.