Characterization and modeling of edge direct tunneling (EDT)leakage in ultrathin gate oxide MOSFETs |
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Authors: | Yang KN Huang HT Chen MJ Lin YM Yu MC Jang SM Yu DCH Liang MS |
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Affiliation: | Inst. of Electron., Nat. Chiao Tung Univ., Hsinchu ; |
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Abstract: | This paper examines the edge direct tunneling (EDT) of electron from n+ polysilicon to underlying n-type drain extension in off-state n-channel MOSFETs having ultrathin gate oxide thicknesses (1.4-2.4 nm). It is found that for thinner oxide thicknesses, electron EDT is more pronounced over the conventional gate-induced-drain-leakage (GIDL), bulk band-to-band tunneling (BTBT) and gate-to-substrate tunneling, and as a result, the induced gate and drain leakage is better measured per unit gate width. A physical model is for the first time derived for the oxide field EOX at the gate edge by accounting for electron subband in the quantized accumulation polysilicon surface. This model relates EOX to the gate-to-drain voltage, oxide thickness, and doping concentration of drain extension. Once fox is known, an existing DT model readily reproduces EDT I-V consistently and the tunneling path size extracted falls adequately within the gate-to-drain overlap region. The ultimate oxide thickness limit due to EDT is projected as well |
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