lecture_05_MOS_modeling_II

lecture_05_MOS_modeling_II - Handout#5 EE 214 Winter 2009...

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Handout #5 EE 214 Winter 2009 MOS Transistor Modeling for Analog Design Part II B. Murmann and B. A. Wooley Stanford University Corrections: 1/23/09: Fixed ω p2 expression on slide 32; see also text p. 641 Re-cap Subthreshold Operation Transition to ? Strong Inversion What causes the discrepancy between 2/V OV and 0.18 μ m NMOS in strong inversion? B. A. Wooley, B. Murmann EE214 Winter 2008-09 2
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Short Channel Effects Velocity saturation due to high lateral field Mobility degradation due to high vertical field V t dependence on channel length and width V t = f(V DS ) r o = f(V DS ) We will limit the discussion in EE214 to the first two aspects of the above list, with a focus on qualitative understanding B. A. Wooley, B. Murmann EE214 Winter 2008-09 3 Velocity Saturation (1) I th d i ti f th l d l it i d th t th i In the derivation of the square law model, it is assumed that the carrier velocity is proportional to the lateral E-field, v= μ E Unfortunately, the speed of carriers in silicon is limited At very high fields (high voltage drop across the conductive channel), the carrier velocity saturates Approximation: c c μ E ν (E) μ E for E E 1 d scl v E = = >> c E + 1 2 d c scl v (E ) v = B. A. Wooley, B. Murmann EE214 Winter 2008-09 4
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