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MOSFETs: Drain Voltage Effects on Channel Current

MOSFETs: Drain Voltage Effects on Channel Current. Prof. Paul Hasler. Origin of Drain Dependencies. Increasing Vd effects the drain-to-channel region:. increases barrier height. increases depletion width. Drain Characteristics. Current versus Drain Voltage.

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MOSFETs: Drain Voltage Effects on Channel Current

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  1. MOSFETs: Drain Voltage Effects on Channel Current Prof. Paul Hasler

  2. Origin of Drain Dependencies Increasing Vd effects the drain-to-channel region: • increases barrier • height • increases depletion • width

  3. Drain Characteristics

  4. Current versus Drain Voltage

  5. Current versus Drain Voltage

  6. Current versus Drain Voltage Not flat due to Early effect (channel length modulation)

  7. Current versus Drain Voltage Not flat due to Early effect (channel length modulation) In BJTs --- Base Modulation Effects

  8. Current versus Drain Voltage Not flat due to Early effect (channel length modulation) Id = Id(sat) (1 + (Vd/VA) ) or Id = Id(sat) eVd/VA In BJTs --- Base Modulation Effects

  9. GND Iout Rout Id(sat) Current versus Drain Voltage Not flat due to Early effect (channel length modulation) Id = Id(sat) (1 + (Vd/VA) ) or Id = Id(sat) eVd/VA In BJTs --- Base Modulation Effects

  10. Early Voltage Length Dependence Width of depletion region depends on doping, not L Might expect Vo to linearly vary with L

  11. Full Range of Effects 7 Punchthrough 6 Slow / Exponential Increase: Channel Modulation / DIBL Effect 5 4 Current (nA) 3 2 Other (faster) effects: Punchthrough --- depletion regions converge Avalanche Breakdown --- impact ionization 1 0 100 (Punchthrough voltage = 2 * VA) Current (nA) 10 Exp model VA = 5V 1 0 1 2 3 4 5 6 7 8 9 10 Voltage (V)

  12. Cause of DIBL

  13. Drain Induced Barrier Lowering Data taken from a popular 1.2mm MOSIS process Data taken from a popular 2.0mm MOSIS process

  14. Different Manifestations of DIBL

  15. Different Manifestations of DIBL

  16. Drain Voltage Effects • Channel Length Modulation / Early Effect • Exponential Modeling • Drain Induced Barrier Lowering (DIBL): Source of Exponential I-V dependence • Punchthrough: Highest Drain-Source voltage available

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