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 depletion width increases barrier height

3. Drain Characteristics

4. Current versus Drain Voltage

6. 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) I d = I d (sat) (1 + (V d /V A ) ) or I d = I d (sat) e Vd/VA In BJTs --- Base Modulation Effects

9. Current versus Drain Voltage Not flat due to Early effect (channel length modulation) I d = I d (sat) (1 + (V d /V A ) ) or I d = I d (sat) e Vd/VA R out I d (sat) GND I out 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 0 1 2 3 4 5 6 7 012345678910 1 100 Punchthrough Current (nA) Voltage (V) Exp model Slow / Exponential Increase: Channel Modulation / DIBL Effect Other (faster) effects: Punchthrough --- depletion regions converge Avalanche Breakdown --- impact ionization (Punchthrough voltage = 2 * V A ) V A = 5V

12. Cause of DIBL

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

14. 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