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Chap.1 Physics and Modelling of MOSFETs

Chap.1 Physics and Modelling of MOSFETs. 반도체 연구실 신입생 세미나 박 장 표 2009 년 1 월 8 일. Contents. Basic MOSFET Characteristics Current – Voltage Characteristics p-Channel MOSFETs Geometric Scaling Theory Small – Device Effects Small Device Model. 2.

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Chap.1 Physics and Modelling of MOSFETs

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  1. Chap.1 Physics and Modelling of MOSFETs 반도체 연구실 신입생 세미나 박 장 표 2009 년 1 월 8 일

  2. Contents • Basic MOSFET Characteristics • Current – Voltage Characteristics • p-Channel MOSFETs • Geometric Scaling Theory • Small – Device Effects • Small Device Model 2

  3. 1.1 Basic MOSFET Characteristics • The MOS Threshold Voltage • Body Bias 3

  4. Basic MOSFET Characteristics • MOSFET used as a Switch • ID determine by VGS &VDS ( also VSB affects lesser degree ) 4

  5. Basic MOSFET Characteristics • W, L are important dimension for electrical characteristics • Aspect ratio : W / L 5

  6. Basic MOSFET Characteristics • The MOS Threshold Voltage : used to enhance the conduction between the drain and source • VGS < VT : cutoff ( no current flow - ideally ) , VGS > VT : active mode • ID depends on the voltages applied 6

  7. Basic MOSFET Characteristics • MOS system : altering the charge distribution at the surface 7

  8. Basic MOSFET Characteristics For small values of VG • Create depletion region referred to as bulk charge • The surface charge is made up entirely of bulk charge • Bulk charge consists of ionized acceptor atom, it is immobile 8

  9. Basic MOSFET Characteristics For VG > VT • initiates thin electron inversion layer when VG = VT 9

  10. Basic MOSFET Characteristics • The MOS Threshold Voltage 10

  11. Basic MOSFET Characteristics • Body Bias 11

  12. 1.2 Current – Voltage Characteristics • Square-Law Model • Bulk-Charge Model 12

  13. Current – Voltage Characteristics • Cutoff when VGS < VT 13

  14. Current – Voltage Characteristics • Active when VGS > VT 14

  15. Current – Voltage Characteristics • Square-Law Model 15

  16. Current – Voltage Characteristics • Channel Length Modulation 16

  17. Current – Voltage Characteristics 17

  18. Current – Voltage Characteristics 18

  19. Current – Voltage Characteristics • Bulk-Charge Model 19

  20. 1.3 p-Channel MOSFETs 20

  21. p-Channel MOSFETs • p-Channel MOSFETs 21

  22. p-Channel MOSFETs 22

  23. p-Channel MOSFETs • Cutoff ( VSGp < l VTp l ) • Active (VSGp > l VTp l ) 23

  24. 1.4 MOSFET Modelling • Drain-Source Resistance • MOSFET Capacitances • Junction Leakage Currents 24

  25. MOSFET Modelling 25

  26. MOSFET Modelling • Drain-Source Resistance 26

  27. MOSFET Modelling • MOSFET Capacitances 27

  28. MOSFET Modelling • MOS-Based Capacitances 28

  29. MOSFET Modelling 29

  30. MOSFET Modelling • Depletion Capacitance 30

  31. MOSFET Modelling • Depletion Capacitance in Drain & Source region 31

  32. MOSFET Modelling • Zero-bias source/drain bulk capacitance 32

  33. MOSFET Modelling • Cav using a simpler LTI element General model for voltage-dependent depletion capacitance m : grading coefficient, such that m<1 33

  34. MOSFET Modelling • Device Capacitance Model • Use the LTI average of the depletion capacitance 34

  35. MOSFET Modelling • Junction Leakage Currents 35

  36. MOSFET Modelling • Drain / Source are always at a voltage greater than or equal to 0v • Bulk is will always exhibit leakage flows regardless of the state of the conduction of the transistor 36

  37. MOSFET Modelling General doping profile ( m : grading coefficient ) 37

  38. 1.5 Geometric Scaling Theory • Full-Voltage Scaling • Constant-Voltage Scaling • Second-Order Scaling Effects 38

  39. Geometric Scaling Theory 39

  40. Geometric Scaling Theory 40

  41. Geometric Scaling Theory • Full Voltage Scaling 41

  42. Geometric Scaling Theory • Constant-Voltage Scaling 42

  43. Geometric Scaling Theory • Second-Order Scaling Effects • First-Order Scaling Effects deals with MOSFET dimensions, doping level, voltages, and currents • Second-Order Scaling Effects for example of by increased impurity scattering • Second-Order Scaling Effects for example of in VT In the flat band voltage as is scaled 43

  44. 1.7 Small-Device Effects • Threshold Voltage Modifications • Mobility Variations • Hot Electrons 44

  45. Small-Device Effect • Threshold Voltage Modifications Basic threshold voltage Charge – voltage relation by area • Gate voltage does not support all of the bulk char with an area of WL 45

  46. Small-Device Effect • Short-Channel Effect 46

  47. Small-Device Effect Using Pythagorean theorem 47

  48. Small-Device Effect 48

  49. Small-Device Effect • Narrow Width Effect total area of region 49

  50. Small-Device Effect Since the area for Another approach : empirical factor When W 50

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