1. EE141 © Digital Integrated Circuits 2nd Devices 1 Digital Integrated Circuits A Design Perspective The Devices Jan M. Rabaey Anantha Chandrakasan Borivoje Nikolic July 30, 2002

2. EE141 © Digital Integrated Circuits 2nd Devices 2 Goal of this chapter  Present intuitive understanding of device operation  Introduction of basic device equations  Introduction of models for manual analysis  Introduction of models for SPICE simulation  Analysis of secondary and deep-sub- micron effects  Future trends

3. EE141 © Digital Integrated Circuits 2nd Devices 3 The Diode Mostly occurring as parasitic element in Digital ICs

4. EE141 © Digital Integrated Circuits 2nd Devices 4 Depletion Region

5. EE141 © Digital Integrated Circuits 2nd Devices 5 Diode Current

6. EE141 © Digital Integrated Circuits 2nd Devices 6 Forward Bias Typically avoided in Digital ICs

7. EE141 © Digital Integrated Circuits 2nd Devices 7 Reverse Bias The Dominant Operation Mode

8. EE141 © Digital Integrated Circuits 2nd Devices 8 Models for Manual Analysis

9. EE141 © Digital Integrated Circuits 2nd Devices 9 Junction Capacitance

10. EE141 © Digital Integrated Circuits 2nd Devices 10 Diffusion Capacitance

11. EE141 © Digital Integrated Circuits 2nd Devices 11 Secondary Effects –25.0–15.0–5.05.0 V D (V) –0.1 I D ( A ) 0.1 0 0 Avalanche Breakdown

12. EE141 © Digital Integrated Circuits 2nd Devices 12 Diode Model

13. EE141 © Digital Integrated Circuits 2nd Devices 13 SPICE Parameters

14. EE141 © Digital Integrated Circuits 2nd Devices 14 What is a Transistor? A Switch! |V GS | An MOS Transistor

15. EE141 © Digital Integrated Circuits 2nd Devices 15 The MOS Transistor Polysilicon Aluminum

16. EE141 © Digital Integrated Circuits 2nd Devices 16 MOS Transistors - Types and Symbols D S G D S G G S DD S G NMOS Enhancement NMOS PMOS Depletion Enhancement B NMOS with Bulk Contact

17. EE141 © Digital Integrated Circuits 2nd Devices 17 Threshold Voltage: Concept

18. EE141 © Digital Integrated Circuits 2nd Devices 18 The Threshold Voltage

19. EE141 © Digital Integrated Circuits 2nd Devices 19 The Body Effect

20. EE141 © Digital Integrated Circuits 2nd Devices 20 Current-Voltage Relations A good ol’ transistor Quadratic Relationship 00.511.522.5 0 1 2 3 4 5 6 x 10 -4 V DS (V) I D (A) VGS= 2.5 V VGS= 2.0 V VGS= 1.5 V VGS= 1.0 V ResistiveSaturation V DS = V GS - V T

21. EE141 © Digital Integrated Circuits 2nd Devices 21 Transistor in Linear

22. EE141 © Digital Integrated Circuits 2nd Devices 22 Transistor in Saturation Pinch-off

23. EE141 © Digital Integrated Circuits 2nd Devices 23 Current-Voltage Relations Long-Channel Device

24. EE141 © Digital Integrated Circuits 2nd Devices 24 A model for manual analysis

25. EE141 © Digital Integrated Circuits 2nd Devices 25 Current-Voltage Relations The Deep-Submicron Era Linear Relationship -4 V DS (V) 00.511.522.5 0 0.5 1 1.5 2 2.5 x 10 I D (A) VGS= 2.5 V VGS= 2.0 V VGS= 1.5 V VGS= 1.0 V Early Saturation

26. EE141 © Digital Integrated Circuits 2nd Devices 26 Velocity Saturation  (V/µm)  c = 1.5  n ( m / s )  sat = 10 5 Constant mobility (slope = µ) Constant velocity

27. EE141 © Digital Integrated Circuits 2nd Devices 27 Perspective I D Long-channel device Short-channel device V DS V DSAT V GS - V T V GS = V DD

28. EE141 © Digital Integrated Circuits 2nd Devices 28 I D versus V GS 00.511.522.5 0 1 2 3 4 5 6 x 10 -4 V GS (V) I D (A) 00.511.522.5 0 0.5 1 1.5 2 2.5 x 10 -4 V GS (V) I D (A) quadratic linear Long Channel Short Channel

29. EE141 © Digital Integrated Circuits 2nd Devices 29 I D versus V DS -4 V DS (V) 00.511.522.5 0 0.5 1 1.5 2 2.5 x 10 I D (A) VGS= 2.5 V VGS= 2.0 V VGS= 1.5 V VGS= 1.0 V 00.511.522.5 0 1 2 3 4 5 6 x 10 -4 V DS (V) I D (A) VGS= 2.5 V VGS= 2.0 V VGS= 1.5 V VGS= 1.0 V ResistiveSaturation V DS = V GS - V T Long ChannelShort Channel

30. EE141 © Digital Integrated Circuits 2nd Devices 30 A unified model for manual analysis S D G B

31. EE141 © Digital Integrated Circuits 2nd Devices 31 Simple Model versus SPICE V DS (V) I D (A) Velocity Saturated Linear Saturated V DSAT =V GT V DS =V DSAT V DS =V GT

32. EE141 © Digital Integrated Circuits 2nd Devices 32 A PMOS Transistor -2.5-2-1.5-0.50 -0.8 -0.6 -0.4 -0.2 0 x 10 -4 V DS (V) I D (A) Assume all variables negative! VGS = -1.0V VGS = -1.5V VGS = -2.0V VGS = -2.5V

33. EE141 © Digital Integrated Circuits 2nd Devices 33 Transistor Model for Manual Analysis

34. EE141 © Digital Integrated Circuits 2nd Devices 34 The Transistor as a Switch

35. EE141 © Digital Integrated Circuits 2nd Devices 35 The Transistor as a Switch

36. EE141 © Digital Integrated Circuits 2nd Devices 36 The Transistor as a Switch

37. EE141 © Digital Integrated Circuits 2nd Devices 37 The Sub-Micron MOS Transistor  Threshold Variations  Subthreshold Conduction  Parasitic Resistances

38. EE141 © Digital Integrated Circuits 2nd Devices 38 Threshold Variations V T L Long-channel threshold LowV DS threshold Threshold as a function of the length (for lowV DS ) Drain-induced barrier lowering (for lowL) V DS V T

39. EE141 © Digital Integrated Circuits 2nd Devices 39 Sub-Threshold Conduction 00.511.522.5 10 -12 10 -10 10 -8 10 -6 10 -4 10 -2 V GS (V) I D (A) VTVT Linear Exponential Quadratic Typical values for S: 60.. 100 mV/decade The Slope Factor S is  V GS for I D 2 / I D 1 =10

40. EE141 © Digital Integrated Circuits 2nd Devices 40 Sub-Threshold I D vs V GS V DS from 0 to 0.5V

41. EE141 © Digital Integrated Circuits 2nd Devices 41 Sub-Threshold I D vs V DS V GS from 0 to 0.3V

42. EE141 © Digital Integrated Circuits 2nd Devices 42 Summary of MOSFET Operating Regions  Strong Inversion V GS > V T  Linear (Resistive) V DS < V DSAT  Saturated (Constant Current) V DS  V DSAT  Weak Inversion (Sub-Threshold) V GS  V T  Exponential in V GS with linear V DS dependence

43. EE141 © Digital Integrated Circuits 2nd Devices 43 Parasitic Resistances

44. EE141 © Digital Integrated Circuits 2nd Devices 44 Latch-up

45. EE141 © Digital Integrated Circuits 2nd Devices 45 Future Perspectives 25 nm FINFET MOS transistor