Bridging Theory in Practice

1. Bridging Theory in Practice Transferring Technical Knowledge to Practical Applications

2. Introduction to Semiconductors

3. Introduction to Semiconductors C B D G E S

4. Introduction to Semiconductors Intended Audience: • Engineers with little or no semiconductor background • A basic understanding of electricity is assumed Topics Covered: • What is a semiconductor? • What is a diode? • What is a bipolar transistor? • What is a MOSFET transistor? Expected Time: • Approximately 1 Hour

5. Introduction to Semiconductors • What is a Semiconductor? • What is a N-Type and a P-Type Semiconductor? • What is a Diode? • What is a Bipolar Junction Transistor (BJT)? • What is a Field Effect Transistor (MOSFET)?

6. – – – – – – – – – Si – Si – Si – Si – – Si – Si–Si–Si – – Si – Si – Si – Si – – Si – Si – Si – Si – – Si – Si – Si – Si – – Si – Si – Si – Si – – Si – Si – Si – Si – – Si – Si – Si – Si – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – Silicon Crystal Structure • A crystal is a solid composed of atoms in a single, UNIFIED array • Notice each silicon atom is “connected” to its four nearest neighboring silicon atoms

7. Sharing Electrons Many atoms (including silicon) like to have EIGHT electrons in their outer “orbit” But, silicon only has FOUR outer electrons Solution: Silicon atoms share electrons with each other

8. Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Silicon Atoms Sharing Electrons in a Crystal

9. Semiconductor Silicon • A conductor is a material which “conducts” electricity easily (such as metals) • An insulator is a material which is a very poor conductor of electricity (such as glass) • A semiconductor (silicon) is a material which acts like an insulator, but behaves like a conductor when it is combined with other materials

10. Introduction to Semiconductors • What is a Semiconductor? • What is a N-Type and a P-Type Semiconductor? • What is a Diode? • What is a Bipolar Junction Transistor (BJT)? • What is a Field Effect Transistor (MOSFET)?

11. Phosphorous +5 N-Type Silicon Charge Neutrality • Adding Phosphorous to silicon creates a semiconductor with additional mobile Negative charges (electrons) Phosphorous added to Silicon +5 Plus 1 Mobile Electron (-)

12. Boron +3 P-Type Silicon Charge Neutrality • Adding boron to silicon creates a semiconductor with additional mobile Positive charges (absence of electrons) Boron added to Silicon +3 Plus 1 Mobile Hole (+)

13. Boron and Phosphorous Atomsin a "Sea of Silicon" Boron Phosphorous

14. Introduction to Semiconductors • What is a Semiconductor? • What is a N-Type and a P-Type Semiconductor? • What is a Diode? • What is a Bipolar Junction Transistor (BJT)? • What is a Field Effect Transistor (MOSFET)?

15. Boron and Phosphorous Mobile Charge in a Sea of Silicon Boron Phosphorous

16. Boron and Phosphorous Mobile Charge in a Sea of Silicon Boron Diffusing positive charge leaves behind a stationary negative charge

17. Boron and Phosphorous Mobile Charge in a Sea of Silicon Boron Phosphorous Diffusing negative charge leaves behind a stationary positive charge

18. Boron and Phosphorous Mobile Charge in a Sea of Silicon Boron Phosphorous

19. Electrons Diode Under Forward Bias • Before the forward bias is applied… Holes P N Negative Positive "Built In Voltage" ~ 0.7V

20. 0.7V 0.5V 0.4V 0.6V 0.3V 0.1V 0.2V Diode Under Forward Bias • As the forward bias is applied, it overcomes the built in voltage and current can flow.... - + P N Positive Negative "Built In Voltage" ~ 0.3V "Built In Voltage" ~ 0.2V "Built In Voltage" ~ 0.4V "Built In Voltage" ~ 0.7V "Built In Voltage" ~ 0.0V "Built In Voltage" ~ 0.5V "Built In Voltage" ~ 0.6V "Built In Voltage" ~ 0.1V 0.0V

21. Diode Under Forward Bias • As the forward bias is applied, it overcomes the built in voltage and current can flow.... - + P N "Built In Voltage" ~ 0.0V 0.7V

22. Diode Under Forward Bias • As the forward bias is applied, it overcomes the built in voltage and current can flow.... Current (I) ~0.7 Voltage (V)

23. Electrons Diode Under Reverse Bias • Before the reverse bias is applied… Holes P N Negative Positive "Built In Voltage" ~ 0.7V

24. Electrons Diode Under Reverse Bias • As reverse bias is applied… Holes - + P N Positive Negative "Built In Voltage" ~ 1.7V 1.0V

25. Electrons Diode Under Reverse Bias • As reverse bias is applied… Holes - + P N Positive Negative "Built In Voltage" ~ 1.7V 1.0V

26. Ideal Diode Current-Voltage (I-V) Characteristics V Current (I) Voltage (V) 0.7

27. Actual Diode Current-Voltage (I-V) Characteristics Current (I) Ideal Actual 0.7 Voltage (V)

28. Diode I-V Temperature Characteristics +125C +25C -40C Current (I) -40C 0.7 Voltage (V) +25C +125C

29. Introduction to Semiconductors • What Is a Semiconductor? • What is a N-Type and a P-Type Semiconductor? • What is a Diode? • What is a Bipolar Junction Transistor (BJT)? • What is a Field Effect Transistor (MOSFET)?

30. Bipolar Junction Transistor (BJT) • Formed by back-to-back n-type and p-type semiconductor regions N N P Positive Positive Negative Negative P-type region is very narrow

31. NPN Bipolar Junction Transistor (BJT) Collector (will collect electrons) N Positive Base (of operations, i.e. the control center) Negative P Negative Positive N Emitter (will emit electrons)

32. Current tries to flow N VCollector > VBase VCE Positive Reverse Biased No Current Flows Negative P Negative Positive N NPN Bipolar Junction Transistor (BJT) Collector Base Emitter

33. VCE VBE NPN Bipolar Junction Transistor (BJT) Collector N VBase > VEmitter Positive Negative Base P Forward Biased Current Can Flow Negative Positive N Emitter

34. VCE VBE Current Flows NPN Bipolar Junction Transistor (BJT) Collector Electrons near base- collector interface are pulled across creating a current. We now have an excessively large number of electrons in the base. N VBase > VEmitter Positive Negative Base P Forward Biased Current Can Flow Negative Positive N Emitter

35. N Positive Negative P Negative Positive N NPN Bipolar Junction Transistor (BJT) Collector (will collect electrons) C Base (of operations, i.e. the control center) B E Emitter (will emit electrons)

36. Bipolar Junction Transistor (BJT) Invented in 1947 by: William Shockley (1910-1989) Walter Brattain (1902-1987) John Bardeen (1908-1991) • “Point contact” transistor used a single physical contact as the base • Consisted of a germanium crystal and two “whiskers”

37. Introduction to Semiconductors • What Is a Semiconductor? • What is a N-Type and a P-Type Semiconductor? • What is a Diode? • What is a Bipolar Junction Transistor (BJT)? • What is a Field Effect Transistor (MOSFET)?

38. Metal Oxide Semiconductor Field Effect Transistor (MOSFET) True of False: The transistor was first conceived and patented by W.Shockley, J.Bardeen, and W.Brattain at Bell Labs in the late 1940’s…

39. Metal Oxide Semiconductor Field Effect Transistor (MOSFET) FALSE! The concept of a field effect transistor was first developed and patented by J.Lilienfeld in Canada and the United States in the years 1924-1928. In fact, the Bell Labs engineers’ first patent was written to reflect Lilienfeld’s prior work.

40. n-Channel MOSFET Cross Section (nMOS) “Sea of Silicon with Mobile Holes” P-Type Silicon Substrate

41. n-Channel MOSFET Cross Section (nMOS) SiO2 (An Excellent Insulator) P-Type Silicon Substrate

42. n-Channel MOSFET Cross Section (nMOS) N-Type Silicon “Sea of Silicon with Mobile Electrons” SiO2 N-Type Si N-Type Si P-Type Silicon Substrate

43. n-Channel MOSFET Cross Section (nMOS) Metal Contacts SiO2 N-Type Si N-Type Si P-Type Silicon Substrate

44. n-Channel MOSFET Cross Section (nMOS) “Gate” (or Door) between source and drain Electrons will come from here Electrons will come out out here Source Gate Drain SiO2 N-Type Si N-Type Si P-Type Silicon Substrate

45. Source Gate Drain SiO2 N-Type Si N-Type Si P-Type Silicon Substrate n-Channel MOSFET Cross Section (nMOS) Gate Source Drain

46. n-Channel MOSFET Biasing Source Gate Drain SiO2 N-Type Si N-Type Si P-Type Silicon Substrate Back-to-Back Diodes

47. Current wants to flow n-Channel MOSFET Biasing Source Gate = 0V Drain SiO2 N-Type Si N-Type Si Reverse Bias No Current Flows P-Type Silicon Substrate

48. Above 0 degK, a few mobile electrons will exist in the substrate n-Channel MOSFET Mobile Carriers Source Gate Drain SiO2 N-Type Si N-Type Si P-Type Silicon Substrate Diodes Still Exist

49. n-Channel MOSFET Biasing Source Gate > 0V Drain SiO2 N-Type Si N-Type Si P-Type Silicon Substrate

50. n-Channel MOSFET Biasing Current Flows Source Gate > 0V Drain SiO2 N-Type Si N-Type Si P-Type Silicon Substrate