1. Power Diodes for Cryogenic Operation PESC 2003 Acapulco, Mexico, June 2003

2. 2 R. R. Ward, W. J. Dawson, L. Zhu, R. K. Kirschman GPD Optoelectronics Corp., Salem, New Hampshire O. Mueller, M. J. Hennessy, E. K. Mueller LTE–Low Temperature Electronics, Ballston Lake, New York R. L. Patterson, J. E. Dickman NASA Glenn Research Center, Cleveland, Ohio A. Hammoud Dynacs Corp., Cleveland, Ohio

3. Motivation

4. 4 Cryogenic Power Electronics Semiconductor devices (diodes and transistors) For Power Management and Actuator Control For use down to 30 K = –243°C (and lower) Supported by NASA Glenn Research Center

5. “Very Little of the Solar System (or the Universe) Is at Room Temperature.”

6. 6 Solar System Temperatures Room Temperature

7. 7 Applications Space Solar-system exploration –Reasons: Cold environment, reduced power –For: Outer planets, cold satellites, asteroids, interstellar Scientific spacecraft/observatories –Reason: Cryogenic sensors and optics –For: Motors and actuators

8. 8 Applications Defense, Industry, Commercial Medical instruments (MRI) Electrical power (superconducting electrical power storage, transmission, distribution) Motors/generators (superconducting or cryogenic) Magnetic confinement (superconducting or cryogenic) High-power amplifiers (cell phone base stations, MRI)

9. 9 Applications Defense, Industry, Commercial Medical instruments (MRI) Electrical power (superconducting electrical power storage, transmission, distribution) Motors/generators (superconducting or cryogenic) Magnetic confinement (superconducting or cryogenic) High-power amplifiers (cell phone base stations, MRI) Reasons: Improved efficiency and reliability, reduced size and mass; many systems already incorporate cryogenics

10. 10 Applications Space Solar-system exploration –Reasons: Cold environment, reduced power –For: Outer planets, cold satellites, interstellar Scientific spacecraft/observatories –Reason: Cryogenic sensors and optics –For: Motors and actuators

11. 11 Spacecraft COLD/HOT ENVIRONMENT CONVENTIONAL ELECTRONICS HEATING/COOLING SYSTEM TEMPERATURE CONTROL THERMAL INSULATION (HEAT STORAGE)

12. 12 Spacecraft COLD/HOT ENVIRONMENT CONVENTIONAL ELECTRONICS HEATING/COOLING SYSTEM TEMPERATURE CONTROL 1 3 2 4 4 THERMAL INSULATION (HEAT STORAGE)

13. 13 Spacecraft LOW/HIGH TEMP ELECTRONICS COLD/HOT ENVIRONMENT

14. 14 “Cold” Spacecraft Eliminate heating, thermal control, isolation Reduce power, weight, size, cost, complexity Improve overall reliability Reduce disruption of environment Increase mission duration & capability

15. 15 Applications Space Solar-system exploration –Reasons: Cold environment, reduced power –For: Outer planets, cold satellites, interstellar Scientific spacecraft/observatories –Reason: Cryogenic sensors and optics –For: Motors and actuators

16. Why use Ge?

17. 17 Why Ge Devices? Ea,d (Ge) < Ea,d (Si)

18. 18 Why Ge Devices? Ea,d (Ge) < Ea,d (Si)  Ge can operate at lower T

19. 19 Why Ge Devices? Ea,d (Ge) < Ea,d (Si)  Lower T for Ge Experience with Ge JFETs at cryogenic temperatures

20. 20 Why Ge Devices? Ea,d (Ge) < Ea,d (Si)  Lower T for Ge Experience with Ge JFETs at cryogenic temperatures Ge has advantages over other semiconductor materials  Higher mobility than Si (especially at low temp) –Lower p- n junction forward voltage than Si or III-Vs

21. 21 Mobility Comparison Data from Madelung, 1991, pp. 18,34.

22. 22 Why Ge Devices? Ea,d (Ge) < Ea,d (Si)  Lower T for Ge Experience with Ge JFETs at cryogenic temperatures Ge has advantages over other semiconductor materials –Higher mobility than Si (especially at low temp)  Lower p- n junction forward voltage than Si or III-Vs

23. 23 P-N Junction (Diode) Forward Voltage

24. 24 Why Ge Devices ? (cont’d) Applications require operation to 30 - 40 K range Ge devices of all types can operate to low cryogenic temperatures (~ 20 K or lower)  Diodes can operate to deep cryogenic temperatures –JFETs can operate to deep cryogenic temperatures (down to few K) –Bipolar transistors can operate to deep cryogenic temperatures

25. 25 Commercial 15-A Ge Diode

26. 26 Commercial 15-A Ge Diode

27. 27 Commercial 60-A Ge Diode

28. 28 Commercial 60-A Ge Diode

29. 29 Why Ge Devices? (cont’d) Applications require operation to 30 - 40 K range Ge devices of all types can operate to low cryogenic temperatures (~ 20 K or lower) –Diodes can operate to deep cryogenic temperatures  JFETs can operate to deep cryogenic temperatures (down to few K) –Bipolar transistors can operate to deep cryogenic temperatures

30. 30 Field-Effect Transistor Comparison

31. 31 Ge JFET at 20 K (–253ºC)

32. 32 Ge MISFET at 4 K (–273ºC)

33. 33 Why Ge Devices? (cont’d) Applications require operation to 30 - 40 K range Ge devices of all types can operate to low cryogenic temperatures (~ 20 K or lower) –Diodes can operate to deep cryogenic temperatures –JFETs can operate to deep cryogenic temperatures (down to few K)  Bipolar transistors can operate to deep cryogenic temperatures (down to ~20 K or lower)

34. 34 Ge Bipolar Junction Transistor Zero: upper right Horiz: 0.5 V/div Vert: 1 mA/div I B : 0.02 mA/step at RT, 0.1 mA/step at 4 K 300 K 4 K

35. 35 Ge Bipolar Junction Transistor

36. 36 Bipolar Junction Transistor Comparison

37. Results for New Ge Diodes

38. 38 New Planar Ge Cryo Power Diodes N - N+ implant P+ implantMetal Guard ring

39. 39 New Ge Cryo Power Diodes - Forward

40. 40 New Ge Cryo Power Diodes - Forward

41. 41 Ge Power Diodes - Forward Voltage

42. 42 Ge Power Diodes - Forward Voltage

43. 43 Ge Power Diodes - Reverse Breakdown

44. 44 Ge Power Diodes - Reverse Recovery

45. 45 Ge Power Diodes - Reverse Recovery

46. 46 Ge Power Diodes - Reverse Recovery

47. 47 Ge Power Diodes - Reverse Recovery

48. 48 Ge Power Diodes - Reverse Recovery

49. 49 Summary Cryogenic power electronics is needed for spacecraft going to cold environments and for space observatories Temperatures may be as low as ~30 - 40 K We have characterized Ge devices – diodes, JFETs, and bipolars – at cryogenic temperatures Ge devices can operate to deep cryogenic temperatures – to 20 K and as low as 4 K We are developing Ge diodes specifically for cryogenic applications