1. NEPP - April/May 2002 Semiconductor Device Options for Low-Temperature Electronics R. K. Kirschman, R. R. Ward and W. J. Dawson GPD Optoelectronics Corp., Salem, New Hampshire

2. 2 Topics Why low-temperature electronics? Semiconductor device behavior Semiconductor materials options Summary

3. 3 Topics Why low-temperature electronics? Semiconductor device behavior Semiconductor materials options Summary

4. 4 Cold environment Spacecraft for deep space/solar system Why Low-Temperature Electronics?

5. 5 Cold Spacecraft Eliminate heating, thermal control, isolation Reduce power, weight, size, cost, complexity Increase mission duration & capability Improve overall reliability Reduce disruption of environment

6. 6 Cold environment Spacecraft for deep space & solar system Refrigeration provided for other hardware Space observatories Also superconducting/cryogenic motors & generators, power transmission lines, energy storage, cell-phone filters Why Low-Temperature Electronics?

7. 7 Observatories Cooling detectors for performance Signal-processing electronics (low-power) has been used since ~1980 Drive (power) electronics for mechanical actuators & motors

8. 8 Topics Why low-temperature electronics? Semiconductor device behavior Semiconductor materials options Summary

9. 9 Semiconductor Devices Can operate at cryogenic temperatures, down to the lowest temperatures ~0 K All types –Minority & majority carrier –Bipolar & field-effect –Diodes, transistors Including power devices With appropriate materials and design

10. 10 Characteristics at Cryogenic Temperatures Most characteristics improve - significantly –Gain (field-effect transistors) –On-voltage (field-effect transistors) –Losses & parasitic resistances –Leakage –Speed/frequency –Thermal conductivity –Also lower-loss passives (C, L)

11. 11 Characteristics at Cryogenic Temperatures Most characteristics improve - significantly –Gain (field-effect transistors) –On-voltage (field-effect transistors) –Losses & parasitic resistances –Leakage –Speed/frequency –Thermal conductivity –Also lower-loss passives (C, L) Some characteristics degrade –P-N junction forward voltage –Breakdown voltage –Charge trapping (freeze-out, hot-electron effects)

12. 12 Topics Why low-temperature electronics? Semiconductor device behavior Semiconductor materials options Summary

13. 13 Materials Options Elemental semiconductors –IV –Si, Ge, C (diamond) Compound semiconductors –IV-IV, III-V, (II-VI) –GaAs, GaP, InP, SiC,... (large gap) –InSb, InAs,... (small gap) Alloys (Elemental & Compound) –IV-IV, III-V, (II-VI) –SiGe –InGaAs, AlGaAs,...

14. 14 Elemental Semiconductors Si –Widely available, vast technology base –Power circuits demonstrated down to ~77 K, lower temperatures not demonstrated for power devices –Majority devices (field-effect transistors) work at cryogenic temperatures –Minority devices (bipolar transistors) lose performance upon cooling, not useable at cryogenic temperatures

15. 15 Si Power Circuit Examples (selected)

16. 16 Elemental Semiconductors Ge –Modest technology base –Majority and minority devices work to ~20 K and lower –Higher mobility than Si, room and low temperature –Lower p-n junction V than Si or III-Vs –Lower breakdown V –Good gate insulator difficult (needed for MOS devices)

17. 17 Mobility Comparison Data from Madelung, 1991, pp. 18,34.

18. 18 Field-Effect Transistor Comparison

19. 19 Bipolar Junction Transistor Comparison

20. 20 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

21. 21 P-N Junction (Diode) Forward Voltage

22. 22 Compound Semiconductors GaAs, GaP, InP, SiC, InSb, InAs,... –Medium technology base for GaAs –Minimal technology base for others –Good gate dielectric is difficult –Power devices not developed –Little information on cryogenic power characteristics –Higher p-n junction forward V than Si or Ge –Breakdown - ?

23. 23 Alloy Semiconductors SiGe –Extensive recent development and application for RF –Compatible with existing widely available Si technology base –Design flexibility – band-gap engineering and selective use –Minimal information on power device performance, nothing on cryogenic power device performance InGaAs –Demonstrated to 20 K for power Other materials –Little or no information for cryogenic power devices

24. 24 Topics Why low-temperature electronics? Semiconductor device behavior Semiconductor materials options Summary

25. 25 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 Si, Ge, SiGe are excellent candidates for cryogenic power devices, depending on temperature and other factors

26. 26 Summary (cont’d) Use Si where possible –Extensive technology base and availability –Limitations for deep cryogenic temperatures –Several groups working on Si for low temperature Develop Ge and SiGe –For deep cryogenic temperatures (to ~20 K) and/or performance advantages –Ge being developed for cryogenic power –SiGe investigation just beginning Other materials, GaAs, InGaAs,... –Also possible for cryogenic operation