NEPP - April/May 2002 Semiconductor Device Options for Low-Temperature Electronics

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

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

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

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

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. Why Low-Temperature Electronics? • 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

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

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

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

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. 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. Si Power Circuit Examples(selected)

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

18. Field-Effect Transistor Comparison

19. Bipolar Junction Transistor Comparison

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

21. P-N Junction (Diode) Forward Voltage

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

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. 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