NEPP - April/May 2002

Semiconductor Device Options

forLow-Temperature Electronics

R. K. Kirschman, R. R. Ward and W. J. Dawson

GPD Optoelectronics Corp., Salem, New Hampshire

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Topics

• Why low-temperature electronics?

• Semiconductor device behavior

• Semiconductor materials options

• Summary

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Topics

• Why low-temperature electronics?

• Semiconductor device behavior

• Semiconductor materials options

• Summary

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• Cold environment

Spacecraft for deep space/solar system

Why Low-Temperature Electronics?

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Cold Spacecraft

• Eliminate heating, thermal control, isolation

• Reduce power, weight, size, cost, complexity

• Increase mission duration & capability

• Improve overall reliability

• Reduce disruption of environment

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• 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?

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Observatories

• Cooling detectors for performance

• Signal-processing electronics (low-power) has been used since ~1980

• Drive (power) electronics for mechanical actuators & motors

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Topics

• Why low-temperature electronics?

• Semiconductor device behavior

• Semiconductor materials options

• Summary

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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

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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)

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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)

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Topics

• Why low-temperature electronics?

• Semiconductor device behavior

• Semiconductor materials options

• Summary

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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, ...

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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

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Si Power Circuit Examples(selected)

Circuit/system Power Experimental Results Refs

Three-phase bridgeinverter

50 kW Loss ~1% at 77 K Gardiner’96

Class E RF (6.78 MHz)power amp

~1000 W Efficiency 85% @ 333 K (60°C) 99% @ ~90 K(loss 15% vs 1%)

Mueller‘93

Buck PWM dc-dcconverter

175 W Efficiency 95.8% 300 K 97% 77 K(loss 4.2% vs 3%)

Ray‘95

Boost PWM dc-dcconverter

150 W Efficiency 94% @ 300 K 95.9% @ 77 K Ray‘96

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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)

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Mobility Comparison

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

0

1 104

2 104

3 104

4 104

5 104

80 K 300 K

n-Sip-SiFn-Gep-Ge

np

p

p

p nn

n

Si

Si

Ge

Ge

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Field-Effect Transistor Comparison

0

0.5

1

1.5

2

2.5

3

3.5

0 50 100 150 200 250 300

Temperature, T (K)

Si JFET (U310)

Ge JFET

Si JFET (2N4416)

I (300)dss

dss

I (T)

GaAs MESFET (3SK121)

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Bipolar Junction Transistor Comparison

1

10

100

1000

01020304050

Temperature -1 (1000/K)

SiGe

20 30 50 80 300120

Temperature (K)

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Ge Bipolar Junction Transistor

Zero: upper right Horiz: 0.5 V/div Vert: 1 mA/divIB: 0.02 mA/step at RT, 0.1 mA/step at 4 K

300 K 4 K

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P-N Junction (Diode) Forward Voltage

0

0.5

1

1.5

0.2 A1 A

2 A4 A

0 40 80 120 160 200 240 280 320

Vf vs T Temperature (K)

Ge

Si

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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 - ?

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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

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Topics

• Why low-temperature electronics?

• Semiconductor device behavior

• Semiconductor materials options

• Summary

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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

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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