Ge Semiconductor Devices

for

Cryogenic Power Electronics - II

WOLTE 5

Grenoble, June 2002

2

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

GPD Optoelectronics Corp., Salem, New Hampshire

O. 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

Cryogenic Power Electronics

• Semiconductor devices (diodes and transistors)

• For Power Management and Actuator Control

• For use down to 30 K (and lower)

• Supported by NASA Glenn Research Center

4

ApplicationsSpace

• 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

5

ApplicationsDefense, 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)

6

ApplicationsDefense, 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

7

ApplicationsSpace

• 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

8

Solar System Exploration

• Rovers, fly-by, orbiters, landers, probes, penetrators

• Cold environments - Heating

- Wake/sleep (where possible)

9

Spacecraft

CONVENTIONAL

ELECTRONICS

HEATINGPOWER

TEMPERATURECONTROL

CRYOGENIC

ELECTRONICS

1 2

34

5

COLD ENVIRONMENT

10

“Cold” Spacecraft

• Eliminate heating, thermal control, isolation

• Reduce power, weight, size, cost, complexity

• Improve overall reliability

• Reduce disruption of environment

• Increase mission duration & capability

11

ApplicationsSpace

• 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

12

~30 K

NGST - Next Generation Space TelescopeNASA Goddard Design

13

Why Ge Devices?

• Ea,d (Ge) < Ea,d (Si)

14

Why Ge Devices?

• Ea,d (Ge) < Ea,d (Si) Lower T for Ge

15

Why Ge Devices?

• Ea,d (Ge) < Ea,d (Si) Lower T for Ge

• Experience with Ge JFETs at cryogenic temperatures

16

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

17

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

18

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

19

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

20

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

21

Results – 15-A Ge Diode

0 0.2 0.4 0.6 0.8 1

R7u 4/100/80

R10d 4/100/80

N5u

N6d

M2u

M5d

VH-VL up

VH-VL down

K7d

K10u

VH-VL up

VH-VL down

H13u

H14d0

1

2

3

4

Voltage (V)

77 KRT

40 K 20 K

4 K

22

Results – 15-A Ge Diode

-0.02

-0.01

0

Irev 2(A) downIrev3 (A) upIrev3 (A) upIrev5 (A) downIrev3 (A) downIrev4 (A) upIrev4 (A) downIrev5 (A) upIrev2 (A) upIrev3 (A) down

-100 -80 -60 -40 -20 0

Voltage (V)

4 K

40 K

20 K

77 K

300 K

23

Results – 60-A Ge Diode

0 0.2 0.4 0.6 0.8 1

R2uR3dN10uN11dM12uM13dK18uK19dH21uH21uH22dH23u

0

1

2

3

4

Voltage (V)

77 KRT

40 K

20 K 4 K

24

Results – 60-A Ge Diode

-0.02

-0.01

0

Rrev4u (A)Rrev5d (A)Rrev6u (A)Rrev7d (A)Nrev8u (A)Nrev9d (A)Mrev14u (A) Mrev15d (A)Krev16u (A)Krev17d (A)Hrev24u (A)Hrev25d (A)

-100 -80 -60 -40 -20 0

Voltage (V)

4 K

40 K

20 K

77 K

300 K

25

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

26

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)

27

Low-Power Ge JFET at 4 K

0

20

40

60

80

0 5 10 15 20 25 30 35 40

Vgs = 0 V

Vgs step = 1 V

Drain-source voltage, Vds (V)

Vgs = -5.0 V

Ge JFET A71G4 K

28

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)

29

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

30

Ge Bipolar Junction Transistor

-100

-80

-60

-40

-20

0-2-1.5-1-0.50

IB = -0.5 mA

2N964-3-1229A,B,C

Collector-emitter voltage, V (V)CE

IB = -2.5 mA

IB = 0

20 K

31

Bipolar Junction Transistor Comparison

1

10

100

1000

01020304050

Temperature -1 (1000/K)

SiGe

20 30 50 80 300120

Temperature (K)

32

Ge MIS Structures

Au/Cr electrode

Si3N4

SiO2

Ge substrate

33

0

0.1

0.2

0.3

-20 -10 0 10 20

R2upR2dnN2upN2dnM2upM2dnJ1upJ1dnG1upG1dnE1up (nF)E1dn

Voltage (V)

WA-5

7.9 K

300 K

8.6 K

10 K

77 K

Results – Ge MIS Structures

34

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

35

Plans

• Continue to evaluate and characterize Ge

devices at cryogenic temperatures

• Determine necessary design features for

cryogenic power devices – for 30 K and lower

• Develop related infrastructure– Fixturing and instrumentation for evaluation

– Packaging and interconnections

36

Plans (cont’d)

• Design, fabricate and evaluate Ge power devices for cryogenic operation

– Demonstrate Ge MOSFETs

– Develop Ge cryogenic power devices: diodes, BJTs, JFETs, MOSFETs, IGBTs

– Improve device characteristics (reverse breakdown voltage, for example)

• Evaluate performance in power circuits.

• Investigate SiGe devices for cryogenic power applications

37

Results – Ge MIS Structures

0

0.1

0.2

0.3

0.4

0.5

-20 -15 -10 -5 0 5 10 15 20

R11 up

R11 dn

77a up

77a dn

10a up

10a dn

1476a up

1476a dn

14795a up

14795a dn

1504a up

1504a dnVoltage (V)

E-03

7.5 K

300 K

8.2 K

10 K

77 K

38

Reliability

• Processes involving thermal energy

effectively absent– Electromigration

– Corrosion

– Interdiffusion

• Remaining reliability issues– Thermal expansion differences

– Charge trapping/freeze-out

– Reduce by materials selection, device design, operating conditions