Ge Semiconductor Devices

for

Cryogenic Power Electronics - IV

Electrochemical Society

Seventh International Symposium on Low Temperature Electronics

14 October 2003, Orlando, Florida

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

GPD Optoelectronics Corp., Salem, New Hampshire

M. J. Hennessy, E. K. Mueller

MTECH Laboratories, Ballston Lake, New York

R. L. Patterson, J. E. Dickman

NASA Glenn Research Center, Cleveland, Ohio

A. Hammoud

QSS Group Inc., Cleveland, Ohio

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Cryogenic Power Electronics

• Semiconductor Devices (diodes and transistors)

• For Use down to 30 K and Lower

• For Power Management and Actuator Control

• For Spacecraft

• Supported by NASA Glenn Research Center

Why Use Ge?

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Why Ge Devices?

• Si-Based Circuits Demonstrated, but only > 77 K

• Si Bipolar Devices Cease Operation < ~100 K

• Applications Require Operation < 77 K, to ~30 – 40 K

• Possible Materials for < 77 K are Ge and SiGe

• Ge Devices Can Operate to Lowest Cryogenic

Temperatures (~ 0 K)

• All Device Types – Diodes, Field-Effect Transistors,

Bipolar Transistors

Development Program

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Development Program• Parameters

– Low power (~10 W) and medium power (~100 W)

– Temperature range 300 K to ~20 K

• Past

– Investigated existing Ge semiconductor devices at cryogenic temperatures (diodes, BJTs, JFETs)

– Designed and fabricated Ge cryogenic power diodes (P--N, 10 A, 300 V)

• Devices under Development

– MISFETs (lateral, vertical implanted, vertical epi)

– JFETs (lateral, vertical)

– BJTs (vertical implanted, vertical epi)

– IGBTs (vertical implanted, vertical epi)

Ge Cryo Power Diodes

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Ge Cryo Power DiodesP- - N Bulk Design

N– ( )

N+ implant

P+ implant Metal

Metal

Guard ring(s)

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Ge Cryo Power Diodes - Forward Voltage

0

0.5

1

1.5

0.2 A

0.2 A Si

Vf 0.2 A

Vf 0.2 A

Vf (0.2 A)

Vf (0.2 A)

0 40 80 120 160 200 240 280 320

Temperature (K)

Commercial Ge power diodes

Si power diodes

Ge cryo power diodes (2 thick, 2 thin)

If = 0.2 A

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Ge Cryo Power Diodes - Forward Voltage

0

0.5

1

1.5

2

0 40 80 120 160 200 240 280 320

Temperature (K)

Commercial Ge power diodes

Si power diodes

Ge cryo power diodes (thick)

If = 4 A

Ge cryo power diodes (thick)

Ge cryo power diodes (thin)

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Ge Cryo Power Diodes - Forward I-V

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Ge Cryo Power Diodes - Forward I-V

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Ge Cryo Power Diode – Forward I-V

0 0.2 0.4 0.6 0.8 10

1

2

3

4

Forward Voltage (V)

120 K

300 K

40 K

20 K

4 K80 K

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Ge Power Diodes – Reverse Breakdown

0

100

200

300

400

500

600

0 50 100 150 200 250 300

Temperature (K)

18-1-B2b

18-1-D1d

12-1-Aa

Commercial Ge power diodes

16

-12

-8

-4

0

4

8

12

0 200 400 600 800 1000 1200

Time (ns)

77 K

300 K

18-1-AaJune 2003

Ge Power Diodes – Reverse Recovery

17

-12

-8

-4

0

4

8

12

0 200 400 600 800 1000 1200

Time (ns)

77 K

300 K

18-1-B1cJune 2003

Ge Power Diodes – Reverse Recovery

18

0

1

2

3

4

0 2 4 6 8 10 12

Forward Diode Current (A)

77 K

300 K

Ge Power Diodes – Reverse Recovery

19

-12

-8

-4

0

4

8

12

0 200 400 600 800 1000 1200

Time (ns)

77 K

300 K

30-1-C1bJune 2003

Ge Power Diodes – Reverse Recovery

20

-12

-8

-4

0

4

8

12

0 200 400 600 800 1000 1200

Time (ns)

77 K

300 K

30-2-AaJune 2003

Ge Power Diodes – Reverse Recovery

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Ge Cryo Power Diodes - Future

• Improved Guard-Ring Designs and Tailored Implant– Higher Vr

• Schottky Designs– Lower forward voltage

• N--P (compared to P--N)– Possible improvement in Vf and Vr– Possible improvement in speed/reverse recovery– Possible elimination of “backlash” at 4 K– Possible lower reverse leakage

Ge Cryo Power MISFETs

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Ge Cryo Power JFET or MISFET

~1.8 mm

G

S

D

S

G

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Basic Lateral Ge MISFET Design

Substrate

Source Gate

P+ implant

P substrate

Gate dielectric

N+ implant

Drain

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Ge Power MISFET at 300 K

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Ge Power MISFET at 77 K

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Ge Power MISFET at 4 K

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Basic Vertical Ge MISFET Design

Drain

Source Gate

N+ implant

N substrate

P implant

Gate dielectric

N+ implant

Two versions: double-implant (above) and epi

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Basic Vertical Ge MISFET Design

Two versions: double-implant and epi (above)

Drain

Source Gate

P+ implant

P– substrate

P+ implant

Gate dielectric

N epi

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Ge Cryo Power MISFETs - Plans

• Larger-Area and Modified Doping (for Lateral Ge)– Higher I and higher Vbk

• Vertical Designs for Ge– Higher I and higher Vbk

• Reverse Double-Implant Vertical Design for Ge– Better results than present double-implant

design

Ge Cryo Power JFETs

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Ge JFET Cross-Section (n-channel)

S Gf D

N Epitaxial LayerP+ Implant

N+ Implant

Gb

P+ Ge Substrate

Passivation

Au-Sb Ti-Au

Backside Metalization (Au)

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Power Ge JFET at 300 K

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Power Ge JFET at 77 K

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Power Ge JFET at 4 K

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Another Power Ge JFET at 20 K

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Power JFETs - Plans

• P-Type– Complementary circuits

• Higher I and Vbk

• Vertical (SIT) Design– Higher I and higher Vbk

Ge CryoBipolar Junction Transistors

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Ge Bipolar – Double-Implant

Collector

BaseEmitter

N+ implant

N– substrate

P implant

N+ implant

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Ge Bipolar – Epitaxial

Collector

BaseEmitter

N+ implant

N– substrate

P epi

N+ implant

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Power BJTs - Plans

• Reverse Double-Implant Design for Ge– Better characteristics than present

double-implant design?

• Epitaxial Design for Ge

Ge Cryo IGBTs

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Basic Ge IGBT Design

Collector

Emitter Gate

P+ implant

N– substrate

P implant

Gate dielectric

N+ implant

Two versions: double-implant (above) and epi

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Basic Ge IGBT Design

Two versions: double-implant and epi (above)

Collector

Emitter Gate

N+ implant

P– substrate

P+ implant

Gate dielectric

N epi

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Summary

• We Have Characterized Commercial Ge Devices

(Diodes and Bipolars) at Cryogenic Temperatures

• In a Separate Development We Have Demonstrated

that Ge JFETs Work Well at Cryogenic Temperatures

• All Types of Ge Devices Can Operate to Deep

Cryogenic Temperatures – to 20 K, as Low as 4 K

• Developed 10-A Ge Cryogenic Power Diodes with

High Reverse Breakdown and Low Forward Voltage

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Summary – cont’d

• Characterized Ge MIS Structures

at Room and Cryogenic Temperatures

• Made Ge Power MISFETs that Operate from Room

Temperature down to 4 K

• Made Ge Power JFETs that Operate from Room

Temperature down to 4 K

• Improved MISFETs and JFETs Are in Progress

• Ge BJT and IGBT Fabrication Is in Progress