1. ECE 695 Discussion Session GaN HEMT Technology – Recent Advances
Yen-Sung Chen
Feb. 15th 2017

2. Outline Material Properties Results from some groups MIT Purdue UND
UCSB
Fujitsu
Panasonic
HRL
Summary

3. Comparison of Semiconductors for Power Devices
Left: M. Yoder, TED, 1996
Right up: J. Hudgins et al., IEEE Transactions on Power Electronics, 2003
Right bottom: Y. Zhang et al., TED, 2016

4. MIT – GaN Nanoribbon HEMT
1. Al2O3/AlGaN interface fixed positive charge.
2. Al2O3 passivation layer induces biaxial tensile stress
piezoelectric field in AlGaN layer increases.
2DEG density increases
Sheet resistance decreases
Ron decreases
MOCVD, SiC substrate
ns=9.75x1012(cm-2), µ=2109(cm2/Vs).
S. Joglekar et al., TED, 2016

5. Purdue – GaN MOSHEMT SiC substrate
ALD grown lattice-matched MgCaO improves on-off ratio and Dit
ns=2x1013(cm-2), µ=1200(cm2/Vs).
DC: Ron=1.3(Ω-mm), Vgs~-3V, Vds=5V.
H. Zhou et al., EDL, 2016
InAlN/GaN vs. AlGaN/GaN:
Larger spontaneous polarization difference
Higher 2DEG density
2. Limited SBH and thinner barrier
Higher Leakage

6. UND – GaN HEMT Utilized AlN substrate instead of SiC due to:
wide Eg (6.2 eV vs. 3.3 eV)
lower dislocation density 104 cm-2 vs. 109 cm-2)
Comparable thermal conductivity (340W/m.K vs. 370 W/m.K)
MBE
ns=3.4x1013(cm-2), µ=180(cm2/Vs).
DC: Ron=1.8(Ω-mm), Vds=8V
fT=120GHz, Vds=8V
M. Qi et al., APL, 2017.
MOCVD, SiC substrate
ns=1.92x1013(cm-2), µ=1240(cm2/Vs).
DC: Ron=0.16(Ω-mm), Vgs=-3.6V, Vds=3V
Vds=3V
fmax=33GHz (high resistance of gate geometry)
Y. Yue et al., JJAP, 2013.

7. UCSB – GaN MISHEMT
N-polar GaN: improved electron confinement, lower RC (no AlGaN)
MBE, sapphire substrate
DC: Ron=0.29(Ω-mm), Vds=8V
Vds=8V, Vds=8V
S. Dasgupta et al., APL, 2010 & D. Denninghoff et al., DRC, 2012
MBE, SiC substrate, N-polar GaN
DC: Ron=0.4(Ω-mm), gm=592(mS/mm)
fT=160GHz, fmax=270GHz
PAE=27.8%, Vds=9V, Ids=650mA/mm
Operated in W-band (96GHz)
B. Romanczyk et al., IEDM 3.5, 2016

8. Fujitsu – GaN HEMT SiC substrate
InAlGaN barrier was used instead of InAlN:
Reduced gate leakage.
90% more 2DEG density.
Double layer SiN => prevent oxidation and reduce current collapse.
fmax=200GHz
96 GHz Vds=20V
K. Makiyama et al., IEDM 9.1, 2015

9. Panasonic – GaN HEMT MOCVD, GaN substrate
ns=5.6x1012(cm-2), µ=1900(cm2/Vs).
Thick buffer layer (16µm) reduced output capacitance.
=> Faster switching
GaN substrate improves crystal quality
Suppress current collapse.
BV up to (Ec=1.4MV/cm)
H. Handa et al., IEDM 10.3, 2016.
MOCVD, GaN substrate, vertical structure
ns=6.1x1012(cm-2), µ=1690(cm2/Vs).
Slanted channel results in larger VT
C-doped GaN/p-GaN well hybrid barrier layer (HBL) boosts BV to 1700V.
Regrown triple layer further reduce Ron
D. Shibata et al., IEDM 10.1, 2016.

10. HRL – GaN HEMT (T3 Generation)
Left: E-band (83GHz) 3-stage PA, measured Pout=1.37W, PAE=27%
Right: G-band (180GHz) 1-stage amplifier, Pout=0.296W, PAE=3.5%
DC: Ron=0.81(Ω-mm), Vds=6V
A. Margomenos et al., CSICS, 2014
MBE, SiC substrate
ns=1.3x1013(cm-2), µ=1200(cm2/Vs), BV= 42V.
DC: Ron=0.81(Ω-mm), Vds=6V
Vds=2V
Vds=6V
K. Shinohara et al., IEDM 30.1, 2010

11. HRL – GaN HEMT (T4 & T4A Generation)
Lateral S/D scaling reduces Ron and improves fT.
But scaled Lgd causes short-channel effect and reduce BV and fmax.
Independently control of Lgs and Lgd by different sidewall thickness.
Lgs=30nm, Lgd=80nm (Ec=2.13MV/cm)
Ron=0.34(Ω-mm), gm~1.5S/mm
fT=310GHz, Vds=4V
Ka-band (32GHz) 1-stage MMIC PA with a 59% PAE was demonstrated.
K. Shinohara et al., TED, 2013, 2012 & M. Micovic et al., IEDM 3.3, 2016
ns~1.2x1013(cm-2), µ~1200(cm2/Vs) for both E/D-mode.
BV=14V (Ec=2MV/cm)
fT=342GHz, Vds=4V
BV=14V (Ec=2MV/cm)
Ron=0.26(Ω-mm), Vds=4V
fT=454GHz, Vds=3V
K. Shinohara et al., IEDM 27.2, 2012 & Y. Tang et al., EDL, 2015

12. Summary

13. Thank you for your attention

14. Supplementary To boost fT: Reduce L, increase VGS-VT and mobility
To boost fT:
Reduce L, increase VGS-VT and mobility
To boost efficiency:
Eliminate surface/bulk traps (passivation, growth), decrease leakage.