A Robust AlGaN/GaN HEMT Technology for RF

A Robust AlGaN/GaN HEMT
Technology for RF Switching
Applications
Michael D. Hodge1,2, Rama Vetury1, Jeff Shealy1,
and Ryan Adams2
1) RF Micro Devices, Charlotte, NC
2) University of North Carolina at Charlotte, Charlotte, NC
DPBU
Outline
• Advantages of GaN Materials for RF Switching
• Background on GaN reliability
• OFF-State Step Stress Experiment
• Conclusion
DPBU
GaN Material Advantages
Ruggedness
Power
Handling
Low Loss,
Low Noise
UNREALIZED
Potential
DPBU
Why GaN for RF Switches ?
High Power RF Switch Technologies
Si P-i-N
GaAs FET
GaN FET
Loss
Isolation
Power Handling
Speed
Linearity
Operating Efficiency
Engineering Complexity
• GaN-on-SiC
• Engineer COFF, low Ron
• high BKDN
• high ID,max
• Low RTH
• High Max TCH
• Si PP-i-N:
– Drive Current
Dependence
• GaAs pHEMT:
– BKDN vs RON Trade
DPBU
Device Design - GaN RF switch
LGCFP
LG-O
Source Connected FP
Gate
Gate
SiN
SiN
Source
Drain
PA FET
Path Control FET
S/D
S/D
LG
Switch FET
HPA
• Symmetric Operation
Switch
Power Amp/Switching FET
• Non-symmetric Operation
LNA
DPBU
GaN High Temperature Reliability Test
Tch (C)
GaN High Temperature
Reliability Test
10
10
GaN1
GaN 2
High
Power
High
Linearity
10
325
300
275
250
Total
Devices
10
Wafers
10
Fab Lots
10
200
175
150
RFMD
GaN1
8
High Power
6
4
2
0
18
19
20
21
10
350
8
RFMD
GaN2
22
23
1/kT
Epi Vendors
24
25
26
27
28
Tch (C)
10
Number of
Temperatures
10
GaN1
High
Power
GaN2
300
275
250
225
200
175
150
High Linearity
6
10
High
Linearity
325
MTTF
Results
225
MTTF
Sample
Size
350
10
4
10
MTTF
Hrs
Ea
eV
TCHANNEL
ºC
VDS
V
2
10
0
10
18
19
20
21
22
23
1/kT
24
25
26
27
28
DPBU
Reliability Concerns in GaN HEMTs
Inverse Piezoelectric Effect (IPE)
Hot Electron Induced
Degradation (HEI)
• Requires
• Requires
• High electric field
• High electric field
• Observed to have no time
dependence
• Carriers
• Impact
• Physical crystal defect
• Symptoms
• Parametric degradation
• Ron, Idmax, Idss
• Increased gate leakage
• Time dependent
• Impact
• Hot electrons induce traps in buffer
and/or barrier layers
• Symptoms
• Parametric degradation
• Ron, Idmax, Idss
7
DPBU
Inverse Piezoelectric Related Literature
Study
Stress Conditions
Critical Voltage (V)
Total Stress Time (Mins)
Technology
Notes
(1) Joh 2006
Vds=0V, Vgs=-15V to -34V
17-34V
100
GaN-on-SiC
Lg dependent
(2) Joh 2008
Vds=0V, Vg=-10V to -50V
27V (2T)
38V (3T)
40
GaN-on-SiC
2T stress harsher than
3T
Vgs=-8V, Vd=10V to 50V
(3) Demirtas
2009
Vds=0V, Vgs=-1V to –20V
37V GaN-on-SiC
70V GaN-on-Si
20
GaN-on-SiC
GaN-on-Si
Vcrit of GaN-on-Si >
GaN-on-SiC
(4) Makaram
2010
Vg=-7V, Vd=8V to 50V 150C base
20V
42
GaN-on-SiC
Metal etch to reveal pits
Vg=-7V, Vd=50V 150C base
10 and 1000
• Failure Within Minutes
of Stress
• 20-100 minutes
• 2T is the most stressful
• Critical Voltage
• 17-38V (GaN-on-SiC)
DPBU
Step Stress Test Conditions
Designed to replicate IPE literature stress test conditions2
Lds = 4.25um
Device A
200
200
150
150
100
100
50
50
0
0
Base Temp
Conditions 1&2 = 25C
Conditions 3&4 = 85C
Vgs (V)
Vds = 0V
Vds (V)
Vgs = -8V
Device A - Condition 1&3
Device B - Condition 1&3
Device A - Condition 2&4
-50
-50
-100
-100
-150
-150
-200
Device B - Condition 2&4
-200
0
10
20
30
40
50
60
Time (mins)
2 .J. Joh and J. A. del Alamo, “Critical Voltage for Electrical Degradation of GaN High-Electron
Mobility Transistors,” IEEE Electron Device Lett., vol. 29, no. 4, pp. 287-289, Apr. 2008.
Lds = 3.1um
Vbd = 110V
Device B
Lds = 4.5um
Vbd = 200V
DPBU
Switch Stress Test Results – Device A
Device A - Condition 13
2
4
5
ΔRon (%)
0
-5
A1
-10
A2
A1
A3
A2
A4
-15
-20
A5
-25
0
10
20
30
40 50 60 70
Stress Voltage (V)
80
90
100
Tbase= 25C,
to -100V
85C, Vds= 0V,
0 toVgs=
100V,0Vgs=
-8V
• No degradation of Ron up device breakdown
• No degradation in Idss and Idmax observed
• Any degradation is <1% from initial
• Device B shows the same trends
2T Stress
Base 25C 1
3T Stress
2
Base 85C 3
4
DPBU
Step Stress Test Results – Device A
• No degradation of Id
• Negative threshold shift
• Indicates enhancement of channel carriers
DPBU
Step Stress Test Results – Device A
• Longer term stress
• Held at most stressful condition according to literature
• Vds=0V, Vgs= -100V
• No further parametric change after 6 and 60 hours.
DPBU
Summary of Step Stress
• Comprehensive OFF-state stress test
• Multiple bias configurations
• 2 Terminal
• 3 Terminal
• Multiple base temperatures
• 25C
• 85C
• Devices stressed just before catastrophic breakdown
• No parametric degradation observed
• Ron
• Idss
• Idmax
DPBU
Conclusions
• No degradation observed in the OFF-state stress
• No IPE related degradation observed in AlGaN/GaN switch FETs
• AlGaN/GaN technology robust for RF switching applications
DPBU
Acknowledgements
• The authors would like to thank for their support and discussions
• AFRL
• Dr. John Blevins
• Dr. Chris Bozada
• ONR
• Dr. Paul Maki
DPBU
Appendix
DPBU
Stress Study Results – PA – OFF-State
No crystal defect
Test Condition
Base Temp (°C)
Vds (V)
Approx Id
(mA/mm)
Pdiss (W/mm)
Vgs (V)
1
245
60
0.03
0.0018
-10
2
245
100
2
0.2
-10
• RFMD GaN Power Amplifier
• No difference over extended time
• 300 hours and 1016 hours overlays
DPBU
Constant Stress Test Result
• OFF-State – No degradation observed
• Results are inconsistent with IPE related degradation