Gate current degradation in W-band InAlN/AlN/GaN …...Gate current degradation in W-band...
Transcript of Gate current degradation in W-band InAlN/AlN/GaN …...Gate current degradation in W-band...
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Gate current degradation in W-band InAlN/AlN/GaN HEMTs
under Gate Stress Yufei Wu and Jesús A. del Alamo
Microsystems Technology Laboratories (MTL)Massachusetts Institute of Technology (MIT)
Sponsor: National Reconnaissance OfficeApril 04, 2017
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Purpose
To understand degradation of gate leakage current
in ultra-scaled InAlN/AlN/GaN HEMTs
under positive gate stress
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1. Motivation 2. Devices and experimental approach3. Gate stress experiments
• Harsh step-stress (-recovery) experiments• Mild constant gate stress experiment
4. Thermal stress5. Gate current: dominant charge transport
mechanisms6. Conclusions
Outline
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1. Motivation 2. Devices and experimental approach3. Gate stress experiments
• Harsh step-stress (-recovery) experiments• Mild constant gate stress experiment
4. Thermal stress5. Gate current: dominant charge transport
mechanisms6. Conclusions
Outline
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Benefits of GaN for RF: • Wide bandwidth• High power density• Excellent energy efficiency• Small volume
Promising applications:
Benefits of GaN for RF
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• High spontaneous polarization in InAlN high 2DEG density • InAlN thickness scaling gate length scaling
W- and V-band applications
Al0.2Ga0.8N/GaN ln0.17Al0.83N/GaN
Δ P0 (cm-2) 6.5 x 1012 2.7 x 1013
Ppiezo (cm-2) 5.3 x 1012 0
Ptotal (cm-2) 1.2 x 1013 2.7 x 1013
[J. Kuzmik, EDL 2001]
InAlN as barrier material
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In0.17Al0.83N
In0.17Al0.83N lattice matched to GaN Potentially better reliability!
[M. A. Laurent, JAP 2014]
InAlN as barrier material
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1. Motivation 2. Devices and experimental approach3. Gate stress experiments
• Harsh step-stress (-recovery) experiments• Mild constant gate stress experiment
4. Thermal stress5. Gate current: dominant charge transport
mechanisms6. Conclusions
Outline
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Devices (E-mode)
Thermal models available
BFTEM of virgin device
Gate metal
passivation
InAlN
AlNGaN
InAlN/AlN/GaN HEMTs:• E-mode• Lg = 40 nm• Lgs=Lgd=1 µm• W-band
[Saunier, CSICS 2014]
5 nm1 nm
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FOMs:• IDmax : ID at VGS = 2 V and VDS = 4 V• VTsat : VGS extrapolated from ID at peak gm point at VDS = 4 V• IGoff : IG at VGS = -2 V, VDS = 0.1 V• IDoff : ID at VGS = -2 V, VDS = 0.1 V• RD : at IG = 20 mA/mm• RS : at IG = 20 mA/mm
Detrapping & initialization:• 100 °C bake for 1 hour
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FOMs for benign characterization, detrapping methodology
-2 -1 0 1 210-3
10-2
10-1
100
101
102
103
VDS = 4 Vvirgin device
I D (m
A/m
m)
VGS (V)
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ΔIDmax/IDmax(0)[%]
ΔVTlin[mV] RD/RD(0) RS/RS(0)
After initialization
0 0 1 1
After 200 characterizations
0.70 -23.4 0.95 0.89
After detrapping 0 2.3 1.01 1
Impact of 200 successive characterizations
Nearly complete recovery after thermal detrapping step characterization suite is benign and detrapping step is effective
Impact of characterization and detrapping
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1. Motivation 2. Devices and experimental approach3. Gate stress experiments
• Harsh step-stress (-recovery) experiments• Mild constant gate stress experiment
4. Thermal stress5. Gate current: dominant charge transport
mechanisms6. Conclusions
Outline
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3600 4800 6000 7200101
102
103
I Gst
ress (m
A/m
m)
time (s)
VGS,stress (V)1.3 1.5 1.7 1.9 2.1 2.3
2.3 V
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Stress conditions: • VGS,stress = 0.1 – 2.5 V in 0.1 V steps, VDS = 0 V, RT • Recovery: VDS = VGS = 0 V• Stress time = recovery time = 150 s• Characterization every 15 s
• IGstress ↑ at constant VGS,stress for VGS,stress ≥ 2.3 V
0 1200 2400 3600 4800 6000 7200
10-810-710-610-510-410-310-210-1100101102103
I Gst
ress (m
A/m
m)
time (s)
VGS,stress (V)0.1 0.5 0.9 1.3 1.7 2.1
RT Positive-VG step-stress-recovery experiment
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0 1200 2400 3600 4800 6000 720010-4
10-3
10-2
10-1
100
101
102 2.5
finaldetrapped
stressrecovery
|I Gof
f| (m
A/m
m)
time (s)
2.10.1 0.5 0.9 1.3 1.7VGS,stress (V)
1.7 V
2.3 V
0 1200 2400 3600 4800 6000 720002468
101214161820
2.5
stressrecovery
R D (oh
m.m
m)
time (s)
finaldetrapped
2.10.1 0.5 0.9 1.3 1.7VGS,stress (V)
2.3 V
Time evolution of IGoff and RD
Two mechanisms:• From VGS,stress = 1.7 V: IGoff ↑, trapping ↑ mechanism 1: new defects
generated in AlN• From VGS,stress = 2.3 V:
o IGoff ↑ ↑o RD and RS ↑ ↑
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Mechanisms 2 ?
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Before and after stress: permanent degradation
• IDoff ↑↑• IDmax ↓• ΔVTsat > 0
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Mechanisms 2: consistent with gate sinking
IDoff
VTsat
IDmax
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Stress conditions: • VGS,stress = 0.1 – 2.5 V in 0.1 V steps, VDS = 0 V, Tstress = 150 °C • Stress time = 60 s• Characterization every 15 s
High T Positive-VG step-stress experiment
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0 240 480 720 960 1200 144010-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
101
102
103 2.4VGS,stress (V)
I Gst
ress
(mA/
mm
)
time (s)
0.1 0.4 0.8 1.2 1.6 2.0
960 1080 1200 1320 1440 1560102
103
VGS,stress (V)
I Gst
ress (m
A/m
m)
time (s)
1.6 1.8 2.0 2.2 2.4
2.0 V
• IGstress ↑ at constant VGS,stress for VGS,stress ≥ 2.0 V
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High T Positive-VG step-stress experiment
0 240 480 720 960 1200 1440
2
4
6
8
10
12
14
finaldetrapped
R D (oh
m.m
m)
time (s)
VGS,stress (V)0.1 0.4 0.8 1.2 1.6 2.0 2.4
2.0 V
0 240 480 720 960 1200 144010-4
10-3
10-2
10-1
100
101
VGS,stress (V)
finaldetrapped
|I Gof
f| (m
A/m
m)
time (s)
0.1 0.4 0.8 1.2 1.6 2.0 2.4
1.4 V
2.0 V
• From VGS,stress = 1.4 V: IGoff ↑• From VGS,stress = 2.0 V: IGoff, RD, and RS ↑ ↑• Lower threshold for degradation than at RT Both mechanisms
thermally enhanced17
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1. Motivation 2. Devices and experimental approach3. Gate stress experiments
• Harsh step-stress (-recovery) experiments• Mild constant gate stress experiment
4. Thermal stress5. Gate current: dominant charge transport
mechanisms6. Conclusions
Outline
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Stress conditions: • VGS,stress = 2 V, VDS = 0 V, RT • Characterization every 15 s
RT Constant-VG stress experiment
• IGoff becomes noisy at tstress ~ 500 s; increases afterwards consistent with trap generation in AlN layer (mechanism 1)
• RD changes little throughout experiment• IGstress keeps decreasing no Schottky barrier degradation
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Before and after stress: permanent degradation
• IDoff ↑↑• No significant IDmax degradation• No significant subthreshold characteristics degradation
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IDoff
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Two degradation mechanisms identified:1. Under mild gate stress:
oObservation: IGoff ↑, trapping ↑, thermally enhancedoProposed mechanism 1: high electric field induced
defect generation in AlN interlayer
2. Under harsh gate stress:oObservation: IGoff ↑, RD and RS ↑, ΔVT > 0, IDmax ↓,
thermally enhanceoProposed mechanism 2: self-heating induced Schottky
gate degradation, or gate-sinking
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Summary so far
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1. Motivation 2. Devices and experimental approach3. Gate stress experiments
• Harsh step-stress (-recovery) experiments• Mild constant gate stress experiment
4. Thermal stress5. Gate current: dominant charge transport
mechanisms6. Conclusions
Outline
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-2 -1 0 1 210-3
10-2
10-1
100
101
102
103
IDmax
VTsat
I D (m
A/m
m)
VGS (V)
before stress after 400 °C after 500 °C
VDS = 4 V
IDoff
Thermal stress experiment
Impact of thermal stress: 1 min. RTA in N2
Permanent degradation: • Prominent IDmax ↓ with T• Positive VTsat shift• IDoff ↑
Same signature as that of degradation mechanism 2 consistent with gate sinking
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1. Motivation 2. Devices and experimental approach3. Gate stress experiments
• Harsh step-stress (-recovery) experiments• Mild constant gate stress experiment
4. Thermal stress5. Gate current: dominant charge transport
mechanisms6. Conclusions
Outline
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Virgin device: Thermionic Field Emission fitting
• T dependence well explained by Thermionic Field Emission (TFE) theory• Extracted effective Schottky barrier height (φb): 0.95 eV
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0.1 0.2 0.3 0.4 0.5 0.610-10
10-8
10-6
10-4
10-2
100
experimentTFE fitting
I G (m
A/m
m)
VGS (V)
T: -50 °C to 200 °C
20 24 28 32 36-40
-36
-32
-28
-24
ln[I sk
Tcos
h(E 00
/kT)
]1/E0 (eV-1)
φb = 0.95 eV
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After harsh gate stress: Poole-FrenkelEmission fitting
• T dependence well explained by Poole-Frenkel Emission (P-F) theory• Extracted effective trap energy level (φt): 0.11 eV
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Stress conditions: VGS,stress = 0 – 2.5 V in 0.1 V steps, VDS = 0 V
0.4 0.5 0.6 0.7 0.8-12
-11
-10
-9
-8
-7T: -50 °C to 200 °C
experimentP-F fitting
ln(|I
G|/V
G)
VG0.5 (V)0.5
20 25 30 35 40 45 50 55
-16
-15
-14
-13
φt = 0.11 eV
y-in
t. [ln
(I G/V
G) v
s. V
G0.
5 ]1/kT (eV)-1
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After mild gate stress: Poole-FrenkelEmission fitting
• T dependence well explained by Poole-Frenkel Emission (P-F) theory• Extracted effective trap energy level (φt): 0.36 eV• Close to donor level of N vacancy in AlN of 0.5 eV [T. L. Tansley, PRB
1992] 27
Stress conditions: VGS,stress = 2 V, VDS = 0 V
0.45 0.50 0.55 0.60 0.65-18
-16
-14
-12
-10
experimentP-F fitting
ln(|I
G|/V
G)
VG0.5 (V)0.5
T: -50 °C to 200 °C
20 25 30 35 40 45 50 55-26
-24
-22
-20
-18
-16
φt = 0.36 eV
y-in
t. [ln
(I G/V
G) v
s. V
G0.
5 ]1/kT (eV)-1
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1. Motivation 2. Devices and experimental approach3. Gate stress experiments
• Harsh step-stress (-recovery) experiments• Mild constant gate stress experiment
4. Thermal stress5. Gate current: dominant charge transport
mechanisms6. Conclusions
Outline
28
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Identified two degradation mechanisms:1. Under mild gate stress:
o Observation: IGoff ↑, trapping ↑, thermally enhancedo Proposed mechanism 1: high electric field induced defect
generation in AlN interlayer
2. Under harsh gate stress:o Observation: IGoff ↑, RD and RS ↑, ΔVT > 0, IDmax ↓, thermally
enhancedo Proposed mechanism 2: self-heating induced Schottky gate
degradation, or gate-sinking
Transport model for IG in low forward regime:• Virgin device: TFE with φb = 0.95 eV• After degradation mechanism 1: P-F with φt = 0.36 eV• After degradation mechanism 2: P-F with φt = 0.11 eV
Conclusions
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