gate current degradation in w-band inaln/aln/gan …...gate current degradation in w-band...
TRANSCRIPT
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
1
Purpose
To understand degradation of gate leakage current
in ultra-scaled InAlN/AlN/GaN HEMTs
under positive gate stress
2
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
3
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
4
Benefits of GaN for RF: • Wide bandwidth• High power density• Excellent energy efficiency• Small volume
Promising applications:
Benefits of GaN for RF
5
• 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
6
In0.17Al0.83N
In0.17Al0.83N lattice matched to GaN Potentially better reliability!
[M. A. Laurent, JAP 2014]
InAlN as barrier material
7
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
8
9
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
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
10
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)
11
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
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
12
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
13
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
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 ↑ ↑
14
Mechanisms 2 ?
Before and after stress: permanent degradation
• IDoff ↑↑• IDmax ↓• ΔVTsat > 0
15
Mechanisms 2: consistent with gate sinking
IDoff
VTsat
IDmax
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
16
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
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
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
18
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
19
Before and after stress: permanent degradation
• IDoff ↑↑• No significant IDmax degradation• No significant subthreshold characteristics degradation
20
IDoff
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
21
Summary so far
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
22
-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
23
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
24
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
25
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
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
26
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
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
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
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
29