Impact of high-power stress on
dynamic ON-resistance of
high-voltage GaN HEMTs
Donghyun Jin and Jesús A. del Alamo
Microsystems Technology Laboratory
Acknowledgement: ARPA-E ADEPT, SRC, DRIFT MURI
1
Outline
1. Motivation
2. Dynamic ON-resistance measurement
3. High-power stress experiment
4. Discussion
5. Conclusion
2
Motivation
• Dynamic ON-resistance (RON) a.k.a. “current collapse”
IDS
In OFF-to-ON switching
Tirado et al, TED 2007
ION initial
i) ION right after
OFF-state: RON ↑
ii) Slow recovery of RON
VDS
3
Motivation
• Dynamic ON-resistance (RON) a.k.a. “current collapse”
IDS
In OFF-to-ON switching
Tirado et al, TED 2007
ION initial
i) ION right after
OFF-state: RON ↑
ii) Slow recovery of RON
VDS
‒ Primary concern in GaN power-switching and
RF power-amplifier devices
4
Motivation
• Much less understanding
‒ Impact of electrical stress on dynamic RON
‒ Especially, high-power (HP) state in GaN device operation
5
Motivation
• Much less understanding
‒ Impact of electrical stress on dynamic RON
‒ Especially, high-power (HP) state in GaN device operation
ID
< RF-amplifier >
ID < Power-switching > Hard-switching
RF load line
VDS
ON
OFF
VDS
6
Motivation
• Much less understanding
‒ Impact of electrical stress on dynamic RON
‒ Especially, high-power (HP) state in GaN device operation
Meneghesso et al, TED 2006
7
Motivation
• Much less understanding
‒ Impact of electrical stress on dynamic RON
‒ Especially, high-power (HP) state in GaN device operation
• Goal
Meneghesso et al, TED 2006
‒ New methodology for dynamic RON measurement
‒ Investigate the impact of high-power stress on dynamic RON
8
Outline
1. Motivation
2. Dynamic ON-resistance measurement
3. High-power stress experiment
4. Discussion
5. Conclusion
9
Dynamic RON measurement
• New methodology for RON transient measurement
from 200 ns to any arbitrary length of time
‒ Auriga AU4750 pulsed-IV for RON(200 ns ≤ t ≤ 3 ms) +
Agilent B1500A SDA for RON(3ms < t )
10
Dynamic RON measurement
• New methodology for RON transient measurement
from 200 ns to any arbitrary length of time
‒ Auriga AU4750 pulsed-IV for RON(200 ns ≤ t ≤ 3 ms) +
Agilent B1500A SDA for RON(3ms < t )
• Dynamic RON measurement from pulsed-IV
ID
1/RON
ION @ VGS= 1 V
OFF (VGSQ, VDSQ)
VDS
11
Dynamic RON measurement
• New methodology for RON transient measurement
from 200 ns to any arbitrary length of time
‒ Auriga AU4750 pulsed-IV for RON(200 ns ≤ t ≤ 3 ms) +
Agilent B1500A SDA for RON(3ms < t )
• Dynamic RON measurement from pulsed-IV
VDS
ID
1/RON
ION @ VGS= 1 V
VDSQ
Synchronous switching
of VGS and VDS
OFF (VGSQ, VDSQ)
VGS
t
1V
t
VGSQ
VDS
12
Dynamic RON measurement
• RON(t) from ID(t)-VDS measurements
Q(VGSQ= -10 V, VDSQ= 50 V)
0.08
ID [A/mm]
0.06
0.04
0.02
ID(200 ns ≤ t ≤ 3 ms)
@ VGS= 1 V, VDS ≤ 1.2 V
0
0
1
2
Time [sec]
3
-3
x 10
13
Dynamic RON measurement
• RON(t) from ID(t)-VDS measurements
Q(VGSQ= -10 V, VDSQ= 50 V)
0.08
0.08
0.06
0.02
ID [A/mm]
ID [A/mm]
0.06
0.04
ID(200 ns ≤ t ≤ 3 ms)
@ VGS= 1 V, VDS ≤ 1.2 V
100 μs
10 μs
0.04
200 ns
0.02
1/RON
0
0
ID(t= 1 ms) @ VGS= 1 V
1
2
Time [sec]
0
0
3
-3
x 10
0.4
VDS
0.8
[V]
1.2
‒ Extract RON transients from 200 ns up to 3 ms in OFF-to-ON
14
Dynamic RON measurement
Q(-5 V, 40 V)
* Virgin GaN-onSiC HEMT sample 5.5
Pulsed-IV
200 ns ≤ t ≤ 3 ms
RON [-mm]
5
4.5
4
RON_DC= 3.5 Ω∙mm
3.5 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4
10 10 10 10 10 10 10 10 10 10 10 10
Time [sec]
15
Dynamic RON measurement
Pulsed-IV
OFF(-5 V, 40 V) to ON
Semiconductor
Device Analyzer
200 ns ≤ t ≤ 3 ms
3 ms ≤ t ≤ 2.8 hr
Q(-5 V, 40 V)
* Virgin GaN-onSiC HEMT sample 5.5
RON [-mm]
5
4.5
4
RON_DC= 3.5 Ω∙mm
3.5 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4
10 10 10 10 10 10 10 10 10 10 10 10
Time [sec]
16
Dynamic RON measurement
Pulsed-IV
OFF(-5 V, 40 V) to ON
Semiconductor
Device Analyzer
200 ns ≤ t ≤ 3 ms
3 ms ≤ t ≤ 2.8 hr
Q(-5 V, 40 V)
* Virgin GaN-onSiC HEMT sample 5.5
RON [-mm]
5
4.5
4
RON_DC= 3.5 Ω∙mm
3.5 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4
10 10 10 10 10 10 10 10 10 10 10 10
Time [sec]
• RON transients over 11 decades in time
→ details in DJin ISPSD 2012
17
Outline
1. Motivation
2. Dynamic ON-resistance measurement
3. High-power stress experiment
4. Discussion
5. Conclusion
18
High-power DC-stress
* Constant HP-stress: VDS= 20 V, ID≈0.6 A/mm, P≈12 W/mm
tstress= 10, 20, 30, 40 min (4 samples)
* tstress= 40 min sample
100
RON
1.1
1
10
IDMAX
0.9
0.8
1
IGOFF [mA/mm]
RON/RON(0), IDMAX/IDMAX(0)
1.2
|IGOFF|
0.7
0.6
0.1
0
10
20
30
High power ON-state stress time [min]
40
• Prominent degradation in RON and IDMAX; minor in IGOFF
• Dynamic RON measurement after each HP-stress test
19
Dynamic RON transients
12
Transient from
OFF (VGSQ= -10 V, VDSQ= 50 V)
to ON (VGS= 1 V, VDS ≤ 1.2 V)
RON/RON-DC
10
HP-stress
time
RON_DC
increase
10
7%
20
8%
30
11%
40
16%
8
tstress= 40 min
6
4
2 20
10
30
Virgin
0 -7
-6
-5
-4
-3
-2
-1
0
1
2
3
10 10 10 10 10 10 10 10 10 10 10
Time [sec]
• Dynamic RON↑ ≥ 10 x RON_DC after 40 min HP-stress
- Up to 30 min: minor increases in dynamic RON
• In contrast, small RON_DC↑ (16%)
- minor permanent (non-transient) degradation
• Fast RON recovery in ms range in all cases
20
Time constant spectrum
0.8
40 min
0.6
Amplitude (ai)
RON   ai e(  t / i )  RON 
i
0.4
0.2
30
20
0
10
-7
10
-6
10
Virgin
-5
10
-4
10
-3
10
-2
-1
10 10
 [sec]
0
10
1
10
2
10
3
10
• 40 min HP-stress → fast transient with short time
constants (μs ≤ τ ≤ ms) ↑
• In contrast, negligible changes in long time constants
21
Dynamic RON at different T
* tstress= 40 min sample
12
85
6
105
125
4 150
[-mm]
8 65
ON
45 T= 25 C
40
OFF(-10 V, 50 V)
to ON
30
20
R
RON/RON-DC
10
50
T↑
10
0 -7 -6 -5 -4 -3 -2 -1 0 1 2 3
10 10 10 10 10 10 10 10 10 10 10
Time [sec]
2
0 -7
3
2
1
0
-1
-2
-3
-4
-5
-6
10 10 10 10 10 10 10 10 10 10 10
Time [sec]
• As T ↑, RON transients substantially accelerated
• RON transients → conventional traps
22
Time constant spectrum at different T
* tstress= 40 min sample
2.5
Amplitude [A.U.]
2
25 C
45 C
1.5
65 C
85 C
1
105 C
0.5
125 C
150 C
0 -7
-6
-5
-4
-3
-2
-1
0
10 10 10 10 10 10 10 10
 [sec]
1
10
2
10
3
10
• Evolution of dominant time constant peaks at different T
23
Arrhenius plot
20
0.75 eV
ln(T2τ) [K2s]
0.57 eV
EA= 0.87 eV
15
0.53 eV
10
0.45 eV
5
0.31 eV
0
0.23 eV
-5
25
30
35
40
1/kT [eV-1]
45
50
55
• Dominant trap energy levels at 0.31, 0.45, 0.53 and 0.57 eV
(below EC of AlGaN barrier)
• Responsible for dramatic increase in dynamic RON
24
Outline
1. Motivation
2. Dynamic ON-resistance measurement
3. High-power stress experiment
4. Discussion
5. Conclusion
25
Discussion:
HP-stress with higher VDS
Transient from OFF (-10 V, 50 V) to ON
5
After 3 min HP-stress with
VDS= 30 V, P≈ 9 W/mm
RON/RON-DC
4
3
After 20 min HP-stress with
VDS= 20 V, P≈ 12 W/mm
2
Virgin
1
-6
-5
-4
-3
-2
-1
0
1
2
3
10 10 10 10 10 10 10 10 10 10
Time [sec]
• Fast dynamic RON ↑ only in 3 min with lower P-level
• Again, very fast RON recovery down to ms range
• HP-stress with VDS↑ promotes fast dynamic RON degradation
26
Discussion:
Different epi-supplier
* Red solid line: same GaN-on-SiC HEMT design processed in the same lot on nominally
identical epitaxial wafer from different epi-supplier (denoted by epi-supplier II)
9
Transient from OFF (-5 V, 40 V) to ON
R
ON
[-mm]
8
virgin epi-supplier II
7
6
virgin epi-supplier I
5
4
RON_DC= 4.6 Ω∙mm
RON_DC= 3.5 Ω∙mm
3 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4
10 10 10 10 10 10 10 10 10 10 10 10
Time [sec]
• Very different patterns of dynamic RON transient
27
Discussion:
HP-stress on epi-supplier II
* HP-stress on epi-supplier II device: VDS= 20 V, ID≈ 0.6 A/mm, P≈ 12 W/mm
100
IDMAX
1
10
RON
0.8
IGOFF
0.6
1
0.4
IGOFF [mA/mm]
RON/RON(0), IDMAX/IDMAX(0)
1.2
0.1
0.2
0
0.01
0
20
40
60
80
Time [min]
100
120
• No prominent permanent degradation in RON, IDMAX and IGOFF
- Large increase of IGOFF recoverable
28
Discussion:
Dynamic RON on epi-supplier II
12
OFF(-10 V, 50 V) to ON
RON/RON-DC
10
40 min HP-stress
on epi-supplier I
8
6
2 hr HP-stress
on epi-supplier II
4
2
0
Virgin epi-supplier II
-6
-5
-4
-3
-2
-1
0
1
2
3
10 10 10 10 10 10 10 10 10 10
Time [sec]
• Minor increase in dynamic RON up to 2 hr HP-stress
• Epi-supplier II device more robust than epi-supplier I
- RTH(thermal resistance) of epi-supplier II < RTH of epi-supplier I
- Better heat dissipation through different buffer design
• Epi-supplier II wafer more traps than epi-supplier I
29
Outline
1. Motivation
2. Dynamic ON-resistance measurement
3. High-power stress experiment
4. Discussion
5. Conclusion
30
Conclusion
• Developed new dynamic RON measurement
methodology
• Key findings from HP electrical stress
- Large increase in dynamic RON on a short-time scale
- Formation of shallow traps most likely inside the
AlGaN barrier or at its surface
• GaN HEMTs device operation under RF power or
hard-switching conditions
- Undesirable increase of dynamic RON on a very short
time scale
31