1
AS. 26 May 2008
Transient Electrical and Thermal Characterization of InGaAlAs Thin Films
with Embedded ErAs Nanoparticles
Tela Favaloro, Rajeev Singh, James Christofferson, Younes Ezzahri, Zhixi Bian, and Ali ShakouriElectrical Engineering Department, University of California, Santa Cruz, California 95064, USA
Gehong Zeng, Je-Hyeong Bahk, and John E. BowersDepartment of Electrical and Computer Engineering, University of California, Santa Barbara, California
93106, USA
Hong Lu, and Arthur C. GossardMaterials Department, University of California, Santa Barbara, California 93106, US
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AS. 26 May 2008
Outline• High temperature apparatus for cross plane material
characterization
• Transient electrical measurements
• Thermoreflectance imaging of thermoelectric devices in cooling and heating modes
• Preliminary results
‘Merged’ Thermal Image +500mA, 550K
‘Merged’ Thermal Image -500ma, 550K
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AS. 26 May 2008
Thin Film Material Characterization
TS
ZT2
Material Figure of Merit
Established characterization techniques:
• In-plane electrical conductivity and Seebeck (Van der Pauw, sample bars).
• Need non-conducting substrate (difficult at high T). • Substrate transfer: stress issues
• Cross-plane thermal conductivity• 3 (min ~0.5-1m; need electrical isolation between heater and thin film)• Transient thermoreflectance (top 0.1-0.5 microns of the sample, frequency dependent issues)
1
3
2
4
I13 V24
Also possible: Cross-plane determination of material parameters
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AS. 26 May 2008
High Temperature Characterization System
Currently tested to vacuum of 10-6 mbar and temperatures above 800K
High speed measurement stage
Sample mounted for thermal imaging
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AS. 26 May 2008
Material System:Semimetal nanoparticles in semiconductor alloy
•Thin film element: 50 m n-InGaAlAs, 0.6% ErAs• Substrate: 125 m AlN • Metal pad: 7 m Au• Mask: Dedicated voltage and current pads
Mask design for cross-plane measurements
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AS. 26 May 2008
Cross-Plane Transient Electrical Characterization
0
0.5
1
1.5
2
0 0.1 0.2 0.3 0.4 0.5
300K350K400K450K500K550K600K650K700K
Se
eb
eck
Vol
tag
e (m
V)
Time (ms)
300K
700K
High speed circuitry enables below 100 nanosecond resolution
300K
750K
500 ns
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AS. 26 May 2008
Extraction of Joule and Peltier Voltages
0
0.5
1
1.5
2
2.5
0 20 40 60 80 100 120 140
Peltier Component of Seebeck Voltage
Vsp 300KVsp 400KVsp 500KVsp 600KVsp 700K
Vsp
(m
V)
Current (mA)
0
0.2
0.4
0.6
0.8
1
0 20 40 60 80 100 120 140
Joule Component of Seebeck Voltage
Vsj 300KVsj 400KVsj 500KVsj 700KVsj 600K
Vsj
(m
V)
Current (mA)
2110137079870x70 μm2
16901120560120x120 μm2
700K 300K Vsp (V)
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AS. 26 May 2008
Thermoreflectance Imaging
100 150 200 250 300 350 400
50
100
150
200
250
300
350
400-8
-6
-4
-2
0
2
4
6
8
10
100 150 200 250 300 350 400 450
50
100
150
200
250
300
350
400
450
-10
-5
0
5
10
100 150 200 250 300 350 400 450
100
150
200
250
300
350
400
450
-6
-4
-2
0
2
4
6
50x50μm2 device in heating mode
50x50μm2 device in cooling mode
50x50μm2 device Subtracted Image for Peltier Cooling
I=+95 mA I = -95 mAT=300K
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AS. 26 May 2008
High Temperature Thermoreflectance Imaging
100 200 300 400 500
50
100
150
200
250
300
350
400
450
500
-8
-6
-4
-2
0
2
4
6
8
100 200 300 400 500
50
100
150
200
250
300
350
400
450
500 -4
-3
-2
-1
0
1
2
3
4
100 200 300 400 500
50
100
150
200
250
300
350
400
450
500
-5
-4
-3
-2
-1
0
1
2
3
4
I =+95mA I=- 95mAT=700K
50x50μm2 device in heating mode
50x50μm2 device in cooling mode
50x50μm2 device Subtracted image for Peltier Cooling
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AS. 26 May 2008
Total Cooling Density Varies with Device Size
300 350 400 450
160
180
200
220
240
260
280
300
320
340
360 -6
-4
-2
0
2
4
6
150 200 250 300 350 400
150
200
250
300
350
400 -6
-4
-2
0
2
4
6
100 150 200 250 300 350 400
100
150
200
250
300
350
400
-8
-6
-4
-2
0
2
4
6
8
50x50μm2 with 95mA excitation current
100x100μm2 with 140mA excitation current
150x150μm2 with 150mA excitation current
Current injection nonuniformity and current spreading within the sample result in decreased ΔT in larger samples
ΔT=-3.995 ΔT=-2.067 ΔT=-1.655
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AS. 26 May 2008
Results and ConclusionsDetermination of Seebeck Coefficient for 70x70μm2 Sample:
Measured change in temperature after subtraction of Joule heating at 100mA excitation:
160
180
200
220
240
260
280
300
320
200 300 400 500 600 700 800 900
Comparison of Cross-Plane Seebeck with Independant In-Plane Measurement
Se
ebec
k C
oef
fici
ent
(uV
)
Ambient Temperature (K)
-6.656-5.018-4.215ΔT (K)21101370798Vsp (V)700K 300K
SP
SP
T
VS