high dielectric constant capacitors for power electronic ... · high dielectric constant capacitors...
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High Dielectric Constant Capacitors for Power Electronic Systems*
U. (Balu) BalachandranArgonne National Laboratory
Team members at Argonne: B. Ma, M. Narayanan, and S. E. Dorris
This presentation does not contain any proprietary, confidential, or otherwise restricted information
*Work supported by the U.S. Department of Energy, Office of Vehicle Technologies Program.
Project ID# ape_05_balachandran
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2009 DOE Vehicle Technologies and Hydrogen Program Annual Merit Review & Peer Evaluation Meeting -2-
Overview
• Project start date: FY04• Project end date: FY12• Project continuation & direction
determined annually by DOE• Percent complete: 60
• Overall size and cost of invertersCapacitors are a significant fraction of the inverter volume (≈35%), weight (≈23%), and cost (≈23%).
• High-temperature operationThe performance and lifetime of presently available capacitors degrade rapidly with increasing temperature (coolant temperature of 105°C).• Total project funding
– DOE share: 100%• Funding received in FY08: $940K• Funding for FY09: $800K
Timeline
Budget
Barriers addressed
• Penn State University• Delphi Electronics• Project Lead: Argonne National
Laboratory
Partners
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2009 DOE Vehicle Technologies and Hydrogen Program Annual Merit Review & Peer Evaluation Meeting -3-
Objectives• Overall objective is to develop
technology for fabricating a range of new, high performance, economical, capacitors for power electronic systems in HEVs, PHEVs, and FCVs.
DC bus capacitors for inverters– (600 V, 2000 µF, <3 mΩ ESR, 250 A
ripple current,140°C, benign failure)
• Objective for FY08 was to fabricate and characterize high voltage capable dielectric films on base-metal foils (“film-on-foils”) that meet or exceed the needs of hybrid electric vehicle power inverters.
• Dielectrics films will have:– An operational temperature range of
-50°C to +140°C– 600 V DC bus capability– High k (>1000) and Eb (>3 MV/cm) to
meet weight & volume target
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2009 DOE Vehicle Technologies and Hydrogen Program Annual Merit Review & Peer Evaluation Meeting -4-
Relevance to Overall DOE Objectives of Petroleum DisplacementAdvanced inverters are essential for electric traction operations in HEVs, PHEVs, and FCVs.
Future availability of advanced high-temperature (together with lower cost, weight, & volume) inverters will advance the marketplace application of highly fuel efficient & environmentally beneficial hybrid vehicles.
Capacitors have direct impact on overall size, cost, & performance of inverters.
Capacitor development will reduce the size & increase the temperature of operation of one of the largest components in the inverter: the DC bus capacitor.
This project is developing dielectric films that has potential to reduce size, weight, and cost, concomitant with increased capacitance density & high temperature operation, for capacitors in inverters in HEVs, PHEVs, and FCVs.
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2009 DOE Vehicle Technologies and Hydrogen Program Annual Merit Review & Peer Evaluation Meeting -5-
Milestones2008
Q1 Q2 Q3 Q4
2009
Q1 Q2 Q3 Q4
PLZT/Ni film-on-foil dielectric development and characterization
High voltage breakdown, HALT, reliability, & benign failure study in collaboration with Penn State
Provide samples & test results/data to industrial partner and Penn State University for verification
Decision point: Either continue the two-pronged approach, i.e., PLZT/Ni and PLZT/Cu, or down-select one over the other.
Finalize processing steps: Polishing procedure, surface roughness, & defect density in the foil will be quantified. Defects in foils translate into defects in PLZT films.
PLZT/Cu film-on-foil dielectric development and characterization
Investigate graceful failure mode
Deliver samples
Deliver report
Deliver samples
Identify processing steps
Finalize processsteps
Fabricate 1” x 1” PLZT films with uniform properties
Deliver samples
Fabricate thicker PLZT
Procure components for reliability testing
Go/No-Go
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2009 DOE Vehicle Technologies and Hydrogen Program Annual Merit Review & Peer Evaluation Meeting -6-
Technical Approach• Develop ferroelectric (PLZT) dielectric films on base-metal foil (“film-on-
foil”) that are either stacked on or embedded directly into the printed wire board.
• Integration of base-metal (Ni, Cu) electrodes provides a significant cost advantage over noble metal electrodes that are used in conventional multilayer capacitors.
• Ferroelectrics possess high dielectric constants, breakdown fields, and insulation resistance. With their ability to withstand high temperatures, they can tolerate high ripple currents at under-the-hood conditions.
• Stacked and/or embedded capacitors significantly reduce component footprint, improve device performance, provide greater design flexibility, achieve high degree of volumetric efficiency with less weight, and offer an economic advantage.
• Our approach focuses on fabricating films by chemical solution deposition, developing a fundamental understanding of processing effects on properties, and arriving at robust processing strategies.
Argonne’s project addresses the technology gap in an innovative manner
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2009 DOE Vehicle Technologies and Hydrogen Program Annual Merit Review & Peer Evaluation Meeting -7-
Uniqueness of Project and Impact(caps embedded directly into PWB – caps are “invisible”)
Basic ElementMetal foil coated with thinfilm PLZT dielectric
– PLZT/Ni Film-on-Foil– PLZT/Cu Film-on-Foil
ComponentStack on or embed coated foils directly into printed wire circuit board for power electronics in (P)HEV
AdvantagesReduces component footprintShortens interconnect lengthsReduces parasitic inductive losses & electromagnetic interference
metal foil (bottom electrode)
top electrode
dielectric film
Film-on-foilcapacitor
PWB Embedded capacitor with
interconnections
PWB
B (bottom electrode) T (top electrode)
Reliability is improved because the number & size of interconnections are reduced.Solder joints that are most susceptible to failure are no longer needed.
≈ 30 μm
3~4 mm
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2009 DOE Vehicle Technologies and Hydrogen Program Annual Merit Review & Peer Evaluation Meeting -8-
PLZT/Ni
Bias Field (kV/cm)
tan(δ)
ε r
Cap (pF)
Temperature (˚C)ε r
D-factor
Thickness ≈ 1.15 µm
Fabricated PLZT on Ni foils with k ≈1300 & DF ≈0.08 @ 25°C and ≈1800 & 0.06 @ 150°C; mean breakdown strength >6.0 MV/cm.
(measurements made on 250-500 μm top electrodes)
Accomplishments/Progress/Results
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2009 DOE Vehicle Technologies and Hydrogen Program Annual Merit Review & Peer Evaluation Meeting -9-
Accomplishments/Progress/Results (Cont.)Breakdown strength of PLZT on Ni foil – Weibull analysis
Test condition:
voltage: 200~1000V
step time: 0.5 sec
zero time: 1 sec
Film thickness: 1.15 μm
Electrode diameter: 250 μm
t
V
Higher Eb increases capacitance density and reduces dielectric layer thickness & cost of the capacitors for inverter applications.
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2009 DOE Vehicle Technologies and Hydrogen Program Annual Merit Review & Peer Evaluation Meeting -10-
-150
-100
-50
0
50
100
150
-5000 0 5000
P (μ
C/c
m2 )
E (kV/cm)
Energy density ≈170 J/cm3 was measured at 1000 V.
40
60
80
100
120
140
0 1000 2000 3000 4000 5000
P (μ
C/c
m2 )
Field E (kV/cm)
Area = 168,420 mJ/cm 3
Accomplishments/Progress/Results (Cont.)Polarization & Energy Density Measured on PLZT/Ni Foil
Film thickness ≈2.0 μmApplied voltage = ±1000 V Dielectric constant ≈ 1100 at zero-bias &
115 at 300 V; 65 at 1000 VEnergy density = 168.4 J/cm3
Electrode diameter = 250 μm
0
200
400
600
800
1000
1200
1400
1600
-5000 0 5000
Calculated from PE loopMeasured with HP4192A
Ral
ativ
e Pe
rmitt
ivity
E (kV/cm)
K =115 at 300V
K = 65 at 1000V
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2009 DOE Vehicle Technologies and Hydrogen Program Annual Merit Review & Peer Evaluation Meeting -11-
High-temperature measurement to predict capacitor life-time(preliminary measurement on ≈1.15 μm PLZT/Ni using 250 μm Pt electrode)
Accomplishments/Progress/Results (Cont.)
• Lifetime estimated by measuring time to failure vs. applied voltage as function of temperature.
• Mean time-to-failure (MTF), voltage acceleration factor (N), and activation energy (Ea) are obtained from reliability measurement.
-5
-4
-3
-2
-1
0
1
2
3
10 100 1000 104 105
100V120V150V
Wei
bull
Para
met
er, l
n(ln
(1/(1
-p))
tB (sec)
@ 100°C
102
103
104
105
106
107
108
20 40 60 80 100 300
0.1
1
10
102
103
104
0.2 0.4 0.6 0.8 1
Mea
n Ti
me
to F
ail (
sec)
Applied Voltage (V)
Mea
n Ti
me
to F
ail (
hr)
Applied Field (MV/cm)
N = ‐6.3@ 100°C
-5
-4
-3
-2
-1
0
1
2
3
1 10 100 1000 104
100ºC150ºC
Wei
bull
Para
met
er, l
n(ln
(1/(1
-p))
tB (sec)
@ 150 V bias
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2009 DOE Vehicle Technologies and Hydrogen Program Annual Merit Review & Peer Evaluation Meeting -12-
Breakdown Strength of PLZT film on Ni foil
Test condition:
applied voltage: 200~1000V
step time: 0.5 sec
zero time: 1 sec
Film thickness: 1.15 μm
Electrode diameter: 250 μm
t
V
0
2
4
6
8
10
12
2.3 2.8 3.3 3.8 4.3 4.8 5.3 5.8 6.3 6.8 7.3 7.8 8.3 8.8
2 23
0 01
0 0 0
2 21 1
11
Cou
nts
Breakdown Strength (MV/cm)
Breakdown Strength of PLZT (8/52/48)film on LNO/Ni (25 measurements)
Cap. with large defect Cap. with small defects
Our results show that it is possible to fabricate PLZT film-on-foil dielectric films with Eb >10 MV/cm.
• Controlling the defects through process optimization will yield PLZT films with very high breakdown field (Eb).
• Higher Eb will reduce dielectric layer thickness & cost of the caps for power inverter applications.
Accomplishments/Progress/Results (Cont.)
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2009 DOE Vehicle Technologies and Hydrogen Program Annual Merit Review & Peer Evaluation Meeting -13-
PLZT/Cu
Dielectric constant increased from ≈1100 to ≈1400 and loss factor decreased from 0.07 to 0.05 when temperature was increased from 25°C to 150°C.
Accomplishments/Progress/Results (Cont.)
0
200
400
600
800
1000
1200
0
0.1
0.2
0.3
0.4
0.5
-40 -30 -20 -10 0 10 20 30 40
ε r
Loss (tan δ)
Applied Field (kV/cm)
t ≈ 1µmEB ≈ 2.5 MV/cm
0
200
400
600
800
1000
1200
1400
1600
0
0.05
0.1
0.15
0.2
0.25
0.3
0 50 100 150 200
ε r
Loss (tan δ)
Temperature (°C)
-30
-20
-10
0
10
20
30
-50 0 50 100 150 200 250
TCC
(ΔC
/CR
T, %)
Temperature (°C)
X8R
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2009 DOE Vehicle Technologies and Hydrogen Program Annual Merit Review & Peer Evaluation Meeting -14-
Future Work• Optimize processing conditions to make 1” x 1” size capacitors
with uniform properties (minimize defects).– substrate polishing, drying of individual layers, pyrolysis and
crystallization temperatures, & room environment influence the properties of PLZT films.
– defects in the substrates translate into defects in the dielectric layers.
• Fabricate thicker films for high-voltage applications (600 V rating, up to 700 V transient in inverters).
• Characterize the dielectric properties as function of bias voltage and temperature, and reliability of film-on-foil dielectrics.
• Investigate benign failure in multilayer architecture (demonstrated benign failure mode in single layer film-on-foil dielectrics).
• Produce prototype film-on-foils for power inverters.
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2009 DOE Vehicle Technologies and Hydrogen Program Annual Merit Review & Peer Evaluation Meeting -15-
Summary
• Demonstrated dielectric films with k >1200, Eb ≈6.5 MV/cm, and Ileakage <10-8 A/cm2.
• Dielectric constant increased and loss factor slightly decreased when temperature increased from 25°C to 150°C, both causing ESR to decrease.
• Showed potential for film-on-foils with Eb >10 MV/cm; high Eb increases capacitance density and reduces amount and cost of capacitors in inverters.
• Measured energy density ≈170 J/cm3 in a ≈2 μm-thick PLZT film-on-foil.
• Demonstrated graceful failure by self-clearing method in single layer dielectric films.
• Film-on-foil dielectrics were thermally cycled (≈1000 cycles) between -50°C and +150°C with no measurable degradation in k.
• Thin ceramic dielectric on relatively thick Ni substrate is quite strain tolerant.
• A CRADA with Delphi was established to further develop and commercialize this technology.
• Over 30 publications and presentations have been made.
Developing dielectric films that has potential to reduce size, weight, and cost, concomitant with increased capacitance density & high temperature operation, for capacitors in inverters in electric vehicles.