NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

NREL’s e-Ca Test

Barrier Technologies Workshop

Arrelaine A. Dameron

September 19, 2012

NREL/PR-5200-56665
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Characterization of Water Permeation Barriers

Barrier

Ambient Environment

Sensitive Components

Vapor adsorbs and 

dissolves into 

barrier 

Vapor diffuses

Vapor 

desorbs/outgasses

Desire a characterization method that is:

– Reproducible

– Highly sensitive

– Easy to use

– Scalable
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1 Food Packaging 

0.1 LCDs

0.01

TFTs

10-3

CdTe /Thin Film

10-4

CIGS

10-5

10-6 OPV & OLEDs 

10-7

Application Specific Tolerable Water Permeation

Isostatic Test Limit

ASTM F1249

(~5 × 10-4)

e-Ca Test Limit

(~5 × 10-7)

Gravimetric Test Limit

ASTM E96

(~1 × 10-1)

~7 uL

~7 mL 

~7 L 

Volume in 1 m2

after 20 yrs

WVTR 

(g/m2/day)
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Ca Test Basics

Ca + 2H2O  Ca(OH)2 + H2

Opaque and Conductive  Transparent and Insulating

G.Nisato et al., Proceedings Asia Display/IDW pp. 1435, 2001. R. Paetzold et al., Review of Scientific Instruments, vol. 74, pp. 5147, 2003.

Electrical Characterization:

• Greater range of sensitivity

• Ease of Use

• Scalability & Throughput

Optical Characterization:

• Visual evaluation

• Pinhole identification
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NREL’s e-Ca Test

Barrier Film

Edge Seal

Spacer

Test Card

Edgecard

Connector

Ca +2H2O(g) → Ca(OH)2 +H2

Ca transforms from opaque, conductive metal to transparent, resistive oxide upon exposure 

to water
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WVTR Equation

Reaction Ratio:

Ca +2H2O(g) → Ca(OH)2 +H2

n=2

Ca Density: 

1.55 g/cm3

Ca Resistivity:

4.02×10-6 (Ω·cm) at 230C 

Trace 

Dimensions

Ratio of Apertures

Ratio of 

Molecular Weights

Measured 

Resistance

Time

We measure the resistance with respect to time to calculate the WVTR.
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Samples on test
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Measured e-Ca Test Data

Actual measured data from a barrier film provided by a commercial partner shows 

steady state permeation at ~3 10-5 g/m2/day. 

This data is well above the sensitivity limits of NREL’s e-Ca test.
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Ca Test Components

• Ca Test Assembly

o Cables between electronics and Ca assembly

o Commercial edgecard connector for easy/fast 

connect/disconnect

o Custom Test Card with Ca and Au traces

– Evaporated contacts using shadow mask 

onto glass substrate

o Commercial edgeseal 

o Custom diffusion spacer element

– Machined aluminum block

o Barrier Film

• Computer for Data collection

o Custom software

– Data collection, averaging and calculations, and WVTR display

• Commercial digital multimeter

o 6.5 digit accuracy => ±0.1 mΩ

• Multiplexing Distribution Hardware

o Combination of commercially available and custom assembled 

instrumentation

o Current configuration can measure up to 128 samples
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Test Card

• Ca Traces are fabricated separate from the barrier film

• 3 redundant 4-pt measurements of Ca resistance as a function of time

• Witness line monitors edgeseal integrity and provides internal 

standard of sensitivity limits

• Inert contacts pass signal to the outside of the assembly and fit into 

standard edgecard connector
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Test Card Fabrication
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Test card stability and packaging

• Test cards can be produced in bulk (and stored in inert 

environment) prior to obtaining barriers to be tested

• Storage in ambient conditions for 2 months using simple 

packaging methods resulted in <1% change (worst).

 Equivalent to <1Å/day or WVTR of ~10-9g/m2/day

We even shipped them to Japan!
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Edge Seal Evaluation

Using the Optical Ca Test concept as an effective means of evaluating edge seal 

materials similar to applied environment

Glass

Glass

100nm Ca

Edge Seal

Ca turns 

transparent 

appearing to 

shrink toward 

center

PDMS

85C/

85 %RH

0 h 3 h 4.5 h

X = K t

X

X

X
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Typical Edgeseal Results

PVB EVA PDMS

Desiccant-filled 

Polyisobutylene

0 hr

4.5 hr

3 hr

0 hr

24 hr 3 hr 3 hr

0 hr

234 hr

0 hr

8 hr 7 hr

We tested for hundreds of hours....

Increasing 

Time
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Desiccant Filled PIB Edgeseal

115 h 1488 h 3509 h

We tested for thousands of hours....
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Relative Comparison of Materials

0.01

0.1

1

10

0.1 1 10 100 1000 10000

Distance (cm)

850C/85% RH Exposure Time (h)

PDMS #2 (0.60)

EVA (0.33)

PVB (0.25)

TPU (0.23)

Ionomer (0.067)

PIB #1 (0.024)

PIB #2 (0.018)

Material (K [cm/h1/2])

Typical Edge 

Seal Width Distance (cm)

Finally we picked one! PIB#2 material performed the best and was the easiest to 

use for this application.
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The ‘Spacer’

 

Glass/barrier

The spacer element is a non-absorbing mechanically fabricated 

cavity with apertures on the barrier side and on the test card side 

and sealing surfaces between the spacer to barrier film and spacer 

to the test card.

The spacer provides a means to assemble the test quickly with a 

mechanical press.

Addition of the spacer provides several advantages...

sealing surface
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Spacer Advantage #1: Aperture Ratioing

The ratio of apertures controls the sensitivity range by adjusting the 

barrier area relative to the Ca area 

o Some ratios (barrier area : Ca area) that we can use presently 

are 9:1, 30:1, 60:1, 700:1 
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Advantage #2: Diffusion compensation

• Worst Case Scenario: Ca traces are deposited onto the barrier but the 

barrier has a pinhole defect:

• Resultant measurement is NOT reflective of the average WVTR!

t0 t1 t2

t3 t4 t5
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Advantage #2: Accounting for defects

Without a spacer, the trace closest to the pinhole defect 

produced the highest WVTR

Pinhole

1

2

3
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Advantage #2: Accounting for defects

Without a spacer, the trace closest to the pinhole defect 

produced the highest WVTR.

Pinhole

1

2

3
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0.01

0.1

1

10

0 1 2 3 4 5 6 7 8 9 10

WVTR (g/m2/day)

Time (h)

0.2 mm Aclar, 850C and 85% RH

Modeled Data

Ridge Spacer

Flat Spacer

Advantage #3: Edgeseal Control

• Spacer sealing surface design 

o allows for reproducible testing areas

o limits the influence of the edgeseal 

materials on the measurement

(a) Flat (b) Trench (c) “O” Ring (d) Al Ridge (e) Ridge & Trench
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Device to Device reproducibility
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e-Ca Process Flowchart
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Witness Correction and Data Averaging

Averaging over 1 hrs

Data Averaging Only Averaging and Witness Correction
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Witness Correction and Data Averaging

Averaging over 12 hrs

Data Averaging Only Averaging and Witness Correction
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Witness Correction and Data Averaging

Averaging over 24 hrs

Data Averaging Only Averaging and Witness Correction
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Witness Correction and Data Averaging

Averaging over 48 hrs

Data Averaging Only Averaging and Witness Correction
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Witness Correction and Data Averaging

Averaging over 120 hrs

Data Averaging Only Averaging and Witness Correction
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What we still need to do...

• Understanding Ca Test breakthrough and lag times

o Ca degradation effects?

o Spacer adsorption effects

o Contact compatibility

o Annealing effects

• Develop usable standards
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Conclusions

• e-Ca Test can be used reproducibly for a scalable steady 

state WVTR characterization method

• We have demonstrated measurement in the <10-5

g/m2/day range and have confidence that 10-7 g/m2/day 

can be qualitatively analyzed with this technique. 

• Sensitivity can be modulated by:

o Varying aperture area

o Temperature correction

o Witness correction

o Data Averaging

• For accurate reproducible results, control of the spillover 

of edge seal material, and gas diffusion lengths are 

important.