Motivation:

Barriers to oxygen and moisture are critical packaging components for a widevariety of industries. The requirements of each application vary significantly,with differing needs for cost, flexibility, transparency, and permeation rates. Itis believed that for next generation technologies like OLEDs and organic PV(OPV) modules, extremely low (10−6 to 10−8 g/m2/day) water vapor

transmission rates (WVTR) may be required. To aid in the research anddevelopment of such barriers, a quantitative high-throughput technique thatcan measure many barriers in parallel under a series of conditions isnecessary. NREL’s e-Ca Test is this technique!

Test Method

Standards

andReferences

Description Range (g/m2/day) Advantages Disadvantages

Cup Test ASTM	E96	

Scavenger	method	using	gravimetric	evaluation	

0.1	‐	1000	

•	ASTM	Standard		•	Commercially	available		•	High	throughput		•	Wide	range	of	environmental	control	possible		•	Inexpensive	

•	Very	low	sensitivity		•	Can	not	monitor	transients		•	Prone	to	user	error	

Isostatic(MOCON)

ASTM	F1249	

Diffusion	cell	with	coulometric	moisture	sensor		

0.05	‐	100	(Permatron)	5x10‐4	‐	5	

(Aquatron)	

•	ASTM	Standard		•	Commercially	available		•	Can	monitor	transients		•	Intermediate	sensitivity	

• Temperature	

(5‐50C)		•	Limited	throughput		•	Sensitivity		•	Intermediate	cost	

HTO/RadioactiveTracer

Dameron;		Dunkel		

Diffusion	cell	with	detection	of	water	doped	with	tritium	either	by	ionization	chamber	or	indirectly	by	hygroscopic	salt	and	scintillation	method	

10‐8	‐	10	

•	Extremely	good	sensitivity		•	Potentially	high	throughput	(indirect)	

•	Expensive			

•	Radiation			•	Not	commercially	available		•	Multiplexing	difficult	for	ionization	chamber	method		•	Limited	environmental	control	

Optical CaTest

Nisato		

Scavenger	method	monitoring	Ca	oxide	formation	optically		

10‐6	‐	10	

•	Good	sensitivity		•	Potentially	high	throughput		•	Wide	range	of	environmental	control	possible		•	Can	monitor	transients	

•	High	capital	

investment	•	Not	commercially	available		•	No	standard	‐	potential	for	inaccurate	numbers	

MassSpectroscopy

Zhang;	Renade;	Obrien;	Hulsmann		

Diffusion	cell	with	residual	gas	analyzer,	sometimes	paired	with	programmed	valving	system	to	increase	sensitivity	

10‐7	‐	>10	

•	Very	good	sensitivity		•	Can	monitor	other	species	than	moisture	

•	High	capital	

investment		•	Not	commercially	available		•	Limited	throughput		•	Limited	environmental	control	

Electrical CaTest

Paetzold;	Choi;	NREL	

Scavenger	method	monitoring	Ca	oxide	formation	electrically		

10‐7	‐	10	

•	Good	sensitivity		•	Potentially	high	throughput		•	Low	capital	investment		•	Wide	range	of	environmental	control	possible		

•	Not	commercially	available	yet		•	Moderate	level	of	accuracy.	

Common Water Vapor Transport Testing Methods

NREL’s e-Ca Test Assembly. Components are fabricated separately andassembled in a module design, so that the test can be scaled to manysimultaneous measurements, while retaining high quantitative sensitivity.

A. High Permeation

B. Medium Permeation

C. High Permeation

Top View Side View Barrier in Test Side

Ca Test Card Side

(a) Flat (b) Trench (c) “O” Ring (d) Al Ridge 

Ca Test Basics:The generic electrical Ca Test method uses the resistance of a Ca metal trace orpad as a sensor element to detect water permeation. The premise of the test is thatas water permeates through the barrier on test, it will react with the conductive Cametal to form resistive Ca(OH)2. If the Ca test area and geometry is known, then by

measuring the resistance of the Ca as a function of time, the amount of Caconsumed by water that has permeated through the barrier can be determined and,thus, the rate of permeation is obtained.Assumption:

Ca +2H2O(g)

→ Ca(OH)2 +H2 n=2 ∆G0rxn=-441 (kJ/mol)

Working Equation:

E-Ca Test Components:

Test Card:Evaporated Ca traces are contacted byevaporated Ti/Au contacts in a 4-ptconfiguration. Multiple lines allow severalmeasurements of the WVTR to be made andaveraged. A "witness line" is integrated intothe test structure to examine failure of theedge seal and to provide an estimate ofbackground noise.

Spacer:Pinholes and other defects can create localized and/or nonuniform oxidation of Ca, whichwould give spurious results (see simulation below). In addition to mitigating the effects ofpinholes, the spacer serves to regulate the sensitivity of the test and to control the edgeseal position and flow.

This presentation contains no confidential information. The e-Ca test is available to license from NREL. For licensing information please contact Ty Ferretti. ty.ferretti@nrel.gov; 303-275-4353

NREL’s e-Ca Test: A Scalable, High-Sensitivity Water Permeation Measurem

Arrelaine A. Dameron, Michael D. Kempe, Matthew O. Reese

Spacer Designs. By

adjusting the ratio of barrierarea to exposed Ca area thesensitivity of the test can beoptimized.

Spacer Surface Design. The

sealing surface of the spacerdictates the edgeseal flow andthe exposure of the edgeseal tothe inside of the assembly.

Edgeseal:Several Commewere tested for and overall durabthe distance moithe edge seal as A desiccated PIB for both overall ease of use.Ultimate Se

We have demons

have confidence tmeasured with thi

Simulation oIn this simulation, wedge of the apertureseparation between difficulty of introduciCa test geometries, NREL’s standard speach Ca sensor separation between us to measure an av

t0 

t3 

Barrier FilmEdge SealSpacerTest CardEdgecard

Connector

C. Low Permeation