Vacuum Deposition of High Performance Gas Barrier Materials for Electronics Applications

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1 Vacuum Deposition of High Performance Gas Barrier Materials for Electronics Applications Hélène Suttle DPhil Research Student Department of Materials -University of Oxford AIMCAL Fall Conference October 2008 AIMCAL October 2008

2 OUTLINE Description of Barriers What they're made of Where they're used Requirements of barriers What we're making Substrates PEN and Smoothing layers Coatings RF/DC Sputtering Sample testing Thickness Refractive Index Permeation Surface Morphology Transparency Surface chemistry AIMCAL October

3 Barrier Layers BARRIER LAYER Polyethylene naphthalate (PEN) H 2 O O 2 CO 2 AIMCAL October

4 Barrier Layers for Electronics WVTR (g/m 2 /day) BARRIER TYPE Food Packaging OTFT Pharmaceuticals OLEDs DSSC Excitonic PVs Vacuum Insulation Panels Component Lifetime Tolerance Mechanical Properties Process Speed & Cost Transparency AIMCAL October

polymer substrate Dense Al 2 O 3 layer Flash-evaporated acrylate layer

5 Objective Deposition of acrylate and Al 2 O 3 onto PEN for transparent gas barrier applications This is achievable by using High quality polymer substrate Dense Al 2 O 3 layer Flash-evaporated acrylate layer for smoothing and separation of any multiple layers. AIMCAL October

6 Design of High Barrier Layers for Electronics Decrease density of macrodefects Smooth substrate Processing Control Extend time before equilibrium permeation (lag time) Thick/multiple layers Decrease diffusivity At equilibrium Decrease diffusivity and solubility Dense coating Chemistry AlOx Coating PEN AlOx Coating AlOx Coating PEN AIMCAL October

7 Oxford Web Coater: Exterior Cooled single drum Multiple layers can be deposited in-line or sequentially. Film width = 350mm, Thickness 7 to 24μm Web speed up to 300m/min AIMCAL October

8 Oxford Web Coater: Deposition Plasma treater Dual magnetron sputter deposition Evaporation Polymer coating by flash evaporation and electron beam cure AIMCAL October

DC/RF Sputtering Power to magnetrons supplied by a DC or RF power supply RF sputtering avoids target charge build up pulsed DC must be used to avoid this

9 DC/RF Sputtering Power to magnetrons supplied by a DC or RF power supply RF sputtering avoids target charge build up pulsed DC must be used to avoid this RF power is twice as expensive per unit thickness as DC power DC sputtering allows better control of thickness and is more stable than RF AIMCAL October 2008

10 Substrate Materials PET PEN Upper Processing Temperature (deg C) Glass Transition Temperature (deg C) Continuous Use Temperature (deg C) 105/ Young's 20 deg C 4GPa 5GPa Young's 150 deg C 1GPa 3 Gpa Tensile Strength (MD) 195MPa 200MPa Moisture 20 deg C 40% RH 1000ppm 1000ppm Shrinkage in deg C after 30 mins 0.10% 0.05% Water Vapour Transmission Rate (g/m^2/day) AIMCAL October 2008

11 Al 2 O 3 deposition - Sputtering RF Sputtering - Hysteresis Metal target high sputtering rate (17.5 nm/min) very good H 2 O(g) barrier properties <0.003 g/m 2 day Voltage Oxygen (sccm) per 100sccm Ar Poisoned (oxidised) target very low sputtering rate (2.7 nm/min) very poor H 2 O(g) barrier properties g/m 2 day Decreasing Oxygen from Maximum Increasing Oxygen from 0sccm Al2 O thickness (nm) Metal Poisoned Deposition time (min) 50 m/min; 1.92kW O 2 = 5 sccm; Ar = 95 sccm AIMCAL October

12 Oxygen Delivery Oxygen is introduced in different locations. Sputter zone Adjacent to drum (outside Sputter zone) Main chamber Nature of oxidation is different in each case In sputter zone, oxidation occurs prior to deposition or at deposition Outside sputter zone oxidation occurs after deposition Sputter Zone (Original Oxygen Delivery here) Alternative Oxygen Delivery Location Oxygen introduced outside sputter zone is less likely to poison the target AIMCAL October

13 Appearance of Coated Films Mirror Laser Diode AFM Optical deflection sensor Cantilever and Tip Feedback Image XYZ Piezo Scanner PEN 30 sec 20 min 20 min AIMCAL October

14 AIMCAL October 2008

15 Film Transparency UV-vis Spectra Absorbance Wavelength (nm) AIMCAL October 2008

16 Al 2 O 3 deposition Thickness is measured using single wavelength ellipsometry Refractive Index can also be measured - Stoichiometry & Density AIMCAL October

17 Film Stoichiometry X-ray Photoelectron Spectroscopy (XPS) 10 x 10 5 Name O 1s C 1s F 1s Al 2p Pos FWHM Area At% #2.1 O 1s Peaks show presence of Aluminium, Oxygen and Carbon 8 Average stoichiometric ratio is AlO 2.2 C 1.1 CPS 6 4 Oxygen content is affected by sputtering type RF oxygen content is lower in samples produced to date 2 F 1s Binding Energy (ev) C 1s Al 2p AIMCAL October

18 Permeation Measurement There are several permeation measurement techniques Mocon permatran testing uses an RH sensor to measure the quantity of water travelling across the barrier film Detection levels are ~5x10-3 g/m 2 /day H 2 O(g) PURGE GAS IN RH SENSOR PURGE GAS OUT TEST FILM WATER AIMCAL October

19 Calcium Test GLASS PLATE EPOXY EVAPORATED CALCIUM SPUTTERED GAS BARRIER LAYER FLEXIBLE SUBSTRATE AIMCAL October

Calcium Test Calcium is oxidised (white) by

20 Calcium Test Calcium is oxidised (white) by H 2 O passing through barrier The quantity of water moving across the barrier is calculated by comparing the reacted calcium to unreacted metal at different time intervals 48 Hours 240 Hours 508 Hours AIMCAL October

Permeation Measurement A series relationship exists for multiple layers 1/Ptotal = 1/P1 + 1/P2 + 1/P3 + P = P 0 exp (-E A /RT) P: Transmission rate P 0 :constant related to the gas

21 Permeation Measurement A series relationship exists for multiple layers 1/Ptotal = 1/P1 + 1/P2 + 1/P3 + P = P 0 exp (-E A /RT) P: Transmission rate P 0 :constant related to the gas and barrier materials respectively Defect dominated layers do not contribute to activation energy INTERFACE DEFECTS IN BARRIERS CRYSTALLINE POLYMER GLASSY POLYMER AIMCAL October

Activation Energy, E A Defect dominated layers do not contribute to activation energy E A (Composite) E A (Polymer): Unhindered flow through defects.

22 Activation Energy, E A Defect dominated layers do not contribute to activation energy E A (Composite) E A (Polymer): Unhindered flow through defects. E A (Polymer) < E A (Composite) < E A (Barrier Layer): Hindered flow due to subnanopores or coating matrix? Chemical interaction with the coating? AIMCAL October

23 Barrier Layer Defects Lag time for water to penetrate each layer of a barrier film dependent on Layer thickness Diffusivity Multiple Layers Permeation dominated by diffusion through nanodefects Long time to reach equilibrium permeation AIMCAL October

24 Conclusions Reactively sputtered Aluminium Oxide has been deposited on PEN films RF and DC power supplies have been compared Transparent films have been produced Defect free barriers (<0.001 g/m 2.day WVTR) have been achieved with a single layer of Al 2 O 3 AIMCAL October

Vacuum Deposition of High Performance Gas Barrier Materials

Vacuum Deposition of High Performance Gas Barrier Materials H. Suttle, A. J. Topping, & H. E. Assender Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH ABSTRACT High performance