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
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 2008 2
Barrier Layers BARRIER LAYER Polyethylene naphthalate (PEN) H 2 O O 2 CO 2 AIMCAL October 2008 3
Barrier Layers for Electronics 10 0 10-1 10-2 10-3 10-4 10-5 10-6 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 2008 4
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 2008 5
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 2008 6
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 2008 7
Oxford Web Coater: Deposition Plasma treater Dual magnetron sputter deposition Evaporation Polymer coating by flash evaporation and electron beam cure AIMCAL October 2008 8
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
Substrate Materials PET PEN Upper Processing Temperature (deg C) 150 180-220 Glass Transition Temperature (deg C) 78 120 Continuous Use Temperature (deg C) 105/130 160 Young's Modulus @ 20 deg C 4GPa 5GPa Young's Modulus @ 150 deg C 1GPa 3 Gpa Tensile Strength (MD) 195MPa 200MPa Moisture Pickup @ 20 deg C 40% RH 1000ppm 1000ppm Shrinkage in MD @150 deg C after 30 mins 0.10% 0.05% Water Vapour Transmission Rate (g/m^2/day) 20 3.6 AIMCAL October 2008
Al 2 O 3 deposition - Sputtering 600 500 400 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 300 200 100 0 0 5 10 15 20 25 Oxygen (sccm) per 100sccm Ar Poisoned (oxidised) target very low sputtering rate (2.7 nm/min) very poor H 2 O(g) barrier properties 1-1.3 g/m 2 day Decreasing Oxygen from Maximum Increasing Oxygen from 0sccm Al2 O thickness (nm) 3 300 250 200 150 100 50 Metal Poisoned 0 0 10 20 30 40 50 60 70 80 90 100 Deposition time (min) 50 m/min; 1.92kW O 2 = 5 sccm; Ar = 95 sccm AIMCAL October 2008 11
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 2008 12
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 2008 13
AIMCAL October 2008
Film Transparency UV-vis Spectra 2 1.8 1.6 1.4 Absorbance 1.2 1 0.8 0.6 0.4 0.2 0 0 100 200 300 400 500 600 700 800 900 1000 Wavelength (nm) AIMCAL October 2008
Al 2 O 3 deposition Thickness is measured using single wavelength ellipsometry Refractive Index can also be measured - Stoichiometry & Density AIMCAL October 2008 16
Film Stoichiometry X-ray Photoelectron Spectroscopy (XPS) 10 x 10 5 Name O 1s C 1s F 1s Al 2p Pos. 530.799 284.799 683.799 73.799 FWHM 4.54187 4.78416 5.03118 4.21886 Area 3925921.2 643659.7 78496.9 459364.1 At% 53.66 23.23 0.71 22.40 #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 1000 800 600 400 200 0 Binding Energy (ev) C 1s Al 2p AIMCAL October 2008 17
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 2008 18
Calcium Test GLASS PLATE EPOXY EVAPORATED CALCIUM SPUTTERED GAS BARRIER LAYER FLEXIBLE SUBSTRATE AIMCAL October 2008 19
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 2008 20
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 2008 21
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 2008 22
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 2008 23
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 2008 24