Inorganic Phosphors and ACTFEL Devices on Flexible Plastic Substrates

J. P. Bender and J. F. Wager Department of Electrical Engineering and Computer Science http://ece.oregonstate.edu/matdev S. Park, B. L. Clark, and D. A. Keszler Department of Chemistry Oregon State University Corvallis, Oregon USA 97731-3211

Organization

1. Hydrothermal annealing overview 2. Hydrothermally annealed Zn 2 GeO 4 3. Zn 2 GeO 4 :Mn on flexible plastic substrates 4. Conclusions

Hydrothermal Annealing

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Modification of conventional hydrothermal dehydration technique

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Substrate is sealed in a Teflon-lined reaction vessel with water and heated

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Material is repeatedly dissolved and redeposited, causing crystalline grain growth

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Refractory oxide films crystallized using this technique include MnO 2 , ZrO 2 , Zn 2 SiO 4 , and Zn 2 GeO 4

Hydrothermal Annealing of rf Sputtered Zn 2 GeO 4 :Mn

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Zn 2 GeO 4 :Mn ACTFEL devices with L 40 > 100 nits @ 60 Hz and CIE x,y = 0.300,0.667 have been demonstrated

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Hydrothermal annealing is possible due to small solubility of Zn 2 GeO 4 in water

Hydrothermally Annealed Zn 2 GeO 4 :Mn

Annealed film roughness can be controlled from R q to ~ film ~ 10 nm thickness by adjusting anneal temperature, time, and amount of water added

Hydrothermally Annealed Zn 2 GeO 4 :Mn

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PL emission observed:

– 125 °C for hydrothermal anneal – 625 °C for furnace anneal •

Approximately equal PL intensity:

– 200 °C, 2 hrs for hydrothermal anneal – 680 °C, 2 hrs for furnace anneal

Zn 2 GeO 4 :Mn films on Plastic Substrates

Substrate requirements:

– withstand 150 °C – withstand UV & O radicals – withstand exposure to H 2 O – retain dimensions and flexibility

Three plastics successfully employed:

– polypropylene – Kapton polyimide – Appear 3000

Kapton Polyimide

• • • • •

T g > 360 °C Chemically very stable Relatively low CTE Deep amber or black color Dupont Kapton 500HPP-ST preferred for better thin-film adhesion

Bright PL from Inorganic Phosphor on Flexible Substrate

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Hydrothermally annealed Zn 2 GeO 4 :Mn film shows bright green photoluminescence

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Polyimide film may be bent moderately without cracking or delamination of film

Inverted ACTFEL Device

ITO (320 nm) SiO 2 (300 nm) Zn 2 GeO 4 :Mn (500 nm) Ti adhesion/contact (100 nm) Polyimide film (5 mils)

Appear 3000

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Clear plastic film from Promerus designed for display applications Less attractive than polyimide films in many respects, but: 92% transparent

Normal ACTFEL Device

Al (320 nm) Zn 2 GeO 4 :Mn (500 nm) SiO 2 (300 nm) Ti adhesion (10 nm) ITO (160 nm) Ti adhesion (10 nm) Appear 3000 film (5 mils)

Conclusions

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Thin-films of crystalline refractory oxides have been deposited on flexible plastic substrates

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Operational ACTFEL devices have been fabricated on flexible plastic, exhibiting dim EL

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Further work is needed to improve performance:

– Better low temperature dielectric – Improved performance from hydrothermally annealed Zn 2 GeO 4 :Mn – Investigation of hydrothermal annealing for other oxide phosphors

Acknowledgements

This work was supported by the National Science Foundation under Contract Nos. DMR 0071899 and DMR-0071727. Kellie Schmitt of DuPont, Joe McDaniel of Promerus, and Ivo Thys of AFGA provided plastic film samples for evaluation.

Materials Properties

Young’s modulus (GPa) CTE (ppm/ °C) Tg ( °C) Kapton 500HPP-ST polyimide Promerus Appear 3000

2.8

1.9

(20) 74 360 410 330

Polypropylene

0.9 –1.5 100-180 (~90)