Inorganic Phosphors and ACTFEL Devices on Flexible Plastic Substrates

1. Inorganic Phosphorsand 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

2. Organization • Hydrothermal annealing overview • Hydrothermally annealed Zn2GeO4 • Zn2GeO4:Mn on flexible plastic substrates • Conclusions

3. Hydrothermal Annealing • Modification of conventional hydrothermal dehydration technique • Substrate is sealed in a Teflon-lined reaction vessel with water and heated • Material is repeatedly dissolved and redeposited, causing crystalline grain growth • Refractory oxide films crystallized using this technique include MnO2, ZrO2, Zn2SiO4, and Zn2GeO4

4. Hydrothermal Annealing of rf Sputtered Zn2GeO4:Mn • Zn2GeO4:Mn ACTFEL devices with L40 > 100 nits @ 60 Hz and CIEx,y = 0.300,0.667 have been demonstrated • Hydrothermal annealing is possible due to small solubility of Zn2GeO4 in water

5. Hydrothermally Annealed Zn2GeO4:Mn • Annealed film roughness can be controlled from Rq ~ 10 nm to ~ film thickness by adjusting anneal temperature, time, and amount of water added

6. Hydrothermally Annealed Zn2GeO4:Mn • 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

7. Zn2GeO4:Mn films on Plastic Substrates • Substrate requirements: • withstand 150 °C • withstand UV & O radicals • withstand exposure to H2O • retain dimensions and flexibility • Three plastics successfully employed: • polypropylene • Kapton polyimide • Appear 3000

8. Kapton Polyimide • Tg > 360 °C • Chemically very stable • Relatively low CTE • Deep amber or black color • Dupont Kapton 500HPP-ST preferred for better thin-film adhesion

9. Bright PL from Inorganic Phosphor on Flexible Substrate • Hydrothermally annealed Zn2GeO4:Mn film shows bright green photoluminescence • Polyimide film may be bent moderately without cracking or delamination of film

10. Inverted ACTFEL Device ITO (320 nm) SiO2 (300 nm) Zn2GeO4:Mn (500 nm) Ti adhesion/contact (100 nm) Polyimide film (5 mils)

11. Appear 3000 • Clear plastic film from Promerus designed for display applications • Less attractive than polyimide films in many respects, but: 92% transparent

12. Normal ACTFEL Device Al (320 nm) Zn2GeO4:Mn (500 nm) SiO2 (300 nm) Ti adhesion (10 nm) ITO (160 nm) Ti adhesion (10 nm) Appear 3000 film (5 mils)

13. Conclusions • Thin-films of crystalline refractory oxides have been deposited on flexible plastic substrates • Operational ACTFEL devices have been fabricated on flexible plastic, exhibiting dim EL • Further work is needed to improve performance: • Better low temperature dielectric • Improved performance from hydrothermally annealed Zn2GeO4:Mn • Investigation of hydrothermal annealing for other oxide phosphors

14. 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.

15. Materials Properties