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A Dry Phosphor Screening Method with a Tacky Photopolymer for Emissive Displays

A Dry Phosphor Screening Method with a Tacky Photopolymer for Emissive Displays. Michielle Hurt Jan Talbot Chemical Engineering Program University of California, San Diego December 14, 2004. RESEARCH ISSUES FOR HIGH-PERFORMANCE DISPLAY SYSTEMS.

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A Dry Phosphor Screening Method with a Tacky Photopolymer for Emissive Displays

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  1. A Dry Phosphor Screening Method with a Tacky Photopolymer for Emissive Displays Michielle Hurt Jan Talbot Chemical Engineering Program University of California, San Diego December 14, 2004

  2. RESEARCH ISSUES FOR HIGH-PERFORMANCE DISPLAY SYSTEMS • Portability and multiple-functionality of devices • Issues of light-weight materials, low power consumption, readable displays screens for printor video in various lighting conditions • Applications at the convergence of both wireless communications and display technologies

  3. Talbot’s Group Information Displays Research • Electrophoretic Deposition (EPD) • Fundamentals of EPDJean Siracuse Lopez (MS, 1989) $$$ Hughes Aircraft Co. • Michael Shane (PhD, 1994) & UC MICRO • AdhesionBenjamin Russ (PhD, 1997) $$$ ARPA Phosphor Technology Center of Excellence • Electroplasma & UC MICRO Candescent & UC MICRO • Full-Color (RGB) Deposition$$$ Coloray Corp.David Chang (MS, 1996) SRI, Inc. • American Display Consortium • EPD in a Thermoreversible GelYohan Choi (MS, 1999) $$$ DARPA Phosphor Technology Center of Excellence • Optical Characterization $$$ DARPA Phosphor Technology Dr.Sheng Cheng Luo (2000) Center of Excellence • Sony & UC SMART • Slurry Coating - Development of high-resolution photoresists (PVP) • Jason Swei (MS, 2001, PhD 2004) $$$ Sony & UC SMART

  4. Introduction • Cromalin® is an adhesive that changes properties when exposed to UV light, a photopolymer. The material may be tacky and through polymerization becomes non-tacky (positive) or visa-versa (negative). • Positive Cromalin®, composed of acrylic monomers, polymer binders and free radical initiators, can be patterned with features as small as 4 µm • DuPont created this Tacky Dot® technology for solder bumping of input/output pads to fabricate integrated circuits • DuPont donated this intellectual property to us for use in a new application

  5. Motivation Investigate the potential of DuPont’s Tacky Dot® technology to pattern dots or lines of phosphor particles for dry screening of emissive displays, such as cathode ray tubes (CRTs)

  6. Dry Photolithographic Methods • Electrophotographic • Thermal laser • Electro-erosion • Photopolymeric lithography Uses an aromatic diazonium salt to create a “phototackifiable” polymer that is coated as a slurry onto a glass substrate and patterned with UV light, making the exposed areas tacky. Phosphor particles are then dusted onto the surface and adhere to the tacky areas. [H. Morishita and S. Nonogaki, Journal of Imaging Science, 30 (2), 86 (1986).] • Ref: K. Y. Sasaki and J. B. Talbot, Advanced Materials, 11 (2), 91 (1999).

  7. 450 400 350 300 250 200 150 100 50 0 Temperature (°C) Heating Cycle: degrades organic material Heating Approach Hold Cooling Time (minute) 0 20 30 60 80 100 120 140 160 Display Screen Processing Etch glass panel with hydrofluoric acid solution Deposit black matrix contrast for clear, bright picture Deposit green, blue & red phosphors 446 °C Vacuum deposit aluminum Ref. J. Castellano (1992); www.techneglas.com/web2/products/frit.pdf

  8. Display Screen Criteria • Pinhole-free coverage that does not reduce light output (~1.4 phosphor layers) • Sufficient adhesion strength that withstands manufacturing and consumer handling • Decomposition of organic materials during the heating cycle so gases do not evolve during electron bombardment causing a drop in electrode emission Ref. K. Sasaki and J. Talbot (1999)

  9. Current Research Understanding the patterning possibilities, deposition properties and the decomposition of DuPont’s adhesive materials through: • UV-Vis spectroscopy • Resolution patterns (1951 USAF target) • Deposition mass under various conditions • Light transmittance through deposits • Adhesion tests • Decomposition by thermogravimetric analysis (TGA) or pyrolysis

  10. 12 µm Mylar ® 4 µm Cromalin® 18 µm PP UV light 12 µm Mylar® 4 µm Cromalin® Substrate MASK MASK MASK MASK MASK Patterning Procedure Cromalin® is made up of three layers: Mylar® cover sheet, the tacky photo-polymer and PP cover sheet The polypropylene cover sheet is removed, allowing the Cromalin® to be laminated onto another substrate A Mask is placed over the Cromalin® which is patterned using UV light Positive Negative or Removing the Mylar® cover sheet exposes the tacky photo-polymer Particles may then be loaded onto the tacky surface Creating an either Positive or Negative image depending on the type of Cromalin®

  11. UV-Vis SpectroscopyTo determine absorption wavelength of activator (350-365 nm) material is exposed with a 15W UV lamp and dissolved in acetone

  12. Patterns on Positive Cromalin®15 Watt UV lamp: 3.42 cd/m2Exposure time: 25 sec Scale Nichia ZnS:Cu Green Phosphor ~6µm Nichia ZnS:Ag, Cl Blue Phosphor ~5µm

  13. Group 4 2 Group 4 3 2 4 3 µm 5 98.45 1 4 6 µm 5 98.45 1 6 Resolution Test1951 USAF Target DuPont’s CC28 Cyan Toner Last complete feature, group 4 element 5, shows a resolution of ~ 19.7 µm Carbon Nanotubes

  14. Particle Size Distribution By mixing different phosphor types and sizes a range of particle distributions is obtained B: Nichia Green ~ 3 µm avg. diameter was mixed with either A: Nichia Blue ~ 5 µm avg. diameter or C: Nichia Green ~ 6 µm avg. diameter In mass ratios of 0%, 20%, 50%, 80% and 100% B with either A or C

  15. Deposition Dependence on Average Particle Size A: Nichia Blue ZnS: Ag, Cl ~5 mm B: Nichia Green ZnS: Cu ~3 mm C: Nichia Green ZnS: Cu ~6 mm

  16. Interstitial Void Diameter In close packing, interstitial void diameter = ~0.414R1 =~2.1 µm for mixtures w/ ~5 µm particles = ~2.5 µm for mixtures w/ ~6 µm particles

  17. Luminance Measurement Setup Red Lamp On Stand Box with Cutout 82.5 cm Minolta CS-1000 Spectroradiometer Measures luminance: candela/m2 Glass Slide (7.5 cm X 2.5 cm) with Phosphor Adhered to Cromalin®

  18. Luminance Dependence on Particle Size Distribution A: Nichia Blue ZnS: Ag, Cl ~5 mm B: Nichia Green ZnS: Cu ~3 mm C: Nichia Green ZnS: Cu ~6 mm Blank slide: 855 ± 5.5 cd/m2Cromalin® on slide: 697 ± 3.8 cd/m2

  19. Process Conditions Using A: Nichia Blue ~ 5 µm • No added variables • Heat- on 45 °C heating plate for 2 min • Vibration- in dry sonicator for 5 min • Heat & vibration- heat 2 min, sonicate 5 min • Add layer of B: Nichia Green ~ 3 µm • UV exposure 1 min • Heat w/ UV exposure- on 45 °C heating plate for 2 min • Heat & vibration w/ UV exposure- heat 2 min, sonicate 5 min • Two Cromalin® layers w/ UV exposure • Add layer of B: Nichia Green ~ 3 µm w/ UV exposure

  20. Deposition Mass Dependenceon Process Conditions

  21. Transmittance Dependence on Process Conditions

  22. Adhesion EvaluationScotch Tape® Test tape tabs (3.25 cm2 area) were weighed before and after being pressed against and removed from samples allowing the percentage phosphor removed to be calculated

  23. Thermogravimetric Analysis TGA for determination of decomposition properties under argon at 10 °C/min

  24. Pyrolysis of Positive Cromalin® Acrylic Polymer Binders (28.60 wt.%) polymethylmethacrylate (PMMA) 0.16 wt.% remaining 0.05 wt.% of Cromalin®’s residual mass Acrylic Monomers (63.11 wt.%) 21.91 wt % untested PETA (pentaerythritol triacrylate) 20 wt. % remaining 5.1 wt. % of Cromalin®’s residual mass TDMA (triethylene glycol dimethacrylate) 0.37 wt. % remaining 0.06 wt. % of Cromalin®’s residual mass Photoinitiator (7.31 wt.%) untested Chain Transfer Agent (0.48 wt.%) 0.02 wt. % remaining 0.00 wt. % of Cromalin®’s residual mass Sensitizer (0.44 wt.%) 0.02 wt. % remaining 0.00 wt. % of Cromalin®’s residual mass MeHQ (methylhydroquinone) (0.05 wt.%) untested

  25. Pyrolysis of Positive Cromalin® • Pyrolysis of Cromalin® under argon at 10 °C/min up to 450 °C yielded a residual mass of ~13.6-15.2 wt.%. • With a residual mass of ~20 wt.%, pentaerythritol triacrylate (PETA) comprises ~5.1 wt.% of Cromalin’s® residual mass and is, therefore, a main contributor to the residue. • Untested compounds representing ~30 wt.% of Cromalin®’s composition are assumed to be the remaining ~9-12 wt. % of the photopolymer’s residual mass.

  26. Future Work • Future investigate UV decomposition by FTIR • Study the mechanism of adhesion • Adhesion dependence on applied force after deposition • AFM determination of adhesion • SEM of cross-sections to evaluate particle entrapment

  27. Acknowledgement:DuPont

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