Nano-encapuslated of zinc sulfide:silver with indium tin oxide and aluminum doped zinc oxide for flat panel display applications

Reduction in cathodoluminescent degradation through the application of nanometer thick films of indium tin oxide (ITO) and aluminum doped zinc oxide (ZAO) has been investigated using x-ray photoelectron spectroscopy (XPS), cathodoluminescent degradation, scanning electron microscopy, transmission electron spectroscopy, and optical spectrometry. The partial pressure of water and the oxygen deposition pressure used during the coating process were controlled as parameters critical to degradation. The cathodoluminescent measurements were performed at vacuum levels between 1 · 10−7 to 5 · 10−5 Torr as measured by residual gas analysis. The primary electron beam used in the degradation experiments varied from 5–15 keV and the electron current density varied between two conditions: 10 μA/cm2 and 0.10 μA/cm2. The ITO coatings were deposited at 1 · 10−5 Torr while the ZAO films were deposited at 100 mTorr, 0.6 mTorr, and 0.14 mTorr using a modified pulsed laser ablation technique.; For the ITO coated ZnS:Ag phosphors, the amount of water vapor pressure present during cathodoluminescent degradation had a dramatic effect on the brightness lifetime. The higher the partial pressure of water, the faster the degradation rate of the phosphor. The ITO coating on the ZnS:Ag phosphor reduced the rate of cathodoluminescent degradation at both partial pressures of water that were studied. XPS showed that the coatings provided sufficient protection against the adverse affects from the water vapor.; For the ZAO coated ZnS:Ag phosphors, it was shown that the partial pressure used during the coating process effected the cathodoluminescent degradation lifetimes. The coating performed at the lowest vacuum level of oxygen provided the longest brightness lifetime. This increased phosphor lifetime was attributed to the highly deficient nature of the ZAO coating at this vacuum pressure and the continuous nature of the coating. XPS showed that the ZAO deposited at lower oxygen pressures showed a higher degree of oxidation than the other two cases. Indicating that the ZAO coating was able to behave as a sacrificial layer, which was attacked by the reactive atomic oxygen, created from the electron beam stimulated surface chemical reactions. The TEM results showed that the lower the deposition pressure, the better the coverage of the coatings. The improved conformal coverage provides better protection of the phosphor surface from the harmful residual gases, which led to improved CL degradation lifetimes.