AVS 46th International Symposium
    Flat Panel Displays Topical Conference Monday Sessions
       Session FP+VT-MoM

Paper FP+VT-MoM6
Cathodoluminescent (CL) Degradation Mechanism for ZnS-Based Phosphors and the Impact on Field Emission Displays (FEDs)

Monday, October 25, 1999, 10:00 am, Room 604

Session: Field Emission Displays and Vacuum Packaging Issues
Presenter: B.L. Abrams, University of Florida
Authors: B.L. Abrams, University of Florida
W. Roos, University of Florida
H.C. Swart, University of the Orange Free State
P.H. Holloway, University of Florida
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The surfaces of ZnS powder and thin film phosphors have been subjected to electron beam bombardment.Simultaneous acquisition of CL brightness data and Auger Electron Spectroscopy(AES)data have revealed a correlation between surface chemical reactions and CL degradation.The data were collected in a stainless steel UHV chamber.In the presence of a 2kV primary electron beam in 1e-6 Torr of H2O,the amounts of C and S on the surface decreased while the O concentration increased.XPS data showed that ZnO formed on both the samples.This change in surface chemistry coincided with a decrease in CL brightness.Our model of electron beam stimulated surface chemical reactions(ESSCR)for this degradation process postulates that the primary electrons dissociate physisorbed molecules to reactive atomic species. These atomic species remove surface S and C as volatile SOx and H2S species allowing formation of a non-luminescent ZnO layer in 1e-6 Torr water.However,in a vacuum of 1e-6 Torr dominated by hydrogen and with a low water content, there was no decline in S,no rise in O,but the CL still degraded.These effects are still attributed to ESSCR due to hydrogen assisted by thermal effects.Hydrogen is postulated to dissociate under the electron beam and remove S as H2S while Zn volatilizes due to a high vapor pressure and elevated temperatures from electron beam heating.The desorption of various ions or molecules from the surface of the phosphor caused by surface chemical reactions contaminate the vacuum inside the display tube and create a reactive environment.These reactive atoms or molecules may adsorb,react and consequently form an absorbed or coated layer(sulfide or oxide)on the field emitter tip on the cathode side of the FED.It is thus suggested that the ESSCR mechanism is important to degradation both of the phosphor on the anode and the field emitter tips on the cathode.This work was supported by Darpa Grant MDA 972-93-1-003 through the Phosphor Technology Center of Excellence.