S. L. Jones

Advances in field emission displays phosphors

Field emission displays are rapidly progressing towards the commercial marketplace. Improved technology for performance and manufacture have enabled this progress, including new materials and materials processing. Improvements have been achieved in all aspect of the display, ranging from cathode to anode to spacers to sealing technologies. While all of these technologies are critical to success, the present discussion will focus on improved technology for the phosphors. The performance of the phosphors in FEDs is critically dependent upon a number of factors, including the operating voltage, phosphor efficiency and saturation, residual vacuum level, and phosphor/tip interactions.

Improved luminescence properties of pulsed laser deposited Eu:Y2O3thin films on diamond coated silicon substrates

Europium activated yttrium oxide (Eu:Y2O3) phosphor films have been grown in situ on (100) bare and diamond-coated silicon substrates using a pulsed laser deposition technique. Diamond-coated silicon substrates were prepared using hot filament chemical vapor deposition of diamond onto silicon. Photoluminescence brightness from Eu:Y2O3 films grown at 700u2009°C on diamond-coated silicon substrates was about twice that of films on bare silicon, and reached 80% of the brightness of powders. The higher brightness from Eu:Y2O3 film on diamond-coated silicon substrates is attributed to reduced internal reflections from the Eu:Y2O3 film surface, which results from the roughness of the diamond layer.

Degradation of field emission display phosphors

Degradation of ZnS and Y2O2S cathodoluminescent (CL) phosphors has been studied at 1–4 keV using Auger electron spectroscopy simultaneous with CL. The data are consistent with an electron stimulated surface chemical reaction (ESSCR) which led to destruction of ZnS and formation of a surface nonluminescent ZnO layer as well as injection of oxygen point defects into the near-surface region. In the case of Y2O2S:Eu, the electron beam stimulated removal of S and formation of Y2O3:Eu in the presence of 1×10−6u200aTorr of oxygen. A model is presented which predicts that degradation by the ESSCR should increase with pressure in the vacuum, depend exponentially on electron dose, increase as the primary beam energy was reduced below 4 keV, and depend upon the type of gas present in the vacuum. These trends were demonstrated from the experimental data.

The influence of residual gas pressures on the degradation of ZnS powder phosphors

Phosphor powder of ZnS:Cu,Al,Au has been subjected to electron bombardment (2 keV, 2u2009mA/cm2) in residual gas pressures ranging from 0.6×10−8 to 7.0×10−8u2009Torr. Auger electron spectroscopy and cathodoluminescence (CL), both excited by the same electron beam, were used to monitor changes in the surface chemistry and cathodoluminescent brightness versus vacuum conditions during electron bombardment. A direct correlation between the surface reactions and the degradation of CL brightness was observed. The formation of a nonluminescent ZnO layer on the surface of the phosphor was largely responsible for the degradation of the ZnS. The aging of the phosphor was not only a function of the charge per unit area (Coulomb dose) bombarding the surface, but also a function of residual gas pressure and composition. In particular, H2O had the greatest effect on the rate of degradation. The results are interpreted in terms of an electron-beam stimulated surface chemical reaction.

Degradation Mechanisms and Vacuum Requirements for Fed Phosphors

Degradation of phosphors in field emission displays (FEDs) is described and related to electron beam stimulated surface reactions between ZnS and residual gas in the vacuum system. The requirements for producing and maintaining vacuums in FED packages is reviewed and limitations associated with the size of the FEDs are discussed. It is concluded that vacuum production and maintenance is critical to the performance of FEDs, and this is not a simple task.

A comparison of the degradation mechanisms in ZnS and Y2O2S:Eu powder FED phosphors

The degradation of Y 2 O 2 S:Eu phosphor powders was studied using Auger electron spectroscopy (AES) and cathodoluminescence (CL). The phosphors were exposed to electron bombardment (2 keV, 2 mA/cm 2 ) at residual background gas pressures from 2x10 -8 to 10 x 10 -8 Torr. The results indicate that the degradation is due to electron-stimulated surface reactions caused by electron-beam dissociation of molecular species at the phosphor surface. AES data show that the surface was initially contaminated by C-containing impurities, and that both C and S were depleted during electron bombardment. Increased rates of depletion of C and S were observed for higher pressures, suggesting that the concentration of molecular species on the phosphor surface was limiting the rate of reaction and removal of C and S. Quantification of the AES results and inspection of CL spectrum suggest that the surface was converted to a non-activated Y 2 O 3 . Comparison of the degradation of Y 2 O 2 S:Eu and ZnS:X (X = Ag,Cl or X = Al, Au, Cu) showed that ZnS phosphors were more susceptible to degradation caused by surface changes induced by electron-beam bombardment. The degradation rate of the ZnS phosphors was approximately 3 times faster than the Y 2 O 2 S:Eu.

Electron-stimulated surface reactions between residual vacuum gas and ZnS field-emission-display phosphors

Phosphor films of ZnS on Si (100) have been subject to electron bombardment (2 KeV) over a range of pressures from 1 x 10 -6 to 1 x 10 -9 Torr. Various gases including hydrogen and oxygen were introduced into the ambient during bombardment, in order to assess their effects on surface modification. Auger electron spectroscopy data indicate that in the presence of oxygen and hydrogen, sulfur was depleted from the surface during electron bombardment. The postulated mechanism for this displacement is electron-beam dissociation of molecular species to atomic hydrogen and oxygen, followed by a surface reaction forming high-vapor-pressure sulfur compounds (e.g. SO x and H 2 S).

Flat panel displays: how bright and colorful is the future?

The dominant technologies for flat panel displays are reviewed. The current dominant technology is liquid crystal displays, which is a non-emissive light valve technology requiring backlighting and having tremendous advantages in terms of power consumption and cost. The disadvantages include viewing angle and temperature limitations. The competing emissive technologies include electroluminescent, field emission, plasma, and light emitting diode/diode laser displays. These technologies are reviewed and applications of ferroelectric materials are noted.

Advances in field emission display phosphors

Field emission displays are rapidly progressing towards the commercial marketplace. Improved technology for performance and manufacture have enabled this progress, including new materials and materials processing. Improvements have been achieved in all aspect of the display, ranging from cathode to anode to spacers to sealing technologies. While all of these technologies are critical to success, the present discussion will focus on improved technology for the phosphors. The performance of the phosphors in FEDs is critically dependent upon a number of factors, including the operating voltage, phosphor efficiency and saturation, residual vacuum level, and phosphor/tip interactions.

Blue And Yellow Light Emitting Phosphors For Thin Film Electroluminescent Displays

Following a description of the purpose and participating members in the Phosphor Technology Center of Excellence, research on the growth and characterization of modulation doped ZnS:Mn and of Ca 0.95 Sr 0.05 Ga 2 S 4 :6%Ce are reported. ZnS:Mn has been grown using MOCVD and incorporation of Mn in 1 to 5 layers from 5 to 20 nm thick separated by layers of pure ZnS from 5 to 50 nm thick. This is shown to result in lower threshold voltages for ACTFELD displays. The luminescence spectra from sputter deposited, cerium-doped thiogallate thin films were measured and the diffusion of thin ZnS passivation layers versus temperature of heat treatment was discussed.