In the manufacturing of the screen for field emission display (FED), layers of small(1∼10㎛ diameter) luminescent particles may be deposited by electrophoretic deposition(EPD). During Use, the phosphor screen may be subjected to shocks and vibrations. If the adhesion of the phosphor particles is weak, particles may be dislodged, resulting in diminished screen output and increased screen noise. Therefore, an understanding of the adhesion of the deposited phosphor film is important, as are the deposition conditions which maximize the particle adhesion while minimizing any undesirable effects, such as outgassing or decreased light output.
During the EPD of a phosphor at a cathode, a material forms via electrochemical precipitation. After EPD, usually baking of the deposited material is done. Generally, as a FED manufacturing process, an electrophoretically deposited phosphor is baked in air at 425 ℃ for 1 hour. Previous studies showed that $Mg(OH)_2$ in EPD phosphor deposits was converted to MgO at 425 ℃ in air. Adhesion strength was significantly increased with baking, This effect was attributed to the MgO binder being stronger than the $Mg(OH)_2$ binder.
In this study, the baking process is revisited. Brightness was drastically reduced, and adhesion strength was slightly reduced with the baking at 425 ℃ in air for 1 hour. The compositional and structural analysis of the binder material was performed in order to understand the mechanism of adhesion.
X-ray diffraction analysis demonstrated that binder material generated during baking in air at 425 ℃ for 1 hour is not crystalline but amorphous material. It is found by the FT-IR analysis that adsorbed water remained in the space between particles even after baking above the water's boiling point. In conclusion, adhesion strength of phosphor depends on the remained water in the space between particles and its amorphous binder material.
