Field emission displays (FEDs) have been expected to be one of the most superior flat panel display and were predicted to acquire the flat panel display market in the near future. However, since FEDs are in the early stages of development, it is necessary for commercialization to develop key technologies, such as, emitter fabrication technology with high reliability and uniformity, vacuum packaging technology, low voltage phosphor technology, and driver integrated circuit technology.
Among these, vacuum packaging technology is recognized as one of the most important etchnologies since an FED panel is fabricated by integrating the phosphor screen, getter, spacers, and emitter array with vacuum packaging processes. Usually, a standard panel packaging process includes a panel sealing process using frit as a sealing material and a gas exhausting process. The frit consists of mainly PbO, $SiO_2$, ZnO and $B_2O_3$, and has a good sealing ability. However, it is suspected that both the emitter tip and the phosphor screen, or at least one of them, might be degraded by frit outgassing during the standard panel sealing process since it is often the case that the performance of a FED panel deteriorates considerably after the completion of all packaging processes. On the other hand, it is unlikely that the CL brightness of a FED panel was degraded during the exhausting process. In order to suppress the degradation of the panel, the various carrier gases have been used in the panel sealing process. It is necessary to understand the cause of the degradation of the panel in order to suppress the degradation of the FED panel during the panel sealing process. There have been many studies on the evolution of field emitter tips, but there have been few detailed studies on the changes that occur on the phosphor screen caused by the FED packaging process.
The best method toinvestigate the effect of the phosphor degragation caused by the frit-outgassing during the panel sealing process is to compare the cathodoluminescent intensity of the phosphor screen in-situ before and after the packaging process. But it is almost impossible to examine the phosphor degradation in this way since the emitter tips as well as the phosphor screens might be degraded by the frit-outgassing during the panel sealing process. Also in the case that one breaks the panel to examine the phosphor degradation after packaging, one could not avoid the extra damage of the phosphor screen. In order to overcome these problems, a simplified outgassing process was designed which could offer the same environment as a standard panel sealing process to the phosphorscreen. In the case of the simplified outgassing process, it is unnecessary that one breaks the panel to examine the luminance of the phosphor screen because the panel has not been joined actually. Moreover, this simplified outgassing process has good advantages that it is a simple process and its processing time is shorter than that of the panel packaging process.
Sulfide-based phosphors have been intensively studied as a cathodoluminescent (CL) material used for low-voltage luminescent display devices.Blue- and green-emitting ZnS:X,Y phosphors (X=Ag, Au, Cu; Y=Cl, Al), widely used for cathode ray tubes, have advantages such as high brightness and high efficiency compared with oxide phosphors. However, their rapid degradation and short lifetimes under high current density have been the most important issues limiting their application in low-voltage cathodoluminescent display devices. Surface reactions, including the adsorption of carbon and oxygen, occur on the ZnS surface during electron bombardment, and it has been reported that the compositional changes of the phosphor surface influence the CL intensity and its degradation behavior. The surface reaction that occurs during the thermal process results in the formation of non-luminescent ZnO layers on the surface of phosphor screen, and these layers are responsible for CL degradation of phosphor screen. So, it is desirable to modify the surface of phosphor in order to suppress the formation of ZnO layers. It is reported that the photoluminescence (PL) of ZnS:Mn phosphor was enhanced by acid treatment.
In order to investigate the effect of frit-outgassing on the phosphor screen, the CL degradation of the phosphor screens was measured after experiencing either the panel sealing process or the simplified outgassing process, and the optical property of the outgassed component released from the frit under the panel sealing environment was investigated. And by measuring CL brightness of the phosphor screen samples treated by the simplified outgassing process, we could confirm the usefulness of the process by comparing it with the ones treated by the standard panel sealing process, and examine the degree of the phosphor degradation caused by the frit-outgassing. And also the surface of the phosphor screen treated by the frit-outgassing was analysed in order to investigate what component released from frit had an effect on the phosphor screen during the outgassing process.
It was investigated that the different behaviors of the CL degradation before and after heat treatment at the panel sealing temperature. Using Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), the surface compositional change of the phosphor screen, which occurred during electron bombardment, is also investigated. Moreover, in order to improve the CL properties of ZnS phosphor after panel sealing process, it was performed that the surface modification of phosphor particles with an aqueous solution of various acid/base. Finally it was suggested what reactions happened on the surface of ZnS:Ag,Cl in treating the surface of phosphor particle and what kind of effect it had on the change in luminescent properties of the phosphor.
