Elsevier

Thin Solid Films

Volume 515, Issue 12, 23 April 2007, Pages 5113-5117
Thin Solid Films

Effects of SiO2 addition on discharge characteristics of the MgO protective layer in plasma display panel

https://doi.org/10.1016/j.tsf.2006.10.022Get rights and content

Abstract

In order to improve the discharge characteristics of MgO protective layer, SiO2 was added to MgO thin films. The MgO–SiO2 thin films were deposited by electron beam evaporation method. The crystallinity and surface roughness of thin films were determined by XRD and AFM. Discharge characteristics of MgO–SiO2 protective layers were observed by changes in discharging voltages and SEE and memory coefficients as a function of Si concentration in the protective layer. The discharge characteristics of MgO–SiO2 layer were mainly affected by changes in crystallinity and surface roughness of films with Si concentration in the range of present study. With addition of 12.5 Si at.% in MgO–SiO2 protective layer, the discharge voltages and memory and SEE coefficients were considerably improved in comparison to pure MgO protective layer.

Introduction

Recently, flat panel display (FPD) plays a great role in various application fields. One of the well-known FPDs is the plasma display panels (PDPs). PDP is competing with the liquid crystal display (LCD) in application to wall-mounted TV. Especially PDP has advantages for large dimension TVs over 80 in. The components of PDP are glass substrates, electrodes, a transparent dielectric layer, and a MgO protective layer. MgO has strong ionic bonding and crystal structure of NaCl type, and is known as a thermally and chemically stable material. MgO has been used for the protective layer in PDPs due to its low sputtering yield and work function, excellent plasma resistance, and high secondary electron emission (SEE) coefficient [1]. In addition, MgO is transparent in visible region due to its wide band gap energy (∼ 7.8 eV) [2]. Nevertheless, the MgO protective layer used so far is not considered to meet the demands of advanced PDPs requiring higher luminous efficiency, lower energy consumption, and higher operational speed [1], [3]. Since a protective layer with a higher secondary electron emission coefficient reduces the discharge and sustaining voltage of the PDP, the SEE coefficient of protective layer is the key factor for the demands stated above [4]. Therefore, many researches have been focused on the SEE coefficient. Especially, improvement of characteristics of MgO protective layer has been tried through modification of MgO crystal structure using oxide additives such as CaO [5], ZrO2 [6], TiO2 [7] and so on. It is anticipated that the crystallinity, the crystal orientation, the surface morphology, and the surface composition of protective layer strongly influence the value of SEE, and thereby discharge characteristics [8], [9], [10].

In this study, SiO2 was added as an additive to MgO to replace the conventional pure MgO protective layer, and investigated the effect of SiO2 addition on the discharge characteristics of MgO–SiO2 protective layer. It is anticipated that SiO2 can form solid solution with MgO through interstitial occupation of Si4+ ions in MgO lattice considering much smaller ionic radius of Si4+ (0.040 nm) with respect to that of Mg2+ (0.072 nm). The modification of MgO crystal structure thereby could influence the discharge characteristics of MgO protective layer. However, the study concerning the effect of SiO2 addition to MgO layer has not been reported so far.

Section snippets

Experimental details

The MgO-based thin films were deposited by electron beam evaporation method. As evaporation sources, sintered pellets of MgO–SiO2 with different SiO2 content were prepared. The powder mixtures from starting powders, MgO (99.99%, High Purity Chemical, Japan) and SiO2 (99.6%, Aldrich, U.S.A.), were compacted to pellets and sintered at 1200 °C for 2 h. The deposition rate of MgO–SiO2 films was 3 Å/sec, and base pressure was 3 × 10- 6 Torr. No oxygen gas was introduced into the chamber. The film

Results and discussion

The chemical compositions of deposited MgO–SiO2 films determined by EPMA with that of evaporation sources are listed in Table 1. In all cases, the Si concentrations in the deposited films were lower than that in starting evaporation sources. Moreover, as the SiO2 content in evaporation sources increased, the deviation from the Si concentration in the evaporation sources also increased. This is thought to result from the lower vapor pressure of SiO2 compared to that MgO [2], therefore the

Conclusions

MgO–SiO2 films were prepared by electron beam evaporation method to improve discharge characteristics of MgO protective layer by using SiO2 additions. From the XRD and AFM analysis, it was shown that the crystallinity of MgO–SiO2 films depended on the Si concentration due to occurrence of amorphous phase at higher Si concentrations, and that its surface roughness was also influenced in the same manner. Both SEE and memory coefficients and discharge voltages in MgO–SiO2 protective layer have

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