The Effect of the Dehydration of MgO Films on their XPS Spectra and Electrical Properties

bSamsung SDI Corporate Research and Development Center, Gongse-dong, Kiheung-gu, Yongin-City, Gyenggi Province 446-577, Korea MgO thin films, which are widely used in plasma display panels PDPs, were deposited by E-beam evaporation and exposed to ambient air. The film surface changed from shiny to dull after exposure. The firing voltage of the PDP made using these air-exposed MgO thin films was increased by about 27 V. This increase is known to result from the effect of hydration, but the exact reasons are not well known. For this purpose, X-ray photoelectron spectroscopy XPS analysis was conducted. To dehydrate the hydrated MgO films, surface etching was conducted by an Ar ion beam. The XPS spectra showed that density of states was changed by etching the hydrated MgO films. The valence bandedge shifted to lower binding states, and intensity of the valence band spectrum also increased. Considering the secondary electron emission mechanism, these results mean that the secondary electrons in the valence band can be ejected easier with higher energy after dehydration. Therefore, electron density and energy of the electrons in the discharge area can be increased by dehydration. Consequently, the electrical properties of dehydrated MgO films can be improved. Similar behavior was observed when the film was heat-treated, but the etching process was more effective in dehydrating the films. Recently, much attention has been given to flat panel displays for high-definition TV. Plasma display panels PDPs are especially promising for large screen size displays. However, their power consumption should be reduced and their lifetime should be prolonged. 1,2 MgO thin films have been used as a protective layer in alternating current ac-PDPs due to their high stability against ion bombardment, low optical loss, high thermal stability, and good electrical insulating properties. Moreover, MgO thin films reduce the discharge voltage of ac-PDPs due to their high secondary electron emission coefficient and thus, various attempts to improve the characteristics of these films have been reported. 3-8 MgO films have serious problems such as chemical instability. They can be easily hydrated to MgOH2 under atmospheric conditions. It is well known that the hydration of MgO films in ac-PDPs deteriorates their electrical properties; it increases the discharge voltage and sputtering yield. 9-13 As a result of the hydration of the MgO layer, the power consumption and cost of the PDP increase and its lifetime decreases. Therefore, the heat-treatment process has been adopted in the PDP industry to dehydrate MgO thin films as well as to remove residual gases. As a result of this process, the discharge voltage is decreased and the electrical properties are improved. Several previous studies have reported the effect of hydration on the characteristics of the films. There have also been reports of several methods of preventing the hydration. 9 However, it is not yet known why the electrical properties are improved after dehydration. The aim of this work is to explain the relationship between the dehydration and the electrical properties of MgO films by analyzing their XPS valence band spectra. The results show that the valence band spectra were changed after dehydration, resulting in increased rate and energy of ejected secondary electrons. Experimental