Secondary ionization coefficient γ of MgO, SrO and CaO and the correlation between γ and charge accumulated on CaO in argon

Abstract

An experimental investigation of Townsend's secondary ionization coefficient γ is carried out for MgO, SrO and CaO film electrodes. These oxides are utilized, or are to be utilized, in next-generation plasma display panels. All of the experiments are performed in argon. In particular, in the case of CaO film, our attention is attracted to the effect of charge accumulated on CaO film. For this purpose, the breakdown voltage Vs is observed from waveforms of the gap voltage and charge accumulated on the dielectric film electrodes with the repeated breakdown. Townsend's criterion is utilized to estimate γ from the breakdown voltage. In the case of the CaO film, γ increases gradually with repeated breakdowns and reaches a stationary value. The increase of γ is considered to be due to the charge that accumulates on the dielectric electrode triggering the next breakdown. Therefore, it is concluded that the increased γ is sustained by a combined process consisting of restarted electrons that have accumulated on the CaO film and the original γ action, as observed in metallic electrodes in a low-pressure gas discharge.