Investigation on Field Emission from Metallized Layer Adhering to Alumina Insulator

Abstract

Generally, cathode triple junction (CTJ) is regarded as an electrical weak point for the occurrence of electron emission. In a typical vacuum flashover model, initiation of electron emission starts from the cathode triple junction. Therefore, it is important to investigate electron emission phenomenon around the CTJ region. However, direct measurement of the electron emission from CTJ has not been done for the difficulty of current measurement. In this paper, we researched the electron emission characteristics from the region of boundary between the alumina insulator and the metallized layer. The purpose is to elucidate the electron emission phenomenon from CTJ. From the results, several numbers of breakdowns are observed around the boundary between the insulator and the metallized layer when the applied voltage increased up to several kV. After such experiments repeated several times, the unstable prebreakdown current of several tens of pA was measured under 3–5 kV. That current increased slowly with the elapsed time even when the applied voltage was kept constant. This phenomenon, the slowly increasing current, is probably caused by the influence of alumina being charged by electrons emitted from CTJ and the electron emission current is promoted by the charging of the alumina surface.