Flashover Characteristic of Ti Sub-group Metal Oxide Thin Films on Epoxy Substrate under Nanosecond Pulse in Vacuum

Design and manufacture of pulse power equipment greatly depend on the investigation of flashover on dielectric surface in vacuum under pulsed voltage.It is expected that sputtering coat- ing with semiconductivity and high thermal conductivity can apparently improve the surface flashover characteristic of dielectric materials.Three kinds of thin films(TiO_2,ZrO_2 and HfO_2)were sputtered on epoxy substrate using magnetron sputtering in ultrahigh vacuum.Experiments were carried out under high voltage pulse(50ns rise time and 600ns full width at half maximum)in vacuum to study the flashover characteristics of three kinds of oxide films.The experimental results show that the TiO_2, ZrO_2 films sputtered on the epoxy substrate are amorphous as they are not annealed and surface grains are not crystalized,but HfO_2 film becomes crystalized.The flashover voltage of TiO_2 film is the highest, the flashover voltage of HfO_2 film is close to the epoxy sample.The effect of sputtering time on the flashover voltage is different for different target materials.The vacuum flashover voltage increases with the sputtering time increasing for TiO_2 and HfO_2 films,but decreases for ZrO_2 film.Furthermore,the effects of film properties on flashover performance as well as the distribution of surface charge after flashover are analyzed.