In this paper we present for the first time the simultaneous action of dipolar and space charge polarization charging mechanisms in the dielectric film of capacitive RF MEMS switches. These mechanisms charge the film surface with opposite charges. At room temperature the dominant mechanism is the space charge polarization while at higher temperatures the dipolar
polarization prevails. In Si3N4 the transition occurs at about 380K where the average charging is minimized, an information that can be used to engineer the dielectric properties so that the transition
occurs at room temperature.