When a water drop approaches a solid surface in an ambient oil environment, a thin oil film will be formed between the drop and the solid surface. The lubrication film presents more complex behaviors when the external electrical field varies discretely, and in this work, concentric ripples are found in the thin film under a series of voltage steps, which is obviously different from the film profile when the applied voltage is continuously increased. According to the time evolution of the thin film, each voltage step adds a new concentric ripple outside the existing lubrication film. The radial wavelength and the maximum height of each ripple are revealed to have a linear relationship with the amplitude of the corresponding voltage step. The ripples finally break into microscopic oil droplets, and the size and the number of the droplets can be predicted with the diameter and the radial wavelength of each ripple. Published by AIP Publishing.