Charging method of micropatterned electrets by contact electrification using mercury

This paper describes a new charging method for micropatterned electrets. The charging is based on contact electrification, and is performed by dipping an electret into mercury. By this method, 0.5-mu m-thick silicon-dioxide electrets whose surfaces were treated by hexamethyldisilazane (HMDS) and a fluorinated silane coupling agent were charged up to -50 and -80V, corresponding to a seventh and a forth of the dielectric breakdown limitation, respectively. Micropatterned electrets with line-and-space features were also charged near the surface charge density of the unpatterned electret, but a part of the charges disappeared from both edges of the electrets. The charge stability was propotional to the square of the electret width. This suggests that the charge stability is not dominated by the electret bulk property, but by surface conduction. To reduce the surface conduction, surface modification by the fluorinated silane coupling agent is effective, improving the charge stability by 100 times compared with HMDS treatment.