Stability of Postannealed Silicon Dioxide Electret Thin Films Prepared by Magnetron Sputtering

Abstract

The effect of postannealing on surface potential stability was investigated for silicon dioxide (SiO₂) electret thin films with a thickness of 2 to 5 \\micron. The SiO₂ films were prepared on Al-coated and uncoated Si substrates by r.f. magnetron sputtering using a fused quartz target. Subsequent to the sputter deposition, the SiO₂ films were postannealed in the deposition chamber in order to improve stability for use in a highly humid atmosphere. The obtained surface potential stability was dependent on not only the postannealing conditions but also the deposition conditions. The surface potential of SiO₂ films postannealed in an oxidizing atmosphere at 275 to 350°C for 10 to 60 min was found to be highly stable when tested at a relative humidity of 90% and a temperature of 60°C. In addition, the postannealed SiO₂ films were stable for use in air for a long term at room temperature.