AVS 49th International Symposium
    Microelectromechanical Systems (MEMS) Wednesday Sessions
       Session MM-WeP

Paper MM-WeP2
Inorganic Electret Using SiO@sub 2@ Thin Films Prepared by r.f. Magnetron Sputtering

Wednesday, November 6, 2002, 11:00 am, Room Exhibit Hall B2

Session: Poster Session
Presenter: T. Yamatani, Kanazawa Institute of Technology, Japan
Authors: T. Minami, Kanazawa Institute of Technology, Japan
T. Yamatani, Kanazawa Institute of Technology, Japan
T. Utsubo, Kanazawa Institute of Technology, Japan
T. Miyata, Kanazawa Institute of Technology, Japan
Y. Ohbayashi, Hosiden Corporation, Japan
Correspondent: Click to Email
The ability to fabricate inorganic thin-flim electrets on low temperature substrates is necessary for applications such as electret actuators and sensors in MEMS. In this paper, we describe the fabrication of silicon dioxide (SiO@sub 2@) thin-film electrets that exhibit a highly stable surface potential in tests at high temperatures as well as high relative humidities in air. The SiO@sub 2@ films were prepared on various conductive substrates at a temperature of 250 to 400@super o@C by rf magnetron sputtering using a fused quartz target. It was found that operational stability in highly humid atmospheres can be considerably improved by postannealing in a highly humid atmosphere at a high temperature. In addition, the obtained surface potential stability also proved to be dependent on the deposition conditions. The surface potential of SiO2 films postannealed in a highly humid atmosphere at 350 to 450@super o@C for 10 to 180 min was found to be highly stable even when tested at a relative humidity of 90% and a temperature of 60@super o@C. In addition to the postannealing conditions, the deposition conditions were optimized: substrate temperature, about 350@super o@C; sputter gas pressure,0.3 Pa; and O@sub 2@ partial pressure, 20%. As a result, the surface potential of SiO@sub 2@ electret films prepared under optimized deposition and postannealing conditions exhibited no decay when tested over a long term at a temperature of 60@super o@C and a relative humidity of 90%. SiO@sub 2@ thin-film electrets with a thickness of 2 to 5 µm maintained a surface potential above 300 V when tested at temperatures above 250@super o@C in air or at 60@super o@C with a relative humidity of 90%. It was concluded that highly stable thin-film electrets can be realized by SiO@sub 2@ thin films prepared on various conductive substrates at a temperature of about 350@super o@C and postannealed at 400@super o@C in a highly humid atmosphere.