Soft X-ray Charging Method for a Silicon Electret Condenser Microphone

A novel charging method using soft X-ray irradiation for forming an electret of a silicon condenser microphone was developed. Soft X-rays can penetrate through the microphone diaphragm and are suitable for ionizing gas inside the microphone element. The surface potential of a positively biased SiO2/Si3N4 dielectric film negatively increased with irradiation time, since induced anions and electrons are dragged toward the film by an applied electric field. The charging rate is inversely proportional to the bias voltage and electrode-gap distance. Charged electrets have excellent retention properties; therefore, the method is promising for the realization of silicon-electret condenser microphones.

[1]  H. Amjadi.  Charge storage in double layers of thermally grown silicon dioxide and APCVD silicon nitride , 1999 .

[2]  A. Ando,et al.  High-Performance Condenser Microphone With Single-Crystalline Silicon Diaphragm and Backplate , 2007, IEEE Sensors Journal.

[3]  Gerhard M. Sessler,et al.  Self‐Biased Condenser Microphone with High Capacitance , 1962 .

[4]  Gisela Hess,et al.  Silicon condenser microphones with corrugated silicon oxide/nitride electret membranes , 2002 .

[5]  Débora T. Balogh,et al.  Corona poling and electroactivity in a side-chain methacrylate copolymer , 2000 .

[6]  Inorganic electret membrane for a silicon microphone , 1997 .

[7]  N. Kasagi,et al.  The development of a high-performance perfluorinated polymer electret and its application to micro power generation , 2008 .

[8]  Y. Naruse,et al.  Electrostatic micro power generation from low-frequency vibration such as human motion , 2009 .

[9]  Wouter Olthuis,et al.  A review of silicon microphones , 1994 .

[10]  Toshiyuki Gotoh,et al.  Frequency Response Considerations for an Electrostatic Horn Tweeter Using Electret Elements , 1976 .

[11]  B. L. Henke,et al.  X-Ray Interactions: Photoabsorption, Scattering, Transmission, and Reflection at E = 50-30,000 eV, Z = 1-92 , 1993 .

[12]  T. Ohmi,et al.  Neutralization of static electricity by soft X-rays and vacuum UV radiation , 1994 .

[13]  Masakazu Iwaki,et al.  Silicon microphone with wide frequency range and high linearity , 2007 .

[14]  Masayoshi Esashi,et al.  High-performance ultra-small single crystalline silicon microphone of an integrated structure , 2003 .

[15]  Reimund Gerhard-Multhaupt,et al.  Silicon‐dioxide electret transducer , 1984 .