Electromagnetic Investigation of a CMOS MEMS Inductive Microphone

Abstract

This paper presents a detailed electromagnetic modeling for a new structure of a monolithic CMOS micromachined inductive microphone. We have shown, that the use of an alternative current (AC) in the primary fixed inductor results in a substantially higher induced voltage in the secondary inductor comparing to the case when a direct current (DC) is used. The expected increase of the induced voltage can be expressed by a voltage ratio of AC and DC solutions that is in the range of 3 to 6. A prototype fabrication of this microphone has been realized using a combination of standard CMOS 0.6 µm process with a CMOS-compatible post-process consisting in a bulk micromachining technology. The output voltage of the electrodynamic microphone that achieves the µV range can be increased by the use of the symmetric dual-layer spiral inductor structure.

Keywords

• MEMS
• Electromagnetic modeling
• inductive microphone
• micromachined inductors
• induced voltage