Micromachined optical microphone structures with low thermal-mechanical noise levels

Area of Science:

• Acoustics
• Microelectromechanical Systems (MEMS)

Background:

• Diffraction-based optical displacement detection offers high resolution for micromachined microphones.
• Traditional microphone designs face limitations in mechanical structure flexibility and size constraints.

Purpose of the Study:

• To present novel micromachined microphone structures with advanced backplate designs.
• To achieve broadband frequency response and minimize thermal mechanical noise.

Main Methods:

• Fabrication of polysilicon diaphragms with integrated diffraction grating electrodes.
• Design of backplate architectures deviating from traditional perforated plates.
• Rigorous experimental characterization of diaphragm displacement and noise.

Main Results:

• Achieved diaphragm displacement detection resolution of 20 fm/√Hz.
• Measured thermal mechanical displacement noise density of 60 fm/√Hz.
• Demonstrated an A-weighted sound pressure level detection limit of 24 dB(A).

Conclusions:

• The novel designs show substantial improvements over previous prototypes.
• The technology offers a high performance-to-size ratio.
• Expected impact on instrumentation and hearing aid applications.