Electrostatic Microelectromechanical System Speaker Array with Out-of-Plane Piston Displacement and Simplified Microfabrication

This study presents a new design for a MEMS electrostatic speaker array with out-of-plane piston-like diaphragm displacement using a simplified silicon-on-insulator microfabrication process. The device comprises an array of parallel actuating membranes with small circular mechanically open but acoustically sealed apertures that enable controlled etching of the buried oxide to be released directly from the front side, but retain a high acoustic impedance acting as a flat membrane. This approach simplifies the microfabrication process, requiring only two lithography masks and increasing process tolerances. Preliminary experimental measurements validate the concept and demonstrate the electromechanical and acoustic performance compared with theoretical models.