Piezoelectric microspeaker with compressive nitride diaphragm

A diaphragm-based piezoelectric microspeaker has been fabricated with compressive nitride films, and compared to commercial speakers. The largest sound pressure level (SPL) produced by the fabricated microspeaker is 92 dB (when measured 2 mm away from the microspeaker in open field) at around 3 kHz for 6 V/sub peak-to-peak/ input. The microspeaker produces a comparable sound output to a commercial piezo-ceramic or electrodynamic speaker used in current cellular phones. The key to this success is the usage of a diaphragm that has a very high compressive residual stress, high enough to cause the diaphragm to be wrinkled. And the flatness of the active area in the speaker diaphragm is maintained through a mild tensile stress in the electrode layers, though the non-active area is wrinkled. This way, we produce a large diaphragm deflection (without being hindered by the diaphragm stretching effect) with good control over a flat, active area where the electromechanical transduction is happening.