A study on packaging of PZT MEMS microphone

Packaging is the key issue in the commercialization of micromechanical microphone (also known as MEMS microphone). The ferroelectric-micromechanical microphone would have higher sensitivity and better acoustics performance. The microphone's package will play a role in protecting the MEMS microphone chip, providing signal channel, shielding the electromagnetism interference from circumference as well. Furthermore, the acoustic performance of microphone is affected by package construction. The design and fabrication of a surface mount package for the PZT microphone is presented in this paper. The microphone chip and amplifier are integrated on an organic substrate, on which a metal cap is attached for EMI shielding. The sensitivity at 1kHz is -36.8dB (14.5mV/Pa) for packaged microphone. The selection of adhesives has been optimized to ensure enough shear strength and satisfied performance. Three types of adhesives were used for die attachment. Optical profiler was used to measure the surface topography of the PZT film before and after attachment. A comparison of failure modes after shear test, for different adhesives was made for materials selection. The acoustic performance affected by different configuration of the package has been investigated. The inlet hole on the cap can restrain the response at high frequency. Packaged microphones were evaluated after thermal cycling and thermal storage.