A piezoelectric micro-electromechanical microphone for implantable hearing aid applications

The human ear receives the sound signals from the ambient and converts those signals to the electrical domain and transmits them to the brain. According to the prevalence of human hearing impairments and necessity of using the hearing aid, this paper has been concentrated on the design of microphones to be implanted inside the ear. The intended design for this application is using microelectromechanical technology and piezoelectric material. Based on the important role of the diaphragm in the microphones structure and in order to achieve maximum displacement in diaphragm, variety of accurate studies in terms of shape and dimension have been done and will be presented in this paper. The examined shapes for selecting the optimum diaphragm’s form are circle, square and hexagonal. In the performed simulations and analysis, four dimensions in micrometer have been considered for each selected shape. According to the contemplated the efficiency parameters (diaphragm’s center displacement, first resonant frequency) and results of the simulations, the circular diaphragm’s performance with dimension of 350 µm compared to the other cases is desirable for medical application of the microphone. The analysis and simulations have been performed in COMSOL software. The fabrication process of the proposed diaphragm has been done using bulk and surface micromachining. In addition, AlN was utilized as the piezoelectric material in this structure.