Capacitive (condenser) MEMS microphones have been developed using various design and fabrication techniques to
improve performance. Mechanical sensitivity of a condenser MEMS microphone can be increased by reducing the
residual stress of the diaphragm using several design approaches including corrugated diaphragms, and in recent years,
various spring type diaphragms. The electrical sensitivity of the condenser microphone is proportional to the deflection
of the diaphragm, however, the parabolic deflection of the diaphragm, and thus its effective diaphragm area, has reduced
the sensitivity of parallel plate type capacitor on a condenser MEMS microphone. This paper presents the numerical
analysis on the effective diaphragm area of several condenser MEMS microphone designs of 1.1mm x 1.1mm square.
The analysis shows that the effective area of a spring-supported diaphragm is about 20% higher, and its capacitance
value thus electrical sensitivity, is about 170% higher than a fully clamped flat diaphragm of an equal size. In addition, a
flat deflection and higher effective diaphragm area of a spring-supported diaphragm can be achieved by carefully
designed spring mechanisms.
Capacitive microphones (condenser microphones) work on a principle of variable capacitance and voltage by the movement of its electrically charged diaphragm and back plate in response to sound pressure. There has been considerable research carried out to increase the sensing performance of microphones while reducing their size to cater for various modern applications such as mobile communication and hearing aid devices. This paper reviews the development and current performance of several condenser MEMS microphone designs, and introduces a microphone with spring supported diaphragm to further improve condenser microphone performance. The numerical analysis using Coventor FEM software shows that this new microphone design has a higher mechanical sensitivity compared to the existing edge clamped flat diaphragm condenser MEMS microphone. The spring supported diaphragm is shown to have a flat frequency response up to 7 kHz and more stable under the variations of the diaphragm residual stress. The microphone is designed to be easily fabricated using the existing silicon fabrication technology and the stability against the residual stress increases its reproducibility.