A single-chip microelectromechanical system (MEMS) capacitive microphone is designed and modeled. The mechanical model of the structure is extracted and the mathematical equations for a description of the microphone behavior are obtained. Then the proposed microphone characteristics are considered. In this structure, by adding Z-shape arms around the diaphragm, diaphragm hardness is decreased and diaphragm displacement becomes uniform. The sensitivity and the pull-in voltage are improved despite the decreasing size. The perforated diaphragm of this microphone is supported by Z-shape arms at its four corners. These arms around the diaphragm decrease the stiffness and air damping of the microphone. The behavior of this microphone is also analyzed by the finite element method. The structure has a diaphragm thickness of 2 μm, a diaphragm size of 0.32 × 0.32 mm2, an air gap of 2 μm, and a highly doped monocrystalline silicon wafer as a backplate. The proposed microphone is simulated with IntelliSuite software. According to the results, the new microphone has a sensitivity of 14.245 mV / Pa and a pull-in voltage of 5.83 V. The results show that the proposed MEMS capacitive microphone is one of the best structures in performance. The obtained mathematical equations for description of the microphone’s behavior have good agreement with the simulation results.
This paper presents design, modeling, and fabrication of a crab-shape microphone using silicon-on-isolator (SOI) wafer. SOI wafer is used to prevent the additional deposition of sacrificial and diaphragm layers. The holes have been made on diaphragm to prevent back plate etching. Dry etching is used for removing the sacrificial layer, because wet etching causes adhesion between the diaphragm and the back plate. Crab legs around the perforated diaphragm allow for improving the microphone performance and reducing the mechanical stiffness and air damping of the microphone. In this structure, the supply voltage is decreased due to the uniform deflection of the diaphragm due to the designed low-K (spring constant) structure. An analytical model of the structure for description of microphone behavior is presented. The proposed method for estimating the basic parameters of the microphone is based on the calculation of the spring constant using the energy method. The microphone is fabricated using only one mask to pattern the crab-shape diaphragm, resulting in a low-cost and easy fabrication process. The diaphragm size is 0.3 mm×0.3 mm, which is smaller than the conventional microelectromechanical systems capacitive microphone. The results show that the analytical equations have a good agreement with measurement results. The device has the pull-in voltage of 14.3 V, a resonant frequency of 90 kHz, an open-circuit sensitivity of 1.33 mV/Pa under bias voltage of 5 V. Comparing with previous works, this microphone has several advantages: SOI wafer decreases the fabrication process steps, the microphone is smaller than the previous works, and crab-shape diaphragm improves the microphone performances.
A novel single-chip microelectromechanical systems (MEMS) capacitive microphone with a slotted diaphragm for sound sensing is developed to minimize the microphone size and improve the sensitivity by decreasing the mechanical stiffness of the diaphragm. According to the results, a clamped microphone with a 2.43×2.43-mm2 diaphragm and a slotted one with a 1.5-×1.5-mm2 diaphragm have the same mechanical sensitivity, but the size of slotted microphone is at least 1.62 times smaller than clamped structure. The results also yield a sensitivity of 5.33×10−6 pF/Pa for the clamped and 3.87×10−5 pF/Pa for the slotted microphone with a 0.5×0.5-mm2 diaphragm. The sensitivity of the slotted diaphragm is increased 7.27 times. The calculated pull-in voltage of the clamped microphone is 214 V, the measured pull-in voltage of the slotted one is 120 V. The pull-in voltage of the slotted microphone is about 50% decreased.