Electrical Engineering, Babol University of Technology
In this paper, a novel single-chip MEMS capacitive microphone is presented. The novelties of this method relies on the moveable aluminum (Al) diaphragm positioned over the backplate electrode, where the diaphragm includes a plurality of holes to allow the air in the gap between the electrode and diaphragm to escape and thus reduce acoustical damping in the microphone. Spin-on-glass (SOG) was used as a sacrificial and isolating layer. Back plate is mono crystalline silicon wafer, which is much stiffer. This work will focus on the design, fabrication and characterization of the microphone. The structure has a diaphragm thickness of 3 μm, with 0.5 x 0.5 mm2 size and an air gap of 1.0 μm. The results show that, the pull-in voltage is 105 V, the initial stress of evaporated aluminum diaphragm is around 1500 Mpa and the zero bias capacitance of microphone is 2.12 pF. Compared with the previous works, this microphone has several advantages: The holes have been made on the diaphragm, therefore there is no need for KOH etching to make the back chamber, in this way the chip size of each microphone is reduced. The fabrication process uses minimum number of layers and reduces the fabrication cost.