This study presents the design, fabrication, testing of the capacitive type MEMS microphone with differential sensing electrodes to improve the sensitivity and signal-to-noise ratio (SNR). Based on an existing trench-refilled MOSBE process platform with two poly silicon structure layers, one Si3N4 electrical isolation layer, and two sacrificial SiO2 layers, the microphone is designed and implemented. The microphone consists of top and bottom diaphragms and backplates. The top diaphragm and bottom backplate form a sensing electrode pair, and the bottom diaphragm and top backplate form the second sensing electrode pair. Moreover, the Si3N4 layer is exploited to partition the structures into three different electrical regions. Thus, the differential sensing MEMS microphone is achieved by using only two polysilicon structure layers. Various auxiliary components such as the central post and the U-shape springs are also developed to realize the differential microphone. Measurements show that the typical fabricated microphone with a footprint of 800μm diameter has the single-ended sensitivities of −45.8dB and -47.2dB (ref: 1V/1Pa), and the SNR is over 52dB. Moreover, the ±3dB bandwidth of the microphone ranges from 50Hz to 22kHz. In summary, the presented microphone has the differential sensitivity of -40.5dB (ref: 1V/1Pa) and the SNR of over 57.8dB.

中文翻译：

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使用两种多晶硅工艺提高 SNR 的差分 MEMS 麦克风的设计和实现

本研究介绍了带有差分传感电极的电容式 MEMS 麦克风的设计、制造和测试，以提高灵敏度和信噪比 (SNR)。基于现有的沟槽再填充 MOSBE 工艺平台，具有两个多晶硅结构层、一个 Si3N4 电隔离层和两个牺牲 SiO2 层，设计并实现了麦克风。麦克风由顶部和底部振膜和背板组成。顶部隔膜和底部背板形成感应电极对，底部隔膜和顶部背板形成第二感应电极对。此外，利用 Si3N4 层将结构划分为三个不同的电气区域。因此，差分传感MEMS麦克风是通过仅使用两个多晶硅结构层来实现的。还开发了各种辅助部件，如中心柱和U形弹簧，以实现差分麦克风。测量表明，直径为 800μm 的典型制造麦克风的单端灵敏度为 -45.8dB 和 -47.2dB（参考：1V/1Pa），SNR 超过 52dB。此外，麦克风的±3dB带宽范围从50Hz到22kHz。总之，所提出的麦克风具有 -40.5dB（参考：1V/1Pa）的差分灵敏度和超过 57.8dB 的 SNR。麦克风的 ±3dB 带宽范围从 50Hz 到 22kHz。总之，所提出的麦克风具有 -40.5dB（参考：1V/1Pa）的差分灵敏度和超过 57.8dB 的 SNR。麦克风的 ±3dB 带宽范围从 50Hz 到 22kHz。总之，所提出的麦克风具有 -40.5dB（参考：1V/1Pa）的差分灵敏度和超过 57.8dB 的 SNR。