A compact CMOS MEMS microphone with 66dB SNR

Silicon MEMS microphones that offer small size, ease of integration with CMOS electronics, and the ability to withstand lead-free solder reflow cycles, are becoming increasingly popular for high-volume consumer electronic products, and are competing in price and performance with traditional electret condenser microphones. The design of a MEMS microphone, consisting of a compliant membrane and a stiff back-plate forming a variable capacitor, is a challenging task with a number of design trade-offs. For cost reasons, a small-area membrane is desired; however, lower acoustical noise is obtained with a larger membrane. In this work, we demonstrate a method to increase the SNR of a microphone system without the need for a complicated and risky MEMS die redesign. An SNR of 66 dB is achieved using two microphones (instead of a single one) in a differential configuration, thus doubling the total membrane area.