This article presents a lumped-parameter model providing a deeper understanding of the compliant backplate in capacitive MEMS microphones. Some previous models simplify the backplate as stationary, whereas others treat it as vibrating. This work not only models the backplate as vibrating but also considers the coupling effect between the mechanical and electrical domains. The extended model allows for a more detailed analysis of how the microphone converts sound into an electrical signal. Specifically, the theoretical derivations using Lagrange equations show how backplate motion can impact the microphone’s performance. Analysis of the lumped-parameter model aligns well with the results of finite element analysis when the frequency is below the high-order resonance, validating the theoretical concepts. In particular, the model with electrical coupling of the vibrating backplate effectively captures the sensitivity dip resulting from the backplate resonance, unlike models lacking this coupling. The theoretical framework is also extended to the phenomenon of pull-in. A backplate that is overly compliant can narrow the operating frequency range and increase the likelihood of experiencing pull-in. Thus, there is a trade-off between optimizing the microphone’s acoustic performance and ensuring its mechanical robustness. This work provides valuable insights into navigating these trade-offs.

Different microstructures significantly affect the acoustic performance of MEMS capacitive microphones, particularly in key specifications of interest. This paper presents several microstructures, including rib-reinforced backplates, suspended diaphragms, and outer vent holes. Three MEMS microphone designs were implemented to analyze the impact of these microstructures. Equivalent circuit models corresponding to each design were constructed to simulate specifications such as sensitivity, signal-to-noise ratio (SNR), and low corner frequency (LCF), which were validated through experimental measurements. Finite Element Analysis (FEA) was also employed to calculate the acoustic damping of certain microstructures, the mechanical lumped parameters of the diaphragm, and the pre-deformation of the MEMS structure. A compressed air test (CAT) was conducted to evaluate the mechanical reliability of microphone samples. The results of simulations and measurements indicate that rib-reinforced backplates effectively improve microphone reliability, increasing the pass rate in CAT. Compared to fully clamped diaphragms, suspended diaphragms exhibit higher mechanical compliance, which enhances SNR performance but reduces AOP. Outer vent holes can achieve similar functionality to diaphragm vent holes, but their impact on improving AOP requires further design and testing.