MEMS Microphone Membrane Segmentation for Parasitic Capacitance Reduction
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Solution Overview
Problem
Double backplate microphones in MEMS devices suffer from parasitic capacitances within the support structure, which interfere with the intended capacitance signals, leading to incorrect reproduction of sound inputs.
Innovation Solution
The design incorporates a membrane with a displaceable and fixed portion, where the overlapping area with the backplate electrode is less than maximum, and the use of segmentations and recesses on the electrodes to reduce parasitic capacitances, along with the implementation of guard rings to further minimize these unwanted capacitances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the membrane and backplate electrode are arranged with maximum overlapping area, then the capacitance signal strength is improved, but parasitic capacitances increase interfering with the measurement
Solution Approach 1:
The membrane is divided into an active portion and a fixed portion, with the active portion having maximum overlapping area with the backplate electrode for strong capacitance signals, while the fixed portion has reduced overlapping area to minimize parasitic capacitances. This segmentation allows different regions to serve different functions optimally.
Solution Approach 2:
Different regions of the membrane are given different overlapping characteristics: the active portion has maximum overlapping for high signal strength, while the fixed portion has reduced overlapping for low parasitic capacitance. This local differentiation optimizes both measurement precision and harmful factor reduction in their respective regions.
2Object-generated harmful factors
If the overlapping area of the fixed portion with the backplate electrode is reduced, then parasitic capacitances are reduced, but the structural support may be weakened
Solution Approach 1:
The membrane structure is segmented into active and fixed portions with different overlapping areas. The fixed portion provides structural support through its connection to the support structure, while its reduced overlapping area minimizes parasitic capacitances. The active portion provides the capacitance signal through maximum overlapping with the backplate electrode.
Solution Approach 2:
The fixed portion of the membrane serves multiple functions: it provides structural support through its connection to the support structure and simultaneously minimizes parasitic capacitances through reduced overlapping area with the backplate electrode, while the active portion generates the capacitance signal.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration significantly reduces parasitic capacitances, enhancing the accuracy of sound signal reproduction by isolating non-active portions of the electrodes and minimizing coupling, thereby improving the overall performance of the MEMS device.
Implementation Method 1
Sound pressure waves cause the membrane to vibrate due to a pressure difference over both planes of the membrane
Implementation Method 2
The variation of the membrane in relation to the backplate electrodes causes variation in the capacitances between the membrane and the bottom backplate electrode as well as between the membrane and the top backplate electrode
Implementation Method 3
The membrane may be biased by a bias voltage relative to the bottom backplate electrode and the top backplate electrode
Data Source
AI summary
A MEMS device includes a backplate electrode and a membrane disposed spaced apart from the backplate electrode. The membrane includes a displaceable portion and a fixed portion. The backplate electrode and the membrane are arranged such that an overlapping area of the fixed portion of the membrane with the backplate electrode is less than maximum overlapping.