Non-Planar Counter Electrode for MEMS Sensitivity Compensation
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Solution Overview
Problem
Capacitive MEMS devices, such as microphones, face challenges in achieving uniform mechanical compliance, leading to suboptimal sensitivity due to radial non-uniformity, which affects the conversion of sound waves into electrical signals.
Innovation Solution
The implementation of non-planar counter electrode structures with varying air gap thicknesses and pillar configurations to compensate for mechanical compliance irregularities, allowing for adjusted bias voltages and pillar spacings to optimize sensitivity across different regions of the device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a planar counter electrode structure with uniform air gap is used, then the device structure is simple and easy to manufacture, but the mechanical compliance is radially non-uniform leading to suboptimal sensitivity
Solution Approach 1:
The counter electrode structure is divided into multiple regions with different air gap thicknesses. The non-planar configuration creates local variations in gap distance between the membrane and counter electrode, allowing different regions to have optimized mechanical compliance characteristics. This local quality adjustment compensates for radial non-uniformity and improves overall sensitivity.
Solution Approach 2:
The air gap thickness is varied in the vertical dimension rather than maintaining a uniform planar structure. By introducing non-planar geometry with varying heights, the patent transforms a two-dimensional uniform gap into a three-dimensional structured gap, enabling regional optimization of mechanical compliance without increasing lateral complexity.
2Measurement precision
If non-planar counter electrode structures with varying air gap thicknesses are implemented, then sensitivity is enhanced by up to 1.7 dB to 5.3 dB, but the device complexity increases
Solution Approach 1:
Different regions of the counter electrode are designed with specific air gap thicknesses optimized for their local mechanical compliance requirements. This regional optimization achieves enhanced sensitivity by ensuring uniform compliance characteristics across the device area, with each region contributing maximally to the overall performance.
Solution Approach 2:
The air gap thickness parameter is varied spatially across the counter electrode structure. By changing this critical geometric parameter from a uniform value to a distributed set of values, the patent achieves improved sensitivity while maintaining a relatively simple fabrication approach through standard micromachining techniques.
3Manufacturing precision
If pillars with non-uniform spacing are used to define gap regions, then mechanical compliance uniformity is improved, but the manufacturing complexity increases
Solution Approach 1:
The counter electrode structure is segmented into multiple regions by pillars positioned at different locations. This segmentation creates distinct gap regions with controlled thicknesses, allowing independent optimization of mechanical compliance in each region. The pillar-based segmentation approach uses standard micromachining techniques to achieve precise spatial control.
Solution Approach 2:
The pillar spacing is varied locally to create different gap region thicknesses appropriate for different areas of the device. This local variation in spacing provides regional optimization of mechanical compliance while using a modular pillar-based approach that can be fabricated using conventional micromachining processes.
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 approach enhances the sensitivity and active capacitance of capacitive MEMS devices by up to 1.7 dB to 5.3 dB, improving the conversion efficiency of sound waves into electrical signals.
Implementation Method 1
capacitive MEMS devices... capacitive sensing techniques for transducing the physical phenomenon into electrical signals... the capacitance change in the sensor is converted to a voltage signal
Implementation Method 2
The gap has a gas pressure lower than an ambient pressure
Data Source
AI summary
A MEMS device includes a membrane and a counter electrode structure spaced apart from the membrane. The counter electrode structure includes a non-planar conductive layer. The MEMS device includes an air gap between the membrane and the counter electrode structure. The air gap has a non-uniform thickness.