Piezoelectric MEMS Microphone Electrode Shape Optimization
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Solution Overview
Problem
Conventional capacitive MEMS microphones face issues with high power consumption and reliability in harsh environments, while existing piezoelectric MEMS microphones aim to address these deficiencies but can be optimized for improved sensitivity and voltage output.
Innovation Solution
A piezoelectric microelectromechanical systems microphone design featuring a substrate with a cavity and a piezoelectric film layer supported by an anchor region, with an electrode having a protruding portion that matches the shape of the highest stress and strain area, and additional electrodes to maximize energy conversion from both tensile and compressive stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the electrode area is increased to cover more of the piezoelectric film layer, then the sensitivity is improved, but the capacitance increases and voltage output decreases
Solution Approach 1:
The electrode is designed with a non-uniform shape featuring a protruding portion that concentrates the electrode area specifically over the high-stress region of the piezoelectric film layer. This local concentration of electrode material maximizes the coupling with the stressed piezoelectric material where it generates the most charge, while minimizing the total electrode area to keep capacitance low. The protruding portion shape matches the stress distribution pattern, ensuring optimal energy conversion from mechanical stress to electrical charge without excessive capacitance.
2Quantity of substance
If the electrode is placed to cover the entire piezoelectric film layer, then all generated charge is collected, but the capacitance is too large reducing voltage output
Solution Approach 1:
The electrode design extracts only the essential portion of the piezoelectric film layer that generates the most charge - specifically the high-stress region near the fixed end. The protruding portion shape is derived by matching the stress distribution pattern, taking out only where needed rather than covering the entire layer. This selective coverage collects sufficient charge from the most productive region while minimizing total electrode area and resulting capacitance.
3Ease of manufacture
If a simple rectangular electrode is used, then manufacturing is easier, but it does not match the stress distribution pattern reducing sensitivity
Solution Approach 1:
The electrode geometry parameters are changed from a simple rectangle to a protruding portion shape that matches the stress distribution pattern. This shape transformation aligns the electrode boundaries with the regions of highest stress concentration, ensuring optimal coupling between the electrode and the piezoelectric material where it generates the most charge. The parameter change in electrode shape directly improves sensitivity by matching the physical stress field distribution.
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
The design enhances the sensitivity and output voltage of the microphone by optimizing the electrode placement and shape to cover only the stressed regions, reducing capacitance and increasing voltage output, thereby improving performance in harsh environments.
Implementation Method 1
Piezoelectric MEMS microphones work on the principle of piezoelectric effect, so that they convert acoustic signals to electric signal when sound waves vibrate the piezoelectric sensor. The sound waves bend the piezoelectric film layers of a cantilevered beam or non-cantilevered beam, causing stress and strain, resulting in charges being generated in the piezoelectric film layers.
Data Source
AI summary
A piezoelectric microelectromechanical systems (MEMS) microphone is provided comprising a substrate including walls defining a cavity and at least one of the walls defining an anchor region, a piezoelectric film layer supported by the substrate at the anchor region; an electrode disposed over the piezoelectric film layer and adjacent the anchor region and including an edge adjacent the anchor region having two straight portions and a protruding portion between the two straight portions, and the wall of the cavity that defines the anchor region including an indent corresponding in shape to the protruding portion of the electrode. A method of manufacturing such a MEMS microphone is also provided.