MEMS Piezoelectric Composite Stack for Higher PMUT Sensitivity
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Solution Overview
Problem
Conventional piezoelectric micromachined ultrasonic transducers (PMUTs) have lower sensitivity due to membranes made of homogeneous piezoelectric materials, which limits their effectiveness in sensing and interacting with the environment.
Innovation Solution
The use of a piezoelectric composite stack in MEMS devices, comprising two outer piezoelectric layers with higher piezoelectric coefficients sandwiching an inner layer with a lower piezoelectric coefficient, enhances charge generation and sensitivity by maximizing stress at the top and bottom surfaces, while minimizing local stress and mechanical defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a homogeneous piezoelectric material is used for the membrane, then the structure is simple and easy to manufacture, but the sensitivity of the PMUT is lower
Solution Approach 1:
The patent applies composite materials by constructing a piezoelectric composite stack with multiple layers of different piezoelectric materials having different piezoelectric coefficients. The stack includes a first piezoelectric layer with a first piezoelectric coefficient and a second piezoelectric layer with a second piezoelectric coefficient that is higher than the first. This composite structure combines materials with different properties to achieve both manufacturability and enhanced sensitivity through optimized charge generation at surfaces with maximum stress.
2Measurement precision
If outer piezoelectric layers with higher piezoelectric coefficient are added, then charge generation and sensitivity are improved, but the device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the piezoelectric membrane into distinct layers with different piezoelectric coefficients. The piezoelectric composite stack is segmented into a first piezoelectric layer and a second piezoelectric layer, where each layer contributes differently to charge generation. This segmentation allows optimization of sensitivity while maintaining a structured, manageable device architecture that can be fabricated using standard MEMS 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 configuration improves the sensitivity of MEMS devices by generating more piezoelectric charges, reduces local stress and mechanical defects, and provides better mechanical strength and noise reduction, leading to enhanced performance.
Implementation Method 1
The microscopic devices include both the electronic and mechanical function which is operated based on, for instance, electromagnetic, electrostrictive, thermoelectric, piezoelectric, or piezoresistive effects
Data Source
AI summary
A micro-electro-mechanical system (MEMS) device includes a substrate having a cavity and a MEMS structure disposed over the cavity and attached to the substrate. The MEMS structure includes at least one first piezoelectric layer having a first piezoelectric coefficient and two second piezoelectric layers respectively disposed under and above the first piezoelectric layer, where each second piezoelectric layer has a second piezoelectric coefficient higher than the first piezoelectric coefficient. The MEMS structure further includes a first electrode layer and a second electrode layer sandwiching the two second piezoelectric layers.