Piezoelectric MEMS Electrode Layout for Crack Propagation Mitigation

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Solution Overview

Problem

MEMS capacitive microphones suffer from noise issues due to their backplate and have a smaller dynamic range compared to piezoelectric MEMS microphones, while standard electret condenser microphones cannot be mounted using lead-free solder processing, and all are prone to crack propagation due to the brittleness of piezoelectric materials.

Innovation Solution

A piezoelectric MEMS transducer design with staggered openings in patterned conductive layers to mitigate crack propagation, incorporating more than 60% piezoelectric material, where the openings are positioned to optimize energy output and reduce fragility by aligning with the grain of the piezoelectric material, thereby enhancing durability and performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If piezoelectric material is used to achieve greater sensitivity and dynamic range, then performance is improved, but the device becomes more prone to crack propagation due to material brittleness

Engineering Contradiction:

Improvecrack propagation resistanceVSAvoidmaterial brittleness

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The electrode layers are segmented into multiple sections with openings distributed throughout. These segmented electrode sections are interconnected through vertical vias, creating a network that divides stress pathways and prevents crack propagation across the entire piezoelectric element, thereby maintaining reliability while working with brittle piezoelectric material.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The openings are strategically positioned at specific locations within the piezoelectric element where stress concentration is most likely to occur. By localizing these openings at critical stress points, the design provides targeted crack propagation resistance precisely where needed, without compromising the overall structural integrity or performance of the piezoelectric material.

Inventive Principle:

Principle #3Local quality

2Reliability

If electrode layers are made continuous to ensure electrical connectivity, then electrical performance is improved, but crack propagation risk increases

Engineering Contradiction:

Improvecrack propagation mitigationVSAvoidcrack propagation through continuous structure

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The continuous electrode structure is divided into multiple discrete sections with openings between them. These segmented sections remain electrically connected through vertical conductive vias, creating a discontinuous yet electrically functional structure that interrupts crack propagation paths while maintaining electrical connectivity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Vertical conductive vias act as intermediary elements that bridge the gap between separated electrode sections. These vias provide the necessary electrical connection between discontinuous electrode layers while the openings prevent cracks from propagating continuously through the electrode structure.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If openings are added to electrode layers to mitigate cracks, then durability is improved, but device complexity increases

Engineering Contradiction:

Improvedevice durabilityVSAvoidpatterned conductive layers with multiple openings

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Multiple functional elements are merged into a single integrated structure: the openings serve both as crack propagation barriers and as part of the electrode pattern design. The vertical vias simultaneously provide electrical connectivity and structural support, combining multiple functions into unified structural features that reduce overall device complexity.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The openings in the electrode layers serve multiple purposes: they act as crack propagation barriers, define electrode section boundaries, and work in conjunction with vertical vias to maintain electrical connectivity. This multi-functionality reduces the need for separate dedicated features, thereby managing device complexity while improving durability.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 staggered opening design significantly reduces crack propagation, increases output energy, and improves the durability of piezoelectric MEMS devices, maintaining optimal performance while minimizing fragile areas, thus addressing the limitations of existing MEMS microphone technologies.

Implementation Method 1

a piezoelectric layer; a first patterned conductive layer that is patterned with a first opening; a second patterned conductive layer that is patterned with a second opening; wherein at least one piezoelectric layer is between the first and the second patterned conductive layers

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS11871664B1Staggering of openings in electrodes for crack mitigation

Publication Date: 2024.01.09 QUALCOMM INC

AI summary

A transducer comprising: at least one piezoelectric layer; a first patterned conductive layer that is patterned with a first opening; a second patterned conductive layer that is patterned with a second opening; wherein at least one piezoelectric layer is between the first and the second patterned conductive layers in a stack; and wherein a position of the first opening is staggered relative to a position of the second opening in the stack to mitigate an occurrence of crack propagation through the layers.