Piezoelectric MEMS Hybrid Active Structure Stress Gradient

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Solution Overview

Problem

Existing MEMS devices, such as microphones, face challenges with high vertical stress gradients and poor stress uniformity in piezoelectric thin films, leading to increased deflection and reduced sensitivity, which affects their performance and yield.

Innovation Solution

A hybrid active structure is introduced, comprising a piezoelectric stack portion and a mechanical portion, where the piezoelectric stack portion overlaps the mechanical portion at its edges, with the mechanical portion having a low stress gradient to reduce deflection and maintain sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a piezoelectric thin film is used to convert acoustic waves to electric signals, then the device can function as a MEMS microphone, but the film exhibits high vertical stress gradient and poor stress uniformity leading to high deflection and reduced sensitivity

Engineering Contradiction:

Improvedevice sensitivityVSAvoidstress uniformity

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The device is divided into two functional segments: a piezoelectric stack portion for signal generation and a mechanical portion for structural support and acoustic coupling. This segmentation allows each portion to be optimized independently - the piezoelectric stack can be designed for maximum sensitivity while the mechanical portion can be engineered for stress uniformity and low deflection.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention uses a composite structure combining piezoelectric materials (for electromechanical conversion) with mechanical materials (for structural integrity and stress distribution). This composite approach leverages the strengths of both material types to achieve both high sensitivity and low deflection simultaneously.

Inventive Principle:

Principle #40Composite materials

2Manufacturing precision

If the membrane size is reduced to reduce deflection and mismatch, then the stress uniformity may improve, but the sensitivity of the MEMS microphone is undesirably lowered

Engineering Contradiction:

Improvestress uniformityVSAvoidsensitivity

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

By segmenting the device into piezoelectric stack and mechanical portion, the functional responsibilities are separated. The mechanical portion can maintain a larger size for better stress uniformity and acoustic coupling, while the piezoelectric stack is optimized for sensitivity. This resolves the trade-off between size and sensitivity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the device have different properties optimized for their specific functions. The piezoelectric stack region is designed for maximum electromechanical coupling and sensitivity, while the mechanical portion is designed for stress uniformity and structural stability. This local optimization allows the whole device to achieve both low deflection and high sensitivity.

Inventive Principle:

Principle #3Local quality

3Manufacturing precision

If a bi-layer piezoelectric film with different stress is employed to mitigate the vertical stress gradient, then the stress uniformity may improve, but the design is not good enough particularly when cantilever/membrane length is longer

Engineering Contradiction:

Improvestress uniformityVSAvoidfilm structure complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

Instead of complicating the piezoelectric film structure with bi-layer designs, the invention segments the device into piezoelectric stack and mechanical portion. This simpler segmentation approach achieves stress uniformity without requiring complex multi-layer piezoelectric films, particularly benefiting longer cantilever/membrane structures.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention extracts the stress management function from the piezoelectric film itself and places it in the mechanical portion. This allows the piezoelectric stack to focus on signal generation while the mechanical portion handles stress distribution, simplifying the overall design compared to complex bi-layer piezoelectric solutions.

Inventive Principle:

Principle #2Taking out (Extraction)

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 effectively reduces deflection while maintaining high sensitivity and yield, allowing for effective signal generation and improved device performance without compromising the device's dimensions.

Implementation Method 1

a piezoelectric thin film to convert acoustic waves to electric signals

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS11631800B2Piezoelectric MEMS devices and methods of forming thereof

Publication Date: 2023.04.18 GLOBALFOUNDRIES SINGAPORE PTE LTD

AI summary

In a non-limiting embodiment, a device may include a substrate, and a hybrid active structure disposed over the substrate. The hybrid active structure may include an anchor region and a free region. The hybrid active structure may be connected to the substrate at least at the anchor region. The anchor region may include at least a segment of a piezoelectric stack portion. The piezoelectric stack portion may include a first electrode layer, a piezoelectric layer over the first electrode layer, and a second electrode layer over the piezoelectric layer. The free region may include at least a segment of a mechanical portion. The piezoelectric stack portion may overlap the mechanical portion at edges of the piezoelectric stack portion.