Suspended MEMS Platform Stress Isolation

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Solution Overview

Problem

Microelectromechanical systems (MEMS) devices face challenges in packaging due to thermal and package stresses, which cause instability and output shifts, particularly in applications requiring smaller size and low cost packaging.

Innovation Solution

A MEMS device is fabricated on a silicon-on-insulator (SOI) substrate with a cantilevered platform structure, where the insulator layer is removed to suspend the MEMS device, isolating it from external stresses through a trench and openings in the substrate layers, using etching processes to achieve stress isolation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If MEMS devices are packaged using materials with dissimilar coefficients of thermal expansion, then packaging cost and size can be reduced, but thermal stresses cause device instability and output shifts

Engineering Contradiction:

Improvepackaging costVSAvoiddevice stability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The substrate is segmented into multiple layers (first substrate layer, second substrate layer, insulator layer) with the MEMS device formed on a suspended platform. This segmentation allows the first substrate layer to be isolated from package stresses while maintaining electrical connectivity, resolving the contradiction between using cost-effective packaging materials and ensuring device stability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The insulator layer is selectively removed from beneath the MEMS device platform to create a suspended structure. This extraction isolates the MEMS device from thermal and package stresses transmitted through the substrate, allowing the use of dissimilar packaging materials without compromising device reliability.

Inventive Principle:

Principle #2Taking out (Extraction)

2Volume of moving object

If MEMS devices are packaged using materials with dissimilar coefficients of thermal expansion, then packaging size can be reduced, but thermal stresses cause device instability and output shifts

Engineering Contradiction:

Improvepackaging sizeVSAvoiddevice stability

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

The substrate is divided into multiple layers with the MEMS device on a suspended platform, allowing compact packaging while isolating the device from thermal stresses. The segmented structure enables small packaging size without sacrificing device stability.

Inventive Principle:

Principle #1Segmentation

3Reliability

If thermal stress isolation structures are added to protect MEMS devices, then device stability improves, but manufacturing complexity increases

Engineering Contradiction:

Improvedevice stabilityVSAvoidsubstrate structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The insulator layer is removed and the suspended platform structure is created during the substrate fabrication process before MEMS device assembly. This preliminary action integrates stress isolation into the substrate itself, improving device stability without adding complex post-fabrication structures.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The suspended platform structure acts as an intermediary between the MEMS device and the substrate, mechanically isolating the device from package stresses while maintaining electrical connectivity through the platform, thus improving stability without excessive complexity.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Reliability

If thermal stress isolation structures are added to protect MEMS devices, then device performance improves, but manufacturing steps increase

Engineering Contradiction:

Improvedevice performanceVSAvoidmanufacturing efficiency

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The stress isolation structure is created as part of the substrate fabrication process before MEMS device assembly, integrating multiple functions into existing manufacturing steps and minimizing additional process steps while improving device performance.

Inventive Principle:

Principle #10Preliminary action

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 enhances package stress isolation, improves device performance, and simplifies packaging, reducing costs by minimizing the impact of thermal and packaging stresses on MEMS devices.

Implementation Method 1

using etching processes to achieve stress isolation

Methodology Applied

Scientific EffectEtching:

Data Source

PatentUS9458008B1Method of making a MEMS die having a MEMS device on a suspended structure

Publication Date: 2016.10.04 STMICROELECTRONICS INT NV

AI summary

A microelectromechanical systems (MEMS) die includes a substrate having a first substrate layer, a second substrate layer, and an insulator layer interposed between the first and second substrate layers. A structure is formed in the first substrate layer and includes a platform upon which a MEMS device resides. Fabrication methodology entails forming the MEMS device on a front side of the first substrate layer of the substrate, forming openings extending through the second substrate layer from a back side of the second substrate layer to the insulator layer, and forming a trench in the first substrate layer extending from the front side to the insulator layer. The trench is laterally offset from the openings. The trench surrounds the MEMS device to produce the structure in the first substrate layer on which the MEMS device resides. The insulator layer is removed underlying the structure to suspend the structure.