MEMS Beam Isolation Joints for Shock and Seal Reliability
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Solution Overview
Problem
MEMS devices are susceptible to shock damage, interconnect damage, and frit seal failures due to dielectric coating wear, electrical charge accumulation, and material deformation, leading to false acceleration signatures and seal weaknesses.
Innovation Solution
The implementation of MEMS devices with isolation joints made of insulative materials, separate metal layers for interconnects and bond pads, and a continuous metal seal ring surface to prevent electrical charge accumulation and enhance seal integrity, reducing the risk of mechanical shocks and interconnect damage while improving frit seal reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dielectric coating is applied on sidewalls of beams, then electrical isolation is improved, but shock resistance deteriorates due to coating wear and charge accumulation
Solution Approach 1:
The beam is divided into multiple segments by introducing isolation joints that are free to move. This segmentation allows the beam to flex during shock events without causing dielectric coating wear, as the isolation joints absorb the mechanical stress through their movement capability.
Solution Approach 2:
The harmful dielectric coating is removed from critical shock-prone areas, specifically from the isolation joints and beam ends. This extraction eliminates the source of charge accumulation and coating wear while maintaining electrical isolation in areas where it is still needed.
2Reliability
If metal interconnects are used to electrically connect components, then electrical connectivity is improved, but interconnect damage from plastic deformation worsens under thermal and mechanical stress
Solution Approach 1:
Different metal layers are assigned different functions: the first metal layer provides electrical interconnectivity with optimized geometry for connectivity, while the second metal layer provides structural reinforcement and forms the seal ring surface. This local differentiation allows each layer to be optimized for its specific function, reducing overall susceptibility to deformation.
Solution Approach 2:
The interconnect structure uses a composite approach with multiple metal layers having different properties. The first metal layer (e.g., aluminum) provides good electrical conductivity, while the second metal layer provides enhanced mechanical strength and thermal stability, creating a composite structure that resists plastic deformation better than single-layer metals.
3Adaptability or versatility
If multiple materials with different thermal expansion coefficients are joined together, then device functionality is improved, but thermal stress and permanent deformation worsen during temperature excursions
Solution Approach 1:
The patent modifies the geometric parameters of the metal interconnect layers, specifically optimizing their thickness and width ratios. By changing these parameters, the structural integrity during thermal cycling is improved while maintaining the necessary electrical and sealing functions.
Solution Approach 2:
The metal layers are strategically positioned and dimensioned to accommodate thermal expansion differences. The interconnect geometry is locally optimized to provide stress relief paths, allowing different materials to expand and contract at different rates without causing permanent deformation.
4Object-affected harmful factors
If isolation joints are introduced to reduce shock damage, then shock resistance is improved, but device complexity increases
Solution Approach 1:
The isolation joint structure is merged with the existing beam geometry and dielectric layers. Rather than adding completely separate components, the isolation joints are integrated into the beam structure itself, sharing common materials and fabrication processes, which reduces overall device complexity.
Solution Approach 2:
The isolation joints serve multiple functions: they provide mechanical flexibility for shock resistance, maintain electrical isolation between beam segments, and accommodate thermal expansion. This multi-functionality reduces the need for additional dedicated components, thereby reducing overall device complexity.
Data Source
AI summary
A micro-electromechanical system (MEMS) device can include a substrate and a first beam suspended relative to a substrate surface. The first beam can include a first portion and a second portion that are separated by an isolation joint made of an insulative material. The first and second portions can each include a first semiconductor and a first dielectric layer. The MEMS device can also include a second beam suspended relative to the substrate surface. The second beam can include a second semiconductor and a second dielectric layer to promote curvature of the second beam. The MEMS device can also include a third beam suspended relative to the substrate surface. The third beam consists essentially of a first material. The second beam is configured to move relative to the third beam in response to an acceleration along an axis perpendicular to the surface of the substrate.