MEMS Central Anchor Stress Isolation
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Solution Overview
Problem
Microelectromechanical systems (MEMS) devices face challenges with thermal stress due to dissimilar materials used in fabrication and packaging, leading to high temperature coefficient of offset (TCO) and package stress, which affects performance by causing deformations and shifts in the substrate, thereby impacting the accuracy of sense signals.
Innovation Solution
A MEMS device design with a centralized anchor configuration and high aspect ratio polysilicon structural layer, utilizing isolation trenches and electrically conductive interconnects to minimize substrate connections and enable differential sensing, reducing the impact of thermal stress and package stress gradients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If multiple anchor points are used to secure the MEMS device to the substrate, then the device stability is improved, but the device becomes more susceptible to substrate stress and thermal stress
Solution Approach 1:
The patent extracts and removes multiple anchor points from the device structure, retaining only a single central anchor point. This reduction in anchor points minimizes the device's coupling to the substrate, thereby reducing susceptibility to substrate stress and thermal stress while maintaining sufficient stability through the centralized anchoring mechanism.
Solution Approach 2:
The patent segments the device into distinct functional regions: a centrally anchored fixed structure and surrounding movable structures (such as proof mass and sense fingers). This segmentation allows the fixed structure to be minimally coupled to the substrate while enabling the movable structures to respond to external stimuli, thus balancing stability with stress isolation.
2Manufacturing precision
If the MEMS device is more closely coupled to the substrate for structural support, then the manufacturing precision is improved, but the temperature coefficient of offset increases
Solution Approach 1:
The patent introduces an intermediary layer or structure between the MEMS device and the substrate that provides mechanical support while decoupling thermal stress transmission. This intermediary structure allows for precise manufacturing and structural integrity while reducing the temperature coefficient of offset by mediating the thermal-mechanical interaction between the device and substrate.
3Adaptability or versatility
If dissimilar materials are used in fabrication and packaging to achieve functional requirements, then the device versatility is improved, but thermal stress and package stress increase
Solution Approach 1:
The patent applies local quality by using dissimilar materials selectively in different regions of the device structure. Critical functional areas use materials optimized for their specific functions, while the anchoring and support structures use materials designed to minimize thermal stress transmission. This localized material selection maintains versatility while managing thermal stress through strategic material placement.
Data Source
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AI summary
A MEMS device (20) includes a proof mass (32) coupled to and surrounding an immovable structure (30). The immovable structure (30) includes fixed fingers (36, 38) extending outwardly from a body (34) of the structure (30). The proof mass (32) includes movable fingers (60), each of which is disposed between a pair (62) of the fixed fingers (36, 38). A central area (42) of the body (34) is coupled to an underlying substrate (24), with the remainder of the immovable structure (30) and the proof mass (32) being suspended above the substrate (24) to largely isolate the MEMS device (20) from package stress. Additionally, the MEMS device (20) includes isolation trenches (80) and interconnects (46, 50, 64) so that the fixed fingers (36), the fixed fingers (38), and the movable fingers (60) are electrically isolated from one another to yield a differential device configuration.