MEMS Stress Isolation via Compliant Structures and Segmentation
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Solution Overview
Problem
Microelectromechanical Systems (MEMS) devices face significant thermal and package stresses due to materials with different coefficients of thermal expansion, leading to substrate deformations that affect output performance and sensitivity, and existing solutions either compromise area efficiency or risk proof mass failures from stiction.
Innovation Solution
A MEMS device design featuring a rigid backbone suspended above the substrate by compliant structures, with isolation segments formed through a dielectric trench refill process, providing both mechanical and electrical isolation to mitigate substrate deformations while allowing efficient electrical connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If compliant structures are used to suspend the rigid backbone above the substrate, then substrate deformations are isolated from the MEMS device, but device complexity increases
Solution Approach 1:
The device is segmented into distinct functional components: a rigid backbone for structural integrity, compliant structures for stress isolation, and isolation segments for electrical separation. This segmentation allows each component to perform its specific function optimally while working together as an integrated system.
Solution Approach 2:
Compliant structures serve as intermediary elements between the rigid backbone and the substrate, absorbing thermal and package stresses. These intermediaries protect the sensitive MEMS device from substrate deformations caused by differential thermal expansion between the substrate and overlying materials.
2Reliability
If isolation segments are formed through dielectric trench refill process, then electrical isolation is provided between backbone sections, but manufacturing complexity increases
Solution Approach 1:
The dielectric trenches are formed and refilled during the fabrication process before final device assembly. This preliminary action ensures that electrical isolation structures are already in place, simplifying subsequent packaging and assembly operations while providing reliable electrical separation between backbone sections.
3Area of stationary object
If the rigid backbone is suspended above the substrate, then area efficiency is improved, but mechanical stability may be compromised
Solution Approach 1:
Compliant structures with controlled mechanical properties are used to suspend the rigid backbone. These flexible support structures provide the necessary mechanical stability while maintaining the suspended configuration that improves area efficiency. The compliant structures act as flexible foundations that can accommodate thermal expansions while supporting the backbone.
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 design effectively isolates substrate deformations from the MEMS device, enhancing sensitivity and output performance while maintaining area efficiency and reducing the risk of proof mass failures, thus improving the reliability and accuracy of MEMS devices.
Implementation Method 1
compliant structures isolate the suspended structures extending from a rigid backbone of the transducer from deformations in the underlying substrate
Data Source
AI summary
A MEMS device (20) includes a proof mass structure (26) and beams (28, 30) residing in a central opening (32) of the proof mass structure (26), where the structure and the beams are suspended over a substrate (22). The beams (28, 30) are oriented such that lengthwise edges (34, 36) of the beams are beside one another. Isolation segments (38) are interposed between the beams (28, 30) such that a middle portion (40) of each of the beams is laterally anchored to adjacent isolation segments (38). The isolation segments (38) provide electrical isolation between the beams. The beams (28, 30) are anchored to the substrate (22) via compliant structures (61, 65) that isolate the beams from deformations in the underlying substrate. The compliant structures (61, 65) provide electrically conductive paths (96, 98) to the substrate (22) for the beams (28, 30) where the paths are electrically isolated from one another.