MEMS Device Trench Spring Stress Isolation
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Solution Overview
Problem
MEMS devices face mechanical stress due to differing coefficients of thermal expansion between the chip-level package substrate and the underlying printed circuit board, leading to erroneous output data from substrate bending or flexing.
Innovation Solution
A MEMS device design featuring a substrate with a trench and a spring mechanism that connects the sensor region and a second region, forming a hermetically sealed interior chamber, which mitigates stress and maintains hermeticity by using a serpentine spring or insulator layer for sealing, and a recessed sensor region to reduce contact with the printed circuit board.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the MEMS die substrate is bonded to the package interior or printed circuit board, then mechanical support and structural stability are improved, but thermal expansion stress causes substrate bending and measurement errors
Solution Approach 1:
The substrate is divided into a sensor region and a second region separated by a trench. The spring mechanism connects these two regions, allowing differential movement. This segmentation enables the sensor region to remain mechanically isolated from stress while the second region accommodates thermal expansion, resolving the contradiction between mechanical support and measurement accuracy.
Solution Approach 2:
The spring mechanism changes the mechanical parameters of the substrate by introducing compliance. The spring allows controlled deformation and stress redistribution, enabling the substrate to maintain structural integrity while accommodating thermal expansion differences between the package and printed circuit board, thereby preventing measurement errors.
2Object-affected harmful factors
If a trench is formed in the substrate to mechanically isolate the sensor region, then stress mitigation is improved, but hermetic sealing becomes more difficult
Solution Approach 1:
A thin film or membrane is used to seal the trench opening, creating a hermetic barrier while maintaining the mechanical isolation function. This flexible sealing approach allows the trench to remain open for stress mitigation while the thin film prevents contamination, resolving the contradiction between stress mitigation and hermetic sealing.
Solution Approach 2:
The spring mechanism acts as an intermediary element that bridges the sensor region and the second region. It provides both mechanical connection for structural integrity and hermetic sealing by forming a continuous barrier across the trench, while still allowing differential movement to mitigate stress.
3Object-affected harmful factors
If the sensor region is recessed relative to the second region, then stress isolation is improved, but manufacturing complexity increases
Solution Approach 1:
The substrate is segmented into recessed and non-recessed regions by the trench structure. This segmentation naturally creates the stress isolation effect while the trench itself serves as the manufacturing feature, reducing the need for additional complex processing steps to achieve both stress isolation and hermetic sealing.
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
The design effectively reduces mechanical stress on the MEMS device, maintaining accurate data output by isolating the sensitive microstructure and preventing substrate bending or flexing, thus enhancing the reliability of the device's measurements.
Implementation Method 1
a spring integrally formed at least in part within the trench to mechanically connect the sensor region and the second region
Implementation Method 2
the other structure may include an insulator layer (e.g., an oxide) that forms at least a part of the structure surface of the substrate
Data Source
AI summary
A MEMS device has a substrate with a structure surface and an opposing exterior surface, microstructure formed on the structure surface of the substrate, and a cap coupled with the substrate to form a hermetically sealed interior chamber containing the microstructure. The substrate forms a trench extending from, and being open to, the opposing exterior surface to produce a sensor region and a second region. Specifically, the second region is radially outward of the sensor region. The MEMS device also has a spring integrally formed at least in part within the trench to mechanically connect the sensor region and the second region, and other structure integral with the substrate. The spring or the other structure at least in part hermetically seal the interior chamber.