Composite MEMS Encapsulation Substrate for Thermal Stress Reduction
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Solution Overview
Problem
Existing MEMS device encapsulation processes generate significant stress and deformation due to mismatches in thermal expansion coefficients between the MEMS device and the encapsulation substrate, leading to warpage, deformation, and performance issues in microstructures.
Innovation Solution
A substrate composed of multiple materials with controlled thermal expansion properties is used to attach the MEMS device, adjusting the thermal expansion mismatch by varying the proportions, thickness, and contact areas of these materials to minimize encapsulation stress and deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-material substrate is used for MEMS device encapsulation, then the substrate structure is simple and easy to manufacture, but the thermal expansion mismatch between the substrate and MEMS device causes significant encapsulation stress and deformation
Solution Approach 1:
The substrate is constructed from multiple materials with different thermal expansion coefficients (e.g., quartz glass layer with low CTE and ceramic layer with high CTE) to create a composite structure. This composite substrate can be designed to have an effective thermal expansion coefficient that matches the MEMS device, thereby reducing encapsulation stress and deformation while maintaining manufacturability through established multi-layer fabrication processes
Solution Approach 2:
The thermal expansion properties of the substrate are modified by changing its material composition and structure. By adjusting the types, proportions, thicknesses, and arrangements of different materials in the substrate, the effective thermal expansion coefficient can be tuned to match the MEMS device, resolving the contradiction between manufacturing simplicity and deformation control
2Reliability
If the substrate thermal expansion coefficient is matched to the MEMS device, then encapsulation stress is reduced, but the substrate material selection and design become more complex
Solution Approach 1:
Rather than requiring a single exotic material with precise thermal expansion properties, the solution uses common materials (quartz glass, ceramics) in a composite structure. The complexity is managed through standardized multi-layer fabrication techniques, making the composite approach practically implementable while achieving the desired stress reduction and improved reliability
Solution Approach 2:
The substrate is divided into multiple functional layers, each with specific thermal expansion properties. This segmentation allows independent optimization of each layer's material and thickness, and enables the effective thermal expansion to be tuned by adjusting layer proportions, thereby reducing encapsulation stress while managing design complexity through modular layer design
3Reliability
If wire bonding process is performed, then electrical connection is established, but additional encapsulation stress is introduced (though less than attachment process)
Solution Approach 1:
The substrate's thermal expansion is pre-matched to the MEMS device before wire bonding is performed. This preliminary design ensures that the baseline encapsulation stress from the attachment process is minimized, creating a more favorable stress state that can better accommodate the additional stress from subsequent wire bonding without causing deformation or failure
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 proposed substrate design effectively reduces encapsulation stress to near zero, improving the long-term stability and reliability of MEMS devices by minimizing deformation and maintaining performance consistency across temperature variations.
Implementation Method 1
a coefficient of thermal expansion of the first-type material is less than a coefficient of thermal expansion of a base material of the MEMS device, and/or a coefficient of thermal expansion of the second-type material is greater than the coefficient of thermal expansion of the base material of the MEMS device
Data Source
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AI summary
An encapsulation structure includes a MEMS device, a substrate, and an attachment material. Materials included in the substrate at least include a first-type material and a second-type material, a coefficient of thermal expansion of the first-type material is less than a coefficient of thermal expansion of a base material of the MEMS device, and a coefficient of thermal expansion of the second-type material is greater than the coefficient of thermal expansion of the base material of the MEMS device. The attachment material is located between the MEMS device and the substrate, and is configured to attach the MEMS device to the substrate. The substrate includes a plurality of different materials. Properties of the materials in the substrate can be adjusted, to adjust and reduce an encapsulation stress of the MEMS device that is generated due to a mismatch between the coefficient of thermal expansion of the MEMS device and a coefficient of thermal expansion of the substrate in an attachment process, to adjust deformation of the MEMS device. A substrate and an encapsulation method are further provided.