CMOS-MEMS Thin Film Encapsulation via Dummy Insulation
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Solution Overview
Problem
Conventional methods for sealing CMOS-MEMS devices often result in stress on underlying device elements due to lattice mismatch and thermal expansion differences between sealing and dielectric materials, leading to poor sensor sensitivity, increased harmonic distortion, and higher manufacturing costs, especially when attempting to achieve symmetric layers.
Innovation Solution
A method and structure for thin-film encapsulation involving maskless wet etching to form void regions, followed by deposition of sealing material on dummy insulation features rather than directly on the MEMS device surfaces, which reduces stress and allows for symmetric layer formation without additional protective masks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sealing material is deposited directly on MEMS device surfaces, then sealing is achieved, but stress is induced on underlying device elements due to lattice mismatch and thermal expansion differences
Solution Approach 1:
The patent introduces a dummy insulation layer as an intermediary between the sealing material and the MEMS device structures. This dummy layer acts as a stress-absorbing buffer that prevents direct contact between the sealing material and sensitive device elements, thereby eliminating stress-induced damage while maintaining effective sealing of the cavity.
2Reliability
If conventional sealing methods are used to achieve symmetric layers, then manufacturing complexity increases requiring additional protective masks, but sealing is achieved
Solution Approach 1:
The dummy insulation layer is formed in advance as part of the standard CMOS-MEMS fabrication process, before the sealing material deposition. This preliminary action prepares the structure to receive sealing material without requiring additional protective masks or complex masking steps, thereby simplifying the manufacturing process while achieving symmetric layer formation.
3Reliability
If sealing material contacts MEMS device surfaces directly, then sealing is achieved, but sensor sensitivity decreases and harmonic distortion increases due to stress
Solution Approach 1:
The dummy insulation layer serves as a mediator that physically separates the sealing material from the MEMS device surfaces, preventing stress transmission to sensitive sensing elements. This isolation maintains the mechanical integrity and sensitivity of the sensor while still achieving effective sealing of the device cavity.
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 approach improves device performance by reducing stress-induced issues, enhancing sensor sensitivity, and lowering manufacturing costs by preventing direct contact between sealing material and MEMS device surfaces, while enabling symmetric layer formation without additional masking processes.
Implementation Method 1
depositing a sealant material over the void regions
Data Source
AI summary
Representative methods for sealing MEMS devices include depositing insulating material over a substrate, forming conductive vias in a first set of layers of the insulating material, and forming metal structures in a second set of layers of the insulating material. The first and second sets of layers are interleaved in alternation. A dummy insulating layer is provided as an upper-most layer of the first set of layers. Portions of the first and second set of layers are etched to form void regions in the insulating material. A conductive pad is formed on and in a top surface of the insulating material. The void regions are sealed with an encapsulating structure. At least a portion of the encapsulating structure is laterally adjacent the dummy insulating layer, and above a top surface of the conductive pad. An etch is performed to remove at least a portion of the dummy insulating layer.