MEMS Cap Structure With Standoffs for Stable Cavity Pressure
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Solution Overview
Problem
Monolithic integration of MEMS layers restricts flexibility with advanced semiconductor technologies, leading to issues like hillock effect, stiction, and unstable cavity pressure, which affect sensor performance.
Innovation Solution
Form standoffs on a substrate or cap layer separate from the MEMS device layer, using polysilicon electrodes to reduce hillock effect and improve stiction, and employ a getter material to stabilize cavity pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If monolithic integration of MEMS layer and cap layer is used, then device structure is simplified, but flexibility with advanced semiconductor technologies is restricted and hillock effect occurs
Solution Approach 1:
The patent divides the previously monolithic MEMS layer into separate components: a MEMS device layer and a cap layer that are fabricated independently and then bonded together. This segmentation allows each layer to be optimized separately using different fabrication processes and materials, thereby maintaining structural simplicity while enabling flexibility with advanced semiconductor technologies.
Solution Approach 2:
The patent transitions from a single-layer monolithic structure to a multi-layer stacked structure with vertical bonding interfaces. This dimensional change from 2D planar integration to 3D vertical integration enables independent optimization of each layer while maintaining overall device compactness.
2Ease of manufacture
If standoffs are created by etching through MEMS device layer, then bonding of components is enabled, but photoresist pooling issue occurs in lithography
Solution Approach 1:
The patent extracts the standoff formation process from the MEMS device layer etching and relocates it to the cap layer fabrication process. Standoffs are formed by depositing sacrificial material and patterning it on the cap layer before bonding, thereby eliminating the photoresist pooling issue that occurs when etching through the MEMS device layer.
Solution Approach 2:
Instead of forming standoffs by removing material (etching) from the MEMS device layer, the patent inverts the approach by forming standoffs through additive deposition of sacrificial material on the cap layer, followed by patterning. This inversion eliminates lithography issues while achieving the same bonding function.
3Reliability
If high temperatures are used during MEMS layer fabrication, then material properties are improved, but hillock effect on electrodes occurs causing performance degradation
Solution Approach 1:
The patent performs preliminary actions by fabricating the MEMS device layer with electrodes at lower temperatures first, then subsequently bonding the cap layer at higher temperatures. This sequential temperature management prevents thermal damage to electrodes while still achieving proper material properties in the cap layer and bonding interface.
Solution Approach 2:
The patent changes the temperature parameter across different fabrication stages: low-temperature processing for the MEMS device layer to prevent hillock effect, followed by high-temperature processing for cap layer fabrication and bonding. This dynamic parameter adjustment optimizes material properties while avoiding thermal damage.
4Reliability
If bumpstop structure is used to prevent contact between movable components and circuitries, then device protection is improved, but stiction occurs causing movable components to fail to release
Solution Approach 1:
The patent applies local quality by modifying only the surface properties of the bumpstop through coating with a release layer, while maintaining the bumpstop's structural function. The release layer provides low friction and anti-stiction properties locally at the contact interface, enabling movable components to release smoothly while the bumpstop continues to provide mechanical protection.
Solution Approach 2:
The patent introduces a release layer as an intermediary substance between the movable components and the bumpstop. This intermediary layer reduces adhesion and friction, preventing stiction while maintaining the protective function of the bumpstop structure.
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
Enhances MEMS device performance by reducing hillock effects, improving stiction, and stabilizing cavity pressure, allowing for advanced semiconductor integration and tighter lithography alignment.
Implementation Method 1
employ a getter material to stabilize cavity pressure
Data Source
AI summary
A device includes a substrate comprising a first standoff, a second standoff, a third standoff, a first cavity, a second cavity, and a bonding material covering a portion of the first, the second, and the third standoff. The first cavity is positioned between the first and the second standoffs, and the second cavity is positioned between the second and the third standoffs. The first cavity comprises a first cavity region and a second cavity region separated by a portion of the substrate extruding thereto, and wherein a depth associated with the first cavity region is greater than a depth associated with the second cavity. A surface of the first cavity is covered with a getter material.