MEMS Stress Isolation Structure for Measurement Accuracy
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Solution Overview
Problem
MEMS devices face errors due to undesirable movements induced by large external accelerations or shocks, which affect the accuracy of force measurements.
Innovation Solution
A MEMS device with a stress isolation structure, featuring a free layer coupled through stems, where the sense material is disposed over the second portion, allowing it to deform independently of the first portion, maintaining a constant gap and reducing the impact of extraneous forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the MEMS device uses a conventional structure without stress isolation, then the device is simpler and easier to manufacture, but large external accelerations or shocks induce undesirable movements that cause measurement errors
Solution Approach 1:
The free layer is divided into a first portion and a second portion that are coupled through stems. This segmentation allows the second portion to deform independently under external forces while the first portion maintains the electrode gap, thereby improving measurement accuracy without requiring a completely complex redesign of the entire device structure.
Solution Approach 2:
The stems act as intermediary elements connecting the first and second portions of the free layer. These stems transmit minimal stress from the second portion to the first portion, allowing the second portion to move freely in response to external forces while maintaining the structural integrity needed to preserve the electrode gap at the first portion.
2Measurement precision
If the sense material is deposited over the entire free layer, then the manufacturing process is simpler, but stress from the sense material affects the electrode gap and causes measurement errors
Solution Approach 1:
The sense material is deposited only over the second portion of the free layer, not the entire structure. This localized deposition allows the sense material to sense forces in the second portion without introducing stress that would affect the electrode gap at the first portion, thereby maintaining measurement precision while still being compatible with standard deposition processes.
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 stress isolation structure effectively minimizes the impact of external forces on the MEMS device, maintaining measurement accuracy by keeping the gap between electrodes constant, even under residual stress or temperature changes.
Implementation Method 1
The first portion and second portion of the free layer are coupled through a stress isolation structure, such as stems. The stress isolation structure allows the second portion to deform independent of the first portion.
Implementation Method 2
MEMS force sensors have one or more sense material, which react to an external influence imparting a force onto the movable portions. The MEMS force sensor may be configured to measure these movements induced by the external influence to determine the type and extent of the external influence.
Data Source
AI summary
A method and system for a MEMS device is disclosed. The MEMS device includes a free layer, with a first portion and a second portion. The MEMS device also includes a underlying substrate, the free layer movably positioned relative to the underlying substrate. The first portion and second portion of the free layer are coupled through at least one stem. A sense material is disposed over portions of the second portion of the free layer. Stress in the sense material and second portion of the free layer does not cause substantial deflection of the first portion.