MEMS Inertial Sensor Spring Structure Surrounding Anchor
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Solution Overview
Problem
MEMS inertial sensors, particularly accelerometers, face challenges with offset stability due to thermal stress, thermal hysteresis, and process variations, leading to inaccuracies and reduced yield, and require compact size while minimizing the effects of these issues.
Innovation Solution
The design incorporates a suspension system with a spring structure that surrounds the anchor and interconnects the movable element, with strategically placed attach points to improve offset stability and compactness, utilizing a configuration of serially adjoined beam sections to maintain spring constant while reducing space and minimizing the impact of anchor rotation and process variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional suspension systems are used, then the device can be manufactured with standard processes, but the offset stability deteriorates due to thermal stress and process variations
Solution Approach 1:
The spring structure is configured to surround the anchor, with the anchor positioned within the loop formed by the spring structure. This nesting arrangement allows the anchor to be centrally located within the spring loop, creating a symmetric configuration that minimizes the effect of anchor rotation and process variations on offset stability
Solution Approach 2:
The spring structure uses unequal arm lengths (first arm and second arm with different lengths) to compensate for thermal stress and process variations. The asymmetric design allows one arm to compensate for the effects of anchor rotation and thermal expansion, thereby improving offset stability despite manufacturing variations
2Volume of moving object
If the device size is reduced for miniaturization, then compactness is improved, but the suspension system becomes more sensitive to process variations and thermal effects
Solution Approach 1:
The spring structure surrounds the anchor in a compact loop configuration, maximizing space utilization. This nested arrangement achieves a compact device footprint while maintaining the symmetric geometry that improves offset stability, thus resolving the contradiction between miniaturization and reliability
Solution Approach 2:
The spring structure uses a loop configuration that extends in multiple dimensions rather than a simple linear arrangement. This dimensional approach allows the suspension system to maintain adequate length for stability while occupying minimal planar space, achieving both compactness and offset stability
3Reliability
If the spring structure is made longer to reduce sensitivity to anchor rotation, then offset stability improves, but the device size increases
Solution Approach 1:
The spring structure forms a loop that utilizes vertical and lateral dimensions rather than extending purely in one direction. This dimensional approach provides the effective length needed for stability while keeping the projected footprint compact, resolving the contradiction between spring length and device size
Solution Approach 2:
The anchor is positioned within the spring loop, allowing the spring structure to achieve adequate length for stability while the nested configuration minimizes the overall device dimensions. The anchor sits centrally within the loop, maximizing the effective spring length without increasing external device footprint
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 configuration enhances the offset stability and achieves a compact device size, reducing the effects of thermal stress and process variations, thereby improving sensor accuracy and yield while maintaining a low cost and conventional manufacturing feasibility.
Implementation Method 1
a spring structure having a first attach point coupled to the first side of the anchor and a second attach point coupled to the edge of the movable element. The spring structure includes beam sections serially adjoined one another, the beam sections extending from the first side of the anchor and surrounding the anchor to couple to the edge of the movable element
Implementation Method 2
The movement of the movable structure changes capacitance between the movable structure and fixed structures, and an electrical circuit connected to the MEMS accelerometer structure measures the change in capacitance to determine the acceleration forces
Data Source
AI summary
An inertial sensor includes a substrate, a movable element having an edge, and a suspension system retaining the movable element in spaced apart relationship above a surface of the substrate. The suspension system includes an anchor attached to the surface of the substrate, the anchor having a first side laterally spaced apart from the edge of the movable element, and a spring structure having a first attach point coupled to the first side of the anchor and a second attach point coupled to the edge of the movable element. The spring structure includes beam sections serially adjoining one another, the beam sections extending from the first side of the anchor and surrounding the anchor to couple to the edge of the movable element. The spring structure makes no more than one coil around the anchor to position the first attach point in proximity to the second attach point.