Fully Symmetric MEMS Sensing Structures for Stress-Induced Offset Control
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Solution Overview
Problem
Existing MEMS sensors suffer from asymmetrical designs that lead to changes in sensor offset and quadrature errors due to stress-induced rotation of fixed finger anchors, affecting their performance.
Innovation Solution
Implementing fully symmetrical sensing structures in MEMS devices, where the layout of fixed fingers is symmetric in at least one direction, and often in two directions, with aligned anchors to reduce stress-induced offset and errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If asymmetrical sensing structures are used in MEMS sensors, then device complexity is reduced and ease of manufacture is improved, but sensor offset and quadrature errors increase due to stress-induced rotation of fixed finger anchors
Solution Approach 1:
The patent applies asymmetry in reverse by deliberately designing symmetrical sensing structures. The fixed fingers are arranged symmetrically about the proof mass with anchors positioned at symmetric locations, and the movable fingers are configured to move symmetrically relative to the fixed fingers. This symmetrical arrangement ensures that stress-induced rotations affect all sensing elements equally, causing errors to cancel out rather than accumulate, thereby maintaining measurement precision while remaining manufacturable
2Measurement precision
If fully symmetrical sensing structures are implemented, then sensor offset performance improves under stress, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The sensing structure is segmented into multiple identical symmetric units. The fixed fingers are divided into multiple pairs positioned symmetrically on opposite sides of the proof mass, with each pair having identical geometry and anchoring. The movable fingers are similarly segmented and configured to move in symmetric patterns. This segmentation into repeating symmetric units achieves the offset performance benefits of full symmetry while reducing design complexity through modularity and repetition
3Ease of manufacture
If fixed finger anchors are not aligned symmetrically, then manufacturing is simpler, but stress-induced rotation causes changes in sensing gaps and electrical connections
Solution Approach 1:
The symmetrical arrangement of fixed finger anchors creates a balanced stress distribution throughout the structure. When external or package stress is applied, the symmetric anchor positions ensure that stress-induced rotations occur equally in all directions, maintaining equipotential conditions for the sensing gaps. This means that all sensing elements experience equivalent stress states, preserving gap consistency and electrical connection reliability despite the presence of stress
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 symmetrical design significantly improves offset performance under package and internal/external stress, reducing sensor offset and quadrature errors by ensuring consistent sensing gaps and electrical connections.
Implementation Method 1
the sensing structure, such as a capacitive sensing structure having moveable fingers attached to the proof mass and fixed fingers anchored to a substrate. The moveable fingers and the fixed fingers can be interdigitated to form comb finger sets that serve to sense capacitance changes arising from the proof mass moving relative to the substrate.
Data Source
AI summary
Fully symmetric sensing structures for MEMS devices are disclosed herein. In certain embodiments, a MEMS sensor includes a proof mass that moves in a first direction. The proof mass includes moveable fingers that move with the proof mass. The MEMS sensor further includes fixed fingers that are fixed with respect to the moveable fingers, and the fixed fingers and moveable fingers serve to detect movement of the proof mass. For example, the moveable fingers and the fixed fingers can be interdigitated to form a comb finger set for sensing changes in capacitance arising from movement of the proof mass relative to a substrate. A layout of the fixed fingers is fully symmetric in at least the first direction.