MEMS Accelerometer Offset Minimization via Polarity Anti-Symmetry
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Solution Overview
Problem
Microelectromechanical system (MEMS) sensors face challenges in offset stability due to undesirable forces during fabrication and operation, leading to deviations in parallel alignment between the sensor and the sensing reference plane, which affect their accuracy and suitability for various market segments.
Innovation Solution
A MEMS sensor system with a sensing reference plane and a pattern of sensing elements that share multiple axes of polarity anti-symmetry, coupled with a signal processing circuit to combine the sensing elements and provide an output proportional to external excitations, effectively reducing offset caused by deviations in alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional MEMS sensor design is used, then manufacturing is simpler, but offset stability deteriorates under external loads
Solution Approach 1:
The sensing element pattern is segmented into multiple discrete sensing elements arranged in specific geometric patterns with multiple axes of polarity anti-symmetry. This segmentation allows the sensor to independently measure and compensate for offset errors in different directions, improving offset stability without requiring a complete redesign of the MEMS structure.
Solution Approach 2:
The invention employs polarity anti-symmetry in the sensing element patterns, where sensing elements are arranged in asymmetric configurations relative to the proof mass center. This asymmetric arrangement creates differential signals that are sensitive to acceleration but insensitive to offset errors, resolving the contradiction between simplicity and stability.
2Measurement precision
If sensing elements are added to improve offset rejection, then measurement precision improves, but device complexity increases
Solution Approach 1:
The sensing element patterns serve multiple functions simultaneously: they detect acceleration along the sensing axis, reject offset errors through polarity anti-symmetry, and provide structural symmetry for mechanical stability. This multi-functionality improves measurement precision without proportionally increasing device complexity.
Solution Approach 2:
The invention merges the offset rejection function with the acceleration sensing function by integrating polarity anti-symmetric patterns directly into the sensing element arrangement. This combining approach achieves both offset rejection and accurate measurement without requiring separate compensation mechanisms.
3Reliability
If proof mass symmetry is increased, then offset rejection improves, but manufacturing precision requirements increase
Solution Approach 1:
The invention intentionally introduces polarity anti-symmetry in the sensing element patterns rather than requiring perfect geometric symmetry in the proof mass. This approach achieves offset rejection through electrical symmetry compensation rather than mechanical symmetry, reducing manufacturing precision requirements.
Solution Approach 2:
The invention changes the parameter of symmetry from geometric symmetry of the proof mass to polarity symmetry of the sensing element patterns. This parameter transformation allows offset rejection to be achieved through electrical field configuration rather than mechanical precision, relaxing manufacturing constraints.
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 solution enhances offset rejection and stability of MEMS sensors, improving their performance under various external loads and enabling them to meet stringent specifications across different market segments.
Implementation Method 1
a pattern of sensing elements coupled between the sensing reference plane and the at least one proof mass to detect motion normal to the sensing reference plane
Data Source
AI summary
Exemplary embodiment of a tilting z-axis, out-of-plane sensing MEMS accelerometers and associated structures and configurations are described. Disclosed embodiments facilitate improved offset stabilization. Non-limiting embodiments provide exemplary MEMS structures and apparatuses characterized by one or more of having a sensing MEMS structure that is symmetric about the axis orthogonal to the springs or flexible coupling axis, a spring or flexible coupling axis that is aligned to one of the symmetry axes of the electrodes pattern, a different number of reference electrodes and sense electrodes, a reference MEMS structure having at least two symmetry axes, one which is along the axis of the springs or flexible coupling, and/or a reference structure below the spring or flexible coupling axis.