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 from fabrication, packaging, and operational conditions, which affect their accuracy and suitability for various market segments.
Innovation Solution
A MEMS sensor design incorporating a sensing reference plane with a pattern of sensing elements that share multiple axes of polarity anti-symmetry, coupled with a signal processing circuit to combine these elements and provide an output proportional to external excitation, effectively reducing offset caused by deviations in parallel 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 elements are divided into multiple segments arranged in specific patterns with defined polarity relationships. The pattern includes multiple sensing elements (e.g., six elements) arranged symmetrically around the proof mass, with alternating polarity assignments that enable differential measurement and offset rejection
Solution Approach 2:
The sensing elements are arranged with specific asymmetric polarity patterns relative to the proof mass geometry. The pattern uses alternating positive and negative polarity elements in a configuration that creates anti-symmetry, allowing the system to reject common-mode offset signals while maintaining sensitivity to acceleration
2Measurement precision
If standard electrode patterns are used, then device complexity is lower, but measurement precision deteriorates due to offset errors
Solution Approach 1:
The signal processing circuit combines outputs from multiple sensing elements with specific polarity weighting to create a differential measurement. This feedback mechanism cancels offset errors by subtracting common-mode signals while preserving the acceleration signal, improving measurement precision
Solution Approach 2:
The patent changes the polarity parameters of the sensing elements in a specific pattern configuration. By alternating polarity signs of adjacent sensing elements and arranging them symmetrically, the system transforms the measurement equations to reject offset terms while maintaining sensitivity to the acceleration parameter
3Ease of manufacture
If simple anchor design is used, then manufacturing is easier, but offset rejection deteriorates under thermal and mechanical stress
Solution Approach 1:
The patent applies different polarity characteristics to different local regions of the sensing element pattern. Each sensing element position is assigned a specific polarity based on its location relative to the proof mass, creating local quality variations that enable global offset rejection through differential measurement
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, enabling MEMS sensors to perform accurately under various external loads and conditions, making them suitable for diverse applications across 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
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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.