MEMS Sensor Offset Rejection via Polarity Anti-Symmetry
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Solution Overview
Problem
Microelectromechanical system (MEMS) sensors experience undesirable forces during fabrication and operation, leading to deviations in parallel alignment between the MEMS device and the sensing reference plane, causing non-ideal conditions such as tilt and curvature, which result in offset issues that existing technologies struggle to effectively address.
Innovation Solution
A MEMS sensor system comprising a sensing reference plane, anchors, proof masses, and a pattern of sensing elements that share at least three axes of polarity anti-symmetry, coupled with a signal processing circuit to detect motion normal to the sensing reference plane and provide an output proportional to external excitation, thereby reducing offset summation and rejecting tilt and curvature effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional sensing element patterns are used in MEMS sensors, then the device structure is simple, but offset errors occur due to tilt and curvature deviations from parallel alignment between the MEMS device and sensing reference plane
Solution Approach 1:
The patent applies asymmetry by configuring sensing elements with specific polarities arranged in a non-uniform pattern. The sensing elements have different orientations and polarity assignments that create an asymmetric configuration, allowing the system to reject offset errors from tilt and curvature while maintaining measurement accuracy. This asymmetric arrangement enables differential measurement that cancels out common-mode offset errors.
Solution Approach 2:
The sensing element pattern is divided into multiple discrete sensing elements with individually assigned polarities. Each sensing element can be independently configured with specific polarity orientations, allowing the pattern to be segmented into functional groups that collectively reject offset errors. This segmentation enables flexible arrangement of sensing elements to achieve offset rejection across multiple axes.
2Measurement precision
If the MEMS sensor uses a pattern of sensing elements with at least three axes of polarity anti-symmetry, then offset summation is reduced, but the sensing element configuration becomes more complex
Solution Approach 1:
The sensing elements are configured with polarity anti-symmetry across at least three axes, creating an asymmetric pattern where sensing elements on opposite sides of each axis have opposite polarities. This asymmetric configuration with multiple axes of anti-symmetry enables the system to reject offset errors from tilt and curvature in multiple directions simultaneously, improving motion detection accuracy while the systematic arrangement keeps implementation feasible.
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 effectively minimizes offset summation, providing a constant and reduced worst-case maximum offset, enhancing the sensor's ability to reject offset sources and improve motion detection accuracy across various angles and curvature conditions.
Implementation Method 1
The plurality of sensing elements is coupled between the sensing reference plane and the proof mass to detect motion normal to the sensing reference plane
Data Source
AI summary
A MEMS sensor includes a sensing reference plane, an anchor, a proof mass, and sensing elements. The anchor is coupled to the sensing reference plane and to the proof mass that moves under an external excitation. The sensing elements detect motion normal to the sensing reference plane. A summation of a product of polarity for each sensing element, its area, and its distance to the anchor on one side of an axis line is unequal to a summation of a product of a polarity associated with each sensing element, its associated area, and its distance to the anchor on another side of the axis line. As such, external excitation creates an offset. The offset is substantially constant for curvature angles (0°-360°) of the sensing reference plane. The offset is greater than zero and is less than a maximum offset for a MEMS sensor with perfect symmetry for its sensing elements.