Symmetric MEMS Accelerometer Layout for Low Cross-Sensitivity
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Solution Overview
Problem
Conventional microelectromechanical (MEMS) acceleration sensors exhibit undesirable cross-sensitivity to lateral acceleration forces due to a lack of symmetry, leading to inaccurate measurements and increased thermal noise.
Innovation Solution
A microelectromechanical acceleration sensor with a heavy mass and lightweight masses arranged symmetrically around a rotation axis, featuring electrode systems with movable and fixed combs that form electrical capacitances, allowing for symmetrical measurement of accelerations in multiple directions without cross-sensitivity, and incorporating spring elements and lever mechanisms to compensate for substrate bending.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional MEMS sensors use asymmetric mass arrangement, then manufacturing is simpler, but cross-sensitivity to lateral acceleration increases and measurement precision deteriorates
Solution Approach 1:
The patent applies asymmetry in a controlled manner by using a heavy mass and four lightweight masses arranged symmetrically around a rotation axis. This deliberate asymmetric mass distribution (one heavy, four light) creates the desired rotational symmetry for measurement while maintaining manufacturing feasibility through standardized mass geometries and positions.
Solution Approach 2:
The sensor divides the mass system into distinct segments: one heavy mass and four separate lightweight masses. Each lightweight mass is associated with its own electrode system, allowing independent measurement of acceleration components while maintaining overall symmetry to reduce cross-sensitivity.
2Device complexity
If conventional MEMS sensors lack rotational symmetry, then device complexity is reduced, but measurement accuracy deteriorates due to cross-sensitivity
Solution Approach 1:
The patent implements fourfold rotational symmetry (a form of controlled asymmetry) where the heavy mass and four lightweight masses are arranged such that rotating the structure by 90 degrees around the rotation axis produces an identical configuration. This symmetry ensures equal response to acceleration in all radial directions, eliminating cross-sensitivity while maintaining manageable device complexity.
Solution Approach 2:
The measurement function is segmented into four identical electrode systems, each responsible for measuring acceleration in a specific radial direction. This segmentation allows the complex measurement task to be divided into four simpler, identical sub-tasks that can be processed independently and combined to provide accurate three-axis acceleration data.
3Device complexity
If conventional MEMS sensors use single mass design, then device complexity is lower, but thermal noise increases and sensitivity is reduced
Solution Approach 1:
The single mass is segmented into one heavy mass and four lightweight masses distributed around the rotation axis. This segmentation increases the total effective mass for sensing acceleration while distributing the thermal noise across multiple independent elements. The combined signal from all masses provides better signal-to-noise ratio compared to a single mass design.
Solution Approach 2:
The patent merges the output signals from four separate lightweight masses with the heavy mass to create a combined measurement signal. This merging of multiple measurement channels increases the overall sensitivity and reduces the impact of thermal noise through signal integration, while the symmetric arrangement ensures that noise from individual masses does not create cross-sensitivity artifacts.
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 sensor achieves reduced cross-sensitivity, enhanced sensitivity, and lower thermal noise, providing accurate measurements across three axes with improved robustness and reduced signal distortion.
Implementation Method 1
Each electrode structure has a first fixed electrode, a second fixed electrode, a first movable electrode, and a second movable electrode... a first movable comb and a first fixed comb of the electrode structures interlock and form first electrical capacitances. In each case, a second movable comb and a second fixed comb of the electrode structures interlock and form second electrical capacitances.
Implementation Method 2
The heavy mass and the lightweight masses may also be referred to as seismic masses since they are suspended movably above the substrate and, due to their inertia, experience a deflection in response to accelerations acting on the microelectromechanical acceleration sensor
Data Source
AI summary
A microelectromechanical acceleration sensor. The sensor has a substrate, a movably suspended heavy mass, four movably suspended lightweight masses, and four electrode systems, and is designed to be at least rotationally symmetrical. The heavy mass laterally encloses the lightweight masses and the electrode systems. Each electrode system has two electrode structures. Each electrode structure has fixed electrodes and movable electrodes. The movable electrodes are connected to the masses. Movable and fixed electrode surfaces interlock and form electrical capacitances. The masses are coupled to one another such that a deflection of the heavy mass parallel to the substrate and in a direction perpendicular to fixed and movable electrode surfaces of two opposing electrode systems causes the lightweight masses connected to the opposing electrode systems to be deflected in the opposite direction.