MEMS Sensor Electrode Compensation for Offset Error Control
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Solution Overview
Problem
MEMS accelerometers suffer from offset errors due to manufacturing stresses, leading to non-linearity, reduced full-scale value, and increased vibration rectification errors, which are not acceptable in high-performance applications.
Innovation Solution
A microelectromechanical sensor device with an active offset compensation mechanism, where stator electrodes are moved to equidistance with rotor electrodes using a compensation structure, ensuring they remain fixed relative to the sensed quantity, thus compensating for native offsets without altering sensing characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the rotor mass is suspended above the substrate by elastic coupling elements, then the sensor can detect acceleration, but manufacturing stresses cause offset error and non-linearity
Solution Approach 1:
The patent applies preliminary action by introducing a compensation structure during manufacturing that proactively counteracts the offset error caused by manufacturing stresses. The compensation structure is designed to pre-compensate for the expected deformation of elastic coupling elements, thereby eliminating the need for complex electronic compensation and ensuring accurate measurements from the start.
Solution Approach 2:
The compensation structure acts as an intermediary element between the rotor mass and the substrate. It introduces additional elastic elements that mediate the mechanical connection, thereby compensating for the harmful effects of manufacturing stresses in the primary elastic coupling elements while maintaining the acceleration sensing function.
2Measurement precision
If electronic compensation is used to correct offset error, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The patent replaces the electronic compensation system (ASIC circuit) with a mechanical compensation structure. Instead of using electronic circuits to measure and correct offset errors, the invention uses a mechanical compensation structure with additional elastic elements that physically compensate for manufacturing stresses, thereby simplifying the overall device architecture.
Solution Approach 2:
The invention extracts the compensation function from the electronic domain and relocates it to the mechanical domain. By removing the need for complex electronic compensation circuits and implementing the compensation function through mechanical means (additional elastic elements), the patent reduces device complexity while maintaining measurement precision.
3Ease of manufacture
If the rotor mass is not centered with respect to stator electrodes, then manufacturing is simplified, but sensing linearity deteriorates
Solution Approach 1:
The compensation structure is designed to pre-compensate for the inherent miscentering of the rotor mass. By introducing additional elastic elements with specific mechanical properties, the structure creates a preliminary correction that ensures linear sensing characteristics even when the rotor mass is not perfectly centered during assembly.
Solution Approach 2:
The patent changes the mechanical parameters of the coupling system by introducing additional elastic elements with specific stiffness and geometry characteristics. These parameter changes in the mechanical structure compensate for the miscentering condition, thereby restoring linear sensing behavior without requiring precise alignment during manufacturing.
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 compensates for intrinsic offsets, reducing non-linearity and maintaining full-scale value, while being insensitive to external accelerations, thus enhancing the performance of MEMS accelerometers.
Implementation Method 1
a mobile mass moving due to inertial effect, generally defined as 'rotor mass' or simply 'rotor' as it is movable due to the inertial effect (without this however implying for the same inertial mass to necessarily have a rotational movement) in the presence of an acceleration to be sensed
Implementation Method 2
fixed or stator electrodes, integrally coupled to the substrate by respective stator anchors, capacitively coupled to the rotor electrodes to form sensing capacitors, having a sensing capacitance indicative of the quantity to be sensed
Data Source
AI summary
A microelectromechanical sensor device having a sensing structure with: a substrate; an inertial mass, suspended above the substrate and elastically coupled to a rotor anchoring structure by elastic coupling elements, to perform at least one inertial movement due to a quantity to be sensed; first sensing electrodes, integrally coupled to the inertial mass to be movable due to the inertial movement; and second sensing electrodes, fixed with respect to the quantity to be sensed, facing and capacitively coupled to the first sensing electrodes to form sensing capacitances having a value that is indicative of the quantity to be sensed. The second sensing electrodes are arranged in a suspended manner above the substrate and a compensation structure is configured to move the second sensing electrodes with respect to the first sensing electrodes and vary a facing distance thereof, in the absence of the quantity to be sensed, in order to compensate for a native offset of the sensing structure.