Asymmetric Tilt-Mode MEMS Accelerometer Offset Cancellation
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Solution Overview
Problem
Existing MEMS accelerometers face challenges in accurately measuring Z-axis acceleration due to manufacturing asymmetries and uneven substrate stress, leading to offset biases and inaccurate measurements.
Innovation Solution
A single-axis tilt-mode microelectromechanical accelerometer structure is designed with asymmetrically-shaped masses and centrally positioned anchors, which are mechanically coupled to the substrate using torsional springs, allowing each mass to pivot independently or in unison, and featuring electrodes positioned symmetrically to reduce stress effects and enhance sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single tilt-mode MEMS accelerometer is manufactured on a substrate, then the device can measure Z-axis acceleration, but manufacturing asymmetries and uneven substrate stress cause offset biases and measurement inaccuracies
Solution Approach 1:
The invention divides a single accelerometer into two separate tilt-mode accelerometers on the same substrate. Each accelerometer has its own proof mass and sensing electrodes, allowing independent measurement of Z-axis acceleration. The outputs are combined to cancel out common-mode errors from substrate stress and manufacturing asymmetries, thereby improving both measurement precision and reliability.
Solution Approach 2:
The invention merges two tilt-mode accelerometers into a single integrated device on one substrate. By combining the measurements from both accelerometers and processing their outputs together, the system achieves error cancellation for offset biases caused by substrate stress and manufacturing variations, resolving the contradiction between measurement precision and reliability.
2Measurement precision
If asymmetrically-shaped masses are used in tilt-mode accelerometers, then sensitivity to Z-axis acceleration is enhanced, but manufacturing complexity increases
Solution Approach 1:
The invention employs asymmetrically-shaped proof masses in tilt-mode accelerometers where the mass distribution is intentionally made asymmetric about the pivot axis. This asymmetry creates a moment arm that enhances sensitivity to Z-axis acceleration by producing a larger torque for a given acceleration, directly improving measurement precision despite increased manufacturing complexity.
3Measurement precision
If two tilt-mode accelerometers are integrated on a single substrate, then offset biases are canceled, but device complexity increases
Solution Approach 1:
The invention segments the accelerometer function into two separate tilt-mode accelerometers on a single substrate, each with its own proof mass and sensing elements. This segmentation enables offset bias cancellation by combining measurements from both devices, improving precision despite the increased structural complexity of having two accelerometers instead of one.
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
This design improves measurement accuracy by canceling out uneven substrate stresses, reducing Brownian noise, and increasing sensitivity, resulting in comparable performance to a single sensor with lower noise and improved signal-to-noise ratio.
Implementation Method 1
Each asymmetrically-shaped mass pivotable about a first pivot axis located between the first end and the second end and the second asymmetrically-shaped mass is pivotable about a second pivot axis located between the first end and the second end
Implementation Method 2
Each asymmetrically-shaped mass includes a set of electrodes. The first set of electrodes are positioned on the substrate and below the first asymmetrically-shaped mass. The second set of electrodes positioned on the substrate and below the second asymmetrically-shaped mass.
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3A
AI summary
A single-axis tilt-mode microelectromechanical accelerometer structure. The structure includes a substrate having a top surface defined by a first end and a second end. Coupled to the substrate is a first asymmetrically-shaped mass suspended above the substrate pivotable about a first pivot point on the substrate between the first end and the second end and a second asymmetrically-shaped mass suspended above the substrate pivotable about a second pivot point on the substrate between the first end and the second end. The structure also includes a first set of electrodes positioned on the substrate and below the first asymmetrically-shaped mass and a second set of electrodes positioned on the substrate and below the second asymmetrically-shaped mass.