MEMS Accelerometer Z-Axis Sensitivity via Segmented Proofmass
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Solution Overview
Problem
Existing MEMS accelerometers face challenges in achieving high sensitivity while being insensitive to cross-axis, or out-of-plane, accelerations, particularly in detecting Z-axis accelerations while being oblivious to X-and Y-axis accelerations.
Innovation Solution
A MEMS acceleration sensor design featuring a proofmass with specific channels and flexures that allow translation perpendicular to the device plane while restricting motion parallel to it, utilizing hinges and flexures with distinct spring constants and piezoresistive gauges to detect Z-axis accelerations effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a pressure-sensitive element (such as a cantilever) is used in conjunction with a strain-sensing element for measuring acceleration, then sensitivity to acceleration is improved, but susceptibility to cross-axis (out-of-plane) accelerations increases
Solution Approach 1:
The proofmass is divided into multiple segments (first proofmass, second proofmass, third proofmass) connected by hinges and flexures. This segmentation allows the structure to selectively respond to Z-axis accelerations while isolating the sensing elements from X and Y axis disturbances, thereby maintaining high sensitivity while reducing cross-axis susceptibility.
Solution Approach 2:
The channels are positioned asymmetrically relative to the proofmass (first channel right of vertical midline, second channel left of vertical midline). This asymmetric configuration, combined with the hinge-fixture arrangement, creates a mechanical structure that is inherently more sensitive to out-of-plane (Z-axis) accelerations while being less responsive to in-plane accelerations, thus resolving the contradiction between sensitivity and cross-axis susceptibility.
2Ease of manufacture
If the proofmass is configured in a predetermined device plane with traditional sensing elements, then manufacturing is simplified, but sensitivity to Z-axis accelerations is reduced
Solution Approach 1:
The invention transitions from traditional in-plane sensing to out-of-plane sensing by configuring the proofmass with channels and flexures that enable movement perpendicular to the device plane. The hinges and flexures are arranged to allow Z-axis translation while restricting X and Y axis motion, thereby achieving high Z-axis sensitivity without complicating the basic planar proofmass configuration.
Solution Approach 2:
The invention uses flexible elements (flexures and hinges) made as thin film structures that can be integrated into the planar proofmass. These flexible elements allow controlled out-of-plane motion while maintaining the overall planar configuration, enabling Z-axis acceleration sensing without sacrificing manufacturing simplicity.
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 design enhances sensitivity to Z-axis accelerations while minimizing sensitivity to X-and Y-axis accelerations, providing accurate detection of vertical movements with minimal parallel motion interference.
Implementation Method 1
utilizing hinges and flexures with distinct spring constants and piezoresistive gauges to detect Z-axis accelerations effectively
Implementation Method 2
a first channel starting from the top of the first proofmass and extending down into the first proofmass towards the bottom past the horizontal midline to a first channel end, the first channel located right of the vertical midline
Data Source
AI summary
A MEMS acceleration sensor comprising: a frame, a plurality of proofmasses; a plurality of flexures; a plurality of hinges and a plurality of gauges. The frame, proofmasses, flexures, hinges and gauges designed to measure acceleration in a direction perpendicular to the device plane while being generally resistant to motions parallel to the device plane. The measurement of the acceleration is accomplished through the piezoresistive effect of the strain in the gauges.