Three-axis MEMS Accelerometer with Differential Proof Mass
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Solution Overview
Problem
Existing MEMS accelerometers face challenges in reducing die size while maintaining sensitivity and reliability, particularly when implementing a single proof mass design for multiple axis sensing.
Innovation Solution
The use of a spring structure that enables translational motion of a proof mass with differential sections to detect acceleration forces in three orthogonal directions, optimizing sense electrode placement and enhancing restoring force to minimize stiction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a single proof mass design is implemented for multiple axis sensing, then die size is reduced, but sensitivity and reliability deteriorate
Solution Approach 1:
The proof mass is divided into differential sections (first section with first mass, second section with second mass) that move in opposite directions in response to acceleration forces. This segmentation allows the single proof mass to maintain high sensitivity and reliability across multiple axes by creating differential measurement capabilities that reduce noise and improve detection precision.
Solution Approach 2:
Different sections of the proof mass are designed with different mass properties (first mass vs. second mass) to optimize sensing performance for different axes. The spring system is also configured with different stiffness characteristics for different directions, allowing local optimization of sensitivity while maintaining a compact single-proof-mass structure.
2Device complexity
If a single proof mass design is implemented for multiple axis sensing, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The proof mass is divided into differential sections (first section with first mass, second section with second mass) that move in opposite directions in response to acceleration forces. This segmentation allows the single proof mass to maintain high sensitivity and reliability across multiple axes by creating differential measurement capabilities that reduce noise and improve detection precision.
Solution Approach 2:
Multiple sensing capabilities for three orthogonal axes are merged into a single proof mass structure. The spring system connects both sections to a common anchor, and the capacitive sensing mechanism is integrated to detect motion in multiple directions, achieving multi-axis sensing functionality within a unified compact design.
3Measurement precision
If proof mass sections move in opposite directions, then sensing sensitivity is enhanced, but stiction risk increases
Solution Approach 1:
The spring system is configured to provide restoring forces that act as counterweights to the inertial forces experienced by the proof mass sections. This ensures that both sections are continuously pulled toward their neutral positions, preventing them from adhering to the substrate during acceleration events and minimizing stiction-related malfunctions while maintaining differential motion for enhanced sensitivity.
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 approach results in a smaller device size with enhanced sensitivity and reliability, reducing the likelihood of stiction-related malfunctions and improving performance by allowing uniform displacement of the proof mass for efficient sensing.
Implementation Method 1
a spring system interconnected between the anchor and the first and second sections of the proof mass. The spring system is configured to enable translational motion of the first and second sections of the proof mass in response to linear acceleration forces
Implementation Method 2
a proof mass spaced apart from a planar surface of a substrate, the proof mass having a first section and a second section... in response to linear acceleration forces imposed on the inertial sensor
Implementation Method 3
The movement of the movable structure changes capacitance, and an electrical circuit connected to the MEMS accelerometer structure measures the change in capacitance to determine the acceleration forces
Data Source
AI summary
An inertial sensor includes a proof mass spaced apart from a surface of a substrate. The proof mass has a first section and a second section, where the first section has a first mass that is greater than a second mass of the second section. An anchor is coupled to the surface of the substrate and a spring system is interconnected between the anchor and the first and second sections of the proof mass. The spring system enables translational motion of the first and second sections of the proof mass in response to linear acceleration forces imposed on the inertial sensor in any of three orthogonal directions.