Single-Chip 3-Axis Magnetic Sensor With Flux Guides
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Solution Overview
Problem
Existing magnetic field sensors are large, costly, and inefficient for mobile applications, and three-axis sensors often require multi-chip modules with high assembly costs and complex packaging, lacking sensitivity and being affected by temperature changes.
Innovation Solution
A single-chip magnetic field sensor design using ferromagnetic thin-film technology with high aspect ratio flux guides and magnetoresistive sensors, integrated into a CMOS-compatible structure, captures magnetic flux from all three dimensions through asymmetric positioning and Wheatstone bridge configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multi-chip modules with vertically bonded chips are used to achieve three-axis sensing, then out-of-plane field detection capability is improved, but device complexity and manufacturing cost increase significantly
Solution Approach 1:
The patent combines three magnetoresistive sensors oriented along orthogonal axes (x, y, and z-axes) onto a single chip substrate. Each sensor detects magnetic fields along one axis, and their integration enables full three-axis magnetic field detection capability without requiring multiple separate chips, thereby eliminating the complexity of vertical bonding and multi-chip assembly while maintaining versatility.
Solution Approach 2:
The patent utilizes vertical stacking of sensor layers along the z-axis direction to achieve three-dimensional magnetic field sensing. By arranging sensor elements in multiple layers at different heights above the substrate and orienting their sensitive axes differently, the system captures magnetic field components in all three spatial dimensions within a single planar chip structure.
2Measurement precision
If AMR-based sensors are used to achieve required sensitivity and CMOS compatibility, then sensing performance improves, but sensor size increases to square millimeters
Solution Approach 1:
The patent employs flux guide structures positioned adjacent to each magnetoresistive sensor element that concentrate and direct magnetic flux locally onto the active sensing area. This local flux concentration enhances the magnetic field sensitivity at each sensor location without requiring an increase in the overall sensor element dimensions, allowing high sensitivity within a compact footprint.
Solution Approach 2:
The patent uses composite magnetic layer structures in the magnetoresistive sensors, including pinned layers, free layers, and tunnel barrier layers, to achieve both high sensitivity and small size. The composite structure allows for optimized magnetic properties that enhance detection capability while maintaining compact dimensions suitable for integrated circuits.
3Adaptability or versatility
If vertically bonded chips are used for three-axis sensing, then out-of-plane response is achieved, but package vertical extent and assembly cost increase
Solution Approach 1:
The patent achieves out-of-plane (z-axis) magnetic field detection by stacking sensor layers vertically above the substrate plane, with each layer's sensitive axis oriented to detect different spatial components. This vertical layering approach enables three-axis sensing within a single chip's planar footprint, avoiding the need for vertical chip stacking that would increase package height.
4Device complexity
If three-axis sensing is implemented on a single chip, then device complexity and assembly cost decrease, but achieving adequate sensitivity and temperature stability becomes more difficult
Solution Approach 1:
The patent divides the three-axis sensing function into three separate magnetoresistive sensor elements, each optimized for detecting magnetic fields along one specific axis (x, y, or z). Each sensor element is independently configured with its own flux guide structure, allowing individual optimization of sensitivity and temperature compensation for each axis while maintaining compact single-chip integration.
Solution Approach 2:
The patent employs Wheatstone bridge circuit configurations for each magnetoresistive sensor element to compensate for temperature-dependent resistance changes. By arranging the sensor elements and their associated circuitry in differential bridge configurations, the system achieves temperature stability while maintaining high sensitivity to magnetic field variations.
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 provides a compact, sensitive, and temperature-stable three-axis magnetic field sensor suitable for mobile applications, reducing size, cost, and power consumption while maintaining high sensitivity and accuracy.
Implementation Method 1
magnetoresistive sensors
Implementation Method 2
MTJ sensors and GMR sensors have been employed in a Wheatstone bridge structure to increase sensitivity and to eliminate temperature dependent resistance changes
Implementation Method 3
high aspect ratio flux guides
Data Source
AI summary
Three bridge circuits (101, 111, 121), each include magnetoresistive sensors coupled as a Wheatstone bridge (100) to sense a magnetic field (160) in three orthogonal directions (110, 120, 130) that are set with a single pinning material deposition and bulk wafer setting procedure. One of the three bridge circuits (121) includes a first magnetoresistive sensor (141) comprising a first sensing element (122) disposed on a pinned layer (126), the first sensing element (122) having first and second edges and first and second sides, and a first flux guide (132) disposed non-parallel to the first side of the substrate and having an end that is proximate to the first edge and on the first side of the first sensing element (122). An optional second flux guide (136) may be disposed non-parallel to the first side of the substrate and having an end that is proximate to the second edge and the second side of the first sensing element (122).