Single Chip Vector Magnetometer with Perpendicular MTJ
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Solution Overview
Problem
Current vector magnetic sensors face challenges in achieving low cost, high resolution, and compact size for consumer electronics, particularly in detecting all three axes of magnetic fields on a single semiconductor substrate, as existing technologies like Hall Effect, AMR, and GMR sensors are either expensive, complex, or inefficient in measuring perpendicular field components.
Innovation Solution
The use of magnetic tunnel junction (MTJ) sensors with perpendicular anisotropy and specific layering configurations, including pinned and free layers with different spacer materials, allows for sensitivity to out-of-plane magnetic fields, enabling a single chip vector magnetometer by patterning sensors to respond differently to various field components, and employing a permeable ferromagnetic plate to separate magnetic field components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Hall Effect sensors are used for three-axis magnetic field detection, then all three field components can be measured, but the device cost and power consumption increase significantly
Solution Approach 1:
The patent combines multiple MTJ sensor elements with different magnetization orientations on a single substrate to detect all three magnetic field components. By merging the sensing functions into one integrated device, it eliminates the need for separate Hall Effect sensors for each axis, thereby reducing system cost and power consumption while maintaining three-axis detection capability
Solution Approach 2:
The MTJ sensor elements are designed with universal functionality to detect magnetic fields in multiple orientations. By configuring the pinned layer magnetization at different angles (e.g., 0°, 45°, 90°), the same sensor technology can measure Rx, Ry, and Rz components, making the system multi-functional without requiring different sensor types for each axis
2Measurement precision
If AMR or GMR sensors are used for magnetic field detection, then high resolution is achieved, but the signal amplitude is low and electronics design becomes complex
Solution Approach 1:
The patent changes the magnetoresistance effect parameter from AMR/GMR to TMR (tunneling magnetoresistance) in MTJ structures. This parameter change provides both high resolution and large signal amplitude simultaneously, eliminating the need for complex backend electronics while maintaining detection precision
Solution Approach 2:
The MTJ sensor employs composite material structures including tunnel barrier layers (e.g., MgO), ferromagnetic layers with perpendicular magnetic anisotropy, and spacer layers. This composite structure enables high TMR ratio and large signal amplitude, simplifying the electronics design while achieving high resolution magnetic field detection
3Measurement precision
If MTJ sensors with perpendicular anisotropy are used, then out-of-plane magnetic field sensitivity is achieved, but the device structure becomes more complex
Solution Approach 1:
The patent applies local quality by creating different magnetization orientations in different regions of the sensor array. Specific pinned layer elements are configured with magnetization at 0°, 45°, or 90° angles to detect specific field components (Rx, Ry, Rz), while maintaining a uniform perpendicular anisotropy structure throughout. This localized differentiation achieves three-axis detection without requiring fundamentally different structures for each sensor element
Solution Approach 2:
The sensor system is segmented into multiple MTJ elements, each responsible for detecting a specific magnetic field component. By dividing the detection task across multiple specialized elements with different pinned layer orientations, the system achieves out-of-plane sensitivity for all three axes while keeping each individual element's structure relatively simple and manufacturable
4Measurement precision
If multiple substrates are aligned at right angles to detect different field components, then three-axis measurement is achieved, but the device size and cost increase
Solution Approach 1:
The patent merges multiple sensor functions onto a single substrate by fabricating MTJ elements with different pinned layer magnetization orientations in the same planar structure. This integration eliminates the need for multiple separately aligned substrates, significantly reducing device size and packaging complexity while maintaining three-axis measurement capability
Solution Approach 2:
Instead of stacking multiple substrates in the vertical dimension (requiring alignment and packaging), the patent transitions to a planar two-dimensional arrangement where sensor elements with different orientations are laid out on the same substrate plane. This dimensional change simplifies manufacturing and reduces overall device size while achieving the same three-axis detection function
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 simplifies electronics design, reduces system cost, and achieves high-resolution, three-axis magnetic field measurement on a single chip, while minimizing cross-axis sensitivity and non-orthogonality between sensitivity axes, facilitating efficient and accurate magnetic field component isolation.
Implementation Method 1
MTJ sensors detect the magnetic field through the use of the tunneling magnetoresistance (TMR, Tunneling Magnetoresistance) effect
Implementation Method 2
The FL has a perpendicular magnetic anisotropy and the PL has its magnetization oriented perpendicular to the plane of the film
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
A thin film magnetoresistive sensor for detecting a magnetic field components perpendicular and parallel to the plane of the sensor substrate is disclosed. The sensing element comprises a free layer (30), a reference layer (10; 11), and a spacer layer (20; 21) between the free layer and the reference layer. The easy-axis magnetization, which is inherent to the material of the free layer (30), is arranged to be perpendicular to the plane of the sensor substrate. The magnetization direction of the reference layer (10; 11) is confined to a direction parallel to the substrate plane. The reference layer consists of a ferromagnetic layer exchange coupled to an antiferromagnetic layer, or consists of a ferromagnetic layer having a higher coercive force than that of the free layer. The spacer layer (20; 21) is composed of an insulating material or a conductive material. The magnetoresistive sensor further includes an array of aforementioned sensing elements coupled to an electronic device in order to provide three-axis sensing.