Multilayer TMR Sensor Structure for Wide Linear Field Sensing
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Solution Overview
Problem
TMR-based magnetic field sensors face limitations in achieving a high linear range due to technical constraints on increasing the free layer thickness and reducing the diameter, which affects their accuracy and ability to handle strong magnetic fields.
Innovation Solution
Incorporating a multilayer sensing structure with a seed layer and polycrystalline ferromagnetic material with high saturation magnetization, lattice matching, and additional seed layers to enhance the sensor's performance, including materials like CoFe, CoFeB, and NiFe, to improve magnetic properties and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the free layer thickness is increased to extend the linear range, then the linear sensing range is improved, but the manufacturing cost and process time increase due to deposition and etching
Solution Approach 1:
The free layer is segmented into multiple sub-layers with different magnetization directions. This segmentation allows the sensor to achieve an extended linear sensing range without increasing the overall free layer thickness, thereby avoiding increased manufacturing cost and process time while maintaining measurement precision.
2Measurement precision
If the free layer diameter is reduced to extend the linear range, then the linear sensing range is improved, but the device complexity and lithography limitations are worsened
Solution Approach 1:
The free layer is divided into multiple magnetically distinct sub-layers. This segmentation enables the sensor to achieve extended linear range without reducing the overall device diameter, thus avoiding increased lithography complexity while improving measurement precision.
Solution Approach 2:
Instead of reducing the lateral dimension (diameter) to extend the linear range, the patent utilizes the vertical dimension by creating multiple sub-layers with different magnetization directions. This dimensional transition allows extended linear sensing range while maintaining a larger device diameter that is easier to manufacture with standard lithography.
3Device complexity
If a single ferromagnetic layer is used, then the structure is simple, but the hysteresis and grain size are larger reducing sensing accuracy
Solution Approach 1:
The single ferromagnetic layer is segmented into multiple sub-layers with different magnetization directions. This segmentation reduces the effective grain size and hysteresis of each sub-layer, thereby improving sensing accuracy while maintaining reasonable structural complexity.
Solution Approach 2:
The patent creates a composite magnetic structure by combining multiple ferromagnetic sub-layers with different magnetic properties. This composite structure achieves lower hysteresis and smaller effective grain size compared to a single layer, improving sensing accuracy while accepting increased structural complexity.
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 proposed structure enables TMR sensors to measure magnetic fields accurately within a high linear range, ensuring reliability and efficiency by reducing grain size and hysteresis, thus enhancing sensitivity and accuracy.
Implementation Method 1
A TMR-based magnetic field sensor is a device that measures magnetic fields using the tunnel magnetoresistance (TMR) effect. It comprises of multiple thin layers of materials, including a tunnel barrier and ferromagnetic layers. When a magnetic field is applied, the resistance of the sensor changes.
Implementation Method 2
The seed layer structure may help the ferromagnetic material grow properly with low grain size to have a preferably soft magnetic sensing layer with low hysteresis.
Data Source
AI summary
A magnetoresistive sensor includes a substrate, a reference system formed on the substrate, a tunnel barrier formed on the reference system, and a multilayer sensing structure formed on the tunnel barrier. The multilayer sensing structure includes a plurality of layers with at least one seed layer and at least one layer of ferromagnetic material with a saturation magnetization of at least 1.5 Tesla.