Oval Free-Layer Magnetoresistive Angle Sensor for Low-Field Accuracy
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Solution Overview
Problem
Conventional spin valve magnetoresistive angle sensors suffer from low measurement accuracy and high cost due to the need for high external magnetic fields, which increase measurement errors and require strong magnets.
Innovation Solution
A low-magnetic-field magnetoresistive angle sensor with an oval-shaped free layer and a multi-layer thin film structure, where the magnetocrystalline anisotropic field is compensated by the shape anisotropic demagnetizing field, allowing for a low working magnetic field close to the saturation magnetic field of the free layer, reducing measurement errors and costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high external magnetic field is applied to ensure the magnetic moment of the free layer is consistent with the external magnetic field direction, then the measurement reliability is improved, but the measurement precision deteriorates due to increased deflection angles of film layers causing extra measurement angle errors
Solution Approach 1:
The patent changes the shape parameter of the free layer from circular to oval, which fundamentally alters the demagnetizing field distribution. This shape parameter change enables the demagnetizing field to compensate for the magnetocrystalline anisotropic field, reducing the effective anisotropic field and allowing accurate measurement at lower external magnetic fields where layer deflection angles are minimized
Solution Approach 2:
The patent introduces asymmetry by using an oval-shaped free layer instead of a circular one. This asymmetric geometry creates anisotropic demagnetizing fields in different directions, with the shape anisotropic demagnetizing field specifically compensating for the magnetocrystalline anisotropic field, thereby reducing the effective anisotropic field and enabling low-field operation with high measurement precision
2Reliability
If a high external magnetic field is applied to ensure consistent magnetic moment direction, then the measurement reliability is improved, but the device cost increases due to the requirement for strong magnets
Solution Approach 1:
By changing the shape parameter of the free layer to oval, the patent reduces the effective anisotropic field, which directly lowers the external magnetic field strength needed for reliable measurement. This parameter change enables the use of weaker, less expensive magnets while maintaining measurement reliability
Solution Approach 2:
The asymmetric oval shape of the free layer generates shape anisotropic demagnetizing fields that compensate for magnetocrystalline anisotropy. This asymmetric design reduces the net anisotropic field, allowing reliable operation with lower external magnetic fields and thus reducing magnet cost
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 sensor achieves improved angle measurement accuracy and lower implementation costs by utilizing a low external magnetic field, eliminating the need for strong magnets.
Implementation Method 1
the free layer has a saturation magnetic field, a shape anisotropic demagnetizing field, and a magnetocrystalline anisotropic field in the X direction
Implementation Method 2
the magnetocrystalline anisotropic field is compensated by the shape anisotropic demagnetizing field to cause the effective anisotropic field of the free layer to be close to 0
Implementation Method 3
Spin valve magnetoresistive angle sensing units such as TMR or GMR
Implementation Method 4
a free layer of the push magnetoresistive sensing unit and a free layer of the pull magnetoresistive sensing unit have positive and negative X-direction Neel coupling magnetic fields
Data Source
AI summary
Disclosed in the embodiments of the present invention is a low-magnetic-field magnetoresistive angle sensor. The sensor comprises: a substrate located in an X-Y plane, and a magnetoresistive sensing unit located on the substrate. The magnetoresistive sensing unit comprising a multi-layer thin film structure. The multi-layer thin film structure comprises at least a stack of a free layer, a barrier layer, and a reference layer. The magnetoresistive sensing unit has an oval shape. The oval-shaped free layer has a long axis Ly, a short axis Lx, and a thickness Lz. Additionally the free layer has a saturation magnetic field, a shape anisotropy demagnetizing field, and a magnetocrystalline anisotropy field in the X direction. When an external magnetic field rotates by 0-360° in the X-Y plane, the magnetocrystalline anisotropy field is compensated by the shape demagnetizing field to cause the effective anisotropy field of the free layer to be close to 0, such that the external magnetic field has a low working magnetic field value close to that of the saturation magnetic field of the free layer material. The embodiments of the present invention can improve the accuracy of angle measurement of a magnetoresistive angle sensor. Additionally because the required external magnetic field is low, the sensor can be implemented at low cost.