Magnetic Sensor Biasing with Segmented Antiferromagnetic Layers
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Solution Overview
Problem
Existing magnetic sensors face challenges in effectively applying a bias magnetic field to magnetoresistive elements due to the formation of magnetic field generators that ride up on the tapered side surfaces of the elements, leading to thinner film thickness and reduced functionality of the antiferromagnetic and cap layers.
Innovation Solution
A magnetic sensor configuration that includes a ferromagnetic layer overlapping the magnetoresistive element, an insulating layer on both sides, an underlying layer, and an antiferromagnetic layer with a non-facing part, which maintains consistent film thickness and enhances the functionality of the magnetic field generators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the magnetic field generator is formed adjacent to the side surface of the magnetoresistive element via a thin insulating film to decrease the distance, then the strength of the bias magnetic field is increased, but the film thickness of the antiferromagnetic and cap layers becomes smaller and their functionality is reduced
Solution Approach 1:
The antiferromagnetic layer is divided into two distinct portions: a first antiferromagnetic portion that faces the ferromagnetic layer to generate the bias magnetic field, and a second antiferromagnetic portion that faces the magnetoresistive element and provides protective functionality. This segmentation allows each portion to be optimized for its specific function without compromising the other.
Solution Approach 2:
Different regions of the antiferromagnetic layer are assigned different functions: the first portion (facing the ferromagnetic layer) is optimized for magnetic field generation, while the second portion (facing the magnetoresistive element) is optimized for protection and stability. This local differentiation resolves the contradiction by allowing the film thickness to be sufficient in the protective region while maintaining close proximity in the field-generating region.
2Force
If the magnetic field generator is formed adjacent to the side surface of the magnetoresistive element to decrease the distance, then the bias magnetic field strength is increased, but the distance between the magnetic field generator and the magnetoresistive element becomes smaller leading to potential harmful interactions
Solution Approach 1:
An insulating layer is introduced as an intermediary between the magnetic field generator (ferromagnetic layer) and the magnetoresistive element. This insulating layer prevents direct contact and harmful interactions such as corrosion and disturbance fields, while still allowing the bias magnetic field to effectively reach the magnetoresistive element through the thin insulating barrier.
Solution Approach 2:
The protective function is extracted from the antiferromagnetic layer by creating a distinct second portion that specifically faces the magnetoresistive element. This separated protective portion acts as a dedicated barrier against harmful factors, allowing the first portion to focus on magnetic field generation without compromise.
3Force
If the magnetic field generator is formed adjacent to the side surface of the magnetoresistive element, then the distance is decreased and bias magnetic field strength is increased, but the film thickness of the layers becomes non-uniform and smaller
Solution Approach 1:
The antiferromagnetic layer is segmented into two portions with different spatial orientations and functions. The first portion faces the ferromagnetic layer and can be formed with sufficient thickness for magnetic field generation, while the second portion faces the magnetoresistive element and provides uniform protective coverage. This segmentation allows each portion to be optimized for its specific requirements.
Solution Approach 2:
The solution transitions from a single-layer configuration to a multi-layer, multi-directional structure. By stacking the antiferromagnetic layer to create portions facing different directions (one facing the ferromagnetic layer, another facing the magnetoresistive element), the design achieves both close proximity for strong magnetic coupling and sufficient film thickness for functionality and protection.
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 configuration maintains the integrity and functionality of the antiferromagnetic and cap layers, ensuring robust performance of the magnetic field generators and improving the sensor's resistance to disturbance fields and corrosion.
Implementation Method 1
an antiferromagnetic layer disposed on the underlying layer... a first antiferromagnetic portion that faces the first ferromagnetic layer via the underlying layer
Implementation Method 2
Some magnetic sensors have means for applying a bias magnetic field to the magnetoresistive element. The bias magnetic field is used, for example, to enable the magnetoresistive element to respond linearly to a change in the strength of the target magnetic field.
Implementation Method 3
a free layer having a magnetization whose direction is variable depending on the direction of a target magnetic field
Data Source
AI summary
A magnetic sensor includes at least one MR element, a ferromagnetic layer disposed to overlap the at least one MR element when viewed in a first direction, an insulating layer disposed on both sides of the at least one MR element in a second direction, an underlying layer disposed on the at least one MR element, the first ferromagnetic layer, and the insulating layer, and an antiferromagnetic layer disposed on the underlying layer. The antiferromagnetic layer includes an antiferromagnetic portion that faces the ferromagnetic layer via the underlying layer, and a non-facing part that faces the at least one MR element and the insulating layer via the underlying layer but does not face the ferromagnetic layer.