Biased Free Layer MR Sensor for Uniform Low-Noise Magnetic Response
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Solution Overview
Problem
Tunnel magnetoresistance (TMR) sensors face challenges in achieving uniform magnetic performance due to material composition and shape anisotropy, requiring tight control of thickness and composition, and are prone to noise from processing defects.
Innovation Solution
The introduction of a biased free layer structure in MR sensors, comprising antiferromagnetic pinning layers and a tunnel barrier, with a hard axis orientation of the magnetic coupled free layer at 90 degrees to the pinning direction, and an antiferromagnetic coupling layer that controls the saturation field, allowing for improved stability and tunability without altering the free layer thickness or composition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the magnetic behavior of the free layer is determined by material composition and shape anisotropy, then the sensor can operate, but tight control of material thickness, composition and sensor shape is required to achieve desired magnetic performance
Solution Approach 1:
The patent introduces an antiferromagnetic coupling layer to control the saturation field of the free layer through exchange coupling. By adjusting the thickness and material properties of the AF coupling layer, the magnetic performance can be tuned without changing the free layer's thickness or composition, thus reducing manufacturing precision requirements while maintaining device functionality
Solution Approach 2:
The antiferromagnetic coupling layer acts as an intermediary between the free layer and the external environment. It mediates the magnetic interaction by providing exchange coupling that defines the saturation field, allowing independent optimization of the free layer's magnetic behavior without direct control of its thickness or composition
2Ease of manufacture
If non-uniformities in sensor shape such as processing defects are present, then manufacturing is easier, but sensor noise increases
Solution Approach 1:
By controlling the saturation field through the AF coupling layer thickness rather than free layer dimensions, the sensor becomes less sensitive to shape non-uniformities and processing defects. This parameter shift allows easier manufacturing while maintaining low noise performance
Solution Approach 2:
Instead of controlling magnetic performance by precisely defining the free layer's shape and dimensions, the patent inverts the approach by controlling magnetic behavior through the AF coupling layer's exchange coupling strength. This inversion makes the system more tolerant of manufacturing 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
This configuration provides uniform and tunable magnetic performance along the sensor length, reducing noise and allowing for stable magnetization direction alignment, enhancing the accuracy and reliability of magnetic field measurements.
Implementation Method 1
a magnetic coupled free layer disposed on the tunnel barrier; a AF coupling layer disposed on the magnetic coupled free layer
Implementation Method 2
a first antiferromagnetic (AF) pinning layer; a magnetic fixed layer disposed on the first AF layer
Implementation Method 3
A tunnel magnetoresistance (TMR) sensor utilizes the MR effect observed in multilayers comprising an extremely thin nanometer-level, non-magnetic insulation layer, disposed between two ferromagnetic layers
Implementation Method 4
the magnetic behavior of free magnetic layer 101 is primarily determined by its material composition and the shape of the sensor through shape anisotropy
Data Source
AI summary
The enclosed embodiments are directed to a magnetoresistance (MR) sensor with a biased free layer for improved stability of magnetic performance. In an embodiment, an MR sensor comprises: a first antiferromagnetic (AF) pinning layer; a magnetic fixed layer disposed on the first AF layer; a tunnel barrier disposed on the magnetic fixed layer; a magnetic coupled free layer disposed on the tunnel barrier; a AF coupling layer disposed on the magnetic coupled free layer; a magnetic pinned layer disposed on the AF coupling layer; and a second AF pinning layer disposed on the magnetic pinned layer. In an embodiment, a method of unpinning a pinned free layer uses a current pulse through the MR sensor to self-heat above a blocking temperature of the AF pinning layer, and then reading the MR sensor after the current pulse is reduced or removed and the MR sensor cools back below the blocking temperature.