Magnetic Sensor Free Layer Back Edge Angle Optimization
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Solution Overview
Problem
Magnetic read heads with smaller magnetoresistive effect elements face reduced magnetic stability due to decreased exchange coupling between the pinned and AFM layers, leading to weakened pinning strength, which complicates manufacturability and sensor performance.
Innovation Solution
A magnetic sensor design featuring a magnetic free layer extending from the air bearing surface with a back edge formed at an angle of 6 to 10 degrees, and a pinned layer extending beyond, with a non-magnetic layer sandwiched between, optimized through a method involving ion milling at an angle to define the back edge angle and prevent damage or performance degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the magnetoresistive effect element is made smaller to increase data density, then storage capacity increases, but magnetic stability deteriorates due to reduced exchange coupling between pinned layer and AFM layer
Solution Approach 1:
The patent extends the pinned layer in the vertical dimension (stripe height) beyond the free layer, creating a stepped structure where the pinned layer has greater height than width extension. This vertical dimensionality change increases the exchange coupling area without increasing the lateral footprint, thus improving magnetic stability while maintaining small element size for high data density.
Solution Approach 2:
The extended pinned layer structure embeds additional functional area within the existing element footprint. By nesting the extended pinned layer region within the overall sensor structure, the patent increases the effective coupling area without proportionally increasing the total device area, resolving the contradiction between small size and magnetic stability.
2Reliability
If the pinned layer is extended further from the air bearing surface to improve pinning strength, then magnetic stability improves, but manufacturability becomes more difficult
Solution Approach 1:
The patent applies local quality by extending only the pinned layer (not the entire magnetoresistive stack) beyond the free layer. This localized extension concentrates the stability-enhancing function in the pinned layer region while keeping other layers at their original dimensions, simplifying the manufacturing process compared to extending all layers uniformly.
Solution Approach 2:
The magnetoresistive effect element is segmented into regions with different stripe heights: the pinned layer extends to a second stripe height while the free layer terminates at a first stripe height. This segmentation allows independent optimization of each layer's dimensions, improving pinning strength through the extended pinned layer region while maintaining manufacturability by clearly defining discrete layer boundaries.
3Manufacturing precision
If ion milling is performed at a steep angle to define the back edge, then manufacturing precision improves, but the pinned layer may be damaged reducing pinning strength
Solution Approach 1:
The patent optimizes the ion milling angle parameter to a specific range (6 to 10 degrees from normal) that balances two competing requirements: sufficiently steep to define a precise back edge with appropriate angle (6 to 10 degrees relative to air bearing surface), yet gentle enough to prevent damage to the pinned layer. This parameter optimization resolves the contradiction between precision and damage prevention.
4Measurement precision
If the free layer back edge angle is increased to improve sensor performance, then MR ratio improves, but pinned layer stability deteriorates
Solution Approach 1:
The patent identifies and optimizes the back edge angle as a critical parameter, specifying it should be 6 to 10 degrees relative to the air bearing surface. This parameter optimization achieves the dual goal of improving sensor performance (MR ratio) through appropriate angle geometry while maintaining pinned layer stability by avoiding excessive angles that would compromise structural integrity.
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 enhances sensor performance and stability by maintaining optimal pinning strength and MR ratio, avoiding damage to the pinned layer and ensuring robustness, while maintaining high data density capabilities.
Implementation Method 1
An ion milling is then performed to remove portions of the magnetic free layer that are not protected by the first mask, the ion milling being performed at an angle of 6 to 10 degrees relative to normal so as to form the magnetic free layer with a back edge that defines an angle of 6 to 10 degrees relative to the air bearing surface plane.
Implementation Method 2
Magnetic read heads that use magnetoresistive (MR) effect elements are used for reading the information on the magnetic disks of magnetic disk storage devices. Due to the effect of the magnetic disk information magnetic field, the magnetization direction of the free layer is changed with relative to the magnetization direction of the pinned layer, whose magnetic force direction is fixed by the antiferromagnetic layer, and this changes the overall resistance of the magnetoresistive effect element.
Data Source
AI summary
A magnetic read sensor having an extended pinned layer and having a free layer structure with a back edge formed at an angle for optimizing sensor performance and pinned layer pinning. The magnetic free layer has a back edge that is formed at an angle of between 6 and 10 degrees relative to a plane parallel with the air bearing surface plane. The magnetic sensor can be formed by forming the free layer stripe height with an ion milling that is performed at an angle of 6 to 10 degrees relative to normal.