Spin Hall Effect Layer for Hard Disk Drive Noise Reduction
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Solution Overview
Problem
Current hard disk drive (HDD) technologies face challenges in reducing spin torque noise in magnetoresistive (MR) sensors, particularly for sensor widths less than 25 nm and tunnel barrier resistance-area product (RA) below 0.6 Ohm-μm², which affects signal-to-noise ratio (SNR) and bit error rate (BER).
Innovation Solution
The implementation of a Spin Hall Effect (SHE) layer made of giant positive or negative Spin Hall Angle (SHA) materials between the free layer (FL) and the top shield in the reader structure. This configuration allows for a three-terminal or two-terminal design, where the SHE layer splits the current, generating spin torque that opposes the spin torque from the reference layer, thereby reducing magnetic noise in the FL.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the sensor size is reduced to increase areal density, then the areal density capability is improved, but the spin torque noise increases due to lower tunnel barrier RA product
Solution Approach 1:
A Spin Hall Effect (SHE) layer is introduced as an intermediary component between the free layer and the top shield. This SHE layer generates spin torque that opposes and cancels the harmful spin torque noise from the reference layer, enabling noise reduction without increasing sensor size
Solution Approach 2:
The patent modifies the spin torque balance by changing the effective spin torque parameter through the addition of SHE layer contribution. By controlling the SHE layer material properties (spin Hall angle) and geometry, the net spin torque on the free layer is adjusted to cancel noise while maintaining signal detection capability
2Reliability
If the tunnel barrier RA product is reduced to maintain sensor resistance at smaller sizes, then the sensor resistance is maintained, but the spin torque induced magnetic noise increases
Solution Approach 1:
The SHE layer serves as a mediator that generates counteracting spin torque to cancel the harmful spin torque induced by the reduced tunnel barrier RA product, allowing the tunnel barrier to be optimized for resistance stability without compromising noise performance
Solution Approach 2:
The patent converts the harmful spin torque effect into a beneficial noise cancellation mechanism by using the SHE layer to generate spin torque that opposes and neutralizes the harmful spin torque from the reference layer, transforming the noise problem into a controlled counteracting force
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 use of the SHE layer effectively cancels spin torque noise, enhancing the signal-to-noise ratio (SNR) and improving the bit error rate (BER), which enables smaller sensor sizes and higher areal density capabilities (ADC) in HDDs.
Implementation Method 1
a Spin Hall Effect (SHE) layer comprised of a giant positive or negative Spin Hall Angle (SHA) material is formed between a free layer (FL) in a sensor and a top shield (S2)
Data Source
AI summary
A read head is disclosed wherein a Spin Hall Effect (SHE) layer is formed on a free layer (FL) in a sensor and between the FL and top shield (S2). Preferably, the sensor has a seed layer, an AP2 reference layer, antiferromagnetic coupling layer, AP1 reference layer, and a tunnel barrier sequentially formed on a bottom shield (S1). When the stripe heights of the FL and SHE layer are equal, a two terminal configuration is employed where a current flows between one side of the SHE layer to a center portion thereof and then to S1, or vice versa. As a result, a second spin torque is generated by the SHE layer on the FL that opposes a first spin torque from the AP1 reference layer on the FL.