TMR Read Head Gap Reduction via Seed Layer Segmentation
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Solution Overview
Problem
Tunneling magnetoresistance (TMR) read heads in magnetic recording disk drives face challenges in reducing the read gap thickness without compromising magnetoresistance and magnetic properties, which limits their ability to detect smaller data bits effectively.
Innovation Solution
A multilayer seed layer is magnetically coupled to the lower shield, acting as part of the shield rather than the sensor, and an improved free layer/capping layer structure with negative magnetostriction is used, eliminating NiFe from the free layer and incorporating Hf to reduce the read gap thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the read gap thickness is reduced to detect smaller data bits, then the detection capability for smaller bits is improved, but the magnetoresistance and magnetic properties are compromised
Solution Approach 1:
The seed layer is segmented into multiple ferromagnetic layers (first ferromagnetic seed layer, second ferromagnetic seed layer) separated by nonmagnetic spacer layers. This segmentation allows the seed layer to be magnetically coupled to the lower shield while reducing its overall magnetic moment contribution, enabling thinner read gap without sacrificing magnetoresistance.
Solution Approach 2:
The magnetization orientation of the seed layer is changed from perpendicular (out-of-plane) to in-plane orientation through magnetic coupling with the lower shield. This parameter change reduces the seed layer's effective magnetic moment in the perpendicular direction, allowing reduced read gap thickness while maintaining the magnetoresistance ratio required for reliable bit detection.
2Length of moving object
If NiFe is removed from the free layer to reduce magnetostriction, then the read gap thickness can be reduced, but the negative magnetostriction property is lost
Solution Approach 1:
An Hf-containing interface layer is introduced as an intermediary between the CoB/CoFeB upper layer and the MgO tunneling barrier. This interface layer provides the necessary negative magnetostriction effect that was previously achieved only through NiFe, enabling read gap reduction while maintaining the magnetic stability required for reliable operation.
Solution Approach 2:
The free layer uses a composite structure combining CoB or CoFeB upper layer with an Hf-containing interface layer. This composite material approach replaces the traditional NiFe layer, achieving negative magnetostriction through the Hf-containing interface layer while using Co-based materials for the upper layer to optimize magnetoresistance and magnetic properties.
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 solution effectively reduces the read gap thickness while maintaining magnetoresistance and magnetic properties, enabling the detection of smaller data bits and enhancing recording density.
Implementation Method 1
The Hf-containing interface layer possesses negative magnetostriction when the Hf is present within a certain composition range, but at least about 5 at. %.
Implementation Method 2
The barrier layer is typically made of a metallic oxide, typically MgO, that is so sufficiently thin that quantum-mechanical tunneling of charge carriers occurs between the two ferromagnetic layers. This quantum-mechanical tunneling process is electron spin dependent
Implementation Method 3
A multilayer seed layer below the antiferromagnetic layer is magnetically coupled to the lower shield S1 and thus acts as part of the shield rather than part of the sensor.
Data Source
AI summary
A tunneling magnetoresistive (TMR) read head has a read gap with a reduced thickness. A multilayer seed layer includes a first ferromagnetic seed layer on the lower shield, a ferromagnetic NiFe alloy on the first seed layer, and a third seed layer of Ru or Pt on the NiFe seed layer. The first and NiFe seed layers are magnetically part of the lower shield, thereby effectively reducing the read gap thickness. A free layer/capping layer structure includes a multilayer ferromagnetic free layer and a Hf capping layer on the free layer. The free layer includes a B-containing upper layer in contact with the Hf capping layer prior to annealing. When the sensor is annealed Hf diffuses into the B-containing upper layer, forming an interface layer. The Hf-containing interface layer possesses negative magnetostriction, so the free layer is not required to contain NiFe.