Ta-Ru Bilayer Seed for IrMn Pinning in CPP Spin Valves
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Solution Overview
Problem
Conventional seed layers in CPP GMR devices, particularly with a NiFe bottom shield, face reduced effectiveness due to the ordered structure of NiFe interfering with the magnetic performance of the pinning layer, necessitating an improved seed layer that enhances pinning strength, especially in high switching fields.
Innovation Solution
A bilayer seed structure comprising tantalum and either ruthenium or copper is used to prevent structural interference from the NiFe layer, allowing for the growth of an IrMn pinning layer without magnetic complications, thereby increasing pinning strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional single layer seed layer is used in CPP GMR devices with NiFe bottom shield, then the device structure is simple, but the pinning strength of the IrMn layer is reduced due to structural interference from the NiFe layer
Solution Approach 1:
The single layer seed layer is segmented into a bilayer structure consisting of a first seed layer (Ta) and a second seed layer (Ru or Cu). The first seed layer directly contacts the NiFe bottom shield to cancel crystallographic influence, while the second seed layer provides a suitable base for IrMn growth without magnetic interference, thereby resolving the contradiction between structural simplicity and pinning strength.
Solution Approach 2:
The second seed layer (Ru or Cu) acts as an intermediary between the NiFe bottom shield and the IrMn pinning layer. It mediates the interaction by providing a non-magnetic interface that prevents structural interference from propagating to the IrMn layer, thus enhancing pinning strength without requiring complex multi-layer structures.
2Reliability
If a single layer seed layer is used, then the manufacturing process is simple, but the growth of IrMn layer is compromised due to magnetic complications from the NiFe structure
Solution Approach 1:
The seed layer is divided into two functional layers: the first layer (Ta) handles the interface with NiFe bottom shield to cancel crystallographic influence, and the second layer (Ru or Cu) provides a clean growth substrate for IrMn. This segmentation ensures reliable IrMn layer growth while maintaining compatibility with existing manufacturing processes.
Solution Approach 2:
The invention changes the material parameters of the seed layer by introducing a second layer with specific properties (non-magnetic, suitable crystal structure) that optimize the growth conditions for IrMn. This parameter change improves layer growth reliability without significantly complicating the fabrication process, as both layers can be deposited using standard sputtering techniques.
3Reliability
If the NiFe bottom shield structure is maintained, then the device architecture is preserved, but the effectiveness of the seed layer/AFM combination is reduced
Solution Approach 1:
The second seed layer (Ru or Cu) serves as an intermediary that blocks the propagation of structural interference from the NiFe bottom shield to the IrMn pinning layer. This intermediary layer preserves the NiFe bottom shield architecture while eliminating its harmful structural influence on the seed layer/AFM combination effectiveness.
Solution Approach 2:
The invention extracts the harmful crystallographic influence from the NiFe bottom shield by introducing a buffer layer that cancels this influence. The second seed layer effectively removes the adverse structural effects while maintaining the necessary device architecture, thereby improving seed layer/AFM effectiveness.
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 new seed layer structure significantly enhances the pinning strength of the IrMn layer, achieving a higher GMR ratio and maintaining the resistance area product, with a notable increase in the relative pinning strength as evident from the magneto-resistance plots and sample evaluations.
Implementation Method 1
the tantalum serves to cancel out the crystallographic influence of an underlying NiFe layer
Implementation Method 2
the ruthenium or copper provide a suitable base on which to grow an IrMn layer
Implementation Method 3
antiferromagnetic layer 12 whose purpose is to act as a pinning agent for a magnetically pinned layer
Implementation Method 4
Giant Magneto-Resistance or GMR) derives from the fact that electrons in a magnetized solid are subject to significantly less scattering by the lattice when their own magnetization vectors (due to spin) are parallel
Data Source
AI summary
The effectiveness of an IrMn pinning layer in a CPP GMR device at high switching fields has been improved by replacing the conventional single layer seed by a layer of tantalum and either ruthenium or copper. The tantalum serves to cancel out the crystallographic influence of underlying layers while the ruthenium or copper provide a suitable base on which to grow the IrMn layer.