Tri-Layered Free Layer for Magnetoresistive Sensor Optimization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current magnetoresistive read sensors, particularly TMR and GMR configurations, face challenges in achieving high MR ratios while maintaining low areal resistance and adjustable magnetostriction, especially as sensor layers are scaled down for high-density data storage.
Innovation Solution
A novel tri-layered free layer structure comprising CoFe, CoFeB, and NiFe layers is introduced, with specific atomic percentages and thickness ranges, to enhance magnetic softness, interfacial scattering, and bulk scattering properties, thereby improving MR ratios and reducing coercivity and areal resistance in both TMR and GMR sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If sensor layers are scaled down for high-density data storage, then storage density is improved, but areal resistance increases and MR ratio decreases
Solution Approach 1:
The free layer is segmented into three distinct magnetic layers (CoFe, CoFeB, NiFe) with different compositions and thicknesses. Each layer contributes different magnetic and resistive properties, allowing optimization of both MR ratio and areal resistance independently. The CoFe layer provides high spin polarization for MR ratio, the CoFeB layer provides low coercivity for soft magnetic behavior, and the NiFe layer adjusts magnetostriction and resistance.
Solution Approach 2:
The invention uses a composite free layer structure combining three different magnetic materials (CoFe, CoFeB, NiFe) in a specific sequence and thickness ratio. This composite structure leverages the advantageous properties of each material: CoFe for high spin polarization, CoFeB for low coercivity and adjustable magnetostriction, and NiFe for resistance control and magnetostriction adjustment, achieving simultaneous optimization of MR ratio and areal resistance.
2Reliability
If CoFeB layer is added to free layer structure, then MR ratio is improved, but device complexity increases
Solution Approach 1:
The free layer is divided into three manageable magnetic layers with specific thickness ranges (CoFe: 2-30 Å, CoFeB: 5-40 Å, NiFe: 5-80 Å). This segmentation allows each layer to be optimized independently for its specific function while maintaining overall structural coherence. The layered architecture enables precise control of magnetic properties through thickness adjustment without requiring complex multi-material interfaces or unusual structures.
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 tri-layered free layer structure achieves significant improvements in MR ratios, coercivity, and magnetostriction, with MR ratios up to 30% and areal resistance as low as 0.17 ohm-μm² in TMR sensors, and 9.8% in GMR sensors, while maintaining low coercivity and adjustable magnetostriction properties.
Implementation Method 1
The physical basis for the GMR effect is the fact that the conduction electrons are spin polarized by interaction with the magnetic moments of the magnetized layers. This polarization, in turn, affects their scattering properties within the layers and, consequently, results in changes in the resistance of the layered configuration.
Implementation Method 2
The relative orientations of the two planar magnetic moments determines the electrical resistance that is experienced by a current that passes from magnetic layer to magnetic layer through the spacer layer.
Implementation Method 3
The probability of such an electron then tunneling through the intervening tunneling barrier layer into the lower electrode then depends on the availability of states within the lower electrode which the tunneling electron can occupy. This number, in turn, depends on the magnetization direction of the lower electrode. The tunneling probability is thereby spin dependent
Implementation Method 4
The antiferromagnetic layer is required to pin the pinned layer, ie., to fix the direction of its magnetic moment by exchange coupling.
Implementation Method 5
The tri-layered free layer structure achieves significant improvements in MR ratios, coercivity, and magnetostriction, with MR ratios up to 30% and areal resistance as low as 0.17 ohm-μm² in TMR sensors
Data Source
AI summary
A TMR sensor, a CPP GMR sensor and a CCP CPP GMR sensor all include a tri-layered free layer that is of the form CoFe/CoFeB/NiFe, where the atom percentage of Fe can vary between 5% and 90% and the atom percentage of B can vary between 5% and 30%. The sensors also include SyAP pinned layers which, in the case of the GMR sensors include at least one layer of CoFe laminated onto a thin layer of Cu. In the CCP CPP sensor, a layer of oxidized aluminum containing segregated particles of copper is formed between the spacer layer and the free layer. All three configurations exhibit extremely good values of coercivity, areal resistance, GMR ratio and magnetostriction.