TMR Device Oxygen Surfactant Layer Tunnel Barrier Uniformity
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Solution Overview
Problem
Current TMR elements face challenges in achieving high TMR ratio and low RA values due to non-uniform tunnel barrier layers, which affect the performance of magnetic devices such as MRAM and magnetic read heads.
Innovation Solution
A method is introduced to form a TMR element with an oxygen surfactant layer on the inner pinned layer, promoting smoother overlying tunnel barrier and free layer formation, achieved by treating a CoFeXBY/CoFeZ composite pinned layer with oxygen plasma, resulting in a thin and uniform AlOx tunnel barrier layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional pinned layer structure is used, then the device structure is simple, but the tunnel barrier layer uniformity is poor resulting in low TMR ratio and high RA values
Solution Approach 1:
The pinned layer is divided into multiple sub-layers with different compositions (CoFeB, CoFe, CoFeZr) and thicknesses. Each sub-layer serves a specific function: CoFeB provides smooth interface, CoFe provides magnetic properties, and CoFeZr provides structural stability. This segmentation allows optimization of each layer's properties to achieve uniform tunnel barrier formation while maintaining overall device performance.
Solution Approach 2:
The invention uses composite material structure for the pinned layer, combining multiple alloy systems (Co-Fe-B, Co-Fe, Co-Fe-Zr) in a stacked configuration. This composite approach leverages the advantages of each material: boron for interface smoothness, iron for magnetic properties, and zirconium for structural stability, resulting in improved tunnel barrier uniformity and enhanced TMR ratio.
2Reliability
If the tunnel barrier layer is made thinner to reduce RA values, then the resistance decreases, but the uniformity across the wafer deteriorates
Solution Approach 1:
The pinned layer structure is specifically designed and prepared in advance with optimized composition gradients and thickness profiles before the tunnel barrier deposition. The CoFeB bottom sub-layer is engineered to provide a pre-smoothed interface that anticipates and compensates for deposition variations, ensuring uniform barrier formation even at reduced thicknesses for low RA values.
Solution Approach 2:
The invention optimizes multiple parameters including the thickness of each pinned layer sub-layer (ranging from 5-20 nm), the composition ratios (e.g., B content 5-15 at%, Zr content 5-15 at%), and the deposition conditions. By carefully adjusting these parameters, the system achieves the optimal balance between barrier thickness for low RA and uniformity for high TMR ratio.
3Measurement precision
If the TMR ratio is increased to improve signal detection, then the resistance contrast improves, but the RA value increases reducing device performance
Solution Approach 1:
The pinned layer structure implements local quality optimization by assigning different compositions and thicknesses to different sub-layers based on their specific functions. The bottom CoFeB sub-layer is optimized for interface smoothness to enhance TMR ratio, while the overall structure is tuned to maintain appropriate resistance characteristics, achieving local optimization that benefits overall device performance.
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 approach enhances the TMR ratio to at least 20% and maintains RA values below 10 ohm/μm², while ensuring uniformity across a six-inch wafer, improving the performance and reliability of TMR elements in both MRAM and read head applications.
Implementation Method 1
treating a CoFeXBY/CoFeZ composite pinned layer with oxygen plasma, resulting in a thin and uniform AlOx tunnel barrier layer
Implementation Method 2
forming a TMR element with an oxygen surfactant layer on the inner pinned layer
Implementation Method 3
oxidizing the Al layer to form a thin and uniform AlOx tunnel barrier layer
Data Source
AI summary
A high performance TMR element is fabricated by inserting an oxygen surfactant layer (OSL) between a pinned layer and AlOx tunnel barrier layer in a bottom spin valve configuration. The pinned layer preferably has a SyAP configuration with an outer pinned layer, a Ru coupling layer, and an inner pinned layer comprised of CoFeXBY/CoFeZ wherein x=0 to 70 atomic %, y=0 to 30 atomic %, and z=0 to 100 atomic %. The OSL is formed by treating the CoFeZ layer with oxygen plasma. The AlOx tunnel barrier has improved uniformity of about 2% across a 6 inch wafer and can be formed from an Al layer as thin as 5 Angstroms. As a result, the Hin value can be decreased by ⅓ to about 32 Oe. A dR/R of 25% and a RA of 3 ohm-cm2 have been achieved for TMR read head applications.