Cube-Textured pMTJ Reference Layer for High MR and Strong Pinning
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Solution Overview
Problem
Conventional perpendicular magnetic tunnel junctions (pMTJs) face challenges in achieving a highly BCC (100) textured reference layer with strong magnetic pinning due to the deterioration of PMA properties at lower temperatures and difficulties in forming a BCC (100) textured CoFe reference layer on FCC (111) textured substrates, leading to mixed textures and degradation of magnetoresistance ratios.
Innovation Solution
A pMTJ element comprising a perpendicular synthetic anti-ferromagnetic (pSAF) stack, an oxide buffer layer, and a cube-textured reference layer with a texture starting layer and spin polarization layer, where the oxide buffer layer ensures strong magnetic coupling and the cube-textured reference layer is formed through a non-epitaxial texturing method to achieve a BCC (100) texture, enhancing magnetic pinning and magnetoresistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional pMTJ structure with FCC (111) textured substrate is used, then the device can be manufactured with standard processes, but the reference layer develops mixed textures and shows degraded magnetoresistance ratio
Solution Approach 1:
An oxide buffer layer is introduced as an intermediary between the FCC (111) textured substrate and the reference layer. This buffer layer has a different crystal structure that prevents the propagation of FCC texture to the reference layer, enabling the reference layer to develop a uniform BCC (100) texture without being influenced by the substrate's FCC texture, thereby resolving the texture mismatch problem and restoring high magnetoresistance ratio
Solution Approach 2:
The invention changes the crystallographic parameters and texture orientation of the reference layer by controlling the deposition conditions and using the oxide buffer layer as a template. The reference layer is transformed from developing mixed textures to achieving a uniform BCC (100) texture, which has different magnetic and transport properties that enable high magnetoresistance ratio while maintaining compatibility with standard manufacturing processes
2Temperature
If the PMA material multilayer is used directly without oxide buffer, then the magnetic pinning can be achieved, but the PMA properties deteriorate at lower temperatures
Solution Approach 1:
The oxide buffer layer serves as a thermal and magnetic intermediary between the PMA material multilayer and the reference layer. It provides thermal stability by acting as a thermal barrier while maintaining strong magnetic coupling through exchange interaction, allowing the system to retain magnetic pinning strength at lower temperatures without direct contact between the PMA layers and reference layer
Solution Approach 2:
The invention creates a composite structure combining the PMA material multilayer with the oxide buffer layer. This composite structure leverages the high perpendicular magnetic anisotropy of the PMA materials while the oxide buffer provides thermal stability and controlled magnetic coupling, achieving both thermal stability and strong magnetic pinning that neither component could achieve alone
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 achieves a high tunneling magnetoresistance ratio of at least 150% at room temperature, maintaining thermal stability and magnetic pinning, while avoiding the limitations of traditional texture breaking layers, thus improving the performance and reliability of pMTJ elements.
Implementation Method 1
The OB layer sandwiched between the pSAF stack and the cube-textured reference layer is thin enough to produce a strong magnetic parallel-coupling between the reference layer and the pSAF stack
Implementation Method 2
MgO-based magnetic tunnel junctions (MTJs) having a highly textured sandwich structure: BCC (100) CoFe (reference layer)/rocksalt (100) MgO (tunnel barrier layer)/BCC (100) CoFe (free layer), exhibit high magnetoresistance (MR) ratios due to the so-called coherent tunneling effect
Implementation Method 3
perpendicular magnetoresistive elements having perpendicular magnetoresistive elements as basic memory cells
Data Source
AI summary
The invention comprises a method of forming a novel magnetic pinning structure having a (100) textured or cube-textured reference layer through a non-epitaxial texturing approach so that an excellent coherent tunneling effect is achieved in a pMTJ element due to its texture structure of CoFe BCC (100)/MgO rocksalt (100)/CoFe BCC (100). Correspondingly, a high MR ratio and a high pinning strength on the reference layer can be achieved for perpendicular spin-transfer-torque magnetic-random-access memory (pSTT-MRAM) using perpendicular magnetoresistive elements as basic memory cells which potentially replace the conventional semiconductor memory used in electronic chips, especially mobile chips for power saving and non-volatility.