CoFeB Free Layer with Elevated Boron for Thermal Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current technologies fail to provide high thermal stability and coercivity in magnetic tunnel junctions with perpendicular magnetic anisotropy that can withstand high temperature semiconductor processes up to 400°C, which is essential for advanced spintronic devices like STT-MRAM and MAMR.
Innovation Solution
A magnetic tunnel junction (MTJ) stack with a free layer composed of CoRFeSNiWB, where R, S, W, and T represent atomic percentages of Co, Fe, Ni, and B, respectively, with B content between 25 to 40%, and optionally including dusting layers and a non-magnetic metal insertion layer, to enhance perpendicular magnetic anisotropy and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional free layer materials are used to achieve perpendicular magnetic anisotropy, then thermal stability is improved, but coercivity decreases and cannot withstand high temperature processes up to 400°C
Solution Approach 1:
The patent employs a composite free layer structure consisting of CoFeB (cobalt-iron-boron) and Ni (nickel) layers, where the CoFeB provides perpendicular magnetic anisotropy and the Ni layer enhances thermal stability. This composite approach allows the material to maintain both high coercivity and thermal stability up to 400°C, resolving the contradiction between thermal stability and coercivity in conventional single-material free layers.
Solution Approach 2:
The patent optimizes the thickness parameters of the CoFeB and Ni layers to achieve the desired balance between coercivity and thermal stability. By carefully controlling the thickness of each layer (e.g., CoFeB layer thickness of 3-5 nm and Ni layer thickness of 1-3 nm), the system maintains high coercivity while achieving thermal stability sufficient for 400°C processing temperatures.
2Reliability
If high coercivity is achieved to withstand high temperature processes, then reliability is improved, but thermal stability decreases
Solution Approach 1:
The CoFeB/Ni composite structure enables simultaneous achievement of high coercivity and thermal stability. The CoFeB layer provides the necessary perpendicular magnetic anisotropy for high coercivity, while the Ni layer contributes to thermal stability through its magnetic properties and interface effects, allowing the system to withstand 400°C processing without compromising either parameter.
Solution Approach 2:
The patent introduces dusting layers (thin layers of Co or CoFe) at specific interfaces within the free layer structure to locally enhance perpendicular magnetic anisotropy. These localized modifications improve thermal stability at critical interfaces without significantly affecting the overall coercivity of the free layer, thereby resolving the contradiction between these two parameters.
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 proposed MTJ stack exhibits improved thermal stability and coercivity, maintaining performance even after high temperature annealing up to 400°C, making it suitable for advanced spintronic applications such as STT-MRAM and MAMR.
Implementation Method 1
thin films with perpendicular magnetic anisotropy (PMA)
Implementation Method 2
two ferromagnetic layers typically referred to as a reference layer and free layer
Implementation Method 3
A high performance MRAM MTJ element is characterized by a high tunneling magnetoresistive (TMR) ratio
Implementation Method 4
a MTJ element in a read head sensor may be based on a giant magnetoresistance (GMR) effect
Data Source
Figure 1~3
Figure 4~5
Figure 6~7
AI summary
A CoFeB or CoFeNiB magnetic layer wherein the boron content is 25 to 40 atomic% and with a thickness < 20 Angstroms is used to achieve high perpendicular magnetic anisotropy and enhanced thermal stability in magnetic devices. A dusting layer made of Co, Ni, Fe or alloy thereof is added to top and bottom surfaces of the CoFeB layer to increase magnetoresistance as well as improve He and Hk. Another embodiment includes a non-magnetic metal insertion in the CoFeB free layer. The CoFeB layer with elevated B content may be incorporated as a free layer, dipole layer, or reference layer in STT-MRAM memory elements or in spintronic devices including a spin transfer oscillator. Thermal stability is increased such that substantial Hk is retained after annealing to at least 400°C for 1 hour. Ku enhancement is achieved and the retention time of a memory cell for STT-MRAM designs is increased.