Boron-Free STT Memory Cells for High TMR
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Solution Overview
Problem
Current spin transfer torque memory cells face limitations in achieving high tunneling magnetoresistance (TMR) ratios and reliable perpendicular magnetic anisotropy due to the presence of boron, which affects the crystal structure and spin-filtering properties of the storage and tunnel barrier materials.
Innovation Solution
The formation of spin transfer torque memory cells using a process that includes an amorphous material, a boron-free storage material, an interfacial perpendicular magnetic anisotropy (IPMA) material, and a reference material, all with a nearly perfect body-centered cubic structure, where high-temperature annealing is used to diffuse boron out and achieve a relaxed lattice constant, resulting in improved TMR ratios and crystallinity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If boron is added to storage and tunnel barrier materials to improve crystallinity, then crystal structure formation is enhanced, but TMR ratio and spin-filtering properties deteriorate
Solution Approach 1:
The patent removes boron from the storage and tunnel barrier materials to eliminate its harmful effects on TMR ratio and spin-filtering properties. By extracting the problematic element, the invention achieves high TMR ratios (>150%) and reliable perpendicular magnetic anisotropy without compromising crystallinity, as the materials form proper body-centered cubic structures without boron addition.
Solution Approach 2:
The invention changes the compositional parameter by using boron-free materials and adjusts processing parameters through high-temperature annealing (500-700°C) to achieve the desired crystal structure. This parameter change eliminates the trade-off between crystallinity and TMR ratio, allowing both to be optimized simultaneously.
2Ease of manufacture
If conventional materials are used in STT memory cells, then manufacturing process is simpler, but perpendicular magnetic anisotropy and spin-filtering properties are insufficient
Solution Approach 1:
The patent employs composite material structures including CoFeB storage material, MgO tunnel barrier, and CoFeB reference material, each with specific thicknesses and orientations. This composite approach achieves strong perpendicular magnetic anisotropy and high TMR ratios while maintaining compatibility with existing semiconductor manufacturing processes through standardized deposition and annealing techniques.
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 by 150% and improves the reliability of the tunnel barrier, leading to stronger perpendicular magnetic anisotropy and better spin-filtering properties compared to conventional STT cells.
Implementation Method 1
high-temperature annealing is used to diffuse boron out and achieve a relaxed lattice constant
Implementation Method 2
STT utilizes spin-polarized current, e.g., a current where most of the electrons have spins aligned in the same direction, which is applied to the storage material. The electrons may get repolarized due to the orientation of the magnetic moments of the storage layer. This repolarizing of the electrons can lead to the storage material experiencing a torque associated with the change in the angular momentum of the electrons as they are repolarized.
Implementation Method 3
an interfacial perpendicular magnetic anisotropy (IPMA) material formed on the storage material
Data Source
AI summary
Spin transfer torque memory cells and methods of forming the same are described herein. As an example, spin transfer torque memory cells may include an amorphous material, a storage material formed on the amorphous material, wherein the storage material is substantially boron free, an interfacial perpendicular magnetic anisotropy material formed on the storage material, a reference material formed on the interfacial perpendicular magnetic anisotropy material, wherein the reference material is substantially boron free, a buffer material formed on the reference material and a pinning material formed on the buffer material.