STT Device Template Layer Reduces Critical Current Density
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Spin transfer torque (STT) devices with Heusler alloy magnetic layers face challenges in reducing the critical current density, which is exacerbated by high-temperature annealing requirements and affects the reliability of write heads in magnetic recording systems.
Innovation Solution
Incorporating a template layer, such as a ferromagnetic CoFeBTa alloy, beneath the Heusler alloy layer in the ferromagnetic free layer to reduce the critical current density, and using a similar template layer in the polarizing layer to enhance the crystalline structure and spin polarization, thereby reducing the critical current density and improving the reliability of STT devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high-temperature annealing is used to form Heusler alloy magnetic layers, then the crystalline structure is improved, but the reliability of write heads deteriorates due to high temperatures
Solution Approach 1:
The patent divides the magnetic layer into two separate segments: a template layer (CoFeB or CoFeBTa) and a Heusler alloy layer. The template layer is formed first and provides the crystalline structure, while the Heusler alloy layer is deposited on top. This segmentation allows the template layer to be formed at lower temperatures, avoiding the reliability issues of high-temperature annealing while still achieving the desired crystalline structure for spin polarization.
Solution Approach 2:
The template layer acts as an intermediary between the substrate and the Heusler alloy layer. It provides the necessary crystalline template that enables the Heusler alloy to form with proper structure without requiring high-temperature annealing. The template layer mediates the formation process, allowing low-temperature deposition while maintaining the crystalline quality needed for high spin polarization.
2Object-affected harmful factors
If Heusler alloy layers are used to achieve high spin polarization, then the spin polarization is improved, but the critical current density remains too high
Solution Approach 1:
The patent changes the material composition parameters by introducing template layers with specific compositions (CoFeB or CoFeBTa) that have different magnetic and structural properties than conventional Heusler alloys alone. This parameter change in material composition enables achieving high spin polarization with lower critical current density, as the template layer facilitates better spin polarization efficiency.
3Device complexity
If conventional magnetic layers are used, then the device structure is simpler, but the spin polarization is insufficient
Solution Approach 1:
The patent uses composite material structures where a template layer (CoFeB or CoFeBTa) is combined with a Heusler alloy layer. This composite structure leverages the advantages of both materials: the template layer provides excellent crystalline structure and magnetic properties, while the Heusler alloy layer contributes to spin polarization. The composite approach achieves high spin polarization that cannot be obtained with conventional single-layer magnetic 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 implementation of the template layer results in a 30% reduction in critical current density and improved magnetoresistance, enhancing the performance and reliability of STT devices, particularly in high-temperature environments like disk drive write heads.
Implementation Method 1
Spin transfer torque (STT) is an effect in which the orientation of the magnetization of a magnetic layer in a magnetic tunnel junction (MTJ) or giant magnetoresistance (GMR) spin valve can be modified using a spin-polarized current.
Implementation Method 2
Heusler alloy layers are known to have high spin polarization
Implementation Method 3
Heusler alloy layers are difficult to fabricate and require high-temperature annealing to obtain the required crystalline structure
Implementation Method 4
When spin-polarized current above a critical current density is directed into a second, thinner magnetic layer (the 'free' layer), angular momentum can be transferred to the free layer, changing the orientation of the free layer's magnetization.
Data Source
AI summary
A spin transfer torque (STT) device has a free ferromagnetic layer that includes a Heusler alloy layer and a template layer beneath and in contact with the Heusler alloy layer. The template layer may be a ferromagnetic alloy comprising one or more of Co, Ni and Fe and the element X, where X is selected from one or, more of Ta, B, Hf, Zr, W, Nb and Mo. A CoFe nanolayer may be formed below and in contact with the template layer. The STT device may be a spin-torque oscillator (STO), like a STO incorporated into the write head of a magnetic recording disk drive. The STT device may also be a STT in-plane or perpendicular magnetic tunnel junction (MTJ) cell for magnetic random access memory (MRAM). The template layer reduces the critical current density of the STT device.