STT Device Template Layer Reduces Critical Current Density
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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 temperatures that can affect the long-term reliability of write heads in magnetic recording systems.
Innovation Solution
Incorporating a template layer, such as a ferromagnetic CoFeBTa alloy, beneath and in contact with the Heusler alloy layer in the ferromagnetic free layer, and optionally in the polarizing layer, to reduce the critical current density and enhance the crystalline structure of Heusler alloys, thereby improving the reliability and performance of STT devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high-temperature annealing is used to obtain the required crystalline structure of Heusler alloy layers, then the crystalline quality is improved, but the long-term reliability of write heads deteriorates
Solution Approach 1:
A template layer comprising a ferromagnetic alloy (Co, Ni and Fe) and element X (Ta, B, Hf, Zr, W, Nb or Mo) is introduced between the substrate and the Heusler alloy layer. This template layer serves as an intermediary that provides a crystalline template during deposition, enabling the Heusler alloy to form with the required L21 crystalline structure at lower annealing temperatures, thus preventing thermal damage to the write head while ensuring proper crystalline quality
Solution Approach 2:
The invention changes the deposition parameters by using a template layer that enables formation of the Heusler alloy layer at lower temperatures. The template layer modifies the growth conditions and crystalline structure development, allowing the system to achieve the desired crystalline quality at reduced temperatures, thereby resolving the contradiction between manufacturing precision and reliability
2Reliability
If the critical current density is reduced to improve reliability, then the operational safety margin increases, but the ability to switch magnetization becomes insufficient
Solution Approach 1:
The invention uses a composite structure consisting of a template layer (ferromagnetic alloy with element X) and a Heusler alloy layer. This composite material system combines the beneficial properties of both layers: the template layer provides structural stability and crystalline template, while the Heusler alloy layer provides high spin polarization. The synergistic combination achieves both low critical current density and sufficient switching force
Solution Approach 2:
The template layer is strategically positioned beneath the Heusler alloy layer to provide localized structural support and crystalline orientation. This local quality enhancement at the interface enables the Heusler alloy to maintain its high spin polarization properties while reducing the overall critical current density of the magnetic tunnel junction
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 use of template layers effectively reduces the critical current density by up to 30%, enhancing the reliability of STT devices and maintaining performance even at lower annealing temperatures, thus addressing the reliability concerns associated with high temperatures.
Implementation Method 1
Heusler alloy layers are difficult to fabricate and require high-temperature annealing to obtain the required crystalline structure
Implementation Method 2
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
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.