STT Device Multilayer Seed Layers Resistivity
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Solution Overview
Problem
In perpendicular magnetic recording systems, the reduction in magnetic grain size for increased recording density leads to conflicted limitations on magneto-crystalline anisotropy, requiring higher write fields and thermal stability, while conventional seed layers in spin transfer torque devices exhibit high resistance and undesirable characteristics.
Innovation Solution
A spin transfer torque device with a multilayer seed layer stack comprising a first seed layer of Cr, a second seed layer of Ta or Ru, a ferromagnetic free layer, and a nonmagnetic spacer layer, which reduces resistivity and improves ferromagnetic coupling and adhesion, enabling efficient magnetization switching and recording.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional single-layer seed layers are used in STT devices, then the device structure is simple, but the resistivity is high and adhesion is poor
Solution Approach 1:
The single-layer seed layer is segmented into multiple layers (e.g., CoFeB/CoFe) with distinct functions. The CoFeB layer provides low resistivity and good adhesion to the substrate, while the CoFe layer provides excellent ferromagnetic coupling to the free layer. This segmentation allows each layer to optimize its specific function, resolving the contradiction between simplicity and performance.
Solution Approach 2:
The seed layer uses composite material structure combining CoFeB and CoFe alloys. CoFeB contributes low damping and high spin polarization for reduced resistivity, while CoFe contributes high saturation magnetization for improved ferromagnetic coupling. This composite approach achieves superior overall performance without requiring complex multi-component systems.
2Quantity of substance
If magnetic grain size is reduced for increased recording density, then recording density increases, but magneto-crystalline anisotropy becomes conflicted between thermal stability and write field requirements
Solution Approach 1:
The invention changes the material parameters of the seed layer (composition, thickness, magnetization) to optimize the magnetic properties of the free layer. By adjusting the CoFeB/CoFe thickness ratio and magnetic coupling strength, the anisotropy energy barrier can be tuned to maintain thermal stability even as grain size decreases for higher recording density.
Solution Approach 2:
The invention replaces reliance on purely geometric constraints (grain size) for thermal stability with material property optimization (seed layer composition and magnetic coupling). This substitution allows thermal stability to be maintained through material design rather than solely through increasing grain size, enabling higher recording density.
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 multilayer seed layer configuration reduces switching current magnitude, enhances adhesion, and improves thermal stability, allowing for increased recording density and efficient magnetization switching in spin transfer torque devices.
Implementation Method 1
The multilayer seed layer configuration reduces resistivity by one order of magnitude
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
Implementation Method 3
a ferromagnetic free layer on the second seed layer; a ferromagnetic polarizing layer
Data Source
AI summary
Spin transfer torque (STT) devices with multilayer seed layers that can be used in magnetic recording and memory are provided. One such STT device includes a substrate, and a stack of layers formed on the substrate, where the stack includes a first seed layer directly on the substrate and including Cr, a second seed layer on the first seed layer and including Ta, a ferromagnetic free layer on the second seed layer; a ferromagnetic polarizing layer, and a nonmagnetic spacer layer between the free layer and the polarizing layer. One such method includes fabricating the STT device.