Perpendicular Magnetoresistive Element Buffer Layer Design
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Solution Overview
Problem
Conventional perpendicular magnetoresistive elements face challenges in achieving thermal stability and low write current due to insufficient magnetic crystalline anisotropy, leading to increased damping constants and higher write currents, which complicates device miniaturization and power efficiency in spin-transfer-torque MRAM.
Innovation Solution
The proposed solution involves a magnetoresistive element with a recording layer having perpendicular magnetic anisotropy, a reference layer with invariable magnetization, and a buffer layer with a rocksalt crystal structure to induce perpendicular anisotropy, combined with a base layer, allowing for epitaxial growth and reduced damping constants, thereby enabling efficient spin-polarized current switching with reduced write current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If additional perpendicular magnetization layers (such as TbCoFe, CoPt, or multilayer (Co/Pt)n) are added to achieve thermal stability, then perpendicular anisotropy is improved, but damping constant increases and write current increases
Solution Approach 1:
The patent introduces a buffer layer as an intermediary between the recording layer and the substrate. This buffer layer mediates the interaction by providing a specific crystal structure (rocksalt with (100) plane parallel to substrate) that induces perpendicular magnetic anisotropy in the recording layer through epitaxial growth, without requiring additional heavy metal layers that would increase damping and write current.
Solution Approach 2:
The patent changes the crystal structure parameter of the buffer layer to rocksalt with specific orientation ((100) plane parallel to substrate). This parameter change in the buffer layer's crystal structure directly induces perpendicular magnetic anisotropy in the recording layer, achieving thermal stability without adding layers that would increase damping constant and write current.
2Stability of the object's composition
If perpendicular magnetization layers are added to achieve thermal stability, then perpendicular anisotropy is improved, but device complexity increases
Solution Approach 1:
The buffer layer serves as a mediating structure between the substrate and the recording layer. By providing a rocksalt crystal structure with specific orientation, it induces perpendicular anisotropy in the recording layer without requiring complex multilayer stacks of heavy metal layers, thereby simplifying the overall device structure while achieving the desired perpendicular magnetization.
3Area of moving object
If device miniaturization is pursued, then area size is reduced, but write current increases due to spin injection requirements
Solution Approach 1:
The patent changes the magnetic anisotropy parameter from in-plane to perpendicular by introducing the rocksalt buffer layer. This parameter change enables smaller device areas because perpendicular magnetization allows for more compact cell designs. Additionally, the induced perpendicular anisotropy reduces the damping constant, which further reduces write current requirements, thereby resolving the contradiction between miniaturization and write current.
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 configuration achieves thermal stability and low write currents, facilitating device miniaturization and power efficiency in perpendicular spin-transfer-torque MRAM by maintaining perpendicular magnetization and reducing the damping constant, thus enhancing the MR ratio and thermal resistance.
Implementation Method 1
at least the portion of the buffer layer interfacing to the recording layer contains a rocksalt crystal structure having the (100) plane parallel to the substrate plane
Implementation Method 2
a recording layer having magnetic anisotropy in a direction perpendicular to a film surface
Implementation Method 3
there has been suggested a write method (spin torque transfer switching technique) using spin momentum transfers. According to this method, the magnetization direction of a recording layer is reversed by applying a spin-polarized current to the magnetoresistive element
Implementation Method 4
magnetic random access memories (hereinafter referred to as MRAMs) using the magnetoresistive effect of ferromagnetic tunnel junctions
Data Source
AI summary
A perpendicular magnetoresistive element includes a novel recording layer being a multi-layer comprising a first Co-alloy layer including at least one of CoFeB, CoFeB/CoFe and CoFe/CoFeB, a second Co-alloy layer including at least one of CoFeB and CoB, an insertion layer provided between the first Co-alloy layer and the second Co-alloy layer and containing at least one element selected from Zr, Nb, W, Mo, Ru and having a thickness less than 0.5 nm, and a novel buffer layer having rocksalt crystal structure(s) interfacing to the recording layer with lattice parameter mismatch between 3% and 18%. The magnetoresistive element is annealed at an elevated temperature and both the first Co-alloy layer and the second Co-alloy layer are crystallized to form body-center cubic (bcc) CoFe or bcc Co grain having epitaxial growth with (100) plane parallel to substrate and with in-plane expansion and out-of-plane contraction.