Ru Underlayer for Perpendicular MTJ Film Growth
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Solution Overview
Problem
Conventional perpendicularly magnetized films face challenges in achieving high-quality growth with a heat-resistant underlayer and sufficient magnetic anisotropy energy density, as well as lattice mismatch issues and poor heat resistance, which hinder the enhancement of magnetic recording media and MTJ elements.
Innovation Solution
A Ru underlayer with a hexagonal close-packed structure is used, which provides high crystal orientation and heat resistance, allowing for the growth of cubic or tetragonal perpendicularly magnetized films with enhanced magnetic anisotropy and TMR ratio, and can be applied to various materials with similar structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional L10 type alloys or MgO underlayers are used, then the underlayer structure is established, but lattice mismatch of close to 10% occurs and high crystallinity cannot be realized
Solution Approach 1:
The patent changes the crystal structure parameter of the underlayer from cubic (MgO) or complex (L10 alloy) to hexagonal close-packed (hcp) structure with specific lattice constants. This parameter change reduces lattice mismatch from 10% to approximately 3% with Co-based alloys, enabling high crystallinity and proper crystal orientation for perpendicular magnetization.
2Reliability
If conventional underlayers such as Cr or Ta are used for interface-induced perpendicular magnetization, then perpendicular magnetization is achieved, but heat resistance becomes poor and heating treatment cannot be implemented
Solution Approach 1:
The patent changes the material parameter of the underlayer to hcp-structured metals (Ru, Re, Os, Rh, Ir) that possess both perpendicular magnetization capability through interface effects and high heat resistance. This allows heating treatment at temperatures above 400°C to be implemented while maintaining structural integrity and achieving TMR ratio enhancement.
3Manufacturing precision
If conventional underlayers are used, then film growth occurs, but distortion is transmitted to the ferromagnetic layer and sufficient characteristics cannot be extracted
Solution Approach 1:
The patent changes the lattice constant and crystal structure parameters of the underlayer to match closely with Co-based ferromagnetic alloys. The hcp structure with specific lattice constants minimizes lattice mismatch and prevents distortion transmission to the ferromagnetic layer, enabling the extraction of sufficient magnetic characteristics and high recording density.
4Manufacturing precision
If Ru underlayer with hcp structure is used, then high crystal orientation and heat resistance are achieved, but the specific angle range for [0001] direction must be controlled
Solution Approach 1:
The patent specifies precise angular parameters for the [0001] direction of the hcp underlayer relative to the substrate, defining a critical angle range of 42° to 54°. This parameter control ensures optimal crystal orientation that promotes perpendicular magnetization while maintaining manufacturability through standard thin film deposition 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
The Ru underlayer enables the growth of perpendicularly magnetized films with high heat resistance and increased magnetic anisotropy energy density, improving the quality of magnetic recording media and MTJ elements by reducing lattice mismatch and distortion effects.
Implementation Method 1
a Ru underlayer having a high crystal orientation index and having an hcp structure, which is obtained on an MgO layer by controlling the growth conditions, and found that a cubic cobalt-iron-aluminum (Co2FeAl) alloy thin film grown on the Ru underlayer is formed with the (001) orientation
Implementation Method 2
perpendicular magnetization can be realized even for soft magnetic materials such as cobalt-iron-boron (CoFeB) or iron (Fe), which do not exhibit perpendicular magnetization in a bulk state, when the interface effect of an ultrathin film structure is utilized
Data Source
AI summary
Disclosed is a perpendicularly magnetized film structure using a highly heat resistant underlayer film on which a cubic or tetragonal perpendicularly magnetized film can grow, comprising a substrate of a cubic single crystal substrate having a (001) plane or a substrate having a cubic oriented film that grows to have the (001) plane; an underlayer formed on the substrate from a thin film of a metal having an hcp structure in which the [0001] direction of the thin metal film forms an angle in the range of 42° to 54° with respect to the <001> direction or the (001) orientation of the substrate; and a perpendicularly magnetized layer located on the metal underlayer and formed from a cubic material selected from a Co-based Heusler alloy and a cobalt-iron (CoFe) alloy having a bcc structure a constituent material, and grown to have the (001) plane.