Perpendicular MTJ with Metal Insertion Layer for Hc/Jc Ratio
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current perpendicular magnetic tunnel junction (p-MTJ) designs face challenges in achieving low switching current while maintaining high thermal stability and magnetoresistive ratio, due to issues with oxygen diffusion and nitrogen diffusion, which affect the integrity of the free layer and nitride capping layer.
Innovation Solution
Incorporating a metal insertion (MIS) layer within the free layer and optimizing the Hk enhancing layer/nitride capping layer stack with partial oxidation and a buffer layer to minimize diffusion, ensuring sufficient perpendicular anisotropy and thermal stability, and using a nitride capping layer to block nitrogen diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional p-MTJ structure is used with standard oxidation processes, then the device can be manufactured with standard processes, but oxygen diffusion into the free layer degrades the magnetic properties and increases the Hc/Jc ratio
Solution Approach 1:
A boron nitride (BN) interfacial layer is introduced between the MgO tunnel barrier and the CoFeB free layer. This intermediary layer acts as a diffusion barrier that prevents oxygen from the oxidized MgO layer from diffusing into the CoFeB free layer, while also serving as a nitrogen barrier. This resolves the contradiction by enabling standard oxidation processes without compromising magnetic property stability.
Solution Approach 2:
The patent uses a composite structure combining MgO (tunnel barrier), BN (interfacial layer), and CoFeB (free layer). The BN layer within this composite structure provides selective barrier properties that prevent oxygen diffusion while maintaining electrical tunneling characteristics, thus preserving magnetic properties during standard manufacturing oxidation processes.
2Temperature
If the MgO layer is fully oxidized to improve thermal stability, then thermal stability above 400°C is achieved, but nitrogen from the nitride capping layer diffuses into the MgO layer degrading the tunnel barrier
Solution Approach 1:
The boron nitride (BN) interfacial layer serves as a dual barrier: it prevents oxygen diffusion from MgO to CoFeB during oxidation, and also acts as a nitrogen barrier preventing nitrogen diffusion from the nitride capping layer into the MgO tunnel barrier. This intermediary layer enables full oxidation for thermal stability while preserving tunnel barrier integrity.
Solution Approach 2:
The BN interfacial layer is strategically positioned to extract or block harmful diffusion paths. It separates the oxidized MgO layer from the CoFeB free layer, preventing oxygen intrusion, and also blocks nitrogen pathways from the capping layer to the tunnel barrier, thus protecting both interfaces during high-temperature operation.
3Use of energy by moving object
If the CoFeB free layer is made thinner to reduce switching current, then switching current is reduced, but the perpendicular magnetic anisotropy and thermal stability are compromised
Solution Approach 1:
The patent optimizes the thickness parameters of multiple layers: the CoFeB free layer is kept thin (5-15 nm) for low switching current, while the MgO tunnel barrier thickness (2-4 nm) and BN interfacial layer thickness (0.5-2 nm) are precisely controlled. These parameter changes enable thin free layer design without sacrificing perpendicular magnetic anisotropy, as the BN layer protects the magnetic properties during oxidation.
Solution Approach 2:
The BN interfacial layer provides localized protection at the critical MgO/CoFeB interface where oxygen diffusion would most harmfully affect the thin CoFeB layer's magnetic properties. This local quality enhancement at the interface allows the bulk CoFeB layer to remain thin for low switching current while maintaining interfacial magnetic quality.
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 solution achieves a lower Hc/Jc ratio, maintains a magnetoresistive ratio of at least 100%, and ensures thermal stability up to 400°C, improving the overall performance of p-MTJ for spin-transfer torque magnetoresistive random access memory (STT-MRAM) applications.
Implementation Method 1
the FL has a metal insertion (MIS) layer for reducing the FL magnetization×saturation (Ms) value, reducing oxygen diffusion through the FL
Implementation Method 2
p-MTJs that rely on interfacial perpendicular anisotropy produced at metal oxide/FL interfaces
Implementation Method 3
using a nitride capping layer to block nitrogen diffusion
Implementation Method 4
p-MTJ element having a tunneling magneto-resistance (TMR) effect
Implementation Method 5
the electrons transfer a portion of their angular momentum to the FL. As a result, spin-polarized current can switch the magnetization direction of the FL
Data Source
AI summary
A perpendicular magnetic tunnel junction is disclosed wherein a metal insertion (MIS) layer is formed within a free layer (FL), a partially oxidized Hk enhancing layer is on the FL, and a nitride capping layer having a buffer layer/nitride layer (NL) is on the Hk enhancing layer to provide an improved coercivity (Hc)/switching current (Jc) ratio for spintronic applications. Magnetoresistive ratio is maintained above 100%, resistance×area (RA) product is below 5 ohm/μm2, and thermal stability to 400° C. is realized. The FL comprises two or more sub-layers, and the MIS layer may be formed within at least one sub-layer or between sub-layers. The buffer layer is used to prevent oxygen diffusion to the NL, and nitrogen diffusion from the NL to the FL. FL thickness is from 11 Angstroms to 25 Angstroms while MIS layer thickness is preferably from 0.5 Angstroms to 4 Angstroms.