Magnetic Tunnel Junction Electrode Crystallization
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Solution Overview
Problem
Boron in the magnetic tunnel junction construction at the CoFe/MgO interface or inside the MgO lattice undesirably reduces tunneling magnetoresistance (TMR) of the magnetic tunnel junction.
Innovation Solution
Forming a magnetic tunnel junction by initially depositing amorphous CoFe, followed by MgO, and then annealing to induce crystallization into a body-centered-cubic (bcc) 001 lattice structure, while ensuring the CoFe magnetic electrode is devoid of B to maintain high TMR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If CoFe is deposited with Boron to assure initial amorphous deposition, then the amorphous structure is achieved, but Boron diffuses into MgO lattice and reduces tunneling magnetoresistance
Solution Approach 1:
The patent applies preliminary action by forming a protective MgO layer before the CoFeB layer, and then performing a first anneal to crystallize this MgO layer into a buffer layer before Boron diffusion can occur. This pre-established crystalline structure serves as a barrier to prevent harmful Boron diffusion into the tunnel barrier MgO, thereby preserving TMR while allowing amorphous CoFeB formation.
Solution Approach 2:
The patent segments the MgO structure into multiple distinct layers: a tunnel barrier MgO layer and a separate buffer MgO layer. The buffer layer is specifically positioned between the CoFeB layer and the tunnel barrier MgO, creating a physical barrier that segments and isolates the Boron-containing CoFeB from the tunnel barrier MgO, preventing Boron diffusion while maintaining functional separation.
2Stability of the object's composition
If annealing temperature is increased to induce crystallization, then bcc 001 lattice structure is achieved, but Boron diffusion into MgO increases
Solution Approach 1:
The patent performs a first anneal at a lower temperature (200-400°C) before the second anneal to crystallize the buffer MgO layer. This preliminary crystallization creates a stable buffer layer that acts as a diffusion barrier, preventing Boron from migrating into the tunnel barrier MgO during the subsequent higher-temperature second anneal (400-600°C) that crystallizes the CoFe layer.
Solution Approach 2:
The buffer MgO layer serves as an intermediary barrier between the CoFeB layer and the tunnel barrier MgO. During annealing, this buffer layer crystallizes first and forms a stable interface that mediates and blocks Boron diffusion pathways, allowing the CoFe layer to crystallize at higher temperatures without direct Boron contamination of the tunnel barrier.
3Reliability
If CoFe is made devoid of B to maintain high TMR, then tunneling magnetoresistance is improved, but crystallization into bcc 001 lattice becomes difficult
Solution Approach 1:
The patent segments the magnetic layer into two distinct functional layers: a CoFeB layer that provides amorphous structure and magnetic properties, and a separate CoFe layer that crystallizes into the desired bcc 001 lattice. The B-free CoFe layer is positioned adjacent to the tunnel barrier MgO, ensuring high TMR, while the CoFeB layer provides the necessary amorphous structure without requiring B-free composition.
Solution Approach 2:
The patent uses a composite structure combining CoFeB and B-free CoFe layers. The CoFeB layer (with Boron) provides amorphous deposition and magnetic properties, while the B-free CoFe layer provides crystalline bcc 001 structure with high TMR. This composite approach allows each layer to fulfill its specific function without compromise.
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 method enhances the crystallization of CoFe and MgO, maintaining high tunneling magnetoresistance and improving the operational traits of magnetic tunnel junctions.
Implementation Method 1
annealing to induce crystallization into a body-centered-cubic (bcc) 001 lattice structure
Implementation Method 2
using a spin-polarized current to result in a spin-transfer torque (STT) effect. Charge carriers (such as electrons) have a property known as 'spin' which is a small quantity of angular momentum intrinsic to the carrier
Implementation Method 3
The insulator material is sufficiently thin such that electrons can tunnel from one magnetic electrode to the other through the insulator material under appropriate conditions
Data Source
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AI summary
A method of forming a magnetic electrode of a magnetic tunnel junction comprises forming non-magnetic MgO-comprising material over conductive material of the magnetic electrode being formed. An amorphous metal is formed over the MgO-comprising material. Amorphous magnetic electrode material comprising Co and Fe is formed over the amorphous metal. The amorphous magnetic electrode material is devoid of B. Non-magnetic tunnel insulator material comprising MgO is formed directly against the amorphous magnetic electrode material. The tunnel insulator material is devoid of B. After forming the tunnel insulator material, the amorphous Co and Fe-comprising magnetic electrode material is annealed at a temperature of at least about 250°C to form crystalline Co and Fe-comprising magnetic electrode material from an MgO-comprising surface of the tunnel insulator material. The crystalline Co and Fe-comprising magnetic electrode material is devoid of B. Other method and non-method embodiments are disclosed.