MTJ Boron Layer Structure for Low-Defect 400°C Annealing
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Solution Overview
Problem
In magnetic random access memory (MRAM) devices, non-magnetic metals tend to diffuse through magnetic layers into the tunnel barrier during high-temperature annealing, causing device defects and disrupting insulation properties, which is particularly problematic in CMOS processing at temperatures around 400°C.
Innovation Solution
A magnetic layer structure with high boron content layers in the reference and free layers is used to inhibit non-magnetic metal migration into the tunnel barrier, maintaining low defect rates and acceptable magnetostriction, coercivity, and high tunnel magnetoresistance ratio even after high-temperature annealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-temperature annealing is performed to improve crystal structure and TMR ratio, then TMR ratio is improved, but non-magnetic metals diffuse into the tunnel barrier causing device defects
Solution Approach 1:
A boron-containing magnetic layer is introduced as an intermediary barrier between the non-magnetic metal layer and the MgO tunnel barrier. This intermediate layer prevents direct diffusion of non-magnetic metals into the tunnel barrier during high-temperature annealing, while still allowing the annealing process to improve the crystal structure and TMR ratio of the MgO layer.
Solution Approach 2:
The invention changes the compositional parameter of the magnetic layer by incorporating boron (with specific atomic percentages ranging from 10-50%) into the CoFeB or CoFe magnetic layer. This compositional modification creates a diffusion barrier that blocks non-magnetic metal migration while maintaining the desired magnetic and structural properties after annealing.
2Ease of operation
If non-magnetic metals are used in magnetic layers to achieve desired magnetic properties, then magnetic performance is improved, but these metals migrate into the tunnel barrier during annealing disrupting insulation
Solution Approach 1:
The boron-containing magnetic layer serves as a protective intermediary that allows non-magnetic metals (such as Ru, Rh, Ir, Ta, Mo, W, Mg, or Cr) to be present in the magnetic layer structure for achieving desired magnetic properties, while simultaneously preventing these metals from migrating into the MgO tunnel barrier during thermal processing.
Solution Approach 2:
The invention applies local quality modification by creating a specific boron-containing magnetic layer with controlled thickness (1-20 nm) and boron concentration positioned adjacent to the tunnel barrier. This localized modification provides targeted protection at the critical interface where diffusion occurs, while allowing other regions to maintain their magnetic functionality.
3Measurement precision
If amorphous CoFeB or FeB is deposited to enable fcc crystal growth after annealing, then TMR ratio is improved, but boron must diffuse away from the tunnel barrier interface
Solution Approach 1:
The invention creates a spatial gradient in boron distribution within the magnetic layer structure. The boron-containing magnetic layer adjacent to the tunnel barrier has controlled boron content that prevents excessive diffusion, while the overall structure maintains the amorphous-to-crystalline transformation needed for high TMR ratio. This localized control allows boron to remain in appropriate concentrations throughout the structure.
Solution Approach 2:
The invention modifies the boron concentration parameter in the magnetic layer (with specific ranges of 10-50 atomic %) to optimize both the diffusion barrier function and the crystal structure development. This parameter control enables the material to maintain stability during annealing while achieving the desired fcc crystal structure in the MgO tunnel barrier for high TMR performance.
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 proposed structure significantly reduces non-magnetic metal migration into the tunnel barrier, achieving defect levels below 50 ppm and maintaining high performance metrics, including low magnetostriction and high TMR ratio, even after annealing at 400°C, thereby enhancing the reliability and efficiency of MRAM devices.
Implementation Method 1
non-magnetic metals tend to diffuse through magnetic layers into the tunnel barrier during high-temperature annealing
Implementation Method 2
The tunnel barrier is typically about 10 Angstroms thick so that a current through the tunnel barrier can be established by a quantum mechanical tunneling of conduction electrons
Implementation Method 3
two magnetic layers that together generate a tunneling magnetoresistance (TMR) effect
Implementation Method 4
there is no template for crystal structure growth until annealing when B tends to diffuse away from the tunnel barrier
Data Source
AI summary
A magnetic tunnel junction is disclosed wherein the reference layer and free layer each comprise one layer having a boron content from 25 to 50 atomic %, and an adjoining second layer with a boron content from 1 to 20 atomic %. One of the first and second layers in each of the free layer and reference layer contacts the tunnel barrier. Each boron containing layer has a thickness of 1 to 10 Angstroms and may include one or more B layers and one or more Co, Fe, CoFe, or CoFeB layers. As a result, migration of non-magnetic metals along crystalline boundaries to the tunnel barrier is prevented, and the MTJ has a low defect count of around 10 ppm while maintaining an acceptable TMR ratio following annealing to temperatures of about 400° C. The boron containing layers are selected from CoB, FeB, CoFeB and alloys thereof including CoFeNiB.