Small MTJ MRAM Manufacturing via Oxide Hard Mask Etching
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Solution Overview
Problem
Current memory technologies face challenges in scalability, high programming current requirements, and design complexity, particularly with small magnetic tunnel junctions (MTJs) in magnetic random access memory (MRAM), which affect density, reliability, and manufacturing feasibility.
Innovation Solution
A method for manufacturing magnetic memory cells involving the formation of a small pillar-shaped MTJ with a low programming current requirement, achieved through specific steps including deposition of oxide and photo-resist layers, etching, and planarization processes to define precise MTJ structures, allowing for reduced MTJ size and stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the MTJ size is reduced to increase memory density, then the programming current requirement increases, but reducing MTJ size is necessary to achieve higher memory density
Solution Approach 1:
The patent applies local quality by creating a non-uniform magnetic field distribution within the MTJ structure. The magnetic field is concentrated in specific regions (particularly in the free layer) through carefully designed magnetization patterns in the pinned layer and intermediate layers, allowing efficient spin transfer torque to be generated locally rather than requiring uniform high fields throughout the entire structure.
Solution Approach 2:
The patent employs parameter changes by optimizing multiple structural parameters including layer thicknesses (tunnel barrier thickness, magnetic layer thicknesses), material compositions (CoFeB, CoFe, MgO), and magnetization orientations. These parameter optimizations enable smaller MTJ dimensions while maintaining or reducing the programming current requirement through enhanced TMR ratios and improved spin polarization.
2Quantity of substance
If the MTJ size is reduced to increase memory density, then the manufacturing precision requirement increases, but reducing MTJ size is necessary to achieve higher memory density
Solution Approach 1:
The patent applies preliminary action through a carefully sequenced manufacturing process where oxide layers are deposited and patterned first to define precise locations, followed by magnetic layer deposition, and finally magnetization patterning. This step-by-step preliminary structuring ensures that each subsequent layer is positioned with high precision, enabling small MTJ dimensions while maintaining manufacturing feasibility.
Solution Approach 2:
The patent uses intermediary layers (such as Ru, Ta, and MgO layers) that facilitate precise alignment and positioning between the pinned layer and free layer. These intermediary layers act as buffers and alignment references, allowing tight tolerances to be maintained even as overall MTJ dimensions are reduced for higher density.
3Adaptability or versatility
If multiple memory technologies are combined in a system design, then the functionality is improved, but the design complexity increases
Solution Approach 1:
The patent applies universality by designing the MRAM cell to perform multiple functions: data storage through magnetization states, data writing through spin transfer torque, and data reading through TMR measurement. This multi-functionality within a single device structure eliminates the need for separate memory technologies, reducing overall system complexity while maintaining versatility.
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 method enables the creation of small MTJs with lower programming current requirements, enhancing memory cell density and reliability while simplifying the manufacturing process, thereby addressing scalability and complexity issues in MRAM technology.
Implementation Method 1
A magnetic field, H, is applied to the structure in order to align the magnetization of the free layer with the magnetization of the pinned layer
Implementation Method 2
The spin transfer torque, STT, exerted on the free layer magnetization by the spin-polarized current
Data Source
AI summary
A method of making a magnetic random access memory cell includes forming a magnetic tunnel junction (MTJ) on top of a wafer, depositing oxide on top of the MTJ, depositing a photo-resist layer on top of the oxide layer, forming a trench in the photo-resist layer and oxide layer where the trench has a width that is substantially the same as that of the MTJ. Then, the photo-resist layer is removed and a hard mask layer is deposited on top of the oxide layer in the trench and the wafer is planarized to remove the portion of the hard mask layer that is not in the trench to substantially level the top of oxide layer and the hard layer on the wafer. The remaining oxide layer is etched and the MTJ is etched to remove the portion of the MTJ which is not covered by the hard mask layer.