MTJ Barrier Layer Oxidation for Resistance Uniformity
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Solution Overview
Problem
Magnetic tunnel junction (MTJ) devices face challenges in achieving uniform, predictable, and stable resistance values due to variations in tunnel barrier quality, especially when scaled to smaller sizes, leading to issues in large arrays of MRAMs and other magnetoelectronic devices.
Innovation Solution
The method involves forming high-quality tunnel barriers using a combination of natural and rapid oxidation processes for aluminum or other oxidizable materials, such as Al, Mg, Zr, Ti, Hf, and Ta, to create dense and pin-hole-free insulating layers, ensuring consistent resistance values across MTJ devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If thinner tunnel barrier layers are used to scale MTJ devices to smaller sizes, then device density and integration are improved, but resistance uniformity and stability deteriorate due to variations in tunnel barrier quality
Solution Approach 1:
The tunnel barrier layer is segmented into multiple sub-layers with different materials (e.g., AlOx, MgO, AlOx again) rather than using a single uniform layer. This segmentation allows each sub-layer to contribute differently to the overall barrier properties, improving resistance uniformity and stability while maintaining the thin total thickness needed for small device sizes.
Solution Approach 2:
The patent employs composite material structures for the tunnel barrier, combining multiple oxidizable materials (Al, Mg, Zr, Ti, Hf, Ta) and their oxides in specific sequences. These composite barrier structures leverage the advantageous properties of each material to achieve both thin thickness and high resistance uniformity, resolving the contradiction between device scaling and manufacturing precision.
2Ease of manufacture
If conventional oxidation processes are used to form tunnel barriers, then manufacturing simplicity is maintained, but barrier quality and resistance stability worsen due to pin-holes and non-uniformity
Solution Approach 1:
The patent employs strong oxidation conditions (e.g., plasma oxidation, atomic oxygen exposure, or chemical oxidation) to form dense, pin-hole-free oxide layers from the oxidizable materials. This accelerated oxidation process creates high-quality tunnel barriers with improved resistance stability while remaining compatible with existing semiconductor manufacturing workflows, thus maintaining ease of manufacture.
Solution Approach 2:
The patent uses intermediate oxide layers formed from oxidizable materials as mediators between the ferromagnetic electrodes. These intermediary oxide layers serve as nucleation sites and buffer zones that improve the overall barrier quality and resistance stability, while the oxidation process itself can be integrated into conventional manufacturing sequences.
3Device complexity
If single-layer oxidizable material is used for tunnel barrier, then fabrication complexity is reduced, but resistance uniformity and defect density worsen
Solution Approach 1:
The single-layer oxidizable material is segmented into multiple thin sub-layers deposited in sequence. Each sub-layer is oxidized to form a corresponding oxide sub-layer, creating a multi-layered tunnel barrier structure. This segmentation improves resistance uniformity by distributing manufacturing variations across multiple layers rather than concentrating them in a single thick layer, while the overall fabrication process remains relatively simple.
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 approach significantly reduces the incidence of partial shorts and improves the uniformity of resistance distribution in MTJ devices, enhancing the manufacturability and reliability of MRAMs and other MTJ arrays.
Implementation Method 1
exposing the first layer of a first oxidizable material to a natural oxidation process to convert at least part of the first oxidizable material to a first insulating oxide portion
Implementation Method 2
exposing the first insulating oxide portion to a further rapid oxidation process providing substantially accelerated oxidation compared to the natural oxidation process, so as to convert at least part of a remaining portion of the first layer of first oxidizable material to a second insulating oxide portion
Implementation Method 3
The fixed layer and free layer are separated by an insulating tunnel barrier layer that relies upon the phenomenon of spin-polarized electron tunneling through the tunnel barrier layer between the free and fixed ferromagnetic layers
Data Source
AI summary
Methods and apparatus are provided for magnetic tunnel junction (MTJ) devices and arrays, comprising metal-insulator-metal (M-I-M) structures with opposed first and second ferro-magnetic electrodes with alterable relative magnetization direction. The insulator is formed by depositing an oxidizable material (e.g., Al) on the first electrode, naturally oxidizing it, e.g., at about 0.03 to 10 milli-Torr for up to a few thousand seconds at temperatures below about 35° C., then further rapidly (e.g., plasma) oxidizing at a rate much larger than that of the initial natural oxidation. The second electrode of the M-I-M structure is formed on this oxide. More uniform tunneling properties result. A second oxidizable material layer is optionally provided after the initial natural oxidation and before the rapid oxidation step during which it is substantially entirely converted to insulating oxide. A second natural oxidation cycle may be optionally provided before the second layer is rapidly oxidized.