Ultra-Thin Synthetic Antiferromagnetic Reference Layer for STT MRAM
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Solution Overview
Problem
Thick reference layers in spin torque transfer (STT) magnetic random access memory (MRAM) devices suffer from stack roughness, longer growth and etching times, and reduced reproducibility, leading to increased costs and damage to other parts of the magnetic tunnel junction.
Innovation Solution
A synthetic antiferromagnetic reference layer with a thickness of 3-4 nanometers is introduced, comprising a first magnetic layer, a second magnetic layer, and a reference spacer layer, which provides strong perpendicular magnetic anisotropy and thermal stability, achieved through seed layer engineering and strong interface anisotropy between Co or Co alloys and Ir.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a thick reference layer is used in STT MRAM, then thermal stability is improved, but stack roughness increases and manufacturing precision deteriorates
Solution Approach 1:
The reference layer is segmented into multiple thin magnetic sub-layers (e.g., CoFeB layers) separated by non-magnetic spacer layers (e.g., Ru, Rh, Ir). This segmentation allows each sub-layer to be thin enough to maintain smooth stack interfaces while the collective structure provides sufficient thermal stability through cumulative magnetic anisotropy.
Solution Approach 2:
The patent employs composite material structures combining different magnetic (CoFeB, CoFe) and non-magnetic (Ru, Rh, Ir, Ta) layers. This composite approach enables optimization of individual layer thicknesses to achieve both low roughness and high thermal stability, with each material contributing specific properties to the overall reference layer performance.
2Stability of the object's composition
If a thick reference layer is used in STT MRAM, then thermal stability is improved, but etching time increases and productivity decreases
Solution Approach 1:
By segmenting the reference layer into thin sub-layers separated by etchable non-magnetic spacers, the total etching time is reduced. The etch process can selectively remove the spacer layers to define the reference layer pattern, and the thin magnetic sub-layers require less etching depth compared to a single thick reference layer, thereby increasing manufacturing productivity.
Solution Approach 2:
The patent changes the thickness parameter of individual magnetic sub-layers to be much thinner than conventional reference layers. This parameter change reduces the total material volume requiring etching while maintaining thermal stability through the engineered multi-layer structure, thus decreasing etching time and improving productivity.
3Stability of the object's composition
If a thick reference layer is used in STT MRAM, then thermal stability is improved, but device complexity increases and manufacturing cost increases
Solution Approach 1:
The patent applies local quality by making different portions of the reference layer structure serve different functions: thin magnetic sub-layers provide smooth interfaces and reduce roughness, while non-magnetic spacer layers provide structural separation and enable selective etching. This local differentiation allows the overall structure to achieve thermal stability without the complexity of a uniformly thick reference layer.
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 ultra-thin synthetic antiferromagnetic reference layer maintains strong perpendicular magnetic anisotropy and thermal stability, reducing stack roughness and etching time, while achieving similar tunnel magneto-resistance to thicker layers, thus improving semiconductor device performance and reducing manufacturing costs.
Implementation Method 1
provides strong perpendicular magnetic anisotropy and thermal stability, achieved through seed layer engineering and strong interface anisotropy between Co or Co alloys and Ir
Implementation Method 2
strong interface anisotropy between Co or Co alloys and Ir
Implementation Method 3
Due to the magnetic tunnel effect, the electrical resistance of the cell changes with the relative orientation of the fields between the two plates
Data Source
AI summary
Techniques relate to forming a magnetic tunnel junction (MTJ). A synthetic antiferromagnetic reference layer is adjacent to a tunnel barrier layer. The synthetic antiferromagnetic reference layer includes a first magnetic layer, a second magnetic layer, and a reference spacer layer sandwiched between the first magnetic layer and the second magnetic layer. A magnetic free layer is adjacent to the tunnel barrier layer so as to be opposite the synthetic antiferromagnetic reference layer. The synthetic antiferromagnetic reference layer has a thickness of at least one of 3 nanometers (nm), 4 nm, and 3-4 nm.