Composite Seed Layer for STT-MRAM Thermal Robustness
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional bottom-free-layer STT-MRAM cells have low thermal robustness and tunnel magnetoresistance (TMR) due to the use of magnesium oxide seed layers with pinholes and low boron affinity, leading to contamination at the MgO-free layer interface and reduced Figure of Merit (FOM).
Innovation Solution
A composite metal oxide seed layer is introduced, comprising a first amorphous metal layer, a metal oxide layer, and a second oxygen-treated metal layer with high affinity for oxygen and boron, which improves the interface quality and boron distribution, enhancing TMR and FOM by reducing diffusion and increasing thermal robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a thin layer of MgO is used as the seed layer, then the structure is simple, but the thermal robustness is low and pinholes form leading to contamination
Solution Approach 1:
The patent applies composite materials by replacing the simple MgO seed layer with a composite structure consisting of an amorphous metal layer (Ta, W, Mo, Hf, Ni, Co, or Fe) combined with a metal oxide layer (MgO, MgAlO, MgAl2O4, or (MgAl)3O4). This composite structure provides both thermal robustness and pinhole-free characteristics while maintaining interface quality with the free layer.
Solution Approach 2:
The patent applies parameter changes by controlling the thickness of the amorphous metal layer (5-20 nm) and metal oxide layer (2-10 nm), and by adjusting the boron concentration in the free layer (20-40 at%). These parameter optimizations enhance the interface quality and reduce contamination while improving thermal stability.
2Device complexity
If MgO is used as the seed layer, then the material is simple, but the boron affinity is low leading to boron accumulation at the interface
Solution Approach 1:
The patent uses composite materials where the amorphous metal layer in the seed structure has high boron affinity, effectively capturing excess boron from the free layer and preventing boron accumulation at the MgO-free layer interface. This composite approach maintains simple processing while achieving superior interface quality.
Solution Approach 2:
The amorphous metal layer acts as an intermediary between the MgO layer and the boron-containing free layer. It mediates boron distribution by providing high boron affinity, thereby preventing direct boron accumulation at the MgO interface and improving overall interface quality.
3Reliability
If a composite metal oxide seed layer is used, then the TMR and FOM are improved, but the device complexity increases
Solution Approach 1:
The patent employs composite materials (amorphous metal layer + metal oxide layer) in the seed structure to achieve high TMR and FOM. The composite structure provides both thermal robustness and controlled boron distribution, resulting in superior tunnel magnetoresistance performance despite the increased structural complexity.
Solution Approach 2:
The patent optimizes parameters including the thickness of each layer in the composite seed structure, the boron concentration in the free layer, and the oxygen treatment conditions. These parameter changes enable high TMR and FOM while keeping the fabrication process manageable.
4Stability of the object's composition
If the free layer has high boron content, then the magnetic properties are improved, but boron diffusion to the seed layer interface increases causing contamination
Solution Approach 1:
The amorphous metal layer in the composite seed structure serves as an intermediary that captures excess boron through its high boron affinity. This prevents boron from diffusing to the MgO-free layer interface, thereby maintaining interface quality even when the free layer has high boron content for optimal magnetic properties.
Solution Approach 2:
The composite seed layer structure with amorphous metal and metal oxide components works synergistically to manage boron distribution. The amorphous metal layer absorbs excess boron while the metal oxide layer maintains the tunnel barrier integrity, allowing the free layer to have high boron content for improved magnetic properties without interface contamination.
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 composite seed layer improves the uniformity and performance of the bottom-free-layer STT-MRAM cells by increasing TMR and Figure of Merit, achieving better thermal stability and reducing current density, thereby enhancing device efficiency and performance.
Implementation Method 1
reducing diffusion and increasing thermal robustness
Implementation Method 2
a second oxygen-treated metal layer with high affinity for oxygen and boron
Implementation Method 3
improving the interface quality and boron distribution, enhancing TMR and FOM by reducing diffusion and increasing thermal robustness
Implementation Method 4
STT-MRAM utilizes magnetic tunnel junctions (MTJs) written at least in part by a current driven through the magnetic junction
Implementation Method 5
a current driven through the magnetic junction, which has a tunneling barrier stacked between a free magnetic layer and a pinned (or fixed) magnetic layer
Implementation Method 6
The spacer layer 15-2 provides antiferromagnetic coupling between the top pinned layer 15-1 and the bottom pinned layer 15-3/the PEL 15-4
Data Source
AI summary
A perpendicular bottom-free-layer STT-MRAM cell includes a bottom-free-layer magnetic tunnel junction (BMTJ). The BMTJ includes a composite metal oxide seed layer, and a free layer comprising boron (B) on the composite metal oxide seed layer. The composite metal oxide seed layer includes a first metal layer; a metal oxide layer on the first metal layer; and a second metal layer on the metal oxide layer. The second metal layer has been oxygen treated.