B2-MTJ Texture Blocking Decoupling Layer for Sub-25 nm STT-MRAM
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Solution Overview
Problem
As magnetic tunnel junction (MTJ) devices shrink to diameters less than 25 nm, it becomes difficult to reduce the total magnetic field experienced by the free layer to zero, leading to instability and variations in magnetic coupling, which affects the thermal stability and efficiency of the device.
Innovation Solution
The configuration involves a first magnetic reference layer and a free magnetic layer on one side of a tunnel junction barrier, with a second magnetic reference layer having antiparallel magnetization on the other side, canceling the total magnetic coupling and providing more controlled magnetic fields, resulting in a thinner device stack with improved stability and reduced stray fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If MTJ device diameter is reduced to less than 25 nm, then device scaling and integration density are improved, but magnetic field cancellation becomes difficult leading to instability and variations in magnetic coupling
Solution Approach 1:
The reference layer is segmented into two separate reference layers positioned on opposite sides of the tunnel barrier, allowing independent optimization of their positions to achieve better magnetic field cancellation while maintaining device scalability to sub-25 nm dimensions
Solution Approach 2:
A nonmagnetic spacer layer is introduced as an intermediary between the reference layers and the free layer, providing precise control over the spacing and enabling effective magnetic field cancellation without direct contact, thus stabilizing magnetic coupling at scaled dimensions
2Length of stationary object
If second reference layer is positioned closer to free layer, then device thickness is reduced, but magnetic field interference may increase
Solution Approach 1:
The nonmagnetic spacer layer acts as a mediator that allows the second reference layer to be positioned close to the free layer for reduced device thickness while preventing harmful magnetic field interference through the spacer's nonmagnetic properties
Solution Approach 2:
The second reference layer with antiparallel magnetization serves as a counterweight to the first reference layer's magnetic field, creating opposing magnetic fields that cancel each other out and reduce net magnetic interference on the free layer
3Reliability
If antiparallel magnetization configuration is used, then shift field is canceled improving thermal stability, but device complexity increases
Solution Approach 1:
The antiparallel magnetization configuration serves multiple functions simultaneously: it cancels the shift field to improve thermal stability, reduces stray fields to minimize interference with adjacent cells, and enables better magnetic coupling control, making the increased structural complexity worthwhile
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 configuration effectively cancels the shift field, enhances thermal stability, and maintains efficient magnetoresistance, even at smaller device sizes, by positioning the second reference layer closer to the free layer, thus reducing the device thickness and sensitivity to cell-size variations.
Implementation Method 1
A shift field Hshift experienced by the free magnetic material layer is substantially canceled by two antiparallel magnetostatic fields acting on the free layer from the first reference magnetic material layer and the second reference magnetic material layer
Implementation Method 2
The resistance value of the MTJ pattern may be varied according to the magnetization directions of the two magnetic substances with respect to each other
Data Source
AI summary
A magnetic tunnel junction device and a method to make the device are disclosed. The magnetic tunnel junction device comprises a first reference magnetic material layer, a tunnel barrier material layer, a free magnetic material layer between the first reference magnetic material layer and the tunnel barrier material layer, and a second reference magnetic material layer disposed on an opposite side of the tunnel barrier material layer from the free magnetic material layer, in which the second reference magnetic material layer is anti-magnetically exchanged coupled with the first reference magnetic material layer. A shift field Hshift experienced by the free magnetic material layer is substantially canceled by the anti-magnetic exchange coupling between the first reference magnetic material layer and the second reference magnetic material layer.