MTJ Element Single (111) Orientation for STT MRAM
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Solution Overview
Problem
Current Magnetic Tunnel Junction (MTJ) elements in Spin Transfer Torque (STT) Magnetic Random Access Memory (MRAM) face issues due to transitions between incompatible crystalline orientations, leading to weakened Perpendicular Magnetic Anisotropy (PMA) and Magneto-resistance Ratio (MR), affecting data retention and readback signal quality.
Innovation Solution
The solution involves using a single (111) crystalline orientation for all active layers, including PMA, MR, and MgO tunnel barrier layers, eliminating transitions and ensuring proper crystalline growth and magnetic performance by using strongly textured (111) seed layers to induce the correct orientation in the MgO tunnel barrier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If transitions between incompatible crystalline orientations are used in MTJ structure, then it is possible to combine PMA layers with MR layers, but the PMA and MR are both weakened
Solution Approach 1:
The patent applies homogeneity by using a single (111) crystalline orientation for all active layers including both the PMA layer and MR layer, eliminating the heterogeneity caused by transitions between incompatible crystalline orientations. This uniform (111) orientation throughout the stack ensures that both PMA and MR maintain their full strength without being weakened by interface transitions.
2Ease of manufacture
If transitional layers are introduced to mitigate orientation mismatch, then the PMA layer and MR layer can be connected, but the MR layer becomes more difficult to remain in PMA mode
Solution Approach 1:
The patent extracts and eliminates the transitional layer from the MTJ structure, demonstrating that the transition between incompatible crystalline orientations is not necessary. By directly connecting the PMA layer and MR layer through a common (111) oriented MgO tunnel barrier, the structure achieves both manufacturability and reliability without the intermediate transitional layer that would compromise PMA mode stability.
3Ease of manufacture
If (100) oriented MgO layer is used as tunnel barrier, then it is the natural orientation during deposition, but it is incompatible with fcc (111) crystal orientation of PMA materials
Solution Approach 1:
The patent changes the crystalline orientation parameter of the MgO tunnel barrier from the conventional (100) orientation to a (111) orientation. This parameter change enables compatibility with the fcc (111) crystal orientation of PMA materials, allowing both to coexist in the same crystalline system and form a fully crystallized interface without orientation mismatch.
4Adaptability or versatility
If fcc (111) PMA layer is placed above or below MgO layer, then the structure can be configured flexibly, but transitions between incompatible orientations still occur at interfaces
Solution Approach 1:
The patent maintains the flexibility of placing the PMA layer above or below the MgO layer while ensuring that all layers adopt the same (111) crystalline orientation. This homogeneous orientation throughout the stack, regardless of the PMA layer position, eliminates interface transitions between incompatible orientations and ensures full crystallization and optimal performance.
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 enables fully crystallized and properly oriented PMA and MR layers, enhancing both writing and reading performance of PMA STT MRAM devices by maintaining strong PMA and high MR, thereby improving data retention and readback signal quality without the need for transitional layers.
Implementation Method 1
utilization of a single (111) crystalline orientation for all active layers... by providing strongly (111)-textured layers immediately below the MgO layer which induce a (111) orientation therein
Implementation Method 2
PMA STT MRAMs, magnetizations of both the MTJ Free Layer (FL) and the Reference Layer (RL) are perpendicular to the plane of MTJ layers... PMA of the FL should be high enough to provide thermal stability
Implementation Method 3
the resistance difference between the two memory states, expressed as the MTJ Magneto-resistance Ratio (MR=(Rap−Rp)/Rp), should be high enough to provide sufficient readback signal
Data Source
AI summary
An all (111) MTJ stack is disclosed in which there are no transitions between different crystalline orientations when going from layer to layer. This is accomplished by providing strongly (111)-textured layers immediately below the MgO tunnel barrier to induce a (111) orientation therein.