Thermally-Assisted MRAM Storage Layer Design for Write Reliability
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Solution Overview
Problem
Conventional thermally assisted magnetic random access memory (TA-MRAM) cells experience writing errors due to the formation of micromagnetic states in the storage layer during the writing operation, leading to intermediate resistance values between fully switched and unswitched states.
Innovation Solution
A TA-MRAM cell with a low saturation magnetization (low-MS) storage layer comprising a Co, Fe, or Ni-based alloy doped with non-magnetic elements like Ta, Ti, Cr, V, Nb, Hf, Mo, Zn, or Zr, and an alternately multilayer arrangement of ferromagnetic and non-magnetic layers, which reduces the formation of micromagnetic states and enhances tunnel magnetoresistance and exchange field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional storage layer is used in TA-MRAM cells, then the device structure is simpler, but micromagnetic states form during writing leading to intermediate resistance values and writing errors
Solution Approach 1:
The storage layer is segmented into multiple ferromagnetic layers (first ferromagnetic layer, second ferromagnetic layer) separated by a low saturation magnetization storage layer. This segmentation prevents the formation of micromagnetic states by dividing the magnetic moment distribution, ensuring full switching between parallel and antiparallel states without intermediate resistance values, thereby improving writing reliability.
Solution Approach 2:
The storage layer is constructed as a composite structure combining ferromagnetic materials with a low saturation magnetization material. This composite design creates enhanced exchange coupling between layers while maintaining overall low saturation magnetization, which prevents micromagnetic state formation and ensures reliable binary switching states.
2Reliability
If the storage layer has high saturation magnetization, then the magnetic moment is stronger, but micromagnetic states are more likely to form during writing
Solution Approach 1:
The saturation magnetization parameter of the storage layer is changed by introducing a low saturation magnetization material between the ferromagnetic layers. This parameter change reduces the overall saturation magnetization of the storage layer, which prevents micromagnetic state formation during writing operations while ensuring complete switching between magnetic states for reliable binary representation.
3Reliability
If non-magnetic elements are added to the Co, Fe or Ni based alloy, then the saturation magnetization is reduced, but the alloy composition becomes more complex
Solution Approach 1:
Non-magnetic elements (Ta, Ti, Cr, V, Nb, Hf, Mo, Zn, or Zr) are added locally to the Co, Fe or Ni based alloy at specific concentrations (1 at. % to 40 at. %). This local modification of alloy composition reduces the saturation magnetization of the storage layer, preventing micromagnetic state formation and reducing write errors, while the concentration range provides flexibility in optimizing the balance between magnetization reduction and compositional complexity.
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 low-MS storage layer design significantly reduces the likelihood of write errors by ensuring the storage magnetization is fully switched, resulting in reliable high or low resistance states after writing, thereby improving the reliability of the TA-MRAM cell.
Implementation Method 1
an antiferromagnetic layer exchange-coupling the storage layer such as to pin the storage magnetization at a low temperature threshold and free it at a high temperature threshold
Implementation Method 2
the low saturation magnetization storage layer has a saturation magnetization which is lower than the saturation magnetization of the first ferromagnetic layer and lower than the saturation magnetization of the second ferromagnetic layer
Implementation Method 3
The resulting resistance of the magnetic tunnel junction having a 'partially' switched storage magnetization will thus has a value that is intermediate between the resistance value that would be obtained for the fully switched storage magnetization and the unswitched storage magnetization
Data Source
AI summary
MRAM cell including a magnetic tunnel junction including a reference layer, a storage layer having a storage magnetization, a tunnel barrier layer between the reference and the storage layers; and an antiferromagnetic layer exchange-coupling the storage layer such as to pin the storage magnetization at a low temperature threshold and free it at a high temperature threshold. The storage layer includes a first ferromagnetic layer in contact with the tunnel barrier layer, a second ferromagnetic layer in contact with the antiferromagnetic layer, and a low saturation magnetization storage layer including a ferromagnetic material and a non-magnetic material. The MRAM cell can be written with improved reliability.