Multilevel SOT-MRAM via Ion-Implanted Metal Resistivity
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Solution Overview
Problem
Spin-orbit torque magnetoresistive random access memory (SOT-MRAM) devices are limited as single-level memory, unable to store multiple data states efficiently, which is impractical for high-density memory applications due to their inability to switch magnetization direction for multilevel data storage.
Innovation Solution
The development of a multilevel SOT-MRAM structure with ion-implanted metal layers, creating regions of varying electrical resistivity, allowing for multiple resistance states by controlling the electric current density across different regions to switch magnetization states of the free layer, enabling storage of multiple data levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a regular SOT-MRAM structure with uniform metal layer is used, then the device can be manufactured with simple process, but it can only store single-level data (0 or 1) and cannot achieve high-density memory applications
Solution Approach 1:
The metal layer is divided into multiple regions with different electrical resistivities through selective ion implantation. Each region has locally optimized properties (different resistivity values) that enable distinct current density thresholds, allowing the same physical structure to support multiple data levels (0, 1, 2, 3) by controlling which regions exceed their switching thresholds.
Solution Approach 2:
The electrical resistivity parameter of the metal layer is modified through ion implantation to create four distinct regions with different resistivity values. This parameter change enables each region to have different current density thresholds for magnetization switching, transforming a single-level memory into a multilevel memory device capable of storing 2 bits per cell.
2Quantity of substance
If ion implantation is applied to create multiple resistivity regions in the metal layer, then multiple data levels can be stored, but the manufacturing process becomes more complex
Solution Approach 1:
The ion implantation process is performed as a preliminary step before forming the magnetic tunnel junctions. By pre-patterning the metal layer with different resistivity regions before the complex MTJ fabrication, the subsequent memory cell formation becomes more straightforward, and the multilevel capability is built into the structure from the beginning rather than requiring additional processing steps later.
Solution Approach 2:
The metal layer with ion-implanted regions serves as an intermediary element that translates a single write current into multiple distinct magnetization states. The different resistivity regions act as mediators that divide the current pathway, allowing one current source to control multiple storage states through the threshold effects in each region.
3Measurement precision
If multiple regions with different electrical resistivity are created in the metal layer, then multiple resistance states can be achieved, but the control and measurement of current density becomes more difficult
Solution Approach 1:
The metal layer is segmented into four distinct regions (first, second, third, and fourth regions) with different electrical resistivities. This segmentation creates well-defined current pathways with distinct threshold characteristics, making it easier to control and measure the current density required to switch each region's magnetization state, thereby enabling precise discrimination between multiple resistance states.
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 allows for the creation of multiple distinguishable electrical resistance states, representing multiple memory levels, enhancing the storage capacity and practicality of SOT-MRAM devices for high-density memory applications.
Implementation Method 1
As a result of spin-Hall effect (SHE), an electric current induces spin accumulation at the lateral boundaries of a conductor which carries the current. At a SOT-MRAM device, the free layer is disposed on a heavy metal layer. When an electric current flows along the heavy metal layer, a spin current in the transverse direction is created.
Implementation Method 2
The tunnel barrier layer of the MTJ is designed such that an electric current may flow across it due to quantum tunneling.
Implementation Method 3
The tunnel magnetoresistance effect is used for the read operation of a SOT-MRAM device. Two distinct resistance levels of the MTJ may exist. When the magnetization states of the reference layer and the free layer are parallel, the resistance is relatively low. When the magnetization states of the reference and free layers are anti-parallel, the resistance is relatively high.
Data Source
AI summary
Magnetic memory structure and memory device are provided. A magnetic memory structure includes a metal layer, a first magnetic tunnel junction, and a second magnetic tunnel junction. The metal layer includes a first contact region and a second contact region. Electrical resistivity of at least a first part of the first contact region is different than electrical resistivity of the second contact region. The first magnetic tunnel junction is disposed on the metal layer. The first magnetic tunnel junction includes a first free layer in contact with the first contact region of the metal layer. The second magnetic tunnel junction is disposed on the metal layer. The second magnetic tunnel junction includes a second free layer in contact with the second contact region of the metal layer.