Folded SOT MRAM Stack for Thermal Stability and TMR Retention
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Solution Overview
Problem
The semiconductor industry faces challenges in achieving thermal stability and high tunnel magnetoresistance (TMR) in Magnetic Tunnel Junctions (MTJs) during thermal processing, as existing technologies suffer from degradation of magnetization and crystallinity without a seed layer for the pinned layer.
Innovation Solution
A folded spin-orbit torque (SOT) magnetoresistive memory device is formed with a pinned layer in contact with a seed layer, enhancing thermal stability, and a capping layer is used to increase perpendicular magnetic anisotropy (PMA) and improve the retention of the free layer, thereby maintaining high TMR and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pinned layer is formed without a seed layer in thermal processing, then thermal stability is degraded, but adding a seed layer increases manufacturing complexity
Solution Approach 1:
A seed layer is formed prior to the pinned layer to provide a crystalline template that prevents degradation during subsequent thermal processing. This preliminary action ensures the pinned layer maintains its magnetization and crystallinity through thermal cycles without requiring complex additional structures.
Solution Approach 2:
The seed layer acts as an intermediary between the substrate and the pinned layer, providing a stable crystalline foundation that protects the pinned layer from thermal degradation. This intermediate layer mediates the thermal stress and prevents direct damage to the pinned layer's magnetic properties.
2Duration of action of stationary object
If a capping layer is added to increase perpendicular magnetic anisotropy, then retention is improved, but device structure becomes more complex
Solution Approach 1:
A capping layer is introduced to modify the magnetic anisotropy parameters of the free layer, specifically enhancing perpendicular magnetic anisotropy (PMA). This parameter change improves data retention by stabilizing the magnetic state against thermal fluctuations and external disturbances.
Solution Approach 2:
The capping layer forms a composite structure with the free layer, creating a multi-layer system with optimized magnetic properties. This composite approach combines materials with different magnetic characteristics to achieve enhanced retention while maintaining a relatively simple overall device architecture.
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 solution provides improved thermal stability and retention in the memory device by ensuring the pinned layer's stability through contact with a seed layer and increasing PMA with a capping layer, preventing TMR degradation and enhancing the overall performance of the MTJ.
Implementation Method 1
a spin-orbit torque (SOT) layer spaced apart from the memory stack
Implementation Method 2
An MTJ is a device that changes its resistive state based on the state of magnetic materials within the device
Implementation Method 3
a pinned layer in contact with a seed layer, enhancing thermal stability
Implementation Method 4
a capping layer is used to increase perpendicular magnetic anisotropy (PMA) and improve the retention of the free layer
Data Source
AI summary
A magnetoresistive memory device includes a memory stack, a spin-orbit-torque (SOT) layer, and a free layer. The memory stack includes a pinned layer, a spacer layer over the pinned layer, a reference layer over the spacer layer, and a tunnel barrier layer over the reference layer. The SOT layer has a top surface substantially coplanar with a top surface of the tunnel barrier layer of the memory stack. The free layer interconnects the SOT layer and the tunnel barrier layer.