VCMA MRAM Free-Layer Stack for High Coercive Switching
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Solution Overview
Problem
Existing VCMA MRAM devices face challenges in achieving large VCMA coefficients and maintaining high coercive fields, which are essential for efficient data retention and switching, due to the use of transition metal films that affect crystallization and band offset, leading to reduced retention and inefficient magnetization switching.
Innovation Solution
Incorporating engineered interface and cap layers with specific materials and thicknesses, such as 4f and 5d metals, to enhance orbital occupancy and spin-orbit coupling, improve crystallinity, and control the band offset, resulting in a magnetic structure with increased VCMA coefficients and coercive fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thin transition metal film (e.g., iridium) is used as an interface layer to increase perpendicular magneto anisotropy energy, then the VCMA coefficient is improved, but the coercive field decreases due to anti-crystallization barrier effects
Solution Approach 1:
The patent employs a composite interface layer structure combining transition metal (e.g., Ir) with L1(0) ordered alloy (e.g., CoPt) to achieve both high VCMA coefficient and high coercive field. The CoPt L1(0) layer provides strong perpendicular magnetic anisotropy and high coercivity, while the transition metal layer contributes to high VCMA coefficient through spin-orbit coupling at the interface.
Solution Approach 2:
The patent creates different functional zones within the interface layer: the transition metal layer (e.g., Ir) provides high VCMA coefficient through interfacial spin-orbit coupling, while the CoPt L1(0) layer provides high coercive field through its ordered alloy structure and strong PMA. Each layer is optimized for its specific function to resolve the contradiction.
2Reliability
If transition metal films are used to enhance perpendicular magneto anisotropy, then VCMA coefficient increases, but data retention deteriorates due to reduced coercive field
Solution Approach 1:
The composite structure of transition metal layer plus CoPt L1(0) layer simultaneously achieves high VCMA coefficient (for efficient switching) and high coercive field (for data retention). The CoPt layer's robust magnetic anisotropy ensures stable magnetization states for long-term data retention while the transition metal interface enables efficient voltage-controlled switching.
Solution Approach 2:
The patent optimizes the thickness and composition parameters of both transition metal and CoPt layers to achieve the desired balance. By controlling the thickness of each layer and the overall stack composition, the device achieves both high VCMA coefficient and high coercive field for improved data retention.
3Reliability
If transition metal films are used at the interface, then perpendicular magneto anisotropy energy increases, but magnetization switching efficiency decreases due to band offset changes
Solution Approach 1:
The CoPt L1(0) ordered alloy layer acts as an intermediary between the transition metal layer and the magnetic free layer. It mediates the spin-orbit coupling interaction to enhance perpendicular magneto anisotropy while maintaining favorable band alignment for efficient magnetization switching, thus resolving the contradiction between PMA enhancement and switching efficiency.
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 engineered layers enable VCMA coefficients of 100 fJ/Vm or more, ensuring efficient magnetization switching and improved data retention in VCMA MRAM devices.
Implementation Method 1
engineered interface and cap layers with specific materials and thicknesses, such as 4f and 5d metals, to enhance orbital occupancy and spin-orbit coupling
Implementation Method 2
VCMA MRAM devices store information in a magnetic layer that may be referred to as the magnetic free layer. For performing a write of information into this free layer, a voltage is applied across a barrier layer
Implementation Method 3
The Hc is the magnetic field that the magnetization of the free layer is able to withstand without becoming demagnetized or even being switched. The reason for the reduced Hc is that the Ir acts as an anti-crystallization barrier, which prevents crystallization from transferring from the MgO layer to the free layer
Implementation Method 4
the tunneling magnetoresistance (TMR) of tunneling through the barrier layer (thus also called the tunnel barrier layer) between the reference layer and the free layer may be measured to read information from the free layer
Data Source
AI summary
The present disclosure provides improved VCMA MRAM devices that include an engineered magnetic structure. The disclosure also presents the engineered magnetic structure, which includes a magnetic reference layer, a tunnel barrier layer provided on the magnetic reference layer, an interface layer provided on the tunnel barrier layer, a magnetic free layer provided on the interface layer, and a cap layer provided on the magnetic free layer. The interface layer and the cap layer are engineered to enhance an orbital occupancy and/or a spin-orbit-coupling of the magnetic free layer.