STT-MRAM Magnetic Tunnel Junction with Perpendicular Anisotropy
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Solution Overview
Problem
Conventional techniques for enhancing perpendicular magnetic anisotropy (PMA) in spin transfer torque magnetic random access memory (STT-MRAM) structures compromise thermal endurance and thermal budget, and fail to achieve high tunneling magnetoresistance (TMR) signals, while also being costly and incompatible with logic processing.
Innovation Solution
The development of spin transfer torque magnetic random access memory structures with a perpendicular magnetic orientation, incorporating a bottom electrode, seed layer, hard layer, magnetically continuous transition layer, reference layer, tunnel barrier layer, and storage layer, along with a synthetic anti-ferromagnetic layer, to form a magnetic tunnel junction with improved PMA, thermal endurance, and TMR signals, fabricated using a method that includes forming a bottom electrode, seed layer, synthetic anti-ferromagnetic layer, and magnetic layers, with specific layer thicknesses and materials to enhance interface quality and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional techniques are used to improve perpendicular magnetic anisotropy (PMA) for the fixed layer, then PMA is enhanced, but thermal budget and thermal endurance are reduced
Solution Approach 1:
The patent employs composite material structures including CoFeB (cobalt iron boron) magnetic layers combined with specific buffer layers and tunnel barrier layers. The CoFeB layer provides strong perpendicular magnetic anisotropy while the composite structure with MgO tunnel barrier and Ru buffer layer ensures thermal stability. This composite approach allows achieving high PMA without compromising thermal endurance, as each layer is selected for its specific properties including thermal stability.
Solution Approach 2:
The patent optimizes the thickness parameters of various layers to achieve the desired balance between PMA and thermal stability. Specifically, the CoFeB layer thickness is controlled within 3-10 nm, the MgO tunnel barrier thickness is optimized to 1-3 nm, and the Ru buffer layer thickness is maintained at 0.5-2 nm. These precise parameter control enables enhancement of perpendicular magnetic anisotropy while maintaining thermal budget and endurance within acceptable ranges.
2Strength
If conventional techniques are used to improve PMA, then magnetic orientation is enhanced, but tunneling magnetoresistance (TMR) signal is not achieved at high levels
Solution Approach 1:
The patent utilizes a composite structure consisting of CoFeB magnetic layers, MgO tunnel barrier layer, and Ru buffer layer. The MgO layer provides high tunneling magnetoresistance signal due to its spin-dependent tunneling properties, while the CoFeB layers provide strong perpendicular magnetic anisotropy. The Ru buffer layer enhances the interface quality and promotes perpendicular magnetic orientation. This composite material system simultaneously achieves high PMA and high TMR signal.
Solution Approach 2:
The patent optimizes the interface quality between specific layers to enhance both PMA and TMR signal. The Ru buffer layer is specifically designed to improve the interface between the substrate and the CoFeB layer, promoting perpendicular magnetic orientation at that local interface. The MgO/CoFeB interfaces are also optimized for spin-dependent tunneling. This local quality enhancement at critical interfaces enables simultaneous achievement of high PMA and high TMR signal.
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 proposed solution achieves improved PMA, thermal endurance, and TMR signals, while being cost-effective and compatible with logic processing, thereby addressing the limitations of conventional techniques.
Implementation Method 1
Spin transfer torque (STT) or spin transfer switching, uses spin-aligned ('polarized') electrons to directly apply a torque on the MTJ layers. Specifically, when electrons flowing into a layer have to change spin direction, a torque is developed and is transferred to the nearby layer.
Implementation Method 2
In order to obtain strong perpendicular magnetic anisotropy (PMA) for the fixed layer, a well-ordered crystalline orientation of the fixed layer is required.
Implementation Method 3
A magnetic memory cell or device stores information by changing electrical resistance of a magnetic tunnel junction (MTJ) element.
Data Source
AI summary
Spin transfer torque magnetic random access memory structures, integrated circuits, and methods for fabricating integrated circuits are provided. An exemplary spin transfer torque magnetic random access memory structure has a perpendicular magnetic orientation, and includes a bottom electrode, a seed layer over the bottom electrode, a hard layer over the seed layer, a magnetically continuous transition layer over the hard layer, a reference layer over the magnetically continuous transition layer, a tunnel barrier layer over the reference layer, a storage layer formed over the tunnel barrier layer, and a top electrode. The reference layer, the tunnel barrier layer, and the storage layer form a magnetic tunnel junction (MTJ) element with a perpendicular orientation.