Discontinuous Mg Layer for MTJ Shunt Reduction
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Solution Overview
Problem
Current Magnetic Tunneling Junction (MTJ) technology fails to minimize electrical shunting, leading to a significant percentage of MTJ elements with low tunneling magnetoresistive ratio and resistance, which degrades the performance of spin-transfer (STT-RAM) devices.
Innovation Solution
A MTJ structure is developed with a thin discontinuous Mg or MgM layer inserted between the free layer and capping layer, acting as a blocking layer to prevent diffusion of conductive materials and reduce electrical shunting, while maintaining high tunneling magnetoresistive ratio and resistance uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a continuous Mg layer is used to enhance perpendicular magnetic anisotropy, then magnetic switching margin is improved, but electrical shunting increases causing low tail population
Solution Approach 1:
The continuous Mg layer is segmented into discontinuous islands separated by dielectric material. This segmentation prevents electrical shunting pathways while preserving the perpendicular magnetic anisotropy effect in regions where Mg islands contact the free layer, thus resolving the contradiction between magnetic switching margin and electrical shunting.
Solution Approach 2:
The Mg layer transitions from uniform continuous coverage to localized island structures with varying sizes and distributions. This local quality variation allows the structure to provide PMA enhancement where needed (at island locations) while blocking electrical shunt paths in between islands, simultaneously achieving both magnetic performance and electrical isolation.
2Stability of the object's composition
If Mg layer thickness is increased to improve perpendicular magnetic anisotropy, then thermal stability increases, but electrical shunting and low tail population worsen
Solution Approach 1:
By segmenting the Mg layer into discrete islands rather than a continuous thick layer, the patent achieves thermal stability through localized PMA enhancement while preventing the formation of continuous electrical shunt pathways that would degrade resistance uniformity and create low tail population.
Solution Approach 2:
The discontinuous Mg layer structure creates a porous-like configuration where dielectric material fills the spaces between Mg islands. This porous structure provides electrical isolation to prevent shunting while maintaining the magnetic functionality through the remaining Mg island regions, improving resistance uniformity without sacrificing thermal stability.
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 effectively reduces the percentage of MTJ elements with low tunneling magnetoresistive ratio, enhancing the yield of high-performance MTJs and improving the thermal stability and integrity of the tunnel barrier layer.
Implementation Method 1
acting as a blocking layer to prevent diffusion of conductive materials
Implementation Method 2
The tunnel barrier layer is thin enough that a current through it can be established by quantum mechanical tunneling of conduction electrons
Implementation Method 3
When a spin- polarized current transverses a magnetic multilayer in a CPP configuration, the spin angular moment of electrons incident on a ferromagnetic layer interacts with magnetic moments of the ferromagnetic layer near the interface between the ferromagnetic and non-magnetic spacer. Through this interaction, the electrons transfer a portion of their angular momentum to the ferromagnetic layer.
Implementation Method 4
The spin-transfer effect arises from the spin dependent electron transport properties of ferromagnetic-spacer-ferromagnetic multilayers
Implementation Method 5
The BE may be a composite that includes an uppermost Ta layer which is sputter etched to form a amorphous surface that promotes smooth and flat overlying layers in the MTJ
Data Source
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Figure 5~6
AI summary
A MTJ is disclosed with a discontinuous Mg or Mg alloy layer (41) having a thickness from 1 to 3 Angstroms between a free layer (40) and a capping layer (42) in a bottom spin valve configuration. It is believed the discontinuous Mg layer (41) serves to block conductive material in the capping layer (42) from diffusing through the free layer (40) and into the tunnel barrier layer (39) thereby preventing the formation of conductive channels that function as electrical shunts within the insulation matrix of the tunnel barrier (39). As a result, the "low tail" percentage in a plot of magnetoresistive ratio vs Rp is minimized which means the number of high performance MTJ elements in a MTJ array is significantly increased, especially when a high temperature anneal is included in the MTJ fabrication process. The discontinuous layer (41) is formed by a low power physical vapor deposition process.