MgO Capping Layer Conductive Channels for Perpendicular MTJs
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Solution Overview
Problem
Magnetic tunnel junctions (MTJs) with a metal oxide cap layer experience increased parasitic resistance, which reduces the magnetoresistive ratio (DRR) and increases writing voltage, compromising the reading and writing margins of MRAM bits.
Innovation Solution
Forming conductive channels within or around the metal oxide cap layer by depositing unoxidized metal atoms, using co-deposition of noble metals with Mg, or creating discontinuous metal oxide layers to reduce the resistance and maintain high perpendicular magnetic anisotropy (PMA) for thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a metal oxide cap layer is used to enhance perpendicular magnetic anisotropy (PMA) for thermal stability, then thermal stability is improved, but parasitic resistance increases which reduces DRR and increases writing voltage
Solution Approach 1:
The patent applies local quality by creating a non-uniform oxidation state within the metal oxide cap layer. The layer contains both fully oxidized regions (providing PMA) and partially reduced regions (providing conductivity), with the reduction primarily occurring at grain boundaries and interfaces. This spatial variation in oxidation state allows simultaneous achievement of thermal stability and low resistance
Solution Approach 2:
The patent creates a composite metal oxide structure that combines oxidized and reduced phases within the same layer. This composite approach allows the cap layer to exhibit both the magnetic anisotropy properties of the oxidized regions and the electrical conductivity of the reduced regions, resolving the contradiction between thermal stability and reading margin
2Stability of the object's composition
If a metal oxide cap layer is used to enhance perpendicular magnetic anisotropy (PMA) for thermal stability, then thermal stability is improved, but writing voltage increases due to increased parasitic resistance
Solution Approach 1:
The patent creates localized reduced regions within the metal oxide cap layer that serve as conductive pathways. These reduced zones are strategically positioned at grain boundaries and interfaces where they provide low-resistance paths for current flow during writing operations, thereby reducing the energy required to switch magnetic states while preserving thermal stability in the oxidized regions
3Strength
If the metal oxide cap layer is fully oxidized to maximize PMA, then perpendicular magnetic anisotropy is improved, but parasitic resistance increases which compromises device performance
Solution Approach 1:
The patent changes the oxidation state parameter of the metal oxide cap layer from fully oxidized to partially reduced. By controlling the reduction process to achieve a specific oxygen deficiency level, the patent optimizes the balance between maintaining sufficient PMA for thermal stability and reducing parasitic resistance for improved device performance
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
Significantly reduces the cap layer resistance and resistance-area product, enhancing the DRR and lowering the writing voltage while maintaining high thermal stability and reading margins for MRAM bits.
Implementation Method 1
One practical way to obtain strong PMA is through interfacial PMA at an interface between a CoFeB free layer and an MgO tunnel barrier layer
Implementation Method 2
a consequence of employing an MgO cap layer is the addition of parasitic resistance to the p-MTJ device
Data Source
AI summary
A magnetic tunnel junction (MTJ) is disclosed wherein a free layer (FL) interfaces with a first metal oxide (Mox) layer and second metal oxide (tunnel barrier) to produce perpendicular magnetic anisotropy (PMA) in the FL. In some embodiments, conductive metal channels made of a noble metal are formed in the Mox that is MgO to reduce parasitic resistance. In a second embodiment, a discontinuous MgO layer with a plurality of islands is formed as the Mox layer and a non-magnetic hard mask layer is deposited to fill spaces between adjacent islands and form shorting pathways through the Mox. In another embodiment, end portions between the sides of a center Mox portion and the MTJ sidewall are reduced to form shorting pathways by depositing a reducing metal layer on Mox sidewalls, or performing a reduction process with forming gas, H2, or a reducing species.