Multilayer MgO Tunnel Barrier for MRAM
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Solution Overview
Problem
Conventional methods for fabricating magnetic tunnel junctions in MRAM cells result in defects such as pinholes in the MgO tunnel barrier layer, leading to current leakage, lower resistance, and reduced breakdown voltage, especially for low RA values.
Innovation Solution
A method involving the deposition and oxidation of multiple layers of metallic Mg to form a multilayer MgO tunnel barrier, using techniques like sputtering and plasma oxidation, to minimize defect formation and enhance breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single layer of MgO tunnel barrier is formed by RF magnetron sputtering, then the manufacturing process is simple and fast, but defects such as pinholes are formed leading to current leakage and lower breakdown voltage
Solution Approach 1:
The single MgO barrier layer is segmented into multiple thinner MgO layers separated by non-magnetic metal layers. This segmentation prevents the formation of through-pinholes while maintaining manufacturing efficiency, as each thin layer is less prone to defect formation and the metal interlayers provide additional barrier functionality.
Solution Approach 2:
The tunnel barrier is transformed from a simple MgO layer into a composite structure consisting of alternating MgO and non-magnetic metal layers. This composite structure combines the high TMR ratio benefit of MgO with the defect-tolerance and conductivity control benefits of metal interlayers, achieving both high reliability and manufacturing efficiency.
2Reliability
If the MgO tunnel barrier layer is made thicker to reduce pinholes, then defectivity is reduced, but the resistance-area product becomes too large requiring higher driving voltage
Solution Approach 1:
The thick MgO layer is segmented into multiple thin layers separated by conductive metal interlayers. This segmentation reduces the resistance-area product compared to a single thick layer, as the metal interlayers provide additional conduction paths while the segmented structure maintains low defectivity through reduced stress and improved oxidation control in each thin layer.
Solution Approach 2:
The composite structure of alternating MgO and metal layers optimizes the balance between barrier quality and resistance. The MgO layers provide high TMR ratio and oxidation stability, while the metal interlayers provide conductivity and defect tolerance, achieving low defectivity without excessive resistance.
3Productivity
If a single step oxidation is used to form MgO from Mg layer, then the process is simple and fast, but the Mg layer is under-oxidized resulting in lower resistance and breakdown voltage
Solution Approach 1:
The oxidation process is segmented into multiple steps, with each thin Mg layer being oxidized separately. This segmentation allows complete and controlled oxidation of each layer, preventing under-oxidation issues while maintaining overall process efficiency through the thinness of individual layers that oxidize faster and more completely.
Solution Approach 2:
The Mg layers are deposited with controlled thickness and structure before oxidation, preparing them for complete oxidation in subsequent steps. The preliminary deposition of thin, uniform Mg layers ensures that the oxidation process can proceed to completion without under-oxidation, while the segmented structure allows this preparation to be done efficiently.
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 method achieves a magnetic tunnel junction with low defectivity and higher breakdown voltage compared to conventional approaches, maintaining resistance and magnetoresistance levels similar to defect-free barriers.
Implementation Method 1
oxidizing the deposited layer of metallic Mg such as to transform the metallic Mg into MgO
Implementation Method 2
the MgO formation method by the RF magnetron sputtering
Data Source
AI summary
The present disclosure concerns a method of fabricating a magnetic tunnel junction suitable for a magnetic random access memory (MRAM) cell and comprising a first ferromagnetic layer, a tunnel barrier layer, and a second ferromagnetic layer, comprising: forming the first ferromagnetic layer; forming the tunnel barrier layer; and forming the second ferromagnetic layer; wherein said forming the tunnel barrier layer comprises depositing a layer of metallic Mg; and oxidizing the deposited layer of metallic Mg such as to transform the metallic Mg into MgO; the step of forming the tunnel barrier layer being performed at least twice such that the tunnel barrier layer comprises at least two layers of MgO.