MTJ Spacer Layer Composition for Thermal Stability and Coupling
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Solution Overview
Problem
High temperatures during the formation of back-end-of-line interconnects in magnetic tunnel junction (MTJ) memory devices cause atoms to diffuse out of the free magnetic sublayers, reducing data retention and thermal stability, while increasing the thickness of the spacer layer to improve diffusion blocking ability can reduce magnetic coupling.
Innovation Solution
Incorporating magnesium into the spacer layer between the free magnetic sublayers, along with transition metals like tungsten, molybdenum, or tantalum, to enhance diffusion blocking without significantly reducing magnetic coupling, thereby improving thermal stability and allowing for thicker spacer layers without performance degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the spacer layer is increased to improve diffusion blocking ability, then thermal stability is improved, but magnetic coupling between free magnetic sublayers is reduced
Solution Approach 1:
The spacer layer is formed as a composite structure with a first spacer layer and a second spacer layer having different materials. This composite structure provides enhanced diffusion blocking ability while maintaining magnetic coupling between the free magnetic sublayers, resolving the contradiction between thermal stability and magnetic coupling.
Solution Approach 2:
The spacer layer is divided into multiple segments (first spacer layer and second spacer layer) with different thicknesses and materials. The first spacer layer provides diffusion blocking while the second spacer layer maintains magnetic coupling, allowing the system to achieve both thermal stability and magnetic coupling without requiring a single thick spacer layer.
2Ease of manufacture
If high temperatures are used during interconnect formation, then manufacturing process is simplified, but atom diffusion out of free magnetic sublayers increases
Solution Approach 1:
The spacer layer is formed before the high-temperature interconnect formation process. This preliminary action creates a protective barrier that prevents atom diffusion during subsequent high-temperature manufacturing steps, allowing simplified high-temperature processing without material loss.
Solution Approach 2:
The spacer layer acts as an intermediary barrier between the free magnetic sublayers and the high-temperature environment during interconnect formation. It mediates the interaction by blocking atom diffusion while allowing the high-temperature manufacturing process to proceed, thus protecting the magnetic layers from material loss.
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 addition of magnesium to the spacer layer improves thermal stability by reducing boron diffusion and maintaining magnetic coupling, allowing the MTJ to withstand higher temperatures during interconnect formation without substantial data retention loss, thus enabling more interconnect layers without performance reduction.
Implementation Method 1
the spacer layer is disposed within the free magnetic layer directly between the first free magnetic sublayer and the second free magnetic sublayer... the spacer layer includes a transition metal such as, for example, tungsten, molybdenum, tantalum, hafnium, or the like... the spacer layer is to block atoms from diffusing out of the first free magnetic sublayer
Implementation Method 2
magnetoresistive random-access memory (MRAM)... A magnetic tunnel junction (MTJ) is over the substrate... The magnetic tunnel junction includes a reference magnetic layer... a free magnetic layer over the reference magnetic layer... The resistance of the MTJ changes based on the magnetic orientations of the free magnetic layers relative to the reference magnetic layer
Data Source
AI summary
An integrated chip including a reference magnetic layer and a barrier layer over the reference magnetic layer. A first free magnetic layer is over the barrier layer. A second free magnetic layer is over the first free magnetic layer. A spacer layer is between the first free magnetic layer and the second free magnetic layer. The spacer layer includes magnesium and a transition metal. An atomic ratio of the magnesium to the transition metal ranges from 15% to 80%.