Composite MTJ Free Layer with Oxide Insertion for Thermal Stability
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Solution Overview
Problem
Conventional magnetic tunnel junction (MTJ) elements exhibit low thermal stability when exposed to high processing temperatures, which is a challenge in CMOS processing, and require high switching currents, making them unsuitable for cost-effective and stable applications.
Innovation Solution
The implementation of a magnetic tunnel junction (MTJ) element with a composite magnetic free layer comprising first and second magnetic free layers separated by an oxide-based insertion layer, which includes a base layer of Mg or Hf for ferromagnetic coupling, enhancing thermal stability and reducing switching currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional MTJ elements are used, then the structure is simple, but thermal stability is low when exposed to high processing temperatures
Solution Approach 1:
The magnetic free layer is segmented into multiple sub-layers (first magnetic free layer, second magnetic free layer, third magnetic free layer) separated by non-magnetic spacer layers. This segmentation allows each layer to contribute differently to the overall magnetic properties, enhancing thermal stability through improved magnetic anisotropy while maintaining controllable structural complexity through systematic layering.
Solution Approach 2:
The patent employs composite material structures by combining different magnetic layers (CoFeB, CoFe) with non-magnetic spacer layers (Ru, Ta) and oxide insertion layers (MgO). This composite approach creates a multi-layered MTJ element where each material contributes specific properties, achieving high thermal stability through synergistic effects while the systematic composition manages overall device complexity.
2Use of energy by moving object
If conventional MTJ elements are used, then manufacturing is simpler, but switching current is high
Solution Approach 1:
The patent applies local quality by creating regions with different magnetic properties within the free layer. The first, second, and third magnetic free layers have different thicknesses and compositions, creating localized variations in magnetic anisotropy and spin torque characteristics. This allows optimization of switching current in specific regions while maintaining overall manufacturability through standardized layer deposition processes.
Solution Approach 2:
The patent utilizes parameter changes by systematically varying the thickness, composition, and material properties of each magnetic layer and spacer layer. By adjusting parameters such as CoFeB layer thickness, Ru spacer thickness, and MgO insertion layer thickness, the patent optimizes spin transfer torque efficiency to reduce switching current while maintaining compatibility with existing CMOS manufacturing processes.
3Reliability
If conventional MTJ elements are used, then device complexity is low, but thermal stability degrades during BEOL CMOS processing
Solution Approach 1:
The patent implements preliminary action by incorporating oxide insertion layers (MgO) and carefully designed non-magnetic spacer layers (Ru, Ta) during the initial MTJ element fabrication. These layers are pre-configured to provide thermal protection and magnetic decoupling before subsequent high-temperature BEOL CMOS processing, preventing degradation of the magnetic tunnel junction properties during later manufacturing stages.
Solution Approach 2:
The patent uses non-magnetic spacer layers (Ru, Ta) and oxide insertion layers (MgO) as intermediary elements between the magnetic layers. These intermediary layers serve as thermal buffers and magnetic decoupling structures that protect the sensitive MTJ core from high-temperature processing effects while maintaining the necessary magnetic coupling for device operation, thus resolving the conflict between thermal stability and structural complexity.
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
This configuration improves the thermal stability and reduces switching currents, making the MTJ elements more suitable for CMOS processing while being cost-effective and compatible with existing semiconductor technologies.
Implementation Method 1
the insertion layer ferromagnetically couples the first and second magnetic free layers of the composite magnetic free layer
Implementation Method 2
tunnel magnetoresistance (TMR) degrades when exposed to high processing temperatures
Data Source
AI summary
Memory cells and method of forming thereof are presented. The method includes forming a magnetic tunnel junction (MTJ) element which includes a fixed magnetic layer, a tunneling barrier layer and a composite free magnetic layer. The composite free magnetic layer includes an insertion layer between first and second free magnetic layers. The insertion layer includes an oxide or oxidized layer. The insertion layer increases the overall thickness of the free layer, decreasing switching current as well as thermal stability. The oxidized layer may be MgO or HfOx. A surface layer may be provided over the oxide or oxidized layer to further enhance magnetic anisotropy to further decrease switching current. The surface layer is Ta, Ti or Hf.