Ultrathin Ferromagnetic Layer Enhances MRAM TMR Ratio
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Solution Overview
Problem
Existing STT-MRAM devices have relatively low tunneling magnetoresistance ratios, resulting in a small sense margin for sensing the stored logic state, which limits their use in high-density memory arrays.
Innovation Solution
Incorporating an ultrathin ferromagnetic material layer between the insulation layers in the MTJ structure of the MRAM cell, forming an IFI structure, which enhances the tunneling magnetoresistance ratio and sense margin by improving spin filtering efficiency without interfering with the STT switching mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional MTJ structure with continuous insulation layer is used, then the device structure is simple and easy to manufacture, but the tunneling magnetoresistance ratio is low resulting in small sense margin
Solution Approach 1:
The continuous insulation layer is segmented by introducing an ultrathin ferromagnetic material layer in the middle, creating an IFI (insulator-ferromagnet-insulator) structure. This segmentation allows the structure to maintain spin filtering capability while improving TMR ratio, resolving the contradiction between structural simplicity and measurement precision.
Solution Approach 2:
The patent uses composite materials by combining insulating layers (MgO) with an ultrathin ferromagnetic material layer to form the IFI structure. This composite approach enables both structural integrity and enhanced spin filtering efficiency, achieving high TMR ratio without excessive complexity.
2Measurement precision
If the ferromagnetic layer thickness is increased to improve spin filtering, then the TMR ratio improves, but the STT switching mechanism may be interfered with
Solution Approach 1:
The patent optimizes the ferromagnetic material layer thickness to a specific ultrathin range (approximately 0.5-2 nm), which is thick enough to provide spin filtering for improved TMR ratio but thin enough to avoid interfering with the STT switching mechanism. This precise parameter control resolves the contradiction between measurement precision and reliability.
Solution Approach 2:
The ferromagnetic material layer is positioned locally within the insulation layer at a specific depth, creating local spin filtering without affecting the overall MTJ structure's switching mechanism. This localized approach allows TMR improvement while maintaining STT switching reliability.
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 novel MRAM cell achieves a significant increase in TMR values, improving the sense margin by approximately 31% compared to prior art devices, enabling better performance in high-density memory arrays.
Implementation Method 1
enhances the tunneling magnetoresistance ratio and sense margin by improving spin filtering efficiency
Implementation Method 2
Tunneling magnetoresistance is a quantum mechanical effect which occurs when two layers of ferromagnetic material are separated by a few atomic layers of an insulating material
Implementation Method 3
The conductance of such a tunneling junction can vary dramatically depending on whether the ferromagnets are aligned in parallel or antiparallel
Data Source
AI summary
One illustrative MRAM cell disclosed herein includes a bottom electrode, a top electrode positioned above the bottom electrode and an MTJ (Magnetic Tunnel Junction) element positioned above the bottom electrode and below the top electrode. In this example, the MTJ element includes a bottom insulation layer positioned above the bottom electrode, a top insulation layer positioned above the bottom electrode; and a first ferromagnetic material layer positioned between the bottom insulation layer and the top insulation layer.