Hybrid Perpendicular In-Plane STT-MRAM Device
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Solution Overview
Problem
Current STT-MRAM devices face limitations in memory cell miniature size, stability, and storage capacity, with in-plane STT-MRAMs experiencing instability and uniformity issues, while perpendicular STT-MRAMs are restricted to 1-bit storage and require strong magnetic anisotropy for long-term data retention, leading to power consumption and process complexity challenges.
Innovation Solution
A hybrid STT-MRAM device is proposed, featuring face-to-face stacking of perpendicular and in-plane magnetic tunnel junctions (MTJs) separated by a nonmagnetic spacer, utilizing a Synthetic Antiferromagnetic (SAF) free layer structure to enhance writing performance and stability, allowing for 2-bit storage through a two-step writing method.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If perpendicular STT-MRAM is used to resolve memory stability issue, then bit storage stability is improved, but writing torque requirement increases and process complexity increases
Solution Approach 1:
The patent combines perpendicular and in-plane STT-MRAM structures into a hybrid device where perpendicular MTJs provide stable bit storage while in-plane MTJs facilitate easier writing. The two structures are merged at the device level with shared components like the antiferromagnetic layer and tunnel barrier, allowing both stability and writeability benefits to coexist without requiring separate independent systems.
Solution Approach 2:
The hybrid structure enables different functional regions within the same device: the perpendicular MTJ region handles stable data retention while the in-plane MTJ region handles writing operations. This multi-functionality allows a single device to perform both stable storage and easy writing functions that were previously conflicting requirements.
2Area of moving object
If perpendicular STT-MRAM is used to allow cell miniature, then areal storage density is improved, but writing torque requirement increases
Solution Approach 1:
The hybrid structure merges the advantages of perpendicular geometry (small cell size, high density) with in-plane magnetization dynamics (lower writing torque). The perpendicular tunnel barrier maintains small footprint while the in-plane free layer reduces the energy barrier for switching, enabling miniaturization without excessive writing torque requirements.
3Ease of operation
If in-plane STT-MRAM is used to achieve easy writing, then writing performance is improved, but memory stability deteriorates
Solution Approach 1:
The device is segmented into distinct functional regions: in-plane MTJs optimized for writing operations and perpendicular MTJs optimized for stable data retention. This segmentation allows each region to specialize in its respective function without compromising the other, with the in-plane section handling easy writing and the perpendicular section providing stability.
4Duration of action of stationary object
If perpendicular STT-MRAM is used to enable long-term data retention, then bit detain is improved, but power consumption increases
Solution Approach 1:
The hybrid structure combines perpendicular and in-plane configurations to achieve long data retention with reduced power consumption. The perpendicular MTJs provide the magnetic anisotropy needed for stable retention, while the in-plane MTJs offer lower energy switching paths, reducing the overall power required to maintain and update stored data over long periods.
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 hybrid STT-MRAM device achieves improved writing performance, increased storage capacity, reduced power consumption, and enhanced areal density, surpassing the limitations of existing STT-MRAM technologies by enabling multi-bit storage with stable magnetic properties and efficient data retention.
Implementation Method 1
The information stored in the FL layer can be read out after passing a current through the MTJ stack and the maximum resistance or the minimum resistance is obtained, respectively, if the FL magnetisation is stored antiparallel or parallel to the RL magnetisation based on tunneling magneto-resistance (TMR) effect.
Implementation Method 2
one is called free layer (FL) whose magnetisations can be rotated to be parallel or antiparallel to the RL magnetisations by spin transfer torques after passing currents through the MTJ from either RL through MgO barrier to FL or FL through MgO barrier to RL, respectively, to complete the information storage writing
Data Source
AI summary
A memory device, comprising a first magnetic anisotropy magnetic tunnel junction (ma-MTJ) having a first free layer disposed at one end thereof and a second ma-MTJ having a second free layer disposed at one end thereof. The first and second ma-MTJs are stacked with each other with the first free layer facing the second free layer. A tunneling barrier is sandwiched between the first and second free layer. A magnetic anisotropy direction of the first ma-MTJ is perpendicular to a magnetic anisotropy direction of the second ma-MTJ, and a magnetisation direction of the first free layer is perpendicular to a magnetisation direction of the second free layer.