Multi-layer MRAM with Voltage Control Lines and SOT Writing
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Solution Overview
Problem
The existing 3D stacked magnetic random access memory (MRAM) faces challenges in improving storage density and stability due to the difficulty in finding a matching selector for the magnetic tunnel junction (MTJ) and the instability caused by current passing through the junction region during data writing.
Innovation Solution
The proposed solution eliminates the need for a selector in the storage unit by using a multi-layer storage structure with voltage control lines, employing the spin-orbit torque (SOT) and voltage-controlled magnetic anisotropy (VCMA) effects to write data, where a bias voltage is applied to the voltage control line connected to the MTJ, and a current is supplied through an electrode line to reverse the magnetic moment, thereby avoiding current passage through the junction region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a 3D stacked storage array with selector is used, then storage density is improved, but device complexity increases due to difficulty in finding matching selector for MTJ
Solution Approach 1:
The patent removes the selector component from the storage unit, eliminating the complexity of finding and matching selectors for MTJ while maintaining 3D stacked architecture for high storage density
Solution Approach 2:
The bit line serves multiple functions: it provides write current for data writing and also serves as one of the two lines for read operations, eliminating the need for separate selector components
2Productivity
If data is written under STT effect with current passing through junction region, then data writing is achieved, but MTJ stability decreases due to easy breakdown
Solution Approach 1:
The patent introduces a heavy metal layer as an intermediary that generates spin-orbit torque to switch the magnetic moment of the free layer, preventing direct current flow through the MTJ junction region and avoiding breakdown
Solution Approach 2:
The patent replaces the spin transfer torque (STT) mechanism with spin-orbit torque (SOT) mechanism, where current flows through the heavy metal layer instead of the MTJ junction, substituting a more reliable physical mechanism
3Quantity of substance
If 3D stacked storage array is implemented, then storage density is improved, but manufacturing complexity increases due to preparation difficulty
Solution Approach 1:
The patent divides the storage structure into modular layers (MTJ layer, heavy metal layer, insulating layer) that can be independently prepared and stacked, simplifying the manufacturing process while achieving 3D high density
Solution Approach 2:
The patent transitions from 2D planar storage to 3D stacked architecture by adding the vertical dimension with multiple layers, increasing storage density while maintaining manageable manufacturing complexity through standardized layer preparation
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 approach simplifies the storage unit structure, enhances the stability of the magnetic tunnel junction, and increases storage density by reducing the complexity of preparing storage units and minimizing sneak path impacts, while maintaining high resistance values to prevent current flow through the MTJ.
Implementation Method 1
employing the spin-orbit torque (SOT) and voltage-controlled magnetic anisotropy (VCMA) effects to write data, where a bias voltage is applied to the voltage control line connected to the MTJ
Implementation Method 2
employing the spin-orbit torque (SOT) and voltage-controlled magnetic anisotropy (VCMA) effects to write data, where a current is supplied through an electrode line to reverse the magnetic moment
Implementation Method 3
maintaining high resistance values to prevent current flow through the MTJ
Data Source
AI summary
One example magnetic random access memory includes a plurality of structural units and a plurality of voltage control lines. The plurality of voltage control lines are in parallel with each other. Planes in which the plurality of structural units are located are in parallel with each other, and a plane in which each of the plurality of structural units is located is perpendicular to the plurality of voltage control lines. Each structural unit includes a multi-layer storage structure including multiple layers that are stacked in sequence. Each layer of the multi-layer storage structure includes an electrode line and a plurality of storage units disposed on the electrode line. Each of the plurality of storage units includes a magnetic tunnel junction. A first end of each storage unit is connected to the electrode line, and a second end of each storage unit is connected to one of the plurality of voltage control lines.