SOT MRAM Write Line Resistivity Reduction via Composite Metal Stacking
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Solution Overview
Problem
Spin-transfer torque (STT) MRAM devices have a single read/write path, which impairs read reliability and imposes stress on the magnetic tunnel junction, leading to time-dependent degradation, while spin-orbit torque (SOT) MRAM devices separate read and write paths but have a larger footprint and increased resistivity due to the use of heavy metals for spin Hall effect (SHE) write lines, resulting in higher power consumption and reduced integration density.
Innovation Solution
The integration of multiple MRAM cells on a SHE line formed by multiple metals, where a first type of metal with SHE properties is in contact with the free layer of each cell, and a low-resistivity metal is placed between cells, reducing overall resistivity and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If heavy metals are used for spin Hall effect (SHE) write lines in SOT-MRAM devices, then spin-orbit torque switching is achieved, but resistivity increases leading to higher power consumption
Solution Approach 1:
The patent employs a composite metal structure where a heavy metal layer (Ta, W, or Pt) providing spin Hall effect is combined with a low-resistivity metal layer (Cu, Ag, or Al) in a stacked configuration. This composite approach allows the heavy metal to generate the necessary spin-orbit torque for reliable magnetic switching while the low-resistivity metal reduces overall line resistivity and power consumption, resolving the contradiction between switching reliability and power efficiency
Solution Approach 2:
The patent applies different material properties to different regions of the write line structure. The heavy metal layer is positioned where spin Hall effect generation is most effective (adjacent to the magnetic tunnel junction), while the low-resistivity metal forms the current-carrying path. This local optimization ensures that each material performs its specialized function, achieving both reliable switching and reduced power consumption
2Productivity
If heavy metals are used for spin Hall effect (SHE) write lines in SOT-MRAM devices, then spin-orbit torque switching is achieved, but device footprint increases reducing integration density
Solution Approach 1:
The stacked composite metal structure allows for more efficient use of vertical space compared to lateral expansion of heavy metal lines. By stacking the heavy metal layer with the low-resistivity metal layer vertically, the design reduces the lateral footprint while maintaining the spin Hall effect functionality, thereby improving integration density without sacrificing switching reliability
Solution Approach 2:
The patent transitions from a lateral arrangement of metals to a vertical stacked configuration. This dimensional change allows the heavy metal to be positioned directly adjacent to the magnetic tunnel junction in the vertical dimension, maximizing the spin Hall effect efficiency while minimizing the horizontal footprint, thus resolving the contradiction between integration density and switching reliability
3Reliability
If current is injected perpendicularly into the magnetic tunnel junction (MTJ) in STT-MRAM, then write operation is achieved, but read and write paths are combined causing stress on MTJ and time-dependent degradation
Solution Approach 1:
The patent separates the read and write current paths into distinct physical routes. The write current flows through the heavy metal/SOT layer adjacent to the MTJ, generating spin-orbit torque to switch the magnetic state, while the read current flows through the MTJ itself. This segmentation protects the MTJ from the high-stress write current, eliminating time-dependent degradation caused by repeated perpendicular current injection
Solution Approach 2:
The heavy metal layer acts as an intermediary that converts charge current into spin-orbit torque without requiring the current to pass through the MTJ. This intermediary mechanism allows the write operation to be performed indirectly through the SOT effect, protecting the MTJ from direct exposure to high-density write currents and their associated degradation mechanisms
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 decreases the resistivity of the SHE write line and average power consumption per unit cell, improving integration density and reducing bit cell tunnel magnetoresistance degradation, thereby enhancing read stability and device endurance.
Implementation Method 1
A first type of metal is formed on an interlayer dielectric layer with a plurality of embedded contacts, where the first type of metal exhibits spin Hall effect (SHE) properties
Data Source
AI summary
Embodiments of the invention include a method for fabricating a magnetoresistive random-access memory (MRAM) structure and the resulting structure. A first type of metal is formed on an interlayer dielectric layer with a plurality of embedded contacts, where the first type of metal exhibits spin Hall effect (SHE) properties. At least one spin-orbit torque (SOT) MRAM cell is formed on the first type of metal. One or more recesses surrounding the at least one SOT-MRAM cell are created by recessing exposed portions of the first type of metal. A second type of metal is formed in the one or more recesses, where the second type of metal has lower resistivity than the first type of metal.