SOT MRAM Cell With Integrated Selectors for Dense Crossbar Arrays
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The integration density of SOT MRAM is lower due to its 2T1R configuration, making it incompatible with crossbar matrix arrangements, and existing solutions either increase read energy or reduce durability by requiring the write current to pass through the magnetic tunnel junction.
Innovation Solution
A 2S1R magnetoresistive memory cell structure with integrated selectors based on Mott oxides or topological insulators, allowing for asynchronous write modes and minimizing control voltages, along with separate read and write paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a 2T1R configuration is used for SOT MRAM memory cells, then separate write and read paths are achieved, but integration density decreases and compatibility with crossbar matrix arrangements is lost
Solution Approach 1:
The patent merges the selector and transistor functions into a single integrated component. The selector incorporates both the switching function (replacing the transistor) and the selection function, reducing the memory cell from a 2T1R configuration to a 1S1R configuration. This merging enables crossbar matrix compatibility while maintaining separate write and read paths through the selector's voltage-controlled resistance states.
Solution Approach 2:
The selector serves multiple functions simultaneously: it acts as a voltage-controlled switch, a memory cell selector, and a path router for separate write and read operations. By making the selector multi-functional, the patent eliminates the need for dedicated transistors while maintaining the benefits of separate write and read paths, thus improving integration density without sacrificing reliability.
2Device complexity
If conventional selectors (varistors or OTS) are used in 1S1R memory cells, then compactness is achieved, but compatibility with MRAM is lost due to high threshold voltage
Solution Approach 1:
The patent changes the key parameter of the selector—the threshold voltage—by using a different physical mechanism (spin-orbit coupling) compared to conventional selectors. This parameter change enables the selector to operate within the low voltage range (1.3V to 2V) required by MRAM, while still maintaining the compact 1S1R structure. The spin-orbit torque selector achieves voltage control through magnetic field effects rather than high-field breakdown or phase change.
Solution Approach 2:
The patent replaces the mechanical/electrical breakdown mechanism of conventional selectors (varistor filament conduction or OTS phase change) with a spin-orbit coupling mechanism. This substitution eliminates the need for high threshold voltages (5V) and replaces them with a magnetic-field-controlled resistance change that operates at low voltages compatible with MRAM tunnel barriers.
3Ease of operation
If write current passes through the magnetic tunnel junction in existing solutions, then selector voltage thresholds are met, but durability decreases
Solution Approach 1:
The patent introduces a spin-orbit coupling layer as an intermediary between the write current path and the magnetic tunnel junction. The write current flows through this intermediary layer which generates spin-orbit torque to switch the magnetic state, rather than flowing directly through the tunnel junction. This intermediary mechanism enables selector activation and magnetic state switching while protecting the tunnel junction from high current stress, thereby improving durability.
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
Enables dense memory structures with reduced energy consumption and improved durability by using selectors that do not require the write current to pass through the magnetic tunnel junction, facilitating compact and efficient memory cell design.
Implementation Method 1
a write track made of a material with a spin Hall effect or a material with an orbital Hall effect
Implementation Method 2
Magnetoresistive Random Access Memory (MRAM) with Spin-Orbit-Torque (SOT) transfer uses magnetic mechanisms to store data. It is based on magnetic tunnel junctions of which the resistance varies according to the orientation of the magnetic layers. Unlike conventional MRAM, SOT MRAM uses spin-orbit transfer, where currents through a track formed by materials with strong spin-orbit coupling induce switching of the magnetic state in a tunnel junction structure in contact with said track.
Implementation Method 3
a support layer made of a material having a configurable metal-insulator transition; the part of the support layer confined between the first electrode and the write track having a conduction state configurable by the first and second control voltages so as to form a first selector having a high resistive state and a low resistive state
Data Source
AI summary
A magnetoresistive memory cell includes a pillar forming a magnetic tunnel junction and a write track made of a spin Hall effect material or an orbital Hall effect material; a support layer made of a material with a configurable metal-insulator transition; a first electrode arranged on the support layer; the part of the support layer confined between the first electrode and the write track forming a first selector; a second electrode arranged on the support layer; the part of the support layer confined between the second electrode and the write track forming a second selector.