1T-1S SOT Memory Cell Top Electrode Selector Density
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Solution Overview
Problem
The perpendicular spin-orbit torque (pSOT) device, used as a replacement for embedded static random access memory (e-SRAM), faces challenges due to its increased area requirements and limited density caused by the need for two access transistors on either side of the spin orbit coupling (SOC) material, which restricts the density of pSOT-based magnetic random access memory (MRAM).
Innovation Solution
A 1T-1S (one transistor and one selector) SOT memory cell is formed by integrating a selector device with a top spin orbit torque electrode above a magnetic junction, allowing for lower lead resistance and the use of well-developed spin transfer torque (STT) MRAM stacks, thereby reducing the area requirements and improving memory density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If two access transistors are coupled on either side of the SOC material for bidirectional current application, then the pSOT device can achieve bidirectional current control, but the area of the memory bit-cell increases
Solution Approach 1:
The invention extracts one of the two access transistors from the conventional pSOT device structure and replaces it with a selector device. This reduction in transistor count directly decreases the memory bit-cell area while the selector device maintains the necessary bidirectional current control functionality through its selective conduction properties
Solution Approach 2:
The selector device serves multiple functions: it acts as an access element for bidirectional current control, provides data line selection, and enables memory cell addressing. By consolidating these functions into a single component rather than requiring separate transistors, the device achieves bidirectional current control with reduced area
2Reliability
If two access transistors are used for bidirectional current control, then the pSOT device achieves reliable current switching, but the memory density is limited
Solution Approach 1:
By removing one access transistor and replacing it with a selector device, the invention reduces the number of components per memory bit-cell. This extraction directly increases memory density while the selector device maintains reliable current switching through its threshold voltage characteristics that enable precise current control
Solution Approach 2:
The selector device merges the functions of access control and current switching into a single component. This consolidation maintains reliable current switching behavior while reducing the overall component count, thereby increasing the quantity of memory bits that can be packed into a given area
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 configuration enhances memory density by up to 30-50% compared to traditional STT MRAM devices, enabling efficient switching and reduced power consumption while maintaining reliable write times and energy efficiency.
Implementation Method 1
perpendicular spin-orbit torque (pSOT) device comprises a perpendicular magnetic tunneling junction (p-MTJ) stack on a spin orbit coupling (SOC) material
Implementation Method 2
use of well-developed spin transfer torque (STT) MRAM stacks
Data Source
AI summary
An apparatus is provided which comprises: a bit-line; a first word-line; a second word-line; and a source-line; a magnetic junction comprising a free magnet; an interconnect comprising spin orbit material, wherein the interconnect is adjacent to the free magnet of the magnetic junction; and a first device (e.g., a selector device) coupled at one end of the interconnect and to the second word-line; and a second device coupled to the magnetic junction, the first word-line and the source-line.