Multifilament ReRAM Structure With Insulation Layers for Low Variability
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Solution Overview
Problem
Prior art non-volatile memory (NVM) structures with resistive random access memory (ReRAM) elements exhibit high variability due to the formation of narrow, high resistance filaments with few oxygen vacancies, making them unsuitable for large arrays required in neuromorphic computing applications.
Innovation Solution
A grain-boundary self-aligned resistive memory structure is developed, allowing for the closely-packed formation of multiple oxide-based ReRAM elements in parallel, each with its own compliance resistor, reducing variability by forming multiple filaments and using a dielectric isolation structure with a lateral width of 0.5 nm to 5.0 nm to enable tight spacing and efficient filament formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large compliance resistor is used to achieve high resistance for RPU applications, then the resistance value is improved, but the variability increases due to narrow filament formation
Solution Approach 1:
The patent divides a single ReRAM element into multiple ReRAM elements arranged in parallel within the same cross-point structure. Each ReRAM element has its own compliance resistor, creating multiple independent conduction paths. This segmentation reduces variability because the composite conductance is the sum of multiple filaments rather than relying on a single narrow filament, thereby improving reliability for RPU applications.
2Productivity
If multiple ReRAM elements are closely packed to increase array density, then the processing throughput is improved, but the device area decreases making isolation difficult
Solution Approach 1:
The patent merges multiple ReRAM elements and their compliance resistors into a single cross-point structure by forming them within the same pillar. The shared conductive pillars and filament forming layer allow multiple elements to occupy the same physical footprint, achieving high device density without requiring additional lateral space, thus maintaining high processing throughput while minimizing device area.
3Speed
If the compliance resistor is placed close to the ReRAM device to minimize parasitic capacitance, then the speed is improved, but the variability increases due to narrow filament formation
Solution Approach 1:
The patent segments the compliance resistance function across multiple parallel ReRAM elements, each with its own compliance resistor. This allows the total compliance resistance to be achieved through parallel combinations, reducing the need for extremely narrow individual filaments. The multiple filaments provide redundant conduction paths that reduce variability while maintaining close physical proximity for minimal parasitic capacitance.
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 reduces variability in the composite ReRAM cell, enabling the formation of large arrays with reduced parasitic capacitance and improved reliability for neuromorphic computing applications, such as artificial synapses, by allowing tens to hundreds of elements in a substantially smaller area.
Implementation Method 1
A dielectric isolation structure is located between each pillar structure of the plurality of pillar structures
Implementation Method 2
CMOS compatible ReRAM elements based on partial oxide breakdown, forming reversible conductive filaments
Implementation Method 3
the resistive pillar is composed of a resistive material having a higher resistivity than the electrically conductive material
Data Source
AI summary
A grain-boundary self-aligned resistive memory structure is provided enabling the closely-packed formation of multiple, oxide-based, ReRAM elements in parallel, each with its own compliance resistor. The structure is capable of forming multiple filaments, one per element, with the aim of reducing the variability in the composite ReRAM cell.