Resistive Memory Cell With Ovonic Threshold Switch Selector
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Solution Overview
Problem
Phase-change memory cells are limited in density and location by the placement of selection elements on a semiconductor substrate, leading to constraints in memory cell density and placement.
Innovation Solution
A resistive memory cell design featuring a stack of a selector, a resistive element, and a phase-change material with the selector having no physical contact with the phase-change material, where the selector is L-shaped and rests on a conductive track, allowing for increased density without substrate constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If selection elements are formed inside and/or on top of a semiconductor substrate, then current flow can be controlled and limited, but memory cell density and location are constrained by the substrate's capacity
Solution Approach 1:
The memory cell structure transitions from a planar substrate-based architecture to a vertical stack architecture. The selector, resistive element, and phase-change material are arranged in vertical layers, with the selector resting on conductive tracks at lower levels while the phase-change material is at higher levels. This vertical stacking enables higher memory cell density without increasing surface area, as multiple functional layers are stacked in the vertical dimension rather than spreading out horizontally on the substrate.
Solution Approach 2:
A dielectric layer is introduced as an intermediary between the selector and the phase-change material. The selector rests on the conductive track, and the dielectric layer separates the selector from the phase-change material, preventing direct contact. This intermediary layer prevents material diffusion while maintaining electrical functionality, allowing the selector to control current flow without being in direct physical contact with the phase-change material.
2Reliability
If the selector is placed in direct contact with the phase-change material, then current flow is controlled, but material diffusion occurs compromising integrity
Solution Approach 1:
A dielectric layer is introduced as an intermediary between the selector and the phase-change material. The selector rests on the conductive track, and the dielectric layer separates the selector from the phase-change material, preventing direct contact. This intermediary layer prevents material diffusion while maintaining electrical functionality, allowing the selector to control current flow without being in direct physical contact with the phase-change material.
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 design enables higher memory cell density without increasing surface area and prevents material diffusion, maintaining the integrity of the phase-change material, thus enhancing operational efficiency and reducing power loss.
Implementation Method 1
Each selector is an Ovonic Threshold Switch (OTS) that comprises a stack of three layers
Implementation Method 2
The difference in electric resistance between the amorphous phase of the material and its crystal phase is used to define at least two memory states
Implementation Method 3
Phase-change materials are materials which may switch between a crystal phase and an amorphous phase
Data Source
AI summary
The disclosure concerns a resistive memory cell, including a stack of a selector, of a resistive element, and of a layer of phase-change material, the selector having no physical contact with the phase-change material. In one embodiment, the selector is an ovonic threshold switch formed on a conductive track of a metallization level.