Amorphous Silicon Selector Doped with Fluorine for Resistive Memory
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Solution Overview
Problem
Transistor-based flash memory faces limitations in endurance, power consumption, and scalability, making it inadequate for meeting the increasing demands of nonvolatile memory in modern electronic devices.
Innovation Solution
The development of resistive switching memory cells with a selector layer made of amorphous silicon doped with fluorine, which undergoes electrical breakdown at a specific voltage threshold, allowing for high current passage in a controlled manner and reducing leakage by passivating defects with fluorine, and the use of a fluoride ion reservoir to mitigate diffusion-induced degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If transistor-based flash memory is used to achieve nonvolatile storage, then high density and low fabrication costs are obtained, but endurance, power consumption, and scalability are limited
Solution Approach 1:
The patent changes the fundamental operating mechanism from transistor-based charge storage to resistive switching. By altering the physical principle (from quantum tunneling in flash memory to filament formation/breakage in resistive switching), the system achieves improved endurance and scalability while maintaining nonvolatile storage functionality
Solution Approach 2:
The patent replaces the mechanical/transistor-based system with a material-based resistive switching system. Instead of using transistor gate control and charge storage, the invention uses electrical field-induced filament formation and rupture in oxide materials to achieve binary state switching, eliminating the scalability and endurance limitations of transistor-based approaches
2Loss of energy
If amorphous silicon is used for the selector layer, then larger band gap and lower leakage are achieved, but defects and weak bonds remain that increase leakage
Solution Approach 1:
The patent creates a composite material system by doping amorphous silicon with fluorine. This composite approach combines the beneficial properties of amorphous silicon (large band gap) with fluorine's ability to passivate defects, achieving both low leakage current and high reliability by eliminating the weakness of pure amorphous silicon
Solution Approach 2:
Fluorine acts as an intermediary element that mediates between the amorphous silicon matrix and the defects within it. The fluorine atoms bond to dangling bonds and weak bonds, passivating them and preventing them from acting as leakage pathways, thus indirectly reducing leakage current without changing the fundamental amorphous silicon structure
3Loss of energy
If fluorine is added to passivate defects in amorphous silicon, then leakage is reduced, but fluorine diffusion into other components causes degradation
Solution Approach 1:
The patent applies a fluorine-containing protective layer on the electrode surface before fluorine diffusion can occur. This pre-applied fluorine reservoir acts as a cushion that absorbs excess fluorine atoms, preventing them from diffusing into the electrode and causing degradation, while still allowing sufficient fluorine to remain in the amorphous silicon for defect passivation
Solution Approach 2:
The patent creates different fluorine concentration zones: high fluorine concentration in the amorphous silicon selector layer for defect passivation, and a controlled fluorine gradient at the electrode interface managed by the protective layer. This local quality variation ensures fluorine provides benefit where needed while preventing harm where it would cause degradation
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 solution enhances the endurance and scalability of nonvolatile memory by improving the resistive switching mechanism, reducing power consumption, and maintaining performance even at high temperatures, thus addressing the limitations of traditional flash memory.
Implementation Method 1
Dangling bond and weak bond states appearing in the mid-gap position of amorphous silicon are eliminated by adding fluorine. Fluorine binds to and passivates defects.
Implementation Method 2
The selector is configured to undergo an electrical breakdown when a voltage applied to the selector exceeds a selected threshold. For purposes of this disclosure, the breakdown is defined as a reversible process associated with a rapid change in resistance of the selector.
Implementation Method 3
In some embodiments, a fluorine reservoir is positioned in a low current density region of the memory cell to counter diffusion of fluorine from the selector into other components.
Data Source
AI summary
Provided are resistive switching memory cells having selectors and methods of fabricating such cells. A selector may be disposed between an electrode and resistive switching layer. The selector is configured to undergo an electrical breakdown when a voltage applied to the selector exceeds a selected threshold. The selector is formed from amorphous silicon doped with fluorine. The concentration of fluorine may be between about 0.01% atomic and 3% atomic, such as about 1% atomic. Amorphous silicon has a larger band gap than, for example, crystalline silicon and, therefore, has a lower leakage. Dangling bond and weak bond states appearing in the mid-gap position of amorphous silicon are eliminated by adding fluorine. Fluorine binds to and passivates defects. In some embodiments, a fluorine reservoir is positioned in a low current density region of the memory cell to counter diffusion of fluorine from the selector into other components.