OxRAM Memory Cell Oxygen Gradient Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current OxRAM memory cells face challenges in controlling oxygen vacancy content and localizing oxygen diffusion phenomena, which are essential for maintaining the insulating nature and preventing surface oxidation, due to the limitations in depositing sub-stoichiometric hafnium dioxide and the need for expensive equipment to protect hafnium layers from oxidation.
Innovation Solution
The proposed OxRAM cell structure includes a sub-stoichiometric oxide insulator layer between metal layers, with a nitride sub-layer and a ternary or quaternary alloy sub-layer that forms an oxygen gradient, allowing controlled oxygen migration and depletion near the lower electrode, thereby localizing diffusion and maintaining conduction properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a layer of sub-stoichiometric hafnium dioxide HfOz is deposited directly to control oxygen vacancy content, then the oxygen vacancy content can be controlled, but it is not possible to deposit directly with controlled oxygen vacancy content because the first stable compound obtained is directly hafnium dioxide HfO2
Solution Approach 1:
The patent applies preliminary action by first depositing a layer of stoichiometric hafnium dioxide HfO2 with controlled thickness, then subsequently depositing a layer of metallic hafnium Hf on top. This preliminary deposition of the stable compound HfO2 provides a foundation that will later transform into sub-stoichiometric HfOz through oxygen migration during thermal processing, avoiding the impossibility of direct sub-stoichiometric deposition.
Solution Approach 2:
The patent utilizes parameter changes by controlling the thickness ratio between the HfO2 layer and the Hf layer, as well as applying thermal processing parameters. Through these parameter changes, the system transforms from stable HfO2 to sub-stoichiometric HfOz with controlled oxygen vacancy content, enabling precise control without direct deposition of unstable phases.
2Manufacturing precision
If a layer of hafnium Hf is deposited on stoichiometric hafnium dioxide HfO2 to control oxygen vacancy content, then the oxygen migration can be controlled, but the upper layer of hafnium Hf must be protected from air to prevent immediate oxidation into hafnium dioxide HfO2
Solution Approach 1:
The patent merges the Hf layer deposition with the subsequent electrode deposition process. The Hf layer is deposited and immediately covered by the upper electrode in the same manufacturing sequence, eliminating the need for separate protection measures. This merging of steps simplifies the equipment requirements while maintaining control over oxygen vacancy formation.
Solution Approach 2:
The patent ensures continuity of useful action by maintaining an inert or reducing atmosphere throughout the entire deposition sequence without interruption. The Hf layer is deposited and immediately covered by the upper electrode in continuous operation, preventing exposure to air and eliminating the need for complex protection equipment while ensuring controlled oxygen migration.
3Manufacturing precision
If a stack of hafnium dioxide HfO2 on hafnium Hf is used to control oxygen diffusion, then oxygen diffusion can be localized, but the deposition of hafnium dioxide HfO2 in oxidising atmosphere immediately transforms hafnium Hf into hafnium dioxide HfO2
Solution Approach 1:
The patent employs an inert or reducing atmosphere (such as nitrogen or forming gas) during the deposition of both the HfO2 layer and the Hf layer. This inert environment prevents the immediate oxidation of Hf to HfO2 during deposition, allowing the desired HfO2/Hf stack to be formed. The controlled atmosphere is maintained throughout the deposition process, enabling precise control over oxygen diffusion localization.
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 structure enables economical control of oxygen vacancy content and localization of oxygen diffusion, reducing the risk of surface oxidation and maintaining the insulating properties of the OxRAM cell, while avoiding the need for expensive equipment and ensuring efficient operation.
Implementation Method 1
thermodynamic equilibrium is achieved by migration of a part of the oxygen contained in the insulator layer made of hafnium dioxide HfO2 to the layer of titanium Ti situated just above
Implementation Method 2
Thermodynamic equilibrium is achieved by migration of a part of the oxygen contained in the insulator layer
Implementation Method 3
The fact that sub-stoichiometric hafnium dioxide HfOz has oxygen vacancies compared to stoichiometric hafnium dioxide HfO2 enables to facilitate the formation of a filament within the OxRAM cell
Data Source
AI summary
An OxRAM oxide based resistive random access memory cell includes a first electrode; a layer M1Oss of a sub-stoichiometric oxide of a first metal; a layer M2N of a nitride of a second metal M2; a layer M3M4O of a ternary alloy of a third metal M3, a fourth metal M4 and oxygen O, or M3M4NO of a quaternary alloy of the third metal M3, the fourth metal M4, nitrogen N and oxygen O and a second electrode. The standard free enthalpy of formation of the ternary alloy M3M4O, noted ΔGf,T0 (M3M4O), or of the quaternary alloy M3M4NO, noted ΔGf,T0 (M3M4NO), is strictly less than the standard free enthalpy of formation of the sub-stoichiometric oxide M1Oss of the first metal M1, noted ΔGf,T0 (M1Oss), itself less than or equal to the standard free enthalpy of formation of any ternary oxynitride M2NO of the second metal M2, noted ΔGf,T0 (M2NO):ΔGf,T0(M3M4O)<ΔGf,T0(M1Oss)≤ΔGf,T0(M2NO)or ΔGf,T0(M3M4NO)<ΔGf,T0(M1Oss)≤ΔGf,T0(M2NO).