2T2R ReRAM with Shared-Gate VFETs for Filament Control
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Solution Overview
Problem
ReRAM devices face challenges in controlling the position of conducting filaments due to randomness in the electroforming process, leading to higher forming voltage, device variability, and a narrowed memory window, which affects scalability and reliability.
Innovation Solution
A method is developed to form a two-transistor-two-resistor (2T2R) ReRAM structure by integrating two vertical field effect transistors with a shared metal gate, where the epitaxial regions with triangular protrusions act as both the channel and bottom electrode for the ReRAM stack, reducing randomness and enhancing scalability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional ReRAM devices are formed without controlled filament positioning, then the device structure is simpler, but the forming voltage increases and device variability worsens
Solution Approach 1:
The patent applies preliminary action by pre-forming protruding epitaxial regions before the ReRAM electroforming process. These protruding regions are created through selective epitaxial growth on patterned sacrificial structures, establishing predetermined positions where conducting filaments will form. This preliminary structural preparation ensures that subsequent electroforming occurs at controlled locations rather than random positions, directly addressing the filament position control problem while maintaining reasonable device complexity.
Solution Approach 2:
The patent introduces protruding epitaxial regions as intermediary structures that mediate between the top and bottom electrodes. These intermediary protrusions serve as nucleation sites that guide ion migration and conducting filament formation. By introducing this intermediate structural element, the patent achieves controlled filament positioning without requiring direct complex patterning of the electrodes themselves, thus balancing manufacturing precision with device complexity.
2Reliability
If ReRAM devices use random filament formation, then the device fabrication is simpler, but the memory window narrows and reliability decreases
Solution Approach 1:
The patent applies local quality by creating regions with different properties within the ReRAM structure. Specifically, protruding epitaxial regions are formed with higher doping concentrations and different geometries compared to the surrounding areas. These localized quality variations create preferential pathways for conducting filament formation, ensuring that filaments form at specific locations with consistent properties. This local differentiation improves memory window and reliability by ensuring uniform filament characteristics across devices while avoiding the need for completely complex fabrication processes.
Solution Approach 2:
The patent uses preliminary action by pre-defining the structural template for filament formation through selective epitaxial growth. The protruding regions are formed before the ReRAM switching layers are deposited, establishing a predetermined pattern that guides subsequent electroforming. This preliminary structuring ensures reliable and consistent filament formation without requiring complex in-situ control during the electroforming process itself, thus maintaining ease of manufacture while improving reliability.
3Productivity
If ReRAM devices are scaled for high-density storage, then the storage capacity increases, but the forming voltage increases and variability worsens
Solution Approach 1:
The patent applies dimensionality change by transitioning from planar ReRAM structures to vertically-stacked configurations with protruding epitaxial regions. The protrusions extend in the vertical dimension, creating well-defined three-dimensional nucleation sites for filament formation. This vertical dimensionality provides better spatial confinement and control over filament positions, enabling reliable scaling for high-density storage by maintaining precise filament control even as device dimensions are reduced to increase storage capacity.
Solution Approach 2:
The patent uses preliminary action by pre-forming the protruding epitaxial structures that serve as templates for filament formation before device scaling. These pre-formed structures maintain their geometric integrity and positioning function even when overall device dimensions are reduced for high-density integration. The preliminary establishment of these control structures ensures that filament position control is maintained during scaling, enabling increased storage capacity without sacrificing manufacturing precision.
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 ReRAM states, improves device scalability, and enhances the memory window, making the ReRAM technology more reliable and efficient for high-density storage and in-memory computing applications.
Implementation Method 1
The exposed portion of the epitaxial region acts as a bottom electrode for the resistive random access memory stack
Implementation Method 2
A metal gate material is disposed on and around the channel region, with a portion of the metal gate material located between the two vertical field effect transistors
Data Source
AI summary
A two-transistor-two-resistor (2T2R) resistive random access memory (ReRAM) structure, and a method for forming the same includes two vertical field effect transistors (VFETs) formed on a substrate, each VFET includes an epitaxial region located above a channel region and below a dielectric cap. The epitaxial region includes two opposing protruding regions of triangular shape that extend horizontally beyond the channel region. A metal gate material is disposed on and around the channel region. A portion of the metal gate material is located between the two VFETs. A ReRAM stack is deposited within two openings adjacent to a side of each VFET that is opposing the portion of the metal gate material located between the two VFETs. A portion of the epitaxial region in direct contact with the ReRAM stack acts as a bottom electrode for the ReRAM structure.