Multi-Material Vertical NAND Channels for Higher GIDL Current
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Solution Overview
Problem
Conventional polycrystalline silicon channel materials in vertical strings of memory cells in NAND Flash devices face insufficient gate-induced drain leakage (GIDL) current, especially in taller stacks, limiting the effective operation of memory cells due to increased current demands.
Innovation Solution
Incorporating a second channel material with a larger band gap, such as an oxide semiconductor, adjacent to the polysilicon channel material, to enhance current transmission and reduce leakage, allowing for improved electron conductivity and reliability in 3D memory arrays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the stack height is increased to increase memory cell density, then the number of memory cells per unit area increases, but the gate-induced drain leakage current becomes insufficient
Solution Approach 1:
The patent employs a composite channel structure consisting of a first channel material (polycrystalline silicon) and a second channel material (oxide semiconductor such as IGZO) with different band gaps. This composite structure enables the device to achieve both high memory cell density through increased stack height and sufficient GIDL current by utilizing the complementary electrical properties of the two materials, where the oxide semiconductor provides high electron mobility and low leakage current.
Solution Approach 2:
The patent applies different channel materials to different regions of the vertical string structure. The first channel material is positioned in certain regions while the second channel material is positioned in other regions, allowing each material to contribute its specific properties (high carrier concentration from polysilicon and high electron mobility/low leakage from oxide semiconductor) to optimize both density and GIDL current performance locally.
2Ease of manufacture
If conventional polycrystalline silicon is used as channel material, then the manufacturing process is simple, but the GIDL current is insufficient in taller stacks
Solution Approach 1:
The patent combines conventional polycrystalline silicon with oxide semiconductor materials to create a composite channel structure. This approach maintains the manufacturing advantages of polysilicon deposition while adding the electrical performance benefits of oxide semiconductors, achieving sufficient GIDL current in taller stacks without completely abandoning established fabrication processes.
Solution Approach 2:
The patent modifies the channel material composition by introducing a second material with different band gap properties. This parameter change (adding oxide semiconductor with larger band gap) transforms the electrical characteristics of the channel, enabling adequate GIDL current generation in high-density vertical structures while maintaining compatibility with existing manufacturing methodologies.
3Quantity of substance
If the vertical string height is increased to accommodate more memory cells, then memory density increases, but the current transmission capability becomes insufficient
Solution Approach 1:
The patent utilizes a composite channel structure with polycrystalline silicon and oxide semiconductor materials to enable effective current transmission through taller vertical strings. The oxide semiconductor component provides high electron mobility that facilitates current flow over the increased vertical distance, while the polysilicon component provides adequate carrier concentration, together solving the current transmission problem in high-density configurations.
Solution Approach 2:
The patent strategically positions different channel materials within the vertical string to optimize current transmission at different locations. The second channel material (oxide semiconductor) with superior electron mobility is placed in regions where high current transmission is critical, while the first channel material is positioned in regions where carrier concentration is more important, achieving effective current flow through the entire tall structure.
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
The use of multiple channel materials with differing band gaps increases GIDL current and electron mobility, enhancing the reliability and reducing leakage during read and program operations in 3D memory devices, thereby supporting more efficient memory cell operations.
Implementation Method 1
a first channel material extending vertically through the stack, and a second channel material adjacent the first channel material and extending vertically through the stack. The first channel material has a first band gap and the second channel material has a second band gap that is relatively larger than the first band gap
Implementation Method 2
The first channel material has a first band gap and the second channel material has a second band gap that is relatively larger than the first band gap
Data Source
AI summary
An apparatus comprises a stack comprising an alternating sequence of dielectric structures and conductive structures, a first channel material extending vertically through the stack, and a second channel material adjacent the first channel material and extending vertically through the stack. The first channel material has a first band gap and the second channel material has a second band gap that is relatively larger than the first band gap. The apparatus further comprises a conductive plug structure adjacent to each of the first channel material and the second channel material, and a conductive line structure adjacent to the conductive plug structure. Methods of forming the apparatus, memory devices, and electronic systems are also described.