3D NAND Tunneling Structure for Stable Select Gate Vth
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Solution Overview
Problem
In 3D NAND memory devices, unintentional charge loss from the charge trap structure adjacent the select gate tier leads to unstable threshold voltage, affecting the operation and data storage ability, as existing designs struggle to maintain accurate control of select gate threshold voltages.
Innovation Solution
A tiered structure with a high-κ material in the first tunneling structure and an oxide-only structure in the second tunneling structure adjacent the select gate tier, where the oxide-only structure inhibits charge loss and stabilizes the threshold voltage by eliminating unintended conductive pathways.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-κ material is used in the tunneling structure, then charge storage capacity is improved, but charge loss increases leading to unstable threshold voltage
Solution Approach 1:
The tunneling structure is divided into multiple segments: a first tunneling structure with high-κ material for charge storage and a second tunneling structure with oxide-only material adjacent to the select gate tier for charge protection. This segmentation allows each segment to perform its specialized function, resolving the contradiction between charge storage capacity and charge loss prevention.
Solution Approach 2:
Different materials are used in different locations of the tunneling structure. The high-κ material is placed in the first tunneling structure where charge storage is needed, while oxide-only material is placed in the second tunneling structure adjacent to the select gate tier where charge loss prevention is critical. This local differentiation optimizes both charge storage and stability.
2Manufacturing precision
If the tunneling structure is made thinner to improve equivalent oxide thickness, then device scaling is improved, but charge loss increases
Solution Approach 1:
The tunneling structure uses a composite of high-κ material and oxide-only material. The high-κ material provides high dielectric constant for better equivalent oxide thickness, while the oxide-only material forms a protective barrier that prevents charge loss. This composite structure resolves the contradiction between thinning for scaling and preventing charge loss.
3Ease of manufacture
If a uniform tunneling structure is used throughout, then manufacturing complexity is reduced, but select gate control accuracy deteriorates
Solution Approach 1:
The tunneling structure is segmented into a first portion and a second portion with different materials. The first portion uses high-κ material for charge storage while the second portion uses oxide-only material for stable threshold voltage control adjacent to the select gate tier. This segmentation maintains manufacturing feasibility while achieving precise select gate control.
Solution Approach 2:
The structure transitions from uniform to non-uniform by applying different materials in different locations. The oxide-only material is specifically applied in the region adjacent to the select gate tier where precise voltage control is needed, while high-κ material is used in other regions for charge storage. This local quality differentiation achieves both manufacturing ease and control 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
The solution effectively maintains stable select gate threshold voltages, enhancing the operational reliability and data storage capabilities of 3D NAND memory devices by preventing unintentional charge loss and improving the equivalent oxide thickness.
Implementation Method 1
a tunneling structure free of high-γ material by a select gate structure
Implementation Method 2
The charge trap structure may include a charge storage material (e.g., a dielectric material) operable to effectively 'trap' and store an electrical charge
Data Source
AI summary
A vertical structure extends through a tiered structure of alternating conductive and insulative materials. The vertical structure includes a channel structure and a tunneling structure. At least one of the conductive materials of the tiered structure provides a select gate tier (e.g., including a control gate for a select gate drain (SGD) transistor). Adjacent the select gate tier of the tiered structure, the tunneling structure consists of or consists essentially of an oxide-only material. Adjacent the word line tiers of the tiered structure, the tunneling structure comprises at least one material that is other than an oxide-only material, such as a nitride or oxynitride. The oxide-only material adjacent the select gate tier may inhibit unintentional loss of charge from a neighboring charge storage structure, which may improve the stability of the threshold voltage (Vth) of the select gate tier.