Dynamic Pass Voltage Control for 3D Memory Program Disturb
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Solution Overview
Problem
Memory devices face challenges in accurately programming operations due to issues like program disturb, where memory cells are inadvertently programmed, leading to read errors, especially at higher temperatures and in 3D memory structures.
Innovation Solution
The solution involves adjusting pass voltages based on temperature and the position of selected word lines, reducing capacitive coupling between unselected word lines and the channel to minimize program disturb. When the selected word line is among source-side word lines, pass voltages are lowered to reduce channel gradient and hot carrier injection, while being raised when it's not among source-side word lines to counteract reduced channel boosting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pass voltage is increased to prevent program disturb, then reliability improves, but device complexity increases due to temperature and position-dependent voltage control
Solution Approach 1:
The pass voltage is made dynamic rather than fixed, varying based on temperature and word line position. The system transitions from a static voltage approach to a dynamic one where voltage levels adapt to operating conditions, resolving the contradiction between reliability and complexity through intelligent control
Solution Approach 2:
The invention changes the voltage parameter dynamically based on temperature and spatial position parameters. By adjusting pass voltage according to these varying parameters, the system maintains programming accuracy without requiring overly complex hardware, as the control logic is simplified through parameter-based decision making
2Manufacturing precision
If pass voltage is reduced to minimize hot carrier injection, then manufacturing precision improves, but channel boosting is reduced affecting programming speed
Solution Approach 1:
Different pass voltages are applied to different regions (word lines) based on their position relative to the selected word line. Source-side word lines receive reduced pass voltage to minimize hot carrier injection, while other word lines receive standard pass voltage to maintain channel boosting, achieving local optimization of both precision and speed
Solution Approach 2:
The word lines are segmented into different groups (source-side vs. non-source-side) and different pass voltages are applied to each group. This segmentation allows independent optimization of programming precision for source-side cells while maintaining productivity for other cells
3Device complexity
If fixed pass voltage is used, then device complexity is reduced, but temperature-dependent programming errors increase
Solution Approach 1:
The system incorporates temperature feedback to adjust pass voltage accordingly. By monitoring temperature conditions and feeding this information back to the voltage control logic, the system maintains data integrity across temperature variations without requiring complex real-time adjustment mechanisms
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 effectively reduces the likelihood of program disturb and over-programming, maintaining data integrity across varying temperatures and memory cell positions, thereby enhancing programming accuracy and reducing read errors.
Implementation Method 1
reducing capacitive coupling between unselected word lines and the channel to minimize program disturb
Implementation Method 2
lowered to reduce channel gradient and hot carrier injection
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
Techniques are provided for avoiding over-programming can occur on memory cells connected to a data word line at a source-side of a block of word lines. A gradient in the channel potential is created during a program voltage between the data word line and an adjacent dummy word line. This gradient generates electron-hole pairs which can contribute to over programming, where the over programming is worse at higher temperatures. In one aspect, pass voltages of unselected word lines are set to be relatively lower when the temperature is relatively higher, and when the selected word line is among a set of one or more source-side word lines. On the other hand, the pass voltages are set to be relatively higher when the temperature is relatively higher, and when the selected word line is not among the one or more source-side word lines.