Multi-Level Cell Programming with Pre-Verify Voltage Control
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Solution Overview
Problem
Semiconductor memory devices face challenges in efficiently programming memory cells to target program states, particularly those with vulnerable threshold voltage distributions, which can lead to unintended changes during multi-level cell programming, affecting data retention and storage reliability.
Innovation Solution
The semiconductor memory device employs a re-program method for memory cells with vulnerable threshold voltage distributions, using pre-verify voltages to ensure accurate programming, and a normal program method for other cells, thereby maintaining or improving threshold voltage distributions and reducing program time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a normal program method is used for all memory cells, then the programming process is simple and fast, but memory cells with vulnerable threshold voltage distributions cannot be accurately programmed to target states
Solution Approach 1:
The patent divides the memory cell array into two groups: first memory cells with vulnerable threshold voltage distributions and second memory cells with normal distributions. Different programming methods are applied to each group, allowing accurate programming of vulnerable cells through re-programming while maintaining simplicity for normal cells.
Solution Approach 2:
The patent performs preliminary classification of memory cells based on their threshold voltage distribution characteristics before programming. This preliminary identification allows the system to pre-determine which cells require the re-program method, preventing programming errors before they occur.
Solution Approach 3:
The patent implements a feedback mechanism where the threshold voltage distribution of each memory cell is evaluated and used to determine the appropriate programming method. This feedback loop ensures that cells with vulnerable distributions are automatically identified and programmed using the more accurate re-program method.
2Manufacturing precision
If the re-program method is applied to all memory cells, then programming accuracy is improved, but the overall program time increases
Solution Approach 1:
The patent segments the memory cell population into two distinct groups based on threshold voltage distribution characteristics. Only the first group (vulnerable cells) undergoes the time-consuming re-program method, while the second group (normal cells) uses the faster normal program method, thus maintaining high accuracy where needed while preserving overall programming speed.
Solution Approach 2:
The patent applies the more accurate but slower re-program method only partially - specifically to memory cells that require it based on their threshold voltage distribution. This partial application of the enhanced method avoids the excessive time cost of applying it to all cells while still achieving the necessary programming accuracy for vulnerable cells.
3Quantity of substance
If memory cells with weak threshold voltage distributions are programmed to target states, then data storage capacity is increased, but the threshold voltage distributions become unintended and data retention is compromised
Solution Approach 1:
The patent performs preliminary identification and classification of memory cells with vulnerable threshold voltage distributions before attempting to program them to target states. This preliminary action allows the system to apply the re-program method to these specific cells, ensuring their threshold voltages are accurately adjusted to the intended target states without unintended shifts, thus maintaining data retention reliability while enabling multi-level storage.
Data Source
AI summary
There are provided a semiconductor memory device and an operating method thereof. A semiconductor memory device may include a memory cell array, a peripheral circuit, a control logic, and one or more programs. The memory cell array may include a plurality of memory cells. The peripheral circuit may perform a program operation on the memory cell array. The control logic may control the peripheral circuit to program the memory cell array. The one or more programs are configured to be executed by the control logic. The programs may include an instruction for pre-programming one or more memory cells to be programmed to one or more target program states to have threshold voltage distributions lower than the target program state.