Memory Cell Programming for Threshold Voltage Widening
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Solution Overview
Problem
Semiconductor memory devices face challenges in maintaining the integrity of threshold voltage distributions due to temperature changes between programming and read operations, leading to widening of the threshold voltage distribution and potential read errors.
Innovation Solution
The techniques involve adjusting verify tests based on the temperature coefficient (Tco) of individual memory cells by using different word line verify voltages, sense times, and bit line voltages during programming, and classifying memory cells based on their subthreshold slope to optimize the programming process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard programming operations are performed without temperature compensation, then the programming process is simple and fast, but the threshold voltage distribution widens due to temperature changes between programming and read operations
Solution Approach 1:
The patent applies local quality by classifying memory cells into different groups based on their individual temperature coefficients (Tco) and subthreshold slopes. Each group receives tailored programming operations with adjusted verify tests, allowing the system to handle different cell characteristics with customized parameters rather than using a uniform approach for all cells.
Solution Approach 2:
The patent implements parameter changes by dynamically adjusting programming parameters including word line verify voltages, sense times, and bit line voltages based on the classified Tco groups. The controller modifies these parameters during programming operations to compensate for temperature variations, thereby maintaining threshold voltage distribution integrity across different temperature conditions.
2Manufacturing precision
If individual memory cell classification based on subthreshold slope is performed, then programming accuracy is improved, but the time required for classification and programming increases
Solution Approach 1:
The patent applies segmentation by dividing the memory cell population into distinct groups based on their subthreshold slope characteristics and Tco values. This classification allows the system to process different cell groups with appropriate programming operations, improving precision for each group while managing overall programming time through organized categorization.
Solution Approach 2:
The patent implements preliminary action by performing classification of memory cells into Tco groups before the actual programming operation. This preliminary classification enables the controller to pre-determine the appropriate verify test parameters for each group, allowing for more efficient programming execution without requiring real-time classification during the programming process.
3Stability of the object's composition
If different verify tests are used for different temperature coefficients, then threshold voltage distribution widening is reduced, but the control complexity increases
Solution Approach 1:
The patent applies feedback by using the classified Tco information to determine which verify test parameters to apply during programming. The controller receives temperature and subthreshold slope data, processes this information to identify the appropriate cell group, and then selects the corresponding verify test parameters, creating a closed-loop control system that adapts to individual cell characteristics.
Data Source
AI summary
Apparatuses and techniques are provided for programming memory cells while reducing widening of a threshold voltage distribution due to changes in the temperature between the time of programming and the time of a subsequent read operation. One technique is based on a correlation between program speed and temperature coefficient (Tco). A different verify test is used for different memory cells which have a common assigned data state according to the program loop number and the temperature. Another technique is based on sensing the memory cells to measure their subthreshold slope and classifying the memory cells into groups. The sensing can occur as a separate operation before programming or as part of the programming of user data. The subsequent programming of the memory cells involves adjusting the verify test of each memory cell based on its group and the temperature.