Temperature-Dependent Read Compensation for Non-Volatile Memory
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Solution Overview
Problem
Non-volatile semiconductor memory cells face challenges in maintaining accurate read levels due to temperature-dependent threshold voltage shifts, especially when programmed at different temperatures, leading to misalignment of Vth distributions and increased read errors.
Innovation Solution
Implementing temperature-dependent read and verify level compensation that accounts for the temperature at which memory cells were programmed, using a combination of temperature coefficients (Tco) and additional compensation factors independent of Tco to adjust read and verify levels, thereby reducing the threshold voltage distribution window and minimizing read errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If temperature compensation based on Tco is applied to read levels, then read accuracy at different temperatures is improved, but it does not sufficiently address the issue of cells programmed at different temperatures being read at the same temperature
Solution Approach 1:
The patent applies preliminary action by adjusting verify levels during the programming process based on programming temperature, and by storing temperature information at programming. This preliminary adjustment ensures that when cells programmed at different temperatures are later read at the same temperature, the read levels can be accurately determined using the stored temperature data, rather than attempting to compensate during the read operation alone.
Solution Approach 2:
The patent introduces temperature information as an intermediary parameter that mediates between programming temperature and read temperature. This temperature information is stored with the programmed data and used during read operations to calculate appropriate read levels, serving as a bridge that allows accurate reading of cells regardless of the temperature difference between programming and reading conditions.
2Device complexity
If the same verify levels are used for programming at different temperatures, then the programming process is simplified, but the Vth distributions become misaligned when read back, increasing read errors
Solution Approach 1:
The patent applies dynamics by making verify levels temperature-dependent during programming. Instead of using fixed verify levels, the system dynamically adjusts verify levels based on the actual programming temperature, allowing the programming process to adapt to temperature variations. This dynamic adjustment ensures proper Vth distribution alignment while maintaining a relatively simple programming workflow.
Solution Approach 2:
The patent changes the parameter of verify levels based on programming temperature. By adjusting verify levels as a function of temperature, the system ensures that cells programmed at different temperatures achieve proper Vth distribution alignment. This parameter change approach maintains reliability while avoiding the need for completely separate programming procedures for different temperature conditions.
3Device complexity
If read levels are adjusted using only Tco compensation, then the compensation calculation is simple, but it does not account for the width of Vth distribution window which varies with programming temperature
Solution Approach 1:
The patent applies preliminary action by adjusting verify levels during programming based on programming temperature before the read operation occurs. This preliminary adjustment compensates for the width of Vth distribution window variations, ensuring that when reads are performed, the distributed Vth values are already properly aligned. This approach avoids the need for complex real-time calculations during read operations.
Solution Approach 2:
The patent replaces the need for complex mechanical or computational adjustment systems by using a straightforward temperature-based compensation methodology. Instead of implementing complex adaptive systems that continuously adjust during operation, the solution uses temperature information to determine appropriate compensation values, simplifying the overall system while maintaining high read level accuracy.
Data Source
AI summary
Methods and non-volatile storage systems are provided for using compensation that depends on the temperature at which the memory cells were programmed. Note that the read level compensation may have a component that is not dependent on the memory cells' Tco. That is, the component is not necessarily based on the temperature dependence of the Vth of the memory cells. The compensation may have a component that is dependent on the difference in width of individual Vth distributions of the different states across different temperatures of program verify. This compensation may be used for both verify and read, although a different amount of compensation may be used during read than during verify.