Memory Device Extra Programming for Stable Threshold Voltages
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Solution Overview
Problem
Nonvolatile memory devices face challenges in maintaining increased threshold voltages of memory cells due to factors like time and noise, leading to decreased performance over time.
Innovation Solution
A memory device with a program operation controller that performs an extra program operation on under-programmed cells with threshold voltages lower than a main verify voltage, following intermediate and final program operations, to maintain and increase threshold voltages to target states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a final program operation is performed to increase threshold voltages to target states, then data storage capability is improved, but some memory cells remain under-programmed with threshold voltages lower than required due to time and noise influences
Solution Approach 1:
The patent applies preliminary action by performing an extra program operation after the final program operation to proactively address under-programmed cells before they cause read failures. This additional programming step targets specifically those cells whose threshold voltages failed to reach the required level, preventing future reliability issues.
Solution Approach 2:
The patent implements feedback by using an extra verify voltage lower than the main verify voltage to identify under-programmed cells. The verify operation provides feedback information about which cells require additional programming, allowing the system to selectively apply extra program operations only where needed, thus improving precision without excessive overhead.
2Reliability
If an extra program operation is performed on all memory cells to ensure adequate threshold voltages, then reliability is improved, but programming time and energy consumption increase significantly
Solution Approach 1:
The patent applies local quality by differentiating the programming treatment based on individual cell needs. Instead of uniformly programming all cells again, the system identifies under-programmed cells through verify operations and applies extra program operations only to those specific cells, leaving properly programmed cells unchanged.
Solution Approach 2:
The patent uses partial action by performing verify operations with an extra verify voltage on all cells but applying the extra program operation only to the subset of cells that are identified as under-programmed. This partial re-programming approach is sufficient to ensure reliability without the excessive time cost of re-programming all cells.
3Measurement precision
If the main verify voltage is used to check all memory cells, then verification accuracy is maintained, but under-programmed cells with threshold voltages between extra verify voltage and main verify voltage are missed
Solution Approach 1:
The patent applies segmentation by dividing the verification process into two stages: first using an extra verify voltage (lower than main verify voltage) to identify under-programmed cells, then using the main verify voltage for final verification. This segmented approach ensures that cells with intermediate threshold voltages are properly identified and addressed.
Solution Approach 2:
The patent introduces an intermediary verify voltage level between the main verify voltage and the threshold voltage of properly programmed cells. This intermediary extra verify voltage acts as a mediator to detect under-programmed cells without causing misidentification of properly programmed cells, enabling selective re-programming.
Data Source
AI summary
Provided herein is a memory device and a method of operating the memory device. The memory device includes memory cells, a peripheral circuit configured to perform an intermediate program operation and a final program operation on the memory cells, and a program operation controller configured to control the peripheral circuit to perform an extra program operation, after the final program operation is performed, on under programmed cells having threshold voltages, lower than an extra verify voltage lower than a main verify voltage used in the final program operation among the memory cells.