NAND Flash Multi-Pass Programming with Pre-Read Voltage Compensation
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Solution Overview
Problem
Multi-pass programming operations in memory devices experience significant threshold voltage shifts due to charge loss over time, leading to bit errors when there is a substantial delay between program passes, especially in non-volatile memory devices like NAND flash.
Innovation Solution
A pre-read operation is performed between the initial and subsequent program passes to read data from memory cells, allowing for the determination of an updated program voltage that compensates for threshold voltage shifts, thereby reducing bit errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multi-pass programming operations are performed with substantial delay between passes, then productivity is improved by allowing time for other operations, but threshold voltage shifts occur due to charge loss leading to bit errors
Solution Approach 1:
A pre-read operation is performed between the initial and subsequent program passes to detect threshold voltage shifts caused by charge loss. This preliminary detection allows the system to identify cells that have experienced significant voltage shifts and adjust programming parameters accordingly, preventing bit errors while maintaining the delayed multi-pass programming schedule for improved productivity
2Reliability
If pre-read operation is performed between program passes, then reliability is improved by detecting threshold voltage shifts, but device complexity increases due to additional operation
Solution Approach 1:
The pre-read operation leverages the existing read functionality of the memory device, using the same read circuits and mechanisms already present in the device. This multi-functional approach allows the system to perform both normal read operations and pre-read detection for threshold voltage shift compensation without requiring separate dedicated hardware, thereby minimizing the increase in device complexity while improving reliability
Data Source
AI summary
A first program pass of a multi-pass program operation is caused to be performed at a memory array. A first program voltage is applied to a wordline of a block of the memory array to program one or more memory cells during the first program pass. Subsequent to the first program pass of the multi-pass program operation, a pre-read operation is caused to be performed to read data corresponding to the first program pass and from the one or more memory cells. Whether a shift of a threshold voltage corresponding to the one or more memory cells satisfies a condition related to a threshold voltage change is determined based on the pre-read operation. Responsive to determining that the shift of the threshold voltage satisfies the condition, an updated second program voltage of a second program pass of the multi-pass program operation is determined.