Semiconductor Memory Device LSB MSB Programming Voltage Control
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Solution Overview
Problem
The existing incremental step pulse program (ISPP) method for nonvolatile memory devices is inefficient due to prolonged programming times and data interference, especially at the early stages of programming, and requires allocating data to all columns even if only some are used, leading to potential errors.
Innovation Solution
The method involves performing an LSB program operation for selected memory cells when threshold voltages reach a target level, storing relevant data in a flag cell, and then using this data to set an optimal start program voltage for subsequent MSB program operations, reducing overall programming time and minimizing interference by adjusting voltages based on the number of bits to be programmed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the ISPP method is used to program memory cells by supplying gradually rising program voltage, then the threshold voltages of memory cells can be programmed to target level, but the programming time becomes unnecessarily long due to multiple program voltage increases at early stage
Solution Approach 1:
The patent performs preliminary determination of the number of memory cells requiring programming before initiating the program operation. Based on this pre-determined count, the system calculates and applies an optimized start program voltage that directly targets the required programming level, avoiding unnecessary incremental voltage increases and reducing programming time while maintaining precision.
2Reliability
If data is allocated to all columns during program operation, then complete data storage is ensured, but data interference occurs between neighboring strings and columns
Solution Approach 1:
The patent applies local quality by determining the specific number of memory cells that need programming based on the actual data allocation requirements. Instead of uniformly programming all columns, the system identifies and programs only the necessary local cells, thereby reducing data interference between neighboring strings while maintaining reliable data storage in the targeted locations.
3Adaptability or versatility
If program voltage is supplied to neighboring strings during program operation, then complete programming coverage is achieved, but data in memory cells changes due to voltage interference
Solution Approach 1:
The patent segments the programming operation by first determining the exact number of memory cells requiring programming based on data allocation patterns. This segmentation allows the system to apply program voltage only to the specific subset of cells needed, rather than uniformly to all cells in neighboring strings, thereby maintaining data integrity while achieving complete programming coverage for the required data.
Data Source
AI summary
A method of operating a semiconductor memory device includes performing an LSB program operation for selected memory cells while raising a program voltage, when the threshold voltages of some of the selected memory cells reach a target level, storing data, corresponding to a relevant program voltage, in a first flag cell, performing the LSB program operation for some of the selected memory cells, having threshold voltages not reached the target level, until the threshold voltages of all the selected memory cells reach the target level, and after the LSB program operation is completed, performing an MSB program operation for the selected memory cells by using a program voltage, set based on the data stored in the first flag cell, as a start program voltage.