Nonvolatile Memory Read Voltage Adjustment for Data Integrity
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Solution Overview
Problem
The narrowing margin between threshold distributions of memory cells in NAND type flash memory devices makes it difficult to read initial setting data accurately due to deviations caused by repeated erase and write operations, affecting both ordinary and initial setting data.
Innovation Solution
A nonvolatile semiconductor memory device with a control circuit that applies different voltages to memory cells to read initial setting data, using a complementary check to determine errors and adjust the read voltage based on the read results to maintain accurate data retrieval.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If repeated erase and write operations are performed on memory cells holding ordinary data, then data can be updated and modified, but the threshold voltage distribution deviates from the initial state making read operations difficult
Solution Approach 1:
The memory device is divided into two distinct regions: a first memory region for storing ordinary data that can be repeatedly updated, and a second memory region for storing initial setting data that is never updated. This segmentation isolates the threshold voltage distribution deviations caused by repeated operations in the first region from the stable initial setting data in the second region, allowing accurate reading of initial setting data even when ordinary data has been repeatedly modified.
2Adaptability or versatility
If erase and write operations are performed on memory cells holding ordinary data, then data can be modified, but the effect spreads to memory cells holding initial setting data making read operations difficult
Solution Approach 1:
The initial setting data is extracted from the general memory space and stored separately in a dedicated second memory region that is isolated from the first memory region where ordinary data is stored and modified. This extraction ensures that erase and write operations on ordinary data cannot affect the threshold voltage distribution of initial setting data, maintaining their integrity and readability.
3Ease of operation
If a single read voltage is used for all memory cells, then the read operation is simple, but the narrowing margin between threshold distributions makes accurate reading difficult
Solution Approach 1:
Different read voltages are applied to different memory regions: a first read voltage for the first memory region containing ordinary data and a second read voltage for the second memory region containing initial setting data. This local differentiation allows each region to be read at its optimal voltage level, improving overall reading accuracy despite the narrowing margin between threshold distributions.
Data Source
AI summary
A nonvolatile semiconductor memory device includes a memory cell array and a control circuit. The memory cell array comprises a plurality of memory cells and stores initial setting data in the plurality of memory cells. The control circuit is configured to apply a first voltage to gates of the plurality of memory cells to read the initial setting data and, depending on that read result, apply a second voltage different from the first voltage to the gates of the plurality of memory cells to read the initial setting data.