NAND Flash Search Sensing Using Bit Line Voltage Similarity
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Solution Overview
Problem
Existing memory systems face challenges in efficiently performing search operations in NAND flash memories, particularly in determining the similarity between search data and data stored in memory cells, which affects the accuracy and efficiency of read and write operations.
Innovation Solution
A memory device with a control circuit that performs a sense operation by supplying voltages to word lines based on search data, determining similarity through bit line voltage changes, and conducting read operations with specific voltage differences to enhance data determination accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a search operation is performed in NAND flash memory to determine similarity between search data and stored data, then data retrieval accuracy is improved, but operation time and complexity increase
Solution Approach 1:
The search operation is divided into multiple read operations. First read operations are performed on selected memory cells to obtain initial data, then second read operations are performed on non-selected memory cells with adjusted voltages to obtain additional data. This segmentation allows comprehensive data comparison without requiring a single time-consuming operation, thereby improving accuracy while managing operation time through structured multi-step reading.
Solution Approach 2:
Before performing the complete search, preliminary read operations are conducted on selected memory cells to obtain initial data. Based on this preliminary data, voltage adjustments are made for subsequent read operations on non-selected cells. This preliminary action enables the system to focus subsequent reading efforts on areas most likely to contain relevant information, reducing overall search time while maintaining accuracy.
2Measurement precision
If multiple read operations are performed with different voltage levels to improve search accuracy, then data determination accuracy is improved, but device complexity increases
Solution Approach 1:
The read operation voltages are made dynamic rather than static. Second read voltages are adjusted based on the data obtained from first read operations. This dynamic voltage adjustment allows the system to adapt to the actual data distribution in the memory cells, improving determination accuracy by optimizing voltage levels for each specific search scenario rather than using fixed voltage levels.
Solution Approach 2:
The system implements feedback by using data from first read operations to determine voltage adjustments for second read operations. The control circuit analyzes the initial read data and modifies subsequent read voltages accordingly. This feedback mechanism enables the system to learn from previous read results and optimize subsequent reading operations, improving accuracy while the control circuit manages the complexity through automated voltage adjustment based on observed data patterns.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution improves the accuracy and efficiency of search and read operations by effectively comparing search data with stored data, ensuring precise data retrieval and storage in NAND flash memories.
Implementation Method 1
determining a similarity between the search data and data actually stored in the plurality of first memory cells based on a change in voltage of the bit line caused by current flowing between the bit line and the source line via the first string
Implementation Method 2
supplying a source voltage to the source line, supplying a first read voltage to a word line corresponding to the selected first memory cell, and supplying a second read voltage to word lines corresponding to the first memory cells other than the selected first memory cell, wherein a difference between the second read voltage and the source voltage is less than a difference between the first read voltage and the source voltage
Data Source
AI summary
A memory device includes a bit line, a source line, a first string in which a plurality of first memory cells are connected in series between the bit line and the source line, and a control circuit. The control circuit performs a sense operation for a search operation to determine if search data is stored in the plurality of first memory cells by supplying voltages to a plurality of word lines respectively corresponding to the plurality of first memory cells based on the search data and determining a similarity between the search data and data actually stored in the plurality of first memory cells based on a change in voltage of the bit line caused by current flowing between the bit line and the source line via the first string.