Semiconductor Memory Read Voltage Control via Shift Reads
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Solution Overview
Problem
Current memory systems face challenges in efficiently determining the correct read voltages for memory cell transistors to accurately read four-bit data due to variations in threshold voltages, leading to errors in data retrieval.
Innovation Solution
A memory system with a controller that applies different read voltages at various timings to determine the state of memory cell transistors, using a combination of read and shift read operations to estimate and adjust boundary read voltages, ensuring accurate data retrieval by masking and logical operations on read data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple read voltages are applied to read memory cell transistors with threshold voltage variations, then data retrieval accuracy is improved, but the complexity of voltage control and operation increases
Solution Approach 1:
The patent implements dynamic voltage control by adjusting read voltages based on detected threshold voltage distributions of memory cell transistors. The controller dynamically determines optimal read voltages through shift read operations and updates reference voltages accordingly, allowing the system to adapt to threshold voltage variations without requiring complex fixed voltage schedules.
Solution Approach 2:
The patent employs feedback mechanisms where the controller monitors read results and uses this information to adjust subsequent read operations. Through shift read operations and comparison with reference voltages, the system feedback-adjusts the read voltage selection to ensure accurate data retrieval despite threshold voltage variations.
2Measurement precision
If multiple read operations are performed to handle threshold voltage variations, then data accuracy is improved, but the time required for data retrieval increases
Solution Approach 1:
The patent performs preliminary threshold voltage detection and distribution analysis before actual data read operations. By conducting shift read operations to characterize the threshold voltage distribution in advance, the system pre-determines optimal read voltage schedules, eliminating the need for time-consuming real-time voltage adjustments during data retrieval.
Solution Approach 2:
The system dynamically optimizes read operation sequences based on detected threshold voltage distributions. Rather than using fixed multiple read operations, the controller adapts the number and timing of read operations to match the actual device characteristics, reducing unnecessary operations while maintaining accuracy.
3Ease of operation
If conventional read operations are used without voltage adjustment, then operation simplicity is maintained, but data retrieval errors increase due to threshold voltage variations
Solution Approach 1:
The memory system performs self-characterization through automatic threshold voltage detection and distribution analysis. The controller autonomously determines optimal read voltages by conducting shift read operations and comparing results with reference voltages, eliminating the need for external intervention or complex manual voltage scheduling while ensuring reliable data retrieval.
Solution Approach 2:
The patent changes the read voltage parameter dynamically based on detected threshold voltage distributions. Rather than using fixed voltages, the system adjusts read voltage parameters through shift read operations and updates reference voltage tables, allowing simple operations to adapt to varying conditions and maintain high reliability.
Data Source
AI summary
According to one embodiment, a controller is configured to write four-bit data in each of memory cells, and read first data item from the memory cells through application of a first voltage to a word line. The controller is configured to read second data items by repeating a first operation of reading data including data of respective first bits of the memory cells through application of two voltages to the word line at different timings while changing the two voltages in each first operation from the two voltages in another first operation. The controller is configured to mask part of each of the second data items using the first data.