Non-Volatile Memory Read Control for Threshold Voltage Shift
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Solution Overview
Problem
The deterioration of non-volatile memory characteristics due to program/erase cycling and data retention time leads to misjudgment of storage states during read operations, as the fixed control voltage cannot accurately differentiate between programmed and erased states.
Innovation Solution
A control method that dynamically adjusts control voltages based on the characteristics of reference cells, using a control voltage generator to determine and apply specific voltages for read, program verify, and erase verify operations, ensuring accurate state differentiation through a binary search iteration process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed control voltage is used for read operations, then the device complexity is reduced, but the measurement precision of storage state deteriorates due to threshold voltage shifts from program/erase cycling and data retention
Solution Approach 1:
The patent implements dynamic control voltage adjustment by searching for the worst threshold voltage among reference cells and using this information to determine appropriate control voltages for read, program verify, and erase verify operations. This allows the control voltage to adapt to threshold voltage shifts caused by program/erase cycling and data retention, resolving the contradiction between device complexity and measurement precision.
Solution Approach 2:
The patent employs feedback mechanisms by using reference cells to monitor threshold voltage changes and adjusting control voltages accordingly. The control voltage generator receives information about the worst threshold voltage and modifies the control voltage to maintain accurate storage state differentiation, thereby improving measurement precision without significantly increasing device complexity.
2Measurement precision
If reference cells are used to track threshold voltage changes, then the measurement precision of storage state is improved, but the device complexity increases due to additional cells and control logic
Solution Approach 1:
The patent divides the memory cell array into reference cell regions and data cell regions. The reference cells are segregated to perform threshold voltage monitoring, while data cells handle storage operations. This segmentation allows precise threshold voltage characterization through reference cells without significantly complicating the overall device structure, as the reference cells serve a specialized monitoring function.
Solution Approach 2:
The patent uses reference cells as copies of data cells that replicate the same storage device characteristics. These reference cells are maintained in known states (programmed or erased) to provide threshold voltage information. By using identical or similar reference cells, the patent achieves accurate threshold voltage characterization without introducing fundamentally new complex structures.
3Reliability
If control voltage is adjusted according to worst threshold voltage, then the reliability of data storage is improved, but the use of energy increases due to additional control voltage generation and adjustment operations
Solution Approach 1:
The patent performs preliminary actions by searching for the worst threshold voltage among reference cells before executing read, program verify, or erase verify operations. This advance characterization allows the control voltage to be pre-determined for optimal performance, ensuring reliable data storage while minimizing unnecessary energy consumption from excessive voltage adjustment operations during actual data operations.
Data Source
AI summary
A control method for a non-volatile memory is provided. After the non-volatile memory is enabled, a judging step is performed to judge whether the non-volatile memory enters a read mode, a program mode or an erase mode. If the judging result indicates that the non-volatile memory enters the read mode, the program mode or the erase mode, a worst threshold voltage of plural reference cells of the non-volatile memory is searched. Then, at least one of a control voltage for read action, a control voltage for program verify and a control voltage for erase verify is determined. Then, a read action, a program action or an erase action is performed on plural data cells of the non-volatile memory.