Temperature-Compensated Read Voltages for NAND Flash Memory
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Solution Overview
Problem
Temperature variations in non-volatile storage devices, such as NAND flash memory, cause read errors and widen the threshold voltage distributions of storage elements, leading to inefficiencies in data storage and retrieval.
Innovation Solution
Applying temperature-compensated voltages to unselected non-volatile storage elements and/or select gates during read and write operations, which can include using the same temperature-compensated voltage for all unselected word lines or varying voltages based on their relative positions, to reduce the spread of threshold voltage distributions and improve data accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If temperature variations are compensated by changing read/verify voltages applied to selected word line, then average shift in threshold voltage distribution is addressed, but spread of each state's threshold voltage distribution from temperature changes is not sufficiently reduced
Solution Approach 1:
The patent applies different voltage compensation strategies to different word lines based on their position. Specifically, unselected word lines receive a first voltage level while selected word lines receive a second voltage level, creating local variations in voltage application that address the specific needs of each word line region to reduce overall threshold voltage distribution spread
Solution Approach 2:
The patent changes the voltage parameter applied to word lines based on temperature conditions. By adjusting the read/verify voltages applied to unselected word lines in response to detected temperature changes, the system dynamically modifies electrical parameters to compensate for temperature-induced threshold voltage shifts and reduce distribution spread
2Quantity of substance
If multiple distinct threshold voltage ranges are used for multi-state flash memory, then data storage capacity is increased, but temperature variations cause read errors and widen threshold voltage distributions
Solution Approach 1:
The patent implements a feedback mechanism where temperature changes are detected and this information is used to adjust the read/verify voltages applied to unselected word lines. This closed-loop control compensates for temperature-induced threshold voltage shifts, maintaining reliable distinction between multiple threshold voltage ranges even under varying temperature conditions
Solution Approach 2:
The patent applies preliminary voltage adjustments to unselected word lines before reading selected word lines during temperature variations. By pre-compensating for the expected threshold voltage shifts in unselected lines, the system prevents read errors that would otherwise occur when multiple states need to be distinguished under temperature stress
Data Source
AI summary
Reading and verify operations are performed on non-volatile storage elements using temperature-compensated read voltages for unselected word lines, and/or for select gates such as drain or source side select gates of a NAND string. In one approach, while a read or verify voltage is applied to a selected word line, temperature-compensated read voltages are applied to unselected word lines and select gates. Word lines which directly neighbor the selected word line can receive a voltage which is not temperature compensated, or which is temperature-compensated to a reduced degree. The read or verify voltage applied to the selected word line can also be temperature-compensated. The temperature compensation may also account for word line position.