Temperature-Compensated Select Gates in Non-Volatile Memory
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Solution Overview
Problem
Current non-volatile memory devices face challenges in maintaining accurate read and write performance due to temperature variations, which cause shifts in threshold voltage distributions, leading to read errors and widened voltage ranges.
Innovation Solution
Applying temperature-compensated voltages to unselected word lines and select gates, in addition to the selected word line, to reduce the spread of threshold voltage distributions and improve programming 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 segments the word lines into selected word lines and unselected word lines, applying different voltage compensation strategies to each. Selected word lines receive temperature-compensated read/verify voltages to address average threshold shifts, while unselected word lines also receive temperature-compensated voltages to reduce the spread of threshold voltage distributions across all storage elements, thereby improving both read accuracy and reliability.
Solution Approach 2:
The patent applies local quality by providing different voltage characteristics to different regions of the memory array. Specifically, temperature compensation is applied locally to both selected and unselected word lines, with the compensation amount adjusted based on local temperature conditions. This localized approach reduces the threshold voltage distribution spread more effectively than global compensation alone.
2Device complexity
If temperature variations are not compensated, then device complexity is reduced, but read errors increase and threshold voltage distributions widen
Solution Approach 1:
The patent changes the voltage parameter dynamically based on temperature conditions. Temperature sensors detect local temperature variations, and the control circuitry adjusts the read and verify voltages applied to word lines accordingly. This parameter change approach compensates for temperature-induced threshold voltage shifts without requiring fundamental changes to the memory cell structure, balancing complexity and reliability.
3Reliability
If temperature-compensated voltages are applied to unselected word lines and select gates, then threshold voltage distribution spread is reduced, but device complexity increases
Solution Approach 1:
The patent implements a universal temperature compensation mechanism that serves multiple functions simultaneously. The same temperature compensation circuitry provides compensated voltages to both selected and unselected word lines and select gates, reducing threshold voltage distribution spread across the entire memory array. This multi-functional approach improves programming accuracy without proportionally increasing device complexity.
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.