Analog Non-Volatile Memory Cell Read Current Stability via RTN Detection
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Solution Overview
Problem
Analog non-volatile memory devices face read current instability due to random telegraph noise (RTN) caused by electron capture and emission by oxide traps, leading to inaccuracies in memory cell programming and read operations.
Innovation Solution
A method involving a controller that programs memory cells to a target threshold voltage, performs read operations with a reduced control gate voltage to detect RTN, and subjects cells with intolerable RTN to additional programming to ensure stability, using a series of read and program cycles with adjusted voltages to compensate for threshold voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If memory cells are programmed to a target threshold voltage, then programming speed is improved, but read current stability deteriorates due to RTN causing threshold voltage drops
Solution Approach 1:
The patent applies preliminary action by performing an initial programming operation to set the memory cell to the target threshold voltage, then subsequently detecting RTN and applying additional compensatory programming. This preliminary programming followed by detection and correction resolves the contradiction by first achieving fast programming, then stabilizing the read current.
Solution Approach 2:
The patent implements feedback by detecting the read current stability and threshold voltage variations after initial programming, then using this information to determine whether additional programming is needed. The controller continuously monitors the memory cell state and adjusts programming accordingly, resolving the contradiction between speed and stability through closed-loop control.
2Reliability
If additional programming is applied to cells with RTN, then read current stability is improved, but programming time increases
Solution Approach 1:
The patent applies partial or excessive action by performing additional programming only on memory cells that are detected to have RTN issues, rather than programming all cells with the same extended duration. This selective approach improves read current stability for affected cells while minimizing the overall programming time loss.
Solution Approach 2:
The patent implements local quality by applying different programming strategies to different memory cells based on their individual RTN characteristics. Cells exhibiting RTN receive additional compensatory programming, while cells without RTN issues use standard programming, optimizing the balance between stability and time for each cell locally.
3Measurement precision
If read voltage is reduced to detect RTN, then measurement precision is improved, but read current decreases
Solution Approach 1:
The patent applies periodic action by performing read operations at multiple different voltages during the programming and verification process. The controller alternates between reduced voltage reads for RTN detection and normal voltage reads for data verification, achieving both measurement precision and adequate read current through periodic voltage variation.
Data Source
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AI summary
A method and device for programming a non-volatile memory cell, where the non-volatile memory cell includes a first gate. The non-volatile memory cell is programmed to an initial program state that corresponds to meeting or exceeding a target threshold voltage for the first gate of the non-volatile memory cell. The target threshold voltage corresponds to a target read current. The non-volatile memory cell is read in a first read operation using a read voltage applied to the first gate of the non-volatile memory cell that is less than the target threshold voltage to generate a first read current. The non-volatile memory cell is subjected to additional programming in response to determining that the first read current is greater than the target read current.