Read Bias Adjustment for 3D NAND Memory Cells
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Solution Overview
Problem
In semiconductor memory devices, particularly in 3D NAND structures, the threshold voltage (Vth) of memory cells can shift due to lateral charge movement caused by adjacent cells, leading to inaccurate read operations as device dimensions shrink, complicating the reliable reading of data states.
Innovation Solution
Implementing a read operation that compensates for the threshold voltages of adjacent memory cells by classifying their Vth into bins and adjusting read pass voltages or control gate voltages, allowing for accurate data retrieval even after initial uncorrectable errors, and adapting the number of bins based on temperature to account for increased charge diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If device dimensions are shrunk to increase storage capacity, then storage density is improved, but threshold voltage shift due to lateral charge movement increases
Solution Approach 1:
The patent applies preliminary action by reading adjacent memory cells before reading the target memory cell to obtain their threshold voltage values. This advance information is used to calculate compensation values that correct for lateral charge movement effects on the target cell, thereby maintaining reading accuracy despite device scaling.
Solution Approach 2:
The patent changes the reading parameters by adjusting read pass voltages or control gate voltages based on the threshold voltage values of adjacent memory cells. This parameter adjustment compensates for the threshold voltage shift caused by lateral charge movement, allowing accurate data retrieval from scaled-down devices.
2Ease of operation
If conventional reading operations are used without compensation, then operation simplicity is maintained, but reading accuracy deteriorates due to Vth shifts
Solution Approach 1:
The patent implements feedback by using the threshold voltage information from adjacent memory cells to adjust the reading operation for the target memory cell. The compensation values calculated from adjacent cell data are fed back into the reading process, creating a closed-loop system that maintains high reading accuracy while managing complexity through systematic compensation.
3Temperature
If temperature increases, then charge diffusion increases causing greater Vth shifts, but adaptive binning maintains reading accuracy
Solution Approach 1:
The patent applies dynamics by making the number of bins adaptive rather than fixed. The system dynamically adjusts the number of bins used for classification based on temperature conditions and observed charge diffusion levels. At higher temperatures where charge diffusion is greater, more bins are used to maintain classification accuracy, while at lower temperatures fewer bins suffice, optimizing performance across operating conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach ensures accurate and reliable reading of memory cells by compensating for Vth shifts, reducing errors and maintaining data integrity as memory device dimensions decrease, thereby enhancing the operational stability and precision of 3D NAND memory devices.
Implementation Method 1
the threshold voltage (Vth) of memory cells can shift due to lateral charge movement caused by adjacent cells
Implementation Method 2
adapting the number of bins based on temperature to account for increased charge diffusion
Data Source
AI summary
Apparatuses and techniques are provided for accurately reading memory cells by compensating for lateral charge diffusion between adjacent memory cells. A selected memory cell is read with a compensation which is based on classifying the threshold voltages of adjacent memory cells into bins. In one aspect, the compensation is based on the level of the current control gate voltage of the selected word line. In another aspect, the classifying of the threshold voltages of the adjacent memory cells can be a function of temperature. In another aspect, a memory cell can be read with compensation after a previous read operation without compensation results in an uncorrectable error. In another aspect, the classifying uses more bins for a selected edge word line.