Semiconductor Memory Row Control Circuit Neighboring Word Line Interference
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Solution Overview
Problem
Three-dimensional stacked flash memory devices face neighboring word line interference (NWI) issues during data writing, where the threshold voltage of one word line is increased due to adjacent word line interactions, affecting memory cell performance and data storage characteristics.
Innovation Solution
A semiconductor memory device with a row control circuit that applies a stepped-up program voltage to word lines and adjusts pass voltages based on predetermined voltage values to minimize interference, using a compensation voltage to balance electron injection across memory cells, thereby reducing threshold voltage fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a step-up writing method is used to write multi-value data in three-dimensional memory, then writing speed and memory capacity are improved, but neighboring word line interference occurs causing threshold voltage to increase
Solution Approach 1:
The patent applies a preliminary pass voltage to adjacent word lines before applying the program voltage to the target word line. This preliminary action prepares the adjacent memory cells by establishing an initial electrical state that prevents excessive threshold voltage increase during the subsequent programming operation, thereby resolving the neighboring word line interference issue while maintaining the step-up writing method's speed advantages
2Productivity
If program voltage is increased to improve writing efficiency, then data writing speed is improved, but threshold voltage fluctuation increases due to neighboring word line interference
Solution Approach 1:
The patent applies different voltages to different word lines based on their position and role in the writing operation. The target word line receives the full program voltage for efficient data writing, while adjacent word lines receive a reduced pass voltage that prevents interference. This local differentiation of voltage quality allows high writing efficiency without threshold voltage fluctuation in non-target cells
3Quantity of substance
If step-up writing is applied to increase memory capacity utilization, then storage efficiency is improved, but electron injection becomes unbalanced across memory cells
Solution Approach 1:
The patent uses a verify voltage to check the threshold voltage of memory cells after programming, and based on the verification result, adjusts the program voltage for subsequent writing cycles. This feedback mechanism ensures that electron injection is properly balanced across all memory cells, maintaining uniformity in the charge trap film while still utilizing the step-up writing method for high capacity utilization
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
The solution effectively reduces neighboring word line interference, stabilizes threshold voltages, and improves data storage characteristics by optimizing voltage application and electron injection across memory cells.
Implementation Method 1
a write voltage is gradually increased by a so-called step-up writing method for each word line and multi-value data (charge) is written in a charge trap film (a charge retention layer) of each cell
Implementation Method 2
when data is written in a first word line and then written in a second word line adjacent to the first word line, neighboring word line interference (NWI) may occur in which a threshold voltage (Vth) of each cell of the first word line to which writing has already completed is increased
Data Source
AI summary
A semiconductor memory device includes a plurality of memory cells, a plurality of word lines connected to the plurality of memory cells, respectively, and a row control circuit. The row control circuit is configured to apply a program voltage to a first word line among the word lines while stepping up a value of the program voltage; apply a first pass voltage to a second word line among the word lines different from the first word line when applying the program voltage having a voltage value equal to or greater than a predetermined voltage value to the first word line; and apply a second pass voltage having a voltage value higher than the first pass voltage to the second word line when applying the program voltage having a voltage value less than the predetermined voltage value to the first word line.