Semiconductor Storage Device Voltage Control for Data Retention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In NAND-type flash memory, capacity coupling between adjacent memory cells leads to reduced potential differences between word lines and floating gates, causing data retention issues and reduced reliability during read operations, especially as the memory is miniaturized and spacing between word lines decreases.
Innovation Solution
The implementation of a semiconductor storage device with a specific voltage control method, where a first read pass voltage is applied to one or two adjacent word lines, a second read pass voltage higher than the first is applied to another adjacent word line, and a third read pass voltage, higher than the first but lower than the second, is applied to remaining word lines, to manage potential differences and suppress inter-gate dielectric film leakage and read disturbance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If memory is miniaturized and spacing between word lines decreases, then memory capacity increases, but capacity coupling between adjacent memory cells increases causing reduced potential differences and data retention issues
Solution Approach 1:
The patent applies different read pass voltages to different groups of word lines based on their distance from the selected word line. Specifically, first read pass voltage is applied to immediately adjacent word lines, second read pass voltage to next-adjacent word lines, and third read pass voltage to remaining word lines. This local differentiation of voltage levels compensates for the capacity coupling effects that become more severe with miniaturization, thereby maintaining data retention reliability while enabling higher memory capacity.
2Ease of operation
If read pass voltage is applied to adjacent word lines, then non-selected cells are turned ON, but potential differences between word lines and floating gates are reduced causing inter-gate dielectric film leakage
Solution Approach 1:
The patent changes the voltage parameter applied to different word lines during read operations. Instead of applying a uniform read pass voltage to all adjacent word lines, it applies multiple voltage levels (first, second, and third read pass voltages with different magnitudes) to different groups of word lines. This parameter differentiation reduces the potential difference between word lines and floating gates in a controlled manner, suppressing inter-gate dielectric film leakage while still ensuring proper read operation of non-selected cells.
3Reliability
If multiple voltage levels are applied to different word lines, then capacity coupling effects are suppressed, but voltage control complexity increases
Solution Approach 1:
The patent segments the word lines into different groups based on their distance from the selected word line. Each group is assigned a specific read pass voltage level: first read pass voltage for immediately adjacent word lines, second read pass voltage for next-adjacent word lines, and third read pass voltage for remaining word lines. This segmentation approach systematically manages the voltage control complexity by creating clear, distance-based categories, thereby enabling reliable suppression of capacity coupling effects while maintaining manageable control structures.
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 enhances data retention and reliability by reducing potential differences and suppressing inter-gate dielectric film leakage, thereby improving the accuracy of read data and maintaining data integrity as the memory is miniaturized.
Implementation Method 1
a high voltage generator that generate a high voltage from a supply voltage supplied from outside and provides the high voltage to the respective word lines; and a controller that controls the high voltage generator
Implementation Method 2
apply a first read pass voltage to one or two first adjacent word lines adjacent to the selected word line; apply a second read pass voltage to a second adjacent word line adjacent to the first word lines, wherein the second read pass voltage is higher than the first read pass voltage
Data Source
AI summary
In one embodiment, there is provided a semiconductor storage device including: a memory cell array; a high voltage generator; and a controller that controls the high voltage generator. When a word line to is selected from word lines, the controller controls the high voltage generator to: apply a first read pass voltage to one or two first adjacent word lines adjacent to the selected word line; apply a second read pass voltage to a second adjacent word line adjacent to the first adjacent word lines, wherein the second read pass voltage is higher than the first read pass voltage; and apply a third read pass voltage to remaining word lines other than the selected word line, the first adjacent word line and the second adjacent word line, wherein the third read pass voltage is higher than the first read pass voltage and lower than the second read pass voltage.