Flash Memory Word Line Voltage Control for Soft Programming Prevention
Solution Overview
Problem
Flash memory devices experience a soft program effect during read operations due to voltage coupling effects, which can lead to unintended programming of memory cells connected to word lines adjacent to selection lines.
Innovation Solution
The flash memory device divides word lines into two groups and employs a control logic to determine the activation order and read voltages for selection lines, supplying a lower read voltage to word lines adjacent to selection lines to prevent voltage increases that could cause soft programming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a read voltage is supplied to unselected word lines during a read operation, then read operation is enabled, but voltage coupling effects cause unintended programming of memory cells connected to word lines adjacent to selection lines
Solution Approach 1:
The patent applies different voltage levels to different groups of word lines based on their proximity to selection lines. Word lines adjacent to selection lines (prone to coupling effects) receive a first read voltage, while other unselected word lines receive a second read voltage. This localized differentiation prevents soft programming in vulnerable regions while maintaining read functionality elsewhere.
Solution Approach 2:
The patent changes the voltage parameter of read operations by introducing two distinct read voltage levels. The first read voltage is specifically tailored for word lines adjacent to selection lines to counteract coupling effects, while the second read voltage is used for other unselected word lines. This parameter differentiation resolves the contradiction between enabling read operations and preventing unintended programming.
2Measurement precision
If higher read voltage is supplied to all unselected word lines, then read accuracy is improved, but soft programming occurs in memory cells connected to word lines adjacent to selection lines
Solution Approach 1:
The patent implements local quality by assigning different voltage characteristics to different spatial regions of the memory array. Word lines close to selection lines receive a constrained voltage (first read voltage) to prevent coupling-induced programming, while distant word lines receive the standard higher voltage (second read voltage) for accurate reading. This spatially differentiated approach maintains both read accuracy and programming integrity.
Solution Approach 2:
The patent segments the population of unselected word lines into two distinct groups: those adjacent to selection lines and those not adjacent. Each segment is subjected to a different voltage regime during read operations. This segmentation allows the system to optimize for both read accuracy (in non-vulnerable regions) and programming integrity (in vulnerable regions) simultaneously.
3Device complexity
If uniform read voltage is applied to all unselected word lines, then circuit design is simplified, but coupling effects cause voltage increases that lead to soft programming
Solution Approach 1:
The patent introduces local quality into the voltage supply system by providing different read voltages to different groups of word lines. Although this increases circuit complexity slightly, it effectively prevents soft programming by ensuring that word lines adjacent to selection lines receive a constrained voltage level that accounts for coupling effects, while other word lines receive standard read voltage.
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 solution effectively prevents soft programming of memory cells by ensuring that the voltage increase from coupling effects does not exceed the higher read voltage, maintaining accurate read operations and avoiding unnecessary power consumption.
Implementation Method 1
When a read voltage is supplied to the string selection line SSL or the ground selection line GSL during a bit line development interval, a word line adjacent to the string selection line SSL or adjacent to the ground selection line GSL may have a higher voltage than the read voltage as a result of a coupling effect
Data Source
AI summary
A flash memory device includes a memory block including word lines arranged between a first selection line and a second selection line, the word lines being divided into a first group and a second group, a control logic configured to determine an activation order of the first and second selection lines and determine first and second read voltages to be supplied to unselected word lines, the control logic determining the activation order according to whether a selected word line belongs to the first group or the second group, and a row selection circuit configured to, during a read operation, drive the unselected word lines with the first and second read voltages, and activate the first and second selection lines, according to the control logic.