Precharging Unselected Word Lines to Suppress Program Disturb in Flash Memory
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Solution Overview
Problem
Conventional methods for programming semiconductor memory devices often result in inadvertent programming of unselected memory cells due to 'program disturb,' where the programming voltage applied to selected cells also affects unselected cells connected to the same word line, leading to unintended threshold voltage changes.
Innovation Solution
The method involves pre-charging the channel regions of unselected memory cells by applying a second voltage to neighboring word lines before the programming operation, ensuring that the channel regions of unselected transistor strings are self-boosted to prevent unwanted programming during the programming of a selected memory cell.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If programming voltage is applied to selected memory cell to program it, then the selected memory cell is successfully programmed, but unselected memory cells connected to the same word line are inadvertently programmed (program disturb)
Solution Approach 1:
A pre-charge voltage is applied to unselected memory cells before the programming operation begins. This preliminary action raises the potential of channel regions in unselected cells, creating a voltage barrier that prevents electron injection during subsequent programming of selected cells, thereby eliminating program disturb while maintaining programming precision
2Measurement precision
If high programming voltage is applied to ensure precise programming of selected cell, then programming operation is accurate, but electron injection into unselected cells increases causing program disturb
Solution Approach 1:
The pre-charge voltage applied to unselected memory cells creates a counteracting electric field that opposes the electron injection process. By raising the channel potential before programming, the electric field configuration is modified such that even high programming voltages on selected cells cannot induce electron tunneling into unselected cells, thus preventing program disturb while maintaining precise threshold voltage control
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 effectively mitigates or eliminates the inadvertent disturbance of threshold voltages in unselected cell strings, enhancing the precision of programming operations and reducing the risk of device malfunction by ensuring that only the selected memory cell is programmed.
Implementation Method 1
The electron injection is a result of the electric field generated between the control gate of the memory cell to be programmed to which the programming voltage Vpgm is applied, and the channel region of the memory cell to be programmed to which the ground voltage 0V is applied via the bit line
Implementation Method 2
applying a second voltage to at least one neighboring word line that neighbors the selected word line, the neighboring word line connected to a neighboring, unselected memory cell transistor of the selected transistor string, to ensure precharging of a channel region of another, unselected transistor string
Data Source
AI summary
Embodiments are directed to a method of programming a semiconductor memory device, the memory device including: a plurality of memory cell transistors arranged in a plurality of transistor strings; a plurality of word lines, each word line connected to a corresponding memory cell transistor of each of the transistor strings; and a plurality of bit lines, each bit line connected to at least one of the transistor strings, the method comprising: applying a first voltage, and then applying a programming voltage to a selected word line corresponding to the selected memory cell transistor; and in advance of applying the first voltage to the selected word line, applying a second voltage to at least one neighboring word line that neighbors the selected word line, the neighboring word line connected to a neighboring, unselected memory cell transistor of the selected transistor string, to ensure precharging of a channel region of another, unselected transistor string between a first, unselected transistor of the unselected transistor string connected to the neighboring word line and a second, unselected transistor of the unselected transistor string connected to the selected word line, the first, unselected transistor neighboring the second, unselected transistor in the unselected transistor string.