Nonvolatile Memory Device Pass Voltage Control
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Solution Overview
Problem
Conventional programming methods for nonvolatile memory devices often result in program disturbance and increased leakage currents due to junction fields, leading to failed bits and widened threshold voltage distributions, especially in memory cells adjacent to the string selection line.
Innovation Solution
The method involves applying specific pass voltages to unselected word lines adjacent to the selected word line, with a second pass voltage less than the first pass voltage on the string selection line side and a third pass voltage greater than the first pass voltage on the ground selection line side, to blunt the junction field and reduce local boosting, thereby minimizing the likelihood of program-inhibited memory cells being programmed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional programming methods are used with uniform pass voltages on all unselected word lines, then the programming operation is simple to implement, but junction fields cause program disturbance and leakage currents in adjacent memory cells
Solution Approach 1:
The patent applies different pass voltages to different groups of unselected word lines based on their spatial location relative to the selected word line. Specifically, unselected word lines on the string selection line side receive a first pass voltage, while unselected word lines on the ground selection line side receive a second pass voltage. This local differentiation blunts the junction field toward the string selection line, reducing leakage currents and program disturbance in adjacent memory cells while maintaining programming reliability.
2Reliability
If higher pass voltages are applied to unselected word lines to prevent program disturbance, then programming reliability improves, but leakage currents and local boosting increase
Solution Approach 1:
The patent changes the voltage parameter applied to unselected word lines based on their position. By applying a first pass voltage to unselected word lines on the string selection line side and a second pass voltage to unselected word lines on the ground selection line side, the patent optimizes the electrical parameters to blunt the junction field and reduce leakage currents while preventing program disturbance. This parameter differentiation resolves the contradiction between reliability and harmful leakage effects.
3Manufacturing precision
If uniform pass voltage is applied to all unselected word lines, then the control circuitry is simple, but threshold voltage distribution widens due to program disturbance
Solution Approach 1:
The patent implements local quality control by differentiating the pass voltage applied to unselected word lines based on their location. Unselected word lines on the string selection line side receive a first pass voltage, while those on the ground selection line side receive a second pass voltage. This localized voltage control blunts the junction field and reduces program disturbance, thereby maintaining a tighter threshold voltage distribution without excessive control complexity.
Data Source
AI summary
Methods of operating nonvolatile memory devices are described. A bit line program voltage is applied to at least one selected bit line and a bit line program-inhibition voltage is applied to at least one unselected bit line. The methods further include concurrently applying a word line program voltage to a selected word line, a first pass voltage to at least one unselected word line and a second pass voltage less than the first pass voltage to at least one unselected word line immediately adjacent the selected word line on a string selection line side of the selected word line.