3D Memory Device Programming Using Precharged Shut-Off Voltages
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Solution Overview
Problem
Conventional 3-dimensional memory devices experience memory cell disturbance during programming operations due to insufficient voltage control across stacked layers, leading to unintended programming of unselected memory cells.
Innovation Solution
A method and system for 3-dimensional memory devices that involve precharging unselected memory cell strings with an elevated channel voltage, effectively shutting them off during programming operations to prevent disturbance, using a self-boosting mechanism to maintain channel voltages higher than normal, thereby isolating unselected memory cells from the programming process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional programming operations are performed in 3-dimensional memory devices without voltage control on unselected strings, then programming speed is maintained, but memory cell disturbance occurs in unselected memory cells
Solution Approach 1:
The memory device is divided into multiple stacked layers with each layer containing memory arrays. Word lines are segmented into layer-specific word lines (first layer word lines, second layer word lines, etc.) that can be independently controlled. This segmentation allows selective programming of specific layers while isolating unselected layers through shut-off voltages, preventing program disturbance in unselected memory cells.
Solution Approach 2:
Different voltage conditions are applied to different regions of the memory device. Selected strings receive programming voltages (Vpgm on selected word lines, ground voltage on selected bit lines) while unselected strings receive shut-off voltages (elevated voltages on unselected word lines or ground selection lines). This local differentiation of voltage conditions enables precise control over which memory cells are programmed versus protected.
2Reliability
If shut-off voltage is applied to unselected strings to prevent program disturbance, then programming accuracy is improved, but programming operation time increases
Solution Approach 1:
Shut-off voltages are applied to unselected strings before the actual programming operation begins. By pre-charging unselected word lines or ground selection lines with elevated voltages, the memory cells in unselected strings are placed in a high-impedance state in advance, preventing any potential program disturbance during the subsequent programming pulse application.
Solution Approach 2:
The programming operation uses periodic voltage pulses with specific timing sequences. Programming voltages are applied in pulses to selected word lines and bit lines, while shut-off voltages are maintained on unselected strings throughout the programming pulse duration. The periodic nature of these voltage applications allows efficient programming while maintaining protection of unselected cells.
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 significantly reduces the likelihood of program disturbance by ensuring that only selected memory cells are programmed, enhancing the reliability and accuracy of data storage in 3-dimensional memory devices.
Implementation Method 1
for each unselected string associated with an unselected layer in the plurality of layers, charging the channel of memory cells associated with unselected string with a shut-off voltage
Data Source
AI summary
A programming method and a three-dimensional memory device are disclosed. The three-dimensional memory device includes a stacked plurality of layers, each layer having a memory array, and each memory array having a string of memory cells. The programming method includes, for each unselected string associated with an unselected layer in the plurality of layers, charging the channel of memory cells associated with unselected string with a shut-off voltage, and thereafter programming a selected string associated with a selected layer in the plurality of layers.