3D NAND Word-Line Voltage Profiling for Adjacent Cell Isolation
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Solution Overview
Problem
Existing semiconductor memory devices face challenges in efficiently programming memory cells, particularly in 3D NAND flash memory technology, due to the need for precise control of voltages and isolation of adjacent cells during programming operations.
Innovation Solution
A method and device for programming memory cells in a memory cell string using a series connection of bottom-select-gate and top-select-gate transistors, with controlled application of pass and interface voltages on word lines to isolate and program selected memory cells, utilizing a controller to manage these voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a programming voltage is applied to program a selected memory cell, then the selected memory cell can be programmed, but adjacent memory cells may be unintentionally affected due to voltage coupling
Solution Approach 1:
The patent applies different voltage levels to different word lines based on their position relative to the selected memory cell. Specifically, a first pass voltage is applied to a first set of adjacent word lines, a second pass voltage (higher than the first) is applied to a second set of adjacent word lines, and a third pass voltage is applied to a third set of adjacent word lines. This localized differentiation of voltage quality prevents adjacent cell interference while enabling precise programming of the selected cell.
Solution Approach 2:
The patent changes the voltage parameter across different word lines to achieve both programming precision and isolation. By varying the pass voltage levels (first pass voltage, second pass voltage, third pass voltage) applied to different sets of adjacent word lines, the system creates an electric field profile that confines the programming effect to the selected cell while preventing charge leakage to adjacent cells.
2Reliability
If higher pass voltages are applied to isolate adjacent cells, then interference between cells is reduced, but the complexity of voltage control increases
Solution Approach 1:
The patent segments the word lines into different sets (first set, second set, third set) based on their distance and coupling strength to the selected memory cell. Each set receives a different pass voltage level, creating a segmented voltage control strategy. This segmentation allows the system to manage complexity by treating different spatial regions differently, thereby achieving reliable isolation without requiring uniform high-voltage control across all word lines.
Solution Approach 2:
The patent maintains continuous useful action by applying pass voltages to all relevant word lines simultaneously during the programming operation. The first pass voltage, second pass voltage, and third pass voltage are applied in a coordinated manner to different sets of adjacent word lines, ensuring continuous isolation of the selected cell throughout the programming process. This continuous multi-level voltage application enhances reliability while distributing the control complexity across multiple concurrent actions.
3Manufacturing precision
If multiple different pass voltages are applied to different word lines, then adjacent cell interference is minimized, but the energy consumption increases
Solution Approach 1:
The patent applies local quality by differentiating voltage levels only where necessary - specifically to sets of adjacent word lines that have significant coupling to the selected memory cell. The first pass voltage, second pass voltage, and third pass voltage are applied selectively to different sets of word lines based on their spatial relationship to the selected cell. This localized approach achieves high programming accuracy while minimizing overall energy consumption by avoiding uniform high-voltage application across the entire memory array.
Data Source
AI summary
In a method for programming a memory cell string, a programming voltage is applied on a selected word line to program a selected memory cell of the memory cell string. A first pass voltage is applied on a first word line coupled to a first memory cell of the memory cells. A second pass voltage is applied on a second word line coupled to a second memory cell of the memory cells. Further, a third pass voltage is applied on a third word line coupled to a third memory cell of the memory cells. The first, second and third memory cells are located at a first side of the selected memory cell in the memory cell string, and the second memory cell is disposed between the first memory cell and the third memory cell. The second pass voltage is higher than the first pass voltage and the third pass voltage.