Nonvolatile Memory Program Verification Using Reference Voltage
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Solution Overview
Problem
Nonvolatile memory devices face a challenge with under-programmed cells due to the source line bouncing phenomenon, which reduces read margin and affects Multi-Level Cell (MLC) programming by incorrectly determining cells as fully programmed when they are not, leading to decreased current levels and inaccurate threshold voltage assessments.
Innovation Solution
A method is introduced to operate nonvolatile memory devices by performing a first program and verification operation using a first reference voltage, followed by a second program and verification operation using a higher second reference voltage, and potentially a third program and verification operation, to ensure cells are fully programmed and accurately verified, thereby preventing under-programmed cells and maintaining read margin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If verification is performed using a first reference voltage PV1, then program operation can be completed, but under-programmed cells occur due to source line bouncing phenomenon reducing read margin
Solution Approach 1:
The patent applies preliminary action by performing a first verification operation using reference voltage PV1 before the final verification. This initial verification identifies cells that need additional programming, allowing the system to apply extra program pulses to prevent under-programming before the final read margin verification is performed.
Solution Approach 2:
The patent changes the verification parameters by introducing a second verification operation with reference voltage PV2 (where PV2 > PV1). This parameter change allows the system to re-verify cells that failed the first verification, ensuring they achieve sufficient threshold voltage increase to maintain adequate read margin while avoiding under-programmed cells.
2Speed
If source line bouncing phenomenon occurs during program operation, then program speed is maintained, but current level changes cause inaccurate threshold voltage assessment
Solution Approach 1:
The patent implements feedback by using the result of the first verification operation to determine whether to perform additional program operations. The verification outcome feeds back into the program control logic, which decides to apply extra program pulses to cells that did not meet the verification criteria, thereby correcting the threshold voltage assessment accuracy while maintaining program speed.
Solution Approach 2:
The patent performs preliminary verification using PV1 before final verification, allowing the system to identify and correct potentially under-programmed cells before they cause read margin issues. This preliminary check and corrective action ensures accurate threshold voltage assessment without sacrificing overall program speed.
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 prevents under-programmed cells by raising the reference voltage, reducing the occurrence of under-programmed cells and maintaining a sufficient read margin, especially in Multi-Level Cell programming methods.
Implementation Method 1
A nonvolatile memory cell enables an electrical program/erase operation and performs the program and erase operations by varying threshold voltages when electrons are migrated by a strong electric field applied to a thin oxide layer
Data Source
AI summary
A method of operating a nonvolatile memory device includes performing a first program operation and a first verification operation on memory cells until a cell, having a threshold voltage higher than a first reference voltage, occurs and, when a cell having the threshold voltage higher than the first reference voltage occurs, performing a second program operation and performing a second verification operation using a second reference voltage higher than the first reference voltage.