Multi-pass Programming Reduces Floating-gate Perturbation
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Solution Overview
Problem
Current flash memory programming schemes are inefficient in minimizing program disturb due to the 'Yupin effect', which occurs when the electric field of one memory cell is perturbed by neighboring cells, affecting read accuracy as integration increases and intercellular spacing shrinks.
Innovation Solution
An improved multi-pass programming method where memory cells are programmed in stages, with an initial 'Improved LM' pass that verifies cells near the middle of the threshold window and allows additional programming pulses without intervening verification, followed by finer programming passes to reach final destinations, reducing the need for subsequent programming passes and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional multi-pass programming is used, then programming accuracy is maintained, but programming time increases and efficiency decreases
Solution Approach 1:
The patent applies preliminary action by performing an initial programming pass that programs all memory cells to a common intermediate threshold level before final programming. This preliminary pass establishes a baseline state that reduces the programming burden in subsequent passes, allowing cells to reach their final destinations faster while maintaining accuracy.
Solution Approach 2:
The patent segments the programming process into distinct passes: a first pass that programs all cells to an intermediate level, and subsequent passes that complete the programming to final destinations. This segmentation allows different programming strategies to be applied at different stages, optimizing both speed and accuracy.
2Quantity of substance
If integration increases and intercellular spacing shrinks, then memory density improves, but the Yupin effect increases and affects read accuracy
Solution Approach 1:
The patent applies preliminary anti-action by programming cells to an intermediate threshold level in the first pass, which creates a buffer state that reduces the impact of the Yupin effect during subsequent programming and reading operations. This intermediate state minimizes electric field perturbations from neighboring cells.
Solution Approach 2:
The patent changes the threshold voltage parameter dynamically through multiple programming passes. By transitioning cells through an intermediate threshold level rather than directly to final high-threshold states, the patent reduces electric field strength and minimizes the Yupin effect while achieving the desired memory density.
3Manufacturing precision
If conventional programming passes are used, then all memory cells are programmed to final destinations, but the number of passes increases and efficiency decreases
Solution Approach 1:
The first programming pass performs a preliminary action by programming all memory cells to a common intermediate threshold level regardless of their final destination. This preliminary programming establishes a uniform baseline that enables more efficient completion in subsequent passes, reducing the total number of passes needed.
Solution Approach 2:
The patent maintains continuity of useful action by ensuring that all memory cells are programmed in the first pass to an intermediate state, and subsequent passes continue this programming action without unnecessary interruptions or re-verification of already-programmed cells, thereby improving overall efficiency.
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 programs memory cells closer to their final destinations in the initial pass, reducing overall programming time and improving performance by using coarser pulses and minimizing the Yupin effect, thus enhancing the accuracy and speed of programming.
Implementation Method 1
In 'hot electron injection,' a high voltage applied to the drain accelerates electrons across the substrate channel region. At the same time a high voltage applied to the control gate pulls the hot electrons through a thin gate dielectric onto the floating gate.
Implementation Method 2
In 'tunneling injection,' a high voltage is applied to the control gate relative to the substrate. In this way, electrons are pulled from the substrate to the intervening floating gate.
Implementation Method 3
The charge programmed into the floating gate of one memory cell produces an electric field that perturbs the electric field of a neighboring memory cell.
Data Source
AI summary
A nonvolatile memory with a multi-pass programming scheme enables a page of multi-level memory cells to be programmed with reduced floating-gate to floating-gate perturbations (Yuping effect). The memory cells operate within a common threshold voltage range or window, which is partitioned into multiple bands to denote a series of increasingly programmed states. The series is divided into two halves, a lower set and a higher set. The memory cells are programmed in a first, coarse programming pass such that the memory cells of the page with target states from the higher set are programmed to a staging area near midway in the threshold window. In particular, they are programmed closer to their targeted destinations than previous schemes, without incurring much performance penalty. Subsequent passes will then complete the programming more quickly. Yuping effect is reduced since the threshold voltage change in subsequent passes are reduced.