Soft Programming Method for Flash Memory Cell Recovery
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Solution Overview
Problem
Conventional soft programming methods for flash memory face challenges in reducing time and cost associated with recovering over-erased memory cells, particularly due to process inconsistencies in flash memory devices.
Innovation Solution
A soft programming method that applies operations in block-by-block, unit-by-unit, and bit-by-bit scales, using different bias voltages and verification criteria to efficiently recover over-erased memory cells, allowing for smart process adaptations to optimize the soft programming operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional soft programming method is used to recover over-erased memory cells, then recovery capability is achieved, but time and cost required by soft program operation are high
Solution Approach 1:
The patent segments the memory array into multiple memory blocks, and each memory block into multiple memory units. The soft programming operation is then performed at different scales: block-by-block scale (soft program operation by column), unit-by-unit scale (with size smaller than memory block), and bit-by-bit scale. This segmentation allows the system to identify and recover only the problematic units rather than rewriting the entire array, significantly reducing soft program time while maintaining recovery capability.
Solution Approach 2:
The patent applies different bias voltages (first bias voltage, second bias voltage, third bias voltage) to different segments of the memory array based on their specific conditions. Memory units are selectively programmed with different voltages according to their over-erase status, allowing localized recovery operations that are more efficient than uniform programming of the entire array.
2Reliability
If conventional soft programming method is used to recover over-erased memory cells, then recovery capability is achieved, but cost required by soft program operation is high
Solution Approach 1:
By segmenting the memory array into blocks and units, the patent enables selective recovery operations that reduce the number of programming cycles required. This segmentation approach minimizes the overall cost by avoiding unnecessary programming operations on healthy memory cells while ensuring thorough recovery of problematic units.
Solution Approach 2:
The patent applies partial action by performing soft programming only on selected memory units that fail the judging criterion, rather than programming the entire memory array. This partial approach reduces the cumulative cost of soft program operations while maintaining effective recovery of the over-erased cells.
3Productivity
If memory blocks are soft programmed with first bias voltage, then block-level recovery is achieved, but unit-level precision is insufficient
Solution Approach 1:
The patent segments the block-level programming into unit-level programming operations. After initial block programming with first bias voltage, the system performs additional unit-by-unit programming with second bias voltage for selected units that fail verification. This segmentation allows both efficient block-level recovery and precise unit-level correction to be achieved.
Solution Approach 2:
The patent applies different bias voltages to different units based on their specific conditions. Units that fail the judging criterion after block programming are selectively programmed with a second bias voltage, while other units remain unchanged. This local quality approach ensures unit-level precision is achieved only where necessary, maintaining overall productivity.
Data Source
AI summary
A soft program method is provided for recovering memory cells of a memory array. In an embodiment, the method includes the following steps. Memory blocks of the memory array are soft programmed with first bias voltage. A selected memory unit within a selected memory block is then soft programmed with second bias voltage. Next, whether a judging criterion is met is determined. If not, the method is repeated from the step of soft programming with the second bias voltage; if so, whether the selected unit is a last memory unit is determined. If the selected unit is not the last memory unit, other memory unit is assigned as the selected memory unit and the method is repeated from the step of soft programming with the second bias voltage. When the selected unit is the last memory unit, the memory array is bit-by-bit soft programmed with a third bias voltage.