Multilevel Flash Memory Programming Using Adaptive Step Voltages
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Solution Overview
Problem
In flash memory devices, higher program levels experience increased threshold voltage spreading over time, leading to narrower margins between program levels and difficulties in differentiating data values, which affects the reliability of multilevel memory cells.
Innovation Solution
The use of smaller step voltages during programming for higher program levels in multilevel memory cells helps maintain narrower initial threshold voltage ranges, compensating for the spreading and maintaining wider margins between program levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If larger step voltages are used during programming, then programming speed is improved, but threshold voltage spreading increases leading to narrower margins between program levels
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the step voltage magnitude based on the target program level. Lower program levels use larger step voltages for faster programming, while higher program levels use smaller step voltages to minimize threshold voltage spreading and maintain adequate margins between levels. This adaptive parameter adjustment resolves the contradiction between programming speed and reliability.
2Quantity of substance
If higher program levels are programmed, then memory capacity is increased, but threshold voltage spreading becomes more severe leading to difficulties in differentiating data values
Solution Approach 1:
The patent changes the programming parameter (step voltage magnitude) as a function of the target program level. For higher program levels that store more bits per cell, smaller step voltages are applied to reduce threshold voltage spreading, thereby maintaining sufficient separation between adjacent program levels and enabling reliable data differentiation despite increased memory capacity.
3Quantity of substance
If multilevel memory cells are used to increase density, then memory density is improved, but stability of threshold voltages during lifetime operation deteriorates
Solution Approach 1:
The patent implements parameter changes by adapting the step voltage magnitude according to the target program level during multilevel programming. This ensures that higher program levels, which are more susceptible to threshold voltage spreading and instability over time, are programmed with smaller voltage steps, thereby improving the long-term stability of threshold voltages while maintaining high memory density.
Data Source
AI summary
Memory devices and methods are disclosed. An embodiment of one such method includes programming a first memory cell to a first program level by applying a first series of programming pulses to a control gate of the first memory cell, where the programming pulses of the first series have voltages that sequentially increase by a certain first voltage; and programming a second memory cell to a second program level that is higher than the first program level by applying a second series of programming pulses to a control gate of the second memory cell, where the programming pulses of the second series have voltages that sequentially increase by a certain second voltage less than the certain first voltage.