Flash Memory Charge Disturb Correction via Syndrome Bits
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Solution Overview
Problem
In multi-bit flash memory devices, the issue of 'charge disturb' occurs as adjacent memory cells share common bit lines and word lines, leading to excessive charge being placed on un-programmed bits, which shifts their voltage threshold, making it difficult to accurately determine the stored data, especially as memory scales down.
Innovation Solution
A method is introduced to detect and correct charge disturb by comparing the voltage threshold of un-programmed cells against a reference voltage, programming defective bits, and using address syndrome data to identify and account for the location of affected cells, thereby maintaining the threshold voltage sensing window.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If memory cells are scaled down to increase storage capacity, then storage density is improved, but charge disturb between adjacent cells increases causing threshold voltage shifts
Solution Approach 1:
The patent applies preliminary action by performing a read operation on un-programmed bits before final data programming to detect excessive charge early. This allows identification of charge disturb conditions before they corrupt the actual stored data, enabling preventive correction through syndrome bit generation and subsequent re-programming of affected bits.
Solution Approach 2:
The patent implements feedback through the use of syndrome bits that are generated based on detected charge disturb conditions and then used to guide correction actions. The syndrome bits provide feedback information about which bits require re-programming, creating a closed-loop system that continuously monitors and corrects charge disturb effects.
2Device complexity
If adjacent memory cells share common bit lines and word lines to reduce complexity, then device complexity is reduced, but charge disturb occurs causing threshold voltage shifts
Solution Approach 1:
The patent introduces syndrome bits as an intermediary mechanism that mediates between the shared bit line/word line structure and the data storage function. These syndrome bits act as a buffer that captures and records charge disturb effects, allowing the main data bits to continue functioning while the syndrome information enables subsequent correction without requiring structural changes to the memory array.
Solution Approach 2:
The patent applies parameter changes by monitoring and comparing threshold voltage parameters of un-programmed bits against expected ranges. When charge disturb causes threshold voltage shifts outside acceptable parameters, the system triggers correction procedures including re-programming affected bits to restore proper voltage characteristics.
3Quantity of substance
If the threshold voltage sensing window is shifted due to charge disturb, then measurement precision deteriorates, but data storage capacity remains unchanged
Solution Approach 1:
The patent applies preliminary anti-action by detecting threshold voltage shifts in un-programmed bits before they affect the sensing window for programmed data. The syndrome bit generation process creates a counteracting mechanism that identifies and flags affected bits, allowing the system to compensate for the threshold shift effects and maintain accurate data retrieval despite the presence of charge disturb.
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 identifies and corrects charge disturb in un-programmed bits, ensuring accurate data retrieval and storage by shifting defective bits to a programmed state and using address syndrome bits to track location, thus maintaining the integrity of the data within the memory array.
Implementation Method 1
the transistor has two gates, a floating gate and a control gate, instead of one... any electrons placed on it are trapped there and, under normal conditions, will not discharge for many years
Implementation Method 2
When the FG holds a charge, it screens (partially cancels) the electric field from the CG, which modifies the threshold voltage (VT) of the cell
Implementation Method 3
During read-out, a voltage is applied to the CG, and the MOSFET channel will become conducting or remain insulating, depending on the VT of the cell
Data Source
AI summary
A method, system and apparatus for determining whether any un-programmed cell is affected by charge disturb by comparing the voltage threshold of the un-programmed cells against a reference voltage. If the voltage threshold for the un-programmed cell exceeds the reference voltage, the failed or defective un-programmed cell will be then be programmed. This will change the defective un-programmed cell to a new programmed value. To account for the location of the failing memory cell, address syndrome bits are used to identify the location of the defective memory cell.