Flash Memory Cell Sensing with Adjacent State Compensation
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Solution Overview
Problem
Flash memory cells experience sensing errors due to charge storage structure to charge storage structure coupling, which affects the accuracy of data reading, especially as the spacing between adjacent data lines decreases, leading to erroneous data states.
Innovation Solution
The method involves determining the data states of adjacent memory cells, transferring this information to a data line control unit, and using it to determine the state of a target memory cell by applying a plurality of sensing voltages, thereby selecting the appropriate data state based on the adjacent cells' programmed status.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the spacing between adjacent data lines is reduced to increase memory density, then the manufacturing density is improved, but the sensing accuracy deteriorates due to increased FG-FG capacitive coupling
Solution Approach 1:
The patent applies preliminary action by determining the data states of adjacent memory cells before sensing the target cell. The controller reads adjacent cells first, stores their states, and uses this information to compensate for capacitive coupling effects during the subsequent sensing operation, thereby maintaining accuracy despite reduced spacing
Solution Approach 2:
The patent introduces an intermediary mechanism by using shield bit lines and shield word lines as intermediate elements between adjacent data lines. These shield lines act as mediators that reduce the direct capacitive coupling between neighboring floating gates, allowing closer spacing while maintaining sensing accuracy
2Measurement precision
If shielded bit line programming is used to reduce FG-FG coupling effects, then the sensing accuracy is improved, but the device complexity increases
Solution Approach 1:
The patent implements feedback by using the determined data states of adjacent cells to adjust and compensate for coupling effects during sensing. The controller continuously monitors adjacent cell states and uses this feedback information to correct threshold voltage shifts, maintaining accuracy without requiring complex shielded programming techniques
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting sensing voltages and timing parameters based on the states of adjacent cells. The controller modifies sensing parameters in response to detected coupling effects, allowing accurate sensing without the need for complex shielded bit line programming hardware
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 reduces sensing errors by accounting for the capacitive coupling between adjacent cells, improving the accuracy of data state determination in flash memory cells, even as spacing between data lines decreases.
Implementation Method 1
electric charge can be placed on or removed from a charge storage structure (e.g., a floating gate or a charge trap) of a memory cell to program the cell into one of two data states
Implementation Method 2
the subsequent programming of the cells on the neighboring data lines can shift a threshold voltage (Vt) of the particular cell due to floating gate-to-floating gate (FG-FG) capacitive coupling
Data Source
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AI summary
This disclosure concerns memory cell sensing. One or more methods include determining a data state of a first memory cell coupled to a first data line, determining a data state of a third memory cell coupled to a third data line, transferring determined data of at least one of the first and the third memory cells to a data line control unit corresponding to a second data line to which a second memory cell is coupled, the second data line being adjacent to the first data line and the third data line, and determining a data state of the second memory cell based, at least partially, on the transferred determined data.