Flash Memory Programming Uniform Channel Precharging
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Solution Overview
Problem
In flash memory devices, especially NAND type, the programming of 2-bit data in a single memory cell often results in interference phenomena that alter the threshold voltage of adjacent cells, leading to incorrect programming due to uneven channel region precharging during the programming operation.
Innovation Solution
A method where the channel region within a string is precharged to a uniform level by applying an activation voltage to a word line between the drain select transistor and the first memory cell, ensuring that the programming operation is performed with a consistent voltage difference, thereby preventing interference and incorrect programming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the programming operation is performed by changing the sequence of word lines to minimize threshold voltage change, then the interference between memory cells is reduced, but the channel region of program-inhibited cells is not properly precharged, causing unintended programming
Solution Approach 1:
The patent applies preliminary action by precharging the channel region of program-inhibited cells to a high level before the programming operation. This is achieved by applying a positive voltage to the drain select line and a program-inhibited voltage to the bit line, ensuring that the channel region is properly prepared and preventing unintended programming when word line sequences are changed.
Solution Approach 2:
The patent applies local quality by differentiating the treatment of different memory cells based on their selection status. Program-selected cells receive programming voltage while program-inhibited cells receive precharging voltage through different voltage applications to the bit line and drain select line, ensuring each cell type receives the appropriate voltage treatment for its specific function.
2Productivity
If the channel region is not uniformly precharged, then the programming operation can be performed faster, but the voltage difference between word line and channel region becomes inconsistent, causing programming errors
Solution Approach 1:
The patent applies preliminary action by precharging the channel region before the programming operation through voltage application to the drain select line and bit line. This ensures uniform precharging of the channel region, maintaining consistent voltage difference during programming while enabling faster operation sequences.
3Reliability
If the sequence of LSB and MSB programming operations is changed, then the threshold voltage change of adjacent cells is minimized, but the channel precharging becomes uneven, leading to incorrect programming
Solution Approach 1:
The patent applies preliminary action by precharging the channel region of program-inhibited cells before performing LSB and MSB programming operations in any sequence. This preliminary precharging ensures that regardless of the programming sequence, the channel region is properly prepared, preventing incorrect programming while allowing flexible sequencing for threshold voltage stability.
Solution Approach 2:
The patent applies local quality by selectively precharging only the channel regions of program-inhibited cells through targeted voltage application to specific bit lines and drain select lines, while leaving program-selected cells ready for programming. This localized treatment ensures uniform precharging where needed without affecting the programming operation.
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 method allows for accurate programming of 2-bit data in flash memory devices by maintaining a consistent voltage difference between the word line and the channel region, preventing unintended programming of memory cells and minimizing threshold voltage changes.
Implementation Method 1
activating a programmed memory cell by applying an activation voltage for activating the programmed memory cell to a word line to which the programmed memory cell is connected
Implementation Method 2
precharging a channel region corresponding to a second string including a program-inhibited cell, to precharge up to a channel region below a selected word line in the second string
Data Source
AI summary
A memory device comprises a drain select line, a source select line, word lines, and a string connected between a bit line and a common source line. A program-inhibited voltage is applied to the bit line and a first voltage of a positive potential is applied to the drain select line. A second voltage for activating a programmed memory cell is applied to a word line to which the programmed memory cell is connected. A programming operation is performed by applying a program voltage to a selected word line and applying a pass voltage to the unselected word lines.