Stacked NAND Flash Memory Write Control Circuit
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Solution Overview
Problem
Stacked NAND type flash memory devices face challenges in preventing erroneous writing into non-target memory transistors due to the conductive state of select transistors with negative threshold voltages, which can lead to unintended data retention.
Innovation Solution
The control circuit raises the voltage of writing-prohibited bit lines to a higher voltage than in ordinary operations, and utilizes couplings between bit lines and the source line to maintain the writing-prohibited bit lines in a floating state, ensuring that non-selected memory units' select transistors remain nonconductive, thereby preventing erroneous writing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If stacked NAND type flash memory is used to improve bit density, then storage capacity increases, but erroneous writing into non-target memory transistors occurs due to conductive select transistors with negative threshold voltages
Solution Approach 1:
The patent changes the voltage parameter of bit lines during write operations. Specifically, it raises the voltage of writing-prohibited bit lines to a higher level than in ordinary operations, which alters the electrical state of select transistors connected to these bit lines. This voltage change ensures that even select transistors with negative threshold voltages remain nonconductive, preventing erroneous writing while maintaining the high-density stacked architecture.
2Productivity
If select transistors with negative threshold voltages are used in stacked memory, then device performance improves, but unintended data retention occurs in non-selected memory units
Solution Approach 1:
The patent applies preliminary anti-action by proactively raising the voltage of writing-prohibited bit lines before write operations occur. This preemptive voltage adjustment creates a protective state that counteracts the potential harmful effect of negative threshold voltage select transistors becoming conductive. By establishing this protective voltage state in advance, the patent prevents unintended data retention in non-selected memory units while preserving the performance benefits of negative threshold voltage transistors.
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 prevents erroneous writing into non-target memory transistors by maintaining select transistors in a nonconductive state, even when they have negative threshold voltages, thus enhancing data integrity and bit density in stacked NAND type flash memory devices.
Implementation Method 1
utilizes couplings between bit lines and the source line to maintain the writing-prohibited bit lines in a floating state
Data Source
AI summary
In a writing operation, a control circuit raises the voltage of a writing-prohibited bit line among a plurality of bit lines to a first voltage, and thereafter brings the writing-prohibited bit line into a floating state. Then, the control circuit raises the voltage of a writing bit line other than the writing-prohibited bit line to a second voltage. In this way, the control circuit prohibits writing into a memory transistor corresponding to the writing-prohibited bit line. On the other hand, the control circuit executes writing into a memory transistor corresponding to the writing bit line.