Bit-Line Floating for Channel Boosting in NAND Flash
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Solution Overview
Problem
Program disturb occurs in non-volatile storage systems, particularly in NAND flash memory, due to shifts in threshold voltage of unselected storage elements during programming, which affects the operating window and efficiency of memory devices.
Innovation Solution
A method is introduced to enhance channel boosting by allowing selected and unselected bit lines to float and electromagnetically couple voltage, followed by reconnection to voltage sources to apply program voltage, thereby reducing program disturb and improving programming efficiency without requiring higher voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If channel boosting is applied to reduce program disturb, then programming accuracy is improved, but device complexity increases due to additional voltage sources and control circuits
Solution Approach 1:
The bit line serves dual functions: it acts as both the data transmission line and the channel boosting voltage source. By allowing the bit line to float and electromagnetically couple voltage during the programming operation, the system eliminates the need for separate channel boosting voltage sources and control circuits, thereby reducing device complexity while maintaining programming accuracy
Solution Approach 2:
The bit line is made multi-functional by enabling it to perform both data transmission and channel boosting functions. The bit line is electrically connected to both the storage element and the channel region, allowing it to serve as both the signal carrying line and the voltage source for boosting, thus reducing the overall device complexity
2Reliability
If higher voltages are applied to enhance channel boosting, then program disturb is reduced, but energy consumption increases
Solution Approach 1:
Instead of applying higher voltages, the system changes the voltage parameter dynamically by allowing the bit line to float and electromagnetically couple voltage during programming. This enables the bit line to reach higher effective voltages without requiring external high voltage sources, thereby reducing energy consumption while maintaining reliable program disturb reduction
Solution Approach 2:
The channel boosting is applied periodically during the programming operation rather than continuously. The bit line is allowed to float and couple voltage only during the programming pulse periods, then returned to normal operation. This periodic application reduces overall energy consumption while maintaining effective program disturb reduction during critical programming moments
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 reduces program disturb by enhancing channel boosting efficiency, allowing for deeper erased storage element utilization and maintaining low threshold voltages, thus improving the operating window and programming accuracy of non-volatile storage systems.
Implementation Method 1
allowing the at least one selected bit line and the at least one unselected bit line to float while electromagnetically coupling a voltage to the at least one selected bit line and the at least one unselected bit line from at least one conductive element
Data Source
AI summary
Channel boosting is improved in non-volatile storage to reduce program disturb. A pre-charge module voltage source is used to pre-charge bit lines during a programming operation. The pre-charge module voltage source is coupled to a substrate channel via the bit lines to boost the channel. An additional source of boosting is provided by electromagnetically coupling a voltage from a conductive element to the bit lines and the channel. To achieve this, the bit lines and the channel are allowed to float together by disconnecting the bit lines from the voltage sources. The conductive element can be a source line, power supply line or substrate body, for instance, which receives an increasing voltage during the pre-charging and is proximate to the bit lines.