NAND Flash Memory LSB MSB Start Voltage Programming
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Solution Overview
Problem
Conventional NAND flash memory devices use similar start voltages for both least significant bit (LSB) and most significant bit (MSB) programming operations, which limits the speed of multi-level cell programming.
Innovation Solution
A NAND flash memory device and programming method that utilize different start voltages for LSB and MSB programming operations, with the MSB start voltage being higher than the LSB start voltage, allowing for incremental step pulse programming to improve programming speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If similar start voltages are used for both LSB and MSB programming operations, then the programming operation can be simplified, but the programming speed is limited
Solution Approach 1:
The patent applies different start voltages specifically for MSB programming operations while maintaining the same start voltage for LSB programming operations. This local differentiation optimizes the programming speed for MSB operations without complicating the overall programming system, as the voltage selection is based on the specific programming stage (LSB or MSB).
Solution Approach 2:
The patent changes the voltage parameter for MSB programming operations by setting a higher start voltage compared to LSB operations. This parameter adjustment allows faster threshold voltage adjustment during MSB programming, thereby improving programming speed without requiring a complete redesign of the programming architecture.
2Speed
If a higher MSB start voltage is used to increase programming speed, then the threshold voltage is reached faster, but over-programming may occur
Solution Approach 1:
The patent incorporates verification operations after programming pulses are applied to monitor the threshold voltage of memory cells. This feedback mechanism allows the system to detect when the desired threshold voltage is reached and stop further programming, preventing over-programming even when using higher start voltages for faster programming.
Solution Approach 2:
The patent uses a higher start voltage for MSB programming that exceeds what would be needed for LSB programming, accepting this excessive action temporarily to achieve faster programming. However, the verification process limits the total programming effect to the required level, utilizing the excessive voltage only for the duration needed to reach the target threshold voltage faster.
Data Source
AI summary
A NAND flash memory device and a programming method thereof capable of improving a program speed during a multi-level cell programming operation are provided. The device performs a programming operation using an ISPP method. Additionally, the device includes a memory cell storing multi-bit data; a program voltage generating circuit generating a program voltage to be supplied to the memory cell; and a program voltage controller controlling a start level of the program voltage. The device supplies an LSB start voltage to a selected word line during an LSB program, and an MSB start voltage higher than the LSB start voltage to the selected word line during an MSB program.