Effects of Device Dimension on Characteristics and Reliability of Peripheral Devices in NAND Flash Memory

Abstract

　　Recent years NAND flash memory device which has been widely applied to 3C mobile products is suitable for mass storage devices because of high storage density high access speed and low unit cost The main purpose of this thesis is about reliability and performance of peripheral devices in NAND flash memory Since NAND flash memory cell needs high voltage for program - erase cycle the peripheral device of cell word line driver circuit has to transmit high voltage to memory cell from superior circuit The device transmitting signals receives a large VDS and VSB for substrate This thesis investigated about reliability of high voltage peripheral devices affected by hot carrier effect with high voltage signals and body bias during transmitting condition 　　The peripheral device would pass through some specific bias in the process of switching such as high drain bias and high substrate bias or the generating large substrate current condition We did hot carrier stress experiments in these situations and found out degradation mechanisms reliability and lifetime of device These results were verified by TCAD simulations Results indicated that a high drain bias led to hot carrier effect resulting in significant degradation of drain current in linear region(IDlin) and a high substrate bias led to second impact ionization under channel resulting in a threshold voltage(VTH) shift owing to increased vertical electric field inside device 　　The other part of this thesis we research the different LDD(Lightly Doped Drain) length of for the impact of the reliability of devices After stressing different LDD length devices the experimental results conformed to expectation that the degradation mechanisms were the same and characteristics resembled in short channel devices the shorter the LDD length the poor the immunity to stress We also defined the lifetime of devices to investigate impact on lifetime in different dimension The last part gave evidence for result that two devices with the same total LDD length but different length in source and drain region have the same characteristics but obtain different degradation after stress

Date of Award	2014 Jul 25
Original language	English
Supervisor	Jone-Fang Chen (Supervisor)