Charge Storage Characteristics of Si-Rich Silicon Nitride and the Effect of Tunneling Thickness on Nonvolatile Memory Performance

Abstract

Nonvolatile memory (NVM) devices with nitride-nitride-oxynitride (NNO) stack structure using Si-rich silicon nitride (SiNx) as charge trapping layer on glass substrate were fabricated. Amorphous silicon clusters existing in the Si-rich SiNxlayer enhance the charge storage capacity of the devices. Low temperature poly-silicon (LTPS) technology, plasma-assisted oxidation/nitridation method to form a uniform ultra-thin tunneling layer, and an optimal Si-rich SiNxcharge trapping layer were used to fabricate NNO NVM devices with different tunneling thickness 2.3, 2.6 and 2.9 nm. The increase memory window, lower voltage operation but little scarifying in retention characteristics of nitride trap NVM devices had been accomplished by reducing the tunnel oxide thickness. The fabricated NVM devices with 2.9 nm tunneling thickness shows excellent electrical properties, such as a low threshold voltage, a high ON/OFF current ratio, a low operating voltage of less than ±9 V and a large memory window of 2.7 V, which remained greater than 72% over a period of 10 years.