Floating Filler (FF) in an Indium Gallium Zinc Oxide (IGZO) Channel Improves the Erase Performance of Vertical Channel NAND Flash with a Cell-on-Peri (COP) Structure

Abstract

In this study, we developed a V-NAND with an improved IGZO-P type (IP) floating filler (FF) structure based on an IGZO channel verified in previous studies and demonstrated that it has a very fast erase speed through device simulation. The proposed FF structure can supply holes generated through the Gate-Induced Drain Leakage (GIDL) phenomenon in the upper polysilicon string select line (SSL) channel to the IGZO channel through a P-type filler, and the structure proposed by this operation shows a very fast erase speed of 4 μs. A fast erase speed was achieved because the filler adjacent to the IGZO channel, like IP structures in previous studies, functioned as a path through which electrons emitted from the charge storage layer moved easily, rather than simply supplying holes. This assumption was confirmed by assessing the change in electron density of the channel during the erase operation. Next, we investigated the optimum conditions for leakage current reduction through various condition changes of the lower ground select line (GSL) gate in the proposed structure. We confirmed that the leakage current of the proposed structure can be minimized by changing the number of lower GSL gates, changing the length of the GSL channel, and/or changing the work function of the GSL gate material. We obtained a leakage current of 10−17 A when the GSL channel was 480 nm long with six GSL gates, each with a length of 40 nm. The work function of the gates was 4.96 eV.