Design of control oxide thickness for multi-level storage in a stepped NFGM MOSCAP.

In this work, the effect of control oxide thickness on the storage characteristic of MOSCAP based on nano floating gate memory (NFGM) structure was explored in order to apply the results to a stepped NFGM. A stepped MOSCAP structure can realize multi-level storage characteristic via control of electric field strength in the tunneling oxide using a stepped control oxide. Through simulation, we have predicted that a 20 nm step height is optimal to exhibit multi-level storage behavior for a 40 nm thick HfO 2 control oxide. First, we prepared two step-free NFGM MOSCAP structures consisting of Au nanocrystals: one with 20 nm thick HfO 2 control oxide and the other with 40 nm thick HfO 2 control oxide. The C–V behavior of NFGM MOSCAP structures having different control oxide thicknesses was measured in a parallel mode in order to simulate the stepped MOSCAP structure. Finally a stepped NFGM MOSCAP stricture was fabricated. As a consequence, we successfully demonstrated multi-level storage behavior in an NFGM MOSCAP structure with 40/20 nm step-shape control oxide as simulation predicted. [ABSTRACT FROM AUTHOR]