Organic molecular floating gate memories

Abstract

Flash memory devices dominate the non-volatile memory market, with device structures that utilize charge storage in polysilicon floating gates imbedded in insulating silicon oxide films'. As demands for high storage density, high chip memory capacity, and decreasing process costs continue to mount, conventional flash memory has found it challenging to continue scaling and it may reach fundamental scaling limits because of the minimum tunnel oxide thickness and poor charge retention due to defects in the tunneling oxide, necessitating modification in the implementation of the flash memory technology . In this study nano-segmented floating gate memories consisting of a uniform set of identical organic dye molecules were fabricated and evaluated for potential use as programmable charge storage and charge retention elements in a future flash memory technology. Viability of molecular thin films to serve as an energetically-uniform set of ~1nm in size charge- retaining sites is tested on a series of molecular materials, the best performing of which are thermally evaporated thin films of 3,4,9,10- perylenetetracarboxylic bis-benzimidazole (PTCBI). The initial results show device durability over 105 program/erase cycles, with hysteresis window of up to 3.3V, corresponding to charge storage density as high as 5 x 1012 cm2. Data shows that charge retention is improved for molecular films with lower carrier mobility, which for the first time experimentally confirms in a coherent material set that inhibiting charge transport by nano-segmented floating-gate structures benefits the memory retention. These results show a first step towards a possible approach to miniaturization of non-volatile memory by using molecules as segmented charge storage elements in the floating gate flash memory technology.