High charge storage of poly-Si thin film nonvolatile memory devices with oxide–silicon–oxynitride stack structures

Abstract

Polycrystalline silicon (poly-Si) thin film nonvolatile memory (NVM) devices with an oxide–silicon–oxynitride (OSOn) stack structure using an amorphous silicon (a-Si) as a storage layer on a glass panel were fabricated and investigated for high charge storage of memory applications in systems-on-panels (SOPs). Because the band gap of a-Si is lower than that of silicon nitride (SiNx) and a larger band gap offset provides more room for charge storage, a-Si thin layer with high charge injection can be applied to the fabrication of poly-Si NVM devices. The trap densities of a-Si thin films deposited by different flow ratios of H2 and silane (SiH4) were calculated to determine the optimal conditions for the charge storage layer. Poly-Si thin film transistor (TFT) technology, plasma-assisted oxynitridation to deposit an ultra-thin tunneling layer, and an optimal a-Si thin film charge storage layer were used to fabricate poly-Si NVM devices on glass substrate. A large memory window of +3.02 V to −1.68 V was obtained at a low operating voltage with an erasing voltage of +10 V and a programming voltage of −10 V due to high charge storage sites in the a-Si thin film. Our results demonstrate that poly-Si NVM devices with a-Si thin film as a charge storage layer on a glass panel can be applied to system applications of flat panel displays (FPDs) due to their large memory windows at low operating voltage.