Confinement of nanocrystals and possible charge storage mechanism for MIS memory devices with ge nanocrystals embedded in SiO 2

Abstract

Memory effect in a metal-insulator-silicon (MIS) structure with the insulator layer consisting of a sputtered capping SiO 2 / Ge nanocrystals embedded in SiO 2 / rapid thermal oxide structure has been observed. For the devices with a co-sputtered SiO 2+Ge middle layer, larger nanocrystals were formed devices with a higher Ge concentration. It was noted that for such devices, the RTO and the capping oxide layers were able to confine the nanocrystals within the middle layer to some extent. However, in devices with pure sputtered Ge middle layer, the RTO and capping oxide layers were not as effective in confining the Ge nanocrystals. In addition, we have consistently observed memory effect from devices annealed in Ar and the absence of memory effect from devices annealed in forming gas. However, Ge nanocrystals were found in devices annealed in both ambient. This implies that having nanocrystals does not necessarily imply the presence of charge storage or memory effect.