Single layer of Ge quantum dots in HfO2 for floating gate memory capacitors

• Published in: Nanotechnology Vol. 28; no. 17; p. 175707
• Main Authors: Lepadatu, A M, Palade, C, Slav, A, Maraloiu, A V, Lazanu, S, Stoica, T, Logofatu, C, Teodorescu, V S, Ciurea, M L
• Format: Journal Article
• Language: English
• Published: IOP Publishing 28.04.2017
• Subjects: charge storage; floating gate memory capacitors; Ge quantum dots single layer; HfO; magnetron sputtering; nanocrystals; rapid thermal annealing
• ISSN: 0957-4484; 1361-6528
• DOI: 10.1088/1361-6528/aa66b7

High performance trilayer memory capacitors with a floating gate of a single layer of Ge quantum dots (QDs) in HfO2 were fabricated using magnetron sputtering followed by rapid thermal annealing (RTA). The layer sequence of the capacitors is gate HfO2/floating gate of single layer of Ge QDs in HfO2/tunnel HfO2/p-Si wafers. Both Ge and HfO2 are nanostructured by RTA at moderate temperatures of 600-700 °C. By nanostructuring at 600 °C, the formation of a single layer of well separated Ge QDs with diameters of 2-3 nm at a density of 4-5 × 1015 m-2 is achieved in the floating gate (intermediate layer). The Ge QDs inside the intermediate layer are arranged in a single layer and are separated from each other by HfO2 nanocrystals (NCs) about 8 nm in diameter with a tetragonal/orthorhombic structure. The Ge QDs in the single layer are located at the crossing of the HfO2 NCs boundaries. In the intermediate layer, besides Ge QDs, a part of the Ge atoms is segregated by RTA at the HfO2 NCs boundaries, while another part of the Ge atoms is present inside the HfO2 lattice stabilizing the tetragonal/orthorhombic structure. The fabricated capacitors show a memory window of 3.8 0.5 V and a capacitance-time characteristic with 14% capacitance decay in the first 3000-4000 s followed by a very slow capacitance decrease extrapolated to 50% after 10 years. This high performance is mainly due to the floating gate of a single layer of well separated Ge QDs in HfO2, distanced from the Si substrate by the tunnel oxide layer with a precise thickness.