National Institute of Materials Physics, 405A Atomistilor Street, 077125 Magurele, Romania.
Nanotechnology. 2017 Apr 28;28(17):175707. doi: 10.1088/1361-6528/aa66b7. Epub 2017 Mar 14.
High performance trilayer memory capacitors with a floating gate of a single layer of Ge quantum dots (QDs) in HfO were fabricated using magnetron sputtering followed by rapid thermal annealing (RTA). The layer sequence of the capacitors is gate HfO /floating gate of single layer of Ge QDs in HfO /tunnel HfO /p-Si wafers. Both Ge and HfO 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 × 10 m 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 HfO 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 HfO NCs boundaries. In the intermediate layer, besides Ge QDs, a part of the Ge atoms is segregated by RTA at the HfO NCs boundaries, while another part of the Ge atoms is present inside the HfO 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 HfO, distanced from the Si substrate by the tunnel oxide layer with a precise thickness.
采用磁控溅射工艺随后进行快速热退火（RTA），制备了具有单层 Ge 量子点（QDs）浮栅的高性能三层存储电容器，该浮栅位于 HfO 中。电容器的层序为栅极 HfO/单层 Ge QDs 浮栅 HfO/隧道 HfO/p-Si 晶片。通过在 600-700°C 的中等温度下进行 RTA，Ge 和 HfO 都被纳米结构化。在 600°C 下纳米结构化，在浮栅（中间层）中形成了具有 2-3nm 直径和 4-5×10 m 密度的单层均匀分离的 Ge QDs。中间层中的 Ge QDs 排列成单层，彼此之间由直径约 8nm 的具有四方/正交结构的 HfO 纳米晶体（NCs）隔开。单层中的 Ge QDs 位于 HfO NC 边界的交点处。在中间层中，除了 Ge QDs 之外，一部分 Ge 原子通过 RTA 在 HfO NC 边界处偏析，而另一部分 Ge 原子存在于 HfO 晶格中，稳定了四方/正交结构。所制备的电容器表现出 3.8±0.5V 的存储窗口和电容-时间特性，在前 3000-4000s 内电容衰减 14%，随后在 10 年内以非常缓慢的速度进一步衰减至 50%。这种高性能主要归因于单层 Ge QDs 在 HfO 中的浮栅，其通过具有精确厚度的隧道氧化物层与 Si 衬底隔开。
