Department of Materials Science and Engineering, and Inter-University Semiconductor Research Center , Seoul National University , Seoul 08826 , Republic of Korea.
Department of Materials Science and Engineering , KAIST , Deajeon 34141 , Republic of Korea.
ACS Appl Mater Interfaces. 2019 Dec 18;11(50):47063-47072. doi: 10.1021/acsami.9b16499. Epub 2019 Dec 5.
The thin-film growth conditions in a plasma-enhanced atomic layer deposition for the (3.0-4.5) nm thick HfO film were optimized to use the film as the resistive switching element in a neuromorphic circuit. The film was intended to be used as a feasible synapse with analog-type conductance-tuning capability. The 4.5 nm thick HfO films on both conventional TiN and a new RuO bottom electrode required the electroforming process for them to operate as a feasible resistive switching memory, which was the primary source of the undesirable characteristics as the synapse. Therefore, electroforming-free performance was necessary, which could be accomplished by thinning the HfO film down to 3.0 nm. However, the device with only the RuO bottom electrode offered the desired functionality without involving too high leakage or shorting problems, which are due to the recovery of the stoichiometric composition of the HfO near the RuO layer. In conjunction with the Ta top electrode, which provided the necessary oxygen vacancies to the HfO layer, and the high functionality of the RuO as the scavenger of excessive incorporated oxygen vacancies, which appeared to be inevitable during the repeated switching operation, the Ta/3.0 nm HfO/RuO provided a highly useful synaptic device component in the neuromorphic hardware system.
为了将（3.0-4.5）nm 厚的 HfO 薄膜用作神经形态电路中的电阻式开关元件，优化了等离子体增强原子层沉积中的薄膜生长条件，以使该薄膜具有模拟型电导可调能力的可行突触。对于传统的 TiN 和新的 RuO 底部电极上的 4.5nm 厚 HfO 薄膜，需要电成型工艺才能使其作为可行的电阻式开关存储器运行，这是作为突触出现的不理想特性的主要来源。因此，需要无电成型性能，这可以通过将 HfO 薄膜减薄至 3.0nm 来实现。然而，仅使用 RuO 底部电极的器件提供了所需的功能，而不会出现过高的泄漏或短路问题，这是由于 HfO 接近 RuO 层的化学计量组成的恢复。与 Ta 顶部电极结合使用，Ta 顶部电极向 HfO 层提供了必要的氧空位，而 RuO 作为过多掺入氧空位的清除剂具有很高的功能，这在重复开关操作中似乎是不可避免的，Ta/3.0nm HfO/RuO 为神经形态硬件系统中的高度有用的突触器件组件。
