Improvement of NbO x -based threshold switching devices by implementing multilayer stacks

In this work the I–V characteristics of a niobium oxide-based threshold switching device were optimized to match the requirements for its application in neuromorphic circuits. Those neuromorphic circuits rely on coupled oscillators utilizing the volatile resistive switching effect of the memristor. A large voltage extension of the negative differential resistance region of the threshold switch enables enhanced signal amplification, and, furthermore, can lead to a better tolerance to device variability. A symmetric switching behavior as well as a high device stability for the operation in both voltage polarities is mandatory to allow the integration in circuits that utilize the connection of several threshold switching devices operated in different polarities. These properties are similarly important for the adoption of the threshold switches as selector devices in bipolar resistive memory arrays. Furthermore, a low forming voltage is desirable because it leads to a better control during the forming step. To meet all those requirements the application of multilayer stacks consisting of niobium and niobium oxide layers is proposed and their optimization is investigated in detail.