Bipolar, complementary resistive switching and synaptic properties of sputtering deposited ZnSnO-based devices for electronic synapses

Abstract

In this work, ZnSnO-based resistive switching (RS) devices were fabricated with different top electrodes (TEs) to investigate the RS and synaptic characteristics for neuromorphic systems. The Ta/ZnSnO/TiN device exhibits excellent endurance (2000 DC cycles), longer retention (104 s), reliable multilevel retention (103 s) with six distinct resistance states via controlling the reset-stop voltage, and low forming/set voltages with high uniformity. Besides, complementary RS (CRS) behavior is observed in Ta/ZnSnO/TiN device at appropriate current compliance (CC, 5 mA) instead of low (600 μA) and high (10 mA) CC, respectively. X-ray photoelectron spectroscopy (XPS) analysis confirms that both TaO and TiON interface layers are formed at the top Ta/ZnSnO and bottom ZnSnO/TiN interfaces, which are found responsible for CRS behavior. Furthermore, XPS analysis also confirmed that the concentration of oxygen vacancies near the bottom ZnSnO/TiON interface is greater than the oxygen vacancies concentration near the top TaO/ZnSnO interface. Based on the XPS analysis, the switching phenomenon is confined in ZnSnO/TaON bottom interface because of its higher oxygen vacancy levels (prevent oxygen loss) in contrast to the TaO/ZnSnO top interface where the ZnSnO layer acts as series resistances in between these two interfaces. The basic features of an artificial synapse, LTP/ LTD, PPF/ PPD, and STDP, were successfully emulated using a Ta/ZnSnO/TiN device, suggesting potential applications for neuromorphic hardware systems.