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 (10(4) s), reliable multilevel retention (10(3) 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 mu A) 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.