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BB10.07 - The Influence of Water on Memory Characteristics of Transition-Metal-Oxide Resistive Random Access Memory 
April 24, 2014   3:45pm - 4:00pm

For practical use of Resistive Random Access Memory (ReRAM), it is important to ensure reliability. Typical stress parameters for the estimation of reliability include a voltage [1], heat [2], and humidity. However, knowledge on the influence of humidity on reliability and memory characteristics is lacking.In this paper, we investigated the influence of water on memory characteristics, such as operation voltages and data retention, for Pt/NiO/Pt structures. As a result, the decrease in voltages to form a filamentary conduction path, called a filament, () was confirmed. In addition, the degradation of data retention for low resistance values was confirmed by dropping water.NiO films with the thickness of 60 nm were deposited on Pt/Ti/SiO substrates at 380 °C using the RF reactive sputtering method, followed by the deposition of a Pt top electrodes (TEs) with the thickness of 100 nm. We measured current-voltage (-) characteristics for the Pt/NiO/Pt/Ti/SiO (Pt/NiO/Pt) structures before and after providing ultrapure water (HO). The provided HO covers the whole of the area of the Pt-TE.The decrease in the resistance in initial state () and by providing HO was confirmed, suggesting that HO enhances the forming. Then, Pt/NiO/Pt devices that was fabricated on the same wafer was heated in vacuum (6.0×10 Pa) at 200 °C for 10 min, in order to induce desorption of HO that was absorbed in the devices. Consequently, the drastic increase in both and (about three times larger than in air) was confirmed. The large damages the filament at the moment of filament formation [3], and makes the filament too leaky to be reset. These results suggest that HO makes the formation of filaments easy by reducing . Therefore, resistive switching effect developed with very high probability in devices for which the forming operation was performed under the presence of HO.We also investigated the effect of the desorption of HO after the completion of forming on the - characteristics. We provided HO to Pt/NiO/Pt devices and forming operations were performed to set the devices to low resistance state. After the forming, the devices were heated in vacuum. These devices show resistive switching effect, and voltages for both set and reset switching are almost equivalent to those observed under the presence of HO. This result seems to suggest that HO is not necessary for set and reset switching. However, we clarified that HO strongly induces reset switching, resulting in high failure probability of a data retention test for low resistance state. 89 % of the devices which absorbed HO was reset to high resistance state without applying a voltage.This study suggested that HO is closely related to resistive switching effect of ReRAM, and enhances both forming and reset switching.[1] C. H. Ho ., VLSI Tech. Dig. 229 (2007).[2] I. G. Baek ., IEDM Tech. Dig. 587 (2004).[3] B. J. Choi ., JAP 98, 033715 (2005).

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