Thickness effect of ultra-thin Ta2O5 resistance switching layer in 28 nm-diameter memory cell

• Published in: Scientific reports Vol. 5; no. 1; p. 15965
• Main Authors: Park, Tae Hyung, Song, Seul Ji, Kim, Hae Jin, Kim, Soo Gil, Chung, Suock, Kim, Beom Yong, Lee, Kee Jeung, Kim, Kyung Min, Choi, Byung Joon, Hwang, Cheol Seong
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 03.11.2015; Nature Publishing Group
• Subjects: 142/126; 639/301/1005/1007; 639/925/927; 639/925/927/1007; Bias; Electric Conductivity; Humanities and Social Sciences; Lateral diffusion; Materials science; Materials Testing - methods; Microscopy, Electron, Scanning; Microscopy, Electron, Transmission; multidisciplinary; Nanostructures - chemistry; Nanostructures - ultrastructure; Oxides - chemistry; Oxygen; Random access memory; Science; Semiconductor research; Silicon Compounds - chemistry; Silicon Dioxide - chemistry; Tantalum - chemistry; Transmission electron microscopy; Voltage
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/srep15965

Resistance switching (RS) devices with ultra-thin Ta 2 O 5 switching layer (0.5–2.0 nm) with a cell diameter of 28 nm were fabricated. The performance of the devices was tested by voltage-driven current—voltage (I-V) sweep and closed-loop pulse switching (CLPS) tests. A Ta layer was placed beneath the Ta 2 O 5 switching layer to act as an oxygen vacancy reservoir. The device with the smallest Ta 2 O 5 thickness (0.5 nm) showed normal switching properties with gradual change in resistance in I-V sweep or CLPS and high reliability. By contrast, other devices with higher Ta 2 O 5 thickness (1.0–2.0 nm) showed abrupt switching with several abnormal behaviours, degraded resistance distribution, especially in high resistance state and much lower reliability performance. A single conical or hour-glass shaped double conical conducting filament shape was conceived to explain these behavioural differences that depended on the Ta 2 O 5 switching layer thickness. Loss of oxygen via lateral diffusion to the encapsulating Si 3 N 4 /SiO 2 layer was suggested as the main degradation mechanism for reliability and a method to improve reliability was also proposed.