Nanoionics-based neuromorphic function of a Pt/Ti_0.96Co_0.04O_2-δ /Pt multilayer device operating at low pulse voltage

Abstract

We investigated the nanoionics-based neuromorphic function of Pt/Ti0.96Co0.04O2-δ/Pt multilayer with cross-point structure prepared by RF magnetron sputtering. This multilayer exhibits the electro-ion mixed conduction and the nonlinear current-voltage characteristic based on the Schottky barrier between Pt and Ti0.96Co0.04O2-δ layers. When the low electrical pulse of 0.8 V was applied with short interval time of 14 s, the current modulation corresponding to the long-term memorization (LTM) was observed, though the current response at the long interval time of 80 s was the short-term memorization (STM). The O 1s photoemission spectrum showed the OH- peak that contributes to the electron-ion mixed conduction. The current responses with both LTM and STM are considered to be due to the local proton migration at near the Schottky barrier.

Neuromorphic learning and forgetting functions of Pt/Ti0.99Sc0.01O2−δ /Pt multilayer by Schottky barrier modulation

“…This result indicates that thin films have the mixed valence states of Ti 4+ and Ti 3+ . This mixed valence state often has been reported in various Ti oxides such as Y x Ca 1-x TiO 3 , 30) TiO 2-δ with oxygen vacancy, 18) and Ti 0.96 Co 0.04 O 2-δ , 19) which exhibit electronlike conduction.…”

“…25) and top of the valence band, respectively, although DOS does not exist at around the E F . The acceptor-like band, which has been observed in the Co 3+ -doped TiO 2 thin film, 19) reflects DOS that electrons in the valence band transited to the acceptor level slightly formed by Sc substitution. The existence of a donor band composed of Ti 3d-induced DOS is closely related to electron conduction in Ti 0.99 Sc 0.01 O 2-δ thin films.…”

“…Such an OHpeak is often observed in surface proton conducting oxides 33,34) and carrier-doped TiO 2 thin film. 19) The appearance of the OHpeak reflects that the proton taken from the sputtering ceramic target plays a useful role as ion carriers of electron-ion mixed conduction indicated in Fig. 3(b).…”

“…Figure 5 interface is modulated by collaborative behaviors of the electron and ion (or proton). 18,19) Figures 6(a) and 6(b) show the current curves with time for the Pt/Ti 0.99 Sc 0.01 O 2-δ /Pt multilayer when electrical pulses of 0.8 V were applied for 4 s at the interval time of 80 s and 14 s, respectively. An applied voltage during the interval time was 0.1 V. Each upper panel is the input pulse voltage.…”

“…[6][7][8][9] Similar behavior also has been reported in Pt/WO 3-x /Pt, 5,10,11) Pt/Ta 2 O 5 /Pt, [12][13][14] Pt/TiO 2 /Pt [15][16][17] multilayer devices with the cross-point array. These multilayers use an oxide film with electron-ion mixed conduction and operate by applying voltage pulses of 2.5 ∼ 3.2 V. In recent years, we have reported that in Pt/TiO 2-δ /Pt 18) and Pt/Ti 0.96 Co 0.04 O 2-δ /Pt 19) there also occurs neuromorphic memory function operating at lower voltage pulses of 1.0 V. Our device does not form the conducting filament since the local proton and electron migrations at the Schottky barrier are considered to be dominant, 18,19) so one can expect lower voltage operation. However, we had not realized forgetting the LTM function (memory erasure direction) by applying negative voltage pulses.…”