Resistive switching in TiO2 nanocolumn arrays electrochemically grown

Investigation of switching behavior of several metal oxides, which may have their resistance states modulated by voltage applied to or by current flowing through them, is nowadays a growing research field motivating... [ view full abstract ]

Investigation of switching behavior of several metal oxides, which may have their resistance states modulated by voltage applied to or by current flowing through them, is nowadays a growing research field motivating researchers to prepare high-speed low-power nano-dimensional non-volatile Resistive Random Access Memory (ReRAM) devices. In such devices, a layer of metal oxide is usually sandwiched between two metallic electrodes for obtaining metal/semiconductor/metal structures. TiO2, among other metal oxides like Ta2O5, HfO2, ZrO2, ZnO, WO3, or NiO, is one of the most intensively used resistive switching materials because of many advantages, such as its versatile fabrication, wide band gap, and high dielectric constant.[1,2]
Here we investigate the resistive switching behavior of TiO2 nanocolumn arrays prepared via the originally developed porous-anodic-alumina-assisted anodizing of Ti layers sputtered on a SiO2-coated Si wafer. The self-ordered TiO2 nanocolumns are fabricated using a one-step anodization procedure in oxalic acid at 40 V. This leads to growth of ~80 nm long columns embedded in the alumina matrix (Figure 1a). Thermal annealing is applied to alter electrical conductivity of the nanocolumns.
For making a top electrical contact, the TiO2 columns are covered by gold electrochemically deposited into the pores. The electrode area is confined to about 104 μm2 by a combination of photolithography and chemical etching. The remaining Ti layer under the columns is used as the bottom electrode.
Electrical characterization of the nanocolumn arrays by means of I(V) measurements shows resistive switching behavior after a formation cycle, manifested by a set process at negative polarization and a reset process at positive polarization of the Au electrode (Figure 1b). The ratio between the ON and OFF state resistivities ranges between 100 and 10000 whereas the set and reset voltage is temperature dependent. Thus, the TiO2 nanocolumn arrays developed here exhibit promising memristive properties.
This research was supported by GAČR grant no. 15-23005Y and CEITEC 2020 (LQ1601).

[1] W. B. Luo, et. al. Forming free resistive switching in Au/TiO2/Pt stack structure. Thin Solid Films, 2016, in press.
[2] J. J. S. Yang, D. B. Strukov, D. R. Stewart. Memristive devices for computing. Nat. Nanotechnol. 2013, 8, 13–24.