Manipulation of materials’ physicochemical properties on nanoscale offers distinguished possibility to the development of novel electronic devices with ultrasmall dimension, fast operation speed, and low energy consumption characteristics. This is especially important as the state-of-the-art semiconductor manufacturing technique is approaching the end of miniaturization campaign in the near future.

Resistive random access memory (RRAM) distinguishes itself a promising candidate for the next-generation information storage technique, with the advantages of simple structure, low power, high density and fast speed. Over the past few years, research team from Ningbo Institute of Materials Technology and Engineering CAS led by Prof. Run-Wei Li systematically investigate the resistive switching effect and its working mechanism in both inorganic and organic materials. By controlling the migration of active metal/oxygen ions, the adsorption/desorption of functional groups, as well as the doping/dedoping of organic ions, stable resistive switching behavior has been demonstrated in thin films of ZnO (Adv. Mater., 24, 3941 (2012)), HfOx (Adv. Funct. Mater. 24, 2110 (2014); Nanoscale 9, 7037 (2017)), CeO2-x (Adv. Mater. 27, 2797 (2015)), CoFe2-xO4-y (ACS Nano 9, 4210 (2015)), polymer (J. Am. Chem. Soc, 134, 17408 (2012)), and metal-organic frameworks (J. Am. Chem. Soc. 136, 17477 (2014); Adv. Funct. Mater. 25, 2677 (2015)). However, severe leaking and interference problems over the neighboring cells occur when RRAM devices are integrated in high-density crossbar memory arrays, resulting in greatly worsen operating reliability. Thus, it is highly desired to develop reliable selector devices that can overcome the leaking and interference problems.

Vanadium dioxide (VO2) distinguishes itself as a model strongly correlated electron material for immense electronic applications. In particular, the reversible transition between the metallic and insulating states and the concomitant threshold switching behavior makes it promising candidate for selector in high-density crossbar memory array. However, due to the inhomogeneous coexistence and cascading evolution of multiple transitioning nanodomains, avalanche multistep jumps in the transition behavior with much reduced sharpness and uniformity are usually observed. The fluctuation in the MIT transition of VO2 hinders itself from direct application at the moment.

In order to improve the reliability of VO2 selector devices, Dr. Gang Liu and Ps. Wuhong Xue in Run-Wei Li’s group for the first time developed a novel approach of constructing 1D VO2 nanochannel in V2O5 thin film through electric-field-induced oxygen ion migration process, and its superior metal-insulator transition behavior. By reducing the length (~ 80 nm) and diameter (<20 nm) of VO2 nanochannel to much smaller than the typical dimension of transitioning domains (100 nm ~ 1μm), coexistence and random evolution of multiple phases can be greatly suppressed. As such, the occurrence of VO2 MIT can be effectively confined in the specific nanoscale regions, leading to sharp and reliable transition with a steep turn-on voltage slope of <0.5 mV/dec, fast switching speed of 17 ns, low energy consumption of ~ 8 pJ and low variability of less than 4.3% for both the switching voltages and device resistances in hundreds of voltage sweeping cycles. This work also for the first time confirms reliable MIT transition can be obtained in ultrasmall VO2 samples with the dimension of <20 nm. More importantly, the incorporation of the present device into a Pt/HfO2/Pt/VO2/Pt 1S1R unit can ensure the correct reading of the HfO2 memory continuously for 107 cycles, therefore demonstrating its great possibility as a reliable selector in high-density crossbar memory arrays.

This work was supported by the National Natural Science Foundation of China (51525103), National Key R&D Program of China (2016YFA0201102) and Natural Science Foundation of Zhejiang Province (LR17E020001). The manuscript is published as a back cover article on Adv. Mater. (DOI:10.1002/adma.201702162) and can be accessed via http://onlinelibrary.wiley.com/doi/10.1002/adma.201702162/full. A Chinese invention patent was also filed (201710557648.2).

Fig.1 (a) Schematic illustration of the construction of 1D VO2 nanochannel device through ion migration under the electric field. (b) Cross-sectional HRTEM image, (c) MIT transition, and (d) fast and (e) uniform switch characteristics of the as-fabricated 1D VO2 nanochannel device, respectively.