Resistive Switching and Polarization Reversal of Hydrothermal-Method-Grown Undoped Zinc Oxide Nanorods by Using Scanning Probe Microscopy Techniques

Abstract

This paper reports the localized electrical, polarization reversal, and piezoelectric properties of the individual hexagonal ZnO nanorods, which are grown via the hydrothermal method and textured with [0001] orientation. The studies are conducted with conductive atomic force microscopy (c-AFM) and piezoresponse force microscopy (PFM) techniques. The correlation between the resistance switching and polarization reversal is discussed. The c-AFM results show that there is less variation on the set or reset voltage in nanorod samples, compared to that of the ZnO thin film. With increasing aspect ratio of the nanorods, both set and reset voltages are decreased. The nanorods with low aspect ratio show unipolar resistance switching, whereas both unipolar and bipolar resistance switching are observed when the aspect ratio is larger than 0.26. The PFM results further show the ferroelectric-like property in the nanorods. Comparing with that of the ZnO thin film, the enhanced piezoresponse in the nanorods can be attributed to the size effect. In addition, the piezoresponse force spectroscopy (PFS) experiments are conducted in ambient air, synthetic air, and argon gas. It shows that the depolarization field in the nanorod may be due to the moisture in the environment; moreover, the increased piezoresponse may relate to the absence of oxygen in the environment. It is also shown that the piezoelectric responses increase nonlinearly with the aspect ratio of the nanorods. By comparing the piezoresponse hysteresis loops obtained from the nanorod samples of as-grown, air-annealed and vacuum-annealed, it is found that the oxygen vacancies are the origin of the polarization reversal in ZnO nanorods. Finally, the tradeoff between the electrical and ferroelectric-like properties is also observed.

Nanoscale electrical properties of ZnO nanorods grown by chemical bath deposition

“…In addition, the conducting regions of RRAM often generate high electric fields during module operation, disintegrating the region (Long et al, ). As shown in all current images in Figure , the conducting regions are distributed over the edge of the nanorod surface, because the charge accumulation forms a corona discharge‐like region (Beinik et al, ; Xiao, Ong, Guo, Ho, & Zeng, ). The coverage percentage of the conducting region on sample S 1 is as high as 46.6%, which severely limits the stability and lifetime of the RRAM module.…”

Probing of Local Multifield Coupling Phenomena of Advanced Materials by Scanning Probe Microscopy Techniques

“…These coupling behaviors may also influence each other, i.e., one coupling phenomenon may cause another coupling effect. For instance, when ZnO was switched to high resistance state by a large electric field, its polarization dipoles can be reversed by a smaller electric field in a similar way as the polarization switching characteristics in the traditional ferroelectric materials …”

“…For instance, at a metal–semiconductor interface, charge injection due to highly localized electric field might cause the shift of Fermi level, hence changing the electrical conductance of the materials . Another example is ZnO, the external electric field might cause the reorientation of the dielectric dipoles, which affected the resistive switching behavior, and further initiated a polarization switching phenomenon similar to that of the ferroelectric materials …”

Recent Developments and Perspectives for Memristive Devices Based on Metal Oxide Nanowires

“…In addition, it has been demonstrated that the conductivity in ZnO NR array devices can be exploited for the emulation of synaptic functions, since the device conductivity can be progressively modulated by means of voltage spike trains. [266,267] For practical resistive random access memory (RRAM or ReRAM) applications, Tseng et al [244] proposed the realization of resistive switching devices based on ZnO NR array/polymethylmethacrylate (PMMA) heterostructures. In this case, unipolar resistive switching was observed and attributed to a thermochemical mechanism (that is not polar dependent) of formation/rupture of a conductive filament of oxygen vacancies on the NW surface.…”