AN APPLICATION OF R-HiPIMS METHOD FOR TiO2- AND TiO2:Cu-BASED MEMRISTORS: CONTROLLING Cu DOPING USING DC PULSE METHOD

Abstract

Nowadays, the High-Power Impulse Magnetron Sputtering (HiPIMS) as an additional technique to plasma-based sputtering, is applied to depositing or coating of thin films. HiPIMS is based on applying high-power and low-duty-cycle unipolar pulses to the magnetron target by a low repetition frequency, which are produced from the high ionization part of sputtered atoms by high discharge power. By applying voltage to substrate and bombarding it in the presence of an inert gas such as Ar, the growth of the film is controlled by the acceleration of the sputtered material across the highly dense plasma. To deposit compound materials, metal targets are sputtered with gases such as CH4, N2, O2, etc. or by Reactive HiPIMS (R-HiPIMS) techniques. The transparent metal oxide (TiO[Formula: see text] film depositions by R-HiPIMS are denser and have flatter surfaces due to a higher degree of crystallinity than other sputtering methods. The applicable potential of TiO2 thin films and similar metal oxides on the ultra-high-density electronic devices due to the presence of oxygen deficiency, leads them to be chosen for memristor devices. As theory predicted, a current-controlled memristor is possible with metal–TiO2–metal structures. But stability and repeatability with high ON/OFF ratios remain as problems. A high ON/OFF ratio due to filament formation is revealed by Cu doping of TiO2 thin films which leads to two state functions to be applicable for the traditional digital electronics. On the other hand, an ideal memristor has a potential for gray scale with no limitation. This approach has a big potential impact on data storage and computation in electronics. A new spotlight for this prediction is recognized by the high mobility of transition elements such as Cu in semiconductors. In this work, a nano-scale memristor based on Cu-doped TiO2 is fabricated from metallic targets (i.e. Ti and Cu) by the R-HiPIMS method. Cu doping is synchronously controlled by using pulsed DC sputtering onto the TiO2 structure. DC pulse duration and its frequency are used for adjusting the Cu doping concentration during the growth time of TiO2. The memristor properties of Cu–Pt–TiO2–p[Formula: see text]Si–Al and Cu–Pt–TiO2:Cu–p[Formula: see text]Si–Al devices are considered. The electrode change effect on the memristive properties and performance of Cu-doped memristor is investigated. The [Formula: see text]–[Formula: see text] characteristic of the Cu-doped memristor with Cu top electrode is recognized to be asymmetric in comparison with Cu-doped TiO2-based memristor with Pt top electrode. The structural, optical and electrical characterizations are carried out and preliminary findings are given in detail.