Abstract
Physical mechanisms underlying the multilevel resistive tuning over seven orders of magnitude in structures based on TiO2/Al2O3 bilayers, sandwiched between platinum electrodes, are responsible for the nonlinear dependence of the conductivity of intermediate resistance states on the writing voltage. To improve the linearity of the electric-field resistance tuning, we apply a contact engineering approach. For this purpose, platinum top electrodes were replaced with aluminum and copper ones to induce the oxygen-related electrochemical reactions at the interface with the Al2O3 switching layer of the structures. Based on experimental results, it was found that electrode material substitution provokes modification of the physical mechanism behind the resistive switching in TiO2/Al2O3 bilayers. In the case of aluminum electrodes, a memory window has been narrowed down to three orders of magnitude, while the linearity of resistance tuning was improved. For copper electrodes, a combination of effects related to metal ion diffusion with oxygen vacancies driven resistive switching was responsible for a rapid relaxation of intermediate resistance states in TiO2/Al2O3 bilayers.
Highlights
Organization of the controlled electrooxidation reactions between the metal electrode and the active oxide layer of the bilayer structure may be considered as an additional capacity for oxygen-related ions, which could enhance the linearity of analog tuning
Bilayer structures, an active layer, while nm thick titanium oxide layer acts as a reservoir of an active layer, while 30 nm thick titanium oxide layer acts as a reservoir of oxygen vacancies vacancies (Figure (Figure 2)
Concluding, electrochemical reactions involving OH-groups could be experimentally observed in atomic layer deposition (ALD) deposited aluminum and titanium oxide layers in both single-layer and bilayer structures with resistive switching effects
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Organization of the controlled electrooxidation reactions between the metal electrode and the active (switching) oxide layer (in our case, Al2 O3 ) of the bilayer structure may be considered as an additional capacity for oxygen-related ions, which could enhance the linearity of analog tuning. For this purpose, we replace the material of the top platinum electrode of TiO2 /Al2 O3 bilayers with chemically active materials, such as copper and aluminum. The wide memory window of the structures and keeping the possibility of analog tuning of the nonvolatile resistance state of the devices
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