Comprehensive study on fabrication, characterization and performance evaluation of Ag/TiOx/ITO and Au/Ag/TiOx/ITO memristors

Abstract

The structure of electrodes and active materials in memristors plays a critical role in determining their electrical behavior. This study primarily focuses on Ag/TiOₓ/ITO and Au/Ag/TiOₓ/ITO memristors incorporating titanium oxide (TiOₓ) thin films with varying thicknesses (25, 50, and 100 nm), deposited via RF magnetron sputtering onto ITO-coated glass substrates. Comprehensive surface characterization techniques, including scanning electron microscopy (SEM), electron dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), were employed to examine the morphological, structural, and chemical properties of the films. SEM–EDX mapping revealed thickness dependent elemental distributions. AFM analysis showed increased surface roughness (1.69 to 2.15 nm) and grain size (60 to 90 nm) with increasing film thickness. XPS measurements conducted at 8-week intervals provided insights into the oxidation behavior of Ag electrodes and their surface chemistry evolution over time. Raman analysis confirmed the presence of anatase and rutile phases in the titanium oxide thin films, as evidenced by the characteristic peaks observed at 196.83 cm⁻¹ and 607.43 cm⁻¹, respectively. Focused ion beam (FIB) and scanning transmission electron microscopy (STEM)-EDX were also utilized to investigate elemental boundaries between the layers. Bipolar resistive switching behavior, without the need for any electroforming process, was observed in all devices within 7 days of fabrication and remained stable throughout 1000 current–voltage (I–V) cycles. After 8 weeks of storage, further endurance tests were conducted using ± 1.5 V SET and RESET voltages, with HRS and LRS values measured at a read voltage of 0.5 V. Notably, the highest HRS/LRS ratio of 16.07 was achieved in the Ag/TiO_x/ITO memristor with a 100 nm TiO_x layer. These findings underscore the critical influence of oxide thickness on resistive switching performance and endurance. Furthermore, the comparative evaluation of Ag and Au-passivated Ag electrodes highlights the significance of electrode configuration in enhancing memristor reliability and long-term operational stability.