Abstract
The limitations of conventional flash memories lead to the problems like high-speed memory applications in today's world of data. Hence new substitutes are required to overcome the challenges faced by traditional flash memories. Conductive Bridge Random Access Memory (CBRAM) is one of the promising candidates for emerging non-volatile memory technology for memory and neuromorphic applications due to its advantages like high speed, low current, easy CMOS integrity, scalability, and low voltage requirements. For a long time, researchers have shown great interest in AlOx as a switching material for resistive memory technology due to its properties like very low Gibb's free energy (-1582.3 kJ/mol), large energy bandgap (>7 eV), moderate dielectric constant (e ~ 9) and easy device integration. In this study, we propose and investigate the thermally deposited AlOx switching layer in Al/Cu/AlOx/TiN CBRAM memristor structure for the first time, with a device size of 1×1 µm2. The as-fabricated CBRAM device has shown very unstable switching with a memory window of >10 due to many defect sites, which leads to uncontrolled copper migration through the SL. We have fabricated another device with the exact specifications and annealed it at 400 ºC in an N2 environment for 10 min to enhance the switching. The annealed device has significantly improved resistive switching due to controlled copper migration and re-nucleation of conducting filament. Annealing enhanced the surface morphology of the AlOx SL, which reduces the rate of defect generation results in controlled copper migration. Both devices have shown long DC endurance of more than 500 DC cycles and >1.5×108 P/E endurance at low current compliance of 200 µA. The annealed device has demonstrated significant improvement in both LRS and HRS states compared to without annealed device with highly stable low resistance state in both DC and AC pulse measurements. vi Furthermore, we have analysed both the annealed and the as-deposited samples based on statistical analysis with Vform, Vset, Vreset, and Ireset using the Weibull probability distribution method. The results show that annealed samples follow the Weibull distribution with higher slopes (ß) than as-deposited samples. The as-deposited device shows the neuromorphic characteristics owing to the gradual set/reset in the device. In contrast, it is hard to extract the neuromorphic features on the annealed device due to a sharp set/reset. We studied voltage stressed retention characteristics of both devices, and we found that annealing significantly improved the LRS state of the CBRAM device without failure for more than 4000 seconds. Lastly, there has been shown low current operation at 100 µA current for D1 and 50 µA for D2 devices. Annealed devices have shown very stable performance at low current with ~200 resistance ratio for 45 DC cycles compared to an as-deposited device with >10 resistance ratio. The results show the low current operation possibility of annealed device