Nanocharacterisation of zirconia based RRAM devices deposited via PLD

[摘要] With CMOS technology reaching fundamental scaling limitations, innovative data storage technologies have been a topic of great academic and industrial interest. Emergingtechnologies, not all based in semiconductors, that exploit new variables like spin, polarisation, phase and resistance, are being investigated for their feasibility as data storagedevices. One very promising technology is resistive switching random-access memory(RRAM). In RRAM devices memory operation relies on the change in resistance of ametal-insulator-metal structure, typically induced by ion migration combined with redoxprocesses. Here, RRAM devices based on amorphous and crystalline zirconia have beenprepared by means of pulsed laser deposition (PLD). The thesis starts with an overviewof the commissioning of a new PLD system, with a focus on characterisation of the laserablation plume, reduction of the density of “droplets” and development of the optimalsystem parameters, like temperature, oxygen pressure and laser fluence, for the preparationof zirconia based RRAM devices. For both amorphous and crystalline devices, titaniumwas used as an active electrode as it promotes the introduction of oxygen vacancies whichare responsible for inducing resistive switching. In addition, growth of epitaxial Nb dopedstrontium titanate (Nb:STO) via PLD was achieved, as the high temperatures used duringgrowth hinder the use of metallic bottom electrodes. Both types of RRAM devices havegood performance figures, with ON/OFF ratios of 1000 and 10000 and endurance of morethan 10000 cycles. Conduction mechanisms point to two different types of resistive switching:insulator-to-metal transition and trapping and de-trapping at the metal-oxide interfaces.Surprisingly, both conduction mechanisms were found to coexists on amorphous devices.Scanning transmission electron microscopy and electron energy loss spectroscopy wereused to investigate how interfaces can influence resistive switching. Results indicate thattitanium, in addition to introducing oxygen vacancies, creates an ohmic interface withzirconia which forces the resistive switching to take place on the inert metal-oxide Schottkyinterface, which was not described so far.

[发布机构] University:University of Glasgow;Department:School of Physics and Astronomy

[关键词] QC Physics