Tuning Resistive, Capacitive, and Synaptic Properties of Forming Free TiO_(2-x)-Based RRAM Devices by Embedded Pt and Ta Nanocrystals

摘要

Resistive switching memories based on metal oxides arernemerging as a new research field and at the same time arernintensively studied as one of the most promising candidates forrnfuture non-volatile memory applications. However, in manyrnaspects their development has surpassed their understanding,rnarising thus questions about the underlying nature of thernswitching effect and the related uniformity issues. While severalrnphenomenological models have been devised in order tornelucidate on the origins of the switching effect, the conductingrnfilament (CF)-based model is gaining significant ground.[1]rnFollowing this assumption, the data storage takes place at leastrntwo resistance states provided by the generation/rupture of thernCFs. CFs may consist of either oxygenrnvacancies/metal precipitates[2] or a metallicrnchain of electrochemically active electrodernmetal.[3] Nevertheless, practical characteristicsrnof the CFs, such as direction of growth,rncomposition analysis, ruptured region, etc.,rnare difficult to be extracted from the abovernswitching conjectures. Thus, sophisticatedrnexperiments have been performed in orderrnto shed light on the atomic structure andrningredient of the CFs in the low resistancernstate (LRS) andhighresistance state(HRS)[2]rnas well as impedance spectroscopy techniques.[rn4] Despite of the exact nature of thernCFs, the major issue of resistive randomrnaccess memory (RRAM) technology is therninherit variability of the switching characteristics,rnwhich is directly connected with the randomness of the CFsrnformation/annihilation. While it seems practically impossiblernto control their characteristics, we can force them to evolverninto specific locations within the device active core.[5,6] Thus, arnvariety of optimization procedures have been suggested inrnorder to enhance the memory performance,[7,8] while NCsrnincorporation arising as one very promising technique tornovercome the switching variations,[9–11] especially when thernissues related with the uniformity of their distribution, inrnterms of diameter and surface density, will be efficientlyrnharnessed.[12]rnIn this work, we demonstrate that a wide range of non-volatilernmemory properties can be affected and improved by embeddedrnPt and Ta NCs. The concentrated electric field effect inrncombination with the charge trapping effect in the NCs, arernregarded as the driving forces for the recorded switchingrnpatterns. This possibility to tune the resistance levels over severalrnorders of magnitude is not usual to conventional materials andrnindicates the efficiency of NCs to influence the charge transferrnproperties.[13] In addition, insights about the origin of anrnintriguing phenomenon, such as capacitance switching,[14] arernprovided.