Resistive Switching Characteristics of Antimony Oxide Thin Film for Resistive Switching Random Access Memory Application

Abstract

Resistive switching (RS) oxide materials, including various binary metal oxides (BMO) and perovskite structured ternary oxides, have been researched extensively for application to next-generation nonvolatile memory. Among the many candidate materials for resistive random access memory (ReRAM) applications, BMOs have emerged as promising materials due to their simple chemical composition and their compatibility with current complementary metal-oxide semiconductor technology. While earlier studies on the RS of BMO materials focused on materials with distinctive second phases, such as TiO2 or NiO, due to the formation and rupture of evident CFs, recent studies have focused more on materials with less-evident phase transitions with higher binding energy, such as HfO2 and Ta2O5, because of their higher reliability. Nevertheless, it is still technically important to examine the RS of a material with far lower binding energy than those of typical transition metals oxides (TMO) for lower power consumption. This dissertation discusses unipolar and bipolar resistive switching characteristics of antimony oxides (Sb2O5) films as new BMO material for RS application which has low binding energy, low energy band gap, and low melting point. At first, antimony oxide thin films were deposited by reactive dc magnetron sputtering on Pt/Ti/SiO2/Si substrates. Then, 100nm-thick Pt or Sb was formed by using e-beam evaporation and dc magnetron sputtering, respectively. The Pt/Sb2O5/Pt (PSP) and Sb/Sb2O5/Pt (SSP) structures were used for the measurement of electrical characteristics. Both PSP and SSP samples showed URS behavior with switching current lower than those of several other TMO materials by almost two orders of magnitude, but the switching endurance of the PSP sample was insufficient to satisfy the requirement for memory application. The weak binding between the pnictogen element Sb and O and the low melting point of Sb2O5 resulted switching of low energy consumption, but they also made the RS relatively less reliable. When Sb was used as the top electrode, endurance characteristics improved greatly because of the suppression of oxygen loss from the Sb2O5 films by the oxygen blocking effect of Sb TE. In addition, severe oxygen gas evolution from the Sb2O5 films during electroforming can be alleviated by pre-existing Sb clusters. TEM analysis confirmed that the electrical stressing induced the formation of metallic Sb clusters, which would percolate to form conducting filaments during the set switching. Therefore, it can be concluded that the URS phenomenon of Sb2O5 films is controlled by the formation and rupture of localized CF which is composed of metallic Sb. The BRS phenomenon of Sb2O5 film was driven by the abnormal reset process during URS and the recovery of URS was induced by another abnormal reset process during BRS. It can be understood that the migration of oxygen ions from and into the partly ruptured CF region near the anode is responsible for the BRS from the negative and positive bias polarities of the BRS set and reset steps. The Schottky emission and space-charge-limited current in HRS were the dominant conduction mechanisms for URS and BRS, respectively, meaning that the URS and BRS phenomena are induced by more complete (URS) and retarded (BRS) reoxidaton and reduction of the local CF-ruptured region. Finally, the effect of bottom electrode on resistive switching property of Sb2O5 thin film was studied using Ti and TiN as the bottom electrode. A reproducible and stable switching endurance were obtained in Sb/Sb2O5/TiN (SSN) structure. URS and BRS characteristics of of SSN structure were similar with that of SSP structure. Because TiN film is widely used material in electronic memory industry, SSN device can be one of promising candidate for use in ReRAM.