Resistance Switching Characteristics of Metal Oxide and Schottky Junction for Nonvolatile Memory Applications

We evaluated the resistive switching effect of the polycrystalline oxide (Nb₂O₅, ZrO_x and Cr-SrTiO₃) fabricated by reactive sputtering and PLD. It shows a well-developed resistive switching behavior. The reproducible resistance switching cycles were observed and the resistance ratio was as high as 50~100 times. The resistance switching was observed under voltage pulse as short as 10 nsec. The estimated retention lifetime at 85degC was sufficiently longer than 10 years. However, we observed a significant non-uniformity of resistance switching behavior. To improve uniformity of resistance switching, we have investigated single crystal Nb-doped SrTiO₃ in terms of its potential utility in nonvolatile memory applications. Compared with polycrystalline oxide (Nb₂O₅, ZrO_x and Cr-doped SrTiO₃), the Pt/single crystal Nb:SrTiO₃ Schottky junction exhibits excellent memory characteristics including uniformity of set/reset bias, die-to-die reproducibility, data retention at high temperature, reliability under cycle stress, and multi-bit operation characteristics. Considering the area dependent resistance value and low temperature I-V characteristics, resistance switching might be explained by modulation of the Schottky barrier height by charge trapping and detrapping at the interface. In order to introduce Nb:SrTiO₃ into CMOS process and reserve its excellent characteristics of single crystal, we deposited epitaxial Nb:SrTiO₃ film on Si substrate using conducting TiN as a buffer layer. Based on XRD, RBS and TEM measurements, epitaxial growth of TiN and Nb:SrTiO₃ films were confirmed. Moreover, the electrical and reliability properties of Pt/Nb:SrTiO₃/TiN/Si structure are similar with that of Pt/single crystal Nb:SrTiO₃ junction. Considering excellent uniformity and reproducibility of Pt/Nb:SrTiO₃ Schottky - - junction, it shows good promise for future nonvolatile memory applications.