Impact of Joule heating on the microstructure of nanoscale TiO2 resistive switching devices

Abstract

The microstructure of TiO2 functional layers in nanoscale resistive switching devices was analyzed using Scanning Electron and Transmission Electron Microscopies (SEM and TEM). The TiO2 layers in as-fabricated devices were amorphous with very weak lattice fringes in High Resolution TEM. After electroformation with low power dissipation (PDIS < 0.4 mW), the microstructural changes in the TiO2 layer were limited to an area approximately 75∼100 nm in radius indicating that the current path and Joule heating were localized. Since the reset power (≈2.4 mW) was greater than the electroformation power, switching cycles resulted in an increased area of the TiO2 affected zone and more morphological changes to the Pt electrodes and functional layers. Electroformation under large power dissipation (15 mW) led to massive redistribution of Pt, including shorting of electrodes through the oxide layer. Modeling temperature distribution in the devices found maximum temperature to be strongly dependent on the power dissipation. Computational estimates of the temperature exceed 323 °C at electroformation (0.4 mW), 819 °C at reset (2.4 mW), and the melting point of Pt electrode at large power (15 mW) dissipation. The microstructural changes appear to be caused by Joule heating during device operation.