Characterization of HfTaO films for gate oxide and metal-ferroelectric-insulator-silicon device applications

Abstract

Characteristics of HfTaO thin films have been investigated from the viewpoints of their applications as insulating buffer layer in the metal-ferroelectric-insulator-semiconductor (MFIS) structure and gate oxide for next generation metal-oxide-silicon devices. HfTaO films with 2, 4, and 6nm in thickness have been deposited on Si substrates using electron beam evaporation and annealed typically at 800°C for 1min in O2 atmosphere. In fabrication of MFIS diodes, SrBi2Ta2O9 (SBT) films have been deposited on HfTaO using a sol-gel spin-coating method. It has been found from C-V (capacitance versus voltage) and I-V (current versus voltage) characteristics of Al∕HfTaO∕Si diodes with different film thicknesses that the optimum annealing temperature is 800°C and the dielectric constant of HfTaO is about 17. For MFIS devices with Pt∕SrBi2Ta2O9 (300nm)∕HfTaO(4nm)∕Si gate structures, a memory window of 0.65V between +4 and −4V gate voltage sweeping was observed. Furthermore, the high and low capacitance values biased at the center of the hysteresis loop are clearly distinguishable for over 24h, demonstrating excellent long-term retentions properties.