Abstract
The electrical conduction mechanism in zirconium oxide (ZrO2) thin films as a function of temperature T and electric field E was studied. Al/ZrO2/p-Si metal-insulator-semiconductor (MIS) capacitors were fabricated. With the Al electrode biased negative, the conduction mechanism in the electrical field of 0.81 MV/cm <E< 1.40 MV/cm and in the temperature range of 375 K <T< 450 K is found to be modified Schottky emission. The intrinsic barrier height between Al and ZrO2 is 1.06 eV. At higher electrical fields of 1.50 MV/cm <E< 2.25 MV/cm and higher temperatures of 375 K <T< 450 K, the electrical conduction is dominated by modified Poole-Frenkel emission. The extracted trap barrier is 0.83 eV. With the Al electrode biased positive, the conduction mechanism is found to be Schottky emission at the electrical field 0.20 MV/cm <E< 0.60 MV/cm and higher temperature range of 425 K <T< 450 K. The barrier height between Si and ZrO2 is 1.0 eV. Based on these results, an energy band diagram of the Al/ ZrO2/p-Si system is proposed. N-channel metal-oxide-semiconductor field effect transistors (MOSFETs) using ZrO2 gate oxide were fabricated successfully. The ZrO2 films were deposited by RF magnetron sputtering. The C-V, ID-VD and ID–VG characteristics are measured. The threshold voltage was 0.20 V. The minimum subthreshold swing was 272 mV/dec. The ION/IOFF ratio is about 104 at VD=0.1 V. Since St=2.3(kT/q)[1+(CD+Cit)/Cox], the interface trapped charge density Dit is extracted to be about 1.35x1013 cm-2-eV-1.Secondary ion mass spectrometry (SIMS), X-ray diffraction (XRD), electron spectroscopy for chemical analysic (ESCA) and transmission electron microscope (TEM) were used to examine the material properties of ZrO2.A comparison with MOSFETs using SiO2 gate oxides was made. The ZrO2/Si interface is generally inferior compared with that of the SiO2/Si interface. But the ZrO2/Si interface is comparable to that of the Ta2O5/Si interface. The thermodynamic stability of ZrO2 gate oxide is much better than that of Ta2O5 gate oxide. In the future, MOSFETs with ZrO2 gate oxide will be a promising candidate for sub-0.1 mm MOSFETs.