Role of hydrogen, oxygen and composite formation in relaxational polarization of hafnium oxide and aluminum oxide

Metal-insulator-metal MIM devices of Al
₂
O
₃
were annealed to various temperatures, 366, 411 and 455 K. Their capacitance measurements were conducted at room temperature. It is illustrated that the annealing process reduces the polarization nonlinearity in high DC bias fields. This way the nonlinearity can be decreased up to 75% of its initial value. Al
₂
O
₃
was also prepared under O
₂
atmosphere. This leads to a drastic suppression of the previously observed electrode polarization for the low frequency region and for high temperatures in the case of samples without O
₂
treatments. With O
₂
treatments also the nonlinearity decreases. Due to the electrode polarization the relaxational polarization of Al
₂
O
₃
above 300 K could not be interpreted by the asymmetric double well potential (ADWP) model. It is shown that the capacitance behavior of oxygen treated samples can be interpreted in a wide temperature range by our model. Furthermore, it is found that the charge injection in the case of HfO2 and the loss are much stronger than for Al
₂
O
₃
Preparing a composite of the two oxides this charge injection as well as the loss was highly suppressed. The composite yields a higher permittivity than that for Al2O3. The capacitance measurements are also conducted for Al
₂
O
₃
MIM samples consisting of Pd and Au as electrodes after exposing them to hydrogen gas. These and the annealing experiments exhibit an important role of hydrogen in contributing to the relaxational polarization of metal oxides.