Comparative study of AlN dielectric films' electrical properties for MEMS capacitive switches

摘要

In the present work the electrical properties of aluminum nitride (AlN) films deposited by plasma-assisted molecular beam epitaxy (PA-MBE) and magnetron sputtering have been investigated in the transient and steady state domains. Charging and discharging current transients have been found to obey stretched exponential law, in agreement to Kohlrausch-Williams-Watts polarization relaxation found in many materials containing some degree of disorder, and both charging and discharging processes are found to be thermally activated. The activation energy for charging process in PA-MBE film differs from the one obtained for the discharging process while in sputtered films charging and discharging processes revealed the same activation energy, which is quite larger from the corresponding values in PA-MBE films. However, in all cases the obtained values for different activation energies are associated to nitrogen vacancies in AlN films. Finally, the temperature and voltage dependence of the leakage current in both films has been investigated, in order to study the carrier transport in AlN films. PA-MBE films revealed different conduction mechanisms from sputtered films, fact that can be attributed to differences in the film structure. Moreover, the dc conductivity in sputtered films has been found to be about three orders of magnitude smaller than the corresponding values obtained in PA-MBE films.