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We proposed and demonstrated a preparation method of (001) preferentially oriented stress-free AlN piezoelectric thin films. The AlN thin films were deposited by a reactive sputtering technique at substrate temperatures up to 330 °C using a dual Kaufman ion-beam source setup. We deposited the AlN on Si (100), Si (111), amorphous SiO2, and a (001) preferentially oriented Ti thin film and compared their crystallographic, optical, and piezoelectric properties. The AlN thin films deposited on the (001) preferentially oriented Ti thin films have the highest crystallographic quality. The stress-free AlN reached a high value of the piezoelectric coefficient d33 = (7.33 ± 0.08) pC·N−1. The properties of the AlN thin film prepared at such low temperatures are suitable for numerous microelectromechanical systems, piezoelectric sensors, and actuators monolithically integrated with complementary metal-oxide-semiconductor signal-processing circuits.

The infrared response of superlattices (SLs) composed of YBa 2 Cu 3 O 7 (YBCO) and La 0.67 Ca 0.33 MnO 3 (LCMO) on SrTiO 3 substrate has been studied by ellipsometry in the range from 400 to 5000 cm -1 . We use a model calculation of the optical response to distinguish the contribution of the SL and the substrate. The infrared data provide an evidence of a strong interaction between the YBCO and LCMO layers. The mid-infrared resonance located at approximately 1000-3000 cm -1 is discussed in terms of the polaronic absorption in LCMO. The resonance could indicate a charge transfer from the YBCO to the LCMO layers.