Growth of AlN oriented films on insulating substrates

Abstract

Abstract-This work describes the structural and piezoelectric assessment of aluminum nitride (AIN) thin films deposited by pulsed-DC reactive sputtering on insulating substrates. We investígate the effect of different insulating seed layers on AIN properties (crystallinity, residual stress and piezoelectric activity). The seed layers investigated, silicon nitride (SÍ3N4), silicon dioxide (Si0 2 ), amorphous tantalum oxide (Ta 2 O s ), and amorphous or nano-crystalline titanium oxide (Ti0 2 ) are deposited on glass plates to a thickness lower than 100 nm. Before AIN films deposition, their surface is pre-treated with a soft ionic cleaning, either with argón or nitrogen ions. Only AIN films grown of Ti0 2 seed layers exhibit a significant piezoelectric activity to be used in acoustic device applications. Puré c-axis oriented films, with FWHM of rocking curve of 6 o , stress below 500 MPa, and electromechanical coupling factors measured in SAW devices of 1.25% are obtained. The best AIN films are achieved on amorphous Ti0 2 seed layers deposited at high target power and low sputtering pressure. On the other hand, AIN films deposited on Si 3 N 4 , Si0 2 and TaO x exhibit a mixed orientation, high stress and very low piezoelectric activity, which invalídate their use in acoustic devices.

On the lateral excitation of shear modes in AlN layered resonators

“…These revealed that despite being grown on the TiO x seed layers, all the films exhibited a significant piezoelectric activity with values of the electromechanical coupling factor ^SAW ranging between 0.6% and 1.2%, which have been associated to coupling factors ^BAW in BAW resonators operating in the longitudinal thickness mode ranging from 3% to 5% [17,19]. On the one hand, the experimental data of Figs.…”

“…Finally, substrates of type III were composed exclusively of insulating materials; as substrates we used Corning glass plates 500 urn-thick which were covered with five insulating layers of Si0 2 The piezoelectric AIN film was deposited directly on top of the mirror without bottom electrode. Titanium oxide (TiO x ) seed layers were used to promote the growth of highly c-axis oriented films [17]. Finally, a molybdenum (Mo) layer was grown on top of the AIN film and patterned into coplanar electrodes of different geometries shown in figure 2.…”