Sputtering of (001)AlN thin films: Control of polarity by a seed layer
The authors report on the ability to control the polarity of sputter deposited AlN001 thin ﬁlms using seed layers. Reactive sputter deposition leads to N-polarity on any substrate hitherto applied, i.e., Si111, sapphire, SiO2, and polycrystalline metals such as Pt111, Mo110, and W110. A site-controlled polarity allows for an efﬁcient excitation of shear modes of surface, bulk, and Lamb waves by interdigitated electrodes. The authors were able to introduce the Al polarity through a metal-organic chemical-vapor deposition seed layer. By subsequently patterning the substrate surface, it was possible to deﬁne the desired ﬁlm polarity of sputter deposited AlN ﬁlm. Polarities were determined by selective etching with KOH solutions and by piezoresponse force microscopy.