Integration of Piezoelectric Aluminum Nitride and Ultrananocrystalline Diamond Films for Implantable Biomedical Microelectromechanical Devices

M. ZALAZAR; P. GURMAN; J. PARK; D. KIM; S. HONG; L. STAN; R. DIVAN; D. CZAPLEWSKI; O. AUCIELLO

Conferencia; New Diamond and Nano Carbons Conference; 2013

Piezoelectric materials are being used for a variety of applications in medicine such as ultrasonic transducers, drug infusion pumps and cochlear implants. In the case of medical implants, an important requirement that must be fulfilled is biocompatibility. In this regard, AlN has emerged as an attractive alternative to other piezoelectric materials such as lead zirconate titanate (PZT) that contains lead, as have been shown by several authors. It is also becoming important to be able to integrate piezoelectric films with materials used in implantable medical devices. Ultrananocrystalline diamond (UNCD), in thin film form, is a multifunctional material, which is extremely bioinert and biocompatible. The physics for integration of piezoelectric aluminum nitride (AlN) films with underlying insulating ultrananocrystalline diamond (UNCD), and electrically conductive grain boundary nitrogen-incorporated UNCD (N-UNCD) and boron-doped UNCD (B-UNCD) layers, as the core materials for piezoelectrically actuated Bio-microelectromechanical systems (BioMEMS), has been investigated. AlN films deposited on Platinum layers on as grown UNCD or N-UNCD layers (5-10 nm rms roughness) required thickness of ~ 400 nm to induce (002) AlN orientation with piezoelectric d33 coefficient ~1.91 pm/V at ~10 V. Chemical mechanical polished B-UNCD films (0.2 nm rms roughness) substrates enabled (002) AlN film 200 nm thick, yielding d33 = 5.3 pm/V. These results support the hypothesis that a rough surface favors a heterogeneous orientation of the AlN crystallites, thus hampering the c-axis (002) orientation. The high density of oblique crystallographic orientations prevents the growth of highly oriented (002) AlN which is necessary to attain the maximum piezoelectric coefficient. Initial AlN/UNCD MEMS structures will be discussed.