Enhancement of piezoelectric response of diluted Ta doped AlN

The authors have investigated the variation of microstructure and piezoelectric response of TaxAl1-xN films with Ta concentrations. The results indicate that moderate Ta doping facilitates the c-axis orientation, crystallinity and enlargement of lattice constants. When the doping content is about 5.1 at.%, the c-axis orientation is optimized in the best with c constant of about 0.5086 nm. The Raman spectra of TaxAl1-xN films further determine the wurtzite structure of AlN after Ta doping. The high resolution transmission electric microscopy demonstrates that the column single crystal was obtained with presence of nano distortion domains. The Ta 4f(7/2) binding energy of TaxAl1-xN shows a shift toward lower binding energy side, indicating that the coordination configuration of Ta with N changed as Ta contents increased. A significant enhancement in piezoelectric response was obtained from 4.2 pC/N to 8.2 pC/N, which is enhanced by ca. 100%, when the Ta content arrived to 5.1 at.%. The expansion of unit cell volume and the competition between Ta and Al atoms about the coordination of nitrogen atoms, which will enhance the internal nitrogen displacement under electric field, are proposed to be the main microscopic origin of the enhancement of piezoelectric response. (C) 2013 Elsevier B. V. All rights reserved.