a-axis oriented AlN thin films sandwiched between Ti-electrodes were prepared on Si (100) substrates using ion beam sputtering in reactive assistance of N-2-plasma. Piezoelectric response of such Ti/AlN/Ti heterostructures was investigated using XRD under applied voltage varying from + 1 V to + 5 V. External electric field induced strain in film microstructure was used to estimate the longitudinal piezoelectric coefficient d(33)(eff). Our results show that AlN thin films with a preferred orientation along a-axis possess enhanced value of d(33)(eff) = 560.5 +/- 68 pm/V. A phenomenological model is proposed to account this enhancement by considering the dielectric an elastic continuum with Al+-N - Al+ quadruples as the constituent unit of the Cosserat medium. (C) 2018 Elsevier B.V. All rights reserved.