Influence of the Li and M (M = V, Nb, Ta, or Zr) Composition Ratio on the Piezoelectric Properties of LiM-doped AlN Films

Abstract

This paper describes the piezoelectric properties of LiM-doped (M = V, Nb, Ta, or Zr) aluminum nitride ((Li_yM_1-y)_xAl_1-xN) films with respect to the composition ratio of Li and M. Films of (Li_yM_1-y)_xAl_1-xN were prepared by a radio frequency magnetron sputtering method and characterized by crystal structure, as well as electrical properties such as the piezoelectric coefficient d₃₃ and resistivity ρ. The films for M = Nb with x = 0.13-0.20 and y = 0.41-0.49 showed |d₃₃| = 8.26-9.54 pC/N, which were 21-38% larger than non-doped AlN. On the other hand, the films for M = V, Ta, and Zr exhibited a decrease in piezoelectricity. The piezoelectric properties in (Li_yM_1-y)_xAl_1-xN films against M can be mainly explained by the combination of the following factors: crystallinity, lattice parameter ratio c/a, ρ, orientation degree, and polarity inversion. This study revealed that the composition ratio of Li and M gives (Li_yM_1-y)_xAl_1-xN films different behaviors on physical properties and the films for M = Nb with similar stoichiometric compositions (y～0.5) are promising candidates as piezoelectric materials for micro-electro-mechanical systems.