Piezoelectric properties of LiM-doped (M = V, Nb, Ta, or Zr) AlN thin films

Characterization of LiM-doped (M = V, Nb, Ta, or Zr) piezoelectric aluminum nitride ((Li y M1−y ) x Al1−x N) was performed by first-principles calculations and experimental approaches. The calculation results show that for all (Li y M1−y ) x Al1−x N, piezoelectric coefficient d 33,f is increased by increasing the LiM doping concentration x up to 0.25. In comparison to the calculation results, the experimental results reveal that only (Li y Nb1−y ) x Al1−x N has increased piezoelectric coefficient d 33. The absolute value of d 33 was 9.54 pC N−1 at x = 0.15 ((Li0.45Nb0.55)0.15Al0.85N) due to elastic softening of the elastic modulus E. In addition, the research investigates how LiM doping inverts the polarity depending on x. Insulating performance was also evaluated, revealing that LiM doping induces resistivity degradation down to 107 and 109 Ω·cm for M = V and Nb, respectively. Results for d 33 indicate that (Li y M1−y ) x Al1−x N systems represented by M = Nb have potential as piezoelectric materials for MEMS applications.