Characterization of physical and mechanical properties of Al₂O₃-doped ZnO (AZO) thin films deposited on transparent polyimide supports with various ALD process parameters

Fabrication of Al₂O₃ doped ZnO (AZO) thin films on transparent polyimide substrates using ex-situ oxygen plasma-assisted atomic layer deposition (ALD) is studied. The alumina composition is controlled by adjusting the ALD cycle ratio in the reaction sequence from 9:1 to 49:1 (diethylzinc/H2O:trimethylaluminum/H2O). Nanoscratch and electromechanical tensile tests are performed to evaluate the mechanical reliability of the AZO thin films fabricated under various processing conditions. Conventionally deposited AZO shows the lowest sheet resistance of 294 Ω/sq at a doping ratio of 19:1 at 150 ℃. However, the resistance of AZO grown on a polymer surface modified by plasma is higher at 429 Ω/sq. Nanoscratch results reveal that the first critical load could be increased by surface hardening and strong adherence as a function of the process temperature and plasma treatment. Under a tensile strain, doping of alumina delayed the strain (%) at crack initiation from 0.58 to 0.82%. The initial elastic modulus of the AZO/transparent polyimide composites showed a transient decrease with an increase in the alumina content from 2.7 to 3.8 at.%. These results demonstrating the mechanical characteristics of thin films as a function of the processing conditions are significant for flexible display manufacturing.