Tuning electrical resistivity anisotropy of ZnO thin films for resistive sensor applications

By in-air annealing the samples from room temperature (RT) up to 200 °C and cooling down to RT again, the differences between the resistivity values along the xx and yy directions become significant, a clear sign of the anisotropic nature of the films. The anisotropy obtained during the annealing cycles of the films increased from 0.98 to 1.10 and, consequently, the Temperature Coefficient of Resistance, TCR, increased in both xx and yy directions, from TCRxx and yy ~9.0 × 10−4 to TCRxx = 6.82 × 10−3 and TCRyy = 5.97 × 10−3 °C−1. Important also to note is that the increase of the grain size of the films showed to have a significant effect in the effective anisotropy, revealing to be a major factor to take into account.