Effect of post deposition annealing temperature of e-beam evaporated Ta2O5 films on sensitivities of electrolyte-insulator-semiconductor devices

In this work, the annealing effects of e-beam deposited Ta
2
O
5
films on the pH sensitivities of EIS based sensors are presented. XPS studies confirmed that the films annealed above 700 °C showed the best stoichiometry (Ta
1.96
O
5.04
) compared to the as deposited film and the films annealed till 600 °C. XRD spectra confirmed the amorphous nature of the as deposited film, which remained amorphous till 600 °C and became polycrystalline above 700 °C. The EIS device showed the maximum sensitivity of 51.4mV/pH for the film annealed at 700 °C, while the device with the as deposited film had a sensitivity of 44.3mV/pH. Further increase in annealing temperature above 700 °C resulted in reduced sensitivity (31.0mV/pH) because of increased interface states (indicated by C-V hysteresis in a MOS device) and enhanced cracks formation in the films (indicated by FESEM). Therefore, the annealing temperature of 700 °C was found to be the optimum annealing temperature for the e-beam deposited Ta
2
O
5
films.