pH sensing reliability of flexible ITO/PET electrodes on EGFETs prepared by a roll-to-roll process

In this work, indium tin oxide (ITO) layers were deposited by radio frequency sputtering using a roll-to-roll process on flexible polyethylene terephthalate substrates as pH-sensing electrodes of extended gate field effect transistors (EGFETs). When the pH sensitivity of EGFETs for ITO layers with different sheet resistances was compared, a higher sensitivity was found for samples with a lower sheet resistance (100 Ω/□), and a reliability evaluation was carried out for this condition. The average sensitivity was 50.1 mV/pH, as measured from pH 2 to pH 12. Over three additional runs, the standard variation of the average sensitivity was found to be ±1.7 mV/pH. The tolerance to light is high; the samples were measured in dark and light conditions, and a difference of only 0.6 mV was observed. The temperatures available for measurement are 25–40 °C. Up to this point, the behavior of samples stored in dry conditions has been found to persist for more than 55 days.