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

Article history: Received 15 August 2011 Received in revised form 6 October 2011 Accepted 25 October 2011 Available online 15 December 2011 0026-2714/$ see front matter 2011 Published by doi:10.1016/j.microrel.2011.10.026 ⇑ Corresponding author at: Biosensor Group, Biom Center, Chang Gung University, 259 Wen-Hwa 1st Roa Taiwan. Tel.: +886 3 2118800x5786. E-mail address: [email protected] (C.-S. Lai). In this work, indium tin oxide (ITO) layers were deposited by radio frequency sputtering using a roll-toroll 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 X/h), 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. 2011 Published by Elsevier Ltd.