ISFET-based pH sensor composed of a high transconductance CMOS chip and a disposable touch panel film as the sensing layer

This study presents a high performance ion-selective field-effect-transistor (ISFET) based pH sensor utilizing commercial touch panel film (TPF) as the sensing material. The coated ITO/SiO₂/Nb₂O₅ multilayer on the TPF is ideal for measuring dissociated hydrogen ions. A high transconductance MOSFET chip composed of 10 parallel FETs is used to convert the effective pH value into the equivalent gate voltage. An on-film Ag/AgCl reference electrode is also produced on the sensing film to further enhance the sensing performance. The industrial roll-to-roll production process for TPF sensing film and the quick plug-in slot make the sensing layer suitable for disposable applications. The pH sensing results show that the TPF-based pH sensor exhibits good response for detecting solutions of the pH values in 3-13. The rapid time response (<; 10 s) and good stability (C. V. <; 2%) confirm the sensing performance of the developed pH sensor. Moreover, the sensor also shows low response to the interference ions of sodium and potassium in the solution. The developed pH sensor has shown its capabilities for rapid and low-cost pH detections.