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To present highly sensitive and precise pH sensor, fabrication of metal oxide based EGFET sensor is needed. The used of TiO2 thin films as sensing electrode for pH sensor is widely known for its best sensitive in pH measurement. The films were prepared by depositing the films onto ITO glass substrate using sol-gel spin coating method. The sensitivity and linearity of TiO2 EGFET sensing electrode for various spin speeds (1000 to 5000 rpm) were obtained from transfer characteristic (IDS -VREF) and output characteristics (IDS -VDS) analysis. The effect of different immersion time (25, 50, and 75 s) and repeatability measurement for each sample were also investigated in this study. Among of all samples, the sensing electrode prepared at 5000 rpm spin speed with 75 s immersion time achieved the highest sensitivity of 52.20 mV/pH and good linearity of 99.64 %. Meanwhile, the sensing electrode prepared at spin speed 3000 rpm produced good repeatability and small standard deviation. The performance EGFET sensor has also been tested at different pH values (pH4, pH7, and pH10) and found TiO2 sensing electrode showed more precise results in an alkaline (pH10). [ABSTRACT FROM AUTHOR]

In this study, the effect of annealing temperature on the extended gate field effect transistor (EGFET) for pH sensors of CuO thin film was investigated. The CuO thin films were deposited on an indium tin oxide (ITO) substrate using the sol-gel spin-coating method. The thin films were then annealed in air ambient at 200 to 500 °C for 30 minutes. The sensitivity and linearity of the sensing electrodes were determined in a pH range from pH 2, 4, 7, 10 and 12. The sensing electrode annealed at 400 °C showed the highest pH sensitivity of 47.3 mV/pH. It showed that the post-annealing process improved the sensing performance of the device. The morphology characteristic was characterized by field emission scanning electron microscopy (FESEM) and showed a porous structure as the annealing temperature increased, indicating that the porous film could be the sensing electrode of an EGFET pH sensor. The hysteresis of the sensing electrode was measured in buffer solutions prepared at pH 7, pH 4, pH 7, pH 10, and pH 7 to find its pH response delay. These findings indicated that sol-gel spin-coated CuO thin film can be considered a promising candidate for applications as an EGFET-pH sensor. [ABSTRACT FROM AUTHOR]

A highly selective and sensitive EGFET-pH sensor based on composite TiO2–PANI had been developed in this work. A sol-gel titanium dioxide (TiO2) and the composite of TiO2 with semiconducting polyaniline (PANI) were deposited using a simple spin-coating method on an indium tin oxide (ITO) substrate. The films have been explored as a sensing electrode (SE) of extended gate field-effect transistor (EGFET) for pH applications in the range of pH 2 to 12. The pH sensitivities between TiO2, TiO2–PANI bilayer composite, and TiO2–PANI composite thin films were discussed. Among these, the TiO2–PANI composite thin film showed a super-Nernstian behavior with high sensitivity of 66.1 mV/pH and linearity of 0.9931; good repeatability with a standard deviation of 0.49%; a low hysteresis value of 3 mV; and drift rates of 4.96, 5.54, and 3.32 mV/h in pH 4, 7, and 10, respectively, for 6 h. Upon applying the TiO2–PANI composite as the SE for nitrate measurement, low sensitivity of 12.9 mV/dec was obtained, indicating that this film is a highly selective sensing electrode as a pH sensor. The surface morphology and crystallinity of the thin films were also discussed. [ABSTRACT FROM AUTHOR]

The post-deposition heat treatment process was studied to improve zinc oxide (ZnO) 's pH sensing performance as the sensing electrode (SE) of extended-gate field effect transistor (EGFET) pH sensor. The low-temperature chemical bath deposited ZnO nanostructured thin film was heated from 200 to 400 °C before being applied as the SE. The heat treatment enhanced the agglomeration of ZnO nanoparticles, and the formation of nanonails was seen at the highest temperature of 400 °C. It was proven by XRD results that the crystallinity of ZnO samples were improved when the ZnO SE was heated at 300 °C and formed different growth orientations at (100), (002) and (101) before turning to (101) growth orientation at 400 °C heat treatment. The heat treatment process also increased the ZnO particle size from 15.47 nm to 260 nm at 300 °C. Further increasing the heat treatment up to 400 °C decreased the particle size to 44.30 nm. The ZnO morphology was correlated with the pH sensor performance. The clustered structure of the untreated ZnO sample exhibited a good pH sensitivity of 52.4 mV/pH with a linearity of 0.93 and a hysteresis value of 46.71 mV. On the other hand, almost similar pH sensitivity was obtained from the sample treated at 300 °C having poly-structure morphology, which was 52.9 mV/pH, but with a significantly improved linearity of 0.99, and hysteresis values of 41.99 mV respectively. The 300 °C heat treatment also improved the stability of ZnO SE performance. The difference in the performance of these two samples can also be related to the crystalline quality of the film. • ZnO nanostructures deposited by the facile CBD method was proposed as an EGFET pH sensor. • Effect of post-deposition heat treatment temperature on the ZnO nanostructures EGFET pH sensor performance was studied. • 300 °C post-deposition heat treatment sample showed the highest sensitivity of 52.9 mV/pH with a linearity value of 0.9947 [ABSTRACT FROM AUTHOR]