Indium tin oxide coated PET for differential pH‐sensing using field‐effect transistor based sensor

Abstract

Indium tin oxide (ITO) on polyethylene terephthalate (PET) substrate is characterised in terms of pH-sensitivity. Commercial ITO/PET sheet was cut in a shape of electrode and was connected to the gate-terminal of a metal-oxide-semiconductor field-effect transistor as the sensory part, creating an extended gate field-effect transistor (EGFET) pH-sensor. The quality of laser micromachining as well as the moulded ITO/ PET electrode is investigated. The pH-sensitivity and linearity of the sensor signal are studied over time for a single hanging ITO/PET electrode. With the help of a constant-charge amplifier circuitry, the reference electrode, dipped in the measurement cell, is grounded. Therefore, the noise level, coupled into the sensor signal from environment, is decreased and also integration of the second sensor to the measurement cell becomes possible. The pH-measurement is carried out while EGFET pair, immersed into a buffer solution next to a pseudo-reference electrode, is working in differential mode to compensate for the high drift signal rate which is common for this type of sensors. As the result, a very low-cost EGFET-based pH-sensor is achieved based on commercially available products independent of costly cleanroom processes.

A comprehensive review of FET‐based pH sensors: materials, fabrication technologies, and modeling

“…Recently, fabrication of EGFET on flexible substrates have been of interest for PoC applications. [ 294,317–322 ] Moreover, recently there has been an interesting development toward dual‐gated EGFETs, where the sensing electrode is connected to the gate electrode of a DG transistor, which amplifies the sensitivity of the device beyond the Nernstian limit due to capacitive coupling effect. [ 322–325 ]…”

“…Recently, fabrication of EGFET on flexible substrates have been of interest for PoC applications. [294,[317][318][319][320][321][322] Moreover, recently there has been an interesting development toward dual-gated EGFETs, where the sensing electrode is connected to the gate electrode of a DG transistor, which amplifies the sensitivity of the device beyond the Nernstian limit due to capacitive coupling effect. [322][323][324][325] Slewa et al reported a work in which they had synthesized 3D V 2 O 5 -doped with Sn, where Sn was prepared on porous silicon via solvothermal process, followed by annealing at 550 • C for 1 h. The sensing film characterization using XRD data showed that the crystal size and lattice expansion of Sn-doped V 2 O 5 had decreased.…”

Indium Zinc Oxide pH Sensors: Fabrication, Measurement, and Applications

“…Over the past decade, the sensing structure of extended-gate field-effect transistors (EGFETs) has been widely studied in related applications such as pH sensing and biomedical sensing. (1)(2)(3)(4) The EGFET structure offers several advantages, including low cost, simple packaging, insensitivity to temperature and light, flexibility in sensor head design, and improved long-term stability. (5) Many studies based on EGFET architecture use oxide-conductive materials as sensing materials, such as indium tin oxide (ITO) or indium zinc oxide (IZO).…”

ITO/Glass as Extended-Gate of FET: A Low-Cost Method for Differential pH-Sensing in Alkaline Solutions

“…glass and polyethylene terephthalate (PET)) along with its electrochemical properties, ITO has been widely applied by researchers as the sensory element of EGFETs for pH-sensing. 27,28 However, they could only show a reliable electrochemical behavior in the case of a hanging ITO electrode at stress-free condition operating next to a glass reference electrode. 27 A reliable ITO package with an integrated low volume cell is still missing.…”

“…27,28 However, they could only show a reliable electrochemical behavior in the case of a hanging ITO electrode at stress-free condition operating next to a glass reference electrode. 27 A reliable ITO package with an integrated low volume cell is still missing. Furthermore, differential sensing and sensor miniaturization using ITO electrode have not yet been achieved.…”