Flexible pH sensors based on polysilicon thin film transistors and ZnO nanowalls

Abstract

A fully flexible pH sensor using nanoporous ZnO on extended gate thin film transistor (EGTFT) fabricated on polymeric substrate is demonstrated. The sensor adopts the Low Temperature Polycrystalline Silicon (LTPS) TFT technology for the active device, since it allows excellent electrical characteristics and good stability and opens the way towards the possibility of exploiting CMOS architectures in the future. The nanoporous ZnO sensitive film, consisting of very thin (20 nm) crystalline ZnO walls with a large surface-to-volume ratio, was chemically deposited at 90 °C, allowing simple process integration with conventional TFT micro-fabrication processes compatible with wide range of polymeric substrates. The pH sensor showed a near-ideal Nernstian response (∼59 mV/pH), indicating an ideality factor α ∼ 1 according to the conventional site binding model. The present results can pave the way to advanced flexible sensing systems, where sensors and local signal conditioning circuits will be integrated on the same flexible substrate.

Enhanced Quality, Growth Kinetics, and Photocatalysis of ZnO Nanowalls Prepared by Chemical Bath Deposition

“…In that case XRD pattern revealed a peculiar splitting of the (002) peak into two components (corresponding to d-spacing of 0.261 nm and 0.265 nm) indicating the occurrence of a non uniform strain applying to the zincite planes [8]. Similar XRD pattern was found for ZNW1 and ZNW1_anod grown at 300 and 900 s, with the (002) peak split into two components at lower diffraction angles (Fig.…”

“…Unlike the vacuum techniques, the low temperature approach is suitable for ZnO NWL growth on flexible (plastic) substrates, which can lead to much lower fabrication cost. This has recently been demonstrated in the fabrication of a fully flexible pH sensor with an extended gate thin film transistor configuration, which showed a near-ideal Nernstian response (59 mV/pH, with an ideality factor close to 1) [8].…”

Nanostructured sensing devices controlled by ultra-flexible polysilicon readout circuits

“…With this procedure, a nanoporous ZnO structure with vertically oriented nanoplateles is obtained, ensuring a large surface-to-/volume ratio. This porous structure appears extremely interesting for the interaction with ions diluted in standard biological fluid and it can provide high sensitivity [7]. …”

Comparison of the Sensing Properties of ZnO Nanowalls-Based Sensors toward Low Concentrations of CO and NO2

“…We used ZnO NWLs as the sensitive element in a fully flexible pH sensor based on an extended gate thin film transistor fabricated on a flexible polymeric substrate [9]. The ZnO NWLs based sensor showed an ideal Nernstian response to pH variation (~59 mV/pH) demonstrating the great potentialities of the nanostructure deposited at low temperature.…”