Flexible thin film pH sensor based on low‐temperature atomic layer deposition

Abstract

Flexible and transparent zinc oxide (ZnO) thin film field-effect transistors (TF-FET) for the use as small volume potentiometric pH sensors are developed. Low temperature atomic layer deposition (ALD) is used for the fabrication of the metal oxides ZnO and aluminum dioxide (Al2O3). Changing the deposition temperature of the ZnO from 150 to 100 °C allowed a significant increase in resistivity by four orders of magnitude. Hence, adjusting the controlled low carrier concentration for the field-effect based sensor is demonstrated. ZnO TF-FET pH sensors fabricated on silicon/silicon dioxide (Si/SiO2) substrates are compared with sensors based on flexible and transparent polyethylene naphthalate (PEN) foil substrates. Comparison of both types of pH sensors showed successful pH sensitivity for pH ranging from 5 to 10 in both cases

Flexible potentiometric pH sensors for wearable systems

“…22 Wearable glucose sensors that provide highly sensitive pH monitoring in the range of pH 5-9 have also been developed using both PET and poly (diallyldimethylammonium chloride) (PDDA), a cationic, water soluble polyelectrolyte as substrates. 127 PEN substrates have also been used to develop small volume, potentiometric zinc oxide (ZnO) thin lm-FET (TF-FET) pH sensors [128][129][130] ( Fig. 2d).…”

Atomic layer–deposited nanostructures and their applications in energy storage and sensing

“…This device reached an average pH sensitivity of 52.35 mV/pH and had a low light response (3.9-8.6 mV) due to its intrinsic property of having a wide band gap. Jakob et al [147] used lowtemperature ALD to fabricate ZnO and Al 2 O 3 thin films for pH sensor. The Al 2 O 3 thin film was applied as a sensitive layer on the ZnO thin film, and meanwhile acted as a gate oxide between the liquid gate potential and the ZnO channel.…”

High Sensitivity of Extended-Gate Field-Effect Transistors Based on 1-D ZnO:Ag Nanomaterials through a Cheap Photochemical Synthesis as pH Sensors at Room Temperature

“…The adsorption rate is proportional to the free holes or electrons of the nanostructure surface. The large surface area-to-volume ratio can increase sensitivity and response time and improve the signal-to-noise ratio because the electrode to the analyze diffusion distance shortens. − The sensing gate of the EG-FET must be a high-conductivity electrode that can transmit sensing signals easily.…”