Controllable liquid water sensitivity of polymer-encapsulated oxide thin-film transistors

Abstract

We demonstrated the controllable liquid water sensitivity of polymer-encapsulated oxide-based thin-film transistors (OxTFTs). The oxide active channels of the fabricated TFTs were utilized as water-sensitive layers. The OxTFTs were encapsulated with several polymers as water controlling layers (WCLs) to investigate and optimize the water sensitivity. It was found that the surface energy and porosity of the WCL significantly affect the water-dependent electrical characteristics of the OxTFTs. By employing poly(vinylidene-trifluoroethylene) (P(VDF-TrFE)) as a WCL and annealing the chosen polymer properly, we achieved a continuous shift of the threshold voltage even after several hours of direct exposure to the liquid phase of water which is crucial for sensor properties of the OxTFTs. The device using P(VDF-TrFE) as the WCL exhibits long-term stable detection characteristics and repeatability, demonstrating its applicability as a low-cost soil moisture sensor.