High performance of temperature sensitive thin film fabricated onto flexible substrates

This work focused on deposition of thin film transistor (TFT)–integrated infrared (IR) detectors using semiconducting materials on a flexible polymer substrate. We used a liquid flow deposition (LFD) technique to grow thin films on flexible polyimide (PI) sheets from an aqueous chloride solution (Ni,Co,Mn)Cl₂, in a wide range of deposition temperature, t = 30–120 °C. The development of the film microstructure with various experimental conditions was studied by field–emission scanning electron microscopy (FE–SEM) and atomic force microscope (AFM). X–ray diffraction (XRD) analysis showed a co–existence of cubic and tetragonal spinel phases in the films after heat treatment at 250 °C. The relationship between ln (R/T) and the reciprocal of the absolute temperature (1000/T) was nearly linear, which indicated a negative temperature coefficient (NTC) characteristic for the films. Surprisingly, the studied films possessed temperature coefficient of resistance (TCR) larger than −2.72%/K and a very low resistivity (ρ) of 250–350 Ω cm at room temperature. This level of electrical performance is even higher than that of films fabricated on silicon substrates, annealed at high temperatures, which highly confirms the eligibility of the resulting TFTs for the use in IR sensing devices. More importantly, on the basis of advantages of a good integration of a high sensitive IR detective element on flexible PI sheets, as well as simple fabricating process, this work demonstrates a feasible approach for reliability of artificial skins by direct deposition of TFTs on polymer substrates.