Pen plotter printing of ITO thin film as a highly CO sensitive component of a resistive gas sensor

In₂O₃-10%SnO₂ (ITO) thin films on various substrates have been obtained by pen plotter printing using a solution of hydrolytically active heteroligand complexes [M(C₅H₇O₂)_x(C₄H₉O)_y] (where М = In³⁺ and Sn⁴⁺) as a functional ink. According to XRD and Raman spectroscopy, it has been established that the film has a bixbyite structure (space group Ia3/T_h⁷), consists of particles with an average size of about 20 nm (according to SEM and AFM) and has a band gap of 3.57 eV. In order to obtain the ITO film, the temperature dependence of resistivity characterised by a minimum at 150 °C has been determined, and its gas-sensitive properties have been studied. It has been shown that the greatest resistive response is observed to carbon monoxide at 200 °C, and the film has a high sensitivity to low concentrations of CO. Two possible models describing the dependence of the sensory response on the CO concentration have been suggested. The mechanisms of defect formation in the ITO film structure and CO detection, including in a humid environment, have been considered in detail.