Fig. 5. (a) Channel current (black curve) and gate current (red curve) as a function of V_GS with V_DS = 2 V. In the inset, a sketch of the longitudinal section of the structure, showing its layer sequence and biasing voltages. (b) Output characteristics measured for V_GS ranging from −1 to 3 V, with a step of 0.5 V. The inset shows optical micrographs of a device before and after TiO₂ printing. The scale bars are 100 μm.