*3.1.6 Atomic layer deposition*

ALD is also a technique for deposition of nano structured IO based thin films [44]. This technique mainly based on sequential pulsing principle of precursor chemicals in vapor state where each pulse is almost one atomic layer thin. The excess reactants as by-products can purge or evacuate with an inert carrier gas (e.g. N2/Ar) [44]. The precursor used in this technique is pulsed into a chamber under vacuum (<1 Torr) condition for a certain period of time during each halfreaction. The process is cycled afterwards until a suitable film thickness reached. By applying this technique, a layer of very high aspect ratio of ITO crystals with nanoporous architecture can be fabricated. These materials can be used in photovoltaic or spectroelectrochemical applications [44]. On the other hand, In2O3 TFTs with ALD Al2O3 gate dielectrics had already been developed with significantly good electrical performance (e.g. field effect mobility, 7.8 cm<sup>2</sup> V−1 s−1 and on/off current ratio, 107 ) [44].
