Reliable monolayer-template patterning of SnO2 thin films from aqueous solution and their hydrogen-sensing properties

We demonstrate a novel lithographic technique utilizing a solvent to fabricate a chemically based semicondutor microdevice from an aqueous solution. According to this technique, SnO2 thin film could be integrated onto predefined sites on a SiO2/Si wafer. A patterned octadecyltrimethoxysilane self-assembled monolayer (ODS-SAM) was prepared by vacuum ultraviolet (VUV) irradiation through a photomask to use as a template for the fabrication of a micropatterned SnO2 thin film on the SiO2/Si surface. A Sn-based thin film was then deposited onto the entire surface of the ODS template from the aqueous solution containing 0.03 mol L-1 of SnCl2.2H(2)O at 60degreesC for 16h in an ambient atmosphere. The thin film deposited on the methyl terminated area of the template then peeled using an ultrasonic rinse in anhydrous toluene for 30 min, while the film deposited on the silanol area remained intact and undamaged. Rinsing in hydrophilic solvents did not facilitate peeling of the thin film from the methyl-terminated area. We succeeded by this process in obtaining a high-resolution, micropatterned Sn-based thin film on an ODS-SAM template on Si. The as-deposited film was composed of fine Sn-based particles. The sensitivity of this SnO2 thin film to H-2 gas increases linearly with improving crystallinity. The effectiveness of anhydrous toluene as a rinse in solution lithography is discussed from the viewpoint of the high hydrophobic affinity between the rinse solvent and the terminal groups in the monolayer template.