Thermolithographic Patterning of Sol-Gel Metal Oxides on Micro Hot Plate Sensing Arrays Using Organosilanes

Sol-gel-derived SnO2 and Fe2O3 were selectively deposited on elements of micro hot plate ((mu)HP) arrays. The silicon micromachined (mu)HP arrays contain heating elements (100 (mu)m × 100 (mu)m) that are electronically addressable and thermally isolated from each other. Thin films of (tridecafluoro-1,1,2,2-tetrahydrooctyl)trichlorosilane (TFS) or hexyltrichlorosilane (HFS) assembled on surfaces of the arrays served as thermally sensitive resists whereby heating of specific (mu)HPs resulted in removal of organosilane films only in heated areas. TFS-masked surfaces were characterized with condensation figures and secondary ion mass spectrometry (SIMS) imaging. TFS was removed from regions heated above 400 (degree)C to expose hydrophilic surfaces, while TFS films in unheated areas were unaffected and remained hydrophobic. Sol-gel tin oxide spin-coated on the thermally patterned arrays adhered only to the hydrophilic regions and was repelled from the hydrophobic areas masked by the TFS films. By using HFS films, it was possible to selectively deposit two sol-gel materials, SnO2 and Fe2O3, on different (mu)HPs in the same array as confirmed by SIMS imaging. Both materials showed varying degrees of electrical response to hydrogen and methanol in gas-sensing measurements.