Growth of tin oxide thick films by plasma spray physical vapor deposition

Tin oxide thick films were deposited by plasma spray physical vapor deposition at various oxygen flow rates and raw powder feeding rates. The films are fundamentally porous and the deposition rates reach 60 μm/min at highest under the present condition. Local structures are however modified with the deposition condition. For example, relatively uniform columnar structure formed at high oxygen flow rate, whereas granular grains were observed when no oxygen gas was introduced. In contrast, granulate films were deposited at high powder feeding rate while rather uniform columnar films formed at low feeding rate. The gas sensors fabricated with these PS-PVD films have exhibited high sensitivity against formaldehyde gas at concentration as low as 100 ppb, which characterizes the sensors prepared by the PS-PVD method. Such sensitivities are found to change with the film microstructures that are in turn controlled by the PS-PVD conditions.