Hydrogen sensing properties of dielectrophoretically assembled SnO ₂ nanoparticles on CMOS-compatible micro-hotplates

We fabricated nanoparticle-based gas through in situ ac dielectrophoretical assembling of drop-coated SnO₂ nanoparticles to bridge the gap between electrodes with high aspect ratio. While the conventional dielectrophoresis (DEP) adopts a microfluidic system for continuous flow of the solution during the process, we just drop-coated a small amount of solution onto the electrodes and executed in situ DEP for a very short time. This is a very simple, cost-effective, time-saving, and highly reproducible process. We fixed the duration time and applied voltage for the DEP at 1s and 1V respectively and changed the frequencies from 1 up to 500kHz. I-V characteristics of the samples were checked and it was found that DEP samples fabricated at 1s, 1V and 150kHz conditions showed considerably higher connectivity of the nanoparticles. This can be attributed to the excellent step coverage achieved by ac DEP under those conditions. The devices drop-coated and dielectrophoretically assembled at other ac frequency conditions showed poor connectivity. Hydrogen gas sensing properties of the sensors fabricated under 1s, 1V and 150kHz conditions were checked by flowing through 160ppm H₂. The sensitivity reaches a maximum value of ∼ 700% at 350 °C. The response time is ∼ 200s at 350 °C.