Spark Ablated Metal Oxide Nanoparticles for Gas Sensing

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Metal oxide nanoparticle gas sensors showpromise due to their high sensitivity towards a wide range of gases, low costs, and low complexity. Particle sizes at nanometers offer a high surface-to-volume ratio which provides more areas on the surface where reactions can occur. This work presents the application of spark ablated nanoparticles on chemiresistors and chemFETs, and does a study on whether spark ablated nanoparticles are a viable alternative to nanoparticles generated using other methods. The focus in this thesis is on pure metal oxide nanoparticles without any addition of dopants or decorations. Devices are fabricated with different interdigitated electrode dimensions. The effect of electrode width and gap size on the gas response is studied by comparing the sensing performance of the devices. In this work, a very high sensitivity of 1300% is achieved towards 35% relative humidity using a 1x1 mm device with SnO2 nanoparticles. Towards 20 ppm of ethanol, sensitivities of 39% and 67% are achieved using 1x1 mm and 4x1 mm devices with SnO2 nanoparticles respectively, which implies that spark ablated nanoparticles could be a viable alternative to particles generated using other methods. The full recovery time after gas exposure seems to be very long and takes around an hour for some devices at 200 °C. Possible solutions for this are setting a higher temperature (not possible with the used setup), or reducing the particle size (∼20 nm in this study). The electrode finger widths and gap sizes are varied between 2-15 μm for each device. However, no correlation is found between electrode geometry and gas response within this range, suggesting that differences in gas response between devices likely stem from nanoparticle layer quality differences.