Flat-Type Gas Sensors Based on ZnO Nanorod Arrays

ZnO seed layers were deposited on silicon and sapphire substrates by the pulsed laser deposition (PLD) method, and ZnO nanorod arrays with different orientation degrees were grown using the chemical vapor deposition (CVD) method. Flat-type gas sensors based on the ZnO nanorod arrays were fabricated, and their gas sensitivity properties were studied. The ZnO seed layer with a thickness of approximately 450 nm exhibits high c-axis orientation and possesses few defects. The ZnO nanorods fabricated on both of the substrates grow along the [0001] direction and contain a large number of oxygen vacancy defects. These nanorods have lengths of 8~10 μm and diameters of 200~500 nm. The ZnO nanorods grown on the silicon substrate are perpendicular to the surface of the substrate, and their areal density is approximately 3.0×10⁸/cm², while those grown on the sapphire substrate exhibit a lower orientation degree, and their areal density is approximately 0.9×10⁸/cm². The largest response of the gas sensor for gaseous alcohol reaches 48.2, and the optimal operating temperature for all of the sensors is approximately 280 °C. The gas sensitivity property of the silicon-based sensor is superior to that of the sapphire-based sensor, and the corresponding sensing mechanism is discussed.