Humidity sensing characteristics of laterally aligned ZnO nanowires by dielectrophoresis method

In this study, the humidity sensing characteristics of zinc oxide (ZnO) nanowires are investigated experimentally. ZnO nanowires are grown by hydrothermal method at low temperature (95°C) for 3-24 hours. Dielectrophoresis (DEP) force is then applied to assemble ZnO nanowires on interdigitated electrode (IDE) patterns to make connection between two electrodes. Prior to the assembling, thermal annealing is used and pure alcohol is dropped on the IDE pattern so that the adhesion of IDE patterns and substrate is improved effectively. The hydrogen sites of water molecules are thought to be positively charged due to the high electronegativity of oxygen compared to hydrogen. These charged hydrogen sites will capture the electrons of ZnO nanowires electrostatically. Thus, the electrical resistance of our sensor increases with increasing relative humidity (RH) level in the tests. Our sensors show extremely fast response time and they can reach 90% of the total change in 16 seconds when increasing RH level from 0% to 100%. These laterally aligned ZnO nanowires are expected to be promising for applications in commercial humidity sensors.