Humidity Sensors Based On Nanomaterials

With the developing of technology and improving of people's living standard, there're more and more demands put forward to humidity sensors. This paper investigated three kinds of humidity sensor based on nano-zinc oxide (ZnO), nano-porous alumina (Al2O3), porous silicon (PS) with KOH post-processing after summarizing the researching status in quo about the sensors based on ZnO, Al2O3 and PS.Nano-ZnO used in this paper was fabricated using hydrothermal process. It was found that the nano-ZnO humidity sensor, fabricated using spin coating method, had excellent linearity and rapid response in the range of 12~97%RH. But the humidity hysteresis of it was 10%RH. It was concluded that spin-coating nano-ZnO humidity sensor was of capacitance and its humidity sensing characteristics were related to the film thickness. In addition, the piece-like humidity sensor fabricated by pressing nano-ZnO was investigated as well. It was found that its humidity sensing characteristics were better than that of commercial ZnO (not nanoscaled) with comparison. That it was of resistance humidity sensor was concluded according as the analysis of humidity sensing mechanism.Nano-porous alumina used in this paper was fabricated using electrochemical process. It was found that the nano-porous alumina humidity sensor has excellent LgZ-%RH and LgC-%RH relation in the range of 33~97%RH. The rapid response and small humidity hysteresis was gained as well. An equivalent circuit was present according as the micro-structure of nano-porous alumina. After analyzing the complex impedance plots the equivalent circuit was simplified. In conclusion, this humidity sensor conducted mainly through electron at low relative humidity, while through proton at high relative humidity.Porous silicon used in this paper was fabricated using electrochemical process. The change of the microscopy, humidity sensing and I-V characteristics was investigated after the PS was processed in 1 mol 'L'1 KOH solution in this part. It was found that the surface of PS with KOH post-processing has better form of pore in2comparison to that without KOH post-processing. The pore diameter was a little larger than that of as-electrochemical PS as well. That the most interesting was a novel nano-structured silicon appeared after 10 seconds KOH processing. It was concluded that the silicon anisotropic etching by KOH was the origin of the novel nano-structured silicon. It was found the linearity and response speed of the humidity sensor based on PS with 2s KOH processing were better and higher than that without KOH processing, respectively. It was also found that the I-V curve of the PS diode circumvolved at 180?angle, which looked like reversion. In conclusion, KOH removed silicon oxide on the surface of PS, which changed the PS diode structure then changed the electron transform mechanism.