Humidity Sensing Properties Of Polyvinylpyrrolidone-modified Nano-zinc Oxide/Silicon Nanoporous Pillar Array

Semiconductor materials have attracted more and more attention in the field of humidity sensor in resent years. As one of the metallic oxides semiconductor materials, zinc oxide nanometer are widely used in space technology, automotive industry, aerospace application, fire detection, industrial exhaust gas testing, climate monitoring, and many other industries for its unique physical and chemical properties. Our team obtained a novel silicon nanoporous pillar array (Si-NPA) with mocron/nanometer hierarchical structure by the hydrothermal etching method, which showed promising prospect in humidity-sensing for its unique morphology and structure feature. In this paper, by simple and low cost sol-gel method we synthesized ZnO nanoparticles, and choosed macromolecule organic matter polyvinylpyrrolidone(PVP) to modify the surface of ZnO nanoparticles. Then the PVP modified ZnO nanoparticles were coated onto the Si-NPA by the spin-coating method, obtaining a ZnO@PVP/Si-NPA composite moisture sensor. A series of characterization and the test were conducted, the results are as follows:1.The surface morphology as well as the microstructure of ZnO nanoparticles was characterized by field emission scanning electron microscope (SEM), transmission electron microscope (TEM).Combining with electron diffraction, high resolution pictures, and the Fourier transform the existence of ZnO nanoparticles was verified. X-ray diffraction (XRD) proved the as-synthesized ZnO nanoparticles had wurzite hexagonal structure. Fourier transform infrared absorption spectra (FTIR) proved the interaction of PVP with Zn2+,which caused the modification of the ZnO and influence the synthesization of ZnO nanoparticles. Ultraviolet-visible absorption spectra showed the size of the ZnO nanoparticles influenced by PVP molar weight. Through theoretical calculation we found that the ZnO nanoparticles size decrease and then increase with the increase of the molar amount of PVP.2.Comparison of PVP/Si-NPA and Si-NPA humidity-sensitive performance found that PVP has had a biggish impact on Si-NPA substrate performance, the near linear relative humidity capacitance functional relationship converted into near exponential. Comparing the ZnO/Si and ZnO@PVP/Si moisture sensing performance showed the capacitance of the ZnO/Si moisture sensor remained linear and the ZnO@PVP/Si moisture sensor C-RH curve changed from linear relationship to the exponential relationship with increase of PVP. Combining ZnO, PVP, and Si-NPA we got different ZnO@PVP/Si-NPA moisture sensor with different molar ratio of Zn2+:PVP. Trough testing different sensors we found that the sensor with a molar ratio of Zn2+:PVP=5:5reached maximum improvement comparing with the original sample with no PVP. So by modifying the ZnO nanoparticles, and combined with the characteristics of the polymer itself, PVP had enormous enhancement effect on performance of humidity sensor on Si-NPA substrate composite structure, which provided experimental basis and reference for subsequent humidity sensor optimization.