Stable aqueous dispersions of ZnO nanoparticles for ink-jet printed gas sensors

For the preparation of printable devices based on ZnO nanoparticles (ZnO NP), stable colloidal dispersions of these materials are highly desirable. ZnO NP have been synthesized by chemical vapor synthesis. The particles have a spherical shape with a narrow size distribution. Stable aqueous dispersions of the ZnO NP have been successfully prepared after the addition of a polymeric stabilizer. The prepared dispersions are stable for at least 2 months without observable sedimentation. These stable dispersions are used to prepare ZnO NP films on different substrates by ink-jet printing. The viscosity and the surface tension of the dispersion as well as the printing parameters have been optimized for forming layers with high quality. Dense and low porosity layers of ZnO NP with a thickness between 100-250 nm have been prepared on different substrates. First measurements on ink-jet printed ZnO films are done on self fabricated inter digital capacitors (IDCs) at room temperature. The ZnO films show resistivity at room temperature of 7.76 k¿.cm. For sensing measurements in hydrogen atmosphere, the sheet resistance decreases rapidly until it reaching metallic behavior. This behavior is reversible.