Study of programmed co-precipitation of aluminum doped zinc oxide for high precision design of gas analytical units

Developed high precision protocols of synthesis and printing of materials doped at a level of a few atomic percent serve as a prerequisite to addressing the problem of discreteness of electronic noses, i.e. multisensor arrays. Reproducible composition and microstructure of functional materials are needed to ensure low sensor-to-sensor variation, while high precision printing techniques help to mitigate non-uniformity of the deposited layers, to further ensure orthogonality of signals of a sensor array, especially when realized on a single chip. In this study, we evaluate two precise methods, programmed co-precipitation and aerosol jet printing, for making x%Al:ZnO layers, where x = 0.5, 1.0, 1.5, 2.5, and 5.0% over SiO₂/Si substrate. We examined the phase and microstructure of the obtained powders depending on the Al content and the synthesis conditions. The obtained powders were utilized to prepare dispersions used as functional inks for aerosol jet printing of oxide microstructures on multielectroded chips to explore their sensing performance. We demonstrated the high influence of both the Al:Zn atomic ratio, and the synthesis conditions on the microstructure of the prepared materials composed of nanoparticles, micro- and nanorods with distinct synthesis-dependent characteristics. All inks based on x%Al:ZnO enabled achieving narrow, down to 50 µm, resolution and printing homogeneous structures, whereas using 0.5 %Al:ZnO nanoparticles ensured the best characteristics of the printed layers. The sensors made of 0.5 %Al:ZnO printed layer demonstrated a high mean sensing response towards 1 ppm of acetone, ethanol, and benzene vapors mixed with air, i.e. 0.75 ± 0.02, 0.51 ± 0.03, and 0.25 ± 0.017 at 250 °C, respectively, and both low detection limit and low sensor-to-sensor variation.