Moisture 0ensor feasibility on paper-based substrate

Nowadays, flexible electronics is a challenging research area cause of the increase of electronics component request for “the internet of things”, the food safety and the medical diagnostic applications. In our research, we work with an unusual substrate for microtechnologies such as paper, which is flexible, brittle, and biodegradable. Also, it can be folded, cut, perforated, crumpled, etc. This article focuses on monitoring porous Anodic Aluminum Oxide (AAO) layer on paper-based substrate for the detection of humidity. Porous AAO is a material with cylindrical pore geometry and high aspect ratio. Further, this material has many advantages, such as, easy fabrication, pore diameter´s uniformity with high pore density (10¹¹/cm²) and its use like humidity sensors. In summary, the AAO process fabrication on paper substrate is challenging causes of his ease of implementation, cost-effective and the use of a highly economical, conformable and ecological substrate. In this study, an experimental setup had been developed to anodize an aluminum layer deposit on flexible substrate by using phosphoric acid. Various anodization parameters (voltage, current density, temperature and concentration) have been investigated to obtain an AAO layer with good electrical properties and high reliability on flexible substrate. An interdigital capacitance has been deposited on the best AAO layer produced to fabricate a moisture sensor. The different sensors produced had been characterized versus humidity concentration and frequency in a climatic chamber. Depending on the AAO morphology parameters, the average sensitivity can be tuned from 0.8 pF/RH% to 9 pF/RH%.