Fabrication and Characterization of Flexible and Miniaturized Humidity Sensors Using Screen-Printed TiO2 Nanoparticles as Sensitive Layer

Abstract

This paper describes the fabrication and the characterization of an original example of a miniaturized resistive-type humidity sensor, printed on flexible substrate in a large-scale manner. The fabrication process involves laser ablation for the design of interdigitated electrodes on PET (Poly-Ethylene Terephthalate) substrate and a screen-printing process for the deposition of the sensitive material, which is based on TiO2 nanoparticles. The laser ablation process was carefully optimized to obtain micro-scale and well-resolved electrodes on PET substrate. A functional paste based on cellulose was prepared in order to allow the precise screen-printing of the TiO2 nanoparticles as sensing material on the top of the electrodes. The current against voltage (I–V) characteristic of the sensor showed good linearity and potential for low-power operation. The results of a humidity-sensing investigation and mechanical testing showed that the fabricated miniaturized sensors have excellent mechanical stability, sensing characteristics, good repeatability, and relatively fast response/recovery times operating at room temperature.

Year 2020: A Snapshot of the Last Progress in Flexible Printed Gas Sensors

“…As the squeegee moves toward the rear of the screen the tension of the mesh pulls the mesh up away from the substrate (named snap-off), leaving the ink upon the substrate surface. An example of TiO 2 based flexible gas sensor made by using screen printing on PET substrate is reported in the reference [57]. Screen printing can be used also changing the screen with a stencil to prepare electrodes [69] or sensing layer.…”

“…It must be highlighted that these devices can undergo thermal treatment not higher than 300 • C. Nevertheless, in the literature many publications on metal oxide gas sensors printed on flexible substrates are reported. As example, in [48] a tin dioxide sensor was developed onto polyimide foil performing electrical measurements toward carbon monoxide and nitrogen dioxide heating the device at temperatures between 200 and 300 • C. Moreover, an example of humidity sensor that works at RT is reported in [57]. TiO 2 nanoparticles were deposited by screen printing on a PET substrate with gold electrodes, obtaining the series of sensors showed in Figure 7.…”

“…(a) Picture of 3 × 3 sensor matrices fabricated on PET substrate; (b) SEM image of the interdigitated electrodes; (c) optical image of the humidity sensors [57]…”

Technologies and Fabrication of Intelligent Packaging for Perishable Products

“…This study introduced a new low-cost and low-temperature procedure that allowed for the large-scale fabrication of humidity sensors on flexible PET substrates. The result showed that the laser ablation was better suited for the patterning of interdigitated electrodes on a microscale, and the screen-printing was better suited for the industrial integration of metal-oxide-based sensitive films on flexible substrate [82]. Screen printing can be combined with inkjet printing in an electronics fabrication process.…”

Organic Thin‐Film Capacitive and Resistive Humidity Sensors: A Focus Review

“…Fabrication of miniaturized humidity sensors can also be made via large‐scale printing onto flexible substrate . The fabrication process includes the layout of interdigitated electrodes on the PET substrate prepared by means of the laser ablation process, whereas a screen‐printing process has been carried out specifically to deposit the humidity‐sensitive film.…”