Performance of Flexible Chemoresistive Gas Sensors after Having Undergone Automated Bending Tests

Abstract

Many sensors are developed over flexible substrates to be used as wearables, which does not guarantee that they will actually withstand being bent. This work evaluates the gas sensing performance of metal oxide devices of three different types, before and after having undergone automated, repetitive bending tests. These tests were aimed at demonstrating that the fabricated sensors were actually flexible, which cannot be taken for granted beforehand. The active layer in these sensors consisted of WO3 nanowires (NWs) grown directly over a Kapton foil by means of the aerosol-assisted chemical vapor deposition. Their response to different H2 concentrations was measured at first. Then, they were cyclically bent, and finally, their response to H2 was measured again. Sensors based on pristine WO3-NWs over Ag electrodes and on Pd-decorated NWs over Au electrodes maintained their performance after having been bent. Ag electrodes covered with Pd-decorated NWs became fragile and lost their usefulness. To summarize, two different types of truly flexible metal oxide gas sensor were fabricated, whereas a third one was not flexible, despite being grown over a flexible substrate following the same method. Finally, we recommend that one standard bending test procedure should be established to clearly determine the flexibility of a sensor considering its intended application.

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

“…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. The printing pattern corresponds to the openings of the stencil.…”

“…Plastic substrates-In general, the polymer substrates should mimic the properties of planar rigid substrates. Dimensional and thermal stability, low coefficient of thermal expansion, good solvent resistance and good barrier properties for moisture, air and gases are necessary for plastic substrates [69][70][71][72]. In addition to physical, chemical, mechanical and optical performances, also the glass transition temperatures of different polymers have to be evaluated depending on the final application and the fabrication process involved.…”

Screen-Printing of Functionalized MWCNT-PEDOT:PSS Based Solutions on Bendable Substrate for Ammonia Gas Sensing

“…For the much larger crack gap of a 0.9 cm bending-radius film ( Figure 12 c), a lack of f -MWCNT pathways was observed. Delamination, channeling and cracking have been reported as important causes for the failure of breakable films on flexible substrates [ 23 , 24 , 25 ]. When decreasing the stress on the film surface, the tensile strain increased.…”

Review of Materials and Fabrication Methods for Flexible Nano and Micro-Scale Physical and Chemical Property Sensors

“…In another report, a hydrogen gas flexible sensor was fabricated from (Tungste oxide) WO3 nanowires grown on Kapton via an aerosol-assisted chemical vapour de tion method [45]. The sensors could measure various concentrations of hydrogen gas ver and silver-platinum were used to coat the sensors.…”