Laser-induced electrodes towards low-cost flexible UV ZnO sensors

Abstract

Flexible electronics is a branch of electric fabrication that allows for increasingly ergonomic devices. However, its production still requires multi-step, expensive, and time-consuming processes. Laserdirect writing (LDW) is a clean and low-cost alternative technique for producing electrodes on flexible substrates with high resolution, without the need of masks or direct contact with the device. Laserinduced graphene (LIG), a particular type of LDW, is a technique in which, by the irradiation of polyimide (PI) and polyetherimide (PEI) films with a pulsed CO 2 infrared laser, a photothermal reaction occurs which leads to the formation of stacked graphene structures. LIG thus emerges as a rising substitute to produce graphene-based devices. This work consists of the development and optimization of flexible UV sensors with zinc oxide nanostructures as the active layer for photodetection, PI or PEI as the substrates, and the respective LIG as electrodes. The nanostructures with higher area-volume ratio, synthesized through a microwave-assisted hydrothermal method, were selected and deposited by drop-casting onto electrodes that in turn were optimized to enhance electrical properties by varying the laser parameters. The assembled sensors were able to successfully detect UV radiation with a responsivity of 92 and 2 nA W −1 for 1 V bias for the PI and PEI substrates, respectively. In addition, the PI sensor has shown to be capable of working under strain and to be stable after several hours of constant cyclic operation.

Recent Advances and a Roadmap to Wearable UV Sensor Technologies

“…A key aspect of developing ZnO-based wearable technologies is to develop the ability to grow their unique morphologies on flexible substrates. [80] To this end, ZnO nanostructures have been fabricated on a wide variety of flexible substrates, such as polyimide (PI), [72c,73c,81] polyester, [82] polyethersulfone (PES), [81a] polyetherimide (PEI), [83] polyethylene terephthalate (PET), [84] polyvinylalcohol (PVA), [85] polyvinyl chloride (PVC), [72a] PDMS, [86] polytetrafluoroethylene (PTFE or Teflon), [87] mica, [88] and paper. [39,73a,89] One popular choice of the substrate has been paper-based devices as they are low cost, lightweight and readily available.…”

Flexible Sensors—From Materials to Applications

“…Among metal oxide semiconductors, the most widely used material in flexible sensors as a TFT channel is amorphous indium-gallium-zinc-oxide (a-IGZO) [14,15,23,24,32,33], while ZnO is widely used for electromagnetic radiation sensors [21,73,74,[168][169][170][171][172]. Other metal oxides which have also been used in flexible sensors as semiconductors are indium-zinc-oxide (IZO) [173,174], and tin-oxide (SnO) [175][176][177].…”

Transduction Mechanisms, Micro-Structuring Techniques, and Applications of Electronic Skin Pressure Sensors: A Review of Recent Advances

“…The most popular piezoelectric materials used in e-skin sensors, energy harvesters, and other types of sensors are lead zirconate titanate (PZT) [ 89 , 90 , 91 ], zinc oxide (ZnO) [ 68 , 87 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 ], barium titanate (BaTiO 3 ) [ 102 , 103 ], poly(vinylidene difluoride) (PVDF) and its co-polymers like poly[(vinylidenefluoride-co-trifluoroethylene] [P(VDF-TrFE)] and poly(vinylidene fluoride-co-hexafluoropropene) [P(VDF-HFP)] [ 88 , 99 , 102 , 103 , 104 , 105 , 106 , 107 , 108 ], and their piezoelectric coefficient, d 33 , can be found in Table 1 . The relation between the d 33 and the output of a piezoelectric sensor can be established by Equation (2): where V is the voltage produced by the sensor, C is the capacitance, and F is the force applied to the sensor [ 109 ].…”

“…Therefore, this review summarizes in one place comprehensive and vital aspects of pressure sensors, namely transduction mechanisms, micro-structuring techniques, most employed materials, and applications, that are typically not found together in other reviews. Regarding other types of interesting sensors and devices, such as strain sensors, humidity sensors, temperature sensors, biosensors, chemical sensors, gas sensors, antennas, energy harvesters, amongst others, many reviews are available for consulting [ 3 , 4 , 5 , 34 , 48 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 ].…”