Flexible a‐IGZO Phototransistor for Instantaneous and Cumulative UV‐Exposure Monitoring for Skin Health

Abstract

The accurate and continuous monitoring of both instantaneous and cumulative exposure to UV-light is of great relevance for dermatology and skin care to avoid damages to the dermis and epidermis and, ultimately, prevent melanoma. Here, we demonstrate flexible thin-film phototransistors based on amorphous Indium-Gallium-Zinc-Oxide (a-IGZO) semiconductor whose optical band-gap (3.05 eV) enables monitoring of the entire UV-spectrum. At the same time, the device structure together with a new read-out scheme consisting of a rectangular modulation of the gate-source voltage allow for both real time and cumulative measurement of UV-light intensity. Thanks to its design and thickness, the optoelectronic properties of the sensor remain unaffected after 2000 bending cycles down to radii of 6 mm. Furthermore, the device can be encapsulated with a thin Polydimethylsiloxane (PDMS) layer to achieve a compliant adhesion with the skin and enable wearable applications.3 Ultraviolet (UV) radiation, which is part of the sunlight spectrum with wavelengths ranging from 280 nm to 400 nm, is considered as one of the main cause of melanoma skin cancers [1] . It is estimated that one out of five Americans will develop skin cancer in their lifetime [2] . As Earth's protective ozone layer becomes thinner [3] the prevention of exposure to dangerous UV-intensities is of crucial interest [4] . Data on instantaneous and cumulative UV exposures provide important information for dermatology, skin and general healthcare and eventually help to prevent damages to the dermis, epidermis [5] or eyes [6] . Wearable and, more recently, epidermal or skin-like devices, such as UV-dosimeter temporary tattoos [7] or highly stretchable photodetectors [8] have shown great potential to achieve accurate and unobtrusive sensing of important bio-signals and represent a promising technology for health monitoring [9,10] .Among the palette of materials, wide bandgap semiconductors, such as ZnO and its composites (Indium-Gallium-Zinc-Oxide (IGZO), Indium-Zinc-Oxide (IZO), Zinc-Tin-Oxide (ZTO), etc.) can be used for UV-photodetection [11] . Research in recent years has established amorphous IGZO (a-IGZO) as one of the most promising semiconductors for thin-film transistors [11] thanks to its attractive properties including high mobility (10 cm 2 /Vs) [12] , low temperature and large area deposition, operational stability [13] and the suitability for integration into flexible electronics [14] . Such technology could also replace polysilicon in the active matrix of displays [15] which could benefit from the integration of UV-light sensors for automated adaption of display brightness to the environmental illumination conditions. In addition, the optical bandgap of a-IGZO is ~3.05 eV [16] , which makes this material an excellent candidate for detection of the whole UV-spectrum [17] in contrast to ZnSnO or ZnO which have bandgaps around 3.3 eV [18,19] , corresponding to 368 nm (Figure 1 (a)). The The photofield-effect and the photosensitive characteristics of rigid...

Geometry-Based Tunability Enhancement of Flexible Thin-Film Varactors

“…1a shows the fabrication flow, which is comparable to our previous work [14], [15]. The devices are fabricated on free-standing 50 µm thick Polyimide foil.…”

Disposable Sensors in Diagnostics, Food, and Environmental Monitoring

“…Optoelectronic sensors can also be integrated into ultrathin wearable devices which can provide more quantitative and precise measurements unlike colorimetric sensors. They can be equipped with near‐field communication (NFC) capabilities to transmit digital information concerning sensors to a smartphone, wirelessly, without the need for an additional source of power . Because of its simplicity, and the increasing number of NFC‐enabled phones in the world, we expect to see a larger number of NFC‐enabled wearable sensors in the future.…”

Flexible Sensors—From Materials to Applications

“…Au has been extensively used in the form of thin-film metallic contacts due to its resistance to oxidation. When using this material, underlayers of titanium (Ti) or Cr are typically used to increase the adhesion to the substrate [33][34][35][36]. Also, Mg has recently been employed as a contact due to its biocompatibility (Figure 2a).…”