Recent advances in biomaterials, thin film processing, and nanofabrication offer the opportunity to design electronics with novel and unique capabilities, including high mechanical stability and biodegradation, which are relevant in medical implants, environmental sensors, and wearable and disposable devices. Combining reliable electrical performance with high mechanical deformation and chemical degradation remains still challenging. This work reports temperature sensors whose material composition enables full biodegradation while the layout and ultrathin format ensure a response time of 10 ms and stable operation demonstrated by a resistance variation of less than 0.7% when the devices are crumpled, folded, and stretched up to 10%. Magnesium microstructures are encapsulated by a compostable‐certified flexible polymer which exhibits small swelling rate and a Young's modulus of about 500 MPa which approximates that of muscles and cartilage. The extension of the design from a single sensor to an array and its integration onto a fluidic device, made of the same polymer, provides routes for a smart biodegradable system for flow mapping. Proper packaging of the sensors tunes the dissolution dynamics to a few days in water while the connection to a Bluetooth module demonstrates wireless operation with 200 mK resolution prospecting application in food tracking and in medical postsurgery monitoring.

Although recent progress in the field of flexible electronics has allowed the realization of biocompatible and conformable electronics, systematic approaches which combine high bendability (<3 mm bending radius), high stretchability (>3-4%), and low complexity in the fabrication process are still missing. Here, we show a technique to induce randomly oriented and customized wrinkles on the surface of a biocompatible elastomeric substrate, where Thin-Film Transistors (TFTs) and circuits (inverter and logic NAND gates) based on amorphous-IGZO are fabricated. By tuning the wavelength and the amplitude of the wrinkles, the devices are fully operational while bent to 13 μm bending radii as well as while stretched up to 5%, keeping unchanged electrical properties. Moreover, a flexible rectifier is also realized, showing no degradation in the performances while flat or wrapped on an artificial human wrist. As proof of concept, transparent TFTs are also fabricated, presenting comparable electrical performances to the nontransparent ones. The extension of the buckling approach from our TFTs to circuits demonstrates the scalability of the process, prospecting applications in wireless stretchable electronics to be worn or implanted.

In the field of flexible electronics, emerging applications require biocompatible and unobtrusive devices, which can withstand different modes of mechanical deformation and achieve low complexity in the fabrication process. Here, the fabrication of a mesa-shaped elastomeric substrate, supporting thin-film transistors (TFTs) and logic circuits (inverters), is reported. High-relief structures are designed to minimize the strain experienced by the electronics, which are fabricated directly on the pillars' surface. In this design configuration, devices based on amorphous indium-gallium-zinc-oxide can withstand different modes of deformation. Bending, stretching, and twisting experiments up to 6 mm radius, 20% uniaxial strain, and 180° global twisting, respectively, are performed to show stable electrical performance of the TFTs. Similarly, a fully integrated digital inverter is tested while stretched up to 20% elongation. As a proof of the versatility of mesa-shaped geometry, a biocompatible and stretchable sensor for temperature mapping is also realized. Using pectin, which is a temperature-sensitive material present in plant cells, the response of the sensor shows current modulation from 13 to 28 °C and functionality up to 15% strain. These results demonstrate the performance of highly flexible electronics for a broad variety of applications, including smart skin and health monitoring.

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...

We present a gas sensitive thin-film transistor (TFT) based on an amorphous Indium–Gallium–Zinc–Oxide (a-IGZO) semiconductor as the sensing layer, which is fabricated on a free-standing flexible polyimide foil. The photo-induced sensor response to NO2 gas at room temperature and the cross-sensitivity to humidity are investigated. We combine the advantages of a transistor based sensor with flexible electronics technology to demonstrate the first flexible a-IGZO based gas sensitive TFT. Since flexible plastic substrates prohibit the use of high operating temperatures, the charge generation is promoted with the help of UV-light absorption, which ultimately triggers the reversible chemical reaction with the trace gas. Furthermore, the device fabrication process flow can be directly implemented in standard TFT technology, allowing for the parallel integration of the sensor and analog or logical circuits.