Electronic devices have advanced from their heavy, bulky origins to become smart, mobile appliances. Nevertheless, they remain rigid, which precludes their intimate integration into everyday life. Flexible, textile and stretchable electronics are emerging research areas and may yield mainstream technologies. Rollable and unbreakable backplanes with amorphous silicon field-effect transistors on steel substrates only 3 μm thick have been demonstrated. On polymer substrates, bending radii of 0.1 mm have been achieved in flexible electronic devices. Concurrently, the need for compliant electronics that can not only be flexed but also conform to three-dimensional shapes has emerged. Approaches include the transfer of ultrathin polyimide layers encapsulating silicon CMOS circuits onto pre-stretched elastomers, the use of conductive elastomers integrated with organic field-effect transistors (OFETs) on polyimide islands, and fabrication of OFETs and gold interconnects on elastic substrates to realize pressure, temperature and optical sensors. Here we present a platform that makes electronics both virtually unbreakable and imperceptible. Fabricated directly on ultrathin (1 μm) polymer foils, our electronic circuits are light (3 g m(-2)) and ultraflexible and conform to their ambient, dynamic environment. Organic transistors with an ultra-dense oxide gate dielectric a few nanometres thick formed at room temperature enable sophisticated large-area electronic foils with unprecedented mechanical and environmental stability: they withstand repeated bending to radii of 5 μm and less, can be crumpled like paper, accommodate stretching up to 230% on prestrained elastomers, and can be operated at high temperatures and in aqueous environments. Because manufacturing costs of organic electronics are potentially low, imperceptible electronic foils may be as common in the future as plastic wrap is today. Applications include matrix-addressed tactile sensor foils for health care and monitoring, thin-film heaters, temperature and infrared sensors, displays, and organic solar cells.

Scientists are exploring elastic and soft forms of robots, electronic skin and energy harvesters, dreaming to mimic nature and to enable novel applications in wide fields, from consumer and mobile appliances to biomedical systems, sports and healthcare. All conceivable classes of materials with a wide range of mechanical, physical and chemical properties are employed, from liquids and gels to organic and inorganic solids. Functionalities never seen before are achieved. In this review we discuss soft robots which allow actuation with several degrees of freedom. We show that different actuation mechanisms lead to similar actuators, capable of complex and smooth movements in 3d space. We introduce latest research examples in sensor skin development and discuss ultraflexible electronic circuits, light emitting diodes and solar cells as examples. Additional functionalities of sensor skin, such as visual sensors inspired by animal eyes, camouflage, self-cleaning and healing and on-skin energy storage and generation are briefly reviewed. Finally, we discuss a paradigm change in energy harvesting, away from hard energy generators to soft ones based on dielectric elastomers. Such systems are shown to work with high energy of conversion, making them potentially interesting for harvesting mechanical energy from human gait, winds and ocean waves.

A monolithically integrated bifunctional frontplane is introduced to large area electronics. The bifunctional frontplane element is based on a composite foil of piezoelectric ceramic lead titanate nanoparticles embedded in a ferroelectric poly(vinylidene fluoride trifluoroethylene) polymer matrix. Bifunctionality to pressure and temperature changes is achieved by a sequential, area selective two-step poling process, where the polarization directions in the nanoparticles and the ferroelectric polymer are adjusted independently. Thereby, sensor elements that are only piezoelectric or only pyroelectric are achieved. The frontplane foil is overlaid on a thin-film transistor backplane. Our work constitutes a step toward multifunctional frontplanes for large area electronic surfaces.

When exposed to sufficiently high electric fields, polymer-foam electret materials with closed cells exhibit ferroelectric-like behavior and may therefore be called ferroelectrets. In cellular ferroelectrets, the influence of the cell size and shape distributions on the application-relevant properties is not yet understood. Therefore, controlled inflation experiments were carried out on cellular polypropylene films, and the resulting elastical and electromechanical parameters were determined. The elastic modulus in the thickness direction shows a minimum with a corresponding maximum in the electromechanical transducer coefficient. The resonance frequency shifts as a function of the elastic modulus and the relative density of the inflated cellular films. Therefore, the transducer properties of cellular ferroelectrets can be optimized by means of controlled inflation.

The performance of organic thin-film transistors (OTFT) for flexible, low cost and disposable "plastic" electronic products advances rapidly: various organic semiconductors display hole or electron carrier mobilities [1] that compare favorably with those of hydrogenated amorphous silicon, [2] the inorganic counterpart for such applications as flexible displays, [3,4] smart cards and radio frequency identification tags, [5,6] nonvolatile memories [7] and sensors. [8,9] The possibility for tailoring functional organic materials, bears potential towards novel electronic products such as smart skins, [10] smart textiles [11] and "invisible electronics", [12] where multiple functionalities, portability and ubiquitous integration is requested. In this context diverse properties of organic thin-film devices are inevitable such as lightweight, low power consumption, low operationvoltage and compatibility with diverse substrates.[12]Reducing the threshold voltage and the subthreshold swing is essential for operating OTFTs at low-voltage levels. When combined with very low gate leakage currents, OTFTs may also become a key element in high-end sensor applications, such as flexible touch pads and screens or thermal imaging tools for night vision, surveillance or for the detection of undesired heat loss paths in buildings.The aforementioned transistor parameters not only critically depend on the thickness and the dielectric properties of the gate insulator, [12][13][14] but also on the trapped charge densities at the interface between these materials. The selection of semiconductors and gate insulators with excellent interface properties is currently the challenge in the quest for improving the performance of OTFTs.Here we show that bottom-gate OTFTs based on the organic semiconductor pentacene and high-k nanocomposite gate dielectrics, exhibit transistor performances with very low gate leakage currents, subthreshold swings close to the theoretical limit, and low-voltage battery operation. The subthreshold swings of OTFTs with different organic and hybrid gate dielectrics follow an inverse dependence on the gate capacitance as is expected by standard MOS theory. The trapped charge carrier density at the interface between the semiconductor and the dielectric surpasses that of the SiO 2 -pentacene interface, being close to the average trap densities in the SiO 2 -Si interface in metal oxide semiconductor transistors. [15] We also report the first application of these OTFTs in an optothermal light sensor. We describe the transistor, the temperature sensitive fluorinated polymer, their combination in an integrated circuit, and the application of this circuit as a thermal infrared sensor and as a switch that can be operated by a laser pointer. Figure 1 shows the structure of low-voltage organic transistors with high dielectric constant (high-k) oxide-polymer nanocomposites. Al 2 O 3 or ZrO 2 were chosen as high-k dielectric materials, combined with poly(a-methyl styrene) (PaMS) or poly(vinyl cinnamate) (PVCi) to form a smooth and ...