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Conventional refrigeration relies on hazardous agents, contributing to global warming. Soft, cheap, biodegradable solid-state elastocaloric cooling based on natural rubber offers an environmentally friendly alternative. However, no such practical cooler has been developed, as conventional soft elastocaloric designs are not fast enough to ensure adiabaticity. Here, we combine snap-through instability with strain-induced crystallization and achieve a sub-100 ms quasi-adiabatic cycling, which is 30 times faster than previous designs. Negligible heat exchange in expansion/contraction stages combined with the latent heat of phase transitions results in a giant elastocaloric crystallization effect. The rubber-based all-soft heat pump enables a specific cooling power of 20.9 W g–1, a heat flux of 256 mW cm–2, a coefficient of performance of 4.7 and a single-stage temperature span between hot and cold reservoirs of 7.9 K (full adiabatic temperature change of rubber membrane exceeding 23 K). The pump permits a compact all-soft voltage-actuated set-up, opening up the opportunity of a viable plug-in-ready cooling device. Solid-state caloric cooling is a promising alternative to vapour compression, yet only a few prototypes have been shown. Greibich et al. now report an elastocaloric cooling device based on natural rubber with a cooling power of over 20 W g–1 that exploits snap-through instability and strain-induced crystallization.

A dielectric elastomer transducer is a deformable capacitor, and is under development as a sensor, actuator, or generator. Among various geometric configurations, laterally-constrained transducer, also known as pure-shear transducer, is easy to implement and effective to couple mechanical force and electrical voltage. This analytical study reveals that lateral pre-stretch enhances actuation, far exceeding previously reported actuation strokes. Laterally-constrained transducers exhibit complex electromechanical behavior. As voltage increases, an actuator may undergo electromechanical instability, or form wrinkles, or suffer electrical breakdown. We survey the behavior of actuators under all possible states of pre-stretches, and identify five modes of actuation. Our analysis predicts that laterally-constrained actuators can achieve actuation stroke of 1000% for an acrylic elastomer, and 230% for natural rubber. This analysis opens the door to design actuators of simple geometry capable of a very large range of electromechanical actuation.

Large-bandwidth, low-operation-voltage, and uniform organic amplifiers are fabricated on ultrathin foils. By the integration of short-channel OTFTs and AlOx capacitors, organic amplifiers with a bandwidth of 25 kHz are realized, demonstrating the highest gain-bandwidth product (GBWP) reported to date. Owing to material and process advancements, closed-loop architectures operate at frequencies of several kilohertz with an area smaller than 30 mm(2) .

Polymeric semiconductors have been prepared whose molecular properties make them stretchable and healable — a milestone in the development of sophisticated organic electronic surfaces that mimic human skin. See Letter p.411 There is great interest and potential in the development of skin-inspired flexible and wearable electronic devices. Such devices require materials that twist, fold and bend with no loss in electronic—or material—properties. Zhenan Bao and colleagues report a conjugated polymer that also incorporates non-covalent interactions between adjacent chains, enabling the material to accommodate up to 100% strain whilst maintaining high charge-carrier mobility. In this proof-of-principle study the authors use the polymers to fabricate flexible and stretchable organic transistors that combine robustness with good electronic properties.

Metal oxide thin films for soft and flexible electronics require low cost, room temperature fabrication, and structuring processes. We here introduce an anodic printing process to realize the essential building blocks of electronic circuitry, including resistors, capacitors, field-effect transistors, diodes, rectifiers, and memristors directly on imperceptible plastic substrates. Largely independent on surface properties, we achieve high-quality, few nanometer thin dielectric and semiconducting films even on rough substrates via localized anodisation of valve metals using a scanning droplet cell microscope. We demonstrate printing-like fabrication of 3D multilayer solid-state capacitors with a record-high areal capacity of 4 µF cm−2. Applicable to the whole class of valve metals and their alloys, our method provides a versatile fabrication technique for the circuits that empower the flexible and stretchable electronics of tomorrow. A simple concept of scanning head-guided anodization is shown to be highly expandable to fabricate various electronic components. A team led by Professor Siegfried Bauer from Johannes Kepler University Linz, Austria develops a universal and patternable printing protocol of anodic oxides for a full range of circuit components for flexible devices. The researchers employ a scanning droplet cell microscope to anodize the pre-deposited thin metal films to form dielectric layers with good control in both lateral dimension and vertical thickness. They demonstrate the versatility of the on-site anodization methods by fabricating oxides-based resistors, diodes, transistors and memristors, and multilayer capacitors with a record-high areal capacity of 4 µF cm−2. The approach is cheap, adaptable, and thus ideal for rapid-prototyping of metal oxides circuits for various applications.

Functional materials such as piezoelectric and pyroelectric polymers or organic photodiodes are promising candidates for flexible sensor surfaces; combining thin films of these materials with large-area resistive electrodes leads to position-sensitivity for passive touch- or light-point localization, respectively. However, this type of large-area sensors for passive stimulus-localization lacks a general theoretical description, which is necessary to understand the physics underlying the sensor concept. To this end we present a one-dimensional, theoretical model for these sensors; the model is based on the solutions of the telegrapher's equations under the appropriate boundary conditions. We specify the applied boundary conditions, list approximate solutions for certain parameter ranges and present two model-based normalization procedures. These normalization procedures allow for stimulus localization independently of its magnitude and significantly increase the quality of the measurement signals. Experimental results agree well with theoretical findings, proving the suitability of the presented theoretical models.

We present two laser ultrasonic receivers based on organic photorefractive polymer composites with 2-[4-bis(2-methoxyethyl)aminobenzylidene]malononitrile (AODCST) or 2-dicyanomethylen-3-cyano-5,5-dimethyl-4-(4′-dihexylaminophenyl)-2,5-dihydrofuran nonlinear optical chromophores. Experimental results show sensitivities of the ultrasonic receivers of ~9.5 × 10−8 nm (W/Hz)0.5 for both composites, and a faster response time (~60 ms) for the AODCST-based laser ultrasonic receiver. We show that such LUS detectors are highly suitable for contactless thickness measurements of aluminum, steel sheets and defect detection with an accuracy of 100 μm.

Films made of 2D networks of single-walled carbon nanotubes (SWNTs) are one of the most promising active-channel materials for field-effect transistors (FETs) and have a variety of flexible electronic applications, ranging from biological and chemical sensors to high-speed switching devices. Challenges, however, still remain due to the current hysteresis of SWNT-containing FETs, which has hindered further development. A new and robust method to control the current hysteresis of a SWNT-network FET is presented, which involves the non-volatile polarization of a ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) gate insulator. A top-gate FET with a solution-processed SWNT-network exhibits significant suppression of the hysteresis when the gate-voltage sweep is greater than the coercive field of the ferroelectric polymer layer (≈50 MV m−1). These near-hysteresis-free characteristics are believed to be due to the characteristic hysteresis of the P(VDF-TrFE), resulting from its non-volatile polarization, which makes effective compensation for the current hysteresis of the SWNT-network FETs. The onset voltage for hysteresis-minimized operation is able to be tuned simply by controlling the thickness of the ferroelectric film, which opens the possibility of operating hysteresis-free devices with gate voltages down to a few volts.

Ultrapure aluminium was thermally evaporated onto various plastics (polyethylene 2.6-naphthalate, PEN; polyethylene terephthalate, PET; polyimide, PI and glass for comparison) and potentiostatically anodized in a citric buffer. The anodisation procedure was monitored coulometrically and each alumina film formed was characterized by impedance spectroscopy. The resulting anodic alumina films were amorphous (proven by X-ray diffraction, XRD) and acted as dielectric material in a solid state capacitor with Au top electrode. The capacitors characteristics were evaluated using IV curves and frequency domain measurements. The performance of the capacitors demonstrated low leakage currents and low dielectric losses. The contrary properties capacity and breakdown voltage could be chosen by selecting the anodisation voltage. For each substrate apparent oxide formation factors and capacities were determined coulometrically. The ratio between apparent formation factor and projected area allowed determining the surface roughness. This surface roughness together with the high purity aluminium films and the anodisation compression was responsible for the unexpected high mechanical stability of this composite material.

We present a flexible polymer sensor for light point localization based on the pyroelectric polymer poly(vinylidene fluoride) (PVDF) in combination with large area resistive electrodes. This large area sensor is simple in design; a division of the sensor surface into an array of individual sensor elements as used in active matrix technology is avoided. Electronic circuitry is placed only at the edges of the device. We have fabricated a flexible sensor strip with a length of 12 cm and a width of 1.6 cm according to the proposed concept. The position sensitive output signals of the sensor strip have been measured in response to the intensity-modulated light of a red laser diode. Two model-based normalization procedures have been developed in order to increase the quality of the measurement signals. The results indicate that the sensor strip can be treated mathematically analogous to a transmission line. Calculations based on the solutions of the telegrapher's equations under the appropriate boundary conditions are in good agreement with the experimental results, proving the suitability of the proposed concept for position sensitive detection.

Despite considerable achievements in organic electronics, including examples of complex integrated circuits, [ 1 ] transistor matrix arrays for optical [ 2 ] and Braille displays, [ 3 ] image scanners, [ 4 ] and large-area electronic skin, [ 5 ] non-volatile organic memories remain underexploited. [ 6 ] Even at the lower end of the market, where potential applications are smart cards, wireless tags, and large-area sensors, no non-volatile memory that meets the minimum requirements in terms of access time, retention, and endurance is currently available. [ 6a ] Although there are several types of memory, such as electret, [ 7 ] ferroelectric polymer, [ 8 ] resistive, [ 9 ] and fl ash, [ 10 ] that may be considered suitable, none of them have reached maturity. Electret memories usually require high operating voltages and suffer from long programming times and low charge retention. [ 7 ] Ferroelectric polymer memories face problems known from their inorganic counterparts: interface charge trapping, fatigue, and imprint. [ 8 ] Resistive memories require currents to operate the memory. [ 9 ] Organic fl ash memories, based on fi eld-effect transistors with a fl oating gate architecture where charges stored in the fl oating gate change the threshold voltage of the transistor, currently suffer from either high voltage operation or low charge retention, typically on the order of a few hours or days. [ 10 ] In fl ash memories, the dielectric used to isolate the fl oating gate from the gate electrode and from the semiconductor is the main problem. The gate dielectric must be dense to achieve extremely low leakage currents, and it must provide very large dielectric breakdown strength. [ 11 ]

Macroelectronic components combining different classes of devices often suffer from the high complexity and costs of the manufacturing processes. The printing of an active-matrix sensor network using only five functional inks is demonstrated. The result is an all-printed monolithically integrated touchless input interface, including ferroelectric sensor pixels, organic transistors for impedance matching, and an electrochromic display.

Environmentally sustainable systems for the design, production, and handling of electronic devices should be developed to solve the dramatic increase in electronic waste. Sustainability in plastic electronics may be the production of electronic devices from natural materials, or materials found in common commodity products accepted by society. Thereby biodegradable, biocompatible, bioresorbable, or even metabolizable electronics may become reality. Transistors with an operational voltage as low as 6 V, a source drain current of up to 0.5 lA and an on–off ratio up to four orders of magnitude, with saturated field effect mobilities in the range of 1.5 10 4

Biocompatible-ingestible electronic circuits and capsules for medical diagnosis and monitoring are currently based on traditional silicon technology. Organic electronics has huge potential for developing biodegradable, biocompatible, bioresorbable, or even metabolizable products. An ideal pathway for such electronic devices involves fabrication with materials from nature, or materials found in common commodity products. Transistors with an operational voltage as low as 4–5 V, a source drain current of up to 0.5 μ A and an on-off ratio of 3–5 orders of magnitude have been fabricated with such materials. This work comprises steps towards environmentally safe devices in lowcost, large volume, disposable or throwaway electronic applications, such as in food packaging, plastic bags, and disposable dishware. In addition, there is signifi cant potential to use such electronic items in biomedical implants.

Two different position sensitive devices for large-area detection of light points and objects are presented. The core of the system consists of a luminescent foil, where impinging laser light is absorbed and the fluorescence light is coupled out via attached silicon photodiodes. Due to a direct relation between the signal amplitude and the distance to the photodiodes, this detector can be used for pinpointing laser spots over large areas. When clamping small stripes of the detector inside a rectangular frame, the foil can be used for object tracing over large-areas as well.

We demonstrate the operation of an Electro Wetting on Dielectrics (EWOD) hybrid lab-on-a-chip system by utilizing a High Fundamental Frequency (HFF; 50MHz) Quartz Crystal Microbalance (QCM) resonator as masssensitive sensor. In a first experiment we have tested the reversible formation of a phosphor-lipid monolayer out of an aqueous buffer suspension of phospholipid vesicles onto the integrated sensor, coated by a Self-Assembled Monolayer (SAM) of 1-octadecanethiol on a gold-covered surface. The altered mass load resulted in a shift of the resonance frequencies. In the second experiment, the formation of a protein multilayer composed of streptavidin and biotinylated immunoglobulin G was monitored. The original resonance frequency was recovered by the complete lipid removal by the detergent octyl-D-glucopyranoside. Using these sample applications, we were able to demonstrate and verify the feasibility of our prototype combining a mass-sensitive QCM sensor with digital microfluidics based on EWOD.

photovoltaicdevicesareclosetobeingcommercialized.However,introducing organic photodiodes to the sensor market showsmuch less progress. Organic photodiodes can be easily producedin large areas on flexible substrates and lucrative applications forsuch sensors will have to be found.Matrices of organic photodiodes combine high sensitivity andspatialresolutionwithlargeareaproduction

The transfer of benchtop knowledge into large scale industrial production processes represents a challenge in the field of organic electronics. Large scale industrial production of organic electronics is envisioned as roll to roll (R2R) processing which nowadays comprises usually solution-based large area printing steps. The search for a fast and reliable fabrication process able to accommodate the deposition of both insulator and semiconductor layers in a single step is still under way. Here we report on the fabrication of organic field effect transistors comprising only evaporable small molecules. Moreover, both the gate dielectric (melamine) and the semiconductor (C60) are deposited in successive steps without breaking the vacuum in the evaporation chamber. The material characteristics of evaporated melamine thin films as well as their dielectric properties are investigated, suggesting the applicability of vacuum processed melamine for gate dielectric layer in OFETs. The transistor fabrication and its transfer and output characteristics are presented along with observations that lead to the fabrication of stable and virtually hysteresis-free transistors. The extremely low price of precursor materials and the ease of fabrication recommend the evaporation processes as alternative methods for a large scale, R2R production of organic field effect transistors.

Research into organic field effect transistors (OFETs) has made significant advances—both scientifically and technologically—during the last decade, and the first products will soon enter the market. Printed electronic circuits using organic resistors, diodes and transistors may become cheap alternatives to silicon-based systems, especially in large-area applications. A key parameter for device operation, besides long term stability, is the reproducibility of the current–voltage behavior, which may be affected by hysteresis phenomena. Hysteresis effects are often observed in organic transistors during sweeps of the gate voltage (V GS). This hysteresis can originate in various ways, but comparative scientific investigations are rare and a comprehensive picture of “hysteresis phenomena” in OFETs is still missing. This review provides an overview of the physical effects that cause hysteresis and discusses the importance of such effects in OFETs in a comparative manner.

Toy bricks are an ideal platform for the cost-effective rapid prototyping of a tabletop tensile tester with measurement accuracy on par with expensive, commercially available laboratory equipment. Here, a tester is presented that is not only a versatile demonstration device in mechanics, electronics, and physics education and an eye-catcher on exhibitions, but also a powerful tool for stretchable electronics research. Following the "open-source movement" the build-up of the tester is described and all the details for easy reproduction are disclosed. A a new design of highly conformable all-elastomer based graded rigid island printed circuit boards is developed. Tough bonded to this elastomer substrate are imperceptible electronic foils bearing conductors and off-the-shelf microelectronics, paving the way for next generation smart electronic appliances.

By using an elastomer as dielectric medium in a parallel plate capacitor, the attractive forces between the differently charged electrodes strongly compress that layer, representing a special type of electrostrictive effect. With an optical interference technique at the metal-insulator-metal layer system we studied the temporal behaviour of this mechanical deformation. We show that the deformation can be enhanced when the capacitor is laterally structured in order to allow the elastomer volume between the electrodes to move laterally, resulting in typical response times below 1 ms. The elastomer together with the metal electrodes is a metal-insulator-metal optical waveguide, whose mode properties can be tuned by electrically controlled mechanical thickness changes, suggesting applications for low-price electro–optical modulators with response speeds comparable to thermo–optical polymer modulators but with much smaller size.

Results on photoresponsive organic field-effect transistors (photOFETs) based on conjugated polymer/fullerene solid-state mixtures as active semiconductor layer and poly-vinyl-alcohol (PVA) or divinyltetramethyldisiloxane-bis(benzocyclobutene) (BCB) as gate dielectrics are presented. With LiF/Al top source–drain contacts all devices show dominantly n-type transistor behaviour. Devices fabricated with PVA as gate insulator reveal gate voltage induced saturation upon illumination but low photostability. Contrary, devices fabricated with BCB as gate insulator show transistor amplification in a wide range of illumination intensities. The increase of the drain–source current by more than two orders of magnitudes upon illumination is explained by the generation of a large carrier concentration due to photoinduced charge transfer at the conjugated polymer/fullerene bulk heterojunction upon illumination (photodoping). After illumination, a change of the dark transfer characteristics with respect to the initial transfer characteristics was observed. The initial dark state is achieved either by applying a large negative gate bias or by annealing.

We present C60-based n-channel organic field-effect transistors with mobility in the range of 0.4–1 cm2 V−1 s−1. A solution-processed organic dielectric divinyltetramethyldisiloxane-bis(benzocyclobutene) (BCB) was used as a gate dielectric and C60 films were grown on top by hot wall epitaxy. Devices characterised in inert atmosphere conditions show high stability with an on/off ratio >104. The determined mobility values are nearly gate voltage independent.

Cellular space-charge electrets have recently emerged as a new class of materials for electromechanical devices, offering chances for a wide range of applications and challenges for materials optimization. However, many fundamental and applied aspects of the physics of these novel materials are not yet explored. Here we summarize our present understanding of the (quasi)-piezo- and -pyroelectricity in such materials. In contrast to the dipole-density piezoelectricity in ferroelectric polymers, the piezoelectric-like response of cellular polymers is intrinsic, with positive d/sub 33/ and negative d/sub 31/ and d/sub 32/ piezoelectric-like coefficients. Similarities with ferroelectric materials are outlined, especially switching of "polarization" and (quasi)-piezoelectricity. First steps towards patterned charging of cellular polymers are reported, an immediate consequence of the possibility for "polarization"-switchingin cellular materials. The results on cellular space-charge electrets suggest that well-known electret devices like microphones may be seen in a new light. Examples include dielectric and electromechanical hysteresis loops obtained with a commercially available electret microphone. In view of the results, cellular polymers may henceforth be called "ferroelectrets" and their material behavior "ferroelectretic". From an applied point of view, the performance of a Fresnel zone plate for focussing ultrasound is shown. Such a device may pave the way for a simple tool in nondestructive materials inspection, and demonstrates the large potential of cellular polymers for applications.

Dielectric elastomer transducers consist of thin electrically insulating elastomeric membranes coated on both sides with compliant electrodes. They are a promising electromechanically active polymer technology that may be used for actuators, strain sensors, and electrical generators that harvest mechanical energy. The rapid development of this field calls for the first standards, collecting guidelines on how to assess and compare the performance of materials and devices. This paper addresses this need, presenting standardized methods for material characterisation, device testing and performance measurement. These proposed standards are intended to have a general scope and a broad applicability to different material types and device configurations. Nevertheless, they also intentionally exclude some aspects where knowledge and/or consensus in the literature were deemed to be insufficient. This is a sign of a young and vital field, whose research development is expected to benefit from this effort towards standardisation.

Microelectronics dominates the technological and commercial landscape of today’s electronics industry; ultrahigh density integrated circuits on rigid silicon provide the computing power for smart appliances that help us organize our daily lives. Integrated circuits function flawlessly for decades, yet we like to replace smart phones and tablet computers every year. Disposable electronics, built to disappear in a controlled fashion after the intended lifespan, may be one of the potential applications of transient single-crystalline silicon nanomembranes, reported by Hwang et al. in this issue of ACS Nano. We briefly outline the development of this latest branch of electronics research, and we present some prospects for future developments. Electronics is steadily evolving, and 20 years from now we may find it perfectly normal for smart appliances to be embedded everywhere, on textiles, on our skin, and even in our body.

We investigate the contribution of the radial component of the magnetic field in the solar wind interaction with Mars. We use Mars Global Surveyor Magnetometer and Electron Reflectometer data during the Science Phasing Orbits to gain a qualitative understanding of the magnitude of the radial magnetic field from the solar wind draping around the dayside of Mars. Using only data far away from the strong crustal magnetic sources, we find that the angle the magnetic field makes to the horizontal within the martian ionosphere has an average closer to zero than that outside the ionosphere. However, we find a much larger spread in angles inside the ionosphere. In addition, we find that the angle of inclination increases with increasing altitude and local time, but more spatial coverage is needed to quantify these relationships.

The idea that a solid material can deform when stimulated by electricity originated in the late-18th century with observations of ruptures in overcharged Leyden jars, the first electrical capacitors. In 1776, Italian scientist Alessandro Volta mentioned in a letter that Italian experimenter Felice Fontana had noted volume changes in the Leyden jar upon electrification ( 1 ), an observation that launched a new field of investigation—“deformable” materials affected by electricity. More than two centuries later, the concept of “electrically stretchable materials” is at the forefront of devising bioinspired robots, tactile and haptic interfaces, and adaptive optical systems ( 2 , 3 ).

The magnetometer and electron reflectometer experiment (MAG/ER) on the Mars Global Surveyor (MGS) spacecraft has obtained magnetic field and electron data which indicates that the solar wind interaction with Mars is primarily an ionospheric-atmospheric interaction similar to that at Venus. However, the global-scale electric currents and resulting magnetic fields due to the interaction at Mars are locally interrupted or perturbed over distance scales of several hundred kilometers by the effects of paleomagnetic fields due to crustal remanence. In this paper we compare the Mars-solar wind interaction with the Venus-solar wind interaction by selecting MGS orbits which do not show significant magnetic perturbations due to crustal magnetic anomalies, and demonstrate that a number of phenomena characteristic of the Venus-solar wind interaction are also observable at Mars.

The MGS MAG/ER investigation provides vector measurements of the magnetic field and the ionospheric electron density near periapsis. The instrumentation consists of twin triaxial fluxgate magnetometers and a “top hat” electrostatic analyzer of electrons in the energy range of 1 eV to 20 keV. Results include extensive mapping of the detached bow shock wave in the solar wind, the nature and structure of the ionopause and magnetic pile-up boundaries. The most surprising result is the discovery of localized magnetic fields of planetary origin, presumably due to remanent crustal magnetization. Maximum fields measured while below the ionosphere exceed 300 nT. We present an initial study of one of these very localized fields and extrapolations to the Martian surface in the Acidalia planitia.

This paper shows that a highly deformable capacitor made of a soft dielectric and two conformal electrodes can switch between two states discontinuously, by a first-order transition, as the total charge varies gradually. When the total charge is small, it spreads evenly over the area of the capacitor, and the capacitor deforms homogeneously. When the total charge is large, it localizes in a small region of the capacitor, and this region thins down preferentially. The capacitor will survive the localization without electrical breakdown if the area of the electrode is small. Such a bistable system may lead to useful devices.

Ultrathin sheets of polymer LEDs that emit light even when being crumpled or stretched have been realized. The 2-μm-thick devices emit red or orange light with a sufficiently high brightness for indoor applications, and they could prove useful for integration with textiles.

We report on a contactless laser ultrasonic (LUS) method to monitor the phase transformation in a titanium alloy (Ti-6%Al-4%V) sheet by using a simple and high resolution LUS interferometer, based on two wave mixing in a fast BSO photorefractive crystal. The temperature dependent phase transformation from the α to the β phase in the Ti samples was observed around 1000°C. During heating the Ti sheets, the velocity of the laser generated longitudinal and shear ultrasonic wave, 5820 and 2950 m/s respectively, decreases fast up to 980°C which shows the start of the phase change region. At 980°C to 1020°C the bulk wave velocity is approximately constant (4820 and 2600 m/s) indicating the phase transformation process from the α to the β phase. Due to microstructural changes in the β phase at higher temperatures, the velocity of the bulk waves decreases slowly in comparison to that of the α phase.

Fluorescent foils are used with silicon photodiodes for large-area detection of objects, when combined with lasers forming a light curtain. An object entering the detection area penetrates the light curtain and casts shadows onto the fluorescent foils. Using a simple mathematical algorithm, the position of the object is detected with high speed. The device is suitable for security applications and can be used as a touch input device for computers, gaming and presentations.

Organic field-effect transistors with a polymeric electret as gate insulator and fullerenes as a molecular semiconductor were fabricated. We observed an amplification of the drain–source current Ids on the order of 104 upon applying a gate voltage Vg. Reversing the gate voltage Vg features large metastable hysteresis in the transfer characteristics Ids(Vg) with a long retention time. The observation of a switchable channel current Ids is proposed to originate from charge storage in the organic electret. As such, this device is a demonstration of an organic nonvolatile memory element switchable with the gate voltage.

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.

We investigate the dielectric response of solar cell devices based on oxygen-doped poly(3-hexylthiophene):[6,6]-phenyl-C${}_{61}$-butyric acid methyl ester (P3HT:PCBM) blends as a function of temperature between $133K$ and $303K$. The spectra are analyzed using a recently introduced model [O. Armbruster, C. Lungenschmied, and S. Bauer, Phys. Rev. B 84, 085208 (2011)] which is based on a trapping and reemission mechanism of charge carriers. A dominating trap depth of $130meV$ is determined and the broadening of this trap level identified as purely thermal. In addition we estimate the density of charge carriers after doping as well as their mobility. We show that the concentration of mobile holes approximately doubles by heating the device from the lowest to the highest measured temperature. This is indicative of a second, shallow trap level of approximately $14meV$. Dielectric spectroscopy hence proves to be a valuable tool to assess device parameters such as dopant concentration, charge carrier transport characteristics, and mobility which are of crucial interest for understanding degradation in organic semiconductor devices.

Electronics can be made on elastically stretchable “skin.” Such skins conform to irregularly curved surfaces and carry arrays of thin-film devices and integrated circuits. Laypeople and scientists intuitively grasp the concept of electronic skins; material scientists then ask “what materials are used?” and “how does it work?” Stretchable circuits are made of diverse materials that span more than 12 orders of magnitude in elastic modulus. We begin with a brief overview of the materials and the architecture of stretchable electronics, then we discuss stretchable substrates, encapsulation, interconnects, and the fabrication of devices and circuits. These components and techniques provide the tools for creating new concepts in biocompatible circuits that conform to and stretch with living tissue. They enable wireless energy transfer via stretchable antennas, stretchable solar cells that convert sunlight to electricity, supercapacitors, and batteries that store energy in stretchable electronic devices. We conclude with a brief outlook on the technical challenges for this revolutionary technology on its road to functional stretchable electronic systems.

Two different position sensitive devices for large-area detection of light points and objects are presented. The core of the system consists of a luminescent foil, where impinging laser light is absorbed and the fluorescence light is coupled out via attached silicon photodiodes. Due to a direct relation between the signal amplitude and the distance to the photodiodes, this detector can be used for pinpointing laser spots over large areas. When fixing small stripes of the detector inside a rectangular frame, the foil can be used for object tracing over large-areas as well.

A brief tour d'horizon is given through recent research on flexible and stretchable dielectrics. Ultrathin dielectrics with low leakage currents and high breakdown strength are essential in flexible electronic devices, illustrated with low voltage field-effect transistors for optothermal sensing and flash memories. Electrets with a permanently stored electrical charge are useful to control the threshold voltage in field-effect devices. Ferroelectrets with internally charged voids have been introduced in a ferroelectret field-effect configuration for piezoelectric transducers and microphones. Flexible dielectrics displaying ferro-, piezo- and pyroelectricity are employed in memories and in transducer functions. Finally compliant dielectrics are investigated in elastomer actuators and energy harvesters. The chosen examples show that research on flexible and soft dielectrics is actively pursued in various branches of science, with prospect for future flexible and stretchable electronic products.

The optical properties of a thin metal film are derived, with a thin film defined as having a thickness smaller than the wavelength of the radiation and the skin depth. The derivation is based on the continuity equation for the electric field and on the energy balance for the incident, reflected, transmitted, and absorbed energy current. The use of thin metal films as anti‐interference coatings, as absorbers for the infrared, as semitransparent mirrors in interferometric devices and beam splitters, and as mirrors is discussed.

Flexible Organic Flash Memory Advances in organic electronics have enabled the fabrication of a number of core devices on flexible plastic substrates. These include transistors, light-emitting diodes, actuators, and sensors. Sekitani et al. (p. 1516 ) use a low-temperature hybrid dielectric based on a thin metal oxide and a self-assembled monolayer to develop flexible floating-gate memory transistors with small program and erase voltages. These are integrated into a flexible large-area sensor area, capable of storing values from applied external pressures.

Several methods for the measurement of the thermal diffusivity of thin films are developed. Common to all methods is the generation of a thermal wave via the absorption of intensity-modulated light on one surface of the film; resistive thin film bolometers and pyroelectric sensors are used for the temperature recording. For free-bearing films the thermal diffusivity is determined from front and rear side temperature spectra as a function of the modulation frequency, measured with resistive bolometers. If a pyroelectric material is mounted on a heat sink, the thermal diffusivity is obtained from the spectrum of the pyroelectric current. For very thin films pyroelectric substrates are recommended as temperature sensors. A novel method is also proposed, in which the thermal diffusivity is obtained without the influence of any other material properties and any sensor characteristics. Experimental results are presented with a 25 μm thick PVDF film and with a 1.25 μm thick Polyglutamate Langmuir-Blodge...

Dielectric elastomer actuators (DEAs) are promising for bionic and robotic applications. Reliability requirements in such applications necessitate better knowledge of the safe operation regimes and possible failure modes of DEAs. Elastomers consist of a network of entangled and cross-linked polymer chains, able to sustain spatially varying stress and strain fields, accompanied by stored elastic energy. Here we introduce a rigorous thermodynamic description of DEAs, based on a statistical mechanical model to gain insight for material development and optimization. We investigate multistability effects in the phase diagrams of elastomer actuators and combine our model with capacitive extensometry experiments.

Large area electronics is mainly driven by the display industry [1]. Advanced technology schemes, like electronic skin for flexible, full body tactile sensors in robotics etc. have emerged recently [2]. In general, large area electronic surfaces consist of a backplane including transistor matrices and a frontplane, giving functionality to the electronic surface. Frontplanes may benefit from functional electrets in memories [3] and in sensors for monitoring changes in ambient pressure or temperature [4, 5].

In this paper, a selection of some functional polymer elements are introduced, interfacing with thin film transistors is discussed and an example for a flexible touchpad of utmost simplicity is presented. This leads to thin stretchable transducer- and sensor skin arrays which we propose. Special emphasis is laid on piezoelectric cellular ferroelectrets which offer not only a wealth of applications but seem also ideally suited as efficient electroactive materials for a low cost all- polymer device technology.

Thin polymer foams with a closed cell void-structure can be internally charged by silent or partial discharges within the voids. The resulting material, which carries positive and negative charges on the internal void surfaces is called a ferroelectret. Ferroelectrets behave like typical ferroelectrics, hence they provide a novel class of ferroic materials. The soft foams are strongly piezoelectric in the 3-direction, but show negligible piezoelectric response in the transverse direction. This, together with a very low pyroelectric coefficient, make ferroelectrets highly suitable for flexible electroactive transducer element which can be integrated in thin bendable organic electronic devices. Here we describe some fundamental characteristics of cellular ferroelectrets and present a number of promising examples for a possible combination with various functional polymer systems. Our examples focus on flexible ferroelectret field-effect transistor systems for large-area sensor skins and microphones, flexible large-array position detectors (touchpad), and stretchable large-array pressure sensors.

A method is described that enables the simultaneous or consecutive determination of the specific heat, the thermal diffusivity, the dielectric constant, and the pyroelectric coefficient of thin pyroelectric films. The sample is heated by the absorption of intensity modulated light at one surface. The pyroelectric current and the transient temperatures of the sample surfaces are recorded as a function of the modulation frequency of the chopped light. The transient temperature recording is performed via thin‐film bolometers. Analysis procedures for the determination of the specific heat, the thermal diffusivity, and the spatially varying pyroelectric coefficient are introduced and discussed. A simulation of the performance of integrated pyroelectric ir sensors on silicon chips is performed by a coupling of the pyroelectric material to a heat sink. It is shown that the response of pyroelectric ir sensors integrated on silicon chips is influenced by heat wave interference effects. Experimental results are giv...