Flexible electronic sensors

Resume : Electronics of the future are expected to be foldable, twistable, and stretchable into curvilinear shapes to enable applications that would be impossible to achieve using today’s rigid, hard electronics. As a revolutionary technology, stretchable electronics has been changing our concept of electronics and brought us amazing features in numerous applications. Generally, such features are designed with soft materials as the interface between electronics and the human body or complex surfaces, e.g. epidermal electronic system. We present the fabrication of stretchable metallic connections patterned by laser ablation. Laser ablation is an ideal process for the production of fine features in materials deposited onto stretchable substrate. A short pulse laser is focused onto the surface to be ablated. The material heats up very rapidly and vaporizes to leave a small pit in the surface. Various sensors are targeted such as pressure, temperature, artificial eye and even biological sensor. For example, we present the integration of an organic electrochemical transistor (OECT) based on Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) onto a polydimethylsiloxane (PDMS) stretchable substrate. This stretchable sensor presents the advantages of superior mechanical matching between the active electronic device and the human body, easy implementation for in vivo recording. Moreover the PDMS substrate of the device, which is largely use for micro fluidics in biology, allows a higher level of integration of the OECT directly inside the fluidic channel for continuous recording.

Resume : We report a method to produce single layer metamorphic stretchable printed circuit boards. Different from most reports the approach delays the use of the stretchable rubber support to the end of the processing sequence. Specifically, the entire circuit containing interconnects, unpackaged chips or chip-scale packaged surface mount devices (SMDs) are fabricated on a hard carrier. This facilitates high temperature processing, automated mounting, and precision alignment. Moreover, it enables “on-hard” carrier functionality tests, which are critical to determine correct functionality and a comparison of the performance metrics after the circuit is released. Application of the rubber support, release, and stretchability tests are last. As an application, the concept of metamorphic electronics is demonstrated. Our demonstrators are inflatable electronic structures and contain arrays with packaged SMDs and bare dies integrating light emitting diodes (LEDs) and transistors within a rubber matrix. The test structures morph from planar, to spherical, to cone like topologies.

Resume : Humidity sensors are of paramount importance in numerous science and technology fields thus are commonly used in industries, hospitals, environmental monitoring, etc. Hitherto, different transduction mechanisms have been explored in order to improve sensitivity, response speed, and recovery time by exploiting different properties as read-out, including optical and electrical characteristics (capacitance, resistance and gate effect in field-effect transistors as well as small mass changes). In this work we report on the use of smartly designed supramolecular fibers as electrical humidity sensors. This system is based on a light-triggered self-assembly of an amphiphilic electron donor–acceptor (D–A) dyad, made by a conjugated backbone, containing a tetrathiophene (4T) and a perylenediimide (PDI), connected by a conformationally rigid ethynylene spacer. These architectures, exposing ethylene glycol in their external shell, are employed as active components in resistive humidity sensors which combine a response rate as fast as 26 ms with an exponential growth of the current from 0 to, at least, 75% of relative humidity (RH). In this RH range, the current changes over up to 7 orders of magnitude, i.e. from a few pA to tens of mA, demonstrating an extremely high sensitivity to humidity variations.

Resume : Comfortable, wearable sensors and computers will enhance every person’s awareness of his or her health condition, environment, chemical pollutants, potential hazards, and information of interest. In agriculture and in the food industry there is a need for a constant control of the condition and needs of plants, animals, and farm products. Yet many of these applications depend upon the development of novel, cheap devices and sensors that are easy to implement and to integrate. Organic semiconductors as well as several inorganic materials and hybrid material systems have proven to combine a number of intriguing optical and electronic properties with simple processing methods. As it will be reviewed in this contribution, these materials are believed to find their application in printed electronic devices allowing for the development of smart disposable devices in food-, health-, and environmental monitoring, diagnostics and control, possibly integrated into arrays of sensor elements for multi-parameter detection. In this contribution we review past and recent achievements in the field. Followed by a brief introduction, we will focus on two topics being on the agenda recently: a) the use of electrolyte-gated organic field-effect transistor (EGOFET) and b) ion-selective membrane based sensors for in-situ sensing of ions and biological substances. Here the realization of the ion-selective EGOFETs is discussed for reversible and selective ion and pH detection. As a second approach a reference electrode free all organic K+ sensitive ion sensing platform on a simple paper sheet is presented.

Resume : The research interest on alternative materials for innovative ionizing radiation detection is rapidly growing, in particular to envisage the need of large-area conformable sensor flat panels for applications that span from cultural heritage preservation to the security of public buildings. Organic materials have a strong potential for such an application, thanks to their mechanical flexibility and the possibility of deposition over large and bendable substrates by means of low-cost wet-technologies as printing techniques. Therefore, these feature permits to overcome the constraint of traditional inorganic materials, i. e. expensive or complex growth techniques and stiff mechanical properties. Recently, the employment of solution-grown organic materials as reliable direct X-ray detectors, operating at room temperature, have been demonstrated [1-3]. These studies opens the way to the development of a new class of fully flexible organic-based direct detectors with higher performances. In this work, we will report about results on organic thin-films based, fully bendable, devices as direct X-ray detectors, obtaining sensitivity values up to several hundreds of nC/Gy at ultra-low bias of 0.2 V. An analytical model accounting the signal amplitude and sensitivity values achieved and describing the mechanisms of collection and transport of the X-ray generated charges have been also developed. Finally, we assessed the possibility to use the detector under mechanical strain and gave the first demonstration of a 2×2 pixelated matrix organic detector. [1] B. Fraboni et al., Adv. Mater., 24, 17, 2289–2293, 2012. [2] B. Fraboni et al., Faraday Discuss., 174, 219, 2014. [3] L. Basiricò et al., IEEE Trans. Nucl. Sci., 62, 4, 1791–1797, 2015.

Resume : Here I review recent work on using natural-origin materials in semiconductor-based devices for interfacing with biology. Many natural materials offer both excellent semiconducting properties, and importantly, electronic as well as ionic conductivity. Biochemical systems are ionic, and not electronic, thus any attempts of active bioelectronics devices must involve ionic/electronic transducing elements. In particular, progress in the use of nanocrystalline and microcrystalline organic hydrogen-bonded pigments will be discussed. These materials have been ubiquitous throughout history and are widely produced today industrially as colorants in everyday products as various as cosmetics and printing inks, and have numerous properties that make them intrinsically biocompatible. The bioconjugation chemistry of these materials and subsequent deployment in electronic devices requiring reliable and specific bio-sensing will be covered.

Resume : Organic Semiconducting Single Crystals (OSSCs) are the ideal candidates in the field of organic electronics . Their application in the particular field of detection of ionizing radiation has been recently describedin a article where authors have shown – as a proof-of-principle - how OSSCs can be used as a new generation of direct electrical sensors . Many techniques are today available to prepare OSSCs suitable for devices fabrication. Among these, solution growth represents the best candidate, due to its: (i) simplicity, also applicable, in a properly developed form, to industrial purposes (e.g. inkjet printing or screen printing) ; (ii) high degree of crystal perfection, allowing good reproducibility of device performance ; (iii) ability of tuning crystal sizes ; (iv) low cost. The effect of systematic changes of some growth parameters (temperature, solution concentration, etc) has been studied. Some different compounds (i.e., 4hydroxycyanobenzene, 4HCB, and 2,4-dinitro-1-naphthol, MY) have been studied. To provide statistically reliable results, 5 batches per each growth condition have been prepared. Growth results have been analyzed in terms of: (i) number of single-crystals, (ii) number of poly-crystals, (iii) size of the crystals (iv) surface topography. Results have been rationalized based on thermodynamics, allowing to find the best growth conditions with respect to desired applications (like X-rays detection).

Resume : High demands of electronic appliances lead to increasing amounts of electronic wastes (E-wastes) that threaten the living organism by polluting the water, soil, and even the air. One potential way to reduce the accumulation of E-wastes is to use material that can be fully or partially naturally degraded or decomposed. Some organic materials have demonstrated their capabilities to accommodate this need. In this study, we introduce chitosan (i.e., a renewable polysaccharide) obtained from deacetylation of chitin and natural rubber (extracted from rubber tree) as substrate and dielectric materials for organic thin film transistors (OTFTs). By looking over the advantages of these biocompatible and biodegradable materials, we fabricated eco-friendly OTFT devices using organic semiconductor PTCDI-C8 and bilayer PVPy/NR and chitosan/NR as gate dielectric materials. The chitosan/NR device exhibited hysteresis free and low voltage performance, and it was found to give an electrical response in the presence of DNA with different concentrations. Moreover, chitosan possessed high transparency and good mechanical properties, and it could be easily casted to form a transparent flexible substrate. Finally, a disposable OTFT device fabricated with PVPy/NR as a dielectric material on chitosan substrate exhibited carrier mobility of 0.14 cm2V–1s–1, Vth of 0.8 V and 103 on/off ratio. The dielectric properties of bilayer films, along with OTFT device performance and sensing mechanism will be discussed.

Resume : In the last years inkjet printing (IJp) has become a very important technology for creating flexible devices for electronics, due to its simplicity, low cost and high precision. One of the currently main prospected applications of IJp is the fabrication of organic electronics-based devices [1]. TIPS-pentacene (TIPS) is one of the most promising materials for organic electronics, because of its excellent semiconducting behavior, which is comparable to that of hydrogenated amorphous silicon[2-3]. Here we report over IJp of solutions precursors to TIPS macroscopic single crystals (SCs), obtained from a single solvent ink. In particular, we will show that: - It is possible to print solutions able to originate SCs onto interdigitated electrodes, exploiting IJp fluorinated SAMs (f-SAMs) as an ink-containing corral; - Working in appropriate conditions it is possible to obtain oriented crystals; - The "printed" crystals have good electrical connection with the underlying electrodes; - The printed crystals can be used in X-rays direct detectors. [1] A. Teichler et al., J. Mater. Chem. C, 2013,1, 1910 [2] Do Hwan Kim et al., Adv. Mater., 19, 2007, 678–682 [3] S. K. Park et al., Appl. Phys. Lett., 2007, 91, 063514

Resume : The detection of ionizing radiations over large areas is crucial for different applications including national security, biological and nuclear research. Inorganic materials are suitable for applications in biomedical fields were sensors dimensions are relatively small. When large areas are needed, the fabrication costs are generally prohibitive, due to the expensive growth methods for inorganic materials. For these applications, organic electronics is attracting a rising interest in the scientific community thanks to its peculiarities, such as low costs for large area fabrication over flexible, light-weighted substrates. In the last years, significant steps forward were made for organic sensors, but less has been done for the development of all organic electronics systems, and the readout of organic X Rays sensors is generally made by means of standard, inorganic electronic circuitries. Here, we report on an organic X Rays sensing system fabricated onto a flexible plastic substrate and working at low voltages, thus allowing battery operation. The core of the system is an organic, thin-film X Rays sensor; a transistor network is responsible for its polarization. The sensor response is employed to trigger the status of a latch composed by organic transistors and printed resistors, capable to perform long time memorization of the X Rays exposure. The status of the memory can be finally used for driving a transistor, whose current level allows an easy read out of the system.

Resume : This seminar introduces three recent progresses that can extend the application of self-powered flexible inorganic electronics. The first part will introduce self-powered flexible piezoelectric energy harvesting technology. Energy harvesting technologies converting external sources (such as vibration and bio-mechanical energy) into electrical energy is recently a highly demanding issue. The high performance flexible thin film nanogenerator was fabricated by transferring the perovskite thin film from bulk substrates for self-powered biomedical devices such as pacemaker and brain stimulation. The second part will introduce flexible electronics including large scale integration (LSI) and high density memory. Flexible memory is an essential part of electronics for data processing, storage, and radio frequency (RF) communication. To fabricate flexible large scale integration and fully functional memory, we integrated flexible single crystal silicon transistors with 0.18 CMOS process and memristor devices. The third part will discuss the flexible GaN/GaAs LED for implantable biomedical applications. Inorganic III-V light emitting diodes (LEDs) have superior characteristics, such as long-term stability, high efficiency, and strong brightness. Our flexible GaN/GaAs thin film LED enable the dramatic extension of not only consumer electronic applications but also the biomedical devices such as biosensor or optogenetics. Finally, we will discuss laser material interaction for flexible and nanomaterial applications. Laser technology is extremely important for future flexible electronics since it can adopt high temperature process on plastics, which is essential for high performance electronics, due to ultra-short pulse duration. (e.g. LTPS process over 1000 °C) We will explore our new exciting results of this field from both material and device perspective.

Resume : Printable electronics allows for moving beyond mass-fabrication of sensors. We propose a new approach for personalized sensors: End-users design and print sensor surfaces of custom geometries. This enables highly personalized solutions, as required for the Internet-of-Things and for wearable computing. For instance, sensor surfaces can be tailored to fit within the physical context of use or can be tailored to fit an individual user’s anatomy. This presentation will focus on two key aspects that are indispensable for the end-user fabrication of printable electronics: 1) Easy-to-use and inexpensive printing processes, and 2) design principles that let end-users create personalized designs at a high level, abstracting from circuitry and the sensor’s inner workings. Based on these principles, we will demonstrate how end-users can realize flexible multi-touch sensor surfaces and touch-displays of custom geometry as well as personalized sensors that are integrated into 3D objects. Our contributions enable new applications for interactive paper, packaging, smart objects, and wearable computing.

Resume : A partial etching mechanism is proposed to meet the requirement for low-visibility patterning of silver nanowire (AgNW)-based transparent conductive electrodes (TCEs) by reducing the difference in optical properties between conductive and nonconductive regions of the pattern. Using the finite difference time domain (FDTD) method, etched geometries that provide the smallest difference in transmittance after etching are theoretically determined. A sodium hypochlorite-based etchant capable that allows the etched geometry to be varied by controlling the pH is used to create a low-visibility pattern with a transmittance and haze difference of 0.07 and 0.04%, respectively. To the best of our knowledge, this is the first time that a partial etching mechanism such as this has been studied in relation to AgNW-based TCEs. Moreover, the TCE composite films with the high refractive index metal oxide nanosheets as the undercoating layer of AgNWs are suggested. The proposed two step partial etching process can result in the low diffuse reflection difference of 0.003% after patterning.

Resume : Inkjet or screen printing of silver nanoparticles on thin polymeric substrates is a versatile and promising technique for depositing highly electrically conductive interconnection lines for flexible electronics sensors. In order to ensure the reliability of such systems, a thorough knowledge of the mechanical stress induced failure mechanisms in the metallic layer is required. This work intends to investigate the cracking and delamination failure mechanisms. The studied samples consist of silver nanoparticles layers with a thickness between 500 nm and 9 µm deposited on 100 µm thick polyimide substrates (Kapton®) and followed by an annealing step at 150°C during 1 h. The mechanical induced failure experiments are performed on a tensile testing device. The samples are deformed up to 20 % strain. A combination of FIB slices and SEM images of tensile tested specimens allow the understanding of the cracking mechanism from initiation to propagation ending by the film delamination. Potential resulting buckling delamination is followed by in situ measurements. These identified mechanisms are modeled by finite element modeling with cohesive zone elements. Adhesion energy between the film and the substrate is then deduced from these simulations.

Resume : Semiconducting single-walled carbon nanotubes (sSWNTs) remain at the forefront of the most prospective materials for electronic device applications "beyond Moore`s law", despite the emergence of many other competing materials, including graphene, and the other graphene-like semiconductors. Their 1D nature appears as the most suitable structure to support the current advancement goals of post-silicon-electronics, i.e. nm dimensions (ultrathin body) allowing high device density and gating them all-around. One greatest challenge for the use of sSWNTs in flexible electronic devices is on how to completely separate and purify them from the metallic species that come together during their synthesis. In this talk, the progress on the separation and purification of sSWNTs using conjugated polymer wrapping will be extensively explained. Polymer selections and optimization of process parameters to obtain pure sSWNTs with controlled diameters will be briefly introduced. The demonstration of high performance FETs of both networks and individual of the polymer-wrapped sSWNTs will be shown, in which combination of both high on/off ratio and high mobility in ambipolar devices are achieved. These demonstrations, together with their solution-processability, have strong implication for their utilization for flexible electronics (e.g. sensors, photovoltaics and thermoelectrics). In the end, the peculiar charge carrier transport mechanism in polymer-wrapped sSWNTs networks will be discussed.

Resume : Healthcare applications of wearable and smart sensors which can monitor human health conditions noninvasively with function of wireless transmission have attracted substantial interests due to the capability of direct detection of biomarkers contained in body fluids. However, the transparent and stretchable sensors integrated on the biomaterials are not yet been realized. In this talk, we presented a multifunctional sensor for human disease diagnosis based on a RLC circuit, where R (resistance) responds to molecular binding of biomarkers in the body fluid while L (inductive) and C (capacitance) change in accordance with structural changes of capacitance materials induced by varying pressure. This device based on hybrid nanostructures using two-dimensional graphene and one-dimensional metal nanowire exhibited high transparency, superb stretchability, and hence enabled the device to be fittable on biomaterials with wireless sensing capability. Furthermore, in-vivo and ex-vivo tests demonstrated its reliable operation. The advance of these electronics using hybrid structures provides a route towards future electronics.

Resume : Recent advance in wearable electronics has contributed to the rapidly increasing interest for the Internet of Things (IoTs) that can consistently monitor signals. For realization of IoTs, the devices should possess sufficient stretchability to attach conformably to any nonplanar objects. In addition, optical transparency is also required to improve the natural look of the devices. In this regard, the conventional transparent conductor must be substituted by stretchable transparent electrodes for wearable devices. For this purpose, we chose metal nanowires (mNW)-graphene hybrid nanostructures due to their superb electrical conductivity (<30 Ω/sq), transparency (>90%), and stretchability. As another key function of IoTs, the wearable devices are required to accompany wireless communication systems for consistent monitoring. For this function, sensors should always transmit acquired data to users for interaction. Here, we report the realization of stretchable graphene sensors based on the silver nanowire-graphene hybrid nanostructures. The device shows high stretchability and transparency while maintaining their sensing capability for the simulant of nerve agent (dimethyl methylphosphonate). The fabricated sensors show outstanding sensing parameters (e.g., sensitivity and recovery, etc.). Furthermore, in order to realize IoTs which can monitor environments continuously, we integrated the sensors with wireless communication systems (Bluetooth and inductive antennas). The integrated sensors also retain high sensing performances on the nonplanar objects (e.g., leaves of live plant). We believe that the realization of wearable and wireless gas sensors suggests a promising strategy toward IoT devices.

Resume : Strain sensors for human health monitoring are of paramount importance in wearable medical diagnostics and personal health monitoring. Despite extensive studies, strain sensors with both high durability and stretchability are still desired, particularly with the stability for different environmental conditions. Here we report a series of strain sensors possessing the graphene network with a high density of intermittent physical interconnections, which produces the relative resistance change by varying the overlap area between the neighboring graphene sheets under stretching and releasing, analogous to the slide rheostat working in electronics. Our in-situ transmission electron microscope observation reveals the full recoverability of the structure from large deformation upon unloading for ensuring the exceptional cycability of our material on monitoring full-range body movements, which has not been achieved by any conventional graphene-based strain sensors before. The stable response is also demonstrated over wide temperature range and frequency range, since the peculiar dynamic structure can be maintained through the self-adjustment to the thermal expansion of the bulk material. Based on the working mechanism of graphene “slide rheostat”, the sensing properties of the strain sensor are tailored by tuning the graphene network structure with different mass densities using different concentration of graphene oxide dispersion, while the stretchability and sensitivity can be separately optimized for different application requirements.

Resume : 1. INTRODUCTION The goal of creating an artificial skin capable of monitoring medical conditions, for instance with electrodes placed directly on patient’s skin or on the heart, requires ultra-thin, flexible, stretchable, conformable and bio-compatible electronics [1, 2]. Furthermore, the biological signals are relatively weak and often need further electrical amplification [3]. The use of hard, thick and inflexible inorganic electronics presents a challenge for soft, oddly shaped, and very porous human bodies and organs, as these electronics have to be embedded in soft organic materials before implantation [4]. Organic electronics promises to fulfil all of the aforementioned constraints without the need of additional encapsulation, resulting in much thinner, flexible, and conformal devices [5]. The bending thickness, and subsequently the conformity, of a thin film is proportional to its thickness cubed [6]. Decreasing the total thickness of the electronics therefore significantly reduces the bending stiffness making the devices much more conformal to the organ’s surface roughness, allowing for more accurate, as well as more comfortable, monitoring of biological signals. Amplifying a signal closer to the source typically leads to a higher signal-to-noise ratio, requiring ultra-thin-film amplifiers, to be deployed, for instance, on the skin or on the brain [3]. We will review past achievements of our group, including the fabrication of ~2 µm thin electronics, such as polymer transistors, polymer light emitting diodes, organic solar cells, and magneto-electronics. We will also present more recent successes, including flexible temperature and pressure sensors, as well as multi-element integration of a photonic e-skin and thin and flexible organic amplifiers. We will discuss the fabrication of the world’s thinnest, sub-300-nm e-skin, fit with transistors, tactile sensors, as well as pseudo CMOS and CMOS amplifiers. Finally, stretchable conductors, integrated with a flexible EMG matrix, will be presented. 2. ACHIEVEMENTS 2.1 Past achievements We have, in the past fabricated an array of thin and flexible organic field effect transistors (OFETs), with DNTT as the active material [7]. Fabricated directly on 1 µm PEN substrate, these electronic circuits were ultra-light, with a bending radius of ~5 µm, and capable of flexing on 230% pre-stretched elastomer. Active matrix array of OFETs, matched with tactile, bolometer, and temperature sensors, was demonstrated. Organic Photovoltaic (OPV) cells, fabricated on 1.4-μm-thick PET, were shown [8]. With PET/PEDOT:PSS/P3HT:PCBM/Ca/Ag architecture, these devices were capable of 80% compression rate and a bending radius of less than 35 µm, with FF of 71%, JSC of 12 mA/cm2, and power conversion of 4.2%. Red and orange polymer light emitting diodes (PLEDs), fabricated on 1.4-μm-thick PET, were revealed [9]. With device architecture of PET/PEDOT:PSS/AnE-PVstat/LiF/Al, devices showed luminance >100 cd/m2, bending radius of ~10 μm, and stretch-compatibility of 100% tensile strain. Flexible (bending radii <3 μm) and lightweight magneto-resistive sensors were fabricated with a total thickness of ~2 μm [10]. Based on multilayers of Co/Cu or Py/Cu, they were shown capable of reaching strains of >270% and enduring over 1,000 cycles without fatigue. 2.2 Temperature and pressure sensor The ability to monitor parameters, such as temperature and pressure, is essential in the healthcare industry. Physically flexible and conformal sensors allow for more accurate monitoring, which is also less intrusive to the patient. To this end, more recently we have fabricated flexible and printable temperature sensor [11]. Based on semi-crystalline acrylate polymers and graphite, this ultra-sensitive sensor (0.02 °C) has a tunable sensing range of 25 °C to 50 °C, fast response time of <100 ms, low bending radius of <700 μm, and a high repeatability of 1800 times. Its utility was demonstrated with in vivo measurement of temperatures changes of a rat lung during breathing. We showed a high transparency and high pressure sensitive sensor that measures only the normal pressure, even under extreme bending conditions [12]. Based on composite nanofibers of carbon nanotubes and graphene, sensor with the bending radii of ~80 μm, and a response time of 20 ms, was achieved. To test its utility, we showed an integrated sensor matrix that was only 2 μm thick. 2.4 Photonic skin and organic amplifiers The ability to measure and display is often taken for granted in standard, thick and bulky electronics. However, while extremely useful, such functionalities are immensely difficult to achieve on the same ultrathin substrate. Ultraflexible organic photonic optoelectronic or OE-skin was fabricated [13]. At about 3 μm thin, with bending radii of 100 μm and tensile strain up to 200%, the OE-skin was fit with tri-color (red, green, and blue) PLEDs and OPVs, and subsequently laminated on human skin. The OE-skin was laminated on a human finger, and used to make a reflective pulse oximeter, to measure and display blood oxygen level. Measuring relatively weak biological signals often requires electrical amplification. We showed e-skin based on highly conductive gel composite comprising of multi-walled carbon nanotube-dispersed sheet with an aqueous hydrogel (admittance of 100 mS/cm2), and ultrathin and mechanically flexible organic active matrix amplifier on a 1.2- μm-thick PEN film, capable of amplifying (up to 46 dB) weak bio-signals [14]. Implantation onto a rat’s heart, for 4 weeks, resulted in low foreign-body reaction (as compared to metal electrodes). 2.6 Sub-300-nm e-skin The bending stiffness, and conformability of a film is proportional to its thickness. To achieve electronics capable of conforming to surface of arbitrary roughness, we have created a world’s thinnest, sub-300-nm thin, including the substrate and encapsulation layers, e-skin. Fit with tactile sensors and organic transistors (parylene/Au/parylene/DNTT/Au/parylene), this e-skin is also the world’s lightest, weighting less than 0.7 g/m2 [15]. Fabricated on a glass substrate, the film was manually delaminated followed by immersion in water. The e-skin can be repeatedly bent to radii less than 2 µm and accommodate repeated stretching (100 times) on a 60% pre-stretched elastomer, while retaining its good electrical characteristics (VDS = -5 V; µ = 0.35 cm2/Vs; ON/OFF ratio ~105; VT = -1.72 V). Biocompatibility of this e-skin was demonstrated by deposition on a human skin without any noticeable irritability. To fully realize the potentials of this ultra-thin and ultra-light e-skin in healthcare and biomedical fields, we have fabricated sub-300-nm thin pseudo-CMOS and CMOS amplifiers. With an operating voltage of 5 volts, the pseudo-CMOS amplifiers showed a maximum gain of up to 37 dB. CMOS amplifiers (PDI-8CN2 as the active n-type material) were fabricated into a multistage arrangement (up to five cascaded stages), with a maximum gain calculated of up to 79 dB. Both, the pseudo-CMOS and CMOS amplifiers were subjected to physical deformation (100 times) on a 50% pre-stretched elastomer, and showed to retain their high electrical performance. 2.7 Stretchable conductors With wearable electronics in mind, we have developed a printable elastic conductor with a high initial conductivity of 738 S/cm and a record high conductivity of 182 S/cm when stretched to 215% strain [16]. This elastic conductor ink was formulated from Ag flakes, a fluorine rubber and a fluorine surfactant, with the surfactant being a key component in the high conductivity and stretchability. Its utility was demonstrated with fabrication of a stretchable organic transistor active matrix on a rubbery stretchability-gradient substrate, with unimpaired functionality when stretched to 110%, and a wearable EMG sensor printed onto a textile garment. REFERENCES 1. Mühl, S. and B. Beyer, Bio-Organic Electronics—Overview and Prospects for the Future. Electronics, 2014. 3(3): p. 444. 2. Gibney, E., The Body Electric; The inside story on wearable electronics. Nature, 2015. 528: p. 26-28. 3. Viventi, J., et al., Flexible, foldable, actively multiplexed, high-density electrode array for mapping brain activity in vivo. Nat Neurosci, 2011. 14(12): p. 1599-1605. 4. Hwang, G.-T., et al., In Vivo Silicon-Based Flexible Radio Frequency Integrated Circuits Monolithically Encapsulated with Biocompatible Liquid Crystal Polymers. ACS Nano, 2013. 7(5): p. 4545-4553. 5. Irimia-Vladu, M., et al., Green and biodegradable electronics. Materials Today, 2012. 15(7–8): p. 340-346. 6. Kim, D.-H., et al., Dissolvable films of silk fibroin for ultrathin conformal bio-integrated electronics. Nat Mater, 2010. 9(6): p. 511-517. 7. Kaltenbrunner, M., et al., An ultra-lightweight design for imperceptible plastic electronics. Nature, 2013. 499(7459): p. 458-463. 8. Kaltenbrunner, M., et al., Ultrathin and lightweight organic solar cells with high flexibility. Nat Commun, 2012. 3: p. 770. 9. White, M.S., et al., Ultrathin, highly flexible and stretchable PLEDs. Nat Photon, 2013. 7(10): p. 811-816. 10. Melzer, M., et al., Imperceptible magnetoelectronics. Nat Commun, 2015. 6. 11. Yokota, T., et al., Ultraflexible, large-area, physiological temperature sensors for multipoint measurements. Proceedings of the National Academy of Sciences, 2015. 112(47): p. 14533-14538. 12. Lee, S., et al., A transparent bending-insensitive pressure sensor. Nat Nano, 2016. 11(5): p. 472-478. 13. Yokota, T., et al., Ultraflexible organic photonic skin. Science Advances, 2016. 2(4). 14. Sekitani, T., et al., Ultraflexible organic amplifier with biocompatible gel electrodes. Nat Commun, 2016. 7. 15. Nawrocki, R.A., et al., 300-nm Imperceptible, Ultraflexible, and Biocompatible e-Skin Fit with Tactile Sensors and Organic Transistors. Advanced Electronic Materials, 2016. 2(4). 16. Matsuhisa, N., et al., Printable elastic conductors with a high conductivity for electronic textile applications. Nat Commun, 2015. 6.

Resume : Electronics of tomorrow will be imperceptible and will form a seamless link between soft, living beings and the digital world. This new form of ultra-conformable electronics places severe physical requirements on the active components that constitute modern foil-like electronic systems. Weight and flexibility become key figures of merit for large area electronics such as robotic skin, as they critically influence the mechanical response and perception of the artificial sensory system. With less than 2 μm total thickness, imperceptible electronic foils are light (≈3-5 g m-2) and unmatched in flexibility, they are operable with radii of curvature below 5 µm, yet highly durable and withstand severe crumpling without any performance degradation. These are prerequisites for intimate contact with soft, biological tissue or organs and complex, arbitrarily shaped 3D free forms that enable applications spanning medical, safety, security, infrastructure, and communication industries. This talk introduces a technology platform for the development of large-area, ultrathin and lightweight electronic and photonic devices, including solar cells[1,2], light emitting diodes[3] and photodetectors[4] active-matrix touch panels[5], implantable organic electronics[6,7], imperceptible electronic wraps[8] and “sixth-sense” magnetoception[9] in electronic skins. Solar cells, less than 2 µm thick, endure extreme mechanical deformation and have an unprecedented power output per weight of 23 W/g. Highly flexible, stretchable organic light emitting diodes are combined with photodetectors for on-skin photonics and pulse oximetry, providing electrical functionality in yet unexplored ways. Tactile sensor arrays based on active-matrix organic thin film transistors can be operated at elevated temperatures and in aqueous environments as an imperceptible sensing system that ensures the smallest possible discomfort for patients requiring medical care and monitoring. Combined with organic amplifiers and biocompatible hydrogels, we demonstrate in vivo recording of vital signals. E-skins with GMR-based magnetic field sensors equip the wearer with an unfamiliar sense that enables perceiving of and navigating in magnetic fields. These large area sensor networks build the framework for electronic foils and artificial sensor skins that are not only highly flexible but become highly stretchable and deployable when combined with engineered soft substrates such as elastomers, shape memory polymers or tissue-like hydrogels. References [1] M. Kaltenbrunner et al, Nature Communications 3:770, 1-7 (2012) [2] M. Kaltenbrunner et al, Nature Materials 14, 1032-1039 (2015) [3] M. White et al, Nature Photonics 7, 811–816 (2013) [4] T. Yokota et al, Science Advances 2:e1501856 (2016) [5] M. Kaltenbrunner et al, Nature 499, 458-464 (2013) [6] T. Sekitani et al, Nature Communications 7:11425 (2016) [7] J. Reeder et al, Advanced Materials 26, 4967-4973 (2014) [8] M. Drack et al, Advanced Materials 27, 34-40 (2015) [9] M. Melzer et al, Nature Communications 6, 1-8 (2015)

Resume : The development of mechanically deformable and thin electronics offers a platform for a variety of exciting new applications through conformal contact to the skin. However a major challenge in achieving a wireless system, is the delivery of electrical power and communication. Near field communication (NFC) is a suitable technology offering wireless power transfer as well as communication capabilities on widely available platforms such as smartphones. Here we present strategies of integrating such an NFC system into an epidermal and fingernail platform allowing for a battery free operation. Mechanical design considerations are made to match the mechanical properties of the electrical system to the human epidermis resulting in conformal contact[1]. Furthermore we demonstrate a miniaturization of such a system to allow for the integration onto a fingernail[2]. Experimental and Finite Element Analysis characterization of the devices is employed to demonstrate electrical and mechanical robustness resulting in uninterrupted operation during daily activities. Additionally we demonstrate the capability of supporting sensor systems which allows for the acquisition of vital signs data. [1] J. Kim, A. Banks, H. Cheng, Z. Xie, S. Xu, K. I. Jang, J. W. Lee, Z. Liu, P. Gutruf, X. Huang, Small 2015, 11, 906-12 [2] J. Kim, A. Banks, Z. Xie, S. Y. Heo, P. Gutruf, J. W. Lee, S. Xu, K. I. Jang, F. Liu, G. Brown, Advanced Functional Materials 2015, 25, 4761-7

Resume : Electrochemical devices based on conjugated polymers such as biosensors and ion transistors have received significant attention in bioelectronic applications. In particular, conjugated polymers have been known to be suitable for integration with biological systems since they can be soft, flexible, biocompatible, and both electronically and ionically conductive. In order for successful demonstration of the integrated bioelectronic systems, in vivo implementation of a battery is essential to supply electric power necessary for each iontronic component. Recently, flexible energy harvesters have emerged as a promising alternative to the batteries as they generate sufficient electrical energy to operate such devices. In this work, we demonstrate a high-performance flexible piezoelectric energy harvester consisting of a large-area PZT thin film on a plastic substrate to operate self-powered iontronic devices. A 2 μm thick crystalline PZT film on a rigid sapphire substrate, which was annealed at 650 °C in air for 45 minutes, is successfully transferred onto a flexible polyethylene terephthalate (PET) substrate via laser lift-off (LLO) without any structural damages or material degradation. The flexible PZT energy harvesting devices typically generate an open circuit voltage of ~200 V and a short circuit current of ~8 μA transduced from small mechanical deformation. The electrical output produced from slight bending and unbending motions by human hands charge capacitors and turn on more than 200 commercial blue LEDs. Finally, a self-powered hybrid ionic circuit is implemented with PZT energy harvesters, full-wave bridge rectifiers, energy storage elements, and iontronic devices, such as organic electronic ion pumps (OEIP) and ion bipolar junction transistors (IBJT). During the rectification followed by the energy storage, AC output of the harvester is converted into the DC to charge a 100 μF capacitor up to 5.3 V within ~25 minutes. The stored energy provides electrical current of ~150 nA to the OEIP lasted for ~20 minutes. The self-powered OEIP made of a biocompatible material known as PEDOT:PSS is utilized to precisely deliver acetylcholine (Ach), a neurotransmitter that regulates neuronal cell signaling and controls amyloid reactions, with a rate of ~10 pmol/μC. In addition to the passive components as OEIPs, the stored energy also successfully operates nonlinear components as IBJTs to examine addressability of the substance delivery. With a square wave emitter-base voltage of +/- 1 V, a small ionic base control signal actively modulates a relatively much larger ionic collector output signal.