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Disposable devices designed for single and/or multiple reliable measurements over a short duration have attracted considerable interest recently. However, these devices often use non-recyclable and non-biodegradable materials and wasteful fabrication methods. Herein, we present ZnO nanowires (NWs) based degradable high-performance UV photodetectors (PDs) on flexible chitosan substrate. Systematic investigations reveal the presented device exhibits excellent photo response, including high responsivity (55 A/W), superior specific detectivity (4x1014 jones), and the highest gain (8.5x1010) among the reported state of the art biodegradable PDs. Further, the presented PDs display excellent mechanical flexibility under wide range of bending conditions and thermal stability in the measured temperature range (5–50 °C). The biodegradability studies performed on the device, in both deionized (DI) water (pH≈6) and PBS solution (pH=7.4), show fast degradability in DI water (20 mins) as compared to PBS (48 h). These results show the potential the presented approach holds for green and cost-effective fabrication of wearable, and disposable sensing systems with reduced adverse environmental impact.

Nano/microstructures of compound semiconductors such as gallium arsenide (GaAs) demonstrate enormous potential for advanced photonic technologies as they provide realistic means for miniaturization of optoelectronic devices that feature better performance and low power consumption. However, intimately integrating them onto flexible substrates is challenging and restricts their use in the next generation of applications such as wearables and soft robotics. Herein, printed arrays of well-defined and laterally aligned semi-insulating (undoped) and doped GaAs microstructures are presented to develop high-performance flexible broadband photodetectors. The direct roll transfer printed GaAs microstructures-based photodetectors exhibit excellent performance under ultraviolet and near-infrared illumination, including ultrafast response (2.5 ms) and recovery (8 ms) times, high responsivity (>104 AW–1), detectivity (>1014 Jones), external quantum efficiency (>106), and photoconductive gain (>104) at low operating voltage of 1 V. The achieved performance is among the best reported for broadband photodetectors but with an added benefit of the developed devices having a flexible form factor. Further, the photodetectors show stable performance under mechanical bending (500 cycles) and twisting loading. The developed materials and manufacturing route can enable high-speed communications and computation via high-performance flexible electronics and optoelectronics and transform numerous emerging applications such as wearable systems and internet of things.

The wearable and flexible sensors are enabling advances in next-generation technologies such as soft robotics, mobile healthcare, internet of things etc. In consequence, novel materials and manufacturing methods have received most of the attention so far. However, with the growing use of these technologies in real applications, other important areas such as mechanical reliability under repeated mechanical deformations also require greater consideration. A few studies covering this aspect have mainly focused on mechanical stress under simple bending conditions and ignored stress evolution under twisting (torsional) movements. The present work studies the influence of different parameters such as carrier substrate dimensions and its material and twisting angles on the stress distribution during torsional movements using finite element method. Following this, highly stretchable strain sensors are fabricated using nanocomposite of carbon nanotubes and Ecoflex™ and tested under various twisting angles. The soft strain sensor possesses excellent repeatable and robust torsional strain detection properties with >100% change in resistance at ±90° of twisting and has shown potential for wearable and robotics applications.

Smart textiles can sense different stimuli such as pressure, temperature etc., to allow users to react and adapt. Such features are accomplished through integration of various fiber-based sensors and electronic components in textile structures. Yarn is 1-dimensional structure which can be modified to behave as a sensor and can further be integrated with other sensors or electronics to form smart textile by techniques like weaving, knitting, and braiding. In this work, a flexible temperature sensor is reported by modifying a stainless-steel yarn with V2O5 nanowires. The current profile and temperature sensing performance is measured from 5 to 50 °C. The device exhibits sensitivity of 3.7 %/°C and response time of ~9s. The present work demonstrates the potential of using yarn as a flexible temperature sensor that can be used to realize smart textile for wearable and healthcare applications.

“Heterogeneous Integration” is a promising approach for high-performance hybrid flexible electronics that combine printed electronics and silicon technology. Despite significant progresses made by integrating rigid silicon chips on flexible substrates, the integration of flexible ultra-thin chips (UTCs) on flexible foils remains a challenge as they are too fragile for conventional bonding methods. Reliable interconnects (low-resistivity and mechanical robustness) and bonding of UTCs are critical to the realization of hybrid flexible systems. Herein, using a non-contact printing approach, an easy and cost-effective method for accessing UTCs on flexible foils is demonstrated. The high-viscosity conductive paste, extruded from a high-resolution printer (1–10 µm line width), is used here to connect the metal oxide semiconductor field effect transistors (MOSFETs) on UTCs with the extended pads on flexible printed circuit boards (PCBs). The electrical characterization of MOSFETs, before and after printing the interconnects, reveals an acceptable level of variation in device mobility (change from 780 to 630 cm2 V−1s−1). This is due to the drop in effective drain bias voltage as a marginally small electrical resistance (≈30 Ω) is added by the printed interconnects. The bonded UTCs show robust device performance under bending conditions, indicating high reliability of both the chip thinning and bonding methods.

Innovative methods to fabricate and integrate biodegradable high-grade electronics on green substrates are needed for the next generation of robust high-performance transient electronics. This is also needed to alleviate the growing problem of electronic waste (e-waste). Herein, the authors present the n-channel silicon (Si) nanoribbons-based high-performance transistors developed on biodegradable metal (magnesium) foils using the direct transfer printing method. The developed transistors present high effective mobility of >600 cm2 V−1 s−1, high on/off current ratio (Ion/off) of >104, negligible hysteresis, transconductance of 0.19 mS, and an on-current of 1.6 mA at a bias of 2 V. Further, the transistors show stable device performance under temperature stress (5–50 °C), gate-bias stress, continuous long-term transfer scans for 24 h (>3000 cycles), and aging test (up to 100 days) demonstrating the excellent potential for futuristic high-performance robust transient devices and circuits. Finally, the effect of transience on the electrical functioning of devices on Mg foils (at pH 8) and degradation of Mg foils at different pH values is studied by hydrolysis. The outcome from these experiments demonstrates the potential of direct transfer printing for high-performance transient electronics and also as the new avenue toward zero e-waste.

High-performance flexible electronics developed with resource efficient printing route will transform the way future electronics is manufactured and used to advance applications such as healthcare, Internet of Things, wearables, consumer electronics, etc. Herein, an innovative approach is presented that involves, for the first time, the in-tandem use of contact and transfer printing methods to realize high-quality electronic layers at selected locations on rigid (Si/SiO2), flexible (polyimide), and biodegradable (magnesium (Mg) foils). Superior grade quality of printed electronic layers is demonstrated by realizing transistors and printed UV photodetectors (PDs) employing high-resolution electrohydrodynamic printing. The all-printed PDs show extremely high performance for UV detection, with extraordinary high responsivity (>107A W−1) and specific detectivity (≈1017Jones) values at low UV intensity of 0.1 µW cm−2. Finally, the fabricated PDs on Mg foil are dissolved in deionized water at room temperature. Thus, in-tandem contact and transfer printing has potential for ecofriendly development of transient electronics. Further, the approach allows printing of wide range of nanomaterials and heterostructures or complex superlattice structures, which can open exciting new possibilities for high-performance electronics.

Wearable UV photodetectors (PDs) have attracted interest recently for detection of excess exposure of the skin to the UV radiation. Despite numerous advances made in this direction, many challenges remain, particularly in terms of device reliability under extreme mechanical deformations simultaneously and self-powering, etc. Herein, a self-powered stretchable PD developed with kirigami-inspired honeycomb-patterned zinc oxide (ZnO) nanowires (NWs) and coupled with a triboelectric nanogenerator (TENG) is presented. After studying in detail the influence of ZnO NWs dispersion medium and metal-ZnO NWs contacts, a novel fabrication approach employing the structural engineering on NWs-elastomer composite is used to achieve high stretchability. The fabricated ZnO NWs-based UV PDs, embedded inside kirigami-inspired honeycomb-patterned elastomeric substrate, exhibit unprecedented stretchability (up to 125%) and high-performance with photo/dark current ratio of ≈5 × 105, responsivity of ≈54 A W−1, and a fast recovery time of 100 ms. Further, the stretchable PD is coupled with flexible TENGs to demonstrate a self-powered system for potential application in real-time UV radiation monitoring using advanced wearable healthcare technology.

This paper presents ultrathin chips (UTCs) based flexible tactile sensing system for dynamic contact pressure measurement. The device comprises of an AlN piezocapacitor based UTCs tightly coupled with another UTCs having metal-oxide-semiconductor field-effect transistors (MOSFETs). In this arrangement the AlN piezocapacitor forms the extended gate of MOSFETs. Both AlN piezocapacitor and MOSFET based UTCs are obtained by post-process reduction of wafer thicknesses to ~35μm using backside lapping. The performances of both UTCs were evaluated both before and after thinning and there was no noticeable performance degradation. The UTC-based AlN piezocapacitor exhibited six times higher sensitivity (43.79mV/N) than the thin filmbased AlN sensors. When coupled with MOSFETs based UTC, the observed sensitivity was 0.43N-1. The excellent performance, flexible form factor and compactness shows the potential of presented device in applications such minimal invasive surgical instruments where high-resolution tactile feedback is much needed.

International audience

The present work describes the seedless approach for the growth of ZnO nanowires (NWs) on flexible polyethylene terephthalate (PET) substrates and fabrication of fully flexible ZnO NW based piezoelectric nanogenerators (NGs). The x-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) confirms the high quality of grown nanomaterial. The performance of the fabricated ZnO NW based NG device is measured under a force of 5N at a frequency of 3Hz. A peak output voltage of ~ 950mV is obtained that corresponds to a power density of ~ 1µW/cm 2. Our results clearly demonstrate the interest of ZnO NWs for the development of autonomous micro-nano systems (MNSs).