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.
Abstract 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 cm 2 V −1 s −1 , high on/off current ratio ( I on / off ) of >10 4 , 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.
Abstract The pursuit of miniaturized Si electronics has revolutionized computing and communication. During recent years, the value addition in electronics has also been achieved through printing, flexible and stretchable electronics form factors, and integration over areas larger than wafer size. Unlike Si semiconductor manufacturing which takes months from tape‐out to wafer production, printed electronics offers greater flexibility and fast‐prototyping capabilities with lesser resources and waste generation. While significant advances have been made with various types of printed sensors and other passive devices, printed circuits still lag behind Si‐based electronics in terms of performance, integration density, and functionality. In this regard, recent advances using high‐resolution printing coupled with the use of high mobility materials and device engineering, for both in‐plane and out‐of‐plane integration, raise hopes. This paper focuses on the progress in printed electronics, highlighting emerging printing technologies and related aspects such as resource efficiency, environmental impact, integration scale, and the novel functionalities enabled by vertical integration of printed electronics. By highlighting these advances, this paper intends to reveal the future promise of printed electronics as a sustainable and resource‐efficient route for realizing high‐performance integrated circuits and systems.
Large-area printed electronics has garnered considerable attention owing to advantages such as low-cost and resource efficiency. Thin films of various organic, inorganic and/or metal oxide materials have been reported in literature along with single gate transistors based on them. Advancing this further, we report here printed dual-gate transistors, which can open new opportunities for implementation of energy efficient neuromorphic electronics. The dual-gate transistor presented here is based on contact printed ZnO nanowires as a channel material. The electrical characterizations, for both top- and bottom-gated transistors confirms excellent channel control, giving peak field-effect mobility of 12 cm 2 /Vs (top-gate) and 5 cm 2 /Vs (bottom-gate) and high on/off current modulation ratio (I on/off ) of >10 5 for both gates. The dual-gate transistors have the capability to tune/adjust their threshold voltage, which can be used for learning process and hence to build with minimal resources the next generation of neuromorphic-based computing hardware.
Abstract Flexible hybrid electronics (FHE) is an emerging area that combines printed electronics and ultra‐thin chip (UTC) technology to deliver high performance needed in applications such as wearables, robotics, and internet‐of‐things etc. The integration of UTCs on flexible substrates and the access to devices on them requires high resolution interconnects, which is a challenging task as thermal and mechanical mismatches do not allow conventional bonding methods to work. To address this challenge, the resource‐efficient, area‐efficient, and low‐cost printing routes for obtaining vertical interconnection accesses (VIAs) are demonstrated here. It is demonstrated how high‐resolution printers (electrohydrodynamic and extrusion‐based direct‐ink writing printers) can be used for patterning of high‐resolution, freeform, vertical conductive structures. To access the transistors on UTCs, the VIAs, obtained using conventional photolithography and plasma etching steps, are filled with conductive silver nanoparticle‐based ink/paste using high‐resolution printers. Comprehensive studies are performed to compare and benchmark in terms of: i) the printing speed and throughput of the printers, ii) the electrical performance of vertically connected transistors in UTCs, and iii) the electrical performance stability of FHE system (interconnects and UTCs) under mechanical bending conditions. This in‐depth study shows the potential use of printing technologies for development of high‐density 3D integrated FHE systems.
Printing is a promising method for the large-scale, high-throughput, and low-cost fabrication of electronics. Specifically, the contact printing approach shows great potential for realizing high-performance electronics with aligned quasi-1D materials. Despite being known for more than a decade, reports on a precisely controlled system to carry out contact printing are rare and printed nanowires (NWs) suffer from issues such as location-to-location and batch-to-batch variations. To address this problem, we present here a novel design for a tailor-made contact printing system with highly accurate control of printing parameters (applied force: 0-6 N ± 0.3%, sliding velocity: 0-200 mm/s, sliding distance: 0-100 mm) to enable the uniform printing of nanowires (NWs) aligned along 93% of the large printed area (1 cm2). The system employs self-leveling platforms to achieve optimal alignment between substrates, whereas the fully automated process minimizes human-induced variation. The printing dynamics of the developed system are explored on both rigid and flexible substrates. The uniformity in printing is carefully examined by a series of scanning electron microscopy (SEM) images and by fabricating a 5 × 5 array of NW-based photodetectors. This work will pave the way for the future realization of highly uniform, large-area electronics based on printed NWs.
The integration of high mobility inorganic materials such as silicon (Si) and gallium arsenide (GaAs) onto flexible substrates is a challenging yet crucial step for the development of high-performance flexible electronics. The development of such integration technologies could also lead to hybrid and heterogeneous integration. Herein, we present 'direct roll transfer printing (DRTP)' - the roll-based manufacturing platform – that allows integration of nano to micro scale structures of inorganic semiconductors onto wide variety of substrates and their subsequent processing leading to different type of devices. The DRTP is used here to develop Si and GaAs nano/microstructures based flexible photosensors. The extensive characterisation of these photosensors shows excellent response of Si nanomembranes (NMs) based device in visible-ultraviolet (UV)-near infrared (NIR) light illumination. The high-speed response (rise time τ Rise = 205μs and fall time τ Fall = 200 μs), and a peak responsivity of 2.48 A/W to UV light at zero bias voltage show the exceptional self-powered operation of these sensors. The printed GaAs based photosensors operate at low voltage (1V) and show high-speed response (rise time (2.5 ms) and recovery time (8 ms)), and high responsivity (>10 4 AW –1 ) under UV-NIR light illumination. These results demonstrate the versatility of DRTP approach towards printing of different types of inorganic semiconductors for hybrid and heterogeneous integration of high-performance flexible electronics.
Abstract The photovoltaic devices offer promising eco‐friendly solution for self‐powered flexible electronics. However, their fabrication on flexible substrate is not easy due to mismatches between the requirements of conventional microfabrication and the thermal, and mechanical features of the substrates. Herein, direct roll printed nanoscale photoactive electronic layers are presented, which are further processed to develop ≈315 µm 2 sized miniaturized photovoltaic microcells. Using a set of 32 microcells, connected in parallel configuration, indoor light harvesting is shown at a maximum power density of ≈10 µW cm −2 under white LED illumination. Further, the dual functionality of developed microcells i.e., energy harvesting as well as wideband photodetection is demonstrated. As self‐powered photo sensors the developed photovoltaic microcells exhibit distinctive photo responses under white LED‐UV (365 nm)‐ NIR (850 nm) light illumination, with exceptionally high‐speed response (rise time τ Rise = 205 µs and fall time τ Fall = 2000 µs), and a peak responsivity of 2.48 A W −1 to UV light at zero bias voltage. The presented results show the potential usage of printed multifunctional photovoltaic microcells in a wide variety of applications such as self‐powered wearable and flexible electronic systems for health monitoring and indoor robotics.
Large area electronics (LAE) with the capability to sense and retain information are crucial for advances in applications such as wearables, digital healthcare, and robotics. The big data generated by these sensor-laden systems need to be scaled down or processed locally. In this regard, brain-inspired computing and in-memory computing have attracted considerable interest. However, suitable architectures have mainly been developed using costly and resource-intensive conventional lithography-based methods. There is a need for the development of innovative, resource-efficient fabrication routes that enable such devices and concepts. Herein, we present ZnO nanowire (NW)-based memristors on a polyimide substrate fabricated by a LAE-compatible and resource-efficient route comprising solution processing and printing technologies. High-resolution "drop-on-demand" and "direct ink write" printers are employed to deposit metallic layers (silver and gold) and a ZnO seed layer, needed for the site-selective growth of ZnO NWs via a low-cost hydrothermal method. The printed memristors show high bipolar resistance switching (ON/OFF ratio >103) between two nonvolatile states and consistent switching at ultralow voltages (all devices showed switching at amplitudes <200 mV), with the best performing device showing consistent cycled resistance switching over 4 orders of magnitude with SET and RESET voltages of about 71 and −57 mV, respectively. Thus, the presented devices offer reliable high resistance switching at the lowest reported voltage for printed memristors and prove to be competitive with many conventional nanofabrication-based devices. The presented results show the potential printed memristors technology holds for large-area, low-voltage sensing applications such as electronic skin.
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