Graphene and Liquid Metal Integrated Multifunctional Wearable Platform for Monitoring Motion and Human-Machine Interfacing

Motion sensors are an essential component of many electronic systems. However, the development of inertial motion sensors based on fatigue-free soft proof mass has not been explored extensively in the field of soft electronics. Nontoxic gallium-based liquid metals are an emerging class of material that exhibit attractive electromechanical properties, making them excellent proof mass materials for inertial sensors. Here, we propose and demonstrate a fully soft laser-induced graphene (LIG) and liquid metal-based inertial sensor integrated with temperature, humidity, and breathing sensors. The inertial sensor design confines a graphene-coated liquid metal droplet inside a fluidic channel, rolling over LIG resistive electrode. The proposed sensor architecture and material realize a highly mobile proof mass and a vibrational space for its oscillation. The inertial sensor exhibits a high sensitivity of 6.52% m^-1 s² and excellent repeatability (over 12 500 cycles). The platform is fabricated using a scalable, rapid laser writing technique and integrated with a programmable system on a chip (PSoC) to function as a stand-alone system for real-time wireless monitoring of movement patterns and the control of a robotic arm. The developed printed inertial platform is an excellent candidate for the next-generation of wearables motion tracking platforms and soft human-machine interfaces.

Ultrasensitive Flexible κ-Phase Ga2O3 Solar-Blind Photodetector

Flexible Ga₂O₃ photodetectors have attracted considerable interest owing to their potential use in the development of implantable, foldable, and wearable optoelectronics. In particular, β-phase Ga₂O₃ has been most widely investigated due to the highest thermodynamic stability. However, high-quality β-phase Ga₂O₃ relies on the ultrahigh crystallization temperature (usually ≥750 °C), beyond the thermal tolerance of most flexible substrates. In this work, we epitaxially grow a high-quality metastable κ-phase Ga₂O₃ (002) thin film on a flexible mica (001) substrate under 680 °C and develop a flexible κ-Ga₂O₃ thin film photodetector with ultrahigh performance. Epitaxial κ-Ga₂O₃ and the mica substrate are maintained to be thermally stable up to 750 °C, suggesting their potential for harsh environment applications. The responsivity, on/off ratio, detectivity, and external quantum efficiency of the fabricated photodetector are 703 A/W, 1.66 × 10⁷, 4.08 × 10¹⁴ Jones, and 3.49 × 10⁵ %, respectively, for 250 nm incident light and a 20 V bias voltage. These values are record-high values reported to date for flexible Ga₂O₃ photodetectors. Furthermore, the flexible photodetector shows robust flexibility for bending radii of 1, 2, and 3 cm. More importantly, it shows strong mechanical stability against 10,000 bending test cycles. These results reveal the significance of high-quality κ-phase Ga₂O₃ grown heteroepitaxially on a flexible mica substrate, especially its potential for use in future flexible solar-blind detection systems.

Quasi-Epitaxial Growth of β-Ga2O3-Coated Wide Band Gap Semiconductor Tape for Flexible UV Photodetectors

The epitaxial growth of technically important β-Ga₂O₃ semiconductor thin films has not been realized on flexible substrates due to the limitations of high-temperature crystallization conditions and lattice-matching requirements. We demonstrate the epitaxial growth of β-Ga₂O₃(-201) thin films on flexible CeO₂(001)-buffered Hastelloy tape. The results indicate that CeO₂(001) has a small bi-axial lattice mismatch with β-Ga₂O₃(-201), inducing simultaneous double-domain epitaxial growth. Flexible photodetectors are fabricated on the epitaxial β-Ga₂O₃-coated tape. Measurements reveal that the photodetectors have a responsivity of 4 × 10⁴ mA/W, with an on/off ratio reaching 1000 under 254 nm incident light and 5 V bias voltage. Such a photoelectrical performance is within the mainstream level of β-Ga₂O₃-based photodetectors using conventional rigid single-crystal substrates. More importantly, it remained robust against more than 20,000 bending test cycles. Moreover, the technique paves the way for the direct in situ epitaxial growth of other flexible oxide semiconductor devices in the future.

Ultraflexible Corrugated Monocrystalline Silicon Solar Cells with High Efficiency (19%), Improved Thermal Performance, and Reliability Using Low-Cost Laser Patterning

Flexible solar cells have received growing attention recently because of their ever-increasing range of applications. Here, the development of ultraflexible, lightweight, and high efficiency (19%) monocrystalline silicon solar cells with excellent reliability, mechanical resilience, and thermal performance is demonstrated by applying a corrugation method combined with laser patterning. The flexing mechanism converts large-scale rigid photovoltaic cells with interdigitated back contacts (IBCs) into a flexible version with a preserved efficiency. The corrugation technique is based on the formation of patterned grooves in active silicon to achieve ultraflexibility. As a result, islands of silicon with different shapes are obtained which are interconnected through the IBCs. Multiple corrugation patterns such as linear, honeycomb, and octagonal designs are studied, each resulting in different flexing capabilities in terms of flexing directionality and minimum bending radius, in addition to providing an atypical appearance with an aesthetic appeal. The corrugation method is shown to improve thermal dissipation (14.6% lower temperature) and to relieve the thermal mismatch challenge compared to the rigid cells because of the finlike architecture. Finally, encapsulation using a transparent polymeric material enables a robust performance of the flexible cells when exposed to different environmental conditions such as acid rain, snow, and mechanical shocks.

Heterogeneous Cubic Multidimensional Integrated Circuit for Water and Food Security in Fish Farming Ponds

Among major food production sectors, world aquaculture shows the highest growth rate, providing more than 50% of the global seafood market. However, water pollution in fish farming ponds is regarded as the leading cause of fish death and financial losses in the market. Here, an Internet of Things system based on a cubic multidimensional integration of circuit (MD-IC) is demonstrated for water and food security applications in fish farming ponds. Both faces of the silicon substrate are used for thin-film-based device fabrication. The devices are interconnected via through-silicon-vias, resulting in a bifacial complementary metal-oxide-semiconductor-compatible electronics system. The demonstrated cubic MD-IC is a complete, small, and lightweight system that can be easily deployed by farmers with no need for specialists. The system integrates on its outer sides simultaneous air and water quality monitoring devices (temperature, electrical conductivity, ammonia, and pH sensors), solar cells for energy-harvesting, and antenna for real-time data-transfer, while data-management circuitry and a solid-state battery are integrated on its internal faces. Microfluidic cooling technology is used for thermal management in the MD-IC. Finally, a biofriendly polymeric encapsulation is used to waterproof the embedded electronics, improve the mechanical robustness, and allow the system to float on the surface of the water.