npj Flexible Electronics最新文献

Organic piezoelectric materials have attracted significant interest for applications in sensing, energy harvesting, and flexible electronics. However, its piezoelectric properties are yet to be improved. This study introduces a facile strategy to fabricate homogenous and dense polyvinylidene fluoride (PVDF) films with high piezoelectric performance via anhydrous CaCl₂ doping. The strong ion–dipole interaction between Ca²⁺ and F atoms, along with directional dipole alignment under an electric field at elevated temperature, as verified by molecular dynamics simulations and material characterizations. This results in an impressive β-phase content of 92.78% and a piezoelectric coefficient of 29.26 pm/V. A piezoelectric device fabricated from this PVDF film delivers an output voltage exceeding 12 V under external pressure and maintains stability over 60,000 cycles. When integrated with an LC resonant circuit, it functions as a wireless sensor for real-time motion monitoring. This scalable approach significantly advances piezoelectric polymer performance for practical applications.

Three-dimensional (3D) conformal electronic skins (E-skins) have been developed for matching the irregularly surfaces. The 3D conformal E-skins manufactured by direct-curved-surface or dimensional converting methods both need curved-surface calibration. With increase of units’ number and complication of mounting-surface morphology, curved-surface calibration becomes intricate. We report a universal cutting and distributing strategy for E-skins. The E-skin incorporates hierarchical and modular tactile sensors to match curvatures and sizes, thereby reducing mounting strain. This strategy enables curved-surface performance of 3D conformal E-skins to be characterized by flat-surface calibration results. An example is provided: Three-level sensors are utilized and calibrated on flat and curved surfaces. Performance variations reduce as sensor size decreases, and performance changes of level II and III sensing units are small after mounting. Their calibration results on curved surface are replaced by those on flat surface, proving low mounting strain facilitates 3D conformal E-skins to avoid complicated curved-surface calibration.

Stretchable circuits based on liquid metals are promising for wearables but the lack of scalable processes for sintering of printed liquid metal dispersions constitutes a challenge for large-area and high-volume manufacturing. In this work, materials and methods for fully screen printed stretchable liquid metal multilayer circuits have been developed. The ink is based on liquid metal droplets dispersed in the green solvent propylene glycol using the harmless dispersion agent polyvinylpyrrolidone. The development of a scalable water-spray sintering method in combination with ink optimization yielded highly conductive prints of ≈7.3 × 10⁵S/m. Interestingly, the printed conductors experienced a resistance increase of less than 10% during 50% strain cycling, which is far below the expected 125% increase due to the geometry factor. The process allows for printing of high-performance multilayer circuits, which is demonstrated by the development of printed stretchable near-field communication tags.

This study investigates laser sintering of Cu particle-free ink (Cu formate tetrahydrate—amino-2-propanol complex) as an alternative to conventional sintering in an oven (under inert/reducing atmosphere). Utilizing benefits of high-speed localized heating using laser, substrate damage can be prevented for low-melting substrates such as Polyethylene Terephthalate (PET). Firstly, a suitable sintering process window is achieved based on energy density for two different flexible polymeric susbtrates: Polyimide and PET using different laser parameters (laser power, scan rate and spot diameter). Subsequently, characterization of laser sintered traces are also made using different laser optic profiles (Gaussian and top hat). Different methodologies for fabrication of metallized Cu layer were also demonstrated. A very low bulk resistivity of 3.24 µΩcm (1.87 times of bulk Cu) was achieved on trace thickness of 0.85 ± 0.15 µm exhibiting good adherence to polymeric substrates. A promising fabrication process of low-cost and reliable flexible printed electronic devices is demonstrated.

Heat exhaustion is a prevalent heat-related illness among firefighters, posing a severe threat to life without timely intervention. However, current firefighter garments are limited by their singular functionality and cannot collect or analyze body fluid during rescue missions. Here, we introduce a wetting gradient effect assisted ultrasensitive meta-garment that incorporates multi-signal biomonitoring, offering an early warning system for heat exhaustion risk. This design enables real-time detection of heart rate, pH value, and the concentrations of glucose, sodium, and potassium in sweat. Benefiting from the surface energy difference, gradient wettability surfaces can be formed, allowing for precise point-to-point fluid control and regulation. Thus, the biosensing fibers require the lowest detection volume (0.1 μL) and fastest response time (1.4 s) reported to date. This innovative garment provides a practical solution for early health warning based on abnormal multi-biomarker changes, representing a significant advancement in firefighter safety.

Stretchable optoelectronic synapses are attractive for intelligent perception, neuromorphic computation and visual adaptation. Here, we demonstrate a highly stretchable organic optoelectronic synaptic transistor (s-OOST) with a transconductance up to 86 mS that can simultaneously accept modulation of electrical pulses and multi-wavelength light signals (from ultraviolet to near-infrared). The s-OOST achieved highly reliable synaptic plasticity for brain-inspired computation and retina-inspired perception even under 50% tensile strain. Furthermore, the devices exibited vision-adaptive near-infrared sensing ability that was verified by single-pixel scanning imaging. Finally, the multi-wavelength (365 nm–1050 nm) optical synaptic properties were investigated under the applications of imaging memory, polychromatic optical communication and information security (coded by wavelength). This research advances the capabilities of the stretchable integrated systems with vision-adaptive sensing characteristic and computing-in-memory ability.

The ballistocardiogram (BCG) represents a promising unconstrained method for capturing cardiac vibrations, effectively mitigating the discomfort and activity limitations often associated with traditional long-term healthcare monitoring. Herein, we introduce a smart wireless flexible sensing system designed for the unconstrained monitoring of BCG and respiration. The core component of the system is a flexible pressure sensor featuring a gradient spherical crown microstructure design, which ensures high sensitivity to weak dynamic pressure signals even under high static pressure. This sensing capability enables the sensor, attached to the seat, to accurately capture subtle physiological signals from seated individuals. Furthermore, the system holds potential for assisting in the diagnosis of heart rate variability, providing new insights into the application of flexible sensors in the realm of unconstrained human health monitoring.

Human fingers have fingerprints and mechanoreceptors for biometric information encryption and tactile perception. Ideally, electronic skin (e-skin) integrates identity information and tactile sensing, but this remains challenging. Research on encryption and tactile sensing rarely overlaps. Here, we report using magnetization structures and combinations of magnetic materials to achieve two types of functions: 6^{n × n} invisible secure encryption is achieved through a n × n dipole magnetic array, and multipole magnets are used to achieve decoupling of pressure at various positions and sliding in different directions. The sliding distance ranges from 0 to 2.5 mm, with speeds between 5 and 25 mm/s. This study is based on flexible magnetic films, which have the potential to be used in wearable devices. The magnetic ring and signal detection modules verify the prospects of this fundamental principle in human-computer interaction (HCI) and demonstrate its applications in user identity recognition and tactile interaction.

Emerging two-dimensional (2D) materials offer significant potential for post-silicon photodetectors but often fall short of matching silicon photodiode performance. Here, we report a flexible, high-performance photodetector with a simple metal-2D semiconductor-metal structure by stacking Ti/WSe₂/Ag layers on a mica substrate. The device demonstrates a low dark current of 0.8 pA, high external quantum efficiency of 49%, a broad linear dynamic range of 86 dB, wide spectral sensitivity (350–1200 nm), and ultrafast response speed (~1 μs rise/fall time by conventional measurement and 337 ps via ultrafast photocurrent method). These advances originate from efficient photocarrier extraction via an ultrashort channel and Schottky barriers facilitated by van der Waals contacts. Additionally, the device’s ultrathin (~200 nm) profile ensures exceptional bending durability, while encapsulation protects against ambient degradation. Our strategy here will promote the development of the post-silicon photodetector and foster next-generation flexible optoelectronic applications.

Correction to: npj Flexible Electronics https://doi.org/10.1038/s41528-024-00374-4, published online 12 January 2025