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Humans rely increasingly on sensors to address grand challenges and to improve quality of life in the era of digitalization and big data. For ubiquitous sensing, flexible sensors are developed to overcome the limitations of conventional rigid counterparts. Despite rapid advancement in bench-side research over the last decade, the market adoption of flexible sensors remains limited. To ease and to expedite their deployment, here, we identify bottlenecks hindering the maturation of flexible sensors and propose promising solutions. We first analyze challenges in achieving satisfactory sensing performance for real-world applications and then summarize issues in compatible sensor-biology interfaces, followed by brief discussions on powering and connecting sensor networks. Issues en route to commercialization and for sustainable growth of the sector are also analyzed, highlighting environmental concerns and emphasizing nontechnical issues such as business, regulatory, and ethical considerations. Additionally, we look at future intelligent flexible sensors. In proposing a comprehensive roadmap, we hope to steer research efforts towards common goals and to guide coordinated development strategies from disparate communities. Through such collaborative efforts, scientific breakthroughs can be made sooner and capitalized for the betterment of humanity.

The thermal conductivity measurement of films with submicrometer thicknesses is difficult due to their exceptionally low thermal resistance, which makes it challenging to accurately measure the temperature changes that occur as heat flows through the film. Thus, specialized and sensitive measurement techniques are required. 3ω method is a widely used and reliable tool for measuring the thermal conductivity of films. However, the high in-plane thermal conductivity in thin films results in rapid heat dissipation across the thin film, resulting in poor measurement sensitivity and making it difficult to accurately measure the temperature gradient with the traditional 3ω method. Also, the traditional 3ω method requires cross-plane thermal conductivity to derive the in-plane counterpart. Here, we introduce a dual-domain 3ω method that adopts AC-modulated heating and electrode arrays facilitating surface temperature profiling: (1) the sensitivity was significantly improved due to the employment of low-thermal-conductivity-substrate, and (2) cross-plane thermal conductivity is not required for the analysis of in-plane counterpart. This measurement platform allows us to control heat penetration in depth via varied heating frequencies as well as spatial temperature detection through laterally distributed electrodes on the thin film surface. By utilizing the described method, we have determined the in-plane thermal conductivity of a copper film, having a thickness of 300 nm, which was found to be 346 Wm−1K−1 and validated by the Wiedemann–Franz law. [ABSTRACT FROM AUTHOR]

In the presence of structural disorders, carrier conduction via localized hopping sites emerges in two-dimensional systems and results in a unique thermopower characteristic with T1/3 dependence. The disorders induced potential differences of hopping sites leading to energy variations along current-carrying paths. A systematic thermoelectric study is presently required in comprehending the statistical effects. Therefore, we proposed a statistical model of the Seebeck coefficient on the basis of percolation theory and hopping mechanisms. With this model, the carrier density and temperature dependences can be practically predicted. Key parameters can be extracted by calibration to molybdenum disulfide and black phosphorus experiments, providing a deeper insight into device physics. Moreover, a Mott-like analytical model is developed to investigate the parametric dependence. The thermopower deviations from the noninteracting Mott picture at high and low temperatures are analyzed. Finally, the temperature dependence on the thermoelectric figure of merit is evaluated in a variable range hopping regime. Our model is essential for a reliable prediction of the disorder induced statistical effects on thermoelectric behaviors, which guides both device optimization and material engineering. [ABSTRACT FROM AUTHOR]

A surface potential based compact model for two-dimensional field effect transistors (2D-FETs) is proposed to incorporate the structural disorders induced transition behaviors among variable range hopping (VRH), nearest neighbor hopping (NNH), and band-like transport in most 2D materials. These functions coupled with effective transport energy and multiple trapping and releasing theory enable our developed model to predict the temperature and carrier density dependent current characteristics. Its validity is confirmed by the experimental results such as the metal insulator transition (MIT) in transition metal dichalcogenides and VRH-NNH transition in black phosphorus nanoribbon. Based on this model, the band-tail effects on the crossover gate voltage of MIT behavior are quantitatively investigated. It is found that the transition behavior is closely related to the distribution of the band-tail states. Furthermore, this model is implemented in Verilog-A for circuit-level prediction and evaluation of 2D-FETs to provide deeper insight into the relationship between material properties, device physics, and circuit performances. [ABSTRACT FROM AUTHOR]