No abstract

Emerging feedback systems based on tracking body conditions can save human lives. In particular, vulnerable populations such as disabled people, elderly, and infants often require special care. For example, the high global mortality of infants primarily owing to sudden infant death syndrome while sleeping makes request for extraordinary attentions in neonatal intensive care units or daily lives. Here, a versatile laser‐induced graphene (LIG)‐based integrated flexible sensor system, which can wirelessly monitor the sleeping postures, respiration rate, and diaper moisture with feedback alarm notifications, is reported. A tilt sensor based on confining a liquid metal droplet inside a cavity can track at least 18 slanting orientations. A rapid and scalable laser direct writing method realizes LIG patterning in both the in‐plane and out‐of‐plane configurations as well as the formation of nonstick conductive structures to the liquid metal. By rationally merging the LIG‐based tilt, strain, and humidity sensors on a thin flexible film, the multimodal sensor device is applied to a diaper as a real‐time feedback tracking system of the sleeping posture, respiration, and wetness toward secure and comfortable lives. User‐friendly interfaces, which incorporate alarming functions, provide timely feedback for caregivers tending to vulnerable populations with limited self‐care capabilities.

systems for IoT, economical fabrication of devices is important. At a minimum, flexible devices currently require signal processing circuits and batteries to operate sensor systems. Integrating these into a sensor while maintaining mechanical flexibility is difficult without increasing the device cost. An approach to overcome this challenge is to separate the sensor system into two film parts: a disposable one for the printable low-cost sensor array and a reusable one for the expensive systems, including circuits, battery, etc. [1-3] Because the connector combining these two components is usually inflexible, mechanical flexibility is often sacrificed. Our group has reported a flexible connector, which electrically connects two flexible sheets (i.e., disposable and reusable sheets) without sacrificing the mechanical flexibility using a liquid metal of eutectic Gallium Indium (EGaIn). [13,14] However, the metal can be readily removed from the connector by scratching it due to the liquid-state of EGaIn at room temperature, which is impractical for IoT applications including human-interactive devices. An interesting approach for sensor applications is to monitor the chemical distribution in a solution for environmental monitoring and even healthcare diagnosis from sweat. Although many studies have monitored the chemical contents in sweat for healthcare and medical applications, [1-9] chemical mapping in a solution using a flexible sensor sheet has yet to be demonstrated. If a flexible chemical sensor array is realized for mapping, applications can be expanded from healthcare/medical to biological and environmental monitoring. Such an array should also be able to map interesting data from an object for the next class of IoT concepts, which has been very difficult to collect using conventional inflexible chip-based sensors. To address the above challenges, this study proposes mechanically flexible and stable macroscale pH distribution and diffusion monitoring in solution with a flexible electrical connector. Figure 1a shows the device concept. First, a flexible connector using a soft 3D Ag electrode is discussed. As a reusable sheet, flexible extended gate ion-sensitive field-effect transistors (ISFETs) are fabricated using thin-film InGaZnO for the n-type transistors. There are two reasons to use ISFETs for pH monitoring in this study. The first one is to show the possibility

A multidirectional flexible tilt sensor, using laser‐ablated non‐wet surfaces and liquid metal, is realized by Kuniharu Takei and co‐workers in article number 2008701, which can wirelessly monitor sleeping posture. In addition, sensors to monitor respiration rate and diaper moisture are successfully integrated with feedback alarm notifications. User‐friendly interfaces, which incorporate alarm functionality, provide timely feedback for caregivers tending vulnerable populations with limited self‐care capabilities.

Heterogeneously integrated nanomaterial devices show interesting characteristics for transistors and sensors due to their band diagram or steep material junctions. If these junctions and band alignments can be tuned by an electrical input bias, the device platform not only could be expanded but also could be used to explore fundamental characteristics. However, most reports on hetero-nanomaterial junctions use a global back-gate voltage, which makes it difficult to control band alignment at an interface. To explore device junctions, this study reports a laterally integrated heterojunction of graphene and a carbon nanotube (CNT) network film with individual gate electrodes to tune the band alignment corresponding to the Fermi level shift of graphene in contact with the semiconducting CNT network film. By developing the fabrication process, multiple gate structures are designed to apply a gate bias to CNTs and graphene separately. The threshold voltage shift of the CNT transistor depends on the gate voltage of graphene. Based on the thermionic emission theory, the barrier height between graphene and CNTs for both the conduction and valence band sides varies from 70 to 85 meV, with a linear change as a function of the applied gate voltage to graphene. Although the current Fermi level shift is small, this device platform may realize the exploration of fundamental properties and device concepts.