Functional materials for powering and implementing next-generation miniature sensors

The advent of the Internet of Things and smart applications such as smart cities, smart health care, and smart electronics will require the use of a vast array of sensors. Sensors are a key part of the revolution in interconnected devices. The growing need for sensing, monitoring, and collecting data at scales from small to large will help, for example, prevent future pandemics, elucidate climate change, optimize industrial processes, and train machine learning models. Recent progress in materials science, micro/nano technologies, and integrated circuits has made it possible to reduce the size and cost of sensors while integrating them into more complex machines, ranging from wearable/implantable devices to onboard laboratories for planetary exploration rovers. However, the small dimensions of miniature sensors present some challenges, including power supply, active sensing materials, and material flexibility. In this article, we review microbatteries to power miniature sensors. We discuss materials and architectures for microbatteries and their fabrication methods. We also discuss energy harvesting materials for self-powered miniature sensors. We review in detail advanced materials for active sensing, including organic, inorganic, and composite materials with emphasis on wearable/implantable sensors targeted at humans and animals. In addition, flexible electronics as well as substrates and encapsulation materials and their integration are reviewed. Finally, future perspectives and challenges of these functional materials for next-generation miniature sensors are highlighted.