Semicondcuting metal oxide nanoparticles in sensors, optoelectronics and electronic devices

Abstract

The Internet of Things (IoT) represents a multi-layer technology connecting diverse hardware (smart appliances, smart gadgets, and wearable, biocompatible, and mobile consumer devices) by middleware to the cloud of things (CoT). It is changing how electronics interface with our physical world in terms of sensing, information display and communication. Gas sensors and sensor nodes are a vital component of the IoT. Modern electronic systems are flexible, transparent, biocompatible and wearable. Semiconducting metal oxides are earth abundant multifunctional materials. Their multifunctionality stems from their complex and widely varied electronic structure and properties. They include a wide range of band gaps, high surface activity, and electrical properties making them the subject of continuous research, especially in the form of nanoparticles for application in sensors, optoelectronics and electronic devices. Metal oxides are stable materials, easy to synthesize and process. In nanostructure form they show a wide range of enhanced properties, such as a suitable band gap, conduction properties and confined conduction pathways for photoelectric electronic devices. They are excellent candidates, in crystalline or amorphous form, for optoelectronic devices, such as flat panel displays, solar cells, organic light-emitting diode displays (OLEDs) and emerging flexible and transparent electronics, as they can exhibit high electrical performance and excellent visible range transparency. The high growing demand for flexible electronics requires low temperature and high-throughput synthesis of oxide thin films on flexible plastic substrates. High sensitivity, fast response/recovery and good selectivity are generally required of a good sensing material. Metal oxides still remain the first choice for application in sensors, especially gas sensors due to their ease of fabrication, low cost, high sensitivity, and stability. Some of their disadvantages are low selectivity and high operating temperature. Over time commercially produced metal oxide gas sensors have reduced in size being produced in different technologies, starting with tube-type sensors in the eighties of the last century, through screen-printed sensors produced in the nineties and completing with state-of-the art micro-electro-mechanical system (MEMS) sensors produced today. Development of low cost, reduced power consumption and reliable sensing devices for the detection of gases for environmental and industrial applications, especially at room temperature remains a significant scientific and technological challenge.