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Micro/nano sensors based on oxide semiconductors have received much interest worldwide due to their remarkable electrical conductivity, good stability, wide range of dimensional structures, large-scale production potential, and cost effectiveness. The present review extensively investigates the physics behind the nanostructure growth, gas sensing, and selectivity mechanisms of different micro/nano-based devices. Mainly, planar, vertical, heterojunction, and thin film devices are discussed along with their pros and cons in relation to gas sensing and transport mechanisms. The sensing behaviours of such devices have been explained considering nanostructure morphology (particles and pore sizes), surface states (type of defect states and defect concentrations), and interfaces (intra- and inter-grain boundaries). Further, nanostructures with different dimensions, such as nanoparticles, nanowires, nanorods, nanoplates/nanosheets, nanotubes, hollow spheres, and nanoflowers, have also been taken under consideration.

An analysis of low power 2–4 decoder and 4–16 decoders are made and comparing it with the proposed decoders. The decoder logic circuit have been made utilizing Dual Value Logic (DVL) and Transmission gate logic to actualize a fourteen transistors 2–4 decoder for limiting the transistor count. By utilizing 2–4 pre-decoders and post-decoders to execute 4–16 decoder. Blended digital logic is additionally utilized for this reason. In correlation we have execute a solitary 2–4 decoder with least transistor check and low power utilization which is utilized to structure a 4–16 decoder. CADENCE Virtuoso simulation at 90 nm technology is used and calculated the power and area. We thus made a tabular comparison of our results with the results from previous researches.

Composite materials especially graphene and metal oxides received much interest recently in chemical sensor applications. Metal oxide like TiO2, SnO2, ZnO etc. in composite form with graphene or graphene derivates offer excellent gas sensing property. Pure graphene has very weak gas adsorption capability whereas derivatives of graphene i.e. graphene oxide (GO) or reduced graphene oxide (rGO) offer efficient adsorption capability and hence offer higher gas sensitivity. A comprehensive study of synthesis, characterization, gas sensing study and sensing mechanism towards various gases has been carried out in the present article. Role of graphene and metal oxide composite junction for gas sensing improvement have been discussed with light of energy band model and carrier transport kinetics.