Since the first graphene gas sensor has been reported, functionalized graphene gas sensors have already attracted a lot of research interest due to their potential for high sensitivity, great selectivity, and fast detection of various gases. In this paper, we summarize the recent development and progression of functionalized graphene sensors for ammonia (NH₃) detection at room temperature. We review graphene gas sensors functionalized by different materials, including metallic nanoparticles, metal oxides, organic molecules, and conducting polymers. The various sensing mechanism of functionalized graphene gas sensors are explained and compared. Meanwhile, some existing challenges that may hinder the sensor mass production are discussed and several related solutions are proposed. Possible opportunities and perspective applications of the graphene NH₃ sensors are also presented.

Measurements of a new type of substrate for the integration of the trap-rich interface passivation solution with the below-buried oxide functionalities required in fully-depleted (FD) Silicon-on-Insulator (SOI) nodes is presented. This is achieved by adding a second thin buried oxide (BOX2) layer in between the substrate and the trap-rich/BOX1/SOI stack. It is shown that the trap-rich layer above BOX2 can effectively passivate the parasitic surface conduction that would be induced below BOX2 if BOX2 remains thinner than 20 nm. This is proven through measurements of substrate losses and non-linearity of coplanar waveguide transmission lines, comparing the fabricated double-BOX samples to reference trap-rich and unpassivated high-resistivity substrates.

This work introduces a new measurement methodology for enhancing gas detection by tuning the magnitude and polarity of back-gate voltage of a field-effect transistor (FET)-based sensor. The aim is to simultaneously strengthen the sensor response and accelerate the sensor recovery. In addition, this methodology can consume less energy compared with conventional measurements by direct current bias. To illustrate the benefits of the proposed methodology, we fabricated and characterized a polypyrrole/graphene (PPy/G) FET sensor for ammonia (NH₃) detection. Our experiment, simulation and calculation results demonstrated that the redox reaction between the NH₃ molecules and the PPy/G sensitive layer could be controlled by altering the polarity and the magnitude of the back-gate voltage. This proof-of-principle measurement methodology, which solves the inherent contradiction between high response and slow recovery of the chemiresistive sensor, could be extended to detect other gases, so as to improve global gas measurement systems. It opens up a new route for FET-based gas sensors in practical applications.

The effect of device fabrication processing conditions is often overlooked in the evaluation of the contact resistance in metal–graphene contact. In this work, we investigate the Ti–graphene contact resistance theoretically and experimentally. A compact model has been proposed to reveal and evaluate the role of different factors in controlling the value of contact resistance. A layer of oxidized Ti or polymer residues at the Ti–graphene interface has been considered to explain the reduced carrier transmission probability through the interface. Experimental results report a low contact resistance as small as 271.45 $\Omega ~\cdot \mu \text{m}$ and our model agrees with the measured values. The proposed model explains the large variation of the contact resistance reported in the literature up to date and help to improve metal–graphene contact for future applications.