Interfacing nanoparticles to CMOS quad instrumentation amplifiers for gas sensing devices

In this study, we demonstrated a novel approach of a low noise performance gas sensory system, which is capable of minimizing the cross talk between four instrumentation amplifiers. These amplifiers will receive gas sensing information from four different nanoparticle assemblies using monolayer Graphene sheets. The cross talk was minimized by using guard rings surrounding the amplifiers. Guard rings serve as dummy collectors for the minority carriers crossing the parasitic BJT devices within the quad instrumentation amplifier System on chip (SOC). This study aims determination of the gas sensing signature array (GSSA), including the type of gas, its concentration, and dynamic performance (rise and fall times). The developed devices were based on the detection of the change in the graphene electrical characteristics when exposed to various gases. The paper presents the first phase of a long-term project, detailing hardware and circuit simulation software design, and its practical implementation, leading to the optimum gas sensing system resulting from the GSSA data. The practical model was based on monolayer graphene films deposited using CVD process on top of SiO2 layers of silicon substrate wafers. Gold electrodes were deposited with sputtering process. The device was then tested with CO2 gas with 100% and 5% concentrations to estimate its sensitivity. As high as 48% change in resistance was detected from 100% CO2 concentration, and near 4% change in response to 5% CO2 concentration, a level of change that can be easily monitored by the quad CMOS instrumentation chip. A gain of 83dB for the instrumentation amplifier was calculated from the circuit simulation. The Quad instrumentation amplifiers were developed using MOSIS service and showed as low attenuation as 90dB.