Abstract
Integration of a complementary metal-oxide semiconductor (CMOS) and monolayer graphene is a significant step toward realizing low-cost, low-power, heterogeneous nanoelectronic devices based on two-dimensional materials such as gas sensors capable of enabling future mobile sensor networks for the Internet of Things (IoT). But CMOS and post-CMOS process parameters such as temperature and material limits, and the low-power requirements of untethered sensors in general, pose considerable barriers to heterogeneous integration. We demonstrate the first monolithically integrated CMOS-monolayer graphene gas sensor, with a minimal number of post-CMOS processing steps, to realize a gas sensor platform that combines the superior gas sensitivity of monolayer graphene with the low power consumption and cost advantages of a silicon CMOS platform. Mature 0.18 µm CMOS technology provides the driving circuit for directly integrated graphene chemiresistive junctions in a radio frequency (RF) circuit platform. This work provides important advances in scalable and feasible RF gas sensors specifically, and toward monolithic heterogeneous graphene–CMOS integration generally.
Highlights
Gas sensors have traditionally been limited to hard-wired applications within the automotive and industrial sectors, monitoring the byproducts of combustion processes, and industrial environmental gases.[1,2,3] In these cases, power and size requirements are not critical, and such sensors tend to be large and bulky
Much of current gas sensor research is directed at the need for low-cost, low-power portable gas sensors, as well as integration with the technology platform best suited to meet that need: silicon complementary metal-oxide semiconductor (CMOS)
With a graphene transducer fabricated atop the CMOS chip, we achieve a 3D stacking of functionally discrete layers on a single substrate, the main barrier of 3D integration mitigated by the low-temperature post-CMOS processing steps of where N is number of inverters, RON is the output resistance of each inverter, Cg and Cd are gate and drain capacitances, respectively, of each inverter
Summary
Gas sensors have traditionally been limited to hard-wired applications within the automotive and industrial sectors, monitoring the byproducts of combustion processes, and industrial environmental gases.[1,2,3] In these cases, power and size requirements are not critical, and such sensors tend to be large and bulky. We have integrated monolayer graphene sensor frequency fS, is modeled as follows: with a back-end CMOS detection system to realize a RF-capable gas sensor with low power and low temperature requirements that incorporates the superior response time and sensitivity of fS. With a graphene transducer fabricated atop the CMOS chip, we achieve a 3D stacking of functionally discrete layers on a single substrate, the main barrier of 3D integration mitigated by the low-temperature post-CMOS processing steps of where N is number of inverters, RON is the output resistance of each inverter, Cg and Cd are gate and drain capacitances, respectively, of each inverter. The device achieves full monolithic CMOS integration (as opposed to, for example, a SiP pairing) and with sensitivity in the 2 parts per million (ppm) range for NO2 and the 4 ppm range for NH3, sensor response is on par with comparable individual graphene gas sensors.[20,30,31] graphene integration
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