In the modern age of sensing technologies for broad applications such as internet of things, the capability to make low power, small form factor, and versatile gas sensors for applications such as wearable devices and cell phones could revolutionize the fields of gas sensing systems and fabrications. Over the past decade, a great number of miniaturized physical sensors, such as light, motion, heart rate, and altitude have been successfully developed for mobile devices to deliver reliable sensing tasks and revolutionize the user experiences. The potential future growth area has been predicted to be the chemical interfaces to sense surrounding environmental conditions, such as gases, biomarkers, and explosives. Specifically, chemical sensors are projected to have a 32% share of the total mobile sensor market in the next decade. For example, gas sensors may monitor critical volatile chemicals (CO, VOC etc.) to determine living conditions from comfort to health threatening and even the possibilities of diagnosing lung related diseases by analyzing exhaled gases from human breath. The proposed project provides unique opportunities by using graphene as the new gas sensing material; electrical turning mechanisms for gas selectivity and responses; and a wafer-level processing platform for low manufacturing cost.
In recent years, graphene based gas sensors have drawn great interests due to its ultra large surface to volume ratio and semiconducting properties. Both room temperature and molecular-level sensing capabilities have been reported, while the gas selectivity is poor without further functionalization with polymers or noble metal particles. This project proposes four unique approaches to address the typical issues associated with electrochemical gas sensors: (1) low power consumption by demonstrating room temperature gas sensing capability using ultrasensitive single-layer graphene as the sensing materials; (2) gas selectivity by graphene FETs (Field Effect Transistors) coupled with DC electrical tuning without adding functional materials; (3) fast responses and drift-free sensing by using AC electrical phase sensing; and (4) wafer-level batch fabrication for small form factor and low manufacturing cost. By utilizing the architecture of an array of graphene FET gas sensors and the development of wafer-level process to integrate the sensor with microelectronics to reduce device size and manufacturing cost, this project aims to result in ultra-low power, low form-factor gas sensors with good sensitivity, stability, response time and gas selectivity all desirable features for current and future mobile gas sensing applications in wearable devices and cell phones. Furthermore, this project also seeks to answer some of the very fundamental questions: How does the electron transferred from graphene surface to adsorbed gas molecules during the sensing process? What are the fundamental limitations in gas selectivity of graphene FET gas sensor arrays? Can one make graphene FET gas sensors to maintain good selectivity at a wide concentration range (for example from 1ppm to 50%) with good reproducibility?
