Electrically Tunable Graphene Gas Sensors

在物联网等广泛应用的传感技术的现代时代，为可穿戴设备和手机等应用制造低功耗、小尺寸和多功能气体传感器的能力可能会彻底改变气体传感系统和制造领域。在过去的十年中，已经成功地为移动设备开发了大量的小型化物理传感器，如光、运动、心率和高度，以提供可靠的传感任务并彻底改变用户体验。据预测，未来潜在的增长领域是用于感知周围环境条件的化学界面，如气体、生物标志物和爆炸物。具体来说，化学传感器预计将在未来十年占据整个移动传感器市场32%的份额。例如，气体传感器可以监测关键的挥发性化学物质（CO， VOC等），以确定从舒适到健康威胁的生活条件，甚至通过分析人体呼出的气体来诊断肺部相关疾病的可能性。拟议的项目提供了独特的机会，使用石墨烯作为新的气敏材料；气体选择性和响应的电转向机构；并提供低制造成本的晶圆级加工平台。近年来，基于石墨烯的气体传感器由于其超大的表面体积比和半导体特性而引起了人们的极大兴趣。室温和分子水平的传感能力都有报道，但如果没有与聚合物或贵金属颗粒进一步功能化，气体选择性很差。本项目提出了四种独特的方法来解决与电化学气体传感器相关的典型问题：(1)通过使用超灵敏单层石墨烯作为传感材料，通过展示室温气体传感能力来实现低功耗；(2)在不添加功能材料的情况下，利用石墨烯场效应晶体管（fet）耦合直流电调谐实现气体选择性；(3)采用交流电相传感，响应快，无漂移；(4)圆片级批量制造，尺寸小，制造成本低。通过利用石墨烯FET气体传感器阵列的架构和晶片级工艺的发展，将传感器与微电子集成在一起，以减小器件尺寸和制造成本，该项目旨在生产超低功耗、低尺寸的气体传感器，具有良好的灵敏度、稳定性、响应时间和气体选择性，这些都是当前和未来可穿戴设备和手机中移动气体传感应用的理想特性。此外，该项目还试图回答一些非常基本的问题：在传感过程中，电子如何从石墨烯表面转移到被吸附的气体分子上？石墨烯FET气体传感器阵列气体选择性的基本限制是什么？是否可以使石墨烯FET气体传感器在宽浓度范围内（例如从1ppm到50%）保持良好的选择性并具有良好的再现性？

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?