Electrically Tunable Graphene Gas Sensors

在用于诸如物联网的广泛应用的感测技术的现代时代，为诸如可穿戴设备和手机的应用制造低功率、小形状因子和多功能气体传感器的能力可以彻底改变气体感测系统和制造领域。 在过去的十年中，已经成功地为移动的设备开发了大量的小型化物理传感器，例如光、运动、心率和高度，以提供可靠的感测任务并彻底改变用户体验。 未来潜在的增长领域已被预测为用于感测周围环境条件的化学界面，例如气体、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内占据整个移动的传感器市场的32%份额。 例如，气体传感器可以监测临界挥发性化学物质（CO、VOC等）。通过分析人类呼出的气体，确定从舒适到威胁健康的生活条件，甚至诊断肺部相关疾病的可能性。 该项目提供了独特的机会，通过使用石墨烯作为新的气敏材料，电气转向机制的气体选择性和响应，以及低制造成本的晶圆级加工平台。近年来，石墨烯基气敏传感器由于其超大的表面积与体积比和半导体特性而引起了极大的兴趣。 已经报道了室温和分子水平的传感能力，而气体选择性差，没有进一步的官能化与聚合物或贵金属颗粒。 该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来展示室温气体传感能力，从而实现低功耗;（2）石墨烯FET的气体选择性（场效应晶体管）与直流电调谐耦合而不添加功能材料;（3）通过使用AC电相位感测的快速响应和无漂移感测;以及（4）用于小形状因子和低制造成本的晶片级批量制造。 通过利用石墨烯FET气体传感器阵列的架构和晶圆级工艺的发展将传感器与微电子集成以减小器件尺寸和制造成本，该项目旨在产生具有良好灵敏度，稳定性，响应时间和气体选择性都是当前和未来可穿戴设备和蜂窝电话中的移动的气体感测应用的期望特征。 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吸附的气体分子？ 石墨烯FET气体传感器阵列的气体选择性的基本限制是什么？ 石墨烯FET气体传感器能否在宽浓度范围内（例如从1 ppm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?