空气绝缘层CuPc单晶纳米线场效应NO2传感器及其机理研究

NO2 is a toxic gas that is released into the atmosphere, and has become one of the most common air pollutants. The lowest concentration of commercial NO2 sensor based on semiconductor is 100 ppb, which is not enough for the environment monitoring. CuPc is sensitive to NO2. Its lowest concentration reaches 40 ppb at the heated temperature. The applicant plans to fabicated the field-effect NO2 sensor based on the single CuPc nanowire and the air dielectric. The lowest concentration is expected to be 10 ppb. The air dielectric sensor will be compared with the solid dielectric sensor in order to study the response mechanism. Such a device is expected to improve the sensitivity which is attributed to: i)the single nanowire with the high aspect ratio has the high surface-volume ratio; ii)the gate voltage limits most of carriers in the conductive channel which locates in only a few atomic layer of the semiconductor in the interface between the semiconductor and the dielectric; iii)the air dielectric facilitates the direct adsorption of the gas molecules onto the surface of the conductive channel and avoids the diffusion process of the molecules in the semiconductor. Other advantage is that the field-effect device can be integrated into the circuits to further improve the sensitivity. In addition, the measurements of a few parameters in the field-effect devices, for example, the channel current, the threshold voltage, and the mobility, facilitates the improvement of the accuracy and selectivity of the gas sensor.

NO2是一种有毒气体，也是最常见的空气污染物之一，对其浓度的精确监控在健康和安全上具有重要意义。目前，商业化半导体NO2传感器的灵敏度为100ppb，不能满足低浓度环境监测的需要。CuPc是一种典型的NO2敏感材料，升温下薄膜器件的最小响应浓度达到40ppb。申请人拟采用空气绝缘层制备单根单晶CuPc纳米线场效应NO2传感器，最低响应浓度目标为10ppb，并通过固体和空气绝缘层传感器性能对比，进行传感器微观响应机理研究。传感器高的灵敏度基于：单根纳米线大的表体积比；栅极使所有载流子几乎都集中在场效应器件半导体/绝缘层界面处的导电沟道中；空气栅极绝缘层使气体分子直接吸附在导电沟道表面。同时，场效应传感器可集成到电路中，进一步放大灵敏度。除沟道电流外，场效应传感器的阈值电压、迁移率等参数变化也能反映气体浓度变化，有利于通过多参数响应提高传感器准确性，也可在此基础上尝试气体甄别。

NO2是有毒气体，同时也是空气中主要污染物之一。美国环境控制局设定的空气质量标准中，NO2含量要求小于53 ppb。申请人拟采用空气作为栅极绝缘层，制备单根单晶纳米线场效应NO2传感器，并研究场效应NO2传感器的气体响应机制和性能，传感器最低响应浓度的目标为10 ppb，满足环境质量监控的要求。.针对这一目标,我们开展了绝缘层沟槽制备、空气绝缘层一维微纳单晶场效应器件制备、气敏测试系统研发、超薄有机单晶场效应器件制备、空气绝缘层有机单晶异质节器件制备等系列研究,成功地在室温条件下实现了对10ppb NO2的高灵敏探测,响应灵敏度可达244%，完成了项目预定目标。空气绝缘层一维微纳单晶场效应器件除了对NO2具有极高的探测灵敏度外，同时对NO和H2S具有非常好的响应，探测下限可达50ppb，灵敏度分别为360%和1099%。更为重要的是，器件对三种气体响应时各个电学参数，如迁移率、阈值电压和亚阈值斜率存在差异，利用这些差异可以实现单一器件对气体种类的甄别，这是一种新的电子鼻工作原理，对推进半导体气体传感器在电子鼻中的应用提供了新途径。这些成果的取得，得益于空气绝缘层将场效应器件载流子传输最集中的导电沟道暴露到了待测气体当中，使待测气体直接与导电沟道相互作用，电学信号响应得以最大化。我们在空气绝缘层场效应器件的基础上，在一维单晶上沉积了另一种半导体，例如在CuPc单晶线表面沉积Ph5T2微晶，形成异质节，进一步提高了响应灵敏度和选择性。.除了空气绝缘层策略之外，我们还将超薄有机单晶片制备的场效应器件用于气体传感，由于气体分子可以相对容易地穿过有机晶体进入器件导电沟道，超薄晶体器件同样显示出良好的气敏性能，对H2S的探测下限可达0.5ppm，相应的 响应达128%，同样为有机半导体气体传感的发展提供了新思路。