Prajapati Chandra Shekhar, Bhat Navakanta
Centre for Nano Science and Engineering, Indian Institute of Science Bangalore-560012 Karnataka India
RSC Adv. 2018 Feb 9;8(12):6590-6599. doi: 10.1039/c7ra13659e. eCollection 2018 Feb 6.
In this study, we have investigated the thickness-dependent nitrogen dioxide (NO) sensing characteristics of a reactive-ion magnetron sputtered tungsten trioxide (WO) film, followed by morphological and electrical characterizations. Subsequently, the sensing material was integrated with an MEMS platform to develop a sensor chip to integrate with electronics for portable applications. Sputtered films are studied for their sensing performance under different operating conditions to discover the optimum thickness of the film for integrating it with a CMOS platform. The optimized film thickness of ∼85 nm shows the 16 ppb lower limit of detection and 39 ppb detection precision at the optimum 150 °C operating temperature. The film exhibits an extremely high sensor response [( - )/ × 100 = 26%] to a low (16 ppb) NO concentration, which is a comparatively high response reported to date among reactively sputtered films. Moreover, this optimum film has a longer recovery time than others. Thus, an intentional temperature overshoot is made part of the sensing protocol to desorb the NO species from the film surface, resulting in full recovery to the baseline without affecting the sensing material properties. Finally, the optimized film was successfully integrated on the sensor platform, which had a chip size of 1 mm, with an inbuilt micro-heater. The minimum power consumption of the microheater is ∼6.6 mW (∼150 °C), which is practically acceptable. Later, the sensor device was packaged on a Kovar heater for the detailed electrical and sensing characterizations. This study suggests that optimization of the sensing material and optimum operating temperature help to develop a highly sensitive, selective, stable, and portable gas sensor for indoor or outdoor applications.
在本研究中，我们研究了反应离子磁控溅射三氧化钨（WO）薄膜的厚度依赖性二氧化氮（NO）传感特性，并进行了形态和电学表征。随后，将传感材料与MEMS平台集成，开发出一种传感器芯片，以便与电子产品集成用于便携式应用。研究了溅射薄膜在不同操作条件下的传感性能，以发现与CMOS平台集成时薄膜的最佳厚度。约85 nm的优化薄膜厚度在150°C的最佳操作温度下显示出16 ppb的检测下限和39 ppb的检测精度。该薄膜对低浓度（16 ppb）的NO表现出极高的传感器响应[（ - ）/ × 100 = 26%]，这是迄今为止反应溅射薄膜中报道的相对较高的响应。此外，这种最佳薄膜的恢复时间比其他薄膜更长。因此，有意的温度过冲成为传感协议的一部分，以从薄膜表面解吸NO物种，从而在不影响传感材料性能的情况下完全恢复到基线。最后，优化后的薄膜成功集成在芯片尺寸为1 mm的传感器平台上，并内置了微型加热器。微型加热器的最小功耗约为6.6 mW（约为150°C），这在实际中是可以接受的。后来，将传感器器件封装在可伐加热器上，以进行详细的电学和传感表征。这项研究表明，传感材料的优化和最佳操作温度有助于开发一种用于室内或室外应用的高灵敏度、选择性、稳定性和便携式气体传感器。
