“Top-down” and “bottom-up” strategies for wafer-scaled miniaturized gas sensors design and fabrication

• Published in: Microsystems & nanoengineering Vol. 6; no. 1; p. 31
• Main Authors: Liu, Lin, Wang, Yingyi, Sun, Fuqin, Dai, Yanbing, Wang, Shuqi, Bai, Yuanyuan, Li, Lianhui, Li, Tie, Zhang, Ting, Qin, Sujie
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 04.05.2020; Springer Nature B.V
• Subjects: 639/925/927/356; 639/925/927/511; Chip formation; Detection; Elastomers; Electric properties; Electrical properties; Engineering; Gas microsensors; Hydrogen sulfide; Microelectromechanical systems; Nanomaterials; Nanotechnology; Nickel compounds; Photolithography; Reproducibility; Sensors; Silicon; Silicon wafers; Slurries; Strategy; Thermoplastic elastomers; Thin films; Wetting
• ISSN: 2055-7434; 2096-1030; 2055-7434
• DOI: 10.1038/s41378-020-0144-4

Manufacture of large-scale patterned nanomaterials via top-down techniques, such as printing and slurry coating, have been used for fabrication of miniaturized gas sensors. However, the reproducibility and uniformity of the sensors in wafer-scale fabrication are still a challenge. In this work, a “top-down” and “bottom-up” combined strategy was proposed to manufacture wafer-scaled miniaturized gas sensors with high-throughput by in-situ growth of Ni(OH) 2 nanowalls at specific locations. First, the micro-hotplate based sensor chips were fabricated on a two-inch (2”) silicon wafer by micro-electro-mechanical-system (MEMS) fabrication techniques (“top-down” strategy). Then a template-guided controllable de-wetting method was used to assemble a porous thermoplastic elastomer (TPE) thin film with uniform micro-sized holes (relative standard deviation (RSD) of the size of micro-holes <3.5 %, n  > 300), which serves as the patterned mask for in-situ growing Ni(OH) 2 nanowalls at the micro-hole areas (“bottom-up” strategy). The obtained gas microsensors based on this strategy showed great reproducibility of electric properties (RSD < 0.8%, n  = 8) and sensing response toward real-time H 2 S detection (RSD < 3.5%, n  = 8). Gas sensors: Combining top-down and bottom-up High-throughput and repeatable fabrication of miniaturized gas sensors is achieved by combining top-down and bottom-up techniques. Miniaturized gas sensors are typically manufactured by top-down techniques such as printing sensing materials on the sensor chips. However, achieving uniform and repeatable device performance is challenging. Here, a group led by Sujie Qin from Xi’an Jiaotong-Liverpool University and Ting Zhang from Suzhou Institute of Nano-tech, CAS combine top-down MEMS-based techniques with bottom-up in-situ growth of sensing materials to fabricate gas sensors. Specifically, MEMS based micro-hotplates are fabricated on a silicon wafer, followed by photolithography, then a de-wetting step assembles an elastomeric thin film with uniform micro-holes. Finally, in-situ growth of Ni(OH) 2 nano-walls at the micro-holes creates the sensing device. The gas sensors showed reproducible electrical properties and sensing behavior for the detection of hydrogen sulfide gas.