Electrostatically formed nanowire (EFN) transistor-An ultrasensitive VOC and gas sensor

The perpetual need for high-performance volatile organic compound (VOC) sensors remains prevalent across diverse sectors including environmental health monitoring, industrial operations, and medical diagnostics. Within this context, the electrostatically formed nanowire (EFN) sensor, a silicon-on-insulator-based multiple-gate field-effect transistor, is an ultrasensitive and selective VOC and gas sensing platform. Unlike conventional silicon nanowires (also known for their superior sensitivity to chemical species), in EFN, the nanowire is defined electrostatically post-fabrication through appropriate biasing of the surrounding gates. The fabrication of the EFN leverages established CMOS compatible silicon processing technologies, facilitating the production of inexpensive, scalable, and robust sensors. By precisely controlling gate biases, a conductive channel with a tunable diameter is formed, allowing for the formation of nanowire with diameter below 20 nm. The adjustable size and shape of the nanowire offer tunable sensing parameters, including sensitivity, limit of detection, and dynamic range. The multiple parameters also yield a unique fingerprint for each VOC, thus enabling selective detection of VOCs. By simply altering the biasing configuration, a single EFN sensor can achieve high sensitivity and a broad dynamic range, which is limited in the case of physically defined silicon NW sensors. This review provides a comprehensive overview encompassing the EFN sensor's design, fabrication considerations, process flow, electrical characterization methods, sensing performances to VOCs, and gases at room temperature. Moreover, the scope of advanced sensor designs with array of EFN sensors and integrated heaters is also discussed. Finally, some future perspectives of this technology are presented. (C) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).