Top-Down Fabrication of Chemical and Biological Sensors

ConspectusFabrication of complex three-dimensional (3D) structures with micro/nanoscale dimensions is crucial for high-performing chemical and biological sensor applications. It not only enables the accurate detection and tracking of minuscule chemical and biological analytes but also determines the commercial viability and practical utilization of the sensors in future intricate applications. Among various structure fabrication approaches, top-down lithography provides invaluable tools for fabricating complex 3D micro/nanoscale structures in sensors, enabling the sensitive and selective detection of low concentration chemical and biological analytes. Moreover, it preserves the inherent advantages of top-down lithography as the sensor attributes, including (i) high-resolution and tight pitch 3D structures in long-range order, (ii) varied pattern shapes, dimensions, and densities, (iii) low device-to-device variation, (iv) high integrated circuit yield, (v) acceptable process cost and processability, and (vi) the ability to accommodate a wide range of materials. Given the variety of top-down lithographic methods available for fabricating sensors and the complex requirements of the sensor such as diverse target analytes, varying concentration levels, and different sensing environments, it is essential to have a comprehensive understanding of the technical nuances associated with each top-down lithography technique and its applications. However, there is a significant gap in the literature regarding targeted evaluations of top-down lithography methods for high-performance chemical and biological sensor fabrication as well as a clear articulation of sensor design rules.This Account outlines the primary top-down lithography methods (photolithography, electron beam lithography, nanoimprint lithography, and secondary sputtering lithography) used in the development of high-performance chemical and biological sensors. We discuss each lithography principle, fabrication process, possible substrates, and derived pros and cons. Further, we examine recent research on exemplary top-down lithography-based chemical and biological sensor applications, discussing the unique structure features and their sensor performance implications. The applications range across versatile analytes in various phases. Lastly, we summarize the target chemical and biological analytes, the measured concentration ranges, the sensor materials, the patterns' widths, heights, and resolutions, as well as the associated lithographic methodologies. Furthermore, substantial opportunities for further development still remain in this field, so we will also address the challenging points and outlook including field validations of top-down nanostructured sensors, data processing, and significant environmental problems arising from the process. The conclusion section of this Account will detail these remaining challenges and future directions. Through this Account, we aim to highlight the importance and capability of top-down lithography in high-performing sensor fabrication and provide new insights into fully realizing its potential.