Direct Laser Writing: From Materials Synthesis and Conversion to Electronic Device Processing

Direct Laser Writing (DLW) has been increasingly selected as a microfabrication route for efficient, cost-effective, high-resolution material synthesis and conversion. Concurrently, lasers participate in the patterning and assembly of functional geometries in several fields of application, of which electronics stand out. In this review, recent advances and strategies based on DLW for electronics microfabrication are surveyed and outlined, based on laser material growth strategies. First, the main DLW parameters influencing material synthesis and transformation mechanisms are summarized, aimed at selective, tailored writing of conductive and semiconducting materials. Additive and transformative DLW processing mechanisms are discussed, to open space to explore several categories of materials directly synthesized or transformed for electronics microfabrication. These include metallic conductors, metal oxides, transition metal chalcogenides and carbides, laser-induced graphene, and their mixtures. By accessing a wide range of material types, DLW-based electronic applications are explored, including processing components, energy harvesting and storage, sensing, and bioelectronics. The expanded capability of lasers to participate in multiple fabrication steps at different implementation levels, from material engineering to device processing, indicates their future applicability to next-generation electronics, where more accessible, green microfabrication approaches integrate lasers as comprehensive tools.

Underpinning transport phenomena for the patterning of biomolecules

Surface-based assays are increasingly being used in biology and medicine, which in turn demand increasing quantitation and reproducibility. This translates into more stringent requirements on the patterning of biological entities on surfaces (also referred to as biopatterning). This tutorial focuses on mass transport in the context of existing and emerging biopatterning technologies. We here develop a step-by-step analysis of how analyte transport affects surface kinetics, and of the advantages and limitations this entails in major categories of patterning methods, including evaporating sessile droplets, laminar flows in microfluidics or electrochemistry. Understanding these concepts is key to obtaining the desired pattern uniformity, coverage, analyte usage or processing time, and equally applicable to surface assays. A representative technological review accompanies each section, highlighting the technical progress enabled by transport control in e.g. microcontact printing, inkjet printing, dip-pen nanolithography and microfluidic probes. We believe this tutorial will serve researchers to better understand available patterning methods/principles, optimize conditions and to help design protocols/assays. By highlighting fundamental challenges and available approaches, we wish to trigger the development of new surface patterning methods and assays.