Introduction: Fabrication at All Scales

Recommendations F abrication refers to "the action or process of manufactur- ing or inventing something".For this special issue, it pertains to the production of "patterned structures" with feature sizes at nano-, micro-, or macroscale.Such structures are indispensable for the development of modern science and technology, as exemplified by their applications in microelectronics, information storage, and display, as well as the construction of microelectromechanical systems (MEMS), sensors, microfluidic devices, biochips, photonic crystals, and diffractive optical elements.In all these applications, fabrication represents the first and the most significant barrier to their realization.Depending on the application, the criteria for judging the success of a fabrication technique can vary substantially.Among them, critical feature size is probably the most obvious measure that one must consider when choosing a fabrication technique.This is particularly important in microelectronics, where the never-ending demand for higher densities of integration, less power consumption, better performance, and lower cost has been and still is the main driving force behind the continuous trend in downsizing the feature size.On the other hand, fabrication often involves a flow of information that typically begins with the design of a pattern in the form of a data set and ends with a patterned structure.There can be many steps in between, and each one of these steps may impose the possibility to lose some information or to distort the original design, causing the fidelity issue.As such, reducing the feature size while remaining faithful continues to be a prerequisite for the development of a fabrication method or technique.In organizing this special issue, we do not intend to cover in depth all the technical details of the fabrication methods or to describe their extended and sophisticated variants.It is also impossible to exhaust all types of fabrication methods.Instead, this special issue focuses on illustrating the different mechanistic and operational principles involved in the fabrication at a specific length scale for a specific application.Broadly speaking, fabrication can be conducted in two different manners, writing and replication, and they differ in terms of characteristics, requirements, and aspects of emphasis.For example, writing is often accomplished in a serial fashion using a technique that is relatively slow, which renders this process practical for making only a few copies of the so-called original.Once created, the patterned structure can serve as a mask, master, or template in a duplication process to replicate the structure in numerous copies rapidly, inexpensively, and with high fidelity.