Laser Direct-Write Processing
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Introduction From the earliest work on laser interactions with materials, direct-write processes have been important and relevant techniques to modify, add, and subtract materials for a wide variety of systems and for applications such as metal cutting and welding. In general, direct-write processing refers to any technique that is able to create a pattern on a surface or volume in a serial or “spot-by-spot” fashion. This is in contrast to lithography, stamping, directed self-assembly, or other patterning approaches that require masks or preexisting patterns. At first glance, one may think that direct-write processes are slower or less important than these parallelized approaches. However, direct-write allows for precise control of material properties with high resolution and enables structures that are either impossible or impractical to make with traditional parallel techniques. Furthermore, with continuing developments in laser technology providing a decrease in cost and an increase in repetition rates, there is a plethora of applications for which laser direct-write (LDW) methods are a fast and competitive
way to produce novel structures and devices. This issue of MRS Bulletin seeks to assess the current status and future opportunities of LDW processes in the context of emerging applications. There are many types of direct-write techniques used in science and engineering.1 For instance, previous MRS Bulletin issues discussed topics such as inkjet printing (November 2003) and focused ion-beam processing (February 2000, July 2001, and December 2005). In the most classical sense, engraving or milling can be considered a direct-write process, since a tool or stylus makes contact with a surface and is moved in a desired pattern to produce a feature. The coupling of a highpowered laser with direct-write processing enables similar features to be produced without requiring physical contact between a tool and the material of interest. Because of this, few techniques share the versatility of LDW in adding, subtracting, and modifying different types of materials over many different length scales, from the nanometer to the millimeter scale.
MRS BULLETIN • VOLUME 32 • JANUARY 2007 • www.mrs.org/bulletin
In LDW, the beam is typically focused or collimated to a small spot (in industrial processes, this “small” spot can be several millimeters in diameter). Patterning is achieved by either rastering the beam above a fixed surface or by moving the substrate or part within a fixed beam. An important feature of LDW is that the desired patterns can be constructed in both two and three dimensions on arbitrarily shaped surfaces, limited only by the degrees of freedom and resolution of the motion-control apparatus. In this manner, LDW can be considered a “rapid prototyping”2⫺4 tool, because designs and patterns can be changed and immediately applied without the need to fabricate new masks or molds. The key elements of any LDW system can be divided into three subsystems: (1) laser source, (2) beam delivery system, and (3) substrate/t
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