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Introduction: An Overview of Conventional Patterning of Electronics Patterning of electronics to obtain specific designs is conventionally carried out on silicon wafers by photolithography. This is a process of transferring images and patterns from a mask to the surface of a silicon wafer. The steps typically involved in the photolithographic process are: wafer cleaning, barrier layer formation, photoresist application, soft baking, mask alignment, exposure and development and hard-baking. 57227
The silicon wafers are 1st chemically treated in order to remove particulate matter, organic contaminants, and ionic and metallic impurities. Next, a passive silicon oxide barrier layer is grown across the surface of the wafer. A layer of either a positive or negative photoresist is then applied by spin coating. Soft-baking plays a very critical role in photo-imaging. In the soft-baking step, most of the solvent is removed from the photoresist coating. This photoresist layer is then covered with an appropriate mask and is exposed to actinic radiation. After photo-exposure and post exposure bake, the resist is developed by a selective solvent to reveal a negative or positive image of the pattern on the mask. (Positive: exposed material is removed, negative: unexposed material is removed). In the final step, the wafer is hard-baked in order to remove residual solvent from the photoresist and improve adhesion of the photoresist to the wafer surface. The resist protects the surface of the wafer and allows selective etching, doping, ionimplantation or metallization. Recent improvements and technological advances in the field of photolithography have made it possible to obtain circuitry of near nanoscale dimensions. [1].
Photolithographic patterning requires a large infrastructure. The industry however is well established and has benefited from continuing improvements in pattern resolution. Photolithography is used in the production of our most important electronic components, integrated circuits and devices. 源1自3优尔8.论~文'网·www.youerw.com
While it is a complex, expensive and capital intensive process, given economies of scale ever lower cost microelectronics have been realized. Electronic circuits and devices patterned on crystalline silicon are, however constrained by limitations of wafer size. Accordingly this process on silicon does not lend itself to wide format applications like those in which novel plastic semiconductive materials can be leveraged [2]. Increased research in the field of printable electronics is being conducted because lithographic processes must accommodate serious environmental hazards like acidic and high heavy metal content effluents and use of volatile organic compounds (VOCs) in photoresist developers [3]. The environmental impact of photolithographic process is significant. The overall processing and development of photolithographic patterns consumes much more material than that contained in circuits and devices produced thereby [4].
The disposal of circuit boards is also a problem. Resin laminate substrates can contain fungicides, fire retardants and organic compound and toxic residues from soldering operations. These constituents necessitate recycling operations and disposal [5].
A Brief Introduction of Printed Electronics
Printed electronics may employ any of a number of printing technologies or processes to create electronic circuits and devices and electrical components and interconnects. Printed electronics can be used alone or in combination with conventional microelectronic components such as silicon chips for a range of different applications. Printing technologies have received increased interest recently because of their ability to pattern a variety of functional materials. Printing technology also allows use of various types of substrates including flexible media. Materials as varied as conductive and semiconductive electronically functional polymers can be patterned using printable technologies. Direct printing of electronic features may create new markets and new low cost microelectronic products.