Rubber Stamping for Plastic Electronics and Fiber Optics
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Rubber Stamping for Plastic Electronics and Fiber Optics John A. Rogers Introduction
Microcontact printing (CP)1 is a lowcost technique for rubber stamping that combines the high spatial resolution of sophisticated forms of photolithography with capabilities (e.g., single-step patterning of large areas2 and nonplanar surfaces3,4) that are not present in other approaches. CP will be useful for applications where established methods are ineffective. Two areas are particularly promising: (1) plastic electronics,2,5–7 where the chemical incompatibility of the constituent materials with common photoresists and developers can preclude the use of photolithography, and where CP with rotating cylindrical stamps5,8 forms an excellent match with the type of reel-to-reel processing that is envisioned for these systems; and (2) new classes of optical-fiber and microcapillarybased devices,9–11 where CP allows highresolution (0.2 m) circuits, photomasks, and actuators to be printed directly on the highly curved surfaces of cylinders with submillimeter diameters. This article describes some highlights of our work in these and related areas.
Printed Plastic Electronics and Paper-Like Displays Plastic electronic systems are attractive because the easy processability of organic semiconductors may make it possible to print circuits in a rapid, continuous fashion on large sheets of plastic. This type of technology will enable not only low-cost versions of existing electronic devices, but also new systems that cannot be realized with inorganic materials and substrates. An important example of the latter is electronic paper, a thin, mechanically flexible display that has the “look and feel” of conventional printed paper. These systems represent important technologies for electronic newspapers and other devices of the future.2,12,13 Realistic applications such
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as this one demand a carefully selected set of organic materials as well as complementary low-cost methods to pattern circuits that incorporate them. Figure 1a shows a schematic crosssectional view of a typical organic thinfilm transistor. Current flows through the semiconductor from the source to the drain electrode; voltage applied to the gate modulates the magnitude of this current. The separation between the source and drain, known as the channel length L, is a critical dimension that determines the performance of the transistor. For a given set of materials and operating voltages, reducing L improves the current output, the switching speed, and other characteristics. As a result, development of low-cost methods for printing the source and drain can drive progress in this field. Organic transistors suitable for electronic-paper displays, for example, can be produced with known organic semiconductors (or other conventional or emerging inorganic and hybrid semiconductors) and spin-cast dielectrics, provided that the channel lengths are, roughly, less than 10–20 m. Our work establishes that CP, which easily meets these resolution requirements, can be used to fabric
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