Cofabrication: A Strategy for Building Multicomponent Microsystems

摘要

Tnhis Account describes a strategy for fabricating multi-ncomponent microsystems in which the structures ofnessentially all of the components are formed in a single stepnof micromolding. This strategy, which we call “cofabrica-ntion”, is an alternative to multilayer microfabrication, innwhich multiple layers of components are sequentially alignedn(“registered”) and deposited on a substrate by photolithog-nraphy.nCofabrication has several characteristics that make it annespecially useful approach for building multicomponent microsystems. It rapidly and inexpensively generates correctly aligned com-nponents (for example, wires, heaters, magnetic field generators, optical waveguides, and microfluidic channels) over very largensurface areas. By avoiding registration, the technique does not impose on substrates the size limitations of common registrationsntools, such as steppers and contact aligners. We have demonstrated multicomponent microsystems with surface areas exceedingn100 cm2n, but in principle, device size is only limited by the requirements of generating the original master.nIn addition, cofabrication can serve as a low-cost strategy for building microsystems. The technique is amenable to a varietynof laboratory settings and uses fabrication tools that are less expensive than those used for multistep microfabrication. More-nover, the process requires only small amounts of solvent and photoresist, a costly chemical required for photolithography; in cofab-nrication, photoresist is applied and developed only once to produce a master, which is then used to produce multiple copies ofnmolds containing the microfluidic channels.nFrom a broad perspective, cofabrication represents a new processing paradigm in which the exterior (or shell) of the desirednstructures are produced before the interior (or core). This approach, generating the insulation or packaging structure first and inject-ning materials that provide function in channels in liquid phase, makes it possible to design and build microsystems with compo-nnent materials that cannot be easily manipulated conventionally (such as solid materials with low melting points, liquid metals,nliquid crystals, fused salts, foams, emulsions, gases, polymers, biomaterials, and fragile organics). Moreover, materials can be altered,nremoved, or replaced after the manufacturing stage. For example, cofabrication allows one to build devices in which a liquid flowsnthrough the device during use, or is replaced after use. Metal wires can be melted and reset by heating (in principle, repairing anbreak). This method leads to certain kinds of structures, such as integrated metallic wires with large cross-sectional areas or opti-ncal waveguides aligned in the same plane as microfluidic channels, that would be difficult or impossible to make with techniquesnsuch as sputter deposition or evaporation.nThis Account outlines the strategy of cofabrication and describes several applications. Specifically, we highlight cofabricatednsystems that combine microfluidics with (i) electrical wires for microheaters, electromagnets, and organic electrodes, (ii) fluidic opti-ncal components, such as optical waveguides, lenses, and light sources, (iii) gels for biological cell cultures, and (iv) droplets for com-npartmentalized chemical reactions, such as protein crystallization.