Sequential self-assembly of micron-scale components with light
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We present a versatile and flexible method to sequentially self-assemble micron-scale components at specific locations onto unconventional substrates, such as glass and plastic. In this method, components are independently batch fabricated and assembled onto a series of receptor sites incorporated onto a substrate in a fluid medium. Initially, all self-assembly sites are blocked with a photoresist polymer. Controlled light exposure can be used to remove the polymer and make a site available for receiving a microcomponent. By repeating this procedure, various microcomponents may be integrated onto specific locations on the substrate. To demonstrate the process, we prepared four types of 20 lm thick, 320 lm diameter circular silicon components and showed their optically controllable self-assembly in arrays of 640 receptor sites on glass and plastic with yields reaching 85%. The integration and operation of two types of functional components, red light-emitting diodes and silicon resistors, on plastic substrates was also demonstrated. I. INTRODUCTION
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2010.20
packaging methods (including self-assembly) is the ability to integrate heterogeneous parts and components to the proper locations. For the self-assembly approach to be effective for heterogeneous integration, means must be devised to control and program the process to be able to guide each component to assemble onto the proper location. Self-assembly has been programmed in the nanoscale using techniques such as DNA hybridization and peptide surface binding.5,6 Using biomolecular interactions as the driving force for self-assembly provides inherent programmability due to the specificity of these reactions and the capability to suppress them. Strong biotin-avidin binding was used to self-assemble nanorods head to tail or side by side.7–9 Hybridization of ss-DNA attached to nano-objects was used to self-assemble specific components such as carbon nanotubes, nanorods, and silicon islands on templates.10–13 Microscale self-assembly has been programmed using various techniques such as controlling surface hydrophobicity, controlling solder alloy activation, and applying dielectrophoresis forces. Xiong et al.14 used the capillary forces between hydrophobic components and pads on the template as the driving force for self-assembly. They were able to assemble two types of components by changing the hydrophobicity of the pads using electrochemical desorption of a self-assembled monolayer. Liu et al.15 used the capillary force between molten alloys on a template and metal pads on the components to drive the self-assembly. They self-assembled two types of components by using alloys with two different melting points. The proper site on the template was activated for each type of component by step heating the fluid environment. Chung et al.16 used microheaters to locally melt solder alloy and assemble different color light-emitting diodes (LEDs) onto designated locations on a flexible template
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