Novel Fabrication of Flexible Electronics by Transfer Printing Process
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Stretchable electronics, represents a class of novel electronic devices fabricated on flexible and bendable substrate, has been researched widely due to its applications cover from epidermal electronics (eSkin), curvillinear display, bio-integrated electronics to photovoltaics. Generally, the electronics can be formed by printing devices onto the flexible substrate (donor) by rubber ‘stamp’, for example, the transistors, diodes, and logic circuits can be picked up after peeling back the elastormeric prepolymer (Polydimethylsiloxane) (PDMS) laminated on the surface of wafer and then contact the ‘inked’ stamp onto target substrate (receiver), peeling off the PDMS will leave the ‘ink’ on the flexible substrate. The ‘pick-up’ process depends strongly on the speed of lamination because the separation energy for elastomer-microstructure interface is related to speed while the one for microstructure-substrate is independent. The yield of the transfer printed is reported as high as 100% without losing function. Besides of solid rubber like PDMS, tape can also be used in the transfer printing process and it’s been reported that this has been implemented to fabricate RF stretchable electronics with liquid metal alloy. In this thesis, a novel balloon transfer printing method (a polymer-coated balloon serves as ‘stamp’) is presented that is useful to fabricate curvillinear electronics, exemplify a smart contact lens similar to Google’s new roll-out. Besides, a tape transfer printing process with high fidelity facilitated by chemically induced adhesive strength modulation is presented. Silicon and metal mesh devices transfer printed by tape on flexible substrate is demonstrated and its functionality is verified by testing. Finally, the corporate project with NASA Johnson Space Center aims to develop a skin mountable patch for exercise monitoring is introduced as well as its related progress.