Application of sacrificial polymers in electronic and transient devices
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Sacrificial polymers are useful polymers to use in variety of applications. They can be used in microelectronic fabrication process to act as temporary placeholder and create air cavities for microelectronic fabrication and electronic packaging. More recently, there is interest in using sacrificial polymers as structural materials for transient electronic and other transient devices. Transient devices can be triggered to decompose or distintegrate by forming small monomer unit or dissolving in aqueous solution. The resulting devices can vanish and leave behind little or no traces. This provides great opportunity for disposal of electronic devices, as well as for military application where device discovery after usage is unfavorable. However, challenges are remaining to use the existing materials to achieve the application purpose to be met. In order to make them feasible for actual application, modification of polymer chemical structure and tuning of formulations are needed. Sacrificial polymers with suitable thermal stability and chemical miscibility with epoxy resin, such as high ceiling temperature epoxide functionalized poly(propylene carbonate), can act as a temporary placeholder to create nanoporous, low dielectric constant and loss printed circuit boards for faster device switching speed while still maintaining the original mechanical properties. Photosensitive, transient low ceiling temperature poly(phthalaldehyde) are of interest because they can make use of sunlight to trigger the transient properties. The transient and mechanical properties of poly(phthalaldehyde) transient polymer were tuned using different types of traditional and ionic liquid plasticizer for possible applications in a variety of conditions. To extend the application horizon of transient polymers, weakly basic amide and lactam were included in the photosensitive transient films and shown to delay the photo-induced degradation by forming weak conjugate acid in-situ. To make the fabrication process of light sensitive transient device easier, proof-of-concept bilayer photosensitive poly(phthalaldehyde) using photoacid diffusion was explored to make device fabrication more friendly. Prototypes of transient aircraft, transient parachute, and transient triboelectric nanogenerator were successfully demonstrated using the developed technologies. The advances in developing transient materials show a pathway forward to apply these technologies in defense and recyclable devices in the future.