12 - Microfabrication Using Polymers Himanshu J Sant...

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Microfabrication Using Polymers Himanshu J. Sant Fundamentals of Microfabrication Polymers for Microfabrication • Examples diverse – Photoresists – PDMS – PMMA – Polyurethane – Polyimide – Polystyrene • Disadvantages – Low thermal stability – Low thermal and electrical conductivity – Techniques for fabrication on microscale not as well developed • Advantages over silicon – Inexpensive – Flexible – Transparent to visible/ UV – Easily molded – Surface properties easily modified – Improved biocompatibility or bioactivity
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Methods • Photolithography • Injection Molding • Casting • Stamping • Hot Embossing • Laser Ablation • Laser Polymerization / Stereolithography • Laminates Plastics • Thermoplastics – Soft, plastic behavior at low temp, high viscosity at high temp – Melting point typically around 170 ° C – Usually soluble in common solvents – Typically linear polymer chains, minimal cross-linking, high crystallization • Thermosets – Very strong, rigid material – High melting points (the don’t melt) – Typically two-part cure (polymerization, some UV cure – Typically 3D polymers with high degree of cross-linking • Elastomers (rubbers) – Soft, elastic behavior at moderate temperatures – Cured or “vulcanized” to induce cross linking or polymerization – Typically high molecular weight, non-crystalline, sparse cross-linking
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SU-8 Lithography High aspect ratio structures With resolution of a few microns SU-8 Pros and Cons • Pros – High aspect ratio micro-structures can be built cheaply – Allows fabrication in polymers – Uses standard lithography equipment in standard cleanroom. • Cons – Processing is tricky and difficult to get consistent results. – Resist almost impossible to remove! – Mostly only single mask structures – Good for small parts, but most useful devices require assembly • SU-8 is popular for molding microchannels
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Uses optical epoxy negative-resist (SU-8) developed by IBM to produce high aspect ratio micro-structures (1995) UofL Micro-reaction wells: 150 um wide, 120 um tall, 50 um wall thickness Poor Man’s LIGA Nanoimprint Lithography
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Nanoimprint Lithography 10nm diameter metal dots fabricated by NIL 10nm diameter holes imprinted in PMMA Imprint mold with 10nm pillars Polymer Injection Molding
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This note was uploaded on 09/02/2010 for the course MEEN 5050 taught by Professor Himanshuj.sant during the Spring '10 term at Utah.

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12 - Microfabrication Using Polymers Himanshu J Sant...

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