Explain in details application of polymers in MEMS. Why and how to make polymer conductive.

• Polymers are extensively used as structural and functional materials for microdevices.

• Elasticity, optical properties, biocompatibility of polymers are used as structural materials for MEMS.

• Polymers strain gauages and capacitors serve as sensing elements for piezoresistive and capacitive microsensors.

• Electrostatic polymer microactuators from polyamide.

• Polyamide based ferrite magnetic composites are used as magnetic micro actuators.

• Polymers are used as electronic material (polymer transistor).

• Currently polymers are used in biomedical applications and adhesive bonding.

• New applications involve using polymers as substrates with electric conductivity made possible by doping.

• Photo-resist polymers are used to produce masks for creating desired patterns on substrates by photolithography technique.

• The same photoresist polymers are used to produce the prime mold with desirable geometry of the MEMS components in a LIGA process in micro manufacturing.

• Conductive polymers are used as organic substrates for MEMS and microsystems.

• The Ferroelectric polymers that behave like piezoelectric crystals can be used as the source of actuation in micro devices such as micro pumping.

• The thin Langmuir - BD Blodgett (LB) films can be used to produce multilayer micro structures.

• Polymers with unique characteristics are used as coating substance to capillary tubes to faciliate effective electro - osmotic flow in microfluidics.

• Thin polymer films are used as electric insulators in micro devices and as dielectric substance in micro capacitors.

• They are widely used for electromagnetic interference [EM5] and radio frequency interference [RF5) shielding in microsystems.

• Polymers are ideal materials for encapsulation of micro sensors and the packaging of other microsystems.

Polymers are poor electric conducting materials by nature :-

• Some polymers can be made electrically conductive by the following 3 methods -

1. Pyrolysis :- A pyro-polymer based on phthalonbile resin can be made electrically conductive by adding an a mine heated above. 600°. The conductivity of the polymer produced by this process can be as high as $2.7*10^4$ s/m, which is slightly better than that of carbon.

2. Doping :- Doping with the introduction of on inherently conductive polymer structure, such as by incorporating a transition metal atom into the polymer backbone can result in electrically conductive polymers. Doping of polymers depends on the dopants and the individual polymer.

   Following are examples of dopants used in producing electrically conductive polymers.

   • For polyacetylenes [PA] Dopants such as $Br_2$, $I_2$, $AsF_5$, $HClO_4$, and $H_2SO_4$, are used to produce the P-type polymers, and sodium napthalide in tetrahydrofuron (THE) is used for the n-type polymers.

   • For polyporophenylenes [PPP]: $AsF_5$ is used for the p-type and alkali metals are used for the n-type polymer.

   1. Insertion of conductive fibers :- Incorporating conductive fillers into both thermosetting and thermoplastic polymer structures can result in electrically conductive polymers. Fillers include such materials as Carbon, aluminum flakes and stainless steel, gold and silver fibers, other inserts include semiconducting fibers.

      Example- Silicon and Germanium fibers are in the order of nonameters in length.