Mumbai University > Electronics Engineering > Sem 8 > MEMS Technology

Marks: 5M

• Polymers are natural or man-made molecules frequently called as macro-molecules. They are composed of smaller units 'monomers' which have reacted together to give a long chain. In simplest polymers, the monomers are identical and polymer is named by prefixing poly to the name of monomer from which it is derived.

e.g. polymer from ethylene is polyethylene.

SU - 8 :

• SU8, a type of epoxy polymer is a new UV-Curable material for constructing micro-mechanical components such as those in MEMS with high aspect ratio.

• This polymer is bio compatible for both in-utro and in vivo applications. It possesses good mechanical properties such as hardness and young's modulus. SU-8 has other capabilities such as photo-sensitivity and transparency to visible light which makes it compatible with micro fabrication processes.

• This is promising structural material for producing novel devices used in MEMS and bio related applications such as drug delivery system, bio-diagnostic. testing kit, bio-MEMS, microfluidics.

• SU8 is a negative tone photoresist.

PMMA [ PolyMethyl Acrylate ]

• PMMA is a positive tone photo-resist often used in x-ray lithography and e.beam lithography process.

• During x-ray lithography process soft x-rays shines on PMMA sheet through a special mask, the exposed PMMA material can be removed in developer and unexposed area remains. Since x-rays have a large, depth of field and a very low diffraction limit microstructure with ultra high aspect ratio and fine lateral resolution is achievable.

• PMMA due to its high transparency is an important polymer in optical applications.

• Researchers have used x-ray lithography and reflow process to obtain microlens with high numerical aperture.

• It is essential step in LIGA Process to develop non-silicon microstructures.

• Polymers like SU8 and PMMA are available in different viscosities which aids in the fabrication of thin film structures and structures with high aspect ratio.

• In some cases receptor molecules can be fictionalized directly onto surface of SU-8 cantilever for variety of sensing applications avoiding additional deposition of a layer for immobilization purpose.