MEMS Fabrication of Infrared Microlenses

As mentioned before, most of the stmctures for infrared detection can be fabricated by microsystem technologies (MST) and the microlenses for optical concentration are not an exception, regardless of the type of the optical element in question 

A point of special importance is the choice of proper material for MWIR and LWIR optical concentrators. A number of materials are customarily used to fabricate infrared optics. Besides these, optical concentrators may be fabricated directly in the photodetector material and indeed be monolithicaUy integrated with it. 

A number of procedures are used to fabricate microlenses for telecommunications and some of them can be modified and adapted to fabricate optical concentrators for the MWIR and LWIR range. Some of these procedures already became standard. 

Chronologically, the oldest approach to microlens fabrication is thermal melting. The action of heat is used to soften or melt convenient material (e.g., germanium in LWIR range) and form it into a desired shape. An alternative is to use material that 

One of the oldest methods used with molding, but at the same time the least accurate, is cast molding (e.g., injection molding, casting, etc.) [111]. This method is used both for refractive and diffractive lenses. First, a high-accuracy master is fabricated. It is subsequently used to produce large series of microlenses. The method is especially convenient for work with plastic materials transparent in IR, like TPX (polymethylpentane, polymerized dimer of propylene.) 

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