New types of microlens arrays for the IR based on inorganic chalcogenide photoresists

Chalcogenide (ChG) glassy films possess properties of IR transparent (0.8-12 μm) glasses with high values of refractive index (2.3-3.3) and are also effective photoresists with very high resolution (>10⁴ lines/mm). Using ChG photoresists, a simple technology can be developed for the fabrication of IR microlens arrays (MA), a growing application in modern optoelectronics. Due to their optical properties, the ChG glasses can be used in numerous applications as the final material for the MA; therefore reactive ion etching generally used for transferring the MA to a substrate material, can be eliminated. Three different methods of MA fabrication are discussed. In the first method As-Se photoresists with a negative developer and proximity lithography are used. In the second method, As-S photoresists with a positive developer and half-tone photomasks are used. The third method, including a stage of thermal reflow, uses low-melting As-Se-I ChG films developed for this purpose. This can result in lens thicknesses greater than that using either of the first two methods.