We present a high-quality UV-lithography process for making high aspect ratio microstructures for microengines using an ultrathick SU-8 photoresist layer. The microreciprocating engine project, which is ongoing at the University of Birmingham, aims to develop a compact power plant to replace batteries. The design of the microengine imposes strict requirements on the geometry of the engine components. The microfabrication research work has been concentrated on developing a SU-8 UV-lithography process to achieve good sidewall angles and high aspect ratio. Based on the study of the photoactive property of ultrathick SU-8 layers, an optimized prebake time is found for obtaining the minimum UV absorption of SU-8. The optimization process is tested and proven effective using a series of UV-lithography experiments on different prebake times. Microstructures with aspect ratios as high as 40:1 are produced in 1000-µm ultrathick SU-8 layers using standard UV-lithography equipment. The sidewall angles are controlled between 85 to 90 deg. The engine components fabricated using this process satisfy microengine design requirements.
A high quality UV-lithographic process for making high aspect ratio micro reciprocating engine parts on ultra-thick SU-8 photoresist CO2 is described. The research work is part of an on-going microengine research project at the University of Birmingham. The project aims to develop a compact power plant for driving MEMS devices and replacing batteries. The novelty of engine design is that the engine is constructed in two layers only, and all parts are designed to suit the 2D microfabrication feature. Due to the strict requirements on the perpendicular geometry of the engine parts, the microfabrication research work has been concentrated in conducting a high quality UV-lithographic process on ultra-thick SU-8 for producing microengine parts. Based on the study of the optical property of ultra-thick SU-8 layer, optimized prebake time has been selected to obtain the minimum UV absorption by SU-8. The optimization principle has proved effective by a series of experiments of UV-lithography on different prebake times, and high aspect ratio structure (about 10) engine parts have been produced in 1000 μm ultra-thick SU-8 layers using the standard UV-lithography equipment. The sidewall angles are controlled between 85~90 degrees, which is a much better improvement than those reported so far.