Micromachining SU-8 pivot structures using AZ photoresist as direct sacrificial layers for a large wing displacement

This paper presents the micromachining of SU-8 pivot structures. A new processing method was proposed using AZ 4562 as sacrificial layers to create a controlled air gap in the pivot region. These three-dimensional SU-8 pivot structures are designed to obtain a large wing displacement of the bio-mimetic flying micromachine. Several sacrificial methods used for the fabrication of SU-8 structures were reviewed and compared. A new process featuring AZ 4562 sacrificial layers was developed. Two relevant effects, the scission and outgassing effects, were greatly weakened to acquire a better SU-8/AZ interface. It was found that AZ 4562 could be directly deposited on SU-8 without any barrier layer between AZ 4562 and SU-8. So, AZ 4562 can be used directly as a thick sacrificial layer, thus greatly simplifying the fabrication process. SU-8 reinforcing patches can be added to compensate for the loss in the thickness of the central beam in the pivot regions. Using this new method, SU-8 pivot structures with different central beams, either straight or L-shaped, were successfully materialized. The air gap obtained was large and reached similar to 100 mu m, thus helping to produce a large wing displacement. The fabrication precision and its main factors were evaluated. The deviation of actual structure size from design value was 2-7%, depending on the material and technique involved. Preliminary measurements of the fabricated structure indicating that a large wing displacement, flexure angle and torsion angle can be achieved. This new process is simple, low cost and compatible with standard MEMS technology.