High Aspect Ratio Pholithography for MEMS Application - Article Example

This is the most prominent technique and is widely used and can be used with tall microstructures in the range of 100 micrometers to 1 mm. This method though resulting into long micro structures does not affect the lateral dimension accuracy making it effective method in achieving this objective. However, the method cannot be universally applied due to lack of a synchronized source and the fabrication cost of LIGA that is prohibitive. The use of X-rays from a synchronized source with the capability of giving high intensity, hard x-rays with low divergent properties, makes this method to achieve great results despite these limitations.

This led to the development of low cost and commonly available process that would meet the above objectives, and that is close to LIGA. An example was the reactive ion Etching (RIE) of polyamide, which has been presented as a method that could fabricate high aspect ratios structures at the lower costs compared to the above process. This was able to achieve a thickness so of more than 100 micrometers, and an aspect ratio of about 10. This process was however found to be more tedious as it required modification of the RIE machine, and hence not effective.

Other methods that have been used to investigate in this process include the photosensitive polyamide together with UV exposure and have been used in fabricating plating molds. This process achieved a thickness of up to 50 micrometers and an aspect ratio close to 8. Other methods that have been investigated include the high aspect commercial photolithography with photoresist and a near UV light source, in fabricating high aspect ratio molds of metal structures. These are some of the motivations behind the research above by Miyajima and Mehregany.

Research background The research involved investigating the fabrication of high-aspect-ratio structures using a commercially available positive photoresist and the UV exposure increasing molds, which would be used together with electroless nickel plating. The research involved an effort to maintain a 2- 3micrometers line width and increasing the photoresists thickness altogether. This was the main point that most of the LIGA high-aspect-ratio process as described above ignored. Using an electrostatic actuator that had been micro machined with 1.

5 micrometers wide active gaps and up to 5 micrometers polysilicon, and increasing the gap side wall height instead of increasing the gap height was found to result to reduced force/torque, and this eliminated the urge to use high aspect ratio structures. This was the remarkable difference in this process as compared to other processes investigating this problem. The use of evaporated solvents during the coating process ensured that films thicker than 8 micrometers were obtained. After carrying out the complete process and the patterns in photoresist, electroless nickel plating was performed to fabricate metal structures, and this required the chemical compatibility of the photoresits with the plating chemicals to be an important considerations.

This photo lithography process was found to be compatible with the electroless nickel plating process described above. Methodology One of the variables that were to be considered and regulated is the spin speed in coating. A slower speed below 1000rpm could have resulted to rough surface in the photoresists and the