A micro cycloid-gear system fabricated by multi-exposure LIGA technique

Abstract

In this paper, a prototype of 2 mm-diameter micro-cycloid gear system fabricated by the multi-exposure LIGA technique is presented. The gear system is composed of a casing and three vertically stacked disks and gears. Each part consists of three different levels. The ®rst level, 40 lm high, was fabricated by UV-lithography, and the second as well as the third level, 195 lm and 250 lm high respectively, were processed by aligned deep X-ray lithography (DXL). The alignment error between two DXL-processed layers has been measured to be within 5 lm range. As a result of the height control process, the deviation of structural height has been maintained within 3 lm range for the UV-lithography-processed structures, and 10 lm for the DXL-processed structures. Preliminary tests of gear assembly have been implemented with 125 lm-diameter commercially available glass ®ber, and the further efforts are being carried out. IntroductionA simple shadow casting in deep X-ray lithography (DXL) creates patterns with quality vertical walls and high aspect ratios. However the requirements for the current microparts application include more complex 3D geometry and multi-level con®gurations [1]. The 3D structural formation with LIGA technique can be primarily classi®ed into two categories, i.e. the one based on the sequential planar formation of individual levels to form 3D structures [2], and the other with spatial alternation of the absorbed dose typically implemented by the mask-dragging [3]. Regarding the sequential approach, the additional processes such as the replanarization after the electroplating as well as the mask-alignment procedure are involved between each conventional DXL cycle. These complementary processes give another constraint in the maximum attainable fabrication precision, and it is considered to approximately be in the range of 5 lm with regard to the typical resist thickness of the several tens to hundreds microns [4]. Whether this precision range can meet the requirement of today's practical movable micro-parts is of great interest.In this paper, a prototype of an encapsulated microcycloid gear system is presented. Following the explication about the design and the fabrication detail, the results of the measurement about the alignment accuracy between two DXL-processed layers are presented. The results on the height controllability of the UV-lithography-processed as well as the DXL-processed components are also reported. The controllability of the structural height by mechanical polishing is discussed as well. 2Design and functionality Figure 1 shows a schematic of the cross-sectional view of the micro-cycloid gear system. The overall dimension is 2 mm in diameter and 1.15 mm in height. The system comprises four parts, namely driving disk, internal 17-tooth gear, output-torque disk and casing. The eight 40 lm-high turbine blades provided underneath the driving disk activate the system by means of the working gas introduced from the inlet hole on the bottom lid. The axis of the 400 lm-diameter boss sits 32 lm o...

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