Research On Fabrication Of Micro Devices And Uniformity Of Micro-electroforming

Miniaturization, integration and portability are the trend for technology development. Micro-Electro-Mechanical System (MEMS) is an important mean to achieve it. In the research field of MEMS, biomedical MEMS has been investigated widely due to its great application potential.The microneedle and microfluidic chip fabricated by MEMS technology are typical devices in the field of biomedical MEMS application. Backside exposure technology and micro electroforming technology are the key technologies of producing microneedle and mold, respectively, however backside exposure mechanism is not yet mature, and electroforming technology has a problem of non-uniform sediment thickness, which severely restricts application of microneedle and chip in biomedicine. In this paper, an optimization method for fabricating 3D microneedle arrays with larger cone angles through backside exposure, and methods to improve thickness uniformity of micro electroformed mold are studied numerically and experimentally. The research work in this paper accumulates experience for the further development of biomedicine.In this paper, based on the scalar angular spectrum theory, a circular aperture diffraction simulation program was built with Matlab to obtain the light intensity distribution.265 μm to 380 μm tall microneedles with cone angles in the range of 5.1° to 15.6° were fabricated by controlling the exposure dose and adjusting the thickness of substrate. The microneedle’s bottom diameter is much bigger than the hole diameter on the mask, which can obviously make the microneedle stronger and more stable. Some problems encountered in the experiments were analyzed and discussed, we defined the ratio of the top diameter of microneedle to the hole diameter on the mask as R, R and cone angles were used to evaluate the sharpness of microneedle in the experiments.With Faraday’s law and electrodeposition theory, the relationship between current density distribution and thickness distribution of the electroformed mold was researched. The cathode current density distribution in the electroforming system was simulated with COMSOL. The effect of different auxiliary cathodes on the cathode current density distribution was investigated, and the morphology of electroformed mold was forecasted. In order to verify simulation result, a series of electroforming experiments were conducted. Their thickness distribution was measured by electronic digital display micrometer.lt is found that the experimental results match well with the simulation results, uniformity of the deposited layer is improved by the addition of an auxiliary cathode, and the unevenness of edge to center is reduced to 68.9%from 142.0%.A 200 μm thick mold was made by micro electroforming technology. In order to improve surface property of microfluidic chip mold, femtosecond laser processing technology was used to fabricate the micro/nano structures on the surface of nickel mold, and the surface wetting property of nickel mold was changed. Hot embossing technology was used to transfer the micro/nano structure to PMMA. A method of water pretreatment was used to improve the thermal bonding rate of PMMA microfluidic chip. The shape of PMMA after bonding was processed by CO2 laser processing technology, and eventually microfluidic chip applied in pathogenic germs detections was successfully made.