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Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim Part 8

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Tham khảo tài liệu 'microsensors, mems and smart devices - gardner varadhan and awadelkarim part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | PROJECTION METHOD 193 Figure 7.27 Some high-aspect-ratio microparts fabricated using surface MSL a microcups b a microtube of inner diameter 50 pm and height 800 pm c 100 pm by 300 pm microchannels in HDDA 1.6 hexanediol diacrylate and d a microcone with a bottom diameter of 500 pm and a height of 250 pm 7.6 PROJECTION METHOD As described in the preceding sections the scanning MSL can be used for very fine high aspect ratio 3-D microstructure fabrication but the fabrication speed is always a major concern - even with the galvano-scanning method. Scanning MSL builds up the objects layer by layer but each layer is itself built up line by line. Thus projection MSL has been proposed for the more rapid building of 3-D microstructures. Although it is still building layer by layer each layer is now written by just one uv exposure through a mask. The reintroduction of a photographic mask plate produces significant savings in time but does add the extra expense of preparing masks. Basically there are two types of projection MSL one is the use of a real photographic mask to project the uv pattern for curing Nakamoto and Yamaguchi 1996 and the other is to use a dynamic mask referred to here as the liquid crystal display LCD projection method Bertsch et al. 1997 . 7.6.1 Mask-Projection MSL As in standard photolithography an image is transferred to the liquid photopolymer by shining an ƯV beam through a patterned mask plate as shown in Figure 7.28 Suzumori 1994 . Then another fresh layer of liquid photopolymer is prepared on top of the patterned solid polymer. By repeating the above process a multilayered 3-D microstructure can be built by this mask projection MSL Katagi and Nakajima 1993 Nakamoto and Yamaguchi 1996 Suzumori et al. 1994 . Let us now consider the equations that govern the optics of mask-projection MSL Nakamoto and Yamaguchi 1996 When a beam of uniform intensity Zo passes through a square mask with the centre of the mask at X 0 and y 0 the depth of the polymer .