SU8-micromechanical structures with in situ fabricated movable parts

Abstract

We report on the versatile application potential of SU8 photoepoxy for movable micromechanical components. Its outstanding resolution, aspect ratio, and attainable ®lm thicknesses enable the design of structures that allow lateral mechanical interaction of voluminous micro parts. We additionally developed a sacri®cial layer process enabling the release of in situ fabricated micro parts as well as large area parts used for capping and packaging. The applicability of this technology is demonstrated on gearwheels in a turbine con®guration, a micro¯uidic channel with integrated check valve, and an advanced multilayer capping technology with precise feather key ®t. 1 Introduction So far, Epon SU8 has mainly been used and investigated for various high aspect ratio patterning purposes such as masking for deep RIE etching [1], electroplating moulds [2, 3], and injection moulding masters [4]. Besides the use for micro¯uidic components [5] and structural parts for micro motors [6], there is little usage of this material for mechanical and especially movable micro parts. SU8 offers material properties that are useful for mechanical applications [7].The SU8 monomere provides a very high group functionality of eight. Cured SU8 forms a highly cross linked matrix of covalent bonds, resulting in glass like mechanical properties. Other advantages are the relatively low price, the feasibility of batch processing, and the high chemical resistance, which becomes important for (bio-) chemical and medical applications. Moreover, the optical transparency allows for monitoring processes or movements inside the SU8 housing.The material properties and the outstanding structural anisotropy in the fabrication of micro structures open up a promising ®eld of applications. In [7] the fabrication and application of in-plane compliant SU8-structures are demonstrated. In contrast, this paper deals with free movable SU8 parts. In order to reduce process steps and unnecessary mounting of micro parts, the movable structures are fabricated in situ. Fabrication processWe optimized a high aspect ratio SU8 process for single layer thicknesses of 300±400 lm. Multilayer processing allows for device fabrication with vertical dimensions of up to 1 mm. Almost vertical side walls and aspect ratios of up to 36 were achieved [3,7]. The process consists of spin coating in a spinning tool with rotating lid, bakes on ramped hot plates, and successive development in two solutions (GBL and PGMEA). These measures were optimized in order to guarantee uniform ®lm thickness with low residual stress, resulting in crack free structures, even for laterally large structures.Using the optimized parameters, it is also possible to fabricate structures with more than one SU8 layer, resulting in three dimensional micro parts. This was used for caps with feather keys which were lifted off completely and precisely ®t onto micro¯uidic systems. The only restriction for multi layer processing is the fact that the structures in superior layers have to be smaller or same sized as the l...

Optimized SU-8 Processing for Low-Cost Microstructures Fabrication without Cleanroom Facilities

“…In the last few years, SU-8 has been used in a large range of applications, namely, in the fabrication of microchannels for microfluidic and lab-on-a-chip devices [19][20][21][22] and as a structural component in MEMS applications [4,23,24]. Some microstructures, fabricated using the process described in Section 2, for the reported applications are briefly shown below.…”

UV-LIGA: From Development to Commercialization

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