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In this research, first a modular polymer-based (PMMA) injection micromixer prototype has been designed, fabricated and tested. This micromixer is easy to be integrated into biochemical microfluidic systems under development for BioMagnetICs DARPA funded project at CAMD. To improve the mixing efficiency, layout of micronozzles of the mixer was optimized according to the simulation results. Also because SU-8, an epoxy-based negative photoresist, has high chemical resistance, an SU-8 injection mixer was designed and fabricated to run some biochemical sample liquids. Internal stress in patterned SU-8 structures has been reduced and multi-layer SU-8 processing has been successfully developed to fabricate SU-8 injection mixer.

This paper presents recent results on the microstructural evolution and the resulting mechanical property changes as a function of elevated temperature exposure of two types of electroplated nanocrystalline LIGA Ni. Electroplated Ni structures are the main candidates for LIGA-based MicroElectroMechanical System (MEMS). Initial studies have been conducted to correlate microstructure of electroplated Ni and resulting mechanical properties. A major drawback is that upon exposure to elevated temperatures, electroplated Ni MEMS components suffer dramatic reductions in strength mainly due to grain coarsening. This kind of strength deterioration at elevated temperatures can be detrimental to many MEMS applications, especially to micro-engines and molding inserts. Thus, in order to improve the high temperature performance of LIGA Ni, knowledge of the underlying mechanism is needed. At present, there is very limited understanding of processing-microstructure-property relationship for LIGA Ni at both room and elevated temperatures. The current research is focused on temperature effects on the microstructure of LIGA Ni and the resulting mechanical properties. Two types of sulfuric acid-based solutions were used to produce electroplated Ni samples with different microstructural characteristics. The DSC technique was used to study the stability of plated Ni at elevated temperatures. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to examine the microstructural changes of plated Ni samples as a function of annealing temperature. Nanoindentation tests were performed to study the effects of the evolved microstructures on mechanical properties. The underlying mechanism correlating microstructure and mechanical properties of LIGA Ni at elevated temperatures is discussed.

The normal process to fabricate an x-ray mask involves two steps: make an optical mask by using an optical pattern generator (OPG), and form the pattern on the x-ray mask membrane with the optical mask by UV lithography. The sole function of the optical mask is the pattern transfer from source to target. It is always possible that pattern distortion would happen during its transference. In this paper we present a new process to fabricate deep x-ray lithography (DXRL) mask by direct pattern writing on the first layer of resist of an x-ray mask membrane. A thin layer of gold (1 ~ 2 μm) is deposited on the revealed plating base of the membrane and serves as the absorber for a following x- ray exposure of the second (thicker) layer of resist. Finally a thick (5-10 μm) gold layer is plated in the stencil formed by developed second layer of resist. This process has been demonstrated with Kapton membranes (Polyimide foil). The principle of the process can be applied to other x-ray mask membrane materials and to make ultra deep x-ray lithography (UDXRL) mask as well. In this paper the initial results of the new process are presented. The performance of the fabricated mask is evaluated and the alternative approaches will be discussed.

In recent year SU-8 has became the most attractive photoresist in both optical and x-ray lithography. In our early work we have optimized its exposure parameters to improve the patterning quality in UV lithography and concluded that the UV absorption in SU-8 is proportional to the concentration of photoacidgenerator (PAG) and limiting the applicable SU-8 thickness in UV lithography. Actually, the PAG concentration plays an important role in all aspects of SU-8 processing in both optical and x-ray lithography. The motivation of this work is to expand the applicable thickness and application scope and improve processing control of SU-8 by optimizing its PAG concentration. In this paper we present the most recent experimental results on lithographic performance of SU-8 with different PAG concentration (varying up to 2 orders of magnitude). It includes determining the minimum bottom dose and minimum effective energy density in x-ray and UV lithography of SU-8, respectively, observing the dimensional change of SU-8 microstructure at different post exposure bake (PEB) temperature and time and measuring UV absorption spectrum of SU-8 as the function of PAG concentration. The modified SU-8 resists have moderate sensitivities and lower absorption coefficients. The application of the modified SU-8 will be addressed and demonstrated.

This paper describes a process to fabricate three-dimensional multilevel high-aspect-ratio microstructures (HARMs) for magnetoelectronic devices using aligned x-ray lithography in conjunction with electrodeposition. In this process, x-ray masks were constructed on a seed layer coated polyimide membrane with ultraviolet (UV) patterned and electrodeposited gold absorbers. The optically transparent polyimide allows one to align and print large areas (>4 inch in diameter) with high alignment accuracies. Patterns that contain 5-10 μm diameter posts and 7-10 μm wide lines were printed to 100-120 μm polymethyl methacrylate (PMMA) resist prepared on silicon wafers using x-ray lithography. Nickel-iron was electroplated to form ferromagnetic HARMs, while electroplated gold formed circuits. The composition profile measured with an electron probe x-ray microanalyzer (EPMA) suggested that iron content increases as NiFe plating proceeds inside the recess. The electrodeposition resulted in well-defined NiFe structures with aspect-ratios up to 20:1, smooth sidewalls and top surfaces. To isolate the magnetic structures and circuits, both wet chemical etching and sputter etching were explored to remove seed layer, and the latter yielded complete removal without noticeable damage to the features. A complete aligned x-ray exposure and electrodeposition protocol applicable to universal multilevel microstructures was established.