Current trends in miniaturized diagnostics indicate an increasing demand for large quantities of mobile devices for health monitoring and point-of-care diagnostics. This comes along with a need for rapid but preferably also green microfabrication. Dry film photoresists (DFPs) promise low-cost and greener microfabrication and can partly or fully replace conventional silicon-technologies being associated with high-energy demands and the intense use of toxic and climate-active chemicals. Due to their mechanical stability and superior film thickness homogeneity, DFPs outperform conventional spin-on photoresists, such as SU-8, especially when three-dimensional architectures are required for micro-analytical devices (e.g. microfluidics). In this study, we utilize the commercial epoxy-based DFP ADEX to demonstrate various application scenarios ranging from the direct modification of microcantilever beams via the assembly of microfluidic channels to lamination-free patterning of DFPs, which employs the DFP directly as a substrate material. Finally, kinked, bottom-up grown silicon nanowires were integrated in this manner as prospective ion-sensitive field-effect transistors in a bio-probe architecture directly on ADEX substrates. Hence, we have developed the required set of microfabrication protocols for such an assembly comprising metal thin film deposition, direct burn-in of lithography alignment markers, and polymer patterning on top of the DFP.

Silicon surface passivation by gallium oxide (Ga $_{2}$ O $_{3}$ ) thin films deposited by thermal- and plasma-enhanced atomic layer deposition (ALD) over a broad temperature range from 75 °C to 350 °C is investigated. In addition, the role of oxidant (O $_{3}$ or O-plasma) pulse lengths insufficient for saturated ALD-growth is studied. The material properties are analyzed including the quantification of the incorporated hydrogen. We find that oxidant dose pulses insufficient for saturation provide for both ALD methods generally better surface passivation. Furthermore, different Si surface pretreatments are compared (HF-last, chemically grown oxide, and thermal tunnel oxide). In contrast to previous reports, the annealing time to activate the surface passivation is found to be significantly shorter. The best surface saturation current densities (J $_{0s}$ ) or surface recombination velocities (S $_{eff}$ ) are 6 and 9 fA/cm² or 0.6 and 1.5 cm/s for n- and p-type Si, respectively. We correlate the surface passivation with the negative fixed charge density (Q $_{fix}$ ; field-effect passivation) and the interface defect density (D $_{it}$ ; chemical passivation). It turns out that a high Q $_{fix}$ is present, irrespective of the utilized ALD-method, deposition temperature, or postannealing, whereas low D $_{it}$ is only achieved for plasma-enhanced ALD at low temperatures. A critical H-density of ∼1016 cm−2 is identified as a necessary but not sufficient condition for excellent surface passivation. Finally, contact resistivities are measured to investigate the possibility of using ALD-Ga $_{2}$ O $_{3}$ as passivating contact material. In order to understand the current-voltage measurements, the energetic positions of the band edges and the Fermi level are determined by ultraviolet photoelectron spectroscopy and Kelvin probe.

A fabrication strategy for high-efficiency passive three-dimensional microfluidic valves with no mechanical parts fabricated in silicon and glass substrates is presented. 3D diffuser-nozzle valve structures were produced and characterized in their added value in comparison to conventional diffuser-nozzle valve designs with rectangular cross sections. A grayscale lithography approach for 3D photoresist structuring combined with a proportional transfer by reactive ion etching allowed to transfer 3D resist valve designs with high precision into the targeted substrate material. The efficiency with respect to the rectification characteristics or so-called diodicity of the studied valve designs is defined as the ratio of the pressure drops in backward and forward flow directions. The studied valve designs were characterized experimentally as well as numerically based on finite element simulations with overall matching results that demonstrate a significantly improved flow rectification of the 3D valves compared to the corresponding conventional structure. Our novel 3D valve structures show, for instance, even without systematic optimization a measured diodicity of up to 1.5 at low flow rates of only about 10 μl/s.