Micro and Nano Engineering最新文献

Superconducting resonators are widely used in fields spanning from quantum computing to electron spin resonance (ESR) spectroscopy. With the goal of realizing superconducting resonators, a broad variety and combination of superconducting materials, substrates and fabrication processes have been used and thoroughly reported in the literature. High temperature superconductors such as YBCO and low temperature superconductors such as Nb, NbN, NbTiN and Al are the major actors in the domain. In this work, we investigate the possibility to extend the family of suitable low temperature superconductors for the realization of planar superconducting microwave resonators for future ESR applications. In particular, this study focuses on NbTi, a widely used material to realize superconducting cables but not investigated for planar resonating structures at GHz frequencies. A 150 nm thick film of NbTi is sputtered and patterned on top of an Al₂O₃ substrate. For devices resonating around 6.8 GHz quality factors greater than 10,000 are observed at 3 K and in magnetic fields up to 250 mT.

Herein, an Intra-level Mix & Match approach (ILM&M) was investigated to combine electron beam lithography (EBL) and i-line stepper lithography on the same resist layer. This technique allows the combination of the advantages from both technologies. EBL enables the manufacturing of small sub 100 nm structures but has the disadvantage of low writing speed especially for larger structures. The i-line stepper mask- or reticle-based lithography are used for the exposure of larger features with reduced exposure time. Here the negative tone resist ma-N 1402 (from Micro Resist Technology GmbH), an UV and electrone sensitive resist was investigated in EBL and an ILM&M approach. An ILM&M process for both EBL and i-line stepper lithography is performed on the same resist layer followed by one developing step. The inspection of the developed patterns via scanning electron microscopy (SEM) showed dimensions with a 1:1 print for EBL and i-line stepper lithography with respect to the layout. By varying the exposure dose of the i-line stepper, the linear dependency to the structure width is investigated. By this means we achieved structures below the 1:1 print down to 86 nm structure width.

This work presents a micromachining process that allows the creation of hierarchical, matryoshka-like MEMS structures that can be used for multi-axis sensing. This novel vibration multi-axis MEMS sensor based on the capacitive open-loop operation can be widely deployed in the structural monitoring systems due to its simple fabrication and operating principle. The device is composed by a double proof-mass hierarchical design with separate sets of electrodes for in-plane differential measurements. The operation principle of this multi-axis device relies on the fact that accelerations in the zz direction will induce a change in the overlapping area of the xx and yy sensing electrodes, extracted from the single-ended capacitance measurement, while xx and yy accelerations will yield a differential capacitance change. To sense the direction of zz accelerations (capacitance decrease independently of the direction), out-of-plane parallel-plates were added to the device using suspended metallic membranes. The devices were fabricated through an in-house process using a seven-mask dicing-free MEMS process on a 10 μm-thick SOI wafer. The proposed devices were successfully validated using a two-degrees of freedom (DoF) setup that induces external accelerations in the three-orthogonal axes and reads the resulting output voltage of the device. It then possible to conclude that using the proposed fabrication process, it is possible to successfully produce functional multi-structure SOI-based devices that integrate suspended metallic membranes.

Development of point-of-care (POC) diagnostic tools is an emerging area with significant potential for disease surveillance, monitoring, and diagnosis, especially for underdeveloped or developing countries. Our current research focuses on rapid, POC technologies for DNA or RNA detection that can be deployed to significantly decrease the turnaround time when encountering demands for massive quantities of tests, e.g. during a pandemic. Hairpin-like DNA or molecular beacon (MB) probes can be used as bioreceptors to specifically bind to a pathogen DNA or RNA. In the presence of complementary DNA, the immobilized MBs undergo a conformational change, and the fluorescent signal of 5’-FAM is restored from the internally quenched fluorophore. Here we studyinvestigating 3D polymer brush (PB) structures with antifouling surface properties, functionalized with a particular MB-DNA probe. Patterns of polymer brushes were created on foils of poly(ethylene-co-tetrafluoroethylene) (ETFE) activated through a metal mask using extreme ultraviolet (EUV) radiation, yielding patterns of initiators for the subsequent graft-copolymerization of vinylpyrrolidone (VP) and glycidyl methacrylate (GMA). The successful copolymerization of VP and GMA on the EUV-exposed areas was proved based on characteristic peaks of VP and GMA in ATR-IR spectra. Structure heights in the range of micrometers were achieved, which enables binding of considerably higher densities of probe molecules compared to monolayer systems. The grown polymer brush structures provide both hydrophilicity, beneficial to minimize bio-fouling, and epoxide functional groups for further functionalization. These were biotinylated and functionalized with streptavidin and 3′-biotinylated MBs, resulting in a promising platform for fluorescence-based DNA detection as demonstrated by significant fluorescence increase upon addition of target DNA down to nM concentrations. Finally, embedding of optimized MB/PB structures into a microfluidic channel and coupling to a mobile-phone-based fluorescence microscope for signal detection was demonstrated.

Metal assisted chemical etching is a promising method for fabricating high aspect ratio micro- and nanostructures in silicon. Previous results have suggested that P-type and N-type silicon etches with different degrees of anisotropy, questioning the use of P-type silicon for nanostructures. In this study, we compare processing X-ray zone plate nanostructures in N and P-type silicon through metal assisted chemical etching with a gold catalyst. Fabricated zone plates were cleaved and studied with a focus on resulting verticality, depth and porosity. Results show that for high aspect ratio nanostructures, both N and P-type silicon prove to be viable alternatives exhibiting different etch rates, but similarities regarding porosity and etch direction.

Spontaneous capillary flow in open microchannels is a phenomenon driven by surface energies. The contact angle that the liquid forms with the channel's substrate material and the cross-section of the microchannel decide whether liquid from a connected reservoir will automatically fill the channel or not. In this work we show how this behavior can be used to design a passive contact angle measurement device (CAMD) based on parabolic open microgrooves. To that end, we present a theory of open capillary flow in such microgrooves and compare the results to minimal energy surface simulations. Additionally, we discuss that the condition for capillary flow of curved microchannels is essentially equal to the condition for their straight counterparts having the same cross-section.

Lastly, we present two demonstrators of our CAMD made out of micromilled poly(methyl methacrylate). The devices consist of five open microchannels with different cross-sections which are connected to a common liquid reservoir. We show how the behavior of a liquid placed into that reservoir can be used to evaluate the contact angle between the liquid and the substrate material. A comparison to conventional contact angle goniometry shows that our approach is able to successfully estimate contact angles with an accuracy of 10° by design which can be improved by employing a greater number of microchannels. Since our devices were automatically designed and can be tuned to specific applications, this provides an easy approach to include contact angle measurement into existing lab-on-a-chip devices.

Field-effect transistors (FETs) based on MoS₂ nanotubes prepared in anodic aluminum oxide (AAO) templates have been fabricated and demonstrated in this work. MoS₂ nanotubes were prepared by the thermal decomposition of (NH₄)₂MoS₄ precursors in the AAO template. The diameter of the MoS₂ nanotubes was approximately 80 nm, which corresponded to the size of the AAO template. Schottky-type FETs were prepared with Au and Pt electrodes, and the FETs exhibited n-type behavior, with on/off ratios that exceeded 10³ at V_SD = 0.5 V.

Direct ink writing (DIW) is a promising additive manufacturing (AM) technique in the field of microsystems technology due to the potential for high detail resolution and the wide choice of materials suitable for the technique. In this study, inks of polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) as well as composite inks with reduced graphene oxide (PVDF-TrFE-rGO) were developed and adapted for continuous flow DIW. The composite PVDF-TrFE-rGO inks achieved percolation after 1.5 wt% and electrical conductivity of 2.8 S/cm at the highest loading investigate in this study (7 wt%). The inks were successfully printed with minimum nozzle diameter of 40 μm on different substrates including glass, metal and a nitrile elastomer. It was also demonstrated that the inks can be used to create a fully 3D-printed piezoelectric device with the predicted response, i.e. the fabrication technique did not deteriorate the functionality of the device. The conductive composite ink was successfully utilized as an effective electrode in the device. It was therefore demonstrated that by combining materials, such as the composite PVDF-TrFE-rGO ink and the co-polymer PVDF-TrFE with additive manufacturing techniques, the fabrication of low-cost, versatile devices can be achieved.

Integrating optically active III-V materials on silicon/insulator platforms is one potential path towards improving the energy efficiency and performance of modern computing. Here we demonstrate the applicability of direct wafer bonding combined with plasma etching to the fabrication of complex nanophotonic systems out of InP layers. We explore and optimise the plasma etching of InP, validating existing processes and developing improved ones. We explore the use of microdisk lasing as a way to evaluate fabrication fidelity, and demonstrate that we can create complex lasing systems of interest to us: coupled disk cavities and random network lasers.

Two-photon polymerization (2PP) has provided the field of cell biology with the opportunity to fabricate precisely designed microscaffolds for a wide range of studies, from mechanobiology to in vitro disease modelling. However, a multitude of commercial and in-house developed photosensitive materials employed in 2PP suffers from high auto-fluorescence in multiple regions of the spectrum. In the context of in vitro cell biological studies, this is a major problem since one of the main methods of characterization is fluorescence microscopy of immuno-stained cells. This undesired auto-fluorescence of microscaffolds affects the efficiency of such an analysis as it often overlaps with fluorescent signals of stained cells rendering them indistinguishable from the scaffolds. Here, we propose two effective solutions to suppress this auto-fluorescence and compare them to determine the superiority of one over the other: photo-bleaching with a powerful UV point source and auto-fluorescence quenching via Sudan Black B (SBB). The materials used in this study were all commercially available, namely IP-L, IP-Dip, IP-S, and IP-PDMS. Bleaching was shown to be 61.7–92.5% effective in reducing auto-fluorescence depending on the material. On the other hand, SBB was shown to be 33–95.4% effective. The worst result in presence of SBB (33%) was in combination with IP-PDMS since the adsorption of the material on IP-PDMS was not sufficient to fully quench the auto-fluorescence. However, auto-fluorescence reduction was significantly enhanced when activating the IP-PDMS structures with oxygen plasma for 30 s. Moreover, we performed a cell culture assay using a human neuroblastoma cell line (SH-SY5Y) to prove the effectiveness of both methods in immunofluorescence characterization. SBB presented a lower performance in the study especially in presence of 2PP-fabricated microchannels and microcages, within which the differentiated SH-SY5Y cells migrated and extended their axon-like processes, since the SBB obstructed the fluorescence of the stained cells. Therefore, we concluded that photo-bleaching is the optimal way of auto-fluorescence suppression. In summary, this study provides a systematic comparison to answer one of the most pressing issues in the field of 2PP applied to cell biology and paves the way to a more efficient immunofluorescence characterization of cells cultured within engineered in vitro microenvironments.