Micro and Nano Engineering最新文献

In this work, we fabricate a hexagonal array of pillars where each pillar has a “micro-hoodoo” shape, i.e., a reentrant cross section. The shape of the pillars makes them more resilient towards total wetting, i.e., transition from a Cassie-Baxter non-wetting state to a Wenzel wetting state. We show the single-step fabrication of 4 × 4 mm² arrays by two-photon polymerization direct laser writing of the polydimethylsiloxane (PDMS)-derived commercial resin IP-PDMS. The use of a hydrophobic resin for rapid prototyping of reentrant structures enables the fabrication of surfaces patterns displaying superhydrophobic behavior despite the use of relatively simple structures, i.e. with a single reentrant surface. By changing the size of the micro-hoodoos and the packing density of the arrays, we map wetting behaviors ranging from the pinning of water droplets in Wenzel state to non-wetting Cassie-Baxter states. The measured contact angles follow quite well the theoretical results obtained by minimizing Gibbs free energy using the Wenzel, Cassie-Baxter and partial wetting theories. Among the tested micropatterns, five exhibited superhydrophobic properties, with a static contact angle with water as high as 158.1° ± 7.1°. This is the first demonstration of superhydrophobic surfaces produced by two-photon polymerization direct laser writing of PDMS in a single-step process.

Tactile sensing is an essential physical-electrical gateway in sensing technology. Creating such sensors is a complex challenge if the goal is to reproduce human-like sensation. Classical MEMS tactile sensor solutions in typical environmental conditions exist few types, but harsh conditions such as space technology or high-temperature range are not solved yet. One proposed material complex is the GaN/AlGaN system. In this study, we present an AlGaN/GaN MEMS force sensor for external force and load direction sensing in the mN range. The demonstrated sensor showed a sensitivity of 100 mV/N/V, which is an order of magnitude higher than the Si-based sensor with the same geometry. The sensing mechanism is based on the interface discontinuity between compound alloy layers, where two-dimensional electron gas (2DEG) is created and in which the carrier concentration can be linearly modulated by the internal crystal stress. The location of the sensing element was optimized by FEM simulation. The maximum load force of the samples varies with direction, which information allows the sensor to be used without fatigue and to obtain safety an electrical response signal under different external tensions. In addition to the advantage of this design for harsh environments, it is also possible to monolithically integrate active elements adjacent to the sensor for local acquisition and processing of the measured signal.

The damage inflicted to silicon nanowires (Si NWs) during the HF vapor etch release poses a challenge to the monolithic integration of Si NWs with higher-order structures, such as microelectromechanical systems (MEMS). This paper reports the development of a stencil lithography-based protection technology that protects Si NWs during prolonged HF vapor release and enables their MEMS integration. Besides, a simplified fabrication flow for the stencil is presented offering ease of patterning of backside features on the nitride membrane. The entire process on Si NW can be performed in a resistless manner. HF vapor etch damage to the Si NWs is characterized, followed by the calibration of the proposed technology steps for Si NW protection. The stencil is fabricated and the developed technology is applied on a Si NW-based multiscale device architecture to protectively coat Si NWs in a localized manner. Protection of Si NW under a prolonged (>3 h) HF vapor etch process has been achieved. Moreover, selective removal of the protection layer around Si NW is demonstrated at the end of the process. The proposed technology also offers access to localized surface modifications on a multiscale device architecture for biological or chemical sensing applications.

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.

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.

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.

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.

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.

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.