Plasmonic metamaterial absorbers (PMAs) designed for multispectral imaging in the infrared (IR) with uncooled microbolometers are investigated. The study presents Fourier transform infrared spectroscopy (FTIR) measurements of PMAs consisting of metal-insulator-metal-stacks (MIM) with square-shaped micropatches as top metal layers. The measurements reveal high absorptances of 82% to 99% for distinct wavelengths within a range from 2 μm to 9.2 μm. The spectra are evaluated with respect to the lateral dimensions of the patches and to the refractive indices of the used dielectrics SiO2, Al2O3 and Ta2O5. Numerical simulations and analytical calculations of the TM010-mode using the transmission line model (TLM) for microstrip antennas show good qualitative agreement with the measurement results. Additionally, bispectral PMAs were fabricated consisting of fields of PMAs with two different patch sizes arranged in a chessboard pattern. The individual fields of this pattern correspond to microbolometers with 12 μm pitch in shape and size. Two distinct absorption maxima can be seen in the spectra measured by FTIR. The choice of materials, deposition methods and patterning processes is suitable for the integration into the existing Fraunhofer IMS's nanotube microbolometer technology to realize multispectral infrared imaging. The fabrication process is CMOS-compatible and carried out on 8-in. wafers.

We present a novel fabrication approach to an integrated nanophotonic platform, based on a III-V membrane bonded to a Si substrate with benzocyclobutene (BCB). The process incorporates a hybrid lithography strategy combining deep-UV and electron-beam lithography on the same wafer. We report for the first time the usage of deep-UV scanner lithography for the fabrication of the active-passive tapers and sub-micron waveguides on the same wafer, which enables better critical dimension control, uniformity, and reproducibility. The platform uses an active-passive butt-joint interface and includes components such as distributed feedback (DFB) and distributed Bragg reflector (DBR) lasers, electro-optical (EO) and electro-absorption (EA) modulators, and sub-micron ultra-confined passive waveguides, all monolithically integrated into a single membrane layer. The active devices have a heat sink achieved by ultra-thin BCB bonding. Lasers demonstrate up to 26 mW of optical power in the waveguide and a direct modulation bandwidth of up to 21 GHz. The modulators show static extinction up to 28.8 dB.

Maskless UV photolithography is increasingly used, especially in research environments where low turn-around time for new designs improves productivity. Here, we fabricate pyrolytic carbon interdigitated microelectrodes with small interelectrode gaps, good adhesion to the carrier substrate, high surface area and excellent electrochemical properties using maskless UV photolithography with two negative epoxy-based photoresists, namely the commonly used SU-8 and the recently developed mr-DWL. The minimum realizable trench width in 15 μm thick photoresist films is 2.4 ± 0.15 μm for mr-DWL 5 and 3.1 ± 0.10 μm for SU-82035. After pyrolysis, the two resulting pyrolytic carbon materials show similar electrochemical properties. However, shrinkage during pyrolysis is significantly lower for mr-DWL compared to SU-8, which is beneficial for the fabrication of interdigitated microelectrodes. Furthermore, delamination of the electrodes during processing and operation is prevented due to the introduction of poly silicon adhesion structures. This work provides valuable insights into maskless UV lithography as well as into the pyrolytic carbon process to increase the yield, performance and productivity for fabrication of microelectrodes.

Gold is a promising material for movable components in MEMS devices by the high mass density, which allows reduction of the Brownian noise. Mechanical properties of metallic materials are known to be affected by the sample size effect. When bending test is utilized, the sample geometry effect is another factor. In this study, effects of the shape of the cross-section, or the cross-sectional geometry effect, are evaluated using micro-cantilevers with a trapezoidal cross-section. The yield stresses are ranged from 112 MPa to 185 MPa in micro-cantilevers composed of single crystalline gold, and the yield stresses varied from 372 MPa to 489 MPa in polycrystalline gold micro-cantilevers. The yield stress is found to be higher in the micro-cantilever having a smaller ratio of the top width over the bottom width, which demonstrates the cross-sectional geometry effect. Also, the cross-sectional geometry effect is more significant in the polycrystalline micro-cantilevers.

The previous decades have seen a massive increase in the research towards reproducible and optimized surface-enhanced Raman spectroscopy (SERS) substrates. While traditional colloidal synthesis methods have commonly been used for SERS substrate fabrication, they lack reproducibility hindering their usage for many applications. The need for reproducible nanostructures showing high orders of enhancement factors has brought about a shift in the methods one can use to fabricate SERS nanostructures. Lithographic techniques have thus piqued the interest of researchers as a viable option for SERS substrate fabrication. Not only do they offer high enhancement factors and reproducible nanostructures, they also provide the ability to fabricate nanostructures with many different geometries, shapes, sizes and periodicities. Some of the most established lithographic techniques include electron beam lithography, nanosphere lithography, laser interference lithography and many more. This review discusses established lithographic techniques, such as mentioned above, along with other upcoming lithographic techniques to understand the principles and the methodology behind them. A deep understanding of how various parameters can influence the nanostructure fabrication and thereby influence the SERS enhancement is developed. A detailed description of how these nanostructures can be fabricated is also provided for better insight. In addition, strengths and limitations of each method are discussed in detail. Lastly, we also discuss the applicability of SERS substrates for commercial applications comparing the performance of chemical synthesis routes and lithography for SERS substrate fabrication. This review serves as a base to understand the concept and application of SERS from a microfabrication perspective.

Over the past few years, water quality monitoring has swiftly emerged as a thrust area for most of the developing nations. Despite its renewable essence, incessant industrialization and urbanization have depleted the natural water resources, culminating in adverse impact on potable water quality. As a consequence, reliable technologies with utmost sensitivity and accurate predictions vis-à-vis authentic qualitative standards are urgently needed. Herein, interest in using gold nanoparticles (Au NPs) biosensors to gauge the qualitative profile of water resources has been quite significant. Major fascinations for Au NPs biosensing driven water quality monitoring are steadfast preparation methodologies, well-understood mechanisms for size-shape modulation and inert sensitivity manifested remarkable functionalization abilities. The size-shape modulated functionalization advances for Au NPs are the dynamic outcomes of their quantum effects, anchored via single or multidimensional quantum confinements (QCs). Morphologies as vibrant as rod, spherical, cylindrical, shells and combinatorial regime have been the backbone aspects of Au NPs based biosensors. With such insights, the present article focuses on last decade noted advances aimed at Au NPs biosensors assessed water quality. The studies discussed herewith were retrieved from Pubmed using the keywords, “Gold Nanoparticle Biosensors for Water Quality Monitoring”. The knowledge shared herein could consolidate the fabrication of future Au nanomaterials based sensing technologies vis-à-vis functionalization mechanisms, cost considerations, precision aspects, integrated possibilities and long-term cautions.

Water is a vital component for all living organisms, yet persistent water scarcity remains a global challenge. One potential solution lies in replicating the atmospheric water collection mechanism observed in the Stenocara beetle, characterized by a dorsal surface featuring alternating hydrophilic and hydrophobic regions. In this study, we have designed and examined two distinct biphilic patterned surface configurations, integrating various technologies, to mimic the beetle's water collection strategy. Our investigation evaluates the efficiency of these surfaces in both capturing water from fog and condensing water from dew. For fog collection two parameters were the most impactful: the roughness and the wettability contrast between hydrophilic and hydrophobic zones. In contrast, dew condensation was influenced by additional parameters notably the patterns' size and density that directly affect the water contact angle. It is worth noting, however, that the optimal surface for fog collection may not necessarily coincide with the most effective surface for dew condensation. Furthermore, our research includes a comparative analysis between the theoretically predicted volume of water droplet departure and the empirically observed results.

This study investigates the interactions between chemical vapor-deposited graphene and metal-organic chemical vapor-deposited molybdenum disulfide (MoS2) in heterostructures assembled via wet transfer. We use Raman spectroscopy to quantitatively determine close coupling between graphene and MoS2 based on the peak separations in graphene. Although annealing seems to be necessary after transfer to establish a close coupling, its parameters do not have a significant impact on the quality of coupling (for 100 °C < T < 400 °C and 5 min < t < 120 min). Furthermore, the method is robust against variations in graphene thickness because bilayers can be distinguished by comparing the full width at half maximum of the graphene 2D peak. We expand our study to mm2-scale areas of graphene-MoS2 heterostructures finding that films assembled via wet-transfer technique exhibit considerable variability in terms of coupling strength. Evaluating such interactions in heterostructures on large areas is important for future practical applications in heterostructure devices.

In this study, the strain rate dependence in yield strengths of electrodeposited gold micro-pillars is evaluated for the design of movable components in MEMS devices. The micro-pillars are fabricated from electrodeposited gold by focused ion beam system. The strain rate dependence is quantified by the strain rate sensitivity, and the strain rate sensitivity is calculated from the yield strength obtained from compression tests of the gold micro-pillars having different sizes at different strain rates. An increase in the yield strength following a reduction in the pillar size is observed, which is the sample size effect. Also, weakening of the yield strength is observed following a decrease in the strain rate, which is the strain rate dependence, and the strain rate sensitivity of the gold micro-pillars is found be at roughly 0.03.

Flexible sensor arrays with multilevel circuits typically require complex production cycles leading to high costs and reliability issues. For establishing flexible arrays of strain sensors in Wheatstone bridge configurations structures on different levels within flexible films have to be connected by robust μ-via technology. Usually, dry etching is used to establish via-holes and direct current (DC) electrodeposition is used to fill them with copper. However, dry etching can lead to damages in the underlying electrode or incomplete removal of polymeric material, as inhomogeneities of polymeric foil thicknesses cannot completely be eliminated. This affects the quality of the plating and the reliability of the μ-via connections. It is aggravated by the fact that DC electroplated copper is often weakened by various defects, such as small voids. This article describes a reliable and less complex fabrication process for a Wheatstone bridge sandwich structure consisting of five polymer interlayers separating four metal layers. The femtosecond-laser μ-via drilling proved to be fast, material selective and therefore tolerant to inhomogeneities of polymeric foil thicknesses. Moreover, pulsed current (PC) electrodeposition significantly improved the quality of the copper filling. No voids were found using electron microscopy. Finally, the respiration monitoring sensors produced using this method were subjected to repetitive cycles of bending and relaxation. At a frequency of five cycles per second, reproducible cycles of signal changes were obtained, indicating the usefulness for detecting respiratory cycles of premature infants.