Micro and Nano Engineering最新文献

Using direct-laser writing, 3D microstructures of almost every shape can be fabricated. However, using liquid photoresists, the fabrication of free-floating structures is still challenging. To give stability to those structures during the printing process, support beams can be implemented which are usually not needed for direct-laser writing. With that, free-floating elements can be fixed and are not distorted due to unwanted movement during fabrication. In this work, the design, realization and characterization of support beams for the printing outcome of 2-photon polymerization processes is examined. The support beams described here connect the static and the rotating part of flap-like structures. Experimental results show that two thin cone-shaped support beams are sufficient to stabilize the flaps (typical size $20\times 50\mu m^2$) so that they are not distorted during printing. After finishing the writing process, the support beams can be broken with a gentle nitrogen stream and the structures move freely. Structures like these can for example be implemented in microfluidic channels to work as flow direction pointers or self-closing cell traps.

Nanomechanical resonators can detect various small physical quantities with high sensitivity using changes in resonant properties. However, viscous damping in liquids significantly reduces the measurement sensitivity. This study proposes convolutional neural network (CNN) vibration spectrum analysis to evaluate the highly sensitive vibration states of nanomechanical resonators, which are useful for in-liquid measurements. This research was carried out through the measurement of acetone concentration. First, we compared the concentration classification ability between the proposed and conventional methods and determined that the proposed method of analyzing vibration spectral changes using the CNN model can provide higher measurement sensitivity than the conventional measurement method of observing resonance properties changes and comparing the values for each measurement condition. This result shows that CNN-based spectral analysis is effective for the vibration spectra of in-liquid measurements. Next, gradient-weighted class activation mapping (Grad-CAM) was applied to verify which frequency bands are important for concentration classification in CNN model decision-making. The vibration states in these frequency bands were analyzed in terms of oscillation modes. This analysis revealed significant oscillation modes of the nanomechanical resonator in the liquid environment. Notably, in addition to the resonance states utilized in the conventional method, several other oscillation modes were found to be significant for measurements. This finding suggests that these oscillation modes may be highly sensitive for measurements in liquid environments. Among these oscillation modes, the mode with very small amplitude is highly promising for achieving unprecedented levels of sensitivity in sensing technologies.

Electron beam lithography (EBL) is pivotal for micro- and nanoscale fabrication, offering sub-micron precision. This study explores the utilization of the Novolac-based negative resist AR-N 7520 for EBL and its potential as an etch mask for reactive ion etching (RIE) of silicon. Recent comparisons of negative EBL resists have revealed promising results for AR-N 7520 in terms of resolution and adaptability with other lithography techniques. In this article, we conduct an exploration of patterning of AR-N 7520 (new) for EBL, addressing key parameters in achieving optimal patterning fidelity. Furthermore, we investigate its compatibility with RIE processes, aiming to provide insights into its effectiveness as an etch mask for creating sub-micron silicon structures. Experimental results show that optimal e-beam dose with 100 kV exposure is 300–350 μC/cm². Selectivity of around 9:1 can be achieved by optimizing etching parameters for a continuous etch and higher than 14:1 for a cyclic etch process.

Considering the goal of lithography under its most general aspect – that is, transferring and recording mask or template information in the form of contrast between the imaged and non-imaged areas of a resist film coated on a flat surface – three lithographic resist imaging mechanisms can be recognized. Depending on the nature of the resist film, this contrast may be based on intrinsic or photo- or radiation-induced differential solubility between the imaged and non-imaged part of the resist film in fine art lithography, photolithography, and radiation lithography, respectively, or pressure driven flow and confinement of resist in imprint lithography, or thermodynamically driven phase separation of resist constituents in directed self-assembly lithography. This contrast forms the basis of the printed image and ultimately derives from the forces that underlie the old chemist's rule: “Oil and water do not mix.” Crucially, to create this contrast, the resist film must transform a two-dimensional image of the mask or template into a three-dimensional relief image on the substrate in a process that is highly non-linear. By creating the contrast in this manner, the resist film serves as a compact imaging system that senses, records, stores, and displays the mask image. Additionally, the resist film must maintain its structural and mechanical integrity to “resist” and withstand the harshness of other post-imaging processes such as etching, ion implantation, electroplating, etc. Following all necessary post-imaging processes, the resist film must be stripped or be left and incorporated into the final device. A versatile material that serves a multiplicity of functions and is operational in many dimensions is not only amazing but also forms the irreducible essence of lithography. By drawing on fundamental, theoretical, and experimental studies of molecular processes involved in lithographic resist imaging, this review paper explains how the resist film performs the above essential functions.

This work presents a Python-based architecture packaged as a standalone tool, to enable the parameterization of lithography structures without the need for scripting. By feeding a lithography template file obtained from an existing layout editor into the tool, a ‘scaffold’ shape is created and recognised. The tool allows for the parameterization of created geometries and the establishment of parameterized rules between geometric features, which can be conveniently modified in tabular format. This work facilitates no-code procedural generation of geometrically distinct instances, significantly reducing the time required for complex lithography template development compared to traditional scripting methods.

We propose aluminum oxide (Boehmite) sputter-deposited with Ag substrates for Surface-Enhanced Raman Spectroscopy (SERS). These substrates are cost-effective and easily fabricated by heating aluminum in an aqueous environment to create Boehmite, followed by Ag sputtering. The metal deposition is optimized, resulting in random arrays of Ag nanostructures with a diameter of ∼100 nm and a spacing of <100 nm leading to significant enhancement of the Raman signal. The performance and sensitivity of the substrates are initially tested with the use of Crystal Violet analyte which results in limits of detection close to 10⁻¹⁰M. These substrates are used for the rapid detection of four different explosive compounds: Nitroglycerin (NG), Picric Acid (PA), Cyclotrimethylene trinitramine (RDX) and 2,4,6-Trinitrophenylmethylnitramine (Tetryl). A series of Raman spectra are collected for these four selected explosives on the fabricated substrates and principal component analysis (PCA) was used for proper evaluation and identification of the corresponding measured spectra.

Membranes play a critical role in diverse applications, including filtration and tissue engineering. The importance of membrane performance optimization highlights the necessity of accurately characterizing the pore structure. Traditional Pore Size Distribution methodologies are widely used to quantify size uniformity. Uniformity though, integrates both size and spatial pore structure aspects, thus necessitating the synergy of complementary techniques to analyze pore structure. This work empowers classic pore metrology with stochastic geometry, specifically the Nearest Neighbour Index (NNI) to assess the spatial uniformity of pores in membrane Scanning Electron Microscopy (SEM) images. Through a comprehensive analysis of Polytetrafluoroethylene (PTFE) before and after plasma etching, along with nanofilament coated Polyethersulfone (PES) membranes, this analysis enhances our understanding of membrane morphology through pore structure and pore spatial arrangement. The findings indicate that increasing magnification leads to a decrease in apparent spatial uniformity, indicative of effects regarding the inclusion in analysis of families of finer pores. In almost all cases, NNI values show higher uniformity compared to a fully random scenario. Additionally, it is found that plasma etching does not have significant effects on spatial uniformity introducing only a slight uniformity in pore centroid arrangement, reflected in a small NNI increase. Furthermore, a pore area shuffling technique reveals the effects of pore density and size on spatial uniformity, highlighting patterns inherent to the materials under study.

Although this opinion paper tracks the career of Mike Hatzakis (as he liked to be called), and explains the impact he made on the IT industry, it is not intended to be comprehensive insofar as the work that was underway during his career is concerned. Thus, the intent is not to cite all relevant work in the field of Semiconductor lithography, where Mike made such an impact, but to provide a historic and human perspective of this remarkable man from the land of the Minotaur (Crete) and his career, the work he championed in his labs in the US and later Greece and his very human approach to science, technology, and to people.

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Hybrid room-temperature (RT) silicon single-electron – field effect transistors (SET-FETs) provide a means to switch between ‘classical’, high current FET, and low-power SET operation, using a gate voltage. While operating as a SET, charge on a silicon quantum dot (QD) within the current channel, can be controlled at the one-electron level using the Coulomb blockade effect. This paper investigates nanofabrication methods for sub-10 nm ‘fin’ channel hybrid RT SET-FETs, and their influence on the energy band diagram, and formation of tunnel barriers and QDs, along the channel. Devices are fabricated in heavily n-doped SOI material using electron beam lithography, with thermal oxidation to reduce the as-defined fin width. Effective channel dimensions, following oxidation and excluding Si/SiO₂ interface dopant deactivation, are ∼2.4 nm $\times$ 32 nm $\times$ 20 nm. Dopant disorder, fin width variation at the nanometre scale, and quantum confinement effects are considered as mechanisms for the formation of tunnel barriers and QDs, with dopant disorder the most likely reason. Arrhenius plots of I_ds vs. 1/T allow extraction of a potential barrier energy ∼0.2 eV along the fin channel. For 180devices fabricated on four chips, 37% show RT SET-FET operation, ∼3 times higher than the corresponding yield observed in previous work on point-contact silicon SETs.

Aquatic germplasm repositories can play a pivotal role in securing the genetic diversity of natural populations and agriculturally important aquatic species. However, existing technologies for repository development and operation face challenges in terms of accuracy, precision, efficiency, and cost-effectiveness, especially for microdevices used in gamete quality evaluation. Quality management is critical throughout genetic resource protection processes from sample collection to final usage. In this study, we examined the potential of using three-dimensional (3-D) stereolithography resin printing to address these challenges and evaluated the overall capabilities and limitations of a representative industrial 3-D resin printer with a price of US$18,000, a consumer-level printer with a price <US$700, and soft lithography, a conventional microfabrication method. A standardized test object, the Integrated Geometry Sampler (IGS), and a device with application in repository quality management, the Single-piece Sperm Counting Chamber (SSCC), were printed to determine capabilities and evaluate differences in targeted versus printed depths and heights. The IGS design had an array of negative and positive features with dimensions ranging from 1 mm to 0.02 mm in width and depth. The SSCC consisted of grid and wall features to facilitate cell counting. The SSCC was evaluated with polydimethylsiloxane (PDMS) devices cast from a typical photoresist and silicon mold. Fabrication quality was evaluated by optical profilometry for parameters such as dimensional accuracy, precision, and visual morphology. Fabrication time and cost were also evaluated. The precision, reliability, and surface quality of industrial-grade 3-D resin printing were satisfactory for operations requiring depths or heights larger than 0.1 mm due to a low discrepancy between targeted and measured dimensions across a range of 1 mm to 0.1 mm. Meanwhile, consumer-grade printers were suitable for microdevices with depths or heights larger than 0.2 mm. While the performance of either of these printers could be further optimized, their current capabilities, broad availability, low cost of operation, high throughput, and simplicity offer great promise for rapid development and widespread use of standardized microdevices for numerous applications, including gamete quality evaluation and “laboratory-on-a-chip” applications in support of aquatic germplasm repositories.