Micro and Nano Engineering最新文献

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.

In the contemporary quest for sustainable energy, the potential of piezoelectric energy harvesters to convert mechanical vibrations into electrical energy has become increasingly important. This study focuses on piezoelectric composites, in particular a BaTiO₃/PLA (Barium Titanate/ Polylactic Acid) system with different volume percentages of BaTiO₃ ceramic particles (20%, 40% and 60%), with the aim of optimizing energy conversion efficiency. A mathematical model is introduced, encompassing material attributes, mechanical loading frequencies and electrical energy outputs. The central role of mathematical modeling in predicting harvested energy is highlighted, offering insights beyond experimental limitations. The model, which is functionally dependent on the properties of the ceramic and polymer, enables the systematic exploration of various compositions and the identification of optimal material ratios. Experimental validation of the model for different strains (0.4%, 0.8% and 1%) and compositions of BaTiO₃/PLA reaffirms its reliability. Notably, the highest power harvest observed is around 4.5 μW under a strain of 1% with a BaTiO₃ composition of 60%. With these specific numerical values, this approach merges materials science and energy technology, propelling the advancement of efficient piezoelectric materials for renewable energy applications.

In recent years, resistive memories have emerged as a pivotal advancement in the realm of electronics, offering numerous advantages in terms of energy efficiency, scalability, and non-volatility [1]. Characterized by their unique resistive switching behavior, these memories are well-suited for a variety of applications, ranging from high-density data storage to neuromorphic computing [2]. Their potential is further enhanced by their compatibility with advanced semiconductor processes, enabling seamless integration into modern electronic circuits [3]. A particularly promising avenue for resistive memory lies in its integration at the Back-End-of-Line (BEOL) stage of semiconductor manufacturing [4]. BEOL integration involves processes that occur after the fabrication of the transistors, primarily focusing on creating interconnections that electrically link these transistors. Integrating resistive memories at this stage can lead to compact, efficient, and high-performance architectures, pivotal for in-memory computing applications where data storage and processing are co-located [5]. This paper studies three ways to integrate TiO_x-based resistive memory into passive crossbar array structures, using chemical mechanical polishing (CMP) processes, focusing on identifying the optimal integration techniques.

Biological ion pumps, such as bacteriorhodopsin (bR), utilize photons to move ions against concentration gradients, offering energy harvesting and spatiotemporal control of chemical gradients. This capability goes far beyond the capabilities of today's synthetic devices, suggesting a hybrid approach to embed bRs in synthetic devices in order to direct the proton flow towards useful system applications. In this study, a hybrid silicon-based nanochannel network with integrated purple membranes (PM) containing bR was fabricated. The fabrication method combines thermal scanning probe lithography, etching techniques, atomic layer deposition, plasma-enhanced chemical vapor deposition, and photolithography to create devices with buried nanochannels on silicon substrates. PM patches were deposited onto specified sites by a tunable nanofluidic confinement apparatus. The resulting device holds the potential for locally controlling directed ion transport in micrometer scale devices, a first step towards applications, such as locally affected proton catalyzed chemical reaction networks. Furthermore, this fabrication strategy, employing a maskless overlay, is a tool for constructing intricate nanofluidic network designs which are mechanically robust and straightforward to fabricate.

Gold-based micro-electro-mechanical-systems (Au-MEMS) capacitive accelerometers can simultaneously realize high sensitivity and miniaturization because of the high mass density of Au. In order to further improve the sensitivity of the Au-MEMS capacitive accelerometers, Young's modulus of the cantilever-like spring part connected to the movable component is a key parameter. Considering the size effect in the mechanical property of metallic materials on micro-scale, the design of the spring part is expected to reflect their Young's modulus; that is, effective Young's modulus (E_eff). In this study, we clarify effects of the structural designs of the Au-based micro-cantilevers on their E_eff by experiments and finite element analyses (FEA) simulations. The E_eff of the Au micro-cantilevers having Ti/Au multi-layered structures is evaluated by resonance frequency method, which demonstrates the key structural parameters affecting their E_eff. The FEA calculations show a consistent trend with that observed in the experimental results.

Focused ion beam (FIB) has become a powerful tool for transmission electron microscopy sample preparation in the nanoelectronics industry and has in recent years also shown its benefits for specific preparation steps in electrical scanning probe microscopy (SPM). Most recently, a novel SPM approach – so-called reverse tip sample (RTS) SPM – has been proposed in which the position of sample and tip are switched compared to standard SPM; in RTS SPM the sample is attached to the end of a cantilever beam. To achieve this configuration, the region of interest must first be extracted from a substrate and then needs to be reliably fixed to the cantilever by FIB. Therefore, we have explored and developed dedicated FIB preparation methods for RTS SPM in this work. Our established procedures ensure a strong mechanical and good electrical connection of the sample to the cantilever for both cross-section and top view sample preparation. Furthermore, we introduce an approach for mounting samples from a full wafer size workflow. This paper presents the developed FIB procedures and discusses the quality and stability of all mounted samples and their electrical evaluation in RTS SPM.

Interdisciplinary research between science and art is becoming more active, because it stimulates the both fields with far different viewpoints. In the field of aerogels, exceptionally low-density porous materials, the authors have been promoting interdisciplinary research based on a unifying aesthetic idea. Since typical silica aerogels consist of nano-scaled colloidal skeletons and mesopores, they show high light transmittance and slight scattering that allows aerogels to be impressive bluish piece of the sky. With various techniques such as molding, inclusion, and surface machining/patterning, a number of artworks has been expressed with the material silica aerogel interpreting aerogels to the sky through fruitful collaborations between an artist and scientists including the present co-authors. In the present paper, we discuss the interactions between human and materials in visual arts and photography, and show how the aerogels are expended as the materia prima for the artworks of the first author. We will emphasize how the synergy between artists and scientists drove and stimulated the both fields through collaborative works.

The advent of two-dimensional (2D) materials has led to innovative and compact electronic devices with remarkable properties. In this work, we introduce a switchable bidirectional diode (2D BDiode), fabricated entirely using different 2D materials, that serves as a fundamental building block for various analog circuit applications. This proof-of-concept diode exhibits the ability to control the flow of current in both forward and reverse bias configurations, enabling advanced functionality in the realm of analog circuit design. We provide a SPICE-based model for the diode based on current-voltage device characterization, capturing its behavior under different biasing conditions, and finally demonstrate a few potential use cases of the 2D BDiode including AC/DC conversion, DC/AC conversion and charge pump circuits.

This study is to develop structures with the ability to convert a compression force into radial extension or shear force, to increase power output through piezo shear mode. In this work, a piezoceramic-spring system was developed with two types of force-spreading spring configurations, the Belleville disc springs and the crinkle washer. A force loading profile is applied to a piezoceramic element and structure causing the force to be distributed in different directions when compared to a conventional helical spring damping system or compression. The performances of these novel structures were studied using Multiphysics simulation and experiments. This work shows that both the Belleville disc and crinkle washer produce improved energy output between 15 and 22% compared to compression alone, whilst the Belleville disc spring outperformed a crinkle washer in both simulations and experiments. The results show that converting compression to shear force in energy harvesting could be a potential approach to increase the energy efficiency and energy density.