Search

A new, scalable process chain for the fabrication of curved micro-structured metallic tools is developed and evaluated. Arrays of arrows, circles, semicircles and rings with final lateral dimensions of 124 to 819 µm are realised on the tools and successfully transmitted in one process step to stainless steel workpieces with a functional area of 6.5 cm2 using pulsed electrochemical machining. Photolithography-etching or micromilling are applied as initial micro-structuring processes, resulting in micro-structured master forms. These forms are copied into reusable silicon forms. This is followed by epoxy casting and electroforming to obtain the final tools. The tools are made of Nickel and have a diameter of 34 mm. Whilst micromilling, photolithography, silicon casting, epoxy casting and electroforming copy the structures very precisely, the wet etching process induces a widening of the dimensions due to the isotropic character of the process. The advantage of the process chain is the reusability of the master as well as of the silicone forms, which can be copied very precisely and easily with scalable processes to get precision tools with relatively large micro-structured areas. The reusability of the forms makes the fabrication of micro-structured tools relatively cost-efficient. The use of photolithography as the initial structuring process enables the generation of arbitrary, user-defined geometries for the micro-structures on the tool surface. The process chain described has the potential to fabricate lateral structure sizes on tools down to one micrometre.

Threshold switching (TS) devices have evolved as one of the most promising elements in memory circuit due to their important significance in suppressing crosstalk current in the crisscross array structure. However, the issue of high threshold voltage (Vth) and low stability still restricts their potential applications. Herein, the vanadium oxide (VOx) films deposited by the pulsed laser deposition (PLD) method are adopted as the switching layer to construct the TS devices. The TS devices with Pt/VOx/Pt/PI structure exhibit non-polar, electroforming-free, and volatile TS characteristics with an ultralow Vth (+0.48 V/−0.48 V). Besides that, the TS devices also demonstrates high stability, without obviously performance degradations after 350 cycles of endurance measurements. Additionally, the transition mechanism is mainly attributed to the synergistic effect of metal-insulator transition of VO2 and oxygen vacancies. Furthermore, the nonvolatile bipolar resistance switching behaviors can be obtained by changing oxygen pressure during the deposition process for switching films. This work demonstrates that vanadium oxide film is a good candidate as switching layer for applications in the TS devices and opens an avenue for future electronics.

The electrical properties of MIS structures with rare-earth element fluorides on germanium substrates were studied to analyze the possibility of using these materials as gate dielectrics of devices. The structures are also studied from the point of view of assessing the degradation of their electrophysical properties under the action of electric fields of ~108 V/m, which act on the dielectric during electroforming, since the MIS structures with rare-earth element fluorides have the property of bistable switching. Studies of the I-V and C-V characteristics show that all structures have approximately the same value of the density of surface states at the rare-earth element / Ge fluoride interface. The leakage currents in the MIS structures with TmF3 and SmF3 film are less than in the MIS structures with NdF3 film of greater thickness. There is also no effect of reducing the current density when using the double film structure CeF3/DyF3. The most promising material with a low leakage current at a fairly high value of the dielectric constant in germanium MIS structures is thin-film samarium fluoride.

Memristor has become the most promising building block for neuromorphic computing. The memristors based on single-crystalline oxide film exhibit some advantages, such as the uniformity of device property. But currently the high energy consumption of memristor still hinders its future application. In this work, we used Ar+ irradiation to modulate the performance of memristor based on single-crystalline LiNbO3 (LN) thin film. During the Ar+ irradiation, the reduction of thin film thickness and the modulation of oxygen vacancies were observed simultaneously. The electroforming voltage and operation voltage of the memristors were reduced effectively, which makes the memristor become more energy-efficient. After Ar+ irradiation, the advantage in uniformity of device properties still maintained. The memristors based on Ar+ irradiated LN thin film also showed synaptic plasticity and self-rectifying property. The etching effect and preferential sputtering effect of Ar+ irradiation were observed and investigated, respectively. The synergy between the two effects was also discussed. This work provides the method to overcome the obstacle of application of memristor based on single-crystalline oxide thin film to neuromorphic computing, which makes the advantages of memristor based on single-crystalline oxide thin film, such as the uniformity of device property, fully used of.

Multilevel resistive switching (RS) is a key property to embrace the full potential of memristive devices for non-volatile memory and neuromorphic computing applications. In this study, we employed nanoparticulated cobaltite oxide (Co3O4) as a model material to demonstrate the multilevel RS and synaptic learning capabilities because of its multiple and stable redox state properties. The Pt/Co3O4/Pt memristive device exhibited tunable RS properties with respect to different voltages and compliance currents (CC) without the electroforming process. That is, the device showed voltage-dependent RS at a higher CC whereas CC-dependent RS was observed at lower CC. The device showed four different resistance states during endurance and retention measurements and non-volatile memory results indicated that the CC-based measurement had less variation. Besides, we investigated the basic and complex synaptic plasticity properties using the analog current-voltage characteristics of the Pt/Co3O4/Pt device. In particular, we mimicked the potentiation–depression and four-spike time-dependent plasticity (STDP) rules such as asymmetric Hebbian, asymmetric anti-Hebbian, symmetric Hebbian, and symmetric anti-Hebbian learning rules. The results of the present work indicate that the cobaltite oxide is an excellent nanomaterial for both multilevel RS and neuromorphic computing applications.

UIDB/50025/2020-2023 In this article, characterization of fully patterned zinc-tin oxide (ZTO)-based memristive devices with feature sizes as small as 25 µm2 is presented. The devices are patterned via lift-off with a platinum bottom contact and a gold-titanium top contact. An on/off ratio of more than two orders of magnitude is obtained without the need for electroforming processes. Set operation is a current controlled process, whereas the reset is voltage dependent. The temperature dependency of the electrical characteristics reveals a bulk-dominated conduction mechanism for high resistance states. However, the charge transport at low resistance state is consistent with Schottky emission. Synaptic properties such as potentiation and depression cycles, with progressive increases and decreases in the conductance value under 50 successive pulses, are shown. This validates the potential use of ZTO memristive devices for a sustainable and energy-efficient brain-inspired deep neural network computation. publishersversion published

This work focused on the effects of electroforming ambient temperature and annealing process on the metal oxide multilayer switching resistive random access memory (RRAM) device. We developed Pt/HfO2/TiO2/HfO2/Pt RRAM cells with annealing and without annealing process. Annealed devices are electroformed at a high ambient temperature 80 °C (A-80). Non-annealed devices are electroformed at low atmosphere temperature 25 °C (NA-25). We investigate the outcomes of NA-25 and A-80 devices. Results confirmed that annealed and high ambient temperature formed devices (A-80) contribute to the low operating voltage, improved uniformity, and reliability compared to NA-25 device.

In Micro-Electro-Mechanical System (MEMS) area, micro metal devices can be fabricated by the micro electroforming process. However, due to the oxide layer of the substrate surface, the electroformi...

In this study, vanadium (V) was used as a top electrode in a vanadium oxide (VOx)-based selector device. Electroforming was performed to form a threshold region with metal–insulator transition (MIT) at both V electrode and VOx switching layers without annealing during fabrication. The simple V/VOx/TiN structure obtained was scalable and compatible with complementary metal–oxide–semiconductors. All electrical measurement results indicated that V/VOx/TiN selectors exhibited excellent characteristics such as high uniformity, a short switching time of 60 ns, a robust endurance of >109 cycles, and high reliability and stability. Both the simulation analysis and current fitting method were applied to further validate experimental results. Consequently, we developed a nanoscale V/VOx/TiN selector with excellent characteristics, which can be potentially applied to future highdensity crossbar memory devices to overcome sneak-path problems.

UV-LIGA process has manifested its potential in the fabrication of high-aspect-ratio metallic microstructures. However, how to attain the complete, fast, and non-swelling removability of the crosslinked SU-8 micromolds remains a grand challenge. To address this challenge, we propose an effective and efficient removing method utilizing CO2 laser ablation followed by O2/CF4 plasma finishing for the fabrication of metallic microstructures in UV-LIGA. As the focused CO2 laser beam with a specific wavelength ablates the non-metal polymers but does not react with the electroformed nickel, it is used as the primary step to remove most of crosslinked SU-8 without swelling in a very short time. As the finishing step, the O2/CF4 plasma is then implemented to remove the residues and keep the metallic structures clean. We quantitatively investigate the effects of laser power, laser scanning speed, and laser pass numbers on the SU-8 ablation thickness to obtain the proper removal conditions. Utilizing the UV-LIGA fabricated micromolds and the proposed removal method, we successfully fabricate the metallic microstructures with aspect ratio up to five. Also, we evaluate the performance of the proposed method by changing various shapes, grating widths, and space intervals for the grating structure. These results prove that our method is effective and efficient in removing the SU-8 micromolds in UV-LIGA for the fabrication of metallic microstructures.

Thin copper-nickel foil with multi-nano layers was prepared by pulse-electroforming to develop a high performance electromagnetic shielding material for electronic devices. The pulse electroforming conditions of the aqueous solution chemistry were selected based on the aqueous copper-nickel-sulfur phase diagram and an evaluation of the deposition rate using the finite element method based on the current distribution in front of a cathodic electrode. The thermodynamic stability diagram revealed that the coppernickel multi-nano layers could be formed at pH1.0 V in a modified sulfide bath. The electro-formed copper-nickel multi-layer was well produced at the pulse plating conditions of –0.2VSHE, –0.5 mA/cm2, and 25 seconds for copper layer and –1.7 VSHE, –50 mA/cm2 and 80 seconds for nickel layer, which was composed of about 25 nm thick copper and about 30 nm thick nickel rich phases, respectively. The average deposition rate of the copper-nickel foil with multi-nano layers was estimated by the finite element method to be about 0.115 mm/sec, which was in good agreement with the real value of the thin multi-nano layered copper-nickel foil. The effectiveness of the electromagnetic shielding of the copper-nickel mesh with multi-nano layers was more than 30% higher than that of copper mesh in the frequency range of 8.2 and 12.5 GHz.

The resistive switching behavior of 1-D TiO2 nanotube-based resistive random access memory (ReRAM) is discussed in this article. Highly oriented TiO2 nanotubes were synthesized by anodic oxidation method on a Ti substrate, which was used as the bottom electrode. To modulate the oxygen vacancy ( ${V}_{O}$ ) in TiO2 nanotubes, hydrazine hydrate reduction was employed in the temperature range 60 °C–100 °C. After charactering the morphological, elemental, and crystallographic properties, the level of reduction in different TiO2 nanotubes array was estimated by Raman, photoluminescence, and X-ray photoelectron spectroscopies. Au/TiO2 nanotubes/Ti devices were fabricated by using TiO2 nanotubes with various levels of reductions where thin and porous Au top electrode was used to make the resistive switching faster. TiO2 Nanotubes array, reduced at 80 °C showed promising resistive switching performance with SET/RESET voltages of 2 V/1.8 V, ${R}_{ \mathrm{\scriptscriptstyle OFF}} / {R}_{ \mathrm{\scriptscriptstyle ON}}$ of 19 at a read voltage of 0.5 V (25 °C) and stable endurance behavior after the 100th cycle. Interestingly, reduction temperature at 60 °C and 100 °C, offered degraded resistive switching within the same voltage range. All the devices showed electroforming free bipolar resistive switching. Efforts were devoted to establish the role of ${V}_{O}$ and its tuning to improve the resistive switching behavior in 1-D TiO2 nanotubes. This article systematically showcases the efficacy of 1-D metal oxide for potential ReRAM application and establishes an easy but efficient approach to improve the resistive switching by modulating oxygen vacancy in it.

The market trends from last few decades have increased the pressure on development of the new products in minimum time. This can be supplemented with modification in the manufacturing processes for product development. Since last two decades, additive manufacturing (AM) also known as rapid prototyping has been used to produce components. The present work aims at optimization of thickness of deposition and surface finish of copper on Acrylonitrile Butadiene Styrene (ABS) components produced by Fused Deposition Modeling (FDM), which can be used for indirect tooling. The different process parameters such as Voltage, Concentration of Copper sulfate Solution (CSS) and deposition time are optimized. The experiment reveals that the best process parameters for maximum deposition rate gives a deposition rate of 0.19 mm/h. The surface roughness is found to be minimum at the lower values of the process parameters as 1.87 [Formula: see text]m. It has been observed that voltage (43.2%) and concentration of CSS (48.8%) significantly affect the deposition rate and for surface finish the concentration of CSS (69.59%) is the major contributor. The microstructure study of the deposited copper reveals a variation in the grain size from coarse to fine as the thickness of the deposited layer increases.

The electrophysical characteristics of a multilayer memristive Au/Ta/ZrO2(Y)/TaOx/TiN structure have been studied. Electron and ion electret effects due to charge carrier trapping and ion migration polarization in the dielectric have been discovered. The influence of traps on electroforming processes and resistive switching has been established. The values of activation energy and ion and trap concentrations have been determined. The effect of resistive switching stabilization has been found, which is associated with the specific bilayer structure of TaOx and self-forming tantalum nanoclusters. The nanoclusters serve as electric field concentrators in the course of electroforming and subsequent resistive switching.

Electroforming-free resistive switching random access memory (RRAM) devices employing magnesium fluoride (MgFx) as the resistive switching layer are reported. The electroforming-free MgFx based RRAM devices exhibit bipolar SET/RESET operational characteristics with an on/off ratio higher than 102 and good data retention of &gt, 104 s. The resistive switching mechanism in the Ti/MgFx/Pt devices combines two processes as well as trap-controlled space charge limited conduction (SCLC), which is governed by pre-existing defects of fluoride vacancies in the bulk MgFx layer. In addition, filamentary switching mode at the interface between the MgFx and Ti layers is assisted by O–H group-related defects on the surface of the active layer.

Nanostructured films of carbon and TiO2 nanoparticles have been produced by means of a simple two-step procedure based on flame synthesis and thermophoretic deposition. At first, a granular carbon film is produced on silicon substrates by the self-assembling of thermophoretically sampled carbon nanoparticles (CNPs) with diameters of the order of 15 nm. Then, the composite film is obtained by the subsequent thermophoretic deposition of smaller TiO2 nanoparticles (diameters of the order of 2.5 nm), which deposit on the surface and intercalate between the carbon grains by diffusion within the pores. A bipolar resistive switching behavior is observed in the composite film of CNP-TiO2. A pinched hysteresis loop is measured with SET and RESET between low resistance and high resistance states occurring for the electric field of 1.35 × 104 V/cm and 1.5 × 104 V/cm, respectively. CNP-TiO2 film produced by flame synthesis is initially in the low resistive state and it does not require an electroforming step. The resistance switching phenomenon is attributed to the formation/rupture of conductive filaments through space charge mechanism in the TiO2 nanoparticles, which facilitate/hinder the electrical conduction between carbon grains. Our findings demonstrate that films made of flame-formed CNP-TiO2 nanoparticles are promising candidates for resistive switching components.

Transparent resistive switching random access memory (ReRAM) is of interest for the future integrated invisible circuitry. However, poor understanding of its working mechanism in transparent ReRAMs with the indium tin oxide (ITO) electrode is still a critical problem and will hinder its widespread applications. To reveal the actual working mechanism in transparent ReRAMs with the ITO electrode, we investigate the transparent ITO/SiOx/ITO memory devices (∼82% transmittance in the visible region) and compare it with ITO/SiOx/Au memory devices, which both can exhibit reproducible bipolar switching. The indium (In) filament evolution, which accounts for the bipolar switching behaviors in the ITO/SiOx/ITO (or Au) memories, is directly observed using transmission electron microscopy on samples with different memory states (electroformed, ON, and OFF). These studies uncover the microscopic mechanism behind the bipolar switching in SiOx-based ReRAM devices with the ITO electrode, providing a general guidance for the design of high-performance ReRAMs with large scalability and high endurance. Agency for Science, Technology and Research (A*STAR) National Research Foundation (NRF) This work is supported by the National Research Foundation Competitive Research Programme (grant no. NRF-CRP13- 2014-02) and the RIE2020 ASTAR AME IAF-ICP Grant (No. I1801E0030). K.Q. acknowledges the “Qilu young scholar” program (grant no. 11500089963022) of Shandong University, China.

In order to obtain higher strength fiber reinforced composite electroforming deposit, carbon fiber reinforced nanocrystalline nickel composite electroforming deposit was prepared by electrodepositing with pulse current and a flexible wheel was applied to rub and extrude the electroforming deposit. Results shown that when the grains of the carbon fiber reinforced nickel composite electroforming deposit were refined from micron to 80nm at room temperature, the microhardness increased from 230Hv to 740Hv, and the tensile strength increased from 1025MPa to 1472MPa. With the further refinement of the grains of the electroforming deposit, the tensile strength decreased significantly due to the decrease of the bonding strength between the carbon fiber and the nickel matrix, while the microhardness still increased to 758Hv. At 200°C, the carbon fiber reinforced nanocrystalline nickel composite electroforming deposit still showed high strength. When the temperature rose to 400°C, the influence of nanocrystalline on the tensile strength of the carbon fiber reinforced nickel composite electroforming deposit was no longer significant, due to the rapid growth of crystal grains and the precipitation of interfacial brittle substances.

In this work, preparation of three-dimensional direct plated copper (3DPC) ceramic substrate was proposed based on multiple lithography and electroforming. Firstly, the effects of current density, stirring speed and bath temperature on electrodeposition rate and residual stress were investigated. An optimal combination of parameters for high electrodeposition rate and low residual stress was the current density of 4 A/dm 2 , the stirring speed of 1000 rpm, and the bath temperature of 50 °C. Secondly, 3DPC ceramic substrate with 0.5 mm nickel dam was prepared through 4 times lithography and electroforming. Finally, the reliability of 3DPC substrate was evaluated by helium leak rate and bonding strength between the electroforming dam and planar DPC substrate during thermal cycle test. The 3DPC substrate exhibited excellent hermeticity and high bonding strength even after 30 thermal cycles. The UV-LED module packaged using 3DPC substrate and quartz glass exhibited excellent hermeticity and high light power. The above results suggested that 3DPC substrate prepared through multiple lithography and electroforming could be a promising candidate for UV-LED hermetic packaging.

Introduction. As household insecticidal agents for mosquito control, electric fumigators are used complete with plates and/or liquid, which can pose an inhalation hazard during work. Material and methods. The toxicity and danger of five samples of electrofumigators on the basis of transfluthrin and prallethrin in the form of liquid and plates were studied. Two modes of application of electric fumigators have been tested: with 30-minutes airing after an hour-long treatment and further stay in the room of people and with the continuous operation of the electric fumigator in a ventilated room in the presence of people. High-performance liquid chromatography was used to determine the active substances in the air; the sensitivity of the method was 0.001 mg / m3. The assessment of the acute inhalation hazard of volatile components released during the operation of the electric fumigator was carried out on white outbred rats. Results. The obtained data showed that when using electric fumigators on transfluthrin and prallethrin, they are observed to increase in the air as compared with the hygienic standards established for them for the atmospheric air of populated areas. The research results depended on the form of the product and the chosen mode of application. Thus, assessing the first mode of application of the plates on transfluthrin, it was revealed that 30 minutes of airing the room is not enough, the excess of environmental tentative safe exposure levels was recorded. The study of the second mode of application of fluid and plates on transfluthrin revealed a tendency to increase its content in the air of the treated room when using both forms. When using the second mode of application of the liquid and the plates on prallethrin, it that after 1 h of operation of the electrofumigator with liquid, the concentration of prallethrin significantly was revealed to exceed the hygienic standard. Conclusion. The use of electrofumigators working for 8 hours in the presence of people is not recommended for use, it is necessary to ventilate the room when the fumigator is in operation for more than 1 hour.

A metal ion threshold switch (MITS) based on an Ag/TiN/HfO2/Pt stack is experimentally demonstrated with improved endurance. The incorporation of a low-temperature atomic layer deposition (ALD) TiN layer as an efficient diffusion barrier enables optimum Ag infiltration during the electroforming step. Further, the tunability of the threshold voltage (VTS) from 0.25 to 1.1V via bottom electrode (BE) work function engineering is demonstrated. The Ag/TiN/HfO2/Al MITS selector exhibits a 4.4x increase in VTS, $100~\mu \text{A}$ ON-current handling capability, low leakage (~10 pA), $10^{{7}}$ half-bias non-linearity and fast (

Silica-based resistive random access memory devices have become an active research area due to complementary metal–oxide–semiconductor compatibility and recent dramatic increases in their performan...

Electrochemical nanomaterial-based resistive switching devices (memristors) have recently attracted significant research interest because of their low cost and potential applications in nonvolatile data storage and artificial neural networks. In this paper, we report an electrochemical method to produce a novel memristor based on copper nanowire-titanium dioxide nanotube arrays (TNTAs), a core-shell composite material. TNTAs are fabricated using a cheap and effective electrochemical anodization method, and high-density copper nanowires are synthesized via excess-electrodeposition with a novel peeling-off strategy. This novel memristor shows both analogue and digital resistive switching properties by controlling the electroforming process. The Roff/Ron ratio of the digital memristor remains greater than 40 during 1000 consecutive I–V sweeps. The device shows good endurance over 104 pulse cycles, with an Roff/Ron ratio greater than 20. Furthermore, the data retention time can be maintained at least for 104 s. The outstanding digital resistive switching performance can be attributed to the numerous parallel copper nanowire nanoelectrodes inside the film.

The failure to release nickel replica from its copper mold occurs sometimes, in particular, when nickel replica is thin, large and has microstructures such as micro prism arrays. The failure is induced by improper adhesion strength between nickel replica and its copper mold. When the adhesion strength becomes too strong, the release of nickel replica from its copper mold can lead to poor surface finish or severe damages on nickel replica and/or copper mold; when the adhesion strength becomes too weak, premature release of nickel replica can happen due to internal stress that has been built up during electrochemical deposition, leading to the failure of electroforming process. To address this challenge, this paper proposes a simple and effective electrochemical approach to control the adhesion strength. The approach is to electrochemically deposit a certain density of lead nuclei on copper mold before electrochemically depositing nickel. Our experiments indicate that: (1) lead nuclei density can be conveniently controlled by nucleation duration time and electrical current; (2) lead nuclei density affects significantly the adhesion strength and hence can be used to control the adhesion strength; (3) the release of nickel replica from its copper mold becomes easy and the associated surface roughness is improved significantly when an optimal lead nuclei density is electrochemically deposited on its copper mold.

Hafnium oxide-based resistive random access memory (RRAM) ( ${\mathrm {TiN/HfO}}_{2-{x}}$ /Pt/Au) stacks were irradiated with 1.1-GeV Au ions with fluences between 1010 and 1012 ions/cm2 and evaluated regarding pristine resistance, forming voltage, and data retention. Only for the highest fluence, the resistance of the pristine state and, in turn, the conducting filament electroforming, as well as the reset voltage, increased. Even for fluences as high as 1012 ions/cm2, only a negligible percentage of the tested devices shows event upsets indicating extremely high data retention of hafnium oxide-based RRAM toward high-energy ionizing radiation.

In this paper, the memristive switching behavior of Cu/ HfO2/p++ Si devices fabricated by an organic-polymer-assisted sol-gel spin-coating method, coupled with post-annealing and shadow-mask metal sputtering steps, is examined. HfO2 layers of about 190 nm and 80 nm, are established using cost-effective spin-coating method, at deposition speeds of 2000 and 4000 rotations per minute (RPM), respectively. For two types of devices, the memristive characteristics (Von, Ion, and Vreset) and device-to-device electrical repeatability are primarily discussed in correlation with the oxide layer uniformity and thickness. The devices presented in this work exhibit an electroforming free and bipolar memory-resistive switching behavior that is typical of an Electrochemical Metallization (ECM) I-V fingerprint. The sample devices deposited at 4000 RPM generally show less variation in electrical performance parameters compared to those prepared at halved spin-coating speed. Typically, the samples prepared at 4000 RPM (n = 8) display a mean switching voltage Von of 3.0 V (±0.3) and mean reset voltage Vreset of −1.1 V (±0.5) over 50 consecutive sweep cycles. These devices exhibit a large Roff/Ron window (up to 104), and sufficient electrical endurance and retention properties to be further examined for radiation sensing. As they exhibit less statistical uncertainty compared to the samples fabricated at 2000 RPM, the devices prepared at 4000 RPM are tested for the detection of soft gamma rays (emitted from low-activity Cs-137 and Am-241 radioactive sources), by assessing the variation in the on-state resistance value upon exposure. The analysis of the probability distributions of the logarithmic Ron values measured over repeated ON-OFF cycles, before, during and after exposing the devices to radiation, demonstrate a statistical difference. These results pave the way for the fabrication and development of cost-effective soft-gamma ray detectors.

Porous copper hollow fibers have been used, for the first time, as both a support structure and a metal source for preparing thin metal-organic framework (Cu-BTC) films via a fast, facile and direct electrochemical route. The focus is on the effects of the presence of a supporting electrolyte and the magnitude of the applied electrical potential on the formation and the morphology of the films. In the absence of a supporting electrolyte, and at low potential, more uniform films with smaller particles are obtained. This is attributed to the more pronounced electric-field driven mass transport of the organic ligand from the liquid bulk towards the surface of the electrode combined with the slower dissolution of copper due to the lower overpotentials. In the presence of a supporting electrolyte the ligand transport is much slower and copper dissolution is higher due to higher overpotentials; this results in the formation of less homogeneous films and the growth of metal-organic framework crystals in the liquid bulk. The localized formation of thin metal-organic framework films on metal porous hollow fibers with high surface area to volume ratio is an important step towards various applications, including membranes, microfluidic devices, sensors and heterogeneous catalysts.

Wearable and bio-implantable health monitoring applications require flexible memory devices that can be used to locally store body vitals prior to transmission or to support local data processing in distributed smart systems. In recent years, non-volatile resistive random access memories composed of oxide-based insulators such as hafnium oxide and niobium pentoxide have attracted a great deal of interest. Unfortunately, hafnium and niobium are not low-cost materials and may also present health challenges. In this work, we have explored the alternative of using titanium dioxide as the insulating oxide using a low-cost solution-phase deposition process. Aqueous sol deposited thin films were deposited on standard RCA-cleaned commercial thermal silicon dioxide (500 nm) wafer (500 μm). Patterned bottom contacts Cr/Au (~200/300 A) using shadow masks were deposited on the substrate using successive DC sputtering, and thermal evaporation, respectively at 5 × 10-6 Torr. A sol was prepared using titanium (IV) butoxide as precursor hydrolysed under water and ethanol to form a colloidal solution (sol) at 50°C under constant stirring. Powder X-Ray Diffraction (PXRD) scans of calcined (from sol at 750°C) nanoparticles show a mixture of anatase and rutile phases, confirming the composition of the material. The sol was slowly cooled to room temperature before being spin coated at low rotational speeds on to the substrate in multiple steps involving several spin coating and drying steps to form a uniform film. Top contacts (Ag) of thickness (~500 A) were deposited on the sol-deposited thin films using thermal evaporation. The resulting devices were coated with a thick layer of polydimethylsiloxane (PDMS) using a 10:1 ratio of base elastomer and curing agent respectively. After drying the PDMS, resistance measurements were carried out. A high resistance state was detected prior to electroforming in the air at ~5 MΩ which remains nearly unchanged (~4.3 MΩ) when dipped in a ~7.4 pH phosphate buffer solution (equivalent to human blood’s pH (reference average value ~7.4 pH)). Unencapsulated devices (UM1) were further characterized in air using a Keithley 4200-SCS semiconductor parameter analyzer in dual sweep mode to observe repeatable hysteresis behavior with a large difference between trace and retrace R-V characteristics (~50±3% over a pristine device), which compares favorably with recent data in the literature on high-performance sputtered TiO2 memristors. Unchanged retention ratio using biocompatible device materials and encapsulation suggests that these devices can be used for biomedical implantable sensor electronics.

The process of molding tubular matrices of porcine carotid arteries by electroforming from polycaprolactone and a mixture of F-26 fluoroplastic with SKF-26 synthetic fluorine-containing rubber (SFR), which is a vinylidene fluoride−hexafluoropropylene copolymer, is studied. The mechanical properties of the formed matrices in dry and wet state are studied and they are compared with native vessels, the composition of the matrix material is optimized, the molding conditions are set, and the desired vessel wall thickness is chosen. It is shown that the matrices fabricated from fluoroplastics are akin to native vessels in functional properties.

The nature printing technique was designed for the electrotyping reproduction of leaves and other natural products. Authentic impressions could be performed by inserting leaves between two lead plates or pressing leaves into the lead plate by a press. The impression obtained in the soft lead plate could then be further reproduced by copper electroplating. Electrochemically deposited copper is hard-wearing and therefore very suitable for the production of printing plates. However, depending on the technical implementation and the choice of the materials used, decisive differences in the faithfulness of reproductions of original motifs may occur during the electrochemical deposition. A central topic in electroforming of printing plates is the choice of the conductive layer on the mould. In the present study, it has been shown that graphite powder represents a conductive phase on the siloxane mould superior to silver and copper powder. The grain size of the copper electrodeposit depended on the powder grain size. The copper plate deposited on graphite powder showed the lowest grain size (5–20 µm) and the highest homogeneity of the print background. Hand polishing of the printing plate resulted in a much better faithfulness of the motif details than that of the machine polished version. However, the background of the print derived from the machine polished plate was the most homogeneous. Electrochemical investigation showed that remnants of the silver powder could result in local elements that could enhance corrosion and thus impair the durability of the printing plates. This phenomenon was negligible with the conductive layers consisting of graphite and copper.

Two types of metal mesh devices with hole diameters of 1.7 and 0.3 μm were prepared by an electroforming method. The metal mesh devices with hole diameters of 1.7 and 0.3 μm transmitted electromagnetic waves with frequencies of approximately 100 and 285 THz, respectively. These spectral frequencies shifted depending on the adsorption amount of protein. The slope in the linear relationship between the adsorption amount and spectral shift (i.e. sensitivity) of the metal mesh device with a hole diameter of 0.3 μm was seven times as great as that of the device with a hole diameter of 1.7 μm. These results agreed with the theoretical concept of the sensitivity for the metal mesh device sensor being proportional to the square of the transmittance frequency. As biosensors, the structurally refined metal mesh devices amplified the output signals.

We present phase diagrams of binary oxides, Hf-O, Zr-O and Y-O, obtained by ab initio evolutionary simulations, in order to explore possible metastable crystalline suboxide structures which could be quenched during the electroforming processes within the conductive filaments in stoichiometric HfO2, ZrO2 and Y2O3 host materials, in resistive switching devices. We find that, in the range MO-MO2 (where M = Hf, Zr, Y), the most energetically favourable atomic configurations have properties which facilitate the ionic conduction of oxygen. Namely, the calculations reveal that oxygen vacancies tend to order in arrays of one-dimensional channels, along which the migration barrier of anions is much lower than for the stoichiometric hosts. We explore for Hf-O and Zr-O a new set of structural patterns, different from those of the host materials, for which a change of oxygen stoichiometry does not change the underlying structural frame. However, a sufficient change of oxygen stoichiometry drives metallic conductivity in oxygen-deficient compounds, whereas their oxygen-rich counterparts are insulating. In contrast to Hf-O and Zr-O, in the Y-O system we find an atomic structure with metallic conductivity, which has the same structural frame as the stoichiometric Y2O3 host. We believe that this property enables the forming-free resistive switching in Y2O3.

Methods for the formation of a porous structure in plastic and thermoplastic calcium-phosphate composites are considered. Plastic compositions were synthesized on the basis of natural polymers (collagen, gelatin and sodium alginate). Biodegradable polymers were used as thermoplastic polymers: polylactide and poly-3-hydroxybutyrate. The approaches to the formation of a porous structure in polymer composites, developed through the use of lyophilic, microwave drying, the use of special devices and gas-releasing additives, the use of 3D printing, and the electroforming of fibers (EPI) indicate the need to combine different methods to achieve a branched porous structure and the required pore sizes in composites.

A new approach to precision electroforming of a wafer scale nickel shim using a rotating cathode with an auxiliary cathode mask is developed to improve thickness uniformity and flatness. The effects of critical process parameters, including cathode rotating speed, cathode mask size, and current density, on the thickness uniformity and flatness of electroformed nickel shim are systematically studied based on experiments and simulations. The results show that the thickness uniformity of the deposits is highly dependent on the current density distribution, where a cathode mask can effectively tune electrical field lines and induce a more uniform current density distribution. The simulations and experimental results consistently agree that a minimum thickness nonuniformity of 8% and below 1% on the wafer with a diameter of 80 mm and 40 mm, respectively, can be achieved using a mask with a 70 mm opening size. However, for flatness, the cathode rotating speed influences the surface warpage due to the intrinsic stress. It is also found that the gradient current density can significantly reduce the intrinsic stress with better flatness. The best flatness is controlled below 47 µm and 32 µm on the wafer with diameters of 80 mm and 40 mm, respectively, under the synergistic effect of optimal cathode rotating speed (30 rpm) and gradient current density.

Memristive devices have led to an increased interest in neuromorphic systems. However, different device requirements are needed for the multitude of computation schemes used there. While linear and time-independent conductance modulation is required for machine learning, non-linear and time-dependent properties are necessary for neurobiologically realistic learning schemes. In this context, an adaptation of the resistance switching characteristic is necessary with regard to the desired application. Recently, bi-layer oxide memristive systems have proven to be a suitable device structure for this purpose, as they combine the possibility of a tailored memristive characteristic with low power consumption and uniformity of the device performance. However, this requires technological solutions that allow for precise adjustment of layer thicknesses, defect densities in the oxide layers, and suitable area sizes of the active part of the devices. For this purpose, we have investigated the bi-layer oxide system TiN/TiOx/HfOx/Au with respect to tailored I-V non-linearity, the number of resistance states, electroforming, and operating voltages. Therefore, a 4-inch full device wafer process was used. This process allows a systematic investigation, i.e., the variation of physical device parameters across the wafer as well as a statistical evaluation of the electrical properties with regard to the variability from device to device and from cycle to cycle. For the investigation, the thickness of the HfOx layer was varied between 2 and 8 nm, and the size of the active area of devices was changed between 100 and 2,500 µm2. Furthermore, the influence of the HfOx deposition condition was investigated, which influences the conduction mechanisms from a volume-based, filamentary to an interface-based resistive switching mechanism. Our experimental results are supported by numerical simulations that show the contribution of the HfOx film in the bi-layer memristive system and guide the development of a targeting device.

The corrosion behavior of the Ni/Ni interface during the Cu sacrificial layer releasing process in micro-electroforming has been investigated. The XPS and SEM results reveal that the pre-existing passive layer and interfacial defects exist on the Ni/Ni interface. Compared with Ni base, the interface is prone to be attacked. Pitting corrosion occurs along interface boundary, which contains three main processes, pit initiation, pit growth and pits fusion, leading to a commensurate reduction in interfacial adhesion strength and ultimately structural integrity. The combination of the substrate modification and heat post treatment is an effective solution to avoid the localized corrosion. We believe that both the surface activation and thermally induced diffusion have worked.

High-density memory devices are essential to sustain growth in information technology (IT). Furthermore, brain-inspired computing devices are the future of IT businesses such as artificial intelligence, deep learning, and big data. Herein, we propose a facile and hierarchical nickel cobaltite (NCO) quasi-hexagonal nanosheet-based memristive device for multilevel resistive switching (RS) and synaptic learning applications. Electrical measurements of the Pt/NCO/Pt device show the electroforming free pinched hysteresis loops at different voltages, suggesting the multilevel RS capability of the device. The detailed memristive properties of the device were calculated using the time-dependent current–voltage data. The two-valued charge-flux properties indicate the memristive and multilevel RS characteristics of the device. Interestingly, the Pt/NCO/Pt memristive device shows a compliance current (CC)-dependent RS property; compliance-free RS was observed from 10−2 to 10−4 A, and the compliance effect dominated in the range of 10−5–10−6 A. In CC control mode, the device demonstrated three resistance states during endurance and retention measurements. In addition, the device was successful in mimicking biological synaptic properties such as potentiation-depression- and spike-timing-dependent plasticity rules. The results of the present investigation demonstrated that solution-processable NCO nanosheets are potential switching materials for high-density memory and brain-inspired computing applications. A simple technique for producing nanostructured oxides shows promise for developing neuromorphic computing systems. Tae Geun Kim from Korea University in Seoul, South Korea, and co-workers report that nickel cobaltite, a low-cost material being considered for non-volatile memory devices, can be synthesized as porous nanosheets through a co-precipitation method. The team demonstrated that when stacked a few hundred nanometers thick, these sheets had properties ideal for ‘resistive switching’, an effect that stores data by transforming insulators into conductors using metal filaments. Characterizations revealed that the material’s morphology proved ideal for fine-tuning filament growth, enabling the memory cell to switch between three conductive states. Because the nanosheet devices retained memories of their switching history, they were capable of mimicking neural network behavior, such as the potentiation, depression and spike-timing-dependent plasticity processes associated with synapses. A resistive switching device is fabricated using nanostructured nickel cobaltite for high-density data storage and synaptic learning applications. The active switching layer of the device consists of quasi-hexagonal porous nanosheets that enable smooth charge transport. The device shows voltage tunable and forming-free resistive switching effect and non-ideal memristive properties. The rational design of the device helps to show controlled multilevel resistive switching property and thereby switch between three conductive states. The analog switching of the device helps to mimic specific neural network behavior, such as the potentiation, depression and four spike-timing-dependent plasticity rules.

International audience; Vanadium dioxide (VO 2 ) has attracted much attention owing to its metal–insulator transition near room temperature and the ability to induce volatile resistive switching, a key feature for developing novel hardware for neuromorphic computing. Despite this interest, the mechanisms for nonvolatile switching functioning as synapse in this oxide remain not understood. In this work, we use in situ transmission electron microscopy, electrical transport measurements, and numerical simulations on Au/VO 2 /Ge vertical devices to study the electroforming process. We have observed the formation of V 5 O 9 conductive filaments with a pronounced metal–insulator transition and that vacancy diffusion can erase the filament, allowing for the system to “forget.” Thus, both volatile and nonvolatile switching can be achieved in VO 2 , useful to emulate neuronal and synaptic behaviors, respectively. Our systematic operando study of the filament provides a more comprehensive understanding of resistive switching, key in the development of resistive switching-based neuromorphic computing.

For mass production of liposomes, we designed a plastic micro-channel device on the basis of 5 μm of micro-nozzle array forming T-junction with 100 μm depth of micro-channel. A micro-channel unit for synthesizing liposomes consisted of two micro-nozzle arrays for mixing two solutions as well as delivery and recovery channels for supplying solutions and collecting liposome suspension. The number of micro-nozzles was approximately 2400 for a micro-channel unit, and seven units were applied independently on a micro-channel plate. The plastic micro-channel plate was injection-molded for mass production using a micro-channel stamper previously fabricated by UV lithography and nickel electroforming process. A plastic cover plate with seven pairs of inlet and outlet ports was machined by mechanical milling and drilling and was assembled with a micro-channel plate using a holder to form a liposome synthesizing device. Flow and mixing of solutions in the micro-channels were tested using colored water to check the micro-fluidic characteristics of the device. Finally, a L-α-phosphatidylcholine (SOY PC) liposome was synthesized using EtOH solution of SOY PC (95%) and saline (0.85% NaOH solution) to find that the liposomes were around 230 and 260 nm in diameter, depending on the flow rate of the lipid solution.

Metal oxide-based Resistive Random-Access Memories (RRAM) exhibit multiple intermediate resistive states, due to the formation/rupture of a conductive filament (CF) inside a switching layer. While there have been extensive studies on the resistive switching behavior caused by a pre-existing CF, the initial stage of the formation and growth of a CF, i.e., the electroforming process has been less understood. In this work, we developed a physical model to fundamentally understand the formation and growth behavior of a CF in a metal oxide layer constrained by the top/bottom electrodes. It is revealed that the CF formation is assisted by the supply of oxygen vacancies at the anode and the oxygen vacancies transport in the oxide layer. The effects of the external conditions (the oxygen exchange rate j 0 and the applied voltage) and the physical properties of the oxides (the electrical σ and thermal conductivity k th ) on the CF morphology evolution, current density evolution, and local temperature and electrical potential distribution have been systematically explored. It is found that larger oxygen vacancy exchange rate and relatively small voltage sweep rate result in a more uniform CF. Furthermore, by choosing oxides with lower Lorenz number (ratio of k th and σ ), CF with more homogeneous morphology can be realized. This work provides a fundamental understanding of the kinetic behaviors of the CF formation and growth during the electroforming process, and could potentially guide the oxide and electrode materials selection, synthesis and working conditions for switching to achieve improved RRAM stability and functionality.