High Aspect Ratio Electrodes Research Articles

О возможности создания эффективных устройств на поверхностных акустических волнах на частотах выше 6 ГГц

In the paper the interaction of surface acoustic waves (SAWs) with reflectors and interdigital transducers (IDTs) with high aspect ratio electrodes (HAR-electrodes) are investigated. The conditions for the SAW resonant reflection and propagation and the effective IDT conversion of the SAW power into electrical power at the load have been obtained. The real possibility of the effective SAW devices creation (filters, delay lines, resonators, RFID tags) at frequencies above 6 GHz (up to 12-15 GHz) using HAR-electrodes was demonstrated.

Shear Horizontal Phononic Metasurface for In-Liquid Gravimetric Biosensing

In-liquid wave attenuation is the major factor that limits the resolution of acoustic wave biosensors. Existing acoustic wave devices rely on shear mode operation to reduce the mechanical motion transferred to the liquid. However, the energy leakage still exists through acoustic radiation. In this article, we combined phononic metasurface based on local mechanical resonators with shear horizontal surface acoustic wave (SH-SAW) to address the above issue. The shear-horizontal phononic metasurface (SH-PM) resonator is made of periodic high-aspect-ratio electrode (HARE). It produces a slow phononic wave that cannot propagate in water due to its low velocity, which suppresses the acoustic radiation. Furthermore, as the particle motion of the HARE is polarized in shear mode, the SH-PM also reduces the mechanical motion transfer to water. The minimization of the total acoustic energy leakage in the SH-PM results in high quality factor (Q) resonance in water. Besides, the increased surface-to-volume ratio of the HAREs also enhances the mass sensitivity of the device. Experimental results show that the SH-PM resonator achieved an in-liquid Q factor of 230 and a normalized mass sensitivity of - 192.4 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cm</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /g. The high in-liquid Q factor together with the high mass sensitivity makes the SH-PM a promising candidate for high-resolution gravimetric detection of biomolecules.

Acoustic radiation-free surface phononic crystal resonator for in-liquid low-noise gravimetric detection

Acoustic wave resonators are promising candidates for gravimetric biosensing. However, they generally suffer from strong acoustic radiation in liquid, which limits their quality factor and increases their frequency noise. This article presents an acoustic radiation-free gravimetric biosensor based on a locally resonant surface phononic crystal (SPC) consisting of periodic high aspect ratio electrodes to address the above issue. The acoustic wave generated in the SPC is slower than the sound wave in water, hence it prevents acoustic propagation in the fluid and results in energy confinement near the electrode surface. This energy confinement results in a significant quality factor improvement and reduces frequency noise. The proposed SPC resonator is numerically studied by finite element analysis and experimentally implemented by an electroplating-based fabrication process. Experimental results show that the SPC resonator exhibits an in-liquid quality factor 15 times higher than a conventional Rayleigh wave resonator at a similar operating frequency. The proposed radiation suppression method using SPC can also be applied in other types of acoustic wave resonators. Thus, this method can serve as a general technique for boosting the in-liquid quality factor and sensing performance of many acoustic biosensors.

Towards Acoustic Radiation Free Lamb Wave Resonators for High-Resolution Gravimetric Biosensing

A novel Lamb wave resonator with fully suppressed acoustic radiation in water is proposed for high-resolution mass-sensitive detection of biomolecules. The elimination of acoustic radiation is achieved by slowing down the Lamb wave to a velocity lower than the sound speed in water. This enables high-quality-factor resonance in water and reduces the sensing frequency noise. High aspect ratio electrodes (HAREs) are used to slow down the Lamb wave. The elastic resonance and large surface area of the HAREs can also enhance the mass sensitivity of the device. The improved mass sensitivity together with the low frequency noise substantially improves the overall sensing resolution. Although reducing the plate thickness can also slow down the Lamb wave, it makes the device very fragile and not practical to use. In contrast, slowing down the Lamb wave by increasing electrode height allows the use of thick plates which is robust. In this article, the behavior and performance of the proposed high aspect ratio electrode Lamb wave resonator (HARE-LWR) are theoretically analyzed using finite element method simulations. Optimum design parameters were found through the simulations. Reported results show that a significant figure of merit improvement was achieved by the proposed HARE-LWR design.

High-frequency Sezawa guided mode of GaN/sapphire using high aspect ratio electrode

The propagation of surface acoustic wave (SAW) on the piezoelectric substrate requires conventionally an interdigitated electrode structure to excite the mechanical displacement at resonance frequency. The control of the electrode thickness could be useful to manipulate the energy confinement and the band dispersion of the surface guided mode. It has been demonstrated recently that high aspect ratio (HAR) electrode could produce a dispersive shear horizontal and vertically polarized surface modes in the bulk piezoelectric substrate. In this theoretical study, we propose to employ a high aspect ratio electrode on top of the GaN/sapphire-layered substrate enabling the presence of Sezawa surface mode. Based from the dispersion band, we obtained a higher frequency of surface guided mode in the non-radiative zone in the GaN/sapphire heterostructure configuration compared to the bulk GaN substrate. Indeed, these guided modes are induced by the hybridization between Sezawa surface mode and the mechanical resonance of the HAR electrode producing nearly a flat band at the limit of First Brillouin Zone. Furthermore, the displacement of each guided modes indicates the confinement of energy mostly in the electrode with a slight amount of energy in the top layer of the substrate. We demonstrated also the frequency tuning of guided mode using diverse materials for the electrode but also the thickness of GaN layer. The obtained results could be useful for the development of high-frequency telecommunication and sensing device based on Sezawa surface acoustic wave.

마스크 기반 전해증착을 통한 미세 전극 형상 제작

Various methods to fabricate micro electrodes exist; however, these methods are generally complex and costly. Although deposition methods for fabricating micro electrodes using a reusable polymer mask have been proposed previously, these cannot address limitations of aspect ratio and shape accuracy of the micro electrodes owing to the process characteristics. This study aims to overcome these limitations by changing the mask structure and improving ion diffusion. The concentration of deposition electrolyte and other basic experimental conditions were the same as used in previous experiments. Various experiments were conducted by changing current density, electrolyte vibration, and electrolyte temperature, which significantly affect ion diffusion during the fabrication process. To verify the feasibility of the proposed process, high aspect ratio electrodes through electrode movement and multiple electrode shapes with a diameter of 200 μm were manufactured.

Recent Progress in Nanostructured Thin Film (NSTF) ORR Electrocatalyst Development for PEM Fuel Cells

Development of highly active, durable, and low cost ORR electrocatalysts and supports for PEM fuel cells remains a key challenge for large-scale commercial deployment. These factors are highly coupled, especially so when incorporated into membrane electrode assemblies (MEAs) at low Platinum Group Metal (PGM) content approaching mid-term U.S. Department of Energy (DOE) targets [1]. 3M Nanostructured Thin Film (NSTF) electrocatalysts and electrodes are a unique approach towards addressing these challenges, due to the thin film electrocatalyst structure and non-carbon, high-aspect ratio, oriented support, and ultrathin (<1µm) NSTF electrodes which do not require ionomer for proton conduction [2]. Our presentation will address recent progress towards development of next generation NSTF ORR electrocatalysts and our efforts to integrate advanced NSTF electrodes into robust, durable, high performance, and low-cost MEAs. Current generation Pt3Ni7/NSTF ORR electrocatalysts have high specific and mass activities (2.7mA/cm2 Pt and 0.75A/mgPGM, 0.900V v. RHE, RDE [3]) and in MEA electrodes have exhibited exceptional tolerance to corrosion and good cyclic durability. The high mass activity of Pt3Ni7/NSTF is in part due to formation of a nanoporous Pt alloy thin film structure upon dealloying, which yields substantially increased specific area and specific activity over nonporous Pt/NSTF cathodes [4]. When dealloyed Pt3Ni7/NSTF electrodes are integrated into an optimized MEA, very high MEA ¼ power, rated power and specific power densities are achieved at low total PGM content (Fig. 1(A)), which approach or exceed these DOE 2020 targets [5]. Development of highly active nanoporous electrocatalysts depends strongly upon simultaneous optimization of the electrocatalyst structure and composition via catalyst deposition, annealing, and dealloying process parameters. Fig. 1(B) summarizes MEA ORR mass activity data for “PtxM1-x” NSTF cathodes over a range of compositions with three different catalyst structures induced by process set variation, all at 0.117-0.123mgPGM/cm2, and includes Pt3Ni7 data for reference. At certain compositions, mass activity can increase over 2.5 times as the catalyst process conditions are varied, whereas at other compositions no significant effect is observed. Through process and composition optimization, mass activities of “PtxM1-x” are nearly 1.3 times higher than Pt3Ni7. Development of high performance MEAs requires not only high cathode mass activity, but also low residual leachable transition metal content to minimize contamination of the PFSA PEM. Fig. 1(C) compares MEA H2/Air performance of otherwise identical MEAs with either a 0.129mgPt/cm2 Pt3Ni7/NSTF cathode or a 0.075mgPt/cm2 Pt3Ni7/NSTF cathode, dealloyed by different methods. H2/Air performance of the lower loaded electrode with dealloy method “B” is similar or superior to the higher loaded cathode which was dealloyed with method “A”, even with 40% lower PGM loading. References U.S. Department of Energy, Office of Energy Efficiency & Renewable Energy, “FUEL CELL TECHNOLOGIES OFFICE MULTI-YEAR RESEARCH, DEVELOPMENT, AND DEMONSTRATION PLAN”, Section 3.4 Table 3.4.13, retrieved from http://energy.gov/sites/prod/files/2014/12/f19/fcto_myrdd_fuel_cells.pdf on April 6th, 2015.M. K. Debe, ECS Transactions, 45(2) 47–68 (2012).D. A. Cullen and S. Kocha, private correspondence.D. A. Cullen et al., J. Mater. Chem. A, accepted, (2015). A. J. Steinbach, U.S. Department of Energy EERE FCTO Annual Merit Review (2015), Project FC104, submitted. Figure 1

AC electrical characterisation and insight to charge transfer mechanisms in DNA molecular wires through temperature and UV effects.

In this study, AC characterisation of DNA molecular wires, effects of frequency, temperature and UV irradiation on their conductivity is presented. λ-DNA molecular wires suspended between high aspect-ratio electrodes exhibit highly frequency-dependent conductivity that approaches metal-like behaviour at high frequencies (∼MHz). Detailed temperature dependence experiments were performed that traced the impedance response of λ-DNA until its denaturation. UV irradiation experiments where conductivity was lost at higher and longer UV exposures helped to establish that it is indeed λ-DNA molecular wires that generate conductivity. The subsequent renaturation of λ-DNA resulted in the recovery of current conduction, providing yet another proof of the conducting DNA molecular wire bridge. The temperature results also revealed hysteretic and bi-modal impedance responses that could make DNA a candidate for nanoelectronics components like thermal transistors and switches. Further, these experiments shed light on the charge transfer mechanism in DNA. At higher temperatures, the expected increase in thermal-induced charge hopping may account for the decrease in impedance supporting the 'charge hopping mechanism' theory. UV light, on the other hand, causes damage to GC base-pairs and phosphate groups reducing the path available both for hopping and short-range tunneling mechanisms, and hence increasing impedance--this again supporting both the 'charge hopping' and 'tunneling' mechanism theories.

Non-contact printing of high aspect ratio Ag electrodes for polycrystalline silicone solar cell with electrohydrodynamic jet printing

This paper presents a non-contact printing mechanism for high aspect ratio silver (Ag) electrodes fabricated by an electrohydrodynamic (EHD) jet printing technique. Using high viscosity Ag paste ink, we were able to fabricate narrow and high aspect ratio electrodes. We investigated the effect of the surface energy of the substrate and improved the aspect ratio of printed lines through multiple printing. We fabricated the polycrystalline silicone solar cell with the Ag electrode and achieved cell efficiency of around 13.7%. The EHD jet printing mechanism may be an alternative method for non-contact fabrication of solar cells electrodes.

Surface acoustic wave guiding in a diffractionless high aspect ratio transducer

We demonstrate efficient three-dimensional surface acoustic wave guidance and confinement in a high-aspect ratio electrode transducer. Each electrode acts as an elastic resonator that is evanescently coupled to its neighbors. We observe high amplitude displacement fields confined within the high aspect ratio electrodes. The stored surface waves are found to present a general shear polarization instead of the sagittal polarization expected for classical Rayleigh waves. The elastic energy is mostly distributed in the mass-loaded areas, and waves propagate within the transducer without diffraction, even for very low acoustic apertures.

Analysis of Electrolyte Flow in Localized Electrochemical Deposition

Localized electrochemical deposition (LECD) is a favorable technology for fabrication of the high-aspect ratio electrodes of various materials. This technology is found to be one of the simple and inexpensive ways to fabricate non-circular electrodes for micro-EDM. In order to fabricate non-circular electrodes a mask of non-conductive material is placed between the anode and cathode, which is immersed in a mixed electrolyte of copper sulfate, 1.0M sulfuric acid and as an additive agent 0.04 gm/liter of thiourea. The deposition of copper is localized on the cathode surface using a mask and applying ultra-short voltage pulses between the anode and cathode. In this set up the cathode is placed above the anode and mask, so that the deposited electrode can be used directly for EDM or any application without changing its orientation. In order to localize the deposited structure on the cathode surface, the electrolyte needs to flow through the mask and needs to touch the cathode and a constant flow rate of the electrolyte is maintained by using a pump. For this reason, micro holes of desired shapes are fabricated in the mask using micro milling. This study shows the effect of electrolyte flow through the micro holes of the mask and micro gap between the mask and anode on the microstructure of deposited electrode using FLUENT analysis. Moreover, an optimum range of electrolyte flow rate through the micro passages is also shown for the LECD process in order to fabricate high aspect ratio microstructures.

결정질 실리콘 태양전지의 효율 향상을 위한 다층 전면 전극 형성

Resistance of the front electrode is the highest proportion of the ingredients of the series resistance in crystalline silicon solar cell. While resistance of the front electrode is decreased with larger area, it induces the optical loss, causing the conversion efficiency drop. Therefore the front electrode with high aspect ratio increasing its height and decreasing is necessary for high-efficiency solar cell in considering shadowing loss and resistance of front electrode. In this paper, we used the screen printing method to form high aspect ratio electrode by multiple printing. Screen printing is the straightforward technology to establish the electrodes in silicon solar cell fabrication. The several printed front electrodes with Ag paste on silicon wafer showed the significantly increased height and slightly widen finger. As a result, the resistance of the front electrode was decreased with multiple printing even if it slightly increased the shadowing loss. We showed the improved electrical characteristics for c-Si solar cell with repeatedly printed front electrode by 0.5%. It lays a foundation for high efficiency solar cell with high aspect ratio electrode using screen printing.

Integrated Polypyrrole Flexible Conductors for Biochips and MEMS Applications

Integrated polypyrrole, a conductive polymer, interconnects on polymeric substrates were microfabricated for flexible sensors and actuators applications. It allows manufacturing of moving polymeric microcomponents suitable, for example, for micro-optical-electromechanical (MOEMS) systems or implanted sensors. This generic technology allows producing “all polymer” components where the polymers serve as both the structural and the actuating materials. In this paper we present two possible novel architectures that integrate polypyrrole conductors with other structural polymers: (a) polypyrrole embedded into flexible polydimethylsiloxane (PDMS) matrix forming high aspect ratio electrodes and (b) polypyrrole deposited on planar structures. Self-aligned polypyrrole electropolymerization was developed and demonstrated for conducting polymer lines on either gold or copper seed layers. The electropolymerization process, using cyclic voltammetry from an electrolyte containing the monomer, is described, as well as the devices’ characteristics. Finally, we discuss the effect of integrating conducting polymers with metal seed layer, thus enhancing the device durability and reliability.

Improving surface acousto-optical interaction by high aspect ratio electrodes

The acousto-optical interaction of an optical wave confined inside a waveguide and a surface acoustic wave launched by an interdigital transducer (IDT) at the surface of a piezoelectric material is considered. The IDT with high aspect ratio electrodes supports several acoustic modes that are strongly confined to the surface, causing a significant increase in the strain underneath the surface. A finite element method is employed to model the surface acoustic waves generated by a finite length IDT with 12 electrode pairs and subsequently to study their interaction with an optical wave propagating in a waveguide buried in the lithium niobate substrate supporting the electrodes. The interaction can be increased up to 600 times using these new types of surface acoustic waves as compared to using a conventional IDT with thin electrodes. This result could find applications in improved acousto-optical integrated modulators.

Energy storage and dispersion of surface acoustic waves trapped in a periodic array of mechanical resonators

It has been shown previously that surface acoustic waves can be efficiently trapped and slowed by steep ridges on a piezoelectric substrate, giving rise to two families of shear-horizontal and vertically polarized surface waves. The mechanisms of energy storage and dispersion are explored by using the finite element method to model surface acoustic waves generated by high aspect ratio electrodes. A periodic model is proposed including a perfectly matched layer to simulate radiation conditions away from the sources, from which the modal distributions are found. The ratio of the mechanical energy confined to the electrode as compared to the total mechanical energy is calculated and is found to be increasing for increasing aspect ratio and to tend to a definite limit for the two families of surface waves. This observation is in support of the interpretation that high aspect ratio electrodes act as resonators storing mechanical energy. These resonators are evanescently coupled by the surface. The dispersion diagram is presented and shows very low group velocities as the wave vector approaches the limit of the first Brillouin zone.

Fabrication of complex shape electrodes by localized electrochemical deposition

Localized electrochemical deposition (LECD) is a promising technology for fabrication of high-aspect ratio electrode of various materials. This technology is found to be one of the simple and inexpensive ways to fabricate electrodes for micro-EDM. This study presents a novel method to manufacture electrodes with complex cross-section using mask of non-conductive material. In this study, the mask is placed between the anode and cathode, which is immersed in mixed electrolyte of copper sulfate, 1.0 M sulfuric acid and as an additive agent 0.04 g/l of thiourea. The deposition of copper is localized on the cathode surface using a mask and applying ultra short voltage pulses between the anode and cathode. In this setup the cathode is placed above the anode and mask, so that the deposited electrode can be used directly for EDM or any application without changing tool orientation. The deposition characteristics such as size, shape, surface, and structural density according to gap between the anode and mask, applied voltage, pulse frequency and duty ratio have been investigated in this study. Finally, appropriate conditions have been found out for effective fabrication of smooth and fine-grained deposited electrodes based on the findings of the various experiments.

Geometrical control of the magnetization direction in high aspect-ratio PdNi ferromagnetic nanoelectrodes

We present a study of electron-beam evaporated ${\text{Pd}}_{0.4}{\text{Ni}}_{0.6}$ alloy thin films by means of ferromagnetic resonance measurements on extended films of varying thickness and anisotropic magnetoresistance measurements of lithographically patterned high aspect-ratio ferromagnetic electrodes, respectively. The results reveal that the direction of the magnetization strongly depends on the electrode lateral dimensions, transitioning from in-plane magnetization for extended films to out-of-the-plane magnetization for electrode widths below 2--3 microns, reaching $\ensuremath{\sim}58\ifmmode^\circ\else\textdegree\fi{}$ off plane for 100 nm-wide nanoelectrodes.

High aspect ratio diamond microelectrode array for neuronal activity measurements

Diamond exhibits several attractive properties for bio-sensing applications. In particular its high bio inertness, high electrochemical stability, and optical transparency provide diamond with high interests for neural activity study. The purpose of this study is the realisation of microelectrodes arrays (MEA) in diamond for neurons slices study. Due to a cellular lysis on the edge of the tissue slices studied, electrodes have to be at least 60 μm in height even though the electrode surface has to be minimised in order to achieve good signal noise rate. Silicon MEA with metal contacts were realised using (Deep Reactive Ion Etching) DRIE and coated with Nanocrystaline Diamond (NCD) using (Bias Enhanced Nucleation) BEN technique. We focus the study on the understanding of the BEN nucleation process on such high aspect ratio electrodes. Several parameters such as slope of the substrate, conductivity and chemical nature of the substrate were studied in order to enable selective nucleation necessary to fabricate diamond MEAs. The study leads to the optimised development of a processing route enabling the selective coating of the active tips of high aspect ratio MEAs without altering the electrical insulation between probes.

Novel Nanocast Method of Creating Implantable High Aspect Ratio Electrodes on Thin Flexible Substrate with Nanoparticles

not Available.

Design and prototyping of Stark atom chip for electric trapping of laser-cooled atoms

An electric trapping of laser-cooled neutral strontium (Sr) atoms on a chip with micro-electrodes has been successful. The device is called “Stark atom chip” since it makes use of Stark effects on neutral atoms in electric fields. In this paper, our design and prototyping of the Stark atom chip with high aspect ratio electrodes precisely built on a surface are described. The functional requirements of the chip are specified during the discussion of designing the device. The authors design a novel process for fabrication of high aspect ratio electrodes. A focused ion beam (FIB) is used for precision fabrication of the prototype.