Electrodeposition Of Multilayers Research Articles

Suppression of Eddy Current Loss in Multilayer NiFe-Polypyrrole Magnetic Cores Fabricated Using a Continuous Electrodeposition Process

Metallic magnetic alloys are of interest as core materials in ultracompact or integrated inductors and transformers. However, when operated at high frequencies, such materials should comprise a multilayer stack of magnetic material laminations and electrically insulating interlayers to suppress eddy current loss. To achieve scalable and continuous fabrication of such a structure, sequential multilayer electrodeposition is an attractive approach. To achieve sequential electrodeposition, interlayer’s electrical conductivity should be sufficiently high to permit electrodeposition of subsequent layers, but sufficiently low to suppress eddy current loss. Polypyrrole, an electrodepositable polymer, was investigated as an interlayer material. Finite element modeling demonstrated a negligible difference in eddy current loss between NiFe/polypyrrole and NiFe/vacuum multilayers. Experimental verification of the efficacy was demonstrated as well. Compared with a single-layer NiFe inductor that has a comparable low-frequency (10 kHz) inductance value, a laminated ten-layer NiFe core showed higher inductance retention (88% of the low-frequency inductance for the laminated core versus 21% for the single-layer core) and lower ac resistance (1.68 versus <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$12.7~\Omega $ </tex-math></inline-formula> ) at 8 MHz, both of which are signs of suppressed eddy current. This scalable fabrication approach to high-frequency inductors will facilitate power converter miniaturizations.

Inhibiting effects of the Ni barrier layer on the growth of porous Cu3Sn in 10-μm microbumps

With the shrinkage of size, porous Cu3Sn has become a new potential threat of the reliability in Cu pillar microbump. The formation of porous Cu3Sn is caused by the decomposition of Cu6Sn5 after Sn atoms in solder depletion. Besides, the stress introduced by the phase transition from η-Cu6Sn5 to η′-Cu6Sn5 will promote the formation of porous Cu3Sn. In this paper, uniform Ф10 µm Cu/Sn and Cu/Ni (~ 0.6 μm)/Sn microbumps have been fabricated by multilayer electrodeposition and the effect of the Ni layer on the growth behavior of porous Cu3Sn was investigated by comparing IMCs’ (Intermetallic Compound) evolution in Cu/Sn and Cu/Ni/Sn bumps aged at 170 °C and 200 °C. The ~ 0.6 μm Ni barrier layer can effectively retard the Cu atoms diffusion, which can hinder IMC from overgrowth. Moreover, the results of X-ray diffraction indicate that the ability of the Ni layer can stabilize Cu6Sn5 phase and weakens the tendency of the porous Cu3Sn formation. Under the conjoint action of retarding the growth of IMC and stabilizing Cu6Sn5 phase, the Ni layer can inhibit the formation of porous Cu3Sn efficaciously.

A New Electrodeposition Approach for Multicomponent Solder Alloys

Enactment and enforcement of international regulations restricting the use of lead-bearing solders has triggered plenty of research on Pb-free alloys for Integrated Circuits (ICs) packaging [1]. Nonetheless, Sn-Pb (63/37) eutectic still possesses unique features (e.g. low melting point, optimum mechanical properties, ideal surface tension allowing for holes and gaps wetting, capability of reducing, inhibiting or eliminating tin whiskers formation, etc.) hardly matched by lead-free solders.Alloys belonging to the SAC (Sn-Ag-Cu) category constitute the most widespread alternative to tin-lead solder because of their relatively low melting point [2], “composition-tunable” wettability [3], and high tensile strength (compared to the Sn-Pb eutectic). Particularly, SAC-305 (Sn = 96.5, Ag = 3, and Cu = 0.5 wt%) and SAC-405 (Sn = 95.5, Ag = 4, and Cu = 0.5 wt%) are by far the most employed solders compatible with the PTH (Plating Through Hole) layers connection method, the SMT (Surface Mounted Technology) components placement approach, and the surface finishes routinely used in PCBs manufacturing (e.g. organic solder preservative, lead-free hot air solder levelling, immersion silver, immersion tin, electroless nickel immersion gold, etc.). Furthermore, near eutectic SAC alloys (i.e. comprising 3-4 wt% of silver and 0.5-1 wt% of copper) also benefit from improved temperature cycling reliability mainly due to the high Ag content.The present work puts forward a new multi-layer electrodeposition technique amenable to wafer level chip scale package. By taking advantage of multiple Dynamic Liquid Drop/Meniscus (DLD/DLM), it is possible to plate binary, ternary and even quaternary solders at high-throughput, high precision and low cost [4]. The DLD/DLM exposes a constantly refreshed confined electrolyte volume in contact with the substrate surface [5]. The core of the method consists in interposing a rinse DLD/DLM into a sequential array of multiple independent electroplating DLD/DLMs (one for each component to deposited). Such a configuration results in a synergistic system composed of different plating outputs (plating head). Thereby, scanning the plating head over the wafer surface allows to coat the substrate with a thin layer of each component. Thus, each plating head pass leads to the deposition of a multilayered structure reflecting the targeted composition of the alloy. In other words, the current density is regulated in each DLD/DLM in order to obtain the desired wt% of every single component in the final solder deposit. Obviously, the total film thickness depends on the number of layers and can be varied in a wide range to allow an homogenous structures even without reflow.As a proof-of-concept, SAC-305 and SAC-405 bumps and caps on top of copper pillars [6] were deposited: 30 μm thick structures were electroplated through more than 350 layers of each element. Bumps as high as 10 µm (attained for net electroplating times as low as 14 seconds) were sectioned by FIB (Focused Ion Beam) to verify the agreement between the expected composition and the actual one. EDX analysis performed before and after reflow proved that the high number of layers produces a compositionally homogenous solder regardless of the metal deposition sequence and reflow temperature. A detailed investigation of SAC and quaternary SAC+Me (e.g. Ni, Zn) alloys composition will be presented (e.g. thermal, mechanical and wetting properties); EDX analysis before and after reflow proving that the high number of layers homogenous solder is obtained independently of metal deposition sequence and even without reflow. Furthermore, the nozzle sizes of the multiple DLD/DLM equipment will be correlated to the aspect ratio of the dry film opening.[1] A. Lancaster and M. Keswani, Integration, 75, 77 (2017).[2] A. B. Frazier, R. O. Warrington and C. Friedrich, IEEE Transactions on Industrial Electronics, 42(5), 423 (1995).[3] X. Xu, A. S. Gurav, P. M. Lessner and C. A. Randall, IEEE Transactions on Industrial Electronics, 58(7), 2636 (2011).[4] K. Kholostov, L. Serenelli, M. Izzi, M. Tucci, D. Bernardi, M.Balucani, IEEE Journal of Photovoltaics 5(2), 404 (2016).[5] M. Balucani, K. Kholostov, P. Nenzi, R. Crescenzi, D. Ciarniello, D. Bernardi, L. Serenelli, M. Izzi, M. Tucci,Energy Procedia, 43, 54 (2013).[6] K. Kholostov, A. Klyshko, D. Ciarniello, P. Nenzi, R. Pagliucci, R. Crescenzi, D. Bernardi and M. Balucani, 43, 2014 IEEE 64th Electronic Components and Technology Conference.

Vertically integrated high voltage Zn-Air batteries enabled by stacked multilayer electrodeposition

We report a scheme for the integrated fabrication of MEMS-scale, series-connected battery cells. The approach exploits multilayer electrodeposition of active and sacrificial layers to generate structures that can be formed into high voltage power sources. Aqueous, non-vacuum-based fabrication, via electrodeposition, enables high throughput and deterministic control of layer thicknesses and battery performance. Batteries manufactured using this technique offer the potential to match supply voltages to system needs, ranging from conventional electronics to direct drive of high voltage electrostatic or piezoelectric MEMS.

Effects of Sn grain size on intermetallic compounds formation in 5 µm diameter Cu/Sn pillar bumps

Uniform 5 µm diameter Cu/Sn micro-bump array has been fabricated by multilayer electrodeposition, and the effect of Sn grain orientation and size on Cu6Sn5 and Cu3Sn growth have been studied through FIB–SEM and electron backscatter diffraction. The solder layer in Ф5 µm Cu/matte Sn micro-bump we fabricated contains only four to five columnar Sn grains with no obvious preferred orientation and there is no significant difference in the growth of Cu6Sn5 in different oriented Sn grains. However, the Sn grain size has much more effect on intermetallic compound (IMC) growth. At 150 °C, the diffusion coefficient of Cu/bright-Sn system(~ 200 nm Sn) is calculated to be 13.09 × 10−17 m2 s−1, nearly three times that of Cu/matte–Sn system (2–5 µm Sn), about 4.51 × 10−17m2 s−1. Also, a simple model of boundary diffusion controlled IMC growth is proposed to explore the mechanism of grain size effect. Large Sn grain size will slow down the interfacial reaction in micro-bump due to low grain boundary density and large bulk diffusion distance.

Electrodeposition of multilayers Ag-Ni-Ag on graphite based paper electrodes

To meet the demand of modern flexible and disposable technology, directly collected lignocelluloses fibers and graphite composite are successfully fabricated with uniformly electrodeposited of thin layers of nickel, silver and nickel. These multilayers (Ni-Ag-Ni) were electrodeposited on lignocelluloses-graphite sheet by using three electrode setup at a constant reduction potential (−0.95 V) between the electrodes. Composition and nanostructures of these nanocomposites (LC-graphite-multilayers) were investigated by using energy dispersive x-ray spectrometry, field emission scanning electron microscopy, Raman spectroscopy, UV–VIS and impedance spectrometer. FE-SEM images revealed that Ni-Ag-Ni layers are uniformly integrated into LC-graphene matrix and EDX analysis confirmed the deposition of multilayers Ni and Ag. Dielectric analysis revealed the non-linear frequency dependent response of the multilayered deposited LC fibers based nanocomposite. Complex impedance spectroscopy analysis presented the multilayered deposited LC fibers based paper electrode for high-tech applications in optical and electronic devices.

A MEMS lamination technology based on sequential multilayer electrodeposition

A MEMS lamination technology based on sequential multilayer electrodeposition is presented. The process comprises three main steps: (1) automated sequential electrodeposition of permalloy (Ni80Fe20) structural and copper sacrificial layers to form multilayer structures of significant total thickness; (2) fabrication of polymeric anchor structures through the thickness of the multilayer structures and (3) selective removal of copper. The resulting structure is a set of air-insulated permalloy laminations, the separation of which is sustained by insulating polymeric anchor structures. Individual laminations have precisely controllable thicknesses ranging from 500 nm to 5 µm, and each lamination layer is electrically isolated from adjacent layers by narrow air gaps of similar scale. In addition to air, interlamination insulators based on polymers are investigated. Interlamination air gaps with very high aspect ratio (>1:100) can be filled with polyvinylalcohol and polydimethylsiloxane. The laminated structures are characterized using scanning electron microscopy and atomic force microscopy to directly examine properties such as the roughness and the thickness uniformity of the layers. In addition, the quality of the electrical insulation between the laminations is evaluated by quantifying the eddy current within the sample as a function of frequency. Fabricated laminations are comprised of uniform, smooth (surface roughness <100 nm) layers with effective electrical insulation for all layer thicknesses and insulator approaches studied. Such highly laminated structures have potential uses ranging from energy conversion to applications where composite materials with highly anisotropic mechanical or thermal properties are required.

Effectiveness of Coulostatic Electrodeposition of Multilayers

A coulomb controller is a device that accurately controls the quantity of electricity used for each layer during potentiostatic multilayer electrodeposition using the single bath method. The device was developed to improve the controllability of the amount of electrodeposited material. Co-Cu/Cu multilayers were electrodeposited using the coulomb controller with a target layer thickness of 50 nm to investigate the effectiveness of coulostatic electrodeposition. Current and X-ray fluorescence analyses showed that the total mass of Co-Cu and Cu layers in a sample were proportional to the integrated current used for the electrodeposition of each layer type. Current efficiencies were relatively high and the mass of electrodeposited material was stabilized by the coulomb controller. Consequently, variations in the effective substrate area became obvious as the cause of variation in the layer thickness. When the coulostatic method was employed, the time at which the intended electrodeposition would be completed was not predetermined. Therefore, there was an unavoidable time lag to remove a sample from the plating bath after completion of the intended electrodeposition, during which time, a part of the sample was re-dissolved in the bath.

Multilayer Film Fabrication Using Flow Injection Coupled with Electrochemical Deposition

AbstractA simple method is proposed for the electrodeposition of multilayers using a modified closed flow injection system. The apparatus incorporates flowing streams of electrolyte through a closed atmosphere flow cell for deposition of multilayers. Computer and software control is used to alternate the flow of electrolyte and control the alternating current or potential of the electrochemical cell. Electrodeposition of metallic multilayers of nickel/iron, iron/copper, cobalt/copper, and nickel/copper were used to test the instrument design. X‐ray diffraction was used to verify the composition and orientation of the films and scanning electron microscopy was used to examine the morphology of the deposited films. Advantages are discussed for using this type of instrumental setup for multilayer fabrication.

Effect of electrode configuration and mode of deposition on magnetoresistance in electrodeposited Co/Cu multilayers on n-Si by a fully electrochemical method

Electrodeposition of metallic multilayers on Si is normally preceded by the vapour deposition of a metallic layer. Since vapour deposition produces an additional step in the production process, direct electrodeposition of multilayers on Si is desirable. However, direct electrodeposition on Si has resulted in low magnetoresistance (MR) – of the order of 1% – at room temperature. With the use of (i) electroless plated copper back contact, (ii) composite potentiostatic pulses, (iii) horizontal electrode configuration and (iv) non-continuous mode of deposition, a room temperature MR of 5.8% has been achieved.

A study on the kinetics of Co–Ni/Cu multilayer electrodeposition in sulfate solution

Electrodeposition of the Co–Ni/Cu multilayer films was carried out in sulfate solution. Cyclic voltammetry and current transient techniques were utilized to characterize the multilayer system and to obtain the nucleation and growth mechanism. The cyclic voltammograms clearly showed that electrodeposition of cobalt–nickel alloy layer was controlled by a kinetic process, where copper ions were reduced under diffusion-controlled mechanism. In addition, the current transients revealed that nucleation mechanism was instantaneous with a typical three-dimensional growth process. The microstructure of the Co–Ni/Cu films was also changed with overpotential. In this system, the growth of multilayer films was observed as layer-by-layer structure up to −1.3 V versus SCE.

Additive Effects in Multilayer Electrodeposition: Properties of Co−Cu/Cu Multilayers Deposited with NaCl Additive

Electrodeposited Co−Cu/Cu multilayers have been produced with current control from a sulfate bath with and without NaCl as an additive. The addition of NaCl decreases the current efficiency of the multilayer deposition and results in multilayers with lower GMR and higher electrical resistivity than the chloride-free bath. The grain size of the deposit and the degree of orientation also decreases if the additive is present. It has been concluded that the adsorption of chloride, the formation of copper(I) intermediate, the change in the deposition mechanism, the increase in nucleation rate, and the occurrence of a non-Faradaic current transient all contribute to the enhancement of the structural disorder that leads to the loss in GMR. Some general conclusions have also been formulated about the role of additives in electrodeposition baths, especially concerning the differences in d.c. plating and pulse-plating.

Induced Crystallographic Orientations in Electrodeposited Ni‐Cu Multilayers

The results of controlling the preferential crystallographic orientation of electrodeposited Ni‐Cu multilayers by means of electrochemical methods are reported. These multilayers were grown on pulse electrodeposited and dc electrodeposited copper foils of (111) and (220) preferential crystallographic orientation, respectively. Since multilayers have a tendency to grow epitaxially, the multilayers grown on these substrates exhibited (111) or (220) preferential crystallographic orientation. Results of electrodeposition of multilayers on cold‐rolled copper foil and on titanium are also presented. Similar results can be obtained using polycrystalline copper foil as compared to single crystal copper substrates. © 1999 The Electrochemical Society. All rights reserved.

Electrodeposition of NiFe Thin Films and NiFe/Cu Multilayers with a Recirculating Electrochemcial Flow Reactor

ABSTRACTNano-structured Ni80Fe20NCu multilayers were electrodeposited by a newly developed electrodeposition process utilizing a recirculating electrochemical flow reactor. This process, which operates in an inert gas environment, overcomes the limitations of conventional multilayer electrodeposition methods (single and dual bath techniques) by depositing pure magnetic layers without codeposition of the nonmagnetic metal and oxidation of metal interfaces. Structure, corrosion resistance and magnetic properties of electrodeposited NiFe (0 to 100 % Fe) thin film alloys were first investigated. Three different crystal regions, α, mixed α and γ, and γ phases were observed at &lt;50,;50, &gt;50 % Fe in the deposit, respectively. The narrow mixed phase regions was around 50 % Fe compared to 70–80% Fe for bulk alloys. The lattice parameters of electrodeposited alloys exhibited the same trends as bulk alloys. Maximum corrosion resistance was obtained at 50% Fe content in 0.5 M NaCl similar to bulk alloys. The corrosion resistance of the α phase was an order of magnitude less than the γ phase. The magnetoresistance (MR) of electrodeposited NiFe thin film alloys was higher than bulk alloys. Based on these studies, Ni80Fe20/Cu multilayers with individual layer thicknesses ranging from 100 nm to 1.26 μm have been electrodeposited in the recirculating electrochemical flow reactor. The layer thicknesses were precisely controlled by adjusting the amount of charge passed.

ダブルパルス法によるＣｕ／Ｃｏ多層膜の電析

Cu/Co multilayer electrodeposition has been studied using a dual-pulsed current from pyrophosphate solutions. A pure copper layer is obtained with a current density lower than the diffusion-limited one of cupric ion. The cobalt content in the alloy layer increases with applied current density, and reaches about 95at.%. When the copper layer becomes thicker than 20nm and the alloy layer thicker than 15nm, the multilayer film becomes smooth. The well-defined modulation in the copper and cobalt composition was observed for Cu/Co multilayer deposits by Auger electron spectroscopy with Ar sputtering. The copper-content depth profile varies within the alloy layer, when the alloy layer is quite thin at a few nanometers. This compositional variation may be due to diffusion-layer disorder by hydrogen evolution or the cobalt hydroxide film formation on deposits.

Electrocrystallisation simulation using a microcomputer

A 48K “Apple” microcomputer programmed in machine language has been used to study simulation of electrocrystallisation. Applying an adapted Monte Corlo method, multilayer electrodeposition onto perfect, hexagonal close packed, surfaces has been simulated. It is shown that under diffusion independent conditions the shape of the computer generated current/time curve is dependent on the size of the lattice used in the simulation. When diffusion is allowed to become important in the simulation the deposit shows a dramatic change in morphology, with some clear parallels to observed deposits of cadmium.