Pd Layer Thickness Research Articles

Experimental study on spheroidal morphology of palladium coated copper wire with different palladium layer thickness

Palladium (Pd) coated copper (PCC) wire is an emerging bonding wire that has been widely researched. In this paper, the effects of electronic flame-off (EFO) current and EFO time on the free air ball (FAB) morphology of four PCC wires with Pd layer thicknesses of 60, 80, 100, and 120 nm, respectively, are first investigated. The larger the EFO current or the longer the EFO time, the larger the FAB diameter. The EFO time or EFO current setting is either too high or too low to form a FAB with good morphology. Taking the ratio of FAB diameter to wire diameter as 2 as the standard, the EFO current of 48 mA and the EFO time of 700 μs are selected as the optimal EFO parameter combination. Under this parameter combination, the symmetry, roundness, and surface smoothness of the FAB of the four PCC wires are all at a better level. It is found that the FAB surface Pd coverage of PCC wire with 120 nm Pd layer thickness is higher through the corrosion test. The Pd transfer law on the FAB at different EFO times under optimal EFO current is also studied. The results show that with the prolongation of the EFO time, the Pd on the FAB surface is gradually transferred from the neck to the middle and lower parts. This study can provide technical reference for the selection of Pd layer thickness and EFO parameters of PCC wire.

A Study on the Effect of Pd Layer Thickness on the Properties of Cu-Ag Intermetallic Compounds at the Bonding Interface.

This paper conducted a high-temperature storage test (HTST) on bonded samples made of Pd100 (Pd-coated Cu wire with a Pd layer thickness of 100 nm) and Pd120, and studied the growth law of Cu-Ag intermetallic compounds and the inhibitory mechanism of Pd thickness on Cu-Ag intermetallic compounds. The results show that the Kirkendall effect at the bonding interface of the Pd100-bonded sample is more obvious after the HTST, the sizes of voids and cracks are larger, and the thickness of intermetallic compounds is uneven. But, the bonding interface of the Pd120-bonded sample has almost no microcracks, the Kirkendall voids are small, and the intermetallic compound size is uniform and relatively thin. The formation sequence of intermetallic compounds is as follows: Cu atoms diffuse into the Ag layer to form Ag-rich compounds such as CuAg4 or CuAg2, and then the CuAg forms with the increase in diffused Cu elements. Pd can significantly reduce the Kirkendall effect and slow down the growth of Cu-Ag intermetallic compounds. The growth rate of intermetallic compounds is too fast when the Cu bonding wire has a thin Pd layer, which results in holes and microcracks in the bonding interface and lead to the peeling of the bonding interface. Voids and cracks will hinder the continuous diffusion of Cu and Ag atoms, resulting in the growth of intermetallic compounds being inhibited.

Influence of Pd-Layer Thickness on Bonding Reliability of Pd-Coated Cu Wire.

In this paper, three Pd-coated Cu (PCC) wires with different Pd-layer thicknesses were used to make bonding samples, and the influence of Pd-layer thickness on the reliability of bonded points before and after a high-temperature storage test was studied. The results show that smaller bonding pressure and ultrasonic power lead to insufficient plastic deformation of the ball-bonded point, which also leads to small contact area with the pad and low bonding strength. Excessive bonding pressure and ultrasonic power will lead to 'scratch' on the surface of the pad and large-scale Ag spatter. The wedge-bonded point has a narrowed width when the bonding pressure and ultrasonic power are too small, and the tail edge will be cocked, resulting in false bonding and low strength. When the bonding pressure or ultrasonic power is too large, it will cause stress concentration, and the pad will appear as an 'internal injury', which will improve the failure probability; a high-temperature environment can make Cu-Ag intermetallic compounds (IMCs) grow and improve the bonding strength. With the extension of high-temperature storage time, the shear force of Pd100 gradually reaches the peak and then decreases, due to Kirkendall pores caused by excessive growth of IMCs, while the shear force of Pd120 continued to increase due to the slow growth rate of IMCs. In the high-temperature storage test, the thicker the Pd layer of the bonding wire, the higher the bonding strength; in the cold/hot cycle test, the sample with the largest Pd-layer thickness has the lowest failure rate. The thicker the Pd layer, the stronger its ability to resist changes in the external environment, and the higher its stability and reliability.

Nanosized Pd@Ag heterojunction with tunable shapes: Morphological modulation for improving plasma-mediated catalytic hydrogen evolution

Catalytic ability of bi-metal hybrid nanoagents largely depends on their phase constitution and morphology, also bearing a close correlation to the fabrication process. We herein design and develop a modified polyol protocol with inorganic ion induction for rationally constructing Ag nanoagents with tunable shapes (nanowire, nanocube, and nanoparticle), followed by evenly anchoring of stepwise reduced Pd nanograins on the surface of Ag nanoagents to foster Ag core - Pd shell (i.e. Pd@Ag) nanosized heterostructure. A home-made photochemical reaction device is used to scientifically evaluate the catalytic ability of the Pd@Ag nanoagents on hydrolyzing ammonia borane to evolve hydrogen gas. The ample characterization reveals that the fabricated Ag nanoagents hold the expected regular and uniform shapes, with 10–15 nm thick Pd layer cladded on their surfaces. The particular shapes of the Ag nanoagents can be duly manipulated via the induction of inorganic ions, and the thickness and compactness of the Pd shell can also be suitably regulated by controlling reduction duration. The verified formation of electron synergistic effect among the both metals is favorable to elevate the catalytic ability. The bimetal Pd@Ag nanoagents perform the superior catalytic activity under visible light irradiation, far exceeding that of the respective monometal counterparts, with the order of catalytic activity: Pd@Ag-NWs > Pd@Ag-NCs > Pd@Ag-NPs. The hydrolysis reaction at the given conditions is confirmed to be quasi first-order reaction, with the apparent activation energy of 53.44 kJ·mol−1 and TOF value of 47.04 min−1. The Pd@Ag-NWs catalyst behaves satisfactory stability, with 87.8 % initial catalytic activity retained after five cyclic use.

Facile self-repair of ultrathin palladium membranes

Pd membranes can play an important role in H2 separation and purification for the development of sustainable and renewable energies. By supporting on porous substrates, Pd layer thickness can be reduced to several micrometers, thus improving the H2 permeance by several orders of magnitude. However, the supported thin Pd membranes are concomitant with pinhole formation due to either fabrication (e.g., electroless-plating) or thermal treatment, which exist as a remarkable challenge for its widespread applications. This study presents a novel and facile approach for self-repair of Pd membrane defects by immersing the stainless-steel supported Pd membranes in PdCl2 solution. Three membranes were deliberately selected with a low selectivity of 152–1687 (400 ​°C, 0.1Mpa), for which disproportionation reactions between Pd2+ and Fe/Cr/Ni at the defect sites spontaneously occur leading to the formation of Pd particles at the exact point of defects. This self-repair process can be enhanced when applying a high pressure of 30–50 ​bar in the PdCl2 solution for 30 ​min, by overcoming the capillary resistance and penetrating through the pinholes. Interestingly, densely distributed hillocks were observed on the membrane surface probably due to reduction of PdCl2 under following H2 treatment, thus increasing the H2 permeance with a higher effective surface area. The H2/N2 selectivity can be improved by more than one order of magnitude (in the best case from 1687 to 8768) and a long-term stability test of 300 ​h was achieved for the repaired membranes, corroborating the application potential of this approach.

The effect of hydrogen gas on Pd/[Co/Pd]30/Pd multilayer thin films

It is known that large perpendicular magnetic anisotropy is found at interfaces of cobalt (Co) with palladium (Pd). We investigated Pd/[Co/Pd]30/Pd multilayer thin films with very thin Co and Pd layers with ferromagnetic resonance (FMR) spectroscopy in air and in hydrogen gas. A number of samples characterised by different Pd thicknesses were studied. A ferromagnetic resonance (FMR) peak shift similar to Co/Pd bilayer thin films was observed in the presence of hydrogen gas in the sample environment for all samples. The FMR peak shift is larger for samples with thicker Pd layers. Additionally, we found a dependence of the linewidth on the Pd layer thickness and explain this with the presence of spin pumping.

Capacitive sensor based on GaN honeycomb nanonetwork for ultrafast and low temperature hydrogen gas detection

Passive devices are highly desired for the detection of H2 gas due to its high safeness and low energy consumption. In this study, GaN with honeycomb nanonetwork structure (GaN-HN) epitaxially grown on Si wafer by molecular beam epitaxy technique was utilized for the fabrication of capacitive H2 gas sensors, on which 10 nm thick Pd layer was deposited as the sensing electrode. XRD, SEM, and AFM results show that the cubic phase Pd is uniformly coated on the surface of GaN-HN and maintains an interesting structure of honeycomb nanonetwork. It is found that the response time decreases gradually with the increase of the operating temperature and it reaches a steady value ∼3 s at temperatures higher than 50 °C. Ultrafast response time of 1.3 s towards 1000 ppm H2 was observed for the Pd-GaN/Si capacitive sensor operated at the temperature of 70 °C. The low limit of detection (LOD) is also evaluated by experiment and IUPAC definition, 500 ppb and 440 ppb, respectively. Moreover, the capacitive sensor exhibits ignorable response to CH4, NO2 and common VOCs gases. The long-term stability and humidity effect on H2 gas detection were also studied. Schottky junction capacitance of Pd/GaN might be dominated by the hydrogen dipole layer. The proposed Pd-GaN/Si capacitive sensor investigated here exhibits ultrafast response speed, low operating temperature, high selectivity and stability, making it attractive for applications in timely H2 leakage detection.

Manipulation of the inverse spin Hall effect in palladium by absorption of hydrogen gas

The spintronic properties of a palladium thin film have been investigated in the presence of hydrogen gas in cobalt/palladium bilayers. Measurements of the inverse spin Hall Effect (ISHE) using cavity ferromagnetic resonance allow estimations of the spin Hall conductivity and spin diffusion length in both nitrogen and hydrogen gas atmospheres. Unwanted spin rectification effects are removed using a simple method of inverting the spin current direction with respect to the measurement setup. Absorption of hydrogen gas in the Pd layer at just 3% concentration results in a reduced ISHE voltage amplitude and bilayer resistance. Fitting the ISHE voltage against the Pd layer thickness demonstrates that the spin diffusion length decreases by 23% in the presence of a hydrogen gas. On the other hand, the results indicate that there is no significant change in the spin Hall conductivity of Pd due to hydrogen absorption.

Layered Au-Pd-Au nanorod catalysts: Pd-layer thickness effects on catalyst performance

Au/Pd/Au and Au/Pd layered nanorods (NR) with different Pd thickness, down to 15 nm, are electrodeposited in Si-supported porous anodized aluminum thin film templates. These structures are, in contrast to Au-Pd core-shells, mechanically relaxed, so that chemical and electronic interaction effects between Au and Pd are expected to predominate in controlling their performance in the electrooxidation of formic acid. The XRD results are conclusive about the formation of pure metal layers, but a corrugated Au/Pd interface is revealed by scanning electron microscopy. The CV behavior of the different structures shows that the PdO reduction peak is shifted towards more noble values as the Pd thickness decreases. Regarding the electrocatalytic oxidation behavior there is a substantial increase in performance with decreasing Pd-layer thickness. It is further shown that the Au/Pd/Au nanostructures perform better than the Au/Pd bilayer structure for the same Pd layer thickness. Also the long term behavior is improved. Both CV and electrocatalytic behaviors are discussed in terms of interfacial intermixing between Pd and Au at the nanoscale and a higher interface contribution for thinner Pd layers.

Controlled Synthesis of 2D Palladium Diselenide for Sensitive Photodetector Applications

AbstractPalladium diselenide (PdSe2), a thus far scarcely studied group‐10 transition metal dichalcogenide has exhibited promising potential in future optoelectronic and electronic devices due to unique structures and electrical properties. Here, the controllable synthesis of wafer‐scale and homogeneous 2D PdSe2 film is reported by a simple selenization approach. By choosing different thickness of precursor Pd layer, 2D PdSe2 with thickness of 1.2–20 nm can be readily synthesized. Interestingly, with the increase in thickness, obvious redshift in wavenumber is revealed by Raman spectroscopy. Moreover, in accordance with density functional theory (DFT) calculation, optical absorption and ultraviolet photoemission spectroscopy (UPS) analyses confirm that the PdSe2 exhibits an evolution from a semiconductor (monolayer) to semimetal (bulk). Further combination of the PdSe2 layer with Si leads to a highly sensitive, fast, and broadband photodetector with a high responsivity (300.2 mA W−1) and specific detectivity (≈1013 Jones). By decorating the device with black phosphorus quantum dots, the device performance can be further optimized. These results suggest the as‐selenized PdSe2 is a promising material for optoelectronic application.

Design Optimization of Pd-Coated Side-Polished Single Mode Optical Fiber Hydrogen Sensors

Palladium (Pd)-based optical fiber sensors exhibit large sensitivity to detect hydrogen. We performed design study on Pd-coated side-polished optical fiber sensors using modal approach. The presence of buffer layer (i.e., the remaining cladding or other material) between core of the side polished single mode fiber and hydrogen absorbing Pd layer shows a strong effect on sensitivity. The thickness of buffer and Pd layers are optimized to achieve higher sensitivity. Use of different materials as buffer layer has been explored and we observed that teflon gives maximum sensitivity.

Fabrication and characterizations of PdAu/thiolation poly (phthalazinone ether ketone) superfine fibrous membrane as a free-standing electrocatalyst for methanol oxidation

Thiolation poly (phthalazinone ether ketone) (PPEK-SH) superfine fibrous membrane (SFM) was successfully fabricated via grafting and electrospinning. The PPEK-SH SFM exhibited high glass transition temperature (314.9 °C), robust tensile strength (14.74 MPa) and high porosity (80.2%), which were critical advantages for the SFM as plating template applied in fuel cells. Au nanoparticles (NPs) were assembled on the SFM as seeds, and then Pd NPs were deposited on the membrane by electroless plating. Characterization with scanning electron microscopy (SEM), energy-dispersive spectrometry (EDX), transmission electron microscopy (TEM) and X-ray diffraction (XRD) indicated that the surface of PPEK-SH fibers was almost fully covered by a thick Pd layer. The PdAu/PPEK-SH SFM inherited the properties of PPEK-SH and conductivity of Pd, thereby was successfully used as a free-standing electrocatalyst towards methanol oxidation without resorting to any conductive support. More importantly, benefiting from the introduction of -SH for anchoring noble metal NPs, the electrocatalyst presented a good stability. The peak current density reduced just 18.7% after 500 cycles, which would meet the needs of long-term use. This work may provide a new approach for the development of free-standing electrocatalyst based on electrospun nanofibers.

Bilayer structures based on metal phthalocyanine and palladium layers for selective hydrogen detection

In this work, bilayer structures in which a Pd layer was deposited on the surface of palladium phthalocyanine film (PdPc/Pd) by a Metal-Organic Chemical Vapor Deposition technique were studied as active layers of chemiresistive sensors for selective detection of hydrogen. Surface morphology, microstructure and composition of Pd layers were investigated by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Three sets of bilayer structures with Pd layer thicknesses of 55–80 nm, 100–120 nm and 140–160 nm were obtained to examine the effect of the thickness on the electrical sensor response toward gaseous hydrogen (1–30 v.%). It has been shown that the bilayer structures with 55–80 nm thick Pd layers exhibit the maximal sensor response and can be effectively used for selective detection of hydrogen in the concentration range from 1 to 30% in the presence of gaseous ammonia, CO2, NO2, and chlorinated alkane vapours.

Solid-state growth kinetics of intermetallic compounds in Cu pillar solder flip chip with ENEPIG surface finish under isothermal aging

Electroless Ni/electroless Pd/immersion Au (ENEPIG) constitutes a promising metallization to replace the conventional ENIG or Ni/Au for 3D IC integrated module and optoelectronic packaging. Different ENEPIG plating thicknesses with copper pillar solder joints are subjected to thermal aging at 150 °C to investigate the intermetallic compounds (IMCs) formation and growth. Due to low temperature solid-state bonding, both Pd and Au layers do not completely diffused into Sn matrix and participated in the interfacial reactions to form (Pd,Au)Sn4 IMCs phase. (Pd,Au)Sn4 IMCs based on PdSn4 phase with dissolved Au, exhibits high growth rate and substantial consumption of Sn from solder. Upon increasing the aging time, it is found that (Cu,Ni)6Sn5 IMCs and (Pd,Cu,Au)Sn4 phase form at interface and follows a diffusion control mechanism, which weakened the solder joint and caused brittle fracture in a die peel test. (Cu,Ni)6Sn5 IMCs growth rate increases with decreases Pd thickness. Therefore, the types of IMCs formation, growth rate, and reliability of Cu pillar joint strongly depend on bonding temperature, Au and Pd thicknesses, and solder volume. Based on this study, the authors recommend suitable ranges of Au and Pd layer thicknesses for reliable Cu pillar solder joints.

Spin transfer torque ferromagnetic resonance induced spin pumping in the Fe/Pd bilayer system

Inconsistencies in estimates of the spin Hall angle (${\ensuremath{\theta}}_{SH}$) and spin diffusion length (${\ensuremath{\lambda}}_{SD}$) of nonmagnetic (NM) layers using the spin transfer torque ferromagnetic resonance (ST-FMR) in ferromagnetic FM/NM bilayer structures are attributed to the inverse spin Hall effect (ISHE) and interfacial parameter contributions, interface spin transparency, interfacial anisotropic magnetoresistance, and effective spin-mixing conductance. These contributions in Fe(10 nm)/Pd(2--8 nm) bilayer structures have been probed employing the simultaneous detection of ST-FMR and ISHE in conjunction with in-plane FMR measurements. The interfacial contributions are found to increase with an increase in Pd layer thickness (${t}_{NM}$), which can be linked to the spin pumping effect in conjunction with spin backflow. Correcting the ${t}_{NM}$ dependence of the ST-FMR spectra for the interfacial and ISHE contributions prior to estimating ${\ensuremath{\theta}}_{SH}$ and ${\ensuremath{\lambda}}_{SD}$ of the Pd layer, the estimated values are found to be $0.10\ifmmode\pm\else\textpm\fi{}0.03$ and $5.4\ifmmode\pm\else\textpm\fi{}1.2\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$, respectively.

The investigation of hydrogen gas sensing properties of SAW gas sensor based on palladium surface modified SnO2 thin film

The sol-gel method and the magnetron sputtering method were used to deposit the SnO2 thin films on 128° YX LiNbO3 piezoelectric substrate for fabricating different kinds of delay-line surface acoustic wave (SAW) hydrogen gas sensors. To improve hydrogen gas sensing performance of SnO2 sensing films, the bi-layer structure sensitive films was used, which was composed of one pure SnO2 layer and one highly dispersed palladium nanoparticle layer. This bi-layer structure evidently enhanced the hydrogen gas sensing properties of SnO2 thin films. The microstructure, surface morphology and composition of as-prepared SnO2 sensitive films were analyzed by XRD, FESEM and XPS. The oscillator circuit with SAW sensor as resonate was designed to transduce the response of sensitive film into the frequency shift of oscillator. One precise temperature control system was used to ensure the temperature stability of SAW device. The Pd-surfaced-modified SnO2 thin film deposited by magnetron sputtering method has the highest frequency shift of 115.9kHz to 2000ppm hydrogen gas at 175°C. The influence of thickness on the morphology of Pd nanoparticles and hydrogen gas sensing performance was studied. The size of Pd nanoparticle increases with thickness of Pd films and too thick Pd layer will reduce the hydrogen gas sensing performance of SnO2 films.

Identification of Carbon Dioxide Electroreduction Products on Multilayered Metallic Catalysts Based on Palladium

Atmospheric carbon dioxide levels have risen rapidly over the last few decades. Electrochemical conversion of carbon dioxide into eligible fuels has potential as a technology that may prevent from a serious environmental problems. Electroreduction of carbon dioxide to hydrocarbons is a complex process that usually involves adsorbed carbon monoxide as an intermediate. The overall electroreduction path is determined to a large extent by the catalyst’s surface affinity to carbon monoxide and hydrogen. Strongly bounded CO inhibits further reduction while weakly bounded CO easily desorbs as a final product [1]. One of primary step is CO2 adsorption followed by its reduction to absorbed carbon monoxide. The presences of adsorbed atomic hydrogen at the catalyst surface can significantly facilitate the formation of hydrocarbons. However, within the potential range of CO2 reduction in the aqueous solution a competitive reaction of hydrogen evolution (HER) takes place, which can even dominate in the electroreduction processes. Our result points out the possibility of tuning catalyst’s affinities to both hydrogen and CO by designing multilayered structures obtained by sequential UPD strategies [2]. Results show that catalytic activity can be finely tuned by using the multilayered near-surface-alloy approach [3]. Our results clearly demonstrate that the Pd-layer thickness and location significantly changes the surface catalytic activity of palladium toward CO2 electroreduction. Interestingly, multilayered films covered with the silver monolayer largely reflect the properties of palladium deposits existing under the Ag surface. Differential Electrochemical Mass Spectrometry method (DEMS) was used to analyze and determine gaseous products of carbon dioxide electroreduction together with evolved hydrogen. Individual molecules are recognized by ionic current mass signals. DEMS method allows to identify reduction products during faradaic reduction [4]. This technique is particularly useful for investigations of electroinactive molecules such as methane or ethylene. Ion current changes are related to applied potential, and were presented as MS-CV (mass spectrum cyclic voltammograms). MS-CV provide useful information on the formation potentials of each products. Electroactive products and intermediates, such as carbon monoxide and formic acid were also detected by using classical electrochemical methods. For this purpose a palladium electrode was used for detection of CO2 electroreduction products obtained in macroelectrolysis. [1]Jitaru, M., et al., Journal of Applied Electrochemistry, 1997. 27(8): p. 875-889. [2]Januszewska, A., R. Jurczakowski, and P.J. Kulesza, Langmuir, 2014. 30(47): p. 14314-14321. [3]Greeley, J. and M. Mavrikakis. Journal of Physical Chemistry B, 2005. 109(8): p. 3460-3471. [4]Baltruschat, H., Journal of the American Society for Mass Spectrometry, 2004. 15(12): p. 1693-1706.

Design of Palladium-Coated Long-Period Fiber Grating for Hydrogen Sensing

We present a detailed numerical analysis that describes the influence of palladium (Pd) layer thickness on the spectral characteristics of long-period fiber gratings (LPFGs) and their response to the uptake of hydrogen. The investigation is carried out with a view of determining an optimal layer thickness to design high-sensitivity LPFG-based hydrogen sensors. Coupled differential equations for a four-layer waveguide structure have been solved using a matrix method considering a layer of Pd with finite thickness on the cladding. Response of higher order cladding modes of the Pd-coated LPFG at turn-around-point and also at mode transition could be computed. It has been shown that if properly designed, the resonant wavelength of a desired mode may shift by about 20 nm for 1% uptake of hydrogen. There is good match between simulations and experiments for LPFGs with coupling to higher order cladding modes

First Observation of Non-Resonant X-Ray Magnetic Diffraction for Multilayers

Co/Pd magnetic multilayers have been prepared by using a sputtering method. Lattice distances and magnetic hysteresis curves have been measured by X-ray diffraction (XRD) measurements and magnetization measurements using a vibrating sample magnetometer (VSM). The XRD measurements have shown that the samples with thinner Pd layers have shorter lattice distances, and the VSM measurements have shown that the samples of thinner Co and thicker Pd layers are closer to those of perpendicular magnetic anisotropy. We have applied the X-ray magnetic diffraction method to the Co/Pd multilayer for the first time and have succeeded in observing a change in the X-ray diffraction intensities by the reversal of the magnetization direction.

Theoretical Study of Magnetic Damping and Anisotropy of Fe/Pd (001) Superlattice

The material properties, magnetic damping and anisotropy, which are critical to spin-transfer-torque magnetic random access memory device performance, are theoretically explored for Fe/Pd superlattices deposited in the (001) orientation. Various superlattice geometries at different Fe and Pd layer thicknesses show perpendicular anisotropy. With the inclusion of the shape anisotropy, thin-film structures with an effective anisotropy of $1.4\,\times \, 10^{7}$ erg/cm3 have been observed. The damping is enhanced due to the broken symmetry at the Pd interface. This interfacial contribution increases when more Pd monolayers are deposited in the superlattice. The superlattice damping is relatively smaller than damping ( $\alpha )$ in the L10 phase FePd. The optimized superlattices are 3Fe/3Pd or 3Fe/2Pd: these multilayers have sufficient energy barriers ( $\sim 1$ eV) to maintain thermal stability in very small devices, yet the switching currents are low ( $\! A/cm $^{2})$ and, thus, expected to lower the energy consumption.