Pd Layer Thickness Research Articles

Evaluation of Ni/Pd/Au as an alternative metal finish on PCB

Multi‐layer surface finish, from the bottom to top, of electroless Ni, electroless Pd, and immersion Au (Ni/Pd/Au) have been introduced in the printed circuit board (PCB) industry recently. This paper reports an evaluation of this surface finish from the perspective of solder joint attachment reliability, especially to see if the Ni/Pd/Au could be immune from the brittle interfacial fracture of PBGA on electroless Ni/immersion Au, recently observed and reported by us. PCBs with Ni/Pd/Au finishes, made from two vendors with varied Pd layer thickness were attached with PBGA packages, and tested in four‐point bending. When joint strength is strong, bending tests resulted in peeling off the PCB pads; otherwise, brittle fractures occurred at the interface between solder balls and PCB pads. After aging, solder joints on all Ni/Pd/Au and reference metal finishes failed by the same brittle fracture at the interface between Ni‐Sn and Au‐Sn intermetallic compounds. It is concluded that the interfacial fracture was controlled by something other than the Pd, and the existence of the Pd did not prevent the interfacial fracture. Also, the presence of Pd could not prevent the Au migration and subsequent fracture.

Stabilization of high spin FCC Fe in (Fe/Pd) n multilayers

Polycrystalline (Fe/Pd) n multilayers are grown onto sapphire substrates at room temperature in a UHV system. The number of periods n=40 and the thickness of Pd layers of t Pd=4 nm are kept constant, whereas the thickness of the Fe layers is varied from 1.5 to 5 nm. Structural properties are studied by in situ reflection high energy diffraction (RHEED), scanning tunnelling microscopy (STM) and ex situ by X-ray diffraction at small angles and large angles. Analyzing the experimental data using the program SUPREX we obtain interplanar distances of d Fe=2.03±0.01 Å for an Fe layer thickness larger than about 2.5 nm as expected for (1 1 0) planes of BCC Fe. For Fe layers with thicknesses less than about 2.5 nm the interplanar distance is d Fe=2.1±0.01 Å, which is close to the distance between (1 1 1) planes of FCC Fe with a lattice parameter of a=3.64 Å. Magnetic susceptibility measurements at temperatures between 1.5 and 300 K for (Fe/Pd) n multilayers with FCC Fe yield a magnetic moment per Fe atom of μ=2.7±0.1 μ B, which is about 20% larger compared to μ=2.2 μ B for BCC Fe. We show that the occurrence of the large magnetic moment originates from FCC Fe being in the high spin (HS) state rather than from polarization effects of Pd at Fe/Pd interfaces.

Optical transmission spectroscopy of switchable yttrium hydride films

The optical transmission of the recently discovered switchable yttrium hydride films is determined spectroscopically as a function of hydrogen content. This is done during electrochemical loading of Pd-capped Y film electrodes, thereby continuously changing the hydrogen concentration. The effect of the Pd cap layer on the film transmission is determined from measurements on a series of films with varying Pd layer thickness. The results are in good agreement with transmission measurements of in situ gas phase loaded, uncapped Y films. Both data sets can be consistently described with simple optical decay lengths such as 277.8 nm for ${\mathrm{YH}}_{3\ensuremath{-}\ensuremath{\delta}}$ and 15.1 nm for Pd at $\ensuremath{\Elzxh}\ensuremath{\omega}=1.96$ eV. The hydrogen concentration dependence of the optical transmission is discussed and compared with previous optical measurements on bulk samples and band-structure calculations.

Sensors on low-dimensional silicon structures

The possibilities of creating sensors on the basis of silicon structures with classical and quantum-dimensional effects have been researched theoretically and experimentally. The technology of forming qnantuln-well and wire structures of porous and amorphous silicon and their modifications by multiparameter monitoring in situ has been studied. H 2S sensor samples, developed on this basis, have a high sensitivity (on the level 10-20 ppb), low operating voltage (1-1.5 V), low power consumption (not more than 10 -8-10 -6 W) and relative selectivity to hydrocarbons, CO and CO 2. The most sensitive to H 2S ate structures having p = 0.03 Ω cm, oxidized porous silicon layer thicknesses of 6-10 μcm, porosity of 0.75-0.8 and Pd layer thicknesses of 50-60 nm. The obtained results verify the principle possibilities in solving all growing contradictions between information processing and its reception by using low-dimensional structures.

Ferromagnetic Resonance in Co–Zr/Pd Multilayers

Co-Zr/Pd multilayers with different thicknesses of Pd layers have been prepared by rf sputtering and studied by ferromagnetic resonance (FMR) spectroscopy. The effective g-factor, g eff , of the multilayers has been obtained by FMR measurements. An oscillatory variation of g eff between 1.95 and 2.18 with the thickness of Pd layers is observed. The oscillation period in g eff is about 1 nm. This oscillatory behaviour of g eff has been interpreted in terms of a system of two magnetic sublattices, one is the Co-Zr layer system, the other is the polarized Pd layer system. Finally the dependence of the effective magnetic anisotropy K 0 of the Co-Zr/Pd multilayers on the thickness of Pd layers has been obtained according to the FMR results. A similar oscillatory behaviour in K c was obtained. This mainly originates from the oscillation of the polarization of Pd layers, which causes an oscillatory additional shape anisotropy.

Magnetic polarization of spacer Pd layer and magnetic properties of Co/Pd multilayers

Magnetic multilayers [Co(1.5 nm)/Pd(x nm)]40 grown by rf sputtering were studied by x-ray diffraction, vibrating sample magnetometer, torque magnetometer and magnetoresistance measurements. The dependences of the interfacial roughness and the structure perfectness of Co/Pd multilayers on the spacer Pd layer thickness have been revealed from x-ray diffraction data. An oscillatory variation of saturation magnetization versus the thickness of the Pd spacer was observed. A similar oscillatory behavior in the dependence of its magnetic anisotropy on the thickness of the Pd spacer was observed. It is suggested from these two phenomena that the magnetic polarization of Pd spacers oscillates between ferromagnetic and antiferromagnetic polarization with the increase of Pd spacer thickness under a RKKY-like interaction. Evidence is found for the antiferromagnetic polarization of the inner-part of the Pd spacer. The antiferromagnetic coupling between two Co layers and giant magnetoresistance effect in Co/Pd multilayer system were not observed. The relationship among structure, interlayer coupling and magnetic polarization effect of the Pd spacer was discussed.

Ferromagnetic resonance in Co - Nb/Pd multilayers

multilayers were prepared by the rf sputtering method. The polarization of Pd layers and the interlayer coupling through Pd layers were studied via magnetic and ferromagnetic resonance measurements. Magnetic measurement shows that the saturation magnetization of Co - Nb/Pd multilayers oscillates periodically when the Pd layer thickness increases, which is caused by the oscillatory polarization of the Pd layers. The spin-wave excitation indicates that a ferromagnetic interlayer coupling can exist until the thickness of the Pd layers is about 7 nm. An oscillatory variation between 2.00 and 2.12 of the effective g-factor, , with the thickness of Pd layers was observed for the first time. The oscillatory period of is about 1 nm. A similar oscillatory behaviour of the effective anisotropy, , was also obtained. This oscillatory behaviour of and was interpreted in terms of a model of two exchange-coupled sublattices: one sublattice is that of the Co - Nb magnetic layers, and the other is that of the polarized Pd layers. This model indicates that the oscillatory behaviour of and mainly originates from the oscillation of the polarization of the Pd layers.

MAGNETIC AND STRUCTURAL PROPERTIES OF Co-Zr/Pd MULTILAYERS

Co-Zr/Pd multilayers were prepared by a radio frequency sputtering method.The thickness of the Co-Zr magnetic layers was fixed at 1.8nm,and the thickness of Pd layers was changed from 0.5 to 6nm.The oscillation of saturation magnetization with a period of about 1nm was obtained as the thickness of Pd layers increased.This can be attributed to the oscillation of the polarization of Pd layers.X-ray diffraction showed that magnetic alloy Co-Zr layers were in a crystalline state when the Pd layers were thicker than 1.3nm though a thick Co-Zr single layer was in an amorphous state.The superlattice peaks in the high angle X-ray diffraction patterns showed that there existed a coherent growth between the Co-Zr layers and Pd layers when the Pd layers were thicker than 1.3nm.Moreover,as the thickness of the Pd layers increased,periodically oscillatory phenomena were found both in the crystalline grain size perpendicular to the film plane and in the interplanar distance of the fcc(111) plane.These phenomena may be related to the oscillatory interlayer coupling between Co-Zr magnetic layers through Pd layers.

Interface anisotropy and magnetization reversal in epitaxial Fe(001)/Pd double layers

In epitaxial Fe/Pd double layers the magnetic anisotropies are found to depend strongly and in a linear way on the Pd layer thickness, d Pd, for d Pd < 5.5 monolayers. Observed anomalies of the coercive field in the submonolayer Pd coverage regime are caused by laterally inhomogeneous anisotropies due to Pd islands.

Bilayer structure of PdAl 2O 3 for UV vidicon applications

A bilayer structure of PdAl 2O 3 was developed as a signal plate for vidicon TV tubes. The 20 Å thick Pd layer served as the conducting plate while the 30–50 Å thick Al 2O 3 coating functioned as the transparent protecting film. The obtained signla plates had a sheet resistance of 2.5 KΩ and a transmission coefficient of 71% at a wavelength of 250 nm. The main advantage of vidicons equipped with such signal plates is to have a dark current of less than 0.05 nA, which is suitable for UV applications. The PdAl 2O 3 bilayers were produced by a novel sputtering method.

Oscillations of the Faraday rotation in Co/Pd multilayer films

We have discovered oscillations of the Faraday rotation as a function of the thickness of Pd layers in Co/Pd multilayer films. A correlation is traced between the behavior of the Faraday rotation as a function of the thickness of the Pd layers and the magnitude of the saturation field determined from the field dependences of the Faraday rotation.

Polarization of Pd Atoms and Interlayer Coupling in Fe—Si/Pd Multilayers

In this paper two series of Fe—Si/Pd multilayers are made by rf sputtering and studied by vibrating sample magnetometry and electronic paramagnetic resonance spectroscopy. For Fe—Si/Pd (5.4 nm) multilayers with increasing Fe—Si layer thickness, the saturation magnetization Ms decreases. This is an evidence of the spin-polarization of Pd atoms. An interlayer coupling is confirmed to exist by spin wave modes in Fe—Si (1.5 nm)/Pd multilayers with Pd layer thickness dpd ⩽ 7.2 nm, except for dpd = 1.8 nm. For dpd = 1.8 nm no interlayer coupling occurs, and both the saturation magnetization Ms and the effective magnetization 4πMeff have a minimum. The resonance linewidth ΔH changes correspondingly with the effective magnetization as a function of dpd and has a maximum at dpd of 1.8 nm.

STRUCTURAL AND MAGNETIC PROPERTIES OF [Pd/Co-Nb/Pd/Si] MULTILAYERED FILMS

Two series of [Pd/Co-Nb/Pd/Si] multilayer films were prepared by rf sputtering. The measurements of structure and magnetism were made by X-ray diffraction and magnetometer, respectively. As the thickness of Pd layers increases, the structure of Pd layers transfers from an amorphous state to a polycrystalline state. The polycrystalline state of the Pd layers shows two adjacent Pd fcc(111) peaks, which originate from the differences of lattice-mismatching degree and polarization of Pd atoms between the interfaces of Co-Nb layers and Pd layers and the interfaces of Pd layers and Si layers. As the thickness of Pd layers increases, the saturation magnetization monotonously increases from a value which is smaller than that of the bulk Co-Nb alloy with the same compositions to another value which is larger, then takes a constant value. This is contributed to the effects of polarization of Pd layers, dimension of Co-Nb magnetic layers and interdiffusion of atoms in the interfaces. The amorphous Co-Nb layers can influence the polarization of Pd atoms in the range of 2.5nm from the interfaces of Co-Nb layers and Pd layers. The is related to the strong interdiffusion of atoms in the interfaces and the large change of the Pd lattice constant in the film normal.

Hydrogenation and Magnetic Properties of Pd/Co Multilayers

ABSTRACTThe magnetic properties of sputtered Pd/Co multilaysers in hydrogen atmospheres were studied. The x-ray diffraction(XRD) patterns in hydrogen atmospheres showed that the lattice expansion of hydrogenated Pd decreased with decreasing thickness of Pd layers, which is reminiscent of nano-crystalline Pd. Perpendicular magnetic anisotropy(PMA) and saturation magnetization were reduced by the hydrogénation. The interface anisotropy energy per unit area, Ks, and volume anisotropy energy per unit volume, Kv are discussed. These results suggest that interface magnetic anisotropy between Pd and Co layers is suppressed by hydrogenation.

Structural and magnetic properties of Co-Nb/Pd multilayers

Co-Nb/Pd multilayers were prepared by a radio-frequency sputtering method. As the thickness of Pd layers increases, the phases of Co-Nb layers periodically alternate from an amorphous state to a crystalline state. The oscillation of the strain of Pd layers and that of the coherent length versus the thickness of Pd layers with a period of about 10 Å are obtained. The strain is caused mainly by the degree of lattice mismatching of Co-Nb layers and Pd layers, but the oscillatory behavior of the strain may be related to the oscillatory interlayer coupling between Co-Nb layers through Pd layers. The oscillation of the saturation magnetization is also obtained. It corresponds to the oscillatory polarization of Pd layers and the structural change in Co-Nb/Pd multilayers.

Magnetic properties of Fe/Pd multilayers grown by electron-beam evaporation

The magnetic properties of [Fe(20 Å)/Pd(x Å)]25 multilayers prepared by ultrahigh vacuum electron-beam evaporation are presented. It is found that the crystal structure of Fe layers change from bcc to fcc when the thickness of Pd layers dPd≥36 Å. The saturation magnetization per unit Fe volume at 5 K is enhanced and oscillates with the increment of the thickness of Pd layers, due to the polarization of Pd atoms. The magnetic hysteresis loops of samples indicate low coercive forces, and ferromagnetic coupling between the Fe layers for all Pd thicknesses (6–60 Å). The conversion electron Mössbauer spectra measurements proved that the magnetic moment of fcc Fe is the same as that of the bcc Fe. It is also found that the magnetic anisotropy dependence on dPd is similar to that of the saturation magnetization, and relates to the Fe layer structure transition. The Curie temperature of Fe/Pd multilayers decreases monotonously with the increasing of dPd. The low temperature magnetization measurement of Fe/Pd multilayers suggests that the interlayer coupling between Fe layers and polarization of Pd layers influences the temperature dependence of saturation magnetization. No evidence of antiferromagnetic coupling between Fe layers and giant magnetoresistance effect is found. The relationship among structure, polarization of Pd layers, and magnetic coupling is discussed.

Polarization of Pd atoms in Ni/Pd magnetic multilayers

Ni/Pd multilayered films with various Ni and Pd layer thicknesses were prepared by electron gun evaporation. These films were all polycrystals with (111) preferential orientation. Also, both experimental analysis and computer simulation results indicated the existence of a diffusion layer at the Ni-Pd interfaces. The nominal magnetic moment per Ni atom measured for these multilayered films varied with change in the Ni layer thickness. For a thinner Ni layer, the magnetic moment was smaller than that of bulk Ni, while it was larger for the thicker Ni layer. This variation is attributed to the opposite effects of two factors, namely the favourable effect of Pd atom polarization versus the magnetic degradation mainly due to the decrease in the Curie temperature with decreasing Ni layer thickness. The effect of Pd atoms polarized by their neighbouring Ni atoms was also verified by the results of thermal annealing the multilayers.

The effect of Pd layer thickness on the magnetic and magneto-optical properties of Pd/(Pt/Co/Pt) modulated multilayers

A series of Pd-t/sub Pd//(Pt-2 /spl Aring//Co-3 /spl Aring//Pt-2 /spl Aring/) modulated multilayer films with Pd layer thickness t/sub Pd/ ranging from 3 to 12 /spl Aring/ have been deposited on oxidized Si substrates. SQUID magnetic and Kerr hysteresis measurements reveal that large magnetic moment and Kerr rotation is achieved in the multilayers with Pd layer thicknesses less than 6 /spl Aring/. This result, and X-ray diffraction data, suggest that the Pd layer thickness strongly affects the magnitude of the induced magnetic moment and Kerr rotation as well as the sharpness of the interfaces of Pd/(Pt/Co/Pt) multilayers. A Kerr rotation of 0.3/spl deg/ is observed near 400 nm in the multilayer film with t/sub Pd/ of 6 /spl Aring/. The multilayers with t/sub Pd/ of 6 to 12 /spl Aring/ exhibit perpendicular magnetic anisotropy energies.

Magnetostriction of Co/Pd multilayers

We have performed magnetostriction measurements on Co/Pd multilayers with different Co and Pd layer thicknesses. The features of the curves as a function of the applied field are strongly related to the magnetic easy axis orientation and, consequently, to the Co layer thickness, and also to the presence of Pd at the interfaces. We present an averaging procedure that explains the observed experimental results and allows the extraction of the in-plane magnetostriction coefficients of the multilayer if the initial magnetic moment distribution without field is obtained independently.

Magnetostriction of Co/Pd multilayers

We have performed magnetostriction measurements on Co/Pd multilayers with different Co and Pd layer thicknesses. The features of the curves as a function of the applied field are strongly related to the magnetic easy axis orientation and, consequently, to the Co layer thickness, and also to the presence of Pd at the interfaces. We present an averaging procedure that explains the observed experimental results and allows the extraction of the in-plane magnetostriction coefficients of the multilayer if the initial magnetic moment distribution without field is obtained independently.