Interconnect Materials Research Articles

A survey on pristine and intercalation doped graphene nanoribbon interconnect for future VLSI circuits

The paper presents a review of recent works on pristine and intercalation doped graphene nanoribbon interconnects. Since the last decade, there have been tremendous research interests on graphene-based nanoelectronics. Graphene nanoribbon (GNR) has been projected as an interconnect material to replace the traditional copper interconnects. Since graphene is a planar material, CMOS compatible processes for patterning and making contacts to it, can be developed. Though, fabricating side-contacts in multilayered GNR (MLGNR) is a challenging task, fabrication of top-contact MLGNR is technologically viable. In addition, intercalation doping in top-contact MLGNR improves effective conductivity further. A number of models have been developed to optimize emerging on-chip interconnect technologies and benchmark them against conventional technologies. In this review, physical and electrical models of pristine and intercalation doped MLGNRs have been discussed in brief. A chronological survey towards analytical and spice compatible modeling of pristine and intercalation doped top-contact (TC) and side-contact (SC) MLGNR interconnect, has been presented in this article. A brief review of experimental work on pristine and intercalated GNRs as on-chip interconnect has also been incorporated in this survey. The stability, signal integrity (SI), and power integrity (PI) analysis of pristine and intercalation doped MLGNR interconnect with the presented models have been depicted further. The performance assessments have been compared with conventional copper, and CNT-based interconnects as well. It has been concluded that the side-contact and intercalation doped top-contact MLGNRs can outperform conventional copper-based interconnects.

Solder joint reliability based on creep strain energy density for SAC305 and doped SAC solders

Parallel to the development of new lead-free solders, electronic packaging has gone through a considerable evolution. A redistribution of layers allows the increase of functionality by increasing the number of inputs/outputsin the packagewhile reducing the size. The reliability of the package is strongly influenced by the reliability of the interconnects. During production and service life, there are thermal processes involved that may lead to thermal fatigue. In this work, a two-dimensional finite elementmodel of a Fan-Out Wafer Level Packaging (FO-WLP) was built, and simulations of thermal test cycles were carried out varying the solder interconnect material: SAC305, SACQ, SACR, orInnoLot. A thermal oscillating load from –40°C to 125°C was applied to the packaging for three hours.State of the art concerning solder joint reliability models based on creep behavior reveals the benefit of using energy-based parameters, as cycles to failure are inversely proportional to the average creep strain energy density.Based on theaverage creep strain energy density simulation results, the reliability of the package withdifferent solderswas compared.The qualitative results suggestthat SACQ has a significant advantage in the operational lifetime compared toSACR, InnoLot, and SAC305.

Synergistic size and shape effect of dendritic silver nanostructures for low-temperature sintering of paste as die attach materials

Electrically conductive epoxy adhesive, which combines with Ag sintering materials rather than traditional Pb-based solder materials, attracts wide research interest in modern die attach technology for power electronic packaging owing to its advantages of low processing temperature and high working temperature. In this work, Cu foil and AgNO3 were used as raw materials to synthesize dendritic silver nanostructure with a central trunk of 5–10 μm along with many primary branches of 200 nm. Subsequently, the sintering behavior of the obtained dendritic Ag nanostructures, as low-temperature interconnect material, was systematically investigated under different sintering conditions. Remarkably, the shear strength of the interconnect joints formed from dendritic Ag nanostructures could reach around 21 MPa after sintering for 30 min at 250 °C under a pressure of 10 MPa, whereas the shear strengths of the interconnect joints, which formed from Ag microspheres and microflakes under similar conditions, were only 9 MPa and 11 MPa. We think that the dramatic increment in the shear strength may result from the higher contact area of nanoscale primary branches of the synthesized dendritic structures than Ag microstructures and the low-temperature sintering of their nanoscale primary branches. In addition, the interconnect joint formed from dendritic Ag nanostructures also exhibited high reliability, and it still maintained a high shear strength of 27 ± 2 MPa even after 1000 cycles thermal quenching between − 55 and 125 °C. The thermal resistance and electrical conductivity of these interconnect joints were about 78.89 Wm−1 K−1 and 9.85 × 10–6 Ω cm, respectively, which makes its further interconnect applications feasible. This means that the synthesized special dendritic Ag nanostructure has an excellent potential as a high-performance die attach material for high- and low-temperature power device.

Ruthenium-Assisted Chemical Etching of Silicon: Enabling CMOS-Compatible 3D Semiconductor Device Nanofabrication.

The semiconductor industry's transition to three-dimensional (3D) logic and memory devices has revealed the limitations of plasma etching in reliable creation of vertical high aspect ratio (HAR) nanostructures. Metal-assisted chemical etch (MacEtch) can create ultra-HAR, taper-free nanostructures in silicon, but the catalyst used for reliable MacEtch-gold-is not CMOS (complementary metal-oxide-semiconductor)-compatible and therefore cannot be used in the semiconductor industry. Here, for the first time, we report a ruthenium MacEtch process that is comparable in quality to gold MacEtch. We introduce new process variables-catalyst plasma pretreatment and surface area-to achieve this result. Ruthenium is particularly desirable as it is not only CMOS-compatible but has also been introduced in semiconductor fabrication as an interconnect material. The results presented here remove a significant barrier to adoption of MacEtch for scalable fabrication of 3D semiconductor devices, sensors, and biodevices that can benefit from production in CMOS foundries.

Influence of Gd deposition on the oxidation behavior and electrical properties of a layered system consisting of Crofer 22 APU and MnCo2O4 spinel

In the study, the surface of the Crofer 22APU ferritic steel was modified with gadolinium oxide nanoparticles and a protective-conducting layer consisting of the MnCo2O4 spinel. This system was studied in the context of application in IT-SOFC interconnects. Four types of samples were studied: unmodified steel, steel coated with a manganese-cobalt spinel layer, steel modified with gadolinium oxide nanoparticles, and a system consisting of steel after both modifications. Steel samples with Gd2O3 nanoparticles were obtained via dip-coating, while the spinel coatings were deposited electrophoretically. All samples were oxidized for 1000 and 2260 h in air at 1073 K. Microstructural and oxidation kinetics studies revealed that gadolinium segregation at grain boundaries in the Cr2O3 scale between the steel and the spinel layer reduces the oxidation rate for the steel/coating system, thereby improving the adhesion of the scale to the substrate. The applied modification decreased the chromium evaporation rate and improved the electrical properties of the interconnect material.

Suzanne Duchamp's Readymade Paintings

Suzanne Duchamp pushed the boundaries of painting by incorporating unorthodox, machine-made materials within interconnected material geometries. Focusing on Un et une menaces (1916), Radiation de deux seuls eloignes (1916–20), and Le Readymade Malheureux de Marcel (1920), this article describes Duchamp’s particular way of integrating readymades into her artwork and reveals her ability to transform modern, store-bought elements into interwoven pictorial structures. Drawing Duchamp into dialogue with the Dada group, this article examines the geometric forms and materials of her artworks as a body of work in their own right and in conjunction with those made by her peers, particularly her husband Jean Crotti, her brother Marcel Duchamp, Francis Picabia, Elsa von Freytag-Loringhoven, Sophie Taeuber-Arp, Beatrice Wood, and Man Ray. It positions Radiation as Suzanne Duchamp’s major work from this period, which she worked on in a durational manner in line with the approach taken up in Marcel Duchamp’s making of The Bride Stripped Bare By Her Bachelor’s, Even (1915–23) in New York. This close consideration of Duchamp’s distinct way of combining unorthodox materials with traditional pictorial mediums makes it possible to contextualize her within early explorations of the readymade taking place between New York, Zurich, and Paris. A better understanding of Duchamp’s individual approach will shed greater light on her own work and on the ideas that she shared with other Dadaists. This is because the particular way that Duchamp integrated readymades within the mediums of painting, drawing, and poetry arguably had an effect on the broader movement.

Effect of Heat Treatment on the Structural, Morphology and Electrochemical Performance of Perovskite Ba<sub>0.5</sub>Sr<sub>0.5</sub>Co<sub>0.8</sub>Fe<sub>0.2</sub>O<sub>3−δ</sub>-Sm<sub>0.2</sub>Ce<sub>0.8</sub>O<sub>1.9</sub> Carbonate Protective Coating for SOFC Metallic Interconnect

A composite perovskite Ba<sub>0.5</sub>Sr<sub>0.5</sub>Co<sub>0.8</sub>Fe<sub>0.2</sub>O<sub>3−δ</sub>-Sm<sub>0.2</sub>Ce<sub>0.8</sub>O<sub>1.9</sub> carbonate (BSCF-SDCC) coating was investigated to enhance the performance of SUS 430 stainless steel as interconnect material for solid oxide fuel cells (SOFCs). BSCF-SDCC powder was successfully obtained by low-speed wet milling method from commercial BSCF, SDC, and binary carbonates. The developed BSCF-SDCC powder were heat-treated 600 °C for 90 min, and then characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM) equipped with energy-dispersive spectroscopy (EDS). FESEM revealed better morphology of BSCF-SDCC powder with heat treatment. However, XRD analysis showed the destruction of BSCF phase in the BSCF-SDCC powder after heat treatment at 600 °C. Moreover, electrophoretic deposition (EPD) of BSCF-SDCC powder in an ethanol-added dispersing agent suspension was investigated under 10 volt 10 minutes by 10 g/l. The coated samples were then heat-treated at 600 °C. The coated samples were characterized by comparing between the samples with and without heat treatment based on XRD, SEM-EDS, and area specific resistance (ASR) analyses. XRD analysis indicated BSCF phases disappeared for the samples with heat treatment. The heat-treated sample performed better coating morphology and fewer pores. The samples underwent 500 hours of air oxidation at 600°C, and ASR was measured by DC 2-point method during in situ oxidation process. The coated sample with heat treatment at 600 °C exhibited excellent low area-specific resistance reading of below 0.1 Ωcm2, which is an essential requirement for interconnect materials. After 500 h of oxidation, the XRD patterns revealed stable phase and maintained good coating morphology.

Sintering and deposition of homo- and heteronanoparticles of aluminum and nickel on aluminum (100) substrate

Nanoparticles are very attractive materials owing to their high chemical reactivity compared to conventional micron-sized particles due to their high surface area to volume ratio. In light of this, nanoparticles may provide enhanced energy release rates for explosive and propellant reactions. However, their performance depends strongly on their surface structure. Thereby, nanoparticle coalescence plays an important role as it determines the resultant structure of the active sites where for example catalytic reactions actually take place, i.e. facets, edges, vertices or protrusions. With this in mind, we conduct molecular dynamics simulations to investigate coalescence of two identical nanoparticles of Al and Ni (homo spheres) and two different nanoparticles Al-Ni (hetero spheres) and their deposition on an Al (1 0 0) substrate at various temperatures from 200 to 800 K using the embedded atom method. Radial distribution function, x-y plane projection, collapsing and spreading indexes are calculated to characterize the coalescence and surface deposition process. Our simulation results show that the degree of coalescence and deposition are strongly temperature dependent. The deposition rate increases with the temperature while the sintering and deposition of hetero nanoparticles is significant at lower temperatures than melting. This trend is important to develop a lead-free metal composite materials for the electrical interconnect material due to their low processing temperature.

Preparation and sintering properties of Cu10Sn3 IMCs nanopaste as die attach material for high temperature power electronics

Cu10Sn3 intermetallic compound (IMC) nanoparticles (NPs) were synthesized by one-step thermal decomposition method with low cost. The in-situ formed metal amide in the presence of LiN(iPr)2 can be reduced and thermally decomposed into metal NPs, and then the Cu10Sn3 NPs were obtained, which have an average diameter of 65 nm and good oxidation resistance. The microstructures and mechanical properties of Cu/Cu10Sn3/Cu joints at different sintering temperatures were investigated. The full-Cu10Sn3 IMC joints show high shear strength of 26.8 MPa after sintering at 300 °C for 20 min, demonstrating its broad potential as an interconnect material for high-temperature power electronics.

Mixed CNT bundles as VLSI interconnects for nanoscale technology nodes

The continuous miniaturization of very large-scale integration devices impacts the performance of integrated circuits. The performance of existing interconnect materials such as copper has become saturated beyond the deep-submicron technology node, motivating the search for new interconnect materials that could be efficiently employed in such circuits. In this study, a temperature-dependent analysis is performed to determine the propagation delay, power dissipation, and power–delay product of copper, single-walled carbon nanotubes (SWCNTs), multiwalled carbon nanotubes (MWCNTs), double-walled carbon nanotubes (DWCNTs), and mixed (multi- and double-wall) carbon nanotube bundle (MDCB) structures. The performance of these bundled structures is examined with the help of a complementary metal–oxide–semiconductor driver interconnect load system at various temperatures (200–500 K) and technology nodes (22 and 16 nm). The proposed novel mixed structure with MWCNTs at the periphery and DWCNTs in the center is interesting due to the combination of the excellent conducting properties of DWCNTs and the reduction of the net capacitive coupling due to the MWCNTs. Indeed, it is observed that this MDCB interconnect structure can outperform not only copper interconnects but also the SWCNT, MWCNT, and DWCNT structures. Such mixed structures could be used as interconnect materials in high-speed integrated circuits at future nanotechnology nodes.

Copper Oxide Passivation Effect on Electromigration Lifetime of Plasma Etched Copper Lines

Copper (Cu) is a widely used interconnection material in high density ICs, large area TFT LCDs etc. CMP is a production method used in etching Cu fine lines in ICs [1,2]. Although plasma etching is widely used in preparing small geometry aluminum and other metal lines [3], it cannot be used to etch Cu at room temperature due to the low volatility of copper halides [4]. A plasma-based high-rate, room-temperature Cu etch process was invented by Kuo’s group [5-7]. It includes the plasma/Cu reaction followed with a dilute HCl dipping step. This process has been successfully demonstrated on BiCMOS and TFT LCD products [8,9]. The electromigration (EM) method has been used in the evaluation the reliability of Cu lines [10-14]. Recently, the authors have reported that copper oxide (CuOx) is a potential useful passivation material for Cu line [15]. In this study, layer thickness effects of Cu and CuOx passivation films on the reliability are studied.The TiW/Cu stack was sputter deposited on a pre-cleaned Corning glass and etched into a 4-point line pattern. The Cu layer was converted into a CuClx layer under the condition of CF4/HCl 5/20 sccm, 70 mTorr, 600W, and room temperature for 2 minutes in a parallel-plate reactor (PlasmaTherm 700C) operated at the RIE mode. The CuClx layer was subsequently dissolved in a H2O:HCl (8:1 v/v) solution for 1 minute. Then, the TiW barrier film was etched in CF4 20 sccm at 60 mTorr and 600 W for 2 minutes in the same RIE reactor. After the photoresist pattern was wet stripped off, the sample was exposed to the O2 plasma at 200 mTorr, 100 W in the same plasma reactor but under the plasma etching mode. The CuOx passivation layer was formed on the exposed Cu surface. The EM lifetime of two types of samples, i.e., TiW/Cu and TiW/Cu/CuOx lines, were measured under the constant current density (J) stress condition.Figure 1 shows the line broken time as a function of the stress current density of TiW/Cu/CuOx lines of different Cu film thickness. The general trend is that the lifetime of the line decreases with the increase of the current density. This result is consistent with previous reports on the TiW or Mo passivated Cu lines [14]. The large stress current accelerated the voids formation and merging process, which shortened the line breakage time. Fig. 1 also shows the sample with the thinner Cu layer has a longer lifetime than with the thicker Cu layer. This can be explained by more resistant to thermal strain and the longer thermal fatigue failure time of the thin Cu film [16].Figure 2 shows the top view of a TiW/Cu/CuOx line broken region observed under the dark-field (DF) of an optical microscope. It clearly shows the distribution of a large number of voids along the current flow direction in this region while the adjacent unbroken region has much fewer voids.More detailed characterization of the EM stressed lines and the CuOx passivation layer thickness effect will be presented and discussed.Authors acknowledge the financial support of this work through NSF CMMI project 1633580. J. Proost, T. Hirato, T. Furuhara, K. Maex and J.-P. Celis, J. Appl. Phys., 87(6), 2792-2802 (2000).C. S. Hau-Riege, S. P. Hau-Riege and A. P. Marathe, J. Appl. Phys., 96(10), 5792-5796 (2004).D. A. Danner, M. Dalvie and D. W. Hess, J. Electrochem. Soc., 134(3), 669-673 (1987).H. Miyazaki, K. Takeda, N. Sakuma, S. Kondo, Y. Homma and K. Hinode., J. Vacuum Science and Technology B, 15(2), 237-240 (1997).Y. Kuo and S. Lee, Japan J. of Appl. Phys., 39(3A), L188 (2000).S. Lee and Y. Kuo, J. Electrochem. Soc., 148(9), G524-G529 (2001).Y. Kuo and S. Lee, Appl. Phys. Lett., 78(7), 1002-1004 (2001).Y. Kuo and S. Lee, Vacuum, 74(3-4), 473-477 (2004).J. Yang, Y. Ahn, J. Bang, W. Ryu, J. Kim, J. Kang, M. S. Yang, I. Kang, I. Cung, ECS Trans., 16(9), 13 (2008).C. S. Hau-Riege, Microelectronics Reliability, 44(2), 195-205 (2004).G. Liu and Y. Kuo, J. Electrochem. Soc., 156(7), H579-H584 (2009).C.-C. Lin and Y. Kuo, J. Appl. Phys., 111(6), 064909 (2012).M. Li and Y. Kuo, ECS Trans., 86(8), 41-47 (2018).J. Q. Su, M. Li, Y. Kuo and S. Hamaguchi, ECS Trans., 92(5), 39-46 (2019).J. Q. Su and Y. Kuo, ECS Trans., Submitted (2020).R. Mönig, Y.-B. Park and C. A. Volkert, AIP Conf. Proc., 817(1), 147-156 (2006). Figure 1

The Effects of Dual Atmosphere Exposure Duration and Temperature on the Growth of Iron Oxide on Ferritic Stainless Steels

Literature within the past two decades has highlighted the ongoing issue of dual atmosphere corrosion in solid oxide fuel cell (SOFC) systems. This corrosion phenomenon occurs as a result of simultaneous exposure of ferritic stainless steel interconnects to the anodic fuel gas on one side and cathodic air stream on the opposing side. In this, the air-exposed side of the metal interconnect undergoes fast, anomalous corrosion and metal loss in the form of iron oxide overgrowth with whisker and platelet-type morphology. Studies have indicated that the corrosion is favored at lower temperatures in comparison to temperatures above 800 °C. This poses an issue for the current trend of lowering SOFC operating temperatures and utilizing cost-effective ferritic stainless steels as interconnect materials. In this study, the oxidation behavior of two ferritic stainless steels is examined under dual atmosphere exposure conditions. A series of experiments with varying time, temperature, and steel compositions were carried out to better understand the effects of these variables on severity and morphology of corrosion products. A mechanism which describes the localized overgrowth of iron oxide in platelet and whisker form and the porous oxide sub-layer is proposed. The transition from a thin, protective, and dense chromia scale under nominal ambient conditions to porous, non-protective scaling under dual atmosphere conditions will be discussed.

Synergist effect of potassium periodate and potassium persulfate on improving removal rate of Ruthenium during chemical mechanical polishing

As technology nodes continue to decrease, traditional Copper (Cu) interconnects in the back end of the line (BEOL) will encounter more and more problems. Ruthenium (Ru) is expected to be a barrier layer or even as a novel type of interconnection material because of its good electrical properties. However, because of its high chemical inertness, Ru is challenging to achieve a higher removal rate in the chemical mechanical polishing (CMP) process. In this study, the synergist effect of potassium periodate (KIO4) and potassium persulfate (K2S2O8) on the removal rate of Ru during CMP was investigated. The theory of advanced oxidation process (AOPs) is used to explain the reaction process of Ru with KIO4 and K2S2O8. X-ray photoelectron spectroscopy (XPS) combined with electrochemical are applied to explore the removal machanism and chemical reaction mechanism of Ru under the synergistic effect of KIO4 and K2S2O8. The CMP tests shows that the Ru removal rate (1123 Å/min) in the presence of KIO4 and K2S2O8 composite could be increased by more than 221% compared to the removal rate (507 Å/min) of KIO4 alone. In addition, Ru oxidation process is more affected by diffusion-controlled. Excessive oxidant concentration will reduce the removal rate of Ru. The mechanism analysis shows that the RuO3-activated persulfate generates sulfate radical (SO4−•), which can further generate more oxides on the Ru surface, and Ru oxide is easily removed under the CMP process. Therefore, the Ru removal rate will be significantly improved. Simultaneously, the surface roughness Sq can be reduced to 0.667 nm after polishing.

Reconstruction of Pressureless Sintered Micron Silver Joints and Simulation Analysis of Elasticity Degradation in Deep Space Environment

With excellent economy and properties, pressureless sintered micron silver has been regarded as an environmentally friendly interconnection material. In order to promote its reliable application in deep space exploration considering the porous microstructural evolution and its effect on macroscopic performance, simulation analysis based on the reconstruction of pressureless sintered micron silver joints was carried out. In this paper, the deep space environment was achieved by a test of 250 extreme thermal shocks of −170 °C~125 °C, and the microstructural evolution was observed by using SEM. Taking advantage of the morphology autocorrelation function, three-dimensional models of the random-distribution medium consistent with SEM images were reconstructed, and utilized in further Finite Element Analysis (FEA) of material effective elastic modulus through a transfer procedure. Compared with test results and two analytical models, the good consistency of the prediction results proves that the proposed method is reliable. Through analyzing the change in autocorrelation functions, the microstructural evolution with increasing shocks was quantitively characterized. Mechanical response characteristics in FEA were discussed. Moreover, the elasticity degradation was noticed and the mechanism in this special environment was clarified.

Low temperature Cu joining by in situ reduction-sintering of CuO nanoparticle for high power electronics

Cu nanoparticles are promising interconnection material due to low cost and superior conductivity while they readily oxidize and need special processing and storing conditions. To solve these problems, a specific in situ reduction-sintering of CuO nanoparticles was developed and oxide free Cu submicron particles suitable for sintering were fabricated. The surfaces of the Cu submicron particles show no obvious oxide structure even after air sintering at 220 °C for 15 min and Cu-Cu joints with high shear strength of 22 MPa were produced. The oxide forms during longer bonding durations had a morphological evolution from stripe into grain and developed different layer structures on Cu particle surface. The micro-fracture mechanism of sintered Cu particles was analyzed and Cu particles were found to deform plastically while the surface oxide show obvious brittle fracture. Variation in shear strength with bonding time was analyzed and simulated based on contact area theory and the degradation of shear strength was correlated to the oxide formation. The proposed method produces similar shear strengths to Cu nanoparticle sintered joints but without the need for pressurized sintering or protective gas atmospheres.

Temperature-Dependent Circuit Modeling and Performance Evaluation Due to Crosstalk in Capacitively Coupled Interconnects of Intercalation-Doped Multilayer Graphene Nanoribbon

The present work explores the temperature-dependent performance evaluation due to crosstalk in coupled interconnects of intercalation-doped multilayer graphene nanoribbons (ID-MLGNR). A temperature-dependent equivalent single conductor (ESC) model of arsenic pentafluoride (AsF5) ID-MLGNR is considered and is employed to analyze its crosstalk performance (i.e., crosstalk-induced noise and crosstalk-induced delay). Other metallic interconnect materials viz. mixed carbon nanotube bundles (MCB) and copper (Cu) are also analyzed in a similar manner. The temperature-dependent crosstalk performance of ID-MLGNR is compared with that of MCB and Cu, at different temperatures from 300 to 500 K. For the specified temperature range, in case of crosstalk-induced noise, the AsF5 ID-MLGNR-based long interconnects demonstrate superior performance to its MCBs and Cu counterparts. Moreover, the temperature-dependent crosstalk-induced delay is less with ID-MLGNR in comparison with both MCB and Cu interconnects. The large values of the mean free path (MFP) and conductivity of AsF5 ID-MLGNR contribute to its improved performance. In addition, the impact of variation in MFP, interlayer spacing and Fermi level is studied on the crosstalk delay performance of ID-MLGNR. From the obtained results, it is revealed that variation in these parameters results in the significant variation of 62 ps, 51 ps and 169 ps, respectively, in the odd mode (OM) crosstalk delay. Hence, for emerging nano-technology nodes (e.g., 14 nm), ID-MLGNR interconnects with its improved crosstalk performance are proposed as a potential alternative to its MCBs and Cu counterparts.

High-temperature oxidation behavior of the Crofer 22 APU steel coated with (La,Sr)(Co,Fe)O3 film prepared by pulsed laser deposition

The La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF48) film was deposited on Crofer 22 APU ferritic stainless steel using the pulsed laser deposition (PLD) technique. The LSCF48 film with a thickness of about 1.1 μm was dense and homogeneous, with good adhesion to the metallic substrate. Transmission electron microscopy combined with the energy-dispersive X-ray spectroscopy studies showed that the stoichiometry of the target was precisely transferred to the film by pulsed laser deposition. Oxidation studies of bare Crofer 22 APU steel, and steel with the LSCF48 film were carried out in laboratory air at 1073 K under both isothermal and cyclic oxidation conditions. The calculated parabolic rate constant kp after oxidation for 200 h for the steel with LSCF48 film was approximately three times lower than the oxidation rate of the steel without surface modification. The oxide scale formed on Crofer 22 APU steel consisted of two layers: an inner layer built of chromia and an outer layer consisting of the Mn1.5Cr1.5O4spinel. In the case of the steel with LSCF48 film, the oxide scale was two times thinner and had a similar phase composition. In both cases, the presence of an internal oxidation zone with SiO2 and Al2O3 precipitates was observed. In addition, small amounts of spinel crystals were observed on the film surface. After 2400 h of oxidation at 1073 K under thermal cyclic conditions, the total mass gain was 1.04 mg · cm−2 and 0.67 mg · cm−2 for the respectively bare and coated substrate. The results indicated that the spallation of the oxide scale and/or the film did not occur. In both cases, the composition of the scales was similar to the scales formed on the samples after isothermal oxidation. Studies of the electrical properties show, that Crofer 22 APU steel with LSCF48 film deposited by PLD method meets criteria for the interconnector materials for intermediate-temperature solid oxide fuel cells applications.

Effect of Hybridization on the Functional Properties of AgMF–MWCNT-Filled Electrically Conductive Adhesive

A combination of metal and non-metal filler in an epoxy resin, called a hybrid electrically conductive adhesive (ECA), is an important development in the field of highly conductive electronic interconnect materials. Carbon nanotubes (CNTs) are well known for contributing strength and stiffness to ECA and silver (Ag) has been widely used as a conductive metal. This study presents the characterization of a hybrid silver micro-flake (AgMF) with multiwalled carbon nanotubes (MWCNT) in an epoxy matrix ECA, in terms of electrical and mechanical properties. The weight percentage of AgMF used was varied, from 1 wt.% to 10 wt.%, whereas the weight percentage of MWCNT filler loading was maintained at 5 wt.%. The properties of the hybrid ECA were characterized using a four-point probe and a universal testing machine for lap shear tests. It was found that the filler hybridization lowered the performance of the ECA in terms of both electrical and mechanical properties, as compared with non-hybrid MWCNT-filled ECA. This may be attributed to the weak interaction between micro- and nano-filler particle sizes and agglomeration of the MWCNT in the epoxy matrix in the hybrid ECA system. The hybrid ECA electrical conductivity was successfully enhanced when a low ratio of AgMF and MWCNT was considered. In addition, failure analysis confirmed that the hybrid ECA with less AgMF filler loading exhibits improved adhesion strength, suggesting a superior epoxy-to-substrate bonding interface.

Electromigration Behavior of Cu Core Solder Joints Under High Current Density

Cu core solder ball (CCSB) is formed by a Cu core surrounded by solder alloy and is used as an interconnection material for 3D packaging. Herein, the electromigration behavior of CCSBs with an organic solderability preservative surface finish is compared with that of Sn–3.0Ag–0.5Cu (SAC) solder joint. The current density and temperature for electromigration test are 0.9 × 104 A/cm2 and 100 °C, which are in compliance with JEP154. The current density of the solder joint is analyzed using finite element method analysis and maximum current density of the SAC solder joint is 1.1 times higher than the CCSB solder joint. The CCSB solder joint is less affected by the current crowding effect because electrons move through the Cu core located at the center of the solder. A void form in the Cu electrode of the cathode that coincides with the simulated maximum current area of the solder joint. The electromigration reliability of the CCSB solder joint is superior to that of the SAC solder joint.

Analysis of top- and side-contact MLGNR interconnects: impact on crosstalk, stability, and electromigration

In a recent nanoregime, the cross-coupling capacitance plays an important role due to the high packing density of integrated circuits. It can significantly affect the overall interconnect performance of an IC that can reduce the reliability, durability, and stability of silicon technology. In order to alleviate these problems, this work demonstrates shielded side-contact (SC) and top-contact (TC) multilayered graphene nanoribbon (MLGNR) interconnect to demonstrate stability and cross talk reliability issues. At 32 nm technology, an equivalent single-conductor Pi-type network is proposed for shielded SC- and TC-MLGNR for different spacing and interconnect lengths. Besides, the impact of temperature and higher current density is demonstrated. It is observed that the conventional interconnect material such as Cu exhibits 52.31% faster electromigration breakdown as compared to graphene at 1000 K. Further, the cross talk-induced delay is analyzed for shielded TC-and SC-MLGNR using driver–interconnect–load arrangement. An improved crosstalk-induced delay of 59.36% and 95.97% is observed for SC-MLGNR as compared to a TC-MLGNR with active shielding for an average spacing range of 5–20 nm at local and global lengths, respectively. Furthermore, the power delay product and peak noise of active-shielded SC-MLGNR exhibit on an average 96.82% and 38.20% improvement in comparison with active-shielded TC-MLGNR for the spacing of 5 nm at global length. Moreover, the Nyquist plot is used to demonstrate higher stability of SC-MLGNR than TC-MLGNR at 32 nm technology. Therefore, the overall system performance demonstrates that the active-shielded SC-MLGNR can be treated as a suitable choice for future VLSI technology.