Interconnect Materials Research Articles

Facile synthesis of Cu10Sn3 nanoparticles and their sintering behavior for power device packaging

Abstract Low temperature nanojoining and high temperature service in the microelectronic packaging technology has received much focused attention. Here, we suggest a facile thermal decomposition method for preparation of Cu10Sn3 nanoparticles (NPs) with high bulk melting point (640 ​°C) by using common organic salts, oleylamine (OLA), and oleic acid (OA). The uniform and dense sintered Cu/Cu10Sn3/Cu joints can obtain at 300 ​°C, 10 ​MPa, 20 ​min, which presents the average shear strength of 25.1 ​MPa. In addition, the interdiffusion of Sn and Cu atoms at interface between the sintered Cu10Sn3 layer and Cu makes the interface a metallurgical bonding. This sintered Cu/Cu10Sn3/Cu joints can provide a new interconnect material and technology for high-power device package.

Copper-graphene heterostructure for back-end-of-line compatible high-performance interconnects

Here, we demonstrate the fabrication of a Cu-graphene heterostructure interconnect by the direct synthesis of graphene on a Cu interconnect with an enhanced performance. Multilayer graphene films were synthesized on Cu interconnect patterns using a liquid benzene or pyridine source at 400 °C by atmospheric pressure chemical vapor deposition (APCVD). The graphene-capped Cu interconnects showed lower resistivity, higher breakdown current density, and improved reliability compared with those of pure Cu interconnects. In addition, an increase in the carrier density of graphene by doping drastically enhanced the reliability of the graphene-capped interconnect with a mean time to failure of >106 s at 100 °C under a continuous DC stress of 3 MA cm−2. Furthermore, the graphene-capped Cu heterostructure exhibited enhanced electrical properties and reliability even if it was a damascene-patterned structure, which indicates compatibility with practical applications such as next-generation interconnect materials in CMOS back-end-of-line (BEOL).

Injectable Cryogels in Biomedicine.

Cryogels are interconnected macroporous materials that are synthesized from a monomer solution at sub-zero temperatures. Cryogels, which are used in various applications in many research areas, are frequently used in biomedicine applications due to their excellent properties, such as biocompatibility, physical resistance and sensitivity. Cryogels can also be prepared in powder, column, bead, sphere, membrane, monolithic, and injectable forms. In this review, various examples of recent developments in biomedical applications of injectable cryogels, which are currently scarce in the literature, made from synthetic and natural polymers are discussed. In the present review, several biomedical applications of injectable cryogels, such as tissue engineering, drug delivery, therapeutic, therapy, cell transplantation, and immunotherapy, are emphasized. Moreover, it aims to provide a different perspective on the studies to be conducted on injectable cryogels, which are newly emerging trend.

Synthesis of Dilute Phosphorous-Embedded Co Alloy Films on a NiSi Substrate with a Superior Gap-Filling Capability for Nanoscale Interconnects

Nanoscale cobalt interconnection wire has a lower mean free path of electrons to reduce the electrical resistivity, therefore it has been increasingly studied as a promising interconnect material to replace the conventionally used copper in state-of-the-art nanoscale devices. This process further limits the space for barrier/seed layer deposition to conformally fill the narrow trenches/contact holes in nanoscale devices. Thus, an electrochemical approach not involving a conventional high-resistivity barrier is presented to study the gap-filling capability and properties of Co(P) films with a controlled composition on a NiSi substrate. Examining electrodeposited Co(P) films reveals that the composition is determined mainly by the deposition potential instead of the amount of NaH2PO2 in the electrolytes, yielding a film with a phosphorous concentration lower than 2.62 at.%. The lightly doped Co(P) film has an hexagonal close-packed Co structure with phosphorous atoms at the interstitial lattice site. A chronoamperometry study on the current transient during the electrochemical deposition indicates that NaH2PO2 addition can enhance the deposition of the Co(P) films. Hence, the Co(P) film developed here is capable of gap filling nanoscale trenches up to an aspect ratio of 5 and is practical as a contact plug material for NiSi in nanoscale devices.

Environmental Consequences of Closing the Textile Loop—Life Cycle Assessment of a Circular Polyester Jacket

The textile industry is recognized as being one of the most polluting industries. Thus, the European Union aims to transform the textile industry with its “European Green Deal” and “Circular Economy Action Plan”. Awareness regarding the environmental impact of textiles is increasing and initiatives are appearing to make more sustainable products with a strong wish to move towards a circular economy. One of these initiatives is wear2wearTM, a collaboration consisting of multiple companies aiming to close the loop for polyester textiles. However, designing a circular product system does not lead automatically to lower environmental impacts. Therefore, a Life Cycle Assessment study has been conducted in order to compare the environmental impacts of a circular with a linear workwear jacket. The results show that a thoughtful “circular economy system” design approach can result in significantly lower environmental impacts than linear product systems. The study illustrates at the same time the necessity for Life Cycle Assessment practitioners to go beyond a simple comparison of one product to another when it comes to circular economy. Such products require a wider system analysis approach that takes into account multiple loops, having interconnected energy and material flows through reuse, remanufacture, and various recycling practices.

A Polymer-Assisted Spinodal Decomposition Strategy toward Interconnected Porous Sodium Super Ionic Conductor-Structured Polyanion-Type Materials and Their Application as a High-Power Sodium-Ion Battery Cathode.

A general polymer‐assisted spinodal decomposition strategy is used to prepare hierarchically porous sodium super ionic conductor (NASICON)‐structured polyanion‐type materials (e.g., Na3V2(PO4)3, Li3V2(PO4)3, K3V2(PO4)3, Na4MnV(PO4)3, and Na2TiV(PO4)3) in a tetrahydrofuran/ethanol/H2O synthesis system. Depending on the boiling point of solvents, the selective evaporation of the solvents induces both macrophase separation via spinodal decomposition and mesophase separation via self‐assembly of inorganic precursors and amphiphilic block copolymers, leading to the formation of hierarchically porous structures. The resulting hierarchically porous Na3V2(PO4)3 possessing large specific surface area (≈77 m2 g−1) and pore volume (≈0.272 cm3 g−1) shows a high specific capacity of 117.6 mAh g−1 at 0.1 C achieving the theoretical value and a long cycling life with 77% capacity retention over 1000 cycles at 5 C. This method presented here can open a facile avenue to synthesize other hierarchically porous polyanion‐type materials.

The mitigation of signal integrity issues in coupled MWCNT bundles and a comparison with Cu interconnects

In the nanoscale regime, carbon nanotubes (CNTs) are being considered as a future alternative interconnect material for traditional copper (Cu) wires in integrated circuit technology. The advances in device scaling and the continuous increase of clock frequencies in very large-scale integration technology have resulted in signal integrity (SI) issues. The reduction of such SI issues in coupled multiwalled CNT bundle interconnects is evaluated herein. The worst-case crosstalk delay and peak noise voltage are simulated for three-line coupled interconnects at the 22-nm technology node. To minimize the crosstalk effects, a passive shielding technique is proposed, resulting in reductions of 15.3% and 40.8% in the dynamic in-phase and out-phase crosstalk condition, respectively. The SI of single- and two-line coupled MWCNT bundle interconnects is also investigated based on eye diagrams in a channel simulator and compared with that of Cu interconnects. The eye-opening height is significantly enhanced in the MWCNT bundle and Cu interconnects when using the proposed technique. Moreover, the MWCNT bundle has a higher eye-opening compared with its Cu counterpart.

Ultrahigh flexoelectric effect of 3D interconnected porous polymers: modelling and verification

Non-conductive materials like rubbers, plastics, ceramics, and even semiconductors have the property of flexoelectricity, which means that they can generate electricity when bent and twisted. However, an irregular shape or a peculiar load has been the necessary condition to realize flexoelectricity, and the weight and deformability specific ratios of flexoelectricity of solids are limited. In this work, we develop a theoretical model of flexoelectricity of three-dimensional interconnected porous materials. Compared to the solid materials, porous materials can exhibit flexoelectricity under arbitrary loading forms due to their complex microstructures, and the weight and deformability specific flexoelectric output is much higher than that of the solids. Then, we verify the model by measuring the flexoelectric response of polydimethylsiloxane (PDMS) and porous polyvinylidene fluoride (PVDF). The porous PDMS with 3D micron-scale interconnected structures exhibits two orders of magnitude higher weight and deformability specific flexoelectric output than that of the solid truncated pyramid PDMS. The flexoelectric signal is found to be linearly proportional to the applied strain, the microstructural size and the frequency. Finally, we apply the theory to a more practical bending sensor, and demonstrate its stable functioning and accurate response. Our model can be applied to other porous materials, and the results highlight the new potential of porous micro-structured materials with a significant flexoelectric effect in the fields of mechanical sensing, actuating, energy harvesting, and biomimetics as light-weight materials.

High electrical conductivity and breakdown current density of individual monolayer Ti3C2Tx MXene flakes

High electrical conductivity and breakdown current density of individual monolayer Ti3C2Tx MXene flakes

On the High-Temperature Oxidation and Area Specific Resistance of New Commercial Ferritic Stainless Steels

Two commercial ferritic stainless steels (FSSs), referred to as Steel A and Steel B, designed for specific high-temperature applications, were tested in static air for 2000 h at 750 °C to evaluate their potential as base materials for interconnects (ICs) in Intermediate Temperature Solid Oxide Fuel Cell stacks (IT-SOFCs). Their oxidation behavior was studied through weight gain and Area Specific Resistance (ASR) measurements. Additionally, the oxide scales developed on their surfaces were characterized by X-ray Diffraction (XRD), Micro-Raman Spectroscopy (μ-RS), Scanning Electron Microscopy, and Energy Dispersive X-ray Fluorescence Spectroscopy (SEM-EDS). The evolution of oxide composition, structure, and electrical conductivity in response to aging was determined. Comparing the results with those on AISI 441 FSS, steels A and B showed a comparable weight gain but higher ASR values that are required by the application. According to the authors, Steel A and B compositions need an adjustment (i.e., a plain substitution of the elements which form insulant oxides or a marginal modification in their content) to form a thermally grown oxide (TGO) with the acceptable ASR level.

Прочность при изгибе анизотропных составных плит со свободными краями

Modern technology shows increased demands on the strength properties of machines, their parts, as well as various structures, reducing their weight, volume and size, which leads to the need to use anisotropic composite materials. Finding criteria to determine the ultimate strength characteristics of structural elements, engineering structures is one of the urgent problems of solid mechanics. Strength problems in structures are often reduced to finding out the nature of the local stress state at the vertices of the joints of the constituent parts. The solution of this urgent problem for composite anisotropic plates can be found in this article, where the author continues the research in this area, extending them to the bending of anisotropic composite plates. The aim of the work is to study the limit stress state of anisotropic composite plates in the framework of the classical theory of plate bending. The outer edges of the plate are considered to be free. Using the classical theory of anisotropic plate bending in the space of physical and geometric parameters, the hypersurface equations determining the low-stress zones for the edge of the contact surface of a composite cylindrical orthotropic plate are obtained. Modern technological processes of welding, surfacing, soldering and bonding allow to produce structural elements of monolithic interconnected dissimilar anisotropic materials. The combination of different materials with qualities corresponding to certain operating conditions opens up great opportunities to improve the technical and economic characteristics of machines, equipment and structures. It can contribute to a significant increase in their reliability, durability, reduce the cost of production and operation. On this basis, the solution proposed in this work can be useful to increase the strength of composite materials.

Reliability Problems of Micro-Electronic Encapsulations

Smaller, lighter, faster, cheaper are today demands; new technologies stack and interconnect materials and components are utilised to achieve high density, small size, low weight, reduced power, and very low cost. Particularly important in this context is the implementation of higher densities, reduced volume hand in hand with improved reliability. A good price-performance ratio is key.

Effect of La0.8Ca0.2Cr0.9Co0.1O3−δ infiltration on the LCCC-YSZ layer as an interconnector material in solid oxide fuel cells

Effect of La0.8Ca0.2Cr0.9Co0.1O3−δ infiltration on the LCCC-YSZ layer as an interconnector material in solid oxide fuel cells

Effect of CNTs on the intermetallic compound growth between Sn solder and Cu substrate during aging and reflowing

Sn is the main interconnect material for three-dimensional (3D) Packaging of chip stacking in electronic packaging. In this paper, the intermetallic compound (IMC) produced through an interfacial reaction between Sn-xCNTs (x = 0, 0.075 wt%) solder and a Cu substrate was evaluated at 130 °C, 150 °C, and 170 °C for 30, 50, 100 h and after multiple reflows (3, 6, 9). In Sn-0.075CNTs system, CNTs inhibited the growth of Cu6Sn5 and refine the microstructure of solder joint. The growth rate of IMC decreased after reflowing and aging for 100 h. Compared to pure Sn/Cu system, the thickness of Cu6Sn5 and Cu3Sn was the thinner when the CNTs addition amount was 0.075 wt%. Some voids and cracks were formed in solder joints after reflowing and thermal aging. At this time, the IMC growth activation energies of Sn solder is 33.256 kJ/mol, and that of Sn-0.075CNTs composite solder is 58.19 kJ/mol.

Interdiffusion reliability and resistivity scaling of intermetallic compounds as advanced interconnect materials

Intermetallic compounds have been proposed as potential interconnect materials for advanced semiconductor devices. This study reports the interdiffusion reliability and resistivity scaling of three low-resistivity intermetallic compounds (Cu2Mg, CuAl2, and NiAl) formed on thermally grown SiO2. Experimental observations and thermodynamic calculations indicated good interdiffusion reliability with CuAl2 and NiAl but not with Cu2Mg. This was due to slow reaction between Al and SiO2 in conjunction with strong chemical bonds of Cu–Al and Ni–Al. As for resistivity scaling, all three intermetallic compounds showed better resistivity scalability than Cu. Resistivity of the thin films was measured and characteristic parameters were obtained by curve fitting using a classical scattering model. First-principles calculations were carried out to determine the electron mean free path and bulk resistivity in order to explain the resistivity scaling. The results showed the importance of having optimum microstructure features, i.e., low-defect-density surface, interface, and grain boundaries in addition to optimum material properties, i.e., a short mean free path and low bulk resistivity. CuAl2 and NiAl appeared to satisfy the interdiffusion and resistivity conditions and be promising candidates to replace Cu interconnections for future devices.

Unconventional Materials Processing Using Spark Plasma Sintering

Spark plasma sintering (SPS) has gained recognition in the last 20 years for its rapid densification of hard-to-sinter conventional and advanced materials, including metals, ceramics, polymers, and composites. Herein, we describe the unconventional usages of the SPS technique developed in the field. The potential of various new modifications in the SPS technique, from pressureless to the integration of a novel gas quenching system to extrusion, has led to SPS’ evolution into a completely new manufacturing tool. The SPS technique’s modifications have broadened its usability from merely a densification tool to the fabrication of complex-shaped components, advanced functional materials, functionally gradient materials, interconnected materials, and porous filter materials for real-life applications. The broader application achieved by modification of the SPS technique can provide an alternative to conventional powder metallurgy methods as a scalable manufacturing process. The future challenges and opportunities in this emerging research field have also been identified and presented.

High-Temperature Oxidation of AISI441 Ferritic Stainless Steel for Solid Oxide Fuel Cells

Several ferritic stainless steel grades are widely studied and used in solid oxide fuel cells (SOFCs) technology as interconnect materials. Their high-temperature oxidation behavior is interesting to evaluate their applicability at SOFCs operating conditions and to design degradation tests and models predicting the lifetime of a SOFC stack. In this work the AISI441 grade was oxidized in static air at 850°C to study its oxidation kinetic by weight gain measurements. It was found a parabolic growth with a rate constant of 9.42 x 10-14 g2cm-4s-1. Data calculated using the diffusion coefficients of the species involved in the oxidation process resulted in higher weight gain. Discrepancies between the measurements and the model were corrected taking into account the chromium volatilization.

Oxidation behavior and electrical conductivity of MAXs phase (Ti,Nb)3SiC2 as a novel intermediate-temperature solid oxide fuel cell interconnect material in anode environment

(Ti,Nb)3SiC2 possesses high oxidation resistance and electrical conductivity in cathode side, endowing it potential application as intermediate-temperature solid oxide fuel cell (IT-SOFC) interconnects. However, the performances of (Ti,Nb)3SiC2 in anode side must be well understood before the application comes true. In this paper, the oxidation resistance and electrical conductivity of (Ti,Nb)3SiC2 in simulated anode reducing atmosphere are systematically investigated. The oxidation kinetics follows parabolic law with a kP value of 7.57 × 10−14 g2 cm−4 s−1. The formed single oxide layer is composed of uniformly distributed Nb-doped rutile TiO2 and amorphous SiO2, without carbon deposition. High partial pressure of H2 and CO in simulated anode reducing atmosphere inhibit the oxidation by H2O and CO2. Nb doping with strengthen the Ti–O bond can also slow down the oxidation rate. ASR of (Ti,Nb)3SiC2 after 605 h cyclic oxidation is 1.6 and 3.7 mΩ cm2 at 800 °C and 500 °C, respectively. The low ASR comes from the induced extra electrons by Nb doping and the dissolution of H2O and H2 in oxide, and the integrated TiO2 conductive network in the scale. (Ti,Nb)3SiC2 exhibits superior performances in simulated anode reducing atmosphere, making it an promising candidate for SOFC interconnect.

Cu-Cu thermo compression wafer bonding techniques for micro-system integration

Copper (Cu) is used as an interconnect material in many applications owing to its high thermal, electrical conductivity and excellent electromigration resistance. Though this material has many advantages, the main drawback is that it gets oxidized on exposure to air. Thermo-compression bonding is a wafer bonding technique that uses metal layers for heaping wafers, which aids in attaining outstanding electrical conductivity without weakening the mechanical properties. The adsorbed oxide layer hurdles the proper bonding to happen between the wafers. In order to enhance the diffusion between the metal layers, the copper oxide layer should be removed which necessitates the requirement of high temperature, pressure, long bonding time and the inert gas atmosphere throughout the Cu-Cu thermo compression wafer bonding process. Simultaneous application of high temperature and pressure for a long time leads to the deterioration of the underlying sensitive components. This paper aims to present several techniques such as surface treatment, chemical pretreatment, surface passivation, crystal orientation modification, stress gradient in the thin film and formic acid vapour treatment which are used in order to avoid the deterioration of underlying sensitive devices and to obtain a proper bonding between the wafers at low temperature and pressure.

Performance Enhancement of Large Crossbar Resistive Memories With Complementary and 1D1R-1R1D RRAM Structures

The paper proposes novel solutions to improve the signal and thermal integrity of crossbar arrays of Resistive Random-Access Memories, that are among the most promising technologies for the 3D monolithic integration. These structures suffer from electrothermal issues, due to the heat generated by the power dissipation during the write process. This paper explores novel solutions based on new architectures and materials, for managing the issues related to the voltage drop along the interconnects and to thermal crosstalk between memory cells. The analyzed memristor is the 1 Diode - 1 Resistor memory. The two architectural solutions are given by a reverse architecture and a complementary resistive switching one. Compared to conventional architectures, both of them are also reducing the number of layers where the bias is applied. The electrothermal performance of these new structures is compared to that of the reference one, for a case-study given by a 4 × 4 × 4 array. To this end, a full-3D numerical Multiphysics model is implemented and successfully compared against other models in literature. The possibility of changing the interconnect materials is also analyzed. The results of this performance analysis clearly show the benefits of moving to these novel architectures, together with the choice of new materials.