AlCu Layer Research Articles

Microstructure and properties of C18150 Cu/8011 Al/C18150 Cu laminated composites

In order to solve the problem of insufficient strength and electrical conductivity of Cu–Al composites, C18150 Cu/8011 Al/C18150 Cu composites with a thickness of 1.6 mm were fabricated by cast rolling method in this paper, followed by cold rolling and annealing. The interfacial microstructure and precipitation behavior were analyzed through electron backscatter diffraction, scanning electron microscopy, and transmission electron microscopy in detail. The research results show that the three-layer interfaces from the Al layer to the Cu layer are Al2Cu, AlCu, and Al4Cu9, respectively. The interface of the Al layer and Al2Cu layer demonstrate a coherent matching relation, the interface of the Al2Cu layer and AlCu layer shows a semi-coherent matching relation, and the interfaces between AlCu and Al4Cu9, and Al4Cu9 and Cu, are incoherent matching relation. In addition, the Al2Fe3Si4 and Cr precipitations were formed in the composites. The composites exhibit extremely outstanding strength-plasticity-conductivity, and the tensile strength and elongation are 295 MPa and 21%, respectively. The electrical conductivity of the Cu and Al layers is 90.6% and 47.6% according to the International Copper Standard, respectively. This study is useful in guiding the further development and application of high-strength and high-conductivity Cu/Al laminated composites.

Characterizing of a unique Al/Cu FGMMC fabricated via the ARB-CRB process followed by annealing

This study investigates the influence of different annealing temperatures on the microstructure and growth of the intermetallic phase in an Al/Cu functionally graded metal matrix composite (FGMMC ( produced by the accumulative roll bonding (ARB)-cold roll bonding (CRB) process. SEM images show the evolving distribution of Cu content in the composite, with the finest and thinnest Cu layer observed in the Al/20Cu region. The annealing at 400°C and 450°C for 2, 4, and 6 hours results in the formation of intermetallic layers (Al2Cu, Al4Cu9, and AlCu) with a clear progression from the Al side to the Cu side, as confirmed by SEM-EDS and TEM analysis. Increasing the annealing conditions increases the thickness of the intermetallic layers. In addition, the intermetallic layers are thicker in the FGMMC sample than in the ARB sample under the same conditions due to the additional strain during the process. The findings demonstrate that a diffusion-controlled mechanism governs the growth of the Al2Cu, Al4Cu9, and AlCu layers. The tensile test results indicate that as the Cu content increases from 20 wt% to 80 wt%, the ultimate tensile strength of the layers increases from 288.24 MPa to 373.66 MPa, while the elongation decreases from 8.2 % to 5.3 %. After annealing, however, these values decreased due to the restoration phenomenon and intermetallic formation. The fracture surface predominantly exhibits a brittle mode, especially with increasing Cu content and annealing conditions.

High damage-tolerance nacre-inspired TiB2/Al-Cu composites with adjustable mechanical performance based on heat-treatment condition tuning

High damage-tolerance nacre-inspired TiB2/Al-Cu composites are successfully prepared by freeze casting and pressure infiltration. The obtained composites have a great application potential as lightweight structural components due to their high strength and toughness. The microstructure and mechanical properties of the nacre-inspired TiB2/Al-Cu composites are characterized, and their fracture and toughening mechanisms are also investigated. The results show that both the as-cast and heat-treated TiB2/Al-Cu composites possess excellent mechanical properties, which can be attributed to several toughening mechanisms, including the passivation, branching, deflection, and bridging of cracks. These are due to the Al phases in the ceramic layers, as well as the plastic deformation of the Al-Cu layers and the interconnected network structure. The heat treatment can significantly improve both the strength and toughness, which can be attributed to the decrease of the crack propagation possibility resulted by the decrease in the Al2Cu content after heat treatment, as well as the existence of metal bridges and the pull-out behavior resulted by the high plasticity of the Al matrix. This study demonstrates that mechanical properties of high damage-tolerance nacre-inspired TiB2/Al-Cu composites can be controlled by tuning the heat-treated conditions, which can be beneficial to the industrial application of such composites in the manufacturing of components such as brake discs and protective armors.

Experimental studies of formability in single point incremental forming of Cu-Al bimetallic sheets

In the sheet metal forming industry, single point incremental forming (SPIF) is gaining popularity for producing asymmetrical shapes in small quantities as well as developing rapid prototypes. In the present experimental study, the effect of process variables on the maximum forming wall angle of Cu-Al bimetallic composite sheet using the SPIF process has been investigated. The Cu-Al bimetallic composite sheet was considered for the investigation because of its qualities, including high strength and outstanding thermal and electrical conductivity. The range of step depth, spindle speed, forming speed, layer arrangement, and lubrication type were used as input process variables during the experiments. Formability is evaluated as an output parameter using the maximum forming wall angle. The findings revealed that the Cu-Al layer arrangement produced the greatest forming wall angle with the highest value, 81.5°, when employing 0.6 mm step depth, 1500 rpm spindle speed, 750 mm/min forming speed, and liquid lubrication. Liquid lubrication produced greater forming wall angle values than solid lubrication in all of the experiments. In both lubrication conditions, the Cu-Al layer arrangement exhibited a larger forming wall angle than the Al-Cu layer arrangement.

Clarification of the solid-state diffusion behavior of a copper alloy/aluminum alloy composite interface assisted by position marking of the second phases

This paper studied the solid-state diffusion behavior of a C70250 copper alloy/8030 aluminum alloy composite interface. The formation sequence, growth direction and formation mechanism of the intermetallic compound (IMC) layers were clarified with the help of second phases and intensive microstructure characterization. The formation sequence of IMC layers at the composite interface is as follows: Al 2 Cu layer, AlCu layer with coarse grains, Al 4 Cu 9 layer, AlCu layer with fine grains, and (Cu,Ni) 5 Si layer. The spatial distribution of IMC layers at the composite interface is as follows: the Cu alloy, the (Cu,Ni) 5 Si layer, the Al 4 Cu 9 layer, the AlCu layer with fine grains, the AlCu layer with coarse grains, the Al 2 Cu layer, and the Al alloy. The Al 2 Cu layer and AlCu layer with coarse grains grow from the original composite interface to the Al alloy side, while the Al 4 Cu 9 layer and AlCu layer with fine grains grow from the original composite interface to the Cu alloy side. Moreover, with Al atoms diffusing toward the Cu alloy side, partial Ni atoms are combined with Al atoms to form the NiAl phase in the Al 4 Cu 9 layer and AlCu layer with fine grains. • The formation sequence of IMCs layers at the composite interface is clarified. • The growth direction of IMCs layers at the composite interface is clarified. • The positional relationship between IMCs layers and the original interface before heating is confirmed.

Formability and densification behavior of two-layered structure powder metallurgical hot-pressed Al-Cu/Al composites during hot-upsetting

An experimental investigation has been performed on the hot formability and densification characteristics of Al-Cu/Al two-layered structure composites. The two-layered composites having different Cu compositions in the Al-Cu layer such as (Cu: 5wt. %, 10wt. %, and 15wt. %) were prepared using the powder metallurgy (P/M) route. The composites were hot-pressed as layer by layer in a steel cylindrical die at 550°C temperature with 0.9 initial relative density (IRD) and 0.1 s−1strain rate. The preforms were hot deformed between two flat dies with a capacity of 50-ton hydraulic press machine at a temperature range of 150°C – 450°C under triaxial stress state condition. The hot-upsetting behaviour of preforms was analyzed until the cracks begin on the cylindrical preform at the outer surface. The effect of different Cu composition and various deformation temperatures on two-layered preforms were discussed. Results revealed that the (10wt. %Cu) preform achieved good cooperative deformation behaviour between Al-Cu and Al layers at the interface region. The relationship between the process parameters was discussed such as the effect of axial stress ([Formula: see text]), relative density ( R) on axial strain ([Formula: see text]) and formability stress index ( β), different stress ratio parameters ([Formula: see text], [Formula: see text]) on relative density ( R).

Influence of Pin Offset and Weave Pattern on the Performance of Al-Cu Joints Reinforced with Graphene Particles

The friction stir welding technique is currently employed for different alloy combinations like magnesium, titanium, copper, nickel-based composites. Dissimilar materials may be efficiently joined by the process and this has been used in several structural applications such as automotive components, aircraft structure, shipbuilding, and space shuttle external tank and train bodies. Even though improvement in the joint strength was achieved, problems such as voids, tunnels, cracks persisted in the weldments. The objective is to achieve defect-free joints. Tool pin offset for joining of aluminum alloy enables better stirring action and an easy flow of plasticised material in the weld nugget. Hence, to overcome the above-mentioned problem, a technique of combined effect of weaving, tool pin offset, and reinforcement of self-lubricated graphene nanoplatelets was attempted. The tensile strength obtained with the effect of tool rotational speed under weave weld with pin offset condition with reinforcement was 13.82 % higher than the weld obtained under the same condition without reinforcement. IMCs such as AlCu, Al2Cu, and Al4Cu9 large size band layers were observed with the linear welding condition, whereas weave welding conditions resulted in the formation of the thin uniform layer.

Effect of Intermetallic Compound Layer on Peel Strength and Crack Propagation Behavior in Cu/Al/Cu Clad Composites

The effects of interfacial modification in tri-layered Cu/Al/Cu composites by heat treatment on interface stability and crack propagation were investigated. In order to investigate the crack path during the peel test, the intermetallic compound layer with the propagating crack was examined using electron backscatter diffraction (EBSD) analyses. The increase of peel strength from 7.8 to 9.1 N/mm in the tri-layered Cu/Al/Cu composite in the presence of thin discontinuous intermetallic compounds with heat treatment at 200–300 °C was accompanied by the increase of electrical conductivity from 65.3% IACS (International Annealed Copper Standard) to 66.8% IACS. Continuous intermetallic layers consisting of Al2Cu, AlCu, and Al4Cu9 were found in Cu/Al/Cu heat-treated at temperatures above 350 °C and its thickness increased rapidly and reached up to 35.2 μm at 500 °C. The peel strength drastically decreased to 5.75 N/mm after heat treatment at 400 °C, and it gradually increased as the heat treatment temperature was increased to 450 °C (5.91 N/mm) and 500 °C (6.16 N/mm). The increased peel strengths after heat treatment at 450 and 500 °C were accompanied by pronounced serrations of the peel strength–displacement curves. The amplitude of serration increased substantially with increasing annealing temperature from 400 to 500 °C. The major crack along the interface propagated, mostly along the Al2Cu/AlCu boundary with some inclined cracks, propagated through the AlCu and Al4Cu9 intermetallic compound layers. The repetition of crack propagation along the interface and crack deflection through the intermetallic layer as an inclined crack induced the serrated surface on the peeled-off Cu plate, enhancing the interface toughening.

Growth characterization of intermetallic compounds at the Cu/Al solid state interface

Cu/Al cold-rolled composite plates were annealed in the temperature range of 573∼773 K. The growth mechanism of intermetallic compounds formed at the Cu/Al solid-state interface was analyzed from the point of view of diffusion kinetics. After annealing, the interfacial reaction layer of the sample consisted of three kinds of intermetallic compound: Al2Cu adjacent to Al, Al4Cu9 adjacent to Cu and AlCu between Al2Cu and Al4Cu9. The formation sequence of the intermetallic layers was Al2Cu, Al4Cu9, and AlCu. The results show that the growth of Al2Cu, Al4Cu9 and AlCu layer were governed by reaction-controlled mechanism in the previous period and by diffusion-controlled mechanism in the latter period in the annealing temperature range of 573 to 773 K, and the higher annealing temperature, the earlier the reaction-controlled stage ends for three kinds of intermetallic compound.

Characteristics of resistance projection–welded aluminum-copper interconnects

This paper describes the use of resistance projection welding of lap joints between tinned copper terminals with flat aluminum conductors. With the exception of resistance brazing, resistance welding, which has been established for many decades, is currently not used for joining dissimilar metal joints made of copper and aluminum. The use of this technology could potentially result in particularly cost-effective joints that are easily scalable to different sizes of terminals. For the necessary current density during the welding process, a mechanically embossed welding projection in the copper conductor surface is required. During the welding process, the projection moves into the softer aluminum material without being deformed. The projection expresses part of the brittle liquid intermetallic compounds produced. Shear tensile tests, electrical conductivity measurements and micrographs are used to assess the technical properties of the joint. The presented results show that the created intermetallic joint has good electrical and mechanical properties despite pronounced intermetallic AlCu layers.

Interfacial bonding mechanism and pouring temperature effect on Al/Cu bimetal prepared by a novel compound casting process

In this work, the Al/Cu bimetal was prepared by a novel lost foam casting (LFC) compound process, and the effect of pouring temperature on microstructure and mechanical properties of the Al/Cu bimetal was studied. The formation mechanism of the Al/Cu interface was also discussed. Results show that the Al/Cu interface consisted of intermetallic compounds layers (IMCs layers) and eutectic layer. The IMCs layers were identified as Al2Cu, AlCu, and Al4Cu9 phase layers, and the eutectic layer was composed of Al2Cu, α(Al) and Si phases. The pouring temperature primarily influenced the morphology and size of the IMCs layers and eutectic layer as well as the pore defect in the interface. Based on the cooling curve and the morphology of the IMCs layers, a new formation mechanism of the Al/Cu interface was proposed. The Al/Cu bimetal obtained with a pouring temperature of 800 °C had the relatively highest bonding strength, up to 81 MPa, resulting from its improvement of the IMCs layers. Shear fracture exhibited a brittle fracture nature, mainly initiating with the IMCs layers, and the Si phase also played an important role in the fracture process.

Effects of Melt-to-Solid Volume Ratio and Pouring Temperature on Microstructures and Mechanical Properties of Cu/Al Bimetals in Compound Casting Process

Cu/Al bimetallic composites were fabricated by compound casting where aluminum melts were cast on Ni-coated Cu substrates. Effects of the melt-to-solid volume ratio (VR) and the pouring temperature on interfacial microstructures and mechanical properties of Cu/Al bimetals were investigated systematically. Results show that a continuous and compact interface can be formed when the pouring temperature exceeds 953 K (680 °C). When the VR or pouring temperature increases, the solidification time of α(Al) increases, resulting in an increase in the dissolution content of Cu substrate. The transition zone consists of α(Al) + Al2Cu eutectic layer and intermetallic compounds (IMCs) layer, and the IMCs are identified as Al2Cu, AlCu, and Al4Cu9. Ni coating participates in the formation of AlCuNi phase between the Al2Cu layer and AlCu layer when the pouring temperature is 973 K (700 °C). The presence/absence of Ni-containing phase has a close relationship with the dissolution of the Cu substrate. Shear-strength tests show that shear fracture mainly occurs at the hard brittle IMCs layer, and the highest shear strength of 36.01 MPa is obtained for the samples fabricated at 993 K + VR 49.24 (720 °C + VR 49.24).

Effect of Nanosecond Laser Dicing on the Mechanical Strength and Fracture Mechanism of Ultrathin Si Dies With Cu Stabilization Layer

Ultrathin dies require a Cu stabilization layer, which is essentially a backside Cu layer, to prevent warpage and cracks during solder die attach and wire bonding. The dicing of Si wafers with a backside Cu layer is challenging. Mechanical blade dicing through the Cu layer causes blade clogging and damage, which eventually results in severe die chipping and cracks. Plasma dicing is costly as it requires additional photolithography and etching steps. Laser dicing is promising and is currently used to singulate thin Si wafers. However, there is no reported work on its application for dicing ultrathin wafers with a backside Cu layer. In this paper, nanosecond laser dicing of $20~\mu \text{m}$ Si dies with 0– $30~\mu \text{m}$ backside Cu was found to be feasible. The effect of nanosecond laser dicing on the die sidewall strength was evaluated with the three-point bend (3PB) test. Analytical and experimental results have shown that the Cu and AlCu layers have gone into plastic condition during the 3PB test. Comparison of the 3PB fracture loads indicates that the Si backside strength is higher than the Si frontside strength. Fractographic analysis has confirmed that the fracture initiation sites during the 3PB tests are at the die sidewall. The die sidewall defect morphologies, structures, and elemental compositions have been characterized in detail by transmission electron microscopy, and their effect on mechanical strength is discussed.

Fabrication of nanoscale metal paths in oxide thin layers by noble-gas ion beams

We investigated the fabrication process of a nanostructure with alumina insulator layer and nanoscale Cu paths punching through an alumina layer inserted between magnetic multilayers. Ion-beam–assisted oxidation was applied to an AlCu layer, where ion beams with three kinds of noble gases of different mass, Ne, Ar and Xe, were compared. The heavy gas overcame the trade-off between the increasing purity of nanoscale Cu paths and the decreasing oxygen defects of the alumina. It is considered that the high mobility of surface atoms in the AlCu layer brought about by the heavy-gas ion beam promotes segregation of alumina and Cu.

Sealing of poly-SiGe surface micromachined cavities for MEMS-above-CMOS applications

This paper presents for the first time a study of different methods to seal SiGe surface micromachined cavities for above-CMOS MEMS applications. Four different sealing layers are proposed: sputter-deposited AlCu, sub-atmospheric pressure chemical vapour deposited Si-oxide and a porous microcrystalline-SiGe cover in combination with either high-density plasma chemical vapour deposited Si-oxide or AlCu. The maximum processing temperature is kept below 460 °C to allow for the post-processing on top of standard CMOS. To verify the sealing process, optical measurements of membrane deflection were carried out both in air and in vacuum. Analytical modelling and finite element analysis were used to study the load-deflection behaviour of the (poly-SiGe/sealing layer) composite membranes and derive the pressure inside the cavities. In order to study the behaviour of the diaphragms under 0-pressure difference, micro-venting holes were drilled, using focused ion beam, in some of the sealed membranes. The results indicate that both oxide and AlCu layers provide air-tight sealing and that, for AlCu direct sealing, a near-vacuum cavity pressure is obtained.

Intermetallic phase formation in diffusion-bonded Cu/Al laminates

Intermetallic phase formation in diffusion-bonded Cu/Al laminates prepared by plasma activated sintering (PAS) was investigated in the temperature range 673–773 K for 10–30 min. Three intermetallic phases, Al4Cu9, AlCu, and Al2Cu, were identified in all the samples. The formation of Al2Cu as the first phase was rationalized on the basis of the effective heat of formation (EHF) model. The thermodynamic driving force for the preferential appearance of Al4Cu9 at the α-Cu(Al)/Al2Cu interface was evaluated. The time and temperature dependences of the growth of the three intermetallic layers were determined, and their apparent activation energies were calculated. The growth kinetic of the layers conformed to the parabolic law, implying that the intermetallic phase formation was volume diffusion-controlled in the temperature range. The apparent activation energies calculated for the growth of the total intermetallic layer, Al4Cu9, AlCu, and Al2Cu layers were about 80.8, 89.8, 84.6, and 71.1 kJ/mol, respectively.

Improved Bipolar Resistive Switching of HfOx/TiN Stack with a Reactive Metal Layer and Post Metal Annealing

Improvement of a reactive metal layer (AlCu, Ti, or Ta) for the bipolar resistance switching (BRS) performance of HfOx based resistive memory (RM) with TiN as electrodes are studied in this work. After appropriate post metal annealing (PMA), the reactive metal layer with high oxygen content serves as an embedded resistor and modifies the insulator properties of theses stacked layers, which show stable repetitive switching through by the migration of oxygen ions in HfOx layer during operation. The Gibbs free energy for the oxidation of the reactive metal with respect to that of HfO2 dominates the optimal PMA temperature for the devices with stable BRS. Except for the reduction of forming voltage and leakage current, the AlCu layer with high resistance after PMA of 500 °C is beneficial for the devices with successive BRS and on/off ratio of 4. The forming voltage of the Ti devices seems insensitive on the PMA. Compared with the Ta device, the Ti/HfOx RM device after the PMA of 450 °C for 5 min exhibits a different current–voltage behavior during the first RESET voltage sweep and a higher resistance ratio (>40). These results are attributed to the higher affinity of oxygen in the Ti capping layer. The combination of HfOx with a reactive metal and an enough PMA shows great potential for future nonvolatile memory application.

$\hbox{HfO}_{x}$ Bipolar Resistive Memory With Robust Endurance Using AlCu as Buffer Electrode

A novel method of fabricating HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> -based resistive memory device with excellent nonvolatile characteristics is proposed. By using a thin AlCu layer as the reactive buffer layer into the anodic side of a capacitor-like memory cell, excellent memory performances, which include reliable programming/erasing endurance (> 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> cycles), robust data retention at high temperature, and fast operation speed (< 50 ns), have been demonstrated. The resistive memory based on AlCu/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> stacked layer in this letter shows promising application in the next generation of nonvolatile memory.

Influence of ARC capping layer on stress induced voiding in narrow AlCu metallisations

The influence of capping layer composition was examined in accelerated stress-migration performance of AlCu(0.5%) narrow stripe lines. Using resistance monitoring and Scanning Electron Microscopy, we determined that metallisation with bilayer Ti TiN ARC top layer induced more stress voiding than metallisation with single TiN ARC layer. These experimental results are discussed on the basis of a void growth mechanism provided by diffusion at the interface between AlCu and ARC top layer.

Progressive Debonding of Multilayer Interconnect Structures

ABSTRACTProgressive (or time dependent) debonding of interfaces poses serious problems in interconnect structures involving multilayer thin films stacks. The existence of such subcriticai debonding associated with environmentally assisted crack-growth processes is examined for a TiN/SiO2 interface commonly encountered in interconnect structures. The rate of debond extension is found to be sensitive to the mechanical driving force as well as the interface morphology, chemistry, and yielding of adjacent ductile layers. In order to investigate the effect of interconnect structure, particularly the effect of an adjacent ductile Al-Cu layer, on subcriticai debonding along the TiN/SiO2 interface, a set of samples was prepared with Al-Cu layer thicknesses varying from 0.2–4.0 μm. All other processing conditions remained the same over the entire sample run. Results showed that for a given crack growth velocity, the debond driving force scaled with Al-Cu layer thickness. Normalizing the data by the critical adhesion energy allowed a universal subcriticai debond rate curve to be derived.