Mechanism of microweld formation and breakage during Cu-Cu wire bonding investigated by molecular dynamics simulation

Currently,wire bonding is the most popular first-level interconnection technology used between the die and package terminals,but even with its long-term and excessive usage,the mechanism of wire bonding has not been completely evaluated.Therefore,fundamental research is still needed.In this study,the mechanism of microweld formation and breakage during Cu-Cu wire bonding was investigated by using molecular dynamics simulation.The contact model for the nanoindentation process between the wire and substrate was developed to simulate the contact process of the Cu wire and Cu substrate.Elastic contact and plastic instability were investigated through the loading and unloading processes.Moreover,the evolution of the indentation morphology and distributions of the atomic stress were also investigated.It was shown that the loading and unloading curves do not coincide,and the unloading curve exhibited hysteresis.For the substrate,in the loading process,the main force changed from attractive to repulsive.The maximum von Mises stress increased and shifted from the center toward the edge of the contact area.During the unloading process,the main force changed from repulsive to attractive.The Mises stress reduced first and then increased.Stress concentration occurs around dislocations in the middle area of the Cu wire.

Intrinsic two-dimensional multiferroicity in CrNCl_(2) monolayer

Two-dimensional multiferroics,which simultaneously possess ferroelectricity and magnetism in a single phase,are well-known to possess great potential applications in nanoscale memories and spintronics.On the basis of first-principles calculations,a CrNCl_(2) monolayer is reported as an intrinsic multiferroic.The CrNCl_(2) has an antiferromagnetic ground state,with a N´eel temperature of about 88 K,and it exhibits an in-plane spontaneous polarization of 200 pC/m.The magnetic moments of CrNCl_(2) mainly come from the dxy orbital of the Cr cation,but the plane of the dxy orbital is perpendicular to the direction of the ferroelectric polarization,which hardly suppresses the occurrence of ferroelectricity.Therefore,the multiferroic exits in the CrNCl_(2).In addition,like CrNCl_(2),the CrNBr_(2) is an intrinsic multiferroic with antiferromagneticferroelectric ground state while CrNI_(2) is an intrinsic multiferroic with ferromagnetic-ferroelectric ground state.These findings enrich the multiferroics in the two-dimensional system and enable a wide range of applications in nanoscale devices.

3D printing of bioinspired compartmentalized capsular structure for controlled drug release

Drug delivery with customized combinations of drugs,controllable drug dosage,and on-demand release kinetics is critical for personalized medicine.In this study,inspired by successive opening of layered structures and compartmentalized structures in plants,we designed a multiple compartmentalized capsular structure for controlled drug delivery.The structure was designed as a series of compartments,defined by the gradient thickness of their external walls and internal divisions.Based on the careful choice and optimization of bioinks composed of gelatin,starch,and alginate,the capsular structures were successfully manufactured by fused deposition modeling three-dimensional(3 D)printing.The capsules showed fusion and firm contact between printed layers,forming complete structures without significant defects on the external walls and internal joints.Internal cavities with different volumes were achieved for different drug loading as designed.In vitro swelling demonstrated a successive dissolving and opening of external walls of different capsule compartments,allowing successive drug pulses from the capsules,resulting in the sustained release for about 410 min.The drug release was significantly prolonged compared to a single burst release from a traditional capsular design.The bioinspired design and manufacture of multiple compartmentalized capsules enable customized drug release in a controllable fashion with combinations of different drugs,drug doses,and release kinetics,and have potential for use in personalized medicine.