Three-dimensional System Integration Research Articles

Mechanisms of copper protrusion in through-silicon-via structures at the nanoscale

Thermal stress-induced copper protrusion is frequently observed in through-silicon-vias (TSVs) based three-dimensional system integration. In this study, the detailed process of Cu protrusion is reproduced on the atomic scale using a two-mode phase-field-crystal (PFC) model, and the mechanisms of protrusion are identified. To simulate thermal loading, a “penalty term” is added to the governing equation of the PFC model. The application of loading on the TSVs induces copper grain deformation and grain boundary (GB) migration at the nanoscale. Furthermore, the simulation results suggest that the Cu protrusion is resulted from diffusional creep, involving both Nabarro–Herring creep and Coble creep. The obtained power index of diffusional creep p is around 2.16, suggesting that lattice diffusion contributes more to protrusion than GB diffusion does. The protrusion height in micron-scale TSVs predicted by extrapolating the relationship between the protrusion height and diameter of nanoscale TSVs agrees with the experimental data.

Novel Three-Dimensional Packaging Approaches Using Magnetically Aligned Anisotropic Conductive Adhesive for Microwave Applications

Upon the application of a magnetic field, ferromagnetic particles will self-align along the field lines of the applied field. Rods are thus formed that can grow until they are stopped by a substrate after application of a material and at the angle of the applied field. The dynamic growth of the columns is beneficial for implementing packages with complicated three-dimensional system integration. The growth of the rods, internal to the material, has the ability to adapt to the gap between pads or even an angle between the substrates. In this work, we demonstrate these advantages by showing multilayer interconnects as well as angled connections for three-dimensional vertical chip stacking concepts. Four layers of silicon on top of each other were integrated with multilayer interconnects and the RF performance is demonstrated. In addition, we implemented a novel three-dimensional packaging structure for a horizontal-to-vertical plane transition, with the performance evaluated for a variety of angles. Consequently, the Z-axis anisotropic conductive adhesive is shown to be a suitable solution to implement advanced three-dimensional integrated microwave applications.

A 33% Improvement in Efficiency of Wireless Inter-Chip Power Delivery by Thin Film Magnetic Material for Three-Dimensional System Integration

An improvement in the efficiency of wireless inductive-coupling inter-chip power delivery using thin film magnetic material is introduced for the first time. In order to improve the efficiency, we proposed a method of attaching thin film magnetic material with the capability of high-frequency operation. The attached magnetic material enhances the magnetic flux generated by on-chip inductors. The proposed technique is cost effective since it does not require modification in LSI manufacturing process. To verify the effectiveness of the proposed technique, we designed and fabricated test chips using 0.18 µm complementary metal oxide semiconductor (CMOS) technology. The measured transferred power was improved from 36 to 48 mW, at which operational frequency is optimized to 140 MHz. The measured results show that efficiency was improved by 33%.