Xingang Yu

Thermal management performance of bent graphene nanoribbons

The models of graphene nanoribbons (GNRs) with angles 0°, 30°, 60°, 90° and 120° were constructed to investigate the thermal conduction by using the reverse non-equilibrium molecular dynamics method. A substantially negative correlation between the thermal conductivity and the bent angle shows a nonlinear decline from 0° to 90°. It also shows that there is a little increase from 90° to 120° due to the edge effect. To weaken the edge effect, the nitrogen doping method is adopted to recompose the bent GNRs. The results show that it is effective for the thermal management, and a strict monotonous relationship between the thermal conductivity and bent angle can be obtained. In the meantime, an interesting phenomenon is observed that the GNRs with edge modification by N-doping can get a much better thermal conduction than original GNRs without edge modification. We can understand the physical mechanism by phonon analysis for these GNRs. The investigation implies that we can change the thermal conductivity of GNRs by design by N-doping.

Investigation of thermal resistance for the graphene-Si interface by molecular dynamics

The thermal resistance of the graphene-Si interface is systematically investigated based on the micro-canonical ensemble (NVE) by using three kinds of interaction potentials. When the system reaches the steady state, the heat flux is applied to the model. The results show that the thermal resistance of the graphene-Si interface is weakened because of the defect in graphene. Defect in graphene leads to a sharp decline of the interfacial thermal resistance. However, the interfacial thermal resistance declines gradually with the defect area increase. When the defect area is increased to 19.7% of the total area, the interfacial thermal resistance tends to be stable.

Numerical investigation on the thermal reliability and layout optimisation of printed circuit board level

The reliability of printed circuit board level is investigated through the optimisation of layout, power and heat dissipating. Different models of AMD HD5550 circuit module are built with different parameters combination based on computational fluid dynamics (CFD) theory. The thermal structures of these models are simulated by FLOTHERM. The result shows that thermal layout has a significant effect on the thermal reliability of the modules. The thickness of heat sink substrate also affects the temperature distribution of the board. The method and result supply a theoretical reference value for thermal design of the printed circuit board level.

First-principle investigation of electronic structure and optical properties of In-doped wurtzite ZnO

The electronic structure and optical properties of pure ZnO and 12.5% In-doped Zn 0.875 In 0.125 O are calculated by first-principle method based on density functional theory (DFT). The results reveal that the lattice constants of ZnO cell become larger but the band gap narrows. Moreover, the absorption of ultraviolet-visible light is enhanced and an absorption peak appears in the near infrared region. The results show that the imaginary part of dielectric function of Zn 0.875 In 0.125 O has the increasing trend compared with pure ZnO. It builds the theoretical basis for the design and practical application of ZnO-based transparent conductive material.

A numerical approach on life-prediction of solder joints under combined loading for chip packaging system

The aim of this paper is to provide a numerical approach to predict the lifetime of solder joints by considering combined loading based on the damage superposition. The deformations of solder joints are calculated under vibration and thermal cycling loading respectively. The calculated results are defined as boundary conditions of the multi-axial loading. The strain/stress is investigated by finite element method based on the Chaboche model. The fatigue damage and creep damage are calculated by using the Manson-Coffin equation. It reveals that there is a strong non-linear impact on the lifetime due to the interaction of the combined loading. The trend of the simulation results basically agrees with that of the tests results. The approach can be used to predict the solder joint lifetime under combined loading.

The effect of N-doping on the electronic structure of graphene nanoribbon

To analyse the effect on electronic structure of nitrogen-doped graphene nanoribbons, the parameters such as the lattice, band structure, density of states of intrinsic graphene nanoribbon, N-doped graphene nanoribbons are calculated by using first-principle method. The results demonstrate that the band gap of graphene nanoribbon mainly comes from the new surface states in the edge. The N-doping in the middle of graphene nanoribbon has less influence on the band gap performance than in the edge region, which indicates the atoms in the edge do great contribution to the band gap properties. The N-doping makes the band gap narrower; the sharp changes of the band gap also show that the N-doping is a promising candidate to make the n-type graphene structures.

Hybrid modeling and analysis on the interfacial characteristics of Cu/Al interface structures in IC packaging with wire bonding

With the development of micro/nano electronic technology and the miniaturization of IC (Integrated Circuit) packaging, the interfacial characteristics of the nanoscale interface structure in IC packaging become more and more serious on the whole performance of IC or devices. The aim of this article is to put forward a hybrid scale method to evaluate the interfacial thermal characteristics of the Cu/Al interface structure in IC packaging with Cu wires and Al pads. In this hybrid method, the EAM (Embedded Atom Method) potential is used to describe the Cu and Al atoms; the LJ (Lennard-Jones) potential is used to describe the Van der Waals force between Cu and Al atoms in MD (Molecular Dynamics) simulation at the nanoscale situation; meanwhile, the FE (Finite Element) and ISE (Interface Stress Element) are used to calculate the performance in the Micro/macroscales. It supplies a hybrid method to evaluate the interfacial properties in the IC packaging, which is helpful to design and manufacture of IC assembly.

Effect of oil film temperature on hydro-viscous drive characteristics

To explore the effect of oil film temperature on hydro-viscous drive (HVD), a 3D physical model of the oil film was established. According to the principle of computational fluid dynamics (CFD), the model was solved by using finite volume method (FVM), and a HVD test-bed was developed to verify the theoretical analysis. The results show that the relationship between the temperature and the time is approximately linear. Meanwhile, the temperature of the oil film goes up gradually along the radial direction, and its value at zone without groove is much higher than that at zone with groove. The theoretical torque transferred by the oil film is larger than the experimental value, and the torque reduces when considering the effect of oil film temperature. The research results play a guiding role in the thorough research on the HVD technology, and provide technical support for the design of the HVD device.