Shuangxi Sun

Vertically aligned CNT-Cu nano-composite material for stacked through-silicon-via interconnects

For future miniaturization of electronic systems using 3D chip stacking, new fine-pitch materials for through-silicon-via (TSV) applications are likely required. In this paper, we propose a novel carbon nanotube (CNT)/copper nanocomposite material consisting of high aspect ratio, vertically aligned CNT bundles coated with copper. These bundles, consisting of hundreds of tiny CNTs, were uniformly coated by copper through electroplating, and aspect ratios as high as 300:1 were obtained. The resistivity of this nanomaterial was found to be as low as ∼10(-8) Ω m, which is of the same order of magnitude as the resistivity of copper, and its temperature coefficient was found to be only half of that of pure copper. The main advantage of the composite TSV nanomaterial is that its coefficient of thermal expansion (CTE) is similar to that of silicon, a key reliability factor. A finite element model was set up to demonstrate the reliability of this composite material and thermal cycle simulations predicted very promising results. In conclusion, this composite nanomaterial appears to be a very promising material for future 3D TSV applications offering both a low resistivity and a low CTE similar to that of silicon.

Mechanical and thermal characterization of a novel nanocomposite thermal interface material for electronic packaging

This paper presents a novel nanocomposite thermal interface material (Nano-TIM) consisting of a silver coated polyimide network and the indium matrix. One of the potential applications of this Nano-TIM is for heat dissipation in integrated circuits and electronic packaging. The shear strength of the Nano-TIM was investigated with DAGE-4000PSY shear tester. The shear strength of Nano-TIM is 4.5 MPa, which is 15% higher than that of the pure indium thermal interface material. The microstructure of cross-section and fracture surface was studied using Scanning Electron Microscopy (SEM). SEM pictures show a uniform polymer fiber distribution and solid interface between silver coated fibers and indium matrix. The thermal fatigue resistance of the Nano-TIM was evaluated by monitoring the variation of thermal interface resistance during the thermal cycling test (-40 to 125 degrees C). The thermal interface resistance was measured with a commercial xenon flash instrument after 100, 200, 300, 400, 500, and 1000 temperature cydes. The results-of thermal cycling test show that Nano-TIM presented consistent reliability performance with pure indium. Furthermore, the tooling effect of Nano-TIM was demonstrated through measuring the power chip temperature in the die attached structure by using an Infrared Camera. In the test, the Nano-TIM shows a comparable cooling effect to pure indium TIM for die attach applications in electronics packaging.

Characterization for graphene as heat spreader using thermal imaging method

Monolayer graphene was synthesized through thermal chemical vapor deposition (TCVD) as heat spreader in electronic packaging. Platinum (Pt) was functioned as hot spot of thermal testing chip. The hot spot temperature of thermal testing chip bonded onto a heat sink measured by an FLIR infrared thermograph was decreased by about 5 °C from 52 °C to 47 °C when driven at a heat flux about 1280W/cm2 with a graphene heat spreader attached. It is conceivable that further improvements to the cooling performance of graphene heat spreader can be made by optimizing the synthesis parameters and transfer process.

Electrically conductive thermal interface materials based on vertically aligned carbon nanotubes mats

In power microelectronics, the trends towards miniaturization and higher performances result in higher power densities and more heat to be dissipated. In most electronic assembly, thermal interface materials (TIM) help provide a path for heat dissipation but still represent a bottleneck in the total thermal resistance of the system. VA-CNTs mats are typically grown on HR silicon substrate with Al2O3 diffusion barrier layer using Thermal CVD process. In many cases, “die attach” thermal interface materials need to be electrically conductive and the growth of dense VA-CNT mats on an electrically conductive substrate remains a challenge. This paper presents the growth of dense VA-CNT mats on doped silicon with Al2O3 and TiN diffusion barrier layer. Processes, thermal and electrical characterization of VA-CNTs based thermal interface materials are studied and reported.

Graphene based heat spreader for high power chip cooling using flip-chip technology

Monolayer graphene was synthesized through thermal chemical vapor deposition (TCVD) as heat spreader for chip cooling. Platinum (Pt) serpentine functioned as hot spot on the thermal testing chip. The thermal testing chip with monolayer graphene film attached was bonded using flip-chip technology. The temperature at the hot spot with a monolayer graphene film as heat spreader was decreased by about 12°C and had a more uniform temperature compared to those without graphene heat spreader when driven by a heat flux of about 640W/cm2. Further improvements to the cooling performance of graphene heat spreader could be made by optimizing the synthesis parameters and transfer process of graphene films.

Dissipating heat from hot spot using a new nano thermal interface material

The need for faster, smaller, more reliable and efficient products has resulted in increased heat generated in microelectronic components. Removal of the heat generated is an important issue in electronic packaging. Therefore, a novel Nano-Thermal Interface Material was developed to improve this. This paper aims at studying the thermal performance of the new nano-structured polymer-metal composite film (Nano-TIM) in application for dissipating around hot spots which exist in non-uniform power generation. Through semiconductor process and Micron-RTD principle, 5*5mm2 thermal test chips were developed to serve as a heat source for detecting the heat dissipation effect of the Nano-TIM. T3Ster test system and IR Camera were used to measure partial thermal resistance of the 50 and 75 um Nano-TIM layer and study the spread of different hot spot positions in 10*10mm2 power chip. We also studied the hot spot dissipation effect under different die attach areas with the Nano-TIM. According to the results of this study, this new class of Nano-TIM can meet the high requirements for hot spot dissipation of highly non-uniform power distribution in electronics packaging.

Control of Nanoplane Orientation in voBN for High Thermal Anisotropy in a Dielectric Thin Film: A New Solution for Thermal Hotspot Mitigation in Electronics

High anisotropic thermal materials, which allow heat to dissipate in a preferential direction, are of interest as a prospective material for electronics as an effective thermal management solution for hot spots. However, due to their preferential heat propagation in the in-plane direction, the heat spreads laterally instead of vertically. This limitation makes these materials ineffective as the density of hot spots increases. Here, we produce a new dielectric thin film material at room temperature, named vertically ordered nanocrystalline h-BN (voBN). It is produced such that its preferential thermally conductive direction is aligned in the vertical axis, which facilitates direct thermal extraction, thereby addressing the increasing challenge of thermal crosstalk. The uniqueness of voBN comes from its h-BN nanocrystals where all their basal planes are aligned in the direction normal to the substrate plane. Using the 3ω method, we show that voBN exhibits high anisotropic thermal conductivity (TC) with a 16-fold difference between through-film TC and in-plane TC (respectively 4.26 and 0.26 W·m-1·K-1). Molecular dynamics simulations also concurred with the experimental data, showing that the origin of this anisotropic behavior is due to the nature of voBNs plane ordering. While the consistent vertical ordering provides an uninterrupted and preferred propagation path for phonons in the through-film direction, discontinuity in the lateral direction leads to a reduced in-plane TC. In addition, we also use COMSOL to simulate how the dielectric and thermal properties of voBN enable an increase in hot spot density up to 295% compared with SiO2, without any temperature increase.

Evaluating CNT-Based Interconnects : A Nummerical Tool to Characterize Hybrid CNT-Copper Interconnects

Nanotechnologies offer a vast number of applications due to the unique features of nanostructured materials [1]. In the electronics field, this new technology could open innovative ways to go beyond Moores law [2], but progress in manufacturing technology still limits the wide dispersion of nanotechnology-based circuits. The bridge between nanoscience and realized devices can be achieved by modeling the multiphysics phenomena at the nanoscale, which will aid in the development of the technology.

Hotspot test structures for evaluating carbon nanotube microfin coolers and graphene-like heat spreaders

The design, fabrication, and use of a hotspot-producing and temperature-sensing test structure for evaluating the thermal properties of carbon nanotubes, graphene and boron nitride for cooling of electronic devices in applications like 3D integrated chip-stacks, power amplifiers and light-emitting diodes is described. The test structure is a simple meander-shaped metal resistor serving both as the hotspot and the temperature thermo-meter. By use of this test structure, the influence of emerging materials like those mentioned above on the temperature of the hotspot has been evaluated with good accuracy (±0.5°C).

2D heat dissipation materials for microelectronics cooling applications

The need for faster and smaller, as well as more reliable and efficient consumer electronic products has resulted in microelectronic components that produce progressively more heat. The resultant reliability issues from the increased heat flux are serious and hinder technological development. One solution for microelectronics cooling applications is 2D materials applied as heat spreaders and these include monolayer graphene, graphene based films, and monolayer hexagonal boron nitride and BN based films. In addition, thermal performances of the graphene heat spreader were also studied under different packaging structures, including wire bonding, cooling fins and flip chips. Finally, 2D hexagonal Boron nitride (h-BN) heat spreaders, fabricated by different methods, were characterized by different thermal characterization methods, such as resistance temperature detector (RTD) and Infrared (IR) methods. In conclusion, these new novel 2D materials developed show great potential for microelectronics cooling applications.