| 1. |
- Bao, Jie, et al.
(author)
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Synthesis and Applications of Two-Dimensional Hexagonal Boron Nitride in Electronics Manufacturing
- 2016
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In: Electronic Materials Letters. - : Springer Science and Business Media LLC. - 1738-8090 .- 2093-6788. ; 12:1, s. 1-16
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Research review (peer-reviewed)abstract
- In similarity to graphene, two-dimensional (2D) hexagonal boron nitride (hBN) has some remarkable properties, such as mechanical robustness and high thermal conductivity. In addition, hBN has superb chemical stability and it is electrically insulating. 2D hBN has been considered a promising material for many applications in electronics, including 2D hBN based substrates, gate dielectrics for graphene transistors and interconnects, and electronic packaging insulators. This paper reviews the synthesis, transfer and fabrication of 2D hBN films, hBN based composites and hBN-based van der Waals heterostructures. In particular, this review focuses on applications in manufacturing electronic devices where the insulating and thermal properties of hBN can potentially be exploited. 2D hBN and related composite systems are emerging as new and industrially important materials, which could address many challenges in future complex electronics devices and systems.
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| 2. |
- Bao, Jie, 1982, et al.
(author)
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Two-dimensional hexagonal boron nitride as lateral heat spreader in electrically insulating packaging
- 2016
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In: Journal of Physics D: Applied Physics. - : IOP Publishing. - 1361-6463 .- 0022-3727. ; 49:July 2016, s. 265501-
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Journal article (peer-reviewed)abstract
- The need for electrically insulating materials with a high in-plane thermal conductivity for lateral heat spreading applications in electronic devices has intensified studies of layered hexagonal boron nitride (h-BN) films. Due to its physicochemical properties, h-BN can be utilised in power dissipating devices such as an electrically insulating heat spreader material for laterally redistributing the heat from hotspots caused by locally excessive heat flux densities. In this study, two types of boron nitride based heat spreader test structures have been assembled and evaluated for heat dissipation. The test structures separately utilised a few-layer h-BN film with and without graphene enhancement drop coated onto the hotspot test structure. The influence of the h-BN heat spreader films on the temperature distribution across the surface of the hotspot test structure was studied at a range of heat flux densities through the hotspot. It was found that the graphene-enhanced h-BN film reduced the hotspot temperature by about 8–10°C at a 1000 W/cm2 heat flux density, a temperature decrease significantly larger than for h-BN film without graphene enhancement. Finite element simulations of the h-BN film predict that further improvements in heat spreading ability are possible if the thermal contact resistance between the film and test chip are minimised.
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| 3. |
- Jiang, Di, 1983, et al.
(author)
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Embedded Fin-Like Metal/CNT Hybrid Structures for Flexible and Transparent Conductors
- 2016
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In: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 12:11, s. 1521-1526
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Journal article (peer-reviewed)abstract
- In this paper, an embedded fin-like metal-coated carbon nanotube (Fin-M/CNT) structure is demonstrated for flexible and transparent conductor wire applications. Embedded in a polydimethylsiloxane polymeric substrate, Fin-M/CNT wires with a minimum width of 5 μm and a minimum pitch of 10 μm have been achieved. Direct current resistances of single Fin-M/CNT wires, where the supporting CNT structures have been covered by Ti/Al/Au metal coatings of different thicknesses, have been measured. The high aspect ratio of the fin-like structures not only improves the adhesion between the wires and the polymeric substrate, but also yields a low resistance at a small surface footprint. In addition, transparent Fin-M/CNT grid lines with hexagonal patterns, with a sheet resistance of as low as 45 Ω sq−1, have been achieved at an optical transmittance of 88%. The robustness of the Fin-M/CNT structures has been demonstrated in bending tests up to 500 cycles and no significant changes in wire resistances are observed.
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| 4. |
- Mu, Wei, 1985, et al.
(author)
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Controllable and fast synthesis of bilayer graphene by chemical vapor deposition on copper foil using a cold wall reactor
- 2016
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In: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 304:15 November 2016, s. 106-114
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Journal article (peer-reviewed)abstract
- Bilayer graphene is attractive for digital device applications due to the appearance of a bandgap under application of an electrical displacement field. Controllable and fast synthesis of bilayer graphene on copper by chemical vapor deposition is considered a crucial process from the perspective of industrial applications. Here, a systematic investigation of the influence of process parameters on the growth of bilayer graphene by chemical vapor deposition in a low pressure cold wall reactor is presented. In this study, the initial process stages have been of particular interest. We have found that the influence of the hydrogen partial pressure on synthesis is completely the opposite from that found for traditional tubular quartz CVD in terms of its influence on the graphene growth rate. H2/CH4 ratio was also found to effectively influence the properties of the synthesized bilayer graphene in terms of its atomic structure, whether it be AB-stacked or misoriented. Different pre-treatments of the copper foil, in combination with different annealing processes, were used to investigate the nucleation process with the aim of improving the controllability of the synthesis process. Based on an analysis of the nucleation activity, adsorption-diffusion and gas-phase penetration were employed to illustrate the synthesis mechanism of bilayer graphene on copper foil. After optimization of the synthesis process, large areas, up to 90% of a copper foil, were covered by bilayer graphene within 15 minutes. The total process time is only 45 minutes, including temperature ramp-up and cool-down by using a low pressure cold wall CVD reactor.
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| 5. |
- Mu, Wei, 1985, et al.
(author)
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Double-Densified VerticallyAligned Carbon Nanotube Bundles for Application in 3D Integration High Aspect Ratio TSV Interconnects
- 2016
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In: Proceedings - Electronic Components and Technology Conference. - 0569-5503. - 9781509012046 ; 2016-August, s. 211-216
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Conference paper (peer-reviewed)abstract
- The treatment of densification by vapor on pristineMWCNT bundles are necessary to improve the effective area of the CNT TSV. However, the CNT bundles might tilt partly because of the non-uniform densification at root of the bundle, especially when it comes to the high aspect ratio CNT bundles. In order to solve these problems, a double densification process has been proposed and developed here. First of all, the shape of partial densified CNT bundles were optimized as a function of time. After several steps such as transferring of partial densified CNT bundles into the via, second densification, epoxy filling and chemical mechanical polishing, the CNT filled TSV with aspect ratio of 10 was achieved. The current voltage response of the CNT TSV interconnection indicated good electrical connection was formed. The resistivity of CNT bundles in via was calculated to be around 2-3 milli-ohmcm.
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| 6. |
- Mu, Wei, 1985, et al.
(author)
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Enhanced Cold Wall CVD Reactor Growth of Horizontally Aligned Single-walled Carbon Nanotubes
- 2016
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In: Electronic Materials Letters. - : Springer Science and Business Media LLC. - 1738-8090 .- 2093-6788. ; 12:3, s. 329-337
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Journal article (peer-reviewed)abstract
- Synthesis of horizontally-aligned single-walled carbon nanotubes (HA-SWCNTs) by chemical vapor deposition (CVD) directly on quartz seems very promising for the fabrication of future nanoelectronic devices. In comparison to hot-wall CVD, synthesis of HA-SWCNTs in a cold-wall CVD chamber not only means shorter heating, cooling and growth periods, but also prevents contamination of the chamber. However, since most synthesis of HA-SWCNTs is performed in hot-wall reactors, adapting this well-established process to a cold-wall chamber becomes extremely crucial. Here, in order to transfer the CVD growth technology from a hot-wall to a cold-wall chamber, a systematic investigation has been conducted to determine the influence of process parameters on the HA-SWCNT’s growth. For two reasons, the cold-wall CVD chamber was upgraded with a top heater to complement the bottom substrate heater; the first reason to maintain a more uniform temperature profile during HA-SWCNTs growth, and the second reason to preheat the precursor gas flow before projecting it onto the catalyst. Our results show that the addition of a top heater had a significant effect on the synthesis. Characterization of the CNTs shows that the average density of HA-SWCNTs is around 1-2 tubes/μm with high growth quality as shown by Raman analysis.
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| 7. |
- Mu, Wei, 1985, et al.
(author)
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Large area and uniform monolayer graphene CVD growth on oxidized copper in a cold wall reactor
- 2016
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In: IMAPS Nordic Annual Conference 2016 Proceedings. - 9781510827226
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Conference paper (peer-reviewed)abstract
- Graphene growth on copper in cold wall chemical vapor deposition (CVD) is not an inherently self- limiting process, which means that adlayers appear as long as there is sufficient growth time. The growth of large area and uniform monolayer becomes crucial and imminent. In this study, the pre-Treatment of oxidation was employed on copper. The results have shown that oxidation pre-Treatment in combination with argon annealing process would not only decrease the density of nucleation site, but also suppress the activity of nucleation site for the multilayer graphene growth. Therefore, large area and uniform monolayer graphene was obtained. The characterization of SEM. AFM and Raman analysis was also performed on either pristine graphene copper or transferred graphene on silicon oxide substrate.
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| 8. |
- Sun, Shuangxi, 1986, et al.
(author)
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Vertically aligned CNT-Cu nano-composite material for stacked through-silicon-via interconnects
- 2016
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In: Nanotechnology. - : IOP Publishing. - 1361-6528 .- 0957-4484. ; 27:33, s. Art no335705-
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Journal article (peer-reviewed)abstract
- 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 similar to 10(-8) Omega 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.
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| 9. |
- Zhang, Yong, 1982, et al.
(author)
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2D HEAT DISSIPATION MATERIALS FOR MICROELECTRONICS COOLING APPLICATIONS
- 2016
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In: China Semiconductor Technology International Conference 2016, CSTIC 2016. - 9781467388047
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Conference paper (peer-reviewed)abstract
- 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, had their heat dissipation performances 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.
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| 10. |
- Zhang, Yong, 1982, et al.
(author)
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Characterization and simulation of liquid phase exfoliated graphene-based films for heat spreading applications
- 2016
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In: Carbon. - : Elsevier BV. - 0008-6223. ; 106, s. 195-201
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Journal article (peer-reviewed)abstract
- This paper concerns the thermal properties of graphene-based films for heat spreading applications. Following liquid phase exfoliation (LPE) films were made by two different methods, vacuum filtration and drop coating. Temperature decreases of up to 6 °C and 4 °C were measured at a heat flux density of 1200 W/cm2 for the vacuum filtrated and drop coated films respectively. For the first time in this paper, three different methods were combined to evaluate and predict the thermal performance of such graphene-based films. Resistance thermometers were used to monitor the hotspot temperature decrease versus the Joule heat flow as a result of using graphene-based heat spreaders. The 3ω method was used to experimentally determine the in-plane and through-plane thermal conductivities of such films. A finite element model of the hotspot test structure was setup using the in-plane and through-plane thermal conductivities (110 and 0.25 W/mK, respectively) obtained from the 3ω measurements. Simulations were performed to predict the hotspot temperature decrease with excellent agreement obtained between all methods. The results indicate that the alignment and purity of the graphene-based films, as well as their thermal boundary resistance with respect to the chip, are key parameters when determining the thermal performance of graphene-based heat spreaders.
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