| 1. |
- Liu, Johan, 1960, et al.
(författare)
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1. Thermal Characterization of Power Devices Using Graphene-based Film
- 2014
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Ingår i: Proceedings - Electronic Components and Technology Conference. - 0569-5503. - 9781479924073 ; , s. 459 - 463
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Konferensbidrag (refereegranskat)abstract
- Due to its atomic structure with sp2 hybrid orbitals and unique electronic properties, graphene has an extraordinarily high thermal conductivity which has been reported to be up to 5000 W/mK. As a consequence, the use of graphene-based materials for thermal management has been subject to substantial attention during recent years in both academia and industry. In this paper, the development of a new type of graphene-based thin film for heat dissipation in power devices is presented. The surface of the developed graphene based film is primarily composed of functionalized graphene oxide, that can be bonded chemically to the device surface and thus minimize the interface thermal resistance caused by surface roughness. A very high in-plane thermal conductivity with a maximum value of 1600 W/mK was detected by laser flash machine regarding to the graphene-based films. To investigate the structure of the graphene-based films, scanning electron microscopy (SEM) and raman spectroscopy were carried out. Finally, LED demonstrators were built to illustrate the thermal performance of graphene-based film and the functional layers. IR camera recorded a 5°C lower temperature of a LED demonstrator with SHT G1000 as the binding layer instead of a commercial thermal conductive adhesive.
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| 2. |
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| 3. |
- Daon, J., et al.
(författare)
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Electrically conductive thermal interface materials based on vertically aligned carbon nanotubes mats
- 2014
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Ingår i: IEEE 20th International Workshop on Thermal Investigation of ICs and Systems (Therminic). Greenwich, London, United Kingdom, 24-26 September 2014. - 9781479954155
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 4. |
- Fan, X., et al.
(författare)
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Reliability of carbon nanotube bumps for chip on glass application
- 2014
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Ingår i: Proceedings of the 5th Electronics System-Integration Technology Conference, ESTC 2014. - 9781479940264 ; , s. Art. no. 6962753-
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Konferensbidrag (refereegranskat)abstract
- Carbon nanotubes (CNTs) are an ideal candidate material for electronic interconnects due to their extraordinary thermal, electrical and mechanical properties. In this study, densified CNT bumps utilizing the paper-mediated controlled method were applied as the interconnection for chip on glass (COG) applications, and the silicon chip with patterned CNT bumps was then flipped and bonded onto a glass substrate using anisotropic conductive adhesive (ACA) at a bonding pressure of 127.4 Mpa, 170°C for 8 seconds. The electrical properties of the COG were evaluated with the contact resistance of each bump measured using the four-point probe method. Three different structure traces, marked as Trace A, Trace B, and Trace C, were tested, respectively. Thermal cycling (-40 to 85°C, 800 cycles) and damp heat tests (85°C/85% RH, 1000 hours) were also conducted to evaluate the reliability of the CNT-COG structure. The average contact resistance of the samples was recorded during these tests, in which there was no obvious electrical failure observed after both the thermal cycling and damp heat tests. The results of these tests indicated that the COG has good reliability and the CNT bumps have promising potential applications in COG.
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| 5. |
- Fu, Yifeng, 1984, et al.
(författare)
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A complete carbon-nanotube-based on-chip cooling solution with very high heat dissipation capacity
- 2012
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Ingår i: Nanotechnology. - : IOP Publishing. - 1361-6528 .- 0957-4484. ; 23:4
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Tidskriftsartikel (refereegranskat)abstract
- Heat dissipation is one of the factors limiting the continuous miniaturization of electronics. In the study presented in this paper, we designed an ultra-thin heat sink using carbon nanotubes (CNTs) as micro cooling fins attached directly onto a chip. A metal-enhanced CNT transfer technique was utilized to improve the interface between the CNTs and the chip surface by minimizing the thermal contact resistance and promoting the mechanical strength of the microfins. In order to optimize the geometrical design of the CNT microfin structure, multi-scale modeling was performed. A molecular dynamics simulation (MDS) was carried out to investigate the interaction between water and CNTs at the nanoscale and a finite element method (FEM) modeling was executed to analyze the fluid field and temperature distribution at the macroscale. Experimental results show that water is much more efficient than air as a cooling medium due to its three orders-of-magnitude higher heat capacity. For a hotspot with a high power density of 5000 W cm(-2), the CNT microfins can cool down its temperature by more than 40 degrees C. The large heat dissipation capacity could make this cooling solution meet the thermal management requirement of the hottest electronic systems up to date.
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| 6. |
- Fu, Yifeng, 1984, et al.
(författare)
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Application of through silicon via technology for in situ temperature monitoring on thermal interfaces
- 2010
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Ingår i: Journal of Micromechanics and Microengineering. - : IOP Publishing. - 1361-6439 .- 0960-1317. ; 20:2, s. id 025027 (5 pp)-
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a series of micro-machining processes have been developed to fabricate a test platform with the ability of in situ temperature monitoring on thermal interface behaviour. Through silicon vias (TSVs) with an aspect ratio up to 13 using Cu as a conductor have been applied to connect an array of platinum-based temperature sensors directly deposited on the thermal interfaces to be measured. The sensors are subsequently calibrated by an industry standard resistance temperature detector. Results show that the temperature sensors function normally in a temperature range up to 250 degrees C. This demonstrates the successful deposition of temperature-sensing materials and their good connection to the TSVs. The realization of direct precise temperature measurement on the thermal interface of this test platform enables thermal characterization with a high accuracy.
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| 7. |
- Fu, Yifeng, 1984
(författare)
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Carbon Nanotubes for Electronic Packaging: Growth, Novel Devices and 3D Networks
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Carbon nanotubes (CNTs) have shown great potential of application in electronics because of their attractive physical properties, such as high surface-to-volume ratio, high electron mobility, high Young’s modulus, high thermal conductivity, low thermal expansion coefficient, etc. However, many obstacles are yet to be removed to use CNTs as building blocks in electronic systems. This thesis is attempting to overcome some of the challenges that hinder the implementation of CNTs in electronic packaging.The first section concerns about the most essential issue in CNT application, the growth of CNTs. A new method is presented and it is capable of highly selective growth of CNTs, which is one of the main challenges in the CNT technology field. By growing CNTs on gold films using thermal chemical vapor deposition (TCVD) method, the number of CNT walls can be well controlled and statistical study shows that a selectivity of 79.4% can be achieved for double-walled CNTs.The second section presents the design and fabrication of a CNT based on-chip cooler, attempting to utilize CNTs for heat dissipation from electronic systems. A test platform with integrated heating elements and temperature sensors is designed and fabricated for this purpose. A new CNT transfer technology is developed to transplant the CNT microfins with pre-defined structures to desired positions on the test platform. Electrical and mechanical characterizations demonstrate that the CNT-substrate interface has been dramatically improved after the transfer process therefore addressed two of the most challenging tasks on integrating CNTs into electronics, i.e. decreasing the huge interfacical contact resistance and improving the weak adhesion between CNTs and substrates. A double-coated single photoresist structure for thick materials deposition is also developed to facilitate and simplify the CNT transfer process. Multi-scale modeling is performed to help design the CNT microfin structure. A molecular dynamics simulation (MDS) is carred out to investigate the interaction between water and CNTs at the nanoscale and a finite element method (FEM) modeling is executed to analyze the fluid field and temperature distribution at the macroscale. A novel packaging process using polydimethylsiloxane (PDMS) is also developed to assemble the CNT microfins, the test platform, the fluid channel and the supporting substrate into an integrated system. Cooling experiments have demonstrated the high efficiency of the CNT-based on-chip cooler.The third section describes a novel concept to grow covalently bonded three dimensional CNT networks, which is potentially applicable to facilitate thermal transportation in micro systems. A nickel nitrate dissolved polymer is electrospun into inter-connected porous nano fiber networks acting as precursor. The polymer fibers are then burned out and nickel nitrate is decomposed at high temperature into nickel oxide fibers. These fibers are subsequently reduced into pure nickel in hydrogen environment. The as-reduced nickel nano fiber network serves as catalyst to grow graphite layers on their surfaces. Ultimately, the nickel core is etched by iron chloride so that graphite tubes, i.e. CNT structures are left. Since the nickel fibers are inter-connected with each other and graphite layers can only grow on the surface, the as-grown CNT network is covalently bonded. Atomic force microscopy (AFM) based bending tests show that the Young’s modulus of the as-grown CNTs is about 〖391〗_(-172)^(+270) GPa, and the covalently bonded CNT structure can effectively distribute external loading throughout the network to improve the mechanical strength of the material.
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| 8. |
- Fu, Yifeng, 1984, et al.
(författare)
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Selective growth of double-walled carbon nanotubes on gold films
- 2012
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Ingår i: Materials Letters. - : Elsevier BV. - 1873-4979 .- 0167-577X. ; 72, s. 78-80
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Tidskriftsartikel (refereegranskat)abstract
- Growth of high-quality vertical aligned carbon nanotube (CNT) structures on silicon supported gold (Au) films by thermal chemical vapor deposition (TCVD) is presented. Transmission electron microscopy (TEM) images show that the growth is highly selective. Statistical study reveals that 79.4% of the as-grown CNTs are double-walled. The CNTs synthesized on Au films are more porous than that synthesized on silicon substrates under the same conditions. Raman spectroscopy and electrical characterization performed on the as-grown double-walled CNTs (DWNTs) indicate that they are competitive with those CNTs grown on silicon substrates. Field emission tests show that closed-ended DWNTs have lower threshold field than those open-ended.
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| 9. |
- Fu, Yifeng, 1984, et al.
(författare)
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Templated Growth of Covalently Bonded Three-Dimensional Carbon Nanotube Networks Originated from Graphene
- 2012
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 24:12, s. 1576-1581
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Tidskriftsartikel (refereegranskat)abstract
- A template-assisted method that enables the growth of covalently bonded three-dimensional carbon nanotubes (CNTs) originating from graphene at a large scale is demonstrated. Atomic force microscopy-based mechanical tests show that the covalently bonded CNT structure can effectively distribute external loading throughout the network to improve the mechanical strength of the material.
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| 10. |
- Fu, Yifeng, 1984, et al.
(författare)
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Thick film patterning by lift-off process using double-coated single photoresists
- 2012
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Ingår i: Materials Letters. - : Elsevier BV. - 1873-4979 .- 0167-577X. ; 76, s. 117-119
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Tidskriftsartikel (refereegranskat)abstract
- A novel method using lift-off process for patterning very thick materials is developed and demonstrated. Unlike conventional lift-off processes, no special lift-off resist is used in this method. Instead, only a double-coated single photoresist is needed. Demonstrations using two commercial photoresists show that good patterning morphology and obvious undercuts as high as 15 mu m are obtained for lift-off, which is very difficult to achieve by existing methods. The application and feasibility of this approach is demonstrated by a carbon nanotube transfer process. This simple and effective method offers wider option to pattern very thick materials in high quality which are in strong demands.
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