| 1. |
- Fu, Yifeng, 1984, et al.
(author)
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A complete carbon-nanotube-based on-chip cooling solution with very high heat dissipation capacity
- 2012
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In: Nanotechnology. - : IOP Publishing. - 1361-6528 .- 0957-4484. ; 23:4
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Journal article (peer-reviewed)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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| 2. |
- Fu, Yifeng, 1984
(author)
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Carbon Nanotubes for Electronic Packaging: Growth, Novel Devices and 3D Networks
- 2012
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Doctoral thesis (other academic/artistic)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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| 3. |
- Fu, Yifeng, 1984, et al.
(author)
-
Selective growth of double-walled carbon nanotubes on gold films
- 2012
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In: Materials Letters. - : Elsevier BV. - 1873-4979 .- 0167-577X. ; 72, s. 78-80
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Journal article (peer-reviewed)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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| 4. |
- Fu, Yifeng, 1984, et al.
(author)
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Templated Growth of Covalently Bonded Three-Dimensional Carbon Nanotube Networks Originated from Graphene
- 2012
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In: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 24:12, s. 1576-1581
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Journal article (peer-reviewed)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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| 5. |
- Fu, Yifeng, 1984, et al.
(author)
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Thick film patterning by lift-off process using double-coated single photoresists
- 2012
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In: Materials Letters. - : Elsevier BV. - 1873-4979 .- 0167-577X. ; 76, s. 117-119
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Journal article (peer-reviewed)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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| 6. |
- Gao, Zhaoli, et al.
(author)
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Graphene Heat Spreader for Thermal Management of Hot Spots in Electronic Packaging
- 2012
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In: Proceedings of the 18th Therminic International Workshop on Thermal Investigations of ICs and Systems. - 9782355000225 ; , s. 217-220
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Conference paper (peer-reviewed)abstract
- Monolayer graphene was fabricated using thermal CVD for the application of heat spreader in electronic packaging. Platinum (Pt) micro-heater embedded thermal testing chips were utilized to evaluate the thermal performance of the graphene heat spreader. The hot spot temperature was decreased by about 5 degrees C at a heat flux of up to 800W/cm2. It is possible to further improve the thermal performance of graphene heat spreader by optimizing the synthesis parameters and transfer process.
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| 7. |
- Hu, Zhili, 1983, et al.
(author)
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Detecting single molecules inside a carbon nanotube to control molecular sequences using inertia trapping phenomenon
- 2012
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 101:13, s. Art. no. 133105-
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Journal article (peer-reviewed)abstract
- Here we show the detection of single gas molecules inside a carbon nanotube based on the change inresonance frequency and amplitude associated with the inertia trapping phenomenon. As its directimplication, a method for controlling the sequence of small molecule is then proposed to realize theconcept of manoeuvring of matter atom by atom in one dimension. The detection as well as theimplication is demonstrated numerically with the molecular dynamics method. It is theoreticallyassessed that it is possible for a physical model to be fabricated in the very near future.
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| 8. |
- Jiang, Di, 1983, et al.
(author)
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Room Temperature Transfer of Carbon Nanotubes on Flexible Substrate
- 2012
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In: Proceedings of the 18th Therminic International Workshop on Thermal Investigations of ICs and Systems, Budapest, 25-27 September 2012. - 9782355000225 ; , s. 213-216
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Conference paper (peer-reviewed)abstract
- In this paper we report a novel method of transferring thermally grown vertically aligned carbon nanotubes (VA-CNTs) onto flexible substrates at room temperature with a single-step process. The transfer process is carried out by placing the CNT forests upside down on a double sided thermal release adhesive tape and peeling off the silicon substrate. Scanning electron microscope (SEM) is used to observe the transfer results. Also a second transfer using the same method but a thermal tape with higher release temperature is repeated on the as-transferred CNTs forests. The results show that this method is able to provide a novel process for transferring CNT forests at room temperature. This process will help to bring close the low cost fabrication of vertically aligned CNT structures for electronics.
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