Carbon nanotube bumps for the flip chip packaging system

Carbon nanotube [CNT] interconnection bump joining methodology has been successfully demonstrated using flip chip test structures with bump pitches smaller than 150 μm. In this study, plasma-enhanced chemical vapor deposition approach is used to grow the CNT bumps onto the Au metallization lines. The CNT bumps on the die substrate are then 'inserted' into the CNT bumps on the carrier substrate to form the electrical connections (interconnection bumps) between each other. The mechanical strength and the concept of reworkable capabilities of the CNT interconnection bumps are investigated. Preliminary electrical characteristics show a linear relationship between current and voltage, suggesting that ohmic contacts are attained

Carbon nanotube fence-wall for radio frequency isolation

With an emergent need to miniaturize multifunctional radio frequency architectures, efficient designs have to be well thought. These include techniques to manage high power demands, electromagnetic compatibility between adjacent components and thermal management, in order to maintain desired performances. One way to address this is, through the use of nano-materials. However, there are many challenges faced with the use of such emerging materials, such as difficulty in implementation and effective integration into electronics. An example of such material is carbon nanotube. Carbon nanotubes have potential to be utilized in such a way due to its exemplary electrical, mechanical and thermal properties supported by both simulations and experimental data. However, like many emerging materials, there are existential issues that have to be addressed before its potential can be realized. One of the biggest challenges is synthesis compatibility with device integration, such as high temperature growth. These issues aside, a new area where carbon nanotubes could play an important role is in the area of on-circuit electromagnetic shielding. Carbon nanotubes are ideal for this due to it being light weight, electrically conductive and having high aspect ratios. This thesis is thus dedicated to the understanding of how, carbon nanotubes may be implemented into, and used to reduce electromagnetic interference in future high density components. The high growth temperature of carbon nanotube was first addressed. A stable and known synthesis technique of carbon nanotube was first evaluated. Key parameters that could affect carbon nanotube growth were identified. This was carried out using statistical design of experiment, to quantify the contribution of each parameter to the growth length of carbon nanotube. An alternate approach, termed the radiative approach was introduced. This approach allowed carbon nanotube growth to be conducted, without subjecting its substrate to high growth temperatures. This technique also allowed the substrate to remain at a lower temperature without compromising the high decomposition temperature of acetylene. As a result of systematic studies and optimization of parameters, substrate temperature of up to 420 °C was obtained, with growth length of 40 µm whilst the growth temperature remained at 600-650 °C. Raman spectroscopy was also used to examine the crystallinity of carbon nanotubes grown at low substrate temperatures. The disorder in sp2 was analyzed by the ratios of the characteristic defect and graphitic bands of carbon nanotubes. The Raman spectra observed in carbon nanotubes grown at different temperatures, and at different substrate temperature were contrasted. Next a study of how high density carbon nanotube forests, termed carbon nanotube fence-wall, were used for electromagnetic shielding was carried out. Here a new radio frequency isolation technique was demonstrated with improvement over current techniques in terms of performance and size. A full spectrum study, including design, simulation, fabrication and measurements were carried out. Passive structures made of microstrip lines and via-fences were first designed using Ansys full wave solver HFSS. A carbon nanotube bulk model that took into account the physical, geometrical and electrical properties of CNTs was used and implemented into the design in HFSS. S-parameters were simulated. Parametric studies were carried out by simulations, to identify factors that had effects on the electromagnetic shielding effectiveness of carbon nanotubes. Various test structures based on silicon, alumina and printed circuit boards were fabricated based on key simulation data. A variety of substrates were used, to take into account low cost applications, ease of implementation, substrate temperature budget and industrial needs. Here, 10 dB improvement in RF isolation was demonstrated, with 80 % reduction in lateral dimension as compared to the classical via-fencing technique. In this proof of concept, the simulation and measurement results were well correlated. In addition, measurements have also shown that, isolation attainable by the carbon nanotube fence-wall was comparable with that of bulk metal. Variants of the carbon nanotube fence-wall such as channelized fence and cavity were tested, to demonstrate different ways in which it may be implemented into electronic packages for electromagnetic shielding. The implication is, a potential light weight electromagnetic shield made of carbon nanotube that may be integrated into future systems. All in all, electromagnetic compatibility using carbon nanotubes for electronic package was studied. Some challenges faced by implementation of carbon nanotubes into nano-packages have been identified and dealt with. A possible solution to mitigate electromagnetic interference in next generation light-weight radio frequency components and applications has been proposed.Doctor of Philosophy (EEE

Synthesis and characterization of nanostructured Cr doped TiO2 materials for photocatalytic applications

Titanium Dioxide for applications as a photocatalyst has received much attention since its water splitting capability was discovered in 1972. However, the efficiency was a big drawback due to its large bandgap of 3.2 eV. Since 1990s, minded researchers have been focusing on shifting its bandgap into the visible light range so as to increase its efficiency. The various techniques utilized are not complex and cost effective. Visible light activity was not observed and efficiency remains low. Hence, its novelty through cheaper alternatives of synthesis suitable for commercialization proved to be very appealing. In this project, Chromium and Chromium Oxide doped titanium dioxide synthesized by high energy ball milling technique are studied. The high energy ball milling technique is cheap and is a solid state top-down method where breaking and making of new bonds can lead to the synthesis of novel materials suitable for photocatalysis applications. Their physical and optical characteristics were studies. A test of its photocatalytic reactivity was also investigated. The powders were then fabricated into composite films, using the modified sol-gel technique, for ease of application testing. In this method, the synthesized powders are distributed and incorporated into a film, whose conditions is symbolic to a coating on a wall. Similarly, their optical and physical properties were discussed.MASTER OF ENGINEERING (EEE

Mildly reduced graphene oxide-Ag nanoparticle hybrid films for surface-enhanced Raman scattering

Large-area mildly reduced graphene oxide (MR-GO) monolayer films were self-assembled on SiO2/Si surfaces via an amidation reaction strategy. With the MR-GO as templates, MR-GO-Ag nanoparticle (MR-GO-Ag NP) hybrid films were synthesized by immersing the MR-GO monolayer into a silver salt solution with sodium citrate as a reducing agent under UV illumination. SEM image indicated that Ag NPs with small interparticle gap are uniformly distributed on the MR-GO monolayer. Raman spectra demonstrated that the MR-GO monolayer beneath the Ag NPs can effectively quench the fluorescence signal emitted from the Ag films and dye molecules under laser excitation, resulting in a chemical enhancement (CM). The Ag NPs with narrow gap provided numerous hot spots, which are closely related with electromagnetic mechanism (EM), and were believed to remarkably enhance the Raman signal of the molecules. Due to the co-contribution of the CM and EM effects as well as the coordination mechanism between the MR-GO and Ag NPs, the MR-GO-Ag NP hybrid films showed more excellent Raman signal enhancement performance than that of either Ag films or MR-GO monolayer alone. This will further enrich the application of surface-enhanced Raman scattering in molecule detection.Published versio

Carbon nanotubes based RF packaging solutions

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Carbon nanotube cavity for compact Radar components

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Flip Chip Based on Carbon Nanotube-Carbon Nanotube Interconnected Bumps for High-Frequency Applications

International audienceThis paper presents a flip-chip structure based on carbon nanotube (CNT) interconnected bumps for high-frequency applications. The CNT bumps are grown directly on gold coplanar lines using the plasma-enhanced chemical vapor deposition approach, and the CNT bumps are interconnected using a flip-chip bonder. DC and high-frequency measurements from flip-chip input to output are characterized and compared against electromagnetic simulation of CNT bumps and gold bumps. S-parameter transmission of -2.5 dB up to 40 GHz was obtained using CNT bumps in this experiment. Experimental transmission across the CNT bumps demonstrates the feasibility of using CNT bundles for future interconnects at smaller scale (few micrometers) and at even higher frequencies. This is the first work using CNT bumps for flip-chip structures and serves as a platform for future studies of CNT interconnects above 40 GHz

Improved rf isolation using carbon nanotube fence-wall for 3-d integrated circuits and packaging

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A light-weight electromagnetic shield using high density carbon nanotube fence-wall for RF packaging

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