Dunlin Tan

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

This 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.

Re-ordering Chaotic Carbon: Origins and Application of Textured Carbon

Formation of nanocrystals with preferred orientation within the amorphous carbon matrix has attracted lots of theoretical and experimental attentions recently. Interesting properties of this films, easy fabrication methods and practical problems associated with the growth of other carbon nanomaterials such as carbon nanotubes (CNTs) and graphene gives this new class of carbon nanostructure a potential to be considered as a replacement for some applications such as thermal management at nanoscale and interconnects. In this short review paper, the fabrication techniques and associated formation mechanisms of these nanostructured films have been discussed. Besides, electrical and thermal properties of these nanostructured films have been compared with CNTs and graphene.

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.

Carbon Nanostructures Dedicated to Millimeter-Wave to THz Interconnects

This paper focuses on the use of CNTs for new mm-to-THz interconnects for nanopackaging. To successfully integrate CNT to be in line with nanoelectronics trends, new growth processes and modeling approaches are proposed. Several experimental works are presented such as millimeter-wave flip-chip bonding. In addition, novel THz 3-D wireless interconnect, based on CNT monopole antennas, working at 200 and 300 GHz are designed, simulated, and fabricated.

Impact of the CNT growth process on gold metallization dedicated to RF interconnect applications

Carbon nanotubes (CNTs) are a unique group of materials with high aspect ratio, mechanical and electrical properties, which are of great interests in the field of interconnects, and radio frequency applications. In order to incorporate CNTs into any of these applications successfully, one important issue that has to be resolved is the critical parameters (temperature and reactant gases) associated with the growth of the CNTs. As such, the effect of these growth requirements on the adjacent components should be studied. In this work, we examined specifically the effect of carbon nanotubes growth on the underlying metallization, in particular gold, dedicated for radio-frequency-based applications. The gold coplanar lines were annealed at 8008C in a plasma-enhanced chemical vapor deposition (PECVD) system to simulate the worst-case condition. The reflection and transmission parameters were analyzed using a probe station connected to a vector network analyzer. Carbon nanotubes grown on different barrier layers were also characterized using a scanning electron microscope and Raman spectroscopy to identify a suitable barrier layer for gold. Our results showed that it is promising to integrate carbon nanotubes grown using PECVD onto Au coplanar waveguide without degrading the S-parameters measurements up to 20 GHz.

Plasmon resonances of carbon-nanotube-based dipole antennas for nano-interconnects

We investigate the use of bundled carbon nanotubes (CNTs) as nano-antennas for chip-to-chip and on-chip communications. We model CNTs as hollow tubes with complex surface conductivity. This is implemented in two finite-elements-method 3D electromagnetic solvers. Single-CNT-arms dipoles are simulated to validate our modeling approach by comparing our results to those found in literature. We then extend the study to bundles of CNTs. Finally we simulate the transmission between two CNT dipoles.

Hybrid EM/circuit modeling for carbon nanotubes based interconnects

In this paper, carbon nanotube models for high-frequency interconnect applications are studied applying electromagnetic and circuit approaches. A first validation of both models gives a better understanding of carbon nanotubes behaviors in RF. The complex surface impedance used in this paper is derived from Hansons conductivity in order to take in consideration the quantum capacitance and all other components existing in nano-scale world. A study of CNT inter-coupling is then possible within a transmission line configuration above a ground plane. In future devices, nano-interconnect based on CNTs will be gathered within bundles, a better comprehension of coupling inside and around this bundle allows developing complex CNT bundle models. A RF device approach using CNT bundle models is brought at the end of this paper.

Study of carbon nanotube flip-chip methodology for interconnect technology via electromagnetic and circuit model approach

Due to their excellent electronic and thermal properties, carbon nanotubes (CNTs) are considered as promising candidates for circuit interconnects. In this paper, we show for the first time both a theoretical and experimental analysis of CNT based flip-chip interconnects in the microwave domain. Two theoretical models of CNT were defined and compared exhibiting good agreement: one is based on electromagnetic simulations whereas the second one is based on circuit simulations. Finally, promising experimental studies were done in order to demonstrate the principle of the CNTs based flip-chip interconnect.

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

A new isolation scheme to improve radio frequency isolation using high aspect carbon nanotube structures is demonstrated. Carbon nanotubes were designed on top of conventional via-fenced guard trace, and showed 10 dB improvement in radio frequency isolation over conventional via-fencing techniques. This shield made of carbon nanotubes have shown to attain similar isolation performance compared to that of Kovar, a common metal used as a guard ring, or cavity in radio frequency integrated circuits. With weight density less than a quarter to that of metals, complementary use of such CNT forest could lead to significant weight reduction in RF packages.

Improved RF Isolation Using Carbon Nanotube Fence-Wall for 3-D Integrated Circuits and Packaging

We demonstrate a proof of concept to implement carbon nanotubes (CNT) in radio frequency (RF) integrated circuits to achieve improved electromagnetic isolation. A densely packed CNT fence-wall was designed on a typical via-fenced guard structure, to create RF isolation between two transmission lines. Both simulations and measurements have shown to further reduce forward and backward coupling by 10 dB over current techniques in the 1-10 GHz range. Such CNT isolation scheme could be implemented in densely packed three-dimensional circuits and packages.