Amin M Saleem

Compatibility assessment of CVD growth of carbon nanofibers on bulk CMOS devices.

We compare the level of deterioration in the basic functionality of individual transistors on ASIC chips fabricated in standard 130 nm bulk CMOS technology when subjected to three disparate CVD techniques with relatively low processing temperature to grow carbon nanostructures. We report that the growth technique with the lowest temperature has the least impact on the transistor behavior.

Nanoimprint lithography using vertically aligned carbon nanostructures as stamps

Nanoimprint lithography using vertically aligned carbon nanostructures as stamps is reported. The functionality of the stamp is demonstrated through lift-off and etch-back processes after pattern replication. The imprint process is robust and the stamp structures survived more than 50 consecutive imprints. In this paper we demonstrate this for feature sizes ranging from 80 nm to 200 microm where the aspect ratio of the individual nanostructures surpasses 1:5 with a pitch down to 100 nm. This demonstration opens up the possibility of utilizing vertically grown carbon nanostructures for manufacturing extremely high aspect ratio and small pitch stamps for nanoimprint lithography.

Carbon Nanofibers (CNF) for enhanced solder-based nano-scale integration and on-chip interconnect solutions

While the density of chip-to-chip and chip-to-package component interconnections increases and their size decreases the ease of manufacture and the interconnection reliability are being dangerously reduced. This paper introduces the use of Carbon Nanofibers (CNF) grown on chip as an embedded reinforcing material for nano-solder interconnections and as bonding material (adhesive) for chip-to-package solutions. Interconnections are realized by means of microbumps which can be less than 10 um in diameter and up to 20 um high. Such micro-bumps are shown to be solderable using conventional thermal-compression and micro-bumps. Using CNF embedded in polymer is shown to provide a robust solution for chip-to-package interconnections.

Low temperature and cost-effective growth of vertically aligned carbon nanofibers using spin-coated polymer-stabilized palladium nanocatalysts

Abstract We describe a fast and cost-effective process for the growth of carbon nanofibers (CNFs) at a temperature compatible with complementary metal oxide semiconductor technology, using highly stable polymer–Pd nanohybrid colloidal solutions of palladium catalyst nanoparticles (NPs). Two polymer–Pd nanohybrids, namely poly(lauryl methacrylate)-block-poly((2-acetoacetoxy)ethyl methacrylate)/Pd (LauMAx-b-AEMAy/Pd) and polyvinylpyrrolidone/Pd were prepared in organic solvents and spin-coated onto silicon substrates. Subsequently, vertically aligned CNFs were grown on these NPs by plasma enhanced chemical vapor deposition at different temperatures. The electrical properties of the grown CNFs were evaluated using an electrochemical method, commonly used for the characterization of supercapacitors. The results show that the polymer–Pd nanohybrid solutions offer the optimum size range of palladium catalyst NPs enabling the growth of CNFs at temperatures as low as 350 °C. Furthermore, the CNFs grown at such a low temperature are vertically aligned similar to the CNFs grown at 550 °C. Finally the capacitive behavior of these CNFs was similar to that of the CNFs grown at high temperature assuring the same electrical properties thus enabling their usage in different applications such as on-chip capacitors, interconnects, thermal heat sink and energy storage solutions.

Performance Enhancement of Carbon Nanomaterials for Supercapacitors

Carbon nanomaterials such as carbon nanotubes, carbon nanofibers, and graphene are exploited extensively due to their unique electrical, mechanical, and thermal properties and recently investigated for energy storage application (supercapacitor) due to additional high specific surface area and chemical inertness properties. The supercapacitor is an energy storage device which, in addition to long cycle life (one million), can give energy density higher than parallel plate capacitor and power density higher than battery. In this paper, carbon nanomaterials and their composites are reviewed for prospective use as electrodes for supercapacitor. Moreover, different physical and chemical treatments on these nanomaterials which can potentially enhance the capacitance are also reviewed.

Hierarchical cellulose- derived CNF/CNT composites for electrostatic energy storage

Today many applications require new effective approaches for energy delivery on demand. Supercapacitors are viewed as essential energy storage devices that can continuously provide quick energy. The performance of supercapacitors is mostly determined by electrode materials that can store energy via electrostatic charge accumulation. This study presents new sustainable cellulose-derived composite electrodes which consist of carbon nanofibrous (CNF) mats covered with vapor-grown carbon nanotubes (CNTs). The CNF/CNT electrodes have high electrical conductivity and surface area: the two most important features that are responsible for good electrochemical performance of supercapacitor electrodes. The results show that the composite electrodes have fairly high values of specific capacitance (101 F g(-1) at 5 mV s(-1)), energy and power density (10.28 W h kg(-1) and 1.99 kW kg(-1), respectively, at 1 A g(-1)) and can retain excellent performance over at least 2000 cycles (96.6% retention). These results indicate that sustainable cellulose-derived composites can be extensively used in the future as supercapacitor electrodes.

On-Chip Integrated Solid-State Micro-Supercapacitor

Following the trend of electronic device miniaturization, on-chip integrated solid-state micro-supercapcaitors (MS) were fabricated based on vertically aligned carbon nanofibers (VACNFs) as electrode materials and polymeric gel electrolyte as the solid electrolyte. The VACNFs were grown at 390 °C and 550 °C temperature on interdigitated micro-patterns, where the dimensions of the digits were kept the same but the gap between the digits varied from 10-100 µm. A maximum capacitance of 1 mF/cm2 and 0.53mF/cm2 (combined footprint area of digits and gaps) were measured for devices with CNFs grown at 390 °C and 20 µm gap, for 550 °C and 10 µm gap, respectively. These capacitances are an order of magnitude higher than the one for solid dielectric based silicon trenches capacitors. The low temperature MS show an inverse capacitance relation with the gap size whereas high temperature shows random behavior. High characteristic frequencies at 45° phase angle are 114 Hz for 100 µm gap and 142 Hz 30 µm gap for 390 °C and 550 °C temperatures. A model for the interdigitated capacitors was developed and the results showed that by eliminating the current collector resistances the characteristic frequencies can be increased to 965 Hz and 866 Hz from 67 Hz and 127 Hz for 10 µm gap patterns for 390 °C and 550 °C temperatures. The entire fabrication was done using CMOS compatible processes thus enabling integration directly on active CMOS chip.

Coin-cell Supercapacitors Based on CVD Grown and Vertically Aligned Carbon Nanofibers (VACNFs)

Complete supercapacitors (SCs) comprising vertically aligned carbon nanofibers (VACNFs) as electrode materials have been assembled as coin-cells. The VACNFs were grown directly onto the current collector by direct current plasma enhanced chemical vapor deposition (DC-PECVD), thereby providing excellent contact with the current collector, but also eliminating the need of any binder. The vertical alignment facilitates fast ion transport and the electrolyte to access the entire surface of the CNFs. The morphology of the VACNFs was evaluated by scanning electron microscopy (SEM), while the performance was assessed by several methods: cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and device related cycling by galvanostatic charge/discharge. The capacitance, 3.64 mF/cm2 , is >15 times higher than the capacitance of a coin-cell without CNFs and the cyclic performance shows these proof-of-concept SCs to retain >80% of the capacitance after 2000 full charge/discharge cycles. The direct growth of VACNFs as electrodes at the current collector opens pathways for SC production using existing coin-cell battery production technology.

Hierarchical cellulose-derived carbon nanocomposites for electrostatic energy storage

The problem of energy storage and its continuous delivery on demand needs new effective solutions. Supercapacitors are viewed as essential devices for solving this problem since they can quickly provide high power basically countless number of times. The performance of supercapacitors is mostly dependent on the properties of electrode materials used for electrostatic charge accumulation, i.e. energy storage. This study presents new sustainable cellulose-derived materials that can be used as electrodes for supercapacitors. Nanofibrous carbon nanofiber (CNF) mats were covered with vapor-grown carbon nanotubes (CNTs) in order to get composite CNF/CNT electrode material. The resulting composite material had significantly higher surface area and was much more conductive than pure CNF material. The performance of the CNF/CNT electrodes was evaluated by various analysis methods such as cyclic voltammetry, galvanostatic charge-discharge, electrochemical impedance spectroscopy and cyclic stability. The results showed that the cellulose-derived composite electrodes have fairly high values of specific capacitance and power density and can retain excellent performance over at least 2 000 cycles. Therefore it can be stated that sustainable cellulose-derived CNF/CNT composites are prospective materials for supercapacitor electrodes.