| 1. |
- Alavian Ghavanini, Farzan, 1978, et al.
(författare)
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A method to evaluate MEMS bonding
- 2006
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Ingår i: Micro Structure Workshop 2006. ; 1:1, s. 47-B3d
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Konferensbidrag (refereegranskat)
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| 2. |
- Alavian Ghavanini, Farzan, 1978, et al.
(författare)
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An easy-to-implement method for evaluation of capacitive resonant sensors
- 2006
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Ingår i: Journal of Micromechanics and Microengineering. - 1361-6439 .- 0960-1317. ; 16:6, s. s156-s160
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Tidskriftsartikel (refereegranskat)abstract
- A novel method that can be used to characterize resonant capacitive sensors is presented. The method is based on measurement of the third harmonic of the current through the capacitor; thus the detection signal is frequencyseparated from the excitation signal. The measurement is time-continuousand only requires a very simple resonant structure where a single electrode is simultaneously used for excitation and detection. The readout circuit iseasily implemented with a single operational amplifier and standard equipment such as a lock-in amplifier or a function generator and a spectrum analyzer. Measurements of a resonant structure confirm the feasibility of the concept.
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| 3. |
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| 4. |
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| 5. |
- Alavian Ghavanini, Farzan, 1978, et al.
(författare)
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CMOS considerations in nanoelectromechanical carbon nanotube-based switches
- 2008
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Ingår i: Nanotechnology. - 1361-6528 .- 0957-4484.
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we focus on critical issues directly related to the viability of carbon nanotube-based nanoelectromechanical switches, to perform their intended functionality as logic and memory elements, through assessment of typical performance parameters with reference to complementary metal-oxide-semiconductor devices. A detailed analysis of performance metrics regarding threshold voltage control, static and dynamic power dissipation, speed, and integration density is presented. Apart from packaging and reliability issues, these switches seem to be competitive in low power, particularly low-standby power, logic and memory applications.
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| 6. |
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| 7. |
- Alavian Ghavanini, Farzan, 1978, et al.
(författare)
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Controlling the initial phase of PECVD growth of vertically aligned carbon nanofibres on TiN
- 2011
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Ingår i: Sensors and Actuators A-Physical. - : Elsevier BV. - 0924-4247 .- 1873-3069. ; 172:1, s. 347-358
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Tidskriftsartikel (refereegranskat)abstract
- We explore the growth of vertically aligned carbon nanofibers by plasma enhanced chemical vapor deposition, using lithographically defined Ni catalyst seeds on TiN. TiN is selected for being an electrically conducting diffusion barrier suitable for the realization of electronic devices. We show that the rate of Ni diffusion correlates to both the level of oxygen content in the TiN film and to the film resistivity. The synthesis of the nanofibers was characterized using electron microscopy with an emphasis on three growth parameters: substrate temperature, plasma power, and chamber pressure. We propose that a catalyst surface free from carbon deposits throughout the process will induce diffusion-limited growth. The growth will shift towards a supply-limited process when the balance between acetylene, as the effective carbon bearing gas, and atomic hydrogen, as the main etching agent, is skewed in favor of acetylene. This determines whether the dominating growth mode will be vertically aligned tip-type or disordered base-type, by affecting the competition between the formation of the first graphitic sheets on the catalyst surface and at the catalyst-substrate interface
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| 8. |
- Alavian Ghavanini, Farzan, 1978, et al.
(författare)
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Direct measurement of bending stiffness and estimation of Young's modulus of vertically aligned carbon nanofibers
- 2013
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 113:19
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Tidskriftsartikel (refereegranskat)abstract
- The bending stiffness of individual, as-grown, vertically aligned carbon nanofibers was measured using a custom-built atomic force microscope placed inside a scanning electron microscope. The internal structure of the nanofiber was best modeled as dual-phase, composed of an inner graphitic core covered with a tapered amorphous carbon shell. It was found that the fibers have a relatively low bending stiffness, with Young's modulus values of about 10 GPa for the inner core and 65 GPa for the outer shell. The low Young's modulus of the inner core is attributed to a non-zero angle between the graphitic sheets and the nanofiber axis. The weak shear modulus between graphitic sheets thereby dominates the mechanical behaviour of the fibers.
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| 9. |
- Alavian Ghavanini, Farzan, 1978, et al.
(författare)
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Direct Measurement of the Bending Stiffness of Individual Vertically Aligned Carbon Nanofibers (VACNFs)
- 2011
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Ingår i: NT11 International Conference on the Science and Application of Nanotubes University of Cambridge, Cambridge, 10 – 16 July, 2011.
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Konferensbidrag (refereegranskat)abstract
- Vertically aligned carbon nanofibers (VACNFs) are synthesized in a plasma-enhanced chemical vapor deposition process (PECVD) in which the position, diameter, length, and alignment of individual nanofibers can be controlled accurately. This has provided an unprecedented opportunity to realize a new bottom-up-engineered material with excellent mechanical and electrical properties which could exploit the third dimension at a reasonable cost. VACNFs have been already employed in a number of applications including electron emitters, gene delivery arrays, and nanoelectromechanical systems. However, no direct measurement of the Young’s modulus of VACNFs has been reported yet. Qi et al. have used nanoindentation method to measure the collective response of a forest of VACNFs with a distribution in length and diameter of the constituent nanofibers. Kaul et al., have reported in situ uniaxial compression tests on individual VACNFs but they have not provided enough information to evaluate the accuracy of their measurements. Indirect estimation of the VACNFs Young’s modulus has also been reported by Eriksson et al. from measurements of the resonance frequency of a nanofiber deposited on top of an excitation electrode. Here, we report on direct measurements of VACNFs Young’s modulus using a piezoresistive atomic force microscope (AFM) cantilever implemented inside a scanning electron microscope (SEM). The VACNFs were grown from Ni catalyst seeds, patterned using electron-beam lithography on top of a stoichiometric TiN underlayer. The VACNFs were grown in a commercially available PECVD chamber (AIXTRON BlackMagic™). The nanofibers were approached from the side and pushed at the tip (resembling a cantilever beam) and force-deflection curves were obtained. By calibrating the AFM sensor the bending stiffness of the nanofiber could be determined. The Young’s modulus was then estimated by taking the nanofibers dimensions into account. The sub-nano Newton force precision provided by the AFM force-sensor together with the fact the individual VACNFs could be observed in the SEM simultaneously during the measurements, has enabled us to measure the nanofibers Young’s modulus with a high precision. Preliminary measurements indicate that VACNFs posses a Young’s modulus between 40 to 100 GPa which is comparable to CVD grown carbon nanotubes of similar diameter.
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| 10. |
- Alavian Ghavanini, Farzan, 1978, et al.
(författare)
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Growth characterization of vertically aligned carbon nanofibers on top of TiN buffer layer for nanoelectromechanical devices
- 2010
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Ingår i: Procedia Engineering, 24th Eurosensor 24th Conference Linz, AUSTRIA, SEP 05-08, 2010. - : Elsevier BV. - 1877-7058. ; 5, s. 1115-1118
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Konferensbidrag (refereegranskat)abstract
- Initial growth of vertically aligned carbon nanofibers (VACNFs) from Ni catalyst seeds in the range of 40 to 100 nm as fabricated using hole-mask colloidal lithography on top of reactively sputtered TiN is studied. We observe that the initial growth conditions could cause a growth mode transition from base-type to tip-type. We attribute this transition to a change in the crystallographic orientation of the Ni catalyst seeds induced by initial growth conditions. A convenient method to deposit stoichiometric TiN films is also presented.
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| 11. |
- Alavian Ghavanini, Farzan, 1978
(författare)
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Synthesis and characterization of vertically aligned carbon nanofibers for nanoscale devices
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The synthesis of vertically aligned carbon nanofibers (VACNFs) by direct current plasma enhanced chemical vapor deposition (dc PECVD) has presented a unique opportunity to realize nanoscale three-dimensional devices at a reasonable cost. The determinism offered by the synthesis process in terms of control over the spatial and the geometrical properties of the resulting nanofibers provides a powerful tool to implement a wide range of applications from nanoelectromechanical systems to biological devices. However, the use of VACNFs as building blocks for nanoscale devices has not been a trivial task. The work presented in this thesis aims at incorporating the synthesis of VACNFs as an integral part of the nanofabrication process. The dc PECVD synthesis process is scrutinized by dividing it into three phases. The effect of growth parameters on each phase is investigated independently. Special attention is paid to the choice of materials involved in the synthesis process. Reactively sputtered TiN is chosen as the growth underlayer and a detailed discussion is given on its optimal deposition conditions. The material and process optimizations manifest themselves by a successful fabrication of individually addressable arrays of VACNFs with a sub-micrometer pitch between the adjacent nanofibers. The potential applications of such three-dimensional nanoscale arrays as well as a suitable measurement scheme are also discussed. As an important parameter for designing VACNF based devices, the bending stiffness of as-grown nanofibers is directly measured. It is shown that the assumption of a uniform internal structure is inadequate in describing nanofibers’ mechanical properties and that a dual phase model is needed in which different Young’s moduli are assigned to the inner graphitic core and the outer amorphous carbon shell. The potential of integrating the VACNF synthesis with CMOS technology is also assessed. The level of deterioration in the basic functionality of individual transistors on ASIC chips fabricated in standard 130 nm bulk CMOS technology are compared when the chips are subjected to three disparate CVD techniques with relatively low processing temperatures.
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| 12. |
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| 13. |
- Alavian Ghavanini, Farzan, 1978
(författare)
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Toward Carbon based NEMS
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A systematic analysis and assessment of carbon nanotube (CNT) based NEMS switches is presented and their features are compared to typical complementary metal-oxide-semiconductor (CMOS) performance parameters. It is shown that CNT-based switches with considerably smaller leakage current compared to CMOS switches can be realized. These switches demonstrate very small standby-power dissipation.This thesis also pays special attention to the future integration of carbon based NEMS with mainstream circuitry. It is our belief that the adoption of novel nanotechnologies are closely tied to their successful integration with CMOS technology, not only to benefit from its versatility and maturity but also to be able to present an added value to the full-fledged platform. This thesis demonstrates a relatively low temperature direct current plasma enhanced chemical vapor deposition (dc PECVD) process capable of growing vertically aligned carbon nanofiber-like structures with negligible deterioration of bulk CMOS transistors’ functionality.A main feature of this thesis is the toolbox composed of analytical and computational components to design and simulate a single-pair VACNF based system. Nanoelectromechanical devices based on this building block have been fabricated. The inherent discharging problem of dc PECVD synthesis method is addressed and resolved. Moreover, two different methods are proposed to extract the Young’s modulus of the synthesized vertically aligned carbon nanofibers.
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| 14. |
- Alavian Ghavanini, Farzan, 1978, et al.
(författare)
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Vertically aligned carbon based varactors
- 2011
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 110:2
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Tidskriftsartikel (refereegranskat)abstract
- This paper gives an assessment of vertically aligned carbon based varactors and validates their potential for future applications. The varactors discussed here are nanoelectromechanical devices which are based on either vertically aligned carbon nanofibers or vertically aligned carbon nanotube arrays. A generic analytical model for parallel plate nanoelectromechanical varactors based on previous works is developed and is used to formulate a universal expression for their voltage-capacitance relation. Specific expressions for the nanofiber based and the nanotube based varactors are then derived separately from the generic model. This paper also provides a detailed review on the fabrication of carbon based varactors and pays special attention to the challenges in realizing such devices. Finally, the performance of the carbon based varactor is assessed in accordance with four criteria: the static capacitance, the tuning ratio, the quality factor, and the operating voltage. Although the reported performance is still far inferior to other varactor technologies, our prognosis which stems from the analytical model shows a promise of a high quality factor as well as a potential for high power handling for carbon based varactors.
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| 15. |
- Bengtsson, Stefan, 1961, et al.
(författare)
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Carbon-based nanoelectromechanical devices
- 2011
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Ingår i: International Journal of High Speed Electronics and Systems. - 1793-6438. ; 20:1, s. 195-204
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Tidskriftsartikel (refereegranskat)abstract
- Carbon-based nanoelectromechanical devices are approaching applications in electronics. Switches based on individual carbon nanotubes deliver record low off-state leakage currents. Arrays of vertically aligned carbon nanotubes or nanofibers can be fabricated to constitute varactors. Very porous, low density arrays of quasi-vertically aligned arrays of carbon nanotubes behave mechanically as a single unit with very unusual material properties.
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| 16. |
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| 17. |
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| 18. |
- Nafari, Alexandra, 1980, et al.
(författare)
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Calibration methods of force sensors in the micro-Newton range
- 2007
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Ingår i: Journal of Micromechanics and Microengineering. - : IOP Publishing. - 1361-6439 .- 0960-1317. ; 17:10, s. 2102-7
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Tidskriftsartikel (refereegranskat)abstract
- A micromachined capacitive force sensor operating in the micro-Newton range has been calibrated using both dynamic and static methods. Both calibrations are non-destructive, accurate and traceable to Systeme International (SI) fundamental units. The dynamic calibration is a differential mass loading resonant method where the resonance frequency with and without an added mass is measured. This gives enough information to compute the spring constant. In this paper, we evaluate the resonant mass loading method for more complex MEMS devices. Analytical calculations and finite element analysis have been performed to investigate the dynamic properties of the sensor, e.g. modal interference. The frequency response was measured with the third harmonic method where the third harmonic of the current through the sensor was measured. To detect and analyse the resonance mode of the structure during excitation, a scanning laser Doppler vibrometer was used. Two designs of a capacitive nanoindenter force sensor with flexure-type springs have been evaluated using these methods. The quality of the resonant calibration method has been tested using static mass loading in combination with transmission electron microscopy imaging of the sensor displacement. This shows that the resonant method can be extended to calibrate more complex structures than plain cantilevers. Both calibration methods used are traceable to SI fundamental units as they are based on masses weighed on a calibrated scale. The masses used do not need to be fixed or glued in any way, making the calibration non-destructive. (10 refs.)
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| 19. |
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| 20. |
- Rehammar, Robert, 1980, et al.
(författare)
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Electromechanically Tunable Carbon Nanofiber Photonic Crystal
- 2013
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Ingår i: Nano letters (Print). - : AMER CHEMICAL SOC. - 1530-6984 .- 1530-6992. ; 13:2, s. 397-401
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate an electrically tunable 2D photonic crystal array constructed from vertically alignedcarbon nanofibers. The nanofibers are actuated by applying a voltage between adjacent carbon nanofiberpairs grown directly on metal electrodes, thus dynamically changing the form factor of the photoniccrystal lattice. The change in optical properties is characterised using optical diffraction andellipsometry. The experimental results are shown to be in agreement with theoretical predictions andprovide a proof-of-principle for rapidly switchable photonic crystals operating in the visible that can befabricated using standard nanolithography techniques combined with plasma CVD growth of thenanofibers.
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| 21. |
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