D.G. Hasko

Publications (103)148.42 Total impact

• Article: Dynamical behavior of damped driven coupled single electron simple harmonic oscillators

  M. Ziaur Rahman Khan, D.G. Hasko, M. S. M. Saifullah, M.E. Welland
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  ABSTRACT: Coherent coupling between a large number of qubits is the goal for scalable approaches to solid state quantum information processing. Prototype systems can be characterized by spectroscopic techniques. Here, we use pulsed-continuous wave microwave spectroscopy to study the behavior of electrons trapped at defects within the gate dielectric of a sol-gel-based high-k silicon MOSFET. Disorder leads to a wide distribution in trap properties, allowing more than 1000 traps to be individually addressed in a single transistor within the accessible frequency domain. Their dynamical behavior is explored by pulsing the microwave excitation over a range of times comparable to the phase coherence time and the lifetime of the electron in the trap. Trap occupancy is limited to a single electron, which can be manipulated by resonant microwave excitation and the resulting change in trap occupancy is detected by the change in the channel current of the transistor. The trap behavior is described by a classical damped driven simple harmonic oscillator model, with the phase coherence, lifetime and coupling strength parameters derived from a continuous wave (CW) measurement only. For pulse times shorter than the phase coherence time, the energy exchange between traps, due to the coupling, strongly modulates the observed drain current change. This effect could be exploited for 2-qubit gate operation. The very large number of resonances observed in this system would allow a complex multi-qubit quantum mechanical circuit to be realized by this mechanism using only a single transistor.
  02/2010;
• Article: Trapped charge dynamics in a sol-gel based TiO(2) high- k gate dielectric silicon metal-oxide-semiconductor field effect transistor.

  M Ziaur Rahman Khan, D G Hasko, M S M Saifullah, M E Welland
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  ABSTRACT: We have studied the response of a sol-gel based TiO(2), high k dielectric field effect transistor structure to microwave radiation. Under fixed bias conditions the transistor shows frequency dependent current fluctuations when exposed to continuous wave microwave radiation. Some of these fluctuations take the form of high Q resonances. The time dependent characteristics of these responses were studied by modulating the microwaves with a pulse signal. The measurements show that there is a shift in the centre frequency of these high Q resonances when the pulse time is varied. The measured lifetime of these resonances is high enough to be useful for non-classical information processing.
  Journal of Physics Condensed Matter 05/2009; 21(21):215902. · 2.55 Impact Factor
• Article: Single shot measurement of the lifetime of a trapped electron in the gate dielectric of a high-k field effect transistor

  M. Ziaur Rahman Khan, D. G. Hasko, M. S. M. Saifullah, M. E. Welland
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  ABSTRACT: The transient behavior of a trapped electron in the TiO2 sol-gel based gate dielectric layer of a silicon-on-insulator metal-oxide-semiconductor field effect transistor is investigated. Defects in this dielectric layer give rise to microwave resonances that are electrically detected via the channel current. The lifetime of the excited state is inferred from the quality factor of the resonance. A single shot measurement, carried out on the same resonance, is used to characterize the transient behavior and to directly measure the lifetime of the excited state. Possible applications of transient measurements on high-k dielectric layers are discussed.
  Applied Physics Letters 11/2008; 93(19):193501-193501-3. · 3.84 Impact Factor
• Article: A Nanogripper Employing Aligned Multiwall Carbon Nanotubes

  Jae Eun Jang, Seung Nam Cha, Youngjin Choi, Dae Joon Kang, D.G. Hasko, Jae Eun Jung, Jong Min Kim, G.A.J. Amaratunga
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  ABSTRACT: Nanogripper structures using aligned multiwall carbon nanotubes (MWCNTs) are demonstrated and their electromechanical properties have been studied in this paper. The balance of electrostatic force, together with elastostatic force and van der Waals force determines the driving conditions. A triode structure drastically reduces the bias between two moving parts, which consist of MWCNTs. Low bias also enables low power consumption as well as the reduction of electrical damage to an object. The moving parts can keep the same state without any applied biases after bending and connection. This also enables power saving during driving. The device can be a base structure for various nanorobotic or other nanoelectromechanical devices.
  IEEE Transactions on Nanotechnology 08/2008; · 2.29 Impact Factor
• Article: Nanoelectromechanical switch with low voltage drive

  J E Jang, S N Cha, Y Choi, T P Butler, D J Kang, D G Hasko, J E Jung, Y W Jin, J M Kim, G A J Amaratunga
  Applied Physics Letters 01/2008; 93(11). · 3.84 Impact Factor
• Article: The Growth and Physics of MBE Structures

  D C Peacock, D A Ritchie, J E F Frost, E H Linfield, A G Davies, C Smith, D A Wharam, C J B Ford, T J Thornton, R Newbury, D G Hasko, H Ahmed, G A C Jones, M Pepper
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  ABSTRACT: Low temperature electrical measurements on particular semiconductor structures can exhibit effects due to the spatial confinement of carriers and reduced dimensionality. Examples are provided by studies of tunnelling in confining structures, transport in narrow channels, ballistic transport through constrictions and quantum interference in rings. These observations rely on the growth of layers by molecular beam epitaxy (MBE) to provide both two-dimensional electron gases (2DEGs) and the very high material quality essential for the observation of some quantum effects. To define the specific geometries necessary for the above experiments electrostatic "squeezing" can be used to confine the planar carrier gas to regions of controllable extent. Recent results obtained from MBE GaAs/AlGaAs 2DEG structures can now be compared with measurements made on hole gases and the use of in situ ion beams in fabrication promises a new class of structures for investigation. However, it is rarely sufficient merely for MBE to provide a carrier gas with the highest maximum carrier mobility. The particular requirements of an experiment affect not only the design of the structure itself but also the MBE growth strategy and the optimum deposition conditions. Growth rate, substrate temperature and source material flux ratios are MBE variables and the suitability of layers for specific postgrowth physics experiments can be shown to depend upon these variables in a systematic manner. Moreover, further requirements for the grown material can include the need to provide specific sheet carrier concentrations, high mobilities in unilluminated samples and the complete absence of conducting paths in parallel with the 2DEG. There are often compromises inherent in attempting to simultaneously optimise several MBE variables and careful management of the MBE machine itself is essential.
  Physica Scripta 02/2007; 1989(T29):141. · 1.20 Impact Factor
• Conference Proceeding: CNT based mechanical devices for ULSI memory

  J.E. Jang, S.N. Cha, Y. Choi, D.J. Kang, T.P. Butler, D.G. Hasko, J.M. Kim, G.A.J. Amaratunga
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  ABSTRACT: Nanoelectromechanical (NEM) devices were developed for memory. The concept of a switch unit employing carbon nanotubes (CNT) was extended to random access memory (RAM). The unique vertical structure of these nanotubes allows a high integration density for devices. The easy fabrication process can give a high yield and reliability to device
  Custom Integrated Circuits Conference, 2006. CICC '06. IEEE; 10/2006
• Source

  Available from: www-g.eng.cam.ac.uk

  Article: Advantages of top-gate, high-k dielectric carbon nanotube field-effect transistors

  M. H. Yang, K. B. K. Teo, Laurent Gangloff, W. I. Milne, D. G. Hasko, Y. Robert, P. Legagneux
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  ABSTRACT: The subthreshold slope, transconductance, threshold voltage, and hysteresis of a carbon nanotube field-effect transistor (CNT FET) were examined as its configuration was changed from bottom-gate exposed channel, bottom-gate covered channel to top-gate FET. An individual single wall CNT was grown by chemical vapor deposition and its gate configuration was changed while determining its transistor characteristics to ensure that the measurements were not a function of different chirality or diameter CNTs. The bottom-gate exposed CNT FET utilized 900 nm SiO2 as the gate insulator. This CNT FET was then covered with TiO2 to form the bottom-gate covered channel CNT FET. Finally, the top-gate CNT FET was fabricated and the device utilized TiO2 (κ ∼ 80, equivalent oxide thickness = 0.25 nm) as the gate insulator. Of the three configurations investigated, the top-gate device exhibited best subthreshold slope (67–70 mV/dec), highest transconductance (1.3 μS), and negligible hysteresis in terms of threshold voltage shift.
  Applied Physics Letters 03/2006; 88(11):113507-113507-3. · 3.84 Impact Factor
• Conference Proceeding: Nanotube based Vertical Nano-devices for High Integration Density

  J.E. Jang, S.N. Cha, Y. Choi, D.J. Kang, T.P. Butler, D.G. Hasko, J.E. Jung, J.M. Kim, G.A.J. Amaratunga
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  ABSTRACT: Various nano-devices based on vertical nanotubes were developed. Carbon nanotubes (CNTs) were employed as a functional part or a nano structure of a nanoelectromechanical (NEM) switch, nano-capacitor, and NEM-dynamic random access memory (DRAM). The unique vertical structure of nanotubes allows high integration density for devices.
  Emerging Technologies - Nanoelectronics, 2006 IEEE Conference on; 02/2006
• Conference Proceeding: Nanoelectromechanical DRAM for ultra-large-scale integration (ULSI)

  J.E. Jang, S.N. Cha, Y. Choi, T.P. Butler, D.J. Kang, D.G. Hasko, J.E. Jung, J.M. Kim, G.A.J. Amaratunga
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  ABSTRACT: A nanoelectromechanical (NEM) device developed for dynamic random access memory (DRAM) is reported. A vertical nanotube structure is employed to form the electromechanical switch and capacitor structure. The mechanical movement of the nanotube defines 'ON' and 'OFF' states and the electrical signals which result lead to charge storage in a vertical capacitor structure as in a traditional DRAM. The vertical structure contributes greatly to a decrease in cell dimension. The main concept of the NEM switch and capacitor can be applied to other memory devices as well
  Electron Devices Meeting, 2005. IEDM Technical Digest. IEEE International; 01/2006
• Article: High performance ZnO nanowire field effect transistor using self-aligned nanogap gate electrodes

  S N Cha, J E Jang, Y Choi, G A J Amaratunga, G W Ho, M E Welland, D G Hasko, D -J Kang, J M Kim
  Applied Physics Letters 01/2006; 89(26). · 3.84 Impact Factor
• Article: Nanoscale capacitors based on metal-insulator-carbon nanotube-metal structures

  J. E. Jang, S. N. Cha, Y. Choi, G. A. J. Amaratunga, D. J. Kang, D. G. Hasko, J. E. Jung, J. M. Kim
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  ABSTRACT: We report the fabrication process and the electrical characteristics of a nanocapacitor structure using metal-insulator-carbon nanotube-metal layers. The structure shows high capacitance and the possibility of ultrahigh integration density due to the unique nanotube structure. Nanoscale and high-aspect-ratio patterns are achieved by electron beam lithography for the fabrication of these vertical nanostructures. This structure can be substituted for capacitors based on the silicon pillar structure in dynamic random access memory or as a nanoscale capacitor for various nanoelectronic devices.
  Applied Physics Letters 12/2005; 87(26):263103-263103-3. · 3.84 Impact Factor
• Source

  Available from: ces.clemson.edu

  Article: Carbon nanotube Schottky diode and directionally dependent field-effect transistor using asymmetrical contacts

  M. H. Yang, K. B. K. Teo, W. I. Milne, D. G. Hasko
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  ABSTRACT: We demonstrate the fabrication and operation of a carbon nanotube (CNT) based Schottky diode by using a Pd contact (high-work-function metal) and an Al contact (low-work-function metal) at the two ends of a single-wall CNT. We show that it is possible to tune the rectification current-voltage (I-V) characteristics of the CNT through the use of a back gate. In contrast to standard back gate field-effect transistors (FET) using same-metal source drain contacts, the asymmetrically contacted CNT operates as a directionally dependent CNT FET when gated. While measuring at source-drain reverse bias, the device displays semiconducting characteristics whereas at forward bias, the device is nonsemiconducting.
  Applied Physics Letters 12/2005; 87(25):253116-253116-3. · 3.84 Impact Factor
• Article: Nanoelectromechanical switches with vertically aligned carbon nanotubes

  J. E. Jang, S. N. Cha, Y. Choi, Gehan A. J. Amaratunga, D. J. Kang, D. G. Hasko, J. E. Jung, J. M. Kim
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  ABSTRACT: Electromechanical switching devices have been fabricated successfully employing vertically grown multiwalled carbon nanotubes (MWCNTs) from the prepatterned catalyst dots on the patterned device electrodes. The devices show various interesting switching characteristics depending on the length and the number of MWCNTs used. The device design not only simplifies the fabrication process, but also improves the integration density greatly. The device has a great potential in realizing technically viable nanoelectromechanical systems, such as switch, memory, fingers, or grippers.
  Applied Physics Letters 11/2005; · 3.84 Impact Factor
• Conference Proceeding: High performance ZnO nanowire field effect transistor

  S.N. Cha, J.E. Jang, Y. Choi, G.W. Ho, D.-J. Kang, D.G. Hasko, M.E. Welland, G.A.J. Amaratunga
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  ABSTRACT: A zinc oxide (ZnO) nanowire field effect transistor having the highest mobility and lowest subthreshold slope obtained to date (from ZnO) is reported. The device consists of a single nanowire with self-aligned gate electrodes having well defined nanoscale spacing, independent of lithographic definition. The fabricated device exhibits a transconductance of 3.06 μS, a mobility of 450 cm²/Vs and a subthreshold swing of 129 mV/decade. The transistor also shows an on/off current ratio of 10⁶.
  Solid-State Device Research Conference, 2005. ESSDERC 2005. Proceedings of 35th European; 10/2005
• Conference Proceeding: In-vacuum resonant tunneling in the nanopentode

  A.M. Blackburn, D.G. Hasko, D A Williams
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  ABSTRACT: Nanopentode device fabrication process and predicted characteristics are presented. The fabrication process involves a combination of reaction ion etching and wet etching. The fabricated device structure makes it possible to simultaneously create an in-vacuum potential-energy barrier and well, creating a gaseous-state device similar in some respects to the solid-state resonant tunneling diode. The calculated transmission probability for electrons through the entire cathode-anode gap, in a one-dimensional approximation, shows resonances at certain gate-voltage arrangement. This strengthens the possibility of observing quantum interference effects in multiple-gate vacuum microelectronic devices.
  Vacuum Nanoelectronics Conference, 2005. IVNC 2005. Technical Digest of the 18th International; 08/2005
• Conference Proceeding: RF modulation of a 3 mA beam current from a carbon nanotube cathode

  L. Hudanski, E. Minoux, J.-P. Schnell, P. Vincent, P. Legagneux, F. Peauger, D. Dieumegard, J.-F. David, K.B.K. Teo, L. Gangloff, R. Lacerda, M. Chhowalla, D.G. Hasko, H. Ahmed, G.A.J. Amaratunga, W.I. Milne
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  ABSTRACT: A micro-triode operating at 30 GHz is currently under development. This triode is composed of two 30 GHz re-entrant resonant cavities (input and output, respectively cathode-grid space and anode-grid space) separated by a grounded thin metallic grid. A dc bias between cathode-grid and anode-grid provides a continuous electron beam. The superposition of a 30 GHz electric field created in the input cavity, leads to increase the average grid current, which is indicative of the electron beam modulation.
  Vacuum Nanoelectronics Conference, 2005. IVNC 2005. Technical Digest of the 18th International; 08/2005
• Conference Proceeding: High current/high current density carbon nanotube cold cathodes

  E. Minoux, P. Vincent, L. Hudanski, J.-P. Schnell, P. Legagneux, K.B.K. Teo, L. Gangloff, R. Lacerda, M. Chhowalla, D.G. Hasko, H. Ahmed, G.A.J. Amaratunga, W.I. Milne
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  ABSTRACT: Field emission measurements on individual carbon nanotubes grown by dc plasma CVD at 700°C have been performed with a high resolution scanning anode field emission microscope. I-V characteristics of as-grown CNs show a saturation for currents above 1 μA and the maximum emission current is in the range 5-10 μA. This saturation is attributed to a bad CN/substrate contact. By improving this electric contact by thermal annealing at 950°C, the saturation is suppressed. To improve emission current density, the effect of CN density on maximum emission current is studied. For this purpose, 0.5 × 0.5 mm² arrays of vertically aligned CNs with a 1.5 μm height, a 15 nm diameter and a 3 μm spacing are grown. The CN density is 10⁷ cm^-2. CNs exhibit almost the same aspect ratio [200] but the CN density is increased by a factor of 10. From such an array, an emission current of 10 mA corresponding to a current density of 4 A cm^-2 is measured.
  Vacuum Nanoelectronics Conference, 2005. IVNC 2005. Technical Digest of the 18th International; 08/2005
• Article: Fabrication of a nanoelectromechanical switch using a suspended carbon nanotube

  S. N. Cha, J. E. Jang, Y. Choi, G. A. J. Amaratunga, D.-J. Kang, D. G. Hasko, J. E. Jung, J. M. Kim
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  ABSTRACT: Fabrication and characterization of a nanoelectromechanical switching device consisting of a suspended multiwalled carbon nanotube and self-aligned electrodes is reported. The device has a triode structure and is designed so that a suspended carbon nanotube is mechanically switched to one of two self-aligned electrodes by repulsive electrostatic forces between the nanotube and the other self-aligned electrode. Carbon nanotubes are dispersed on an SiO2 coated Si wafer and their locations recorded using a scanning electron microscope mapping process. Contact electrodes and self-aligned deflection electrodes are formed by a process comprising electron beam lithography, metallic thin film deposition, and lift-off. The electrical measurements show well-defined ON and OFF states with change of gate voltage. The measured threshold voltage for electromechanical switching is ∼ 3.6 V.
  Applied Physics Letters 02/2005; 86(8):083105-083105-3. · 3.84 Impact Factor
• Article: Carbon nanotube technology for solid state and vacuum electronics

  K.B.K. Teo, R.G. Lacerda, M.H. Yang, A.S. Teh, L.A.W. Robinson, S.H. Dalal, N.L. Rupesinghe, M. Chhowalla, S.B. Lee, D.A. Jefferson, D.G. Hasko, G.A.J. Amaratunga, W.L. Milne, P. Legagneux, L. Gangloff, E. Minoux, J.P. Schnell, D. Pribat
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  ABSTRACT: The authors demonstrate the fabrication of solid state and vacuum electronic devices using carbon nanotubes as the active channel and emitters. Single wall and multiwall carbon nanotubes (CNT) are deposited directly on substrates using chemical vapour deposition (CVD) and plasma enhanced chemical vapour deposition (PECVD), respectively. The fabrication of top gate and side gate field effect transistors is demonstrated using single wall CNTs. Vertically aligned multiwall CNTs are used to fabricate field emitter arrays or micro-gated field emitters, which have potential application in field emission displays, microwave amplifiers or electron guns.
  IEE Proceedings - Circuits Devices and Systems 11/2004; · 0.36 Impact Factor