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• Journal article
  Michelakis K, Prodromakis T, Toumazou C, 2010,

  Cost-effective fabrication of nanoscale electrode memristors with reproducible electrical response

  , Micro & Nano Letters, Vol: 5, Pages: 91-94, ISSN: 1750-0443

  This Letter aims to promote basic research into memristors, which will help provide theorists with much-needed reliable benchmarks and will also aid the technology progress. It addresses an information gap presently in the literature on simple microfabrication techniques for the realisation of such devices. Consequently, a fabrication method is reported for implementing the full active-material stack, requiring a single lithography and evaporation step. A cost-effective technique that can reliably shrink device lateral dimensions towards the nanoscale is also demonstrated. Experimental results confirm the suitability of the proposed methods for fabricating memristors of varying dimensions that exhibit consistent electrical characteristics.

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• Journal article
  Wong W, Georgiou P, Ou C-P, Toumazou Cet al., 2010,
  , ELECTRONICS LETTERS, Vol: 46, Pages: 330-U4847, ISSN: 0013-5194
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  • Citations: 9
• Conference paper
  Constandinou TG, Georgiou P, Prodromakis T, Toumazou Cet al., 2010,
  , Berkeley, CA, 2010 12th International Workshop on Cellular Nanoscale Networks and their Applications (CNNA), Publisher: IEEE, Pages: 1-6

  This paper presents a novel CMOS-based lab-on-chip platform for non-contact magnetic stimulation and recording of neural tissue. The proposed system is the first of its kind to integrate magnetic-stimulation and opto-chemical sensing in a single pixel, tesselated to form an 8 × 8 array. Fabricated in a commercially-available 0.35 ¿m CMOS technology, the system can be intrinsically used for both optical imaging and pH sensing and includes mechanisms for calibrating out sensor variation and mismatch. In addition to sensory acquisition via an integrated 10-bit ADC, a 64-instruction spatiotemporal pattern generator has been embedded within the array for driving the microscale magnetic neural stimulation. In this application the ISFET-based sensors are used to capacitively-couple neuronal charge in close proximity to the floating gate. Optical imaging hardware has also been embedded to provide topographic detail of the neural tissue.

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• Conference paper
  Garner DM, Bai H, Georgiou P, Constandinou TG, Reed S, Shepherd LM, Wong W, Lim KT, Toumazou Cet al., 2010,
  , IEEE International Solid-State Circuits Conference (ISSCC), Publisher: IEEE, Pages: 492 -493-492 -493, ISSN: 0193-6530
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• Journal article
  Prodromakis T, Michelakis K, Toumazou C, 2010,
  , ELECTRON LETT, Vol: 46, Pages: 63-64, ISSN: 0013-5194

  It is only very recently that the memristor, the fourth missing passive element, was discovered, as technological advances and the scaling-down to nanometre dimensions in particular resulted in clearly evident and measurable memristance. At the nanoscale, these devices exhibit variable resistive behaviour, which can be applied in switching networks and memory. Experimental evidence is provided that micrometre-size memristors are viable with practical R-OFF/R-ON ratios.

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• Conference paper
  Prodromakis T, Michelakis K, Toumazou C, 2010,

  Practical micro/nano fabrication implementations of memristive devices

  , Cellular Nanoscale Networks and Applications
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• Journal article
  Prodromakis T, Michelakis K, Toumazou C, 2010,

  Switching mechanisms in microscale Memristors

  , Electronic Letters, Vol: 46, Pages: 63-65

  It is only very recently that the memristor, the fourth missing passive element, was discovered, as technological advances and the scaling down to nanometre dimensions in particular resulted in clearly evident and measurable memristance. At the nanoscale, these devices exhibit variable resistive behaviour, which can be applied in switching networks and memory. Experimental evidence is provided that micrometre-size memristors are viable with practical ROFF/RON ratios.

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• Conference paper
  Degenaar P, Grossman N, Berlinguer-Palmini R, McGovern B, Pohrer V, Dawson M, Toumazou C, Burrone J, Nikolic K, Neil Met al., 2010,
  , IEEE Biomedical Circuits and Systems Conference, BioCAS 2009, Pages: 183-186
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• Journal article
  Prodromakis T, Papavassiliou C, Toumazou C, 2010,
  , Microelectronics Journal, Vol: 41, Pages: 17-24

  The propagation characteristics of metal–insulator–semiconductor (MIS) lines are controlled by the resistivity of the substrate, the operating frequency and the ratio of the semiconductor to insulator layer thicknesses. A strong interfacial polarisation, also known as the Maxwell–Wagner polarisation, is often responsible for the significant slow-down of the propagation velocity of MIS microstrip transmission lines. This phenomenon has been applied in the development of miniature delay lines exhibiting large electrical dimensions. In this paper we review most previously presented designs and we examine the effect of this polarization mechanism under various parameters. Finally, the presented micro-scale delay lines, exhibit comparable slowing factors with our predecessors at the cost of lower attenuation.

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• Conference paper
  Juffali W, El-Imad J, Eftekhar A, Toumazou Aet al., 2010,

  The WiNAM project: Neural data analysis with applications to epilespy

  , Biomedical Circuits and Systems Conference (BioCAS)
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• Conference paper
  El Sharkawy MF, Georgiou P, Toumazou C, 2010,

  A Silicon Pancreatic Islet for the Treatment of Diabetes

  , International Symposium on Circuits and Systems Nano-Bio Circuit Fabrics and Systems (ISCAS 2010), Publisher: IEEE, Pages: 3136-3139, ISSN: 0271-4302
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  • Citations: 3
• Conference paper
  Saremi-Yarahmadi S, Murphy OH, Toumazou C, 2010,

  RF Inductive Sensors for Detection of Change in the Ionic Strength and pH of Liquid Samples

  , International Symposium on Circuits and Systems Nano-Bio Circuit Fabrics and Systems (ISCAS 2010), Publisher: IEEE, Pages: 2279-2282, ISSN: 0271-4302
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  • Citations: 1
• Conference paper
  Eftekhar A, Paraskevopoulou S, Constandinou TG, 2010,
  , IEEE Biomedical Circuits and Systems (BioCAS) Conference, Publisher: IEEE, Pages: 122-125

  In this paper, we review the state-of-the-art in neural interface recording architectures. Through this we identify schemes which show the trade-off between data information quality (lossiness), computation (i.e. power and area requirements) and the number of channels. These trade-offs are then extended by considering the front-end amplifier bandwidth to also be a variable. We therefore explore the possibility of band-limiting the spectral content of recorded neural signals (to save power) and investigate the effect this has on subsequent processing (spike detection accuracy). We identify the spike detection method most robust to such signals, optimize the threshold levels and modify this to exploit such a strategy.

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• Conference paper
  Guven O, Geier F, Banks D, Toumazou Cet al., 2010,
  , Biomedical Circuits and Systems Conference (BioCAS), Publisher: IEEE, Pages: 282-285, ISSN: 2163-4025
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  • Citations: 3
• Journal article
  Nikolic K, Loizu J, Degenaar P, Toumazou Cet al., 2010,
  , Integrative Biology, Vol: 2, Pages: 354-370

  We present a quantitative model for the phototransduction cascade in Drosophila photoreceptors. The process consists of four stages: (1) light absorption by Rhodopsin, (2) signal amplification phase mediated by a G-protein coupled cascade, (3) close/open state kinetics of the transient receptor potential (TRP) ion channels which regulate the ionic current in/out of the cell and (4) Ca regulated positive and negative feedbacks.The model successfully reproduces the experimental results for: single photon absorption "quantum bump" (QB), statistical features for QB (average shape, peak current average value and variance, the latency distribution, etc), arrestin mutant behaviour, low extracellular Ca2+ cases, etc. The TRP channel activity is modeled by a Monod-Wyman-Changeux (MWC) model for allosteric interaction, instead of using the usual ad hoc Hill equation. This approach allows for a plausible physical explanation how Ca/calmodulin regulate the protein activity. The cooperative nature of the TRP channel activation leads to "dark current" suppression at the output allowing for reliable detection of a single photon. Stochastic simulations were produced by using the standard rate equations combined with the Poisson distribution for generating random events from the forward and the reverse reaction rates. Noise is inherent to the system but appears to be crucial for producing such reliable responses in this complex, highly nonlinear system. The approach presented here may serve as a useful example how to treat complex cellular mechanisms underlying sensory processes.

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• Journal article
  Georgiou P, Toumazou C, 2009,
  , SENSORS AND ACTUATORS B-CHEMICAL, Vol: 143, Pages: 211-217
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  • Citations: 147
• Journal article
  Oliver N, Georgiou P, Johnston D, Toumazou Cet al., 2009,
  , J Diabetes Sci Technol, Vol: 3, Pages: 1419-1424

  UNLABELLED: The normal pancreatic beta-cell membrane depolarizes in response to increasing concentrations of glucose in a bursting pattern. At <7 mM (126 mg/dl), the cell is electrically silent. The bursting pulse width increases as glucose rises >7 mM (126 mg/dl) until a continuous train of bursting is seen at >25 mM (450 mg/dl). A bio-inspired silicon device has been developed using analogue electronics to implement membrane depolarization of the beta cell. The device is ultralow powered, miniaturized (5 x 5 mm), and produces a bursting output identical to that characterized in electrophysiological studies. OBJECTIVE: The goal of this study was to demonstrate the ability of silicon implementation of beta-cell electrophysiology to respond to a simulated glucose input and to drive an infusion pump in vitro. METHOD: The silicon device response to a current source was recorded at varying simulated glucose concentrations. Subsequently, the bursting response to a changing analyte concentration measured by an amperometric enzyme electrode was converted to a voltage, driving a syringe pump loaded with a 50-ml syringe containing water. RESULTS: Bursting responses are comparable to those recorded in electrophysiology. Silicon beta-cell implementation bursts with a pulse width proportional to concentration and is able to drive an infusion pump. CONCLUSION: This is the first in vitro demonstration of closed loop insulin delivery utilizing miniaturized silicon implementation of beta-cell physiology in analogue electronics.

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• Journal article
  Constandinou TG, Georgiou J, 2009,
  , IEEE Transactions on Biomedical Circuits and Systems, Vol: 3, Pages: 363-369, ISSN: 1932-4545

  This paper describes a novel analogue circuit for extracting the tilt angle from the output of a linear MEMS accelerometer. The circuit uses the accelerometer signal together with the gravitational acceleration vector to generate the tilt signal. Using a current-mode representation with MOS devices operating in weak inversion, the appropriate trigonometric function has been realised to compute tilt. Furthermore, implementing a long-time constant filter to extract the mean tilt level provides adaptation to the static tilt level. Specifically, this circuit has been designed as part of an implantable vestibular prosthesis to provide inclination signals for bypassing dysfunctional otolith end-organs. The circuit has been fabricated in AMS 0.35um 2P4M CMOS technology and this paper presents the theory, implementation and measured results.

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• Journal article
  Georgiou P, Toumazou C, 2009,
  , ELECTRONICS LETTERS, Vol: 45, Pages: 1112-U17, ISSN: 0013-5194
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  • Citations: 13
• Journal article
  Huang Y, Drakakis EM, Toumazou C, 2009,
  , Microelectronics Journal, Vol: 40, Pages: 1458-1465, ISSN: 0026-2692
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