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Dive into the research topics where Ioannis Zeimpekis is active.

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Featured researches published by Ioannis Zeimpekis.


IEEE\/ASME Journal of Microelectromechanical Systems | 2012

Characterization of a Mechanical Motion Amplifier Applied to a MEMS Accelerometer

Ioannis Zeimpekis; Ibrahim Sari; Michael Kraft

In this paper, a mechanical amplification concept for microelectromechanical systems (MEMS) physical sensors is proposed with the aim to improve their sensitivity. The scheme is implemented using a system of micromachined levers (microlevers) as a deflection amplifying mechanism. The effectiveness of the mechanism is demonstrated for a capacitive accelerometer. A proof-of-concept single-axis mechanically amplified accelerometer with an amplification factor of 40 has been designed, simulated, and fabricated, and results from its evaluation are presented in this paper. The sensors amplified output has a sensitivity of 2.39 V/g using an open-loop capacitive pick-off circuit based on charge amplifiers. Experimental results show that the addition of the mechanical amplifier does not alter the noise floor of the sensor. The measured natural frequency of the first mode of the sensor is at 734 Hz, and the full-scale measurement range is up to 7 g with a maximum nonlinearity of 2%. It is shown, through comparison with a conventional design, that the mechanically amplified accelerometer provides higher deflection without sacrificing bandwidth.


Analytical Chemistry | 2016

Low-Cost Nanoribbon Sensors for Protein Analysis in Human Serum Using a Miniature Bead-Based Enzyme-Linked Immunosorbent Assay

Chunxiao Hu; Ioannis Zeimpekis; Kai Sun; Sally Anderson; P. Ashburn; Hywel Morgan

We describe a low cost thin-film transistor (TFT) nanoribbon sensor for detection of the inflammatory biomarker C-reactive protein (CRP) in human serum via a miniature bead-based enzyme-linked immunosorbent assay (ELISA). The TFT nanoribbon sensor measures the reaction products from the ELISA via pH changes. The bead-based ELISA decouples the protein functionalization steps from the sensor surface, increasing the signal and simplifying the assay. The ability to directly sense proteins in human serum in this way overcomes the Debye length limitation associated with nanowire and nanoribbon biosensors. Compared to classically fabricated nanowires, the TFT nanoribbon sensors are simple, extremely easy to fabricate, and should therefore be much cheaper to manufacture. TFT nanoribbon sensors, configured to measure pH, were used for quantitative detection of CRP spiked into human serum at concentrations as low as 0.2 ng/mL, which is 10 000 times lower than needed for diagnostic purposes, providing the potential for applications that require very high sensitivity.


international conference on micro electro mechanical systems | 2014

Low noise vacuum MEMS closed-loop accelerometer using sixth-order multi-feedback loops and local resonator sigma delta modulator

Fang Chen; Weizheng Yuan; Honglong Chang; Ioannis Zeimpekis; Michael Kraft

This paper reports on the design, implementation of a novel sixth-order sigma-delta modulator (ΣΔM) MEMS closed-loop accelerometer with extended bandwidth in a vacuum environment (~0.5Torr), which can coexist on a single die (or package) with other sensors requiring vacuum packaging. The fully differential accelerometer sensing element with a large proof mass (4×7mm2) was designed and fabricated on a Silicon-on-Insulator (SOI) wafer with 50μm-thick structural layer. Four electronic integrators were cascaded with the sensing element for high-order noise shaping ability. The local feedback paths created a local resonator producing a notch to further suppress the total in-band quantization noise. Measurement results show the overall noise floor achieved was -120dBg/√Hz, which is equivalent to a noise acceleration value of 1.2μg/√Hz in a 500Hz bandwidth; the scale factor was 950mV/g for input accelerations up to ±6g.


Nanotechnology | 2016

Effect of subthreshold slope on the sensitivity of nanoribbon sensors

Kai Sun; Ioannis Zeimpekis; Chunxiao Hu; N.M.J. Ditshego; Owain Thomas; M.R.R. de Planque; Harold Chong; Hywel Morgan; P. Ashburn

In this work, we investigate how the sensitivity of a nanowire or nanoribbon sensor is influenced by the subthreshold slope of the sensing transistor. Polysilicon nanoribbon sensors are fabricated with a wide range of subthreshold slopes and the sensitivity is characterized using pH measurements. It is shown that there is a strong relationship between the sensitivity and the device subthreshold slope. The sensitivity is characterized using the current sensitivity per pH, which is shown to increase from 1.2% ph(-1) to 33.6% ph(-1) as the subthreshold slope improves from 6.2 V dec(-1) to 0.23 V dec(-1) respectively. We propose a model that relates current sensitivity per pH to the subthreshold slope of the sensing transistor. The model shows that sensitivity is determined only on the subthreshold slope of the sensing transistor and the choice of gate insulator. The model fully explains the values of current sensitivity per pH for the broad range of subthreshold slopes obtained in our fabricated nanoribbon devices. It is also able to explain values of sensitivity reported in the literature, which range from 2.5% pH(-1) to 650% pH(-1) for a variety of nanoribbon and nanowire sensors. Furthermore, it shows that aggressive device scaling is not the key to high sensitivity. For the first time, a figure-of-merit is proposed to compare the performance of nanoscale field effect transistor sensors fabricated using different materials and technologies.


IEEE Transactions on Electron Devices | 2014

Three-Mask Polysilicon Thin-Film Transistor Biosensor

Kai Sun; Ioannis Zeimpekis; Marta Lombardini; N.M.J. Ditshego; Stuart Pearce; Kian Shen Kiang; Owain Thomas; Maurits R.R. de Planque; Harold Chong; Hywel Morgan; P. Ashburn

Biosensors are commonly produced using a siliconon-insulator (SOI) CMOS process and advanced lithography to define nanowires. In this paper, a simpler and cheaper junctionless three-mask process is investigated, which uses thin-film technology to avoid the use of SOI wafers, in situ doping to avoid the need for ion implantation and direct contact to a low-doped polysilicon film to eliminate the requirement for heavily doped source/drain contacts. Furthermore, TiN is used to contact the biosensor source/drain because it is a hard resilient material that allows the biosensor chip to be directly connected to a printed circuit board without wire bonding. pH sensing experiments, combined with device modeling, are used to investigate the effects of contact and series resistance on the biosensor performance, as this is a key issue when contacting directly to low-doped silicon. It is shown that in situ phosphorus doping concentrations in the range 4 × 1017-3 × 1019 cm-3 can be achieved using 0.1% PH3 flows between 4 and 20 sccm. Furthermore, TiN makes an ohmic contact to the polysilicon even at the bottom end of this doping range. Operation as a biosensor is demonstrated by the detection of C-reactive protein, an inflammatory biomarker for respiratory disease.


Biosensors and Bioelectronics | 2017

Ultra-fast electronic detection of antimicrobial resistance genes using isothermal amplification and thin film transistor sensors

Chunxiao Hu; Sumit Kalsi; Ioannis Zeimpekis; Kai Sun; P. Ashburn; Carrie Turner; J. Mark Sutton; Hywel Morgan

A low cost thin-film transistor (TFT) nanoribbon (NR) sensor has been developed for rapid real-time detection of DNA amplification using an isothermal Recombinase Polymerase Amplification (RPA) method. The semiconductor chip measures DNA amplification through a pH change, rather than via fluorescence. The utility of the method was demonstrated by amplifying CTX-M and NDM, two genes that confer bacterial resistance to cephalosporins and carbapenems, respectively. It is shown that this approach provides extremely fast and sensitive detection. It can detect <10 copies of the gene in genomic DNA extracted from E. coli or K. pneumoniae clinical isolates within a few minutes. A differential readout system was developed to minimize the effect of primer-dimer amplification on the assay. The simple device has the potential for low cost, portable and real-time nucleic acid analysis as a Point of Care device.


Nanotechnology | 2016

Dual-gate polysilicon nanoribbon biosensors enable high sensitivity detection of proteins

Ioannis Zeimpekis; Kai Sun; Chunxiao Hu; N.M.J. Ditshego; Owain Thomas; M.R.R. de Planque; Harold Chong; Hywel Morgan; P. Ashburn

We demonstrate the advantages of dual-gate polysilicon nanoribbon biosensors with a comprehensive evaluation of different measurement schemes for pH and protein sensing. In particular, we compare the detection of voltage and current changes when top- and bottom-gate bias is applied. Measurements of pH show that a large voltage shift of 491 mV pH(-1) is obtained in the subthreshold region when the top-gate is kept at a fixed potential and the bottom-gate is varied (voltage sweep). This is an improvement of 16 times over the 30 mV pH(-1) measured using a top-gate sweep with the bottom-gate at a fixed potential. A similar large voltage shift of 175 mV is obtained when the protein avidin is sensed using a bottom-gate sweep. This is an improvement of 20 times compared with the 8.8 mV achieved from a top-gate sweep. Current measurements using bottom-gate sweeps do not deliver the same signal amplification as when using bottom-gate sweeps to measure voltage shifts. Thus, for detecting a small signal change on protein binding, it is advantageous to employ a double-gate transistor and to measure a voltage shift using a bottom-gate sweep. For top-gate sweeps, the use of a dual-gate transistor enables the current sensitivity to be enhanced by applying a negative bias to the bottom-gate to reduce the carrier concentration in the nanoribbon. For pH measurements, the current sensitivity increases from 65% to 149% and for avidin sensing it increases from 1.4% to 2.5%.


biomedical circuits and systems conference | 2015

Towards a high-precision, embedded system for versatile sensitive biosensing measurements

Konstantinos I. Papadimitriou; Ioannis Zeimpekis; Despina Moschou; Kai Sun; Chunxiao Hu; P. Ashburn; Hywel Morgan; Themistoklis Prodromakis

This paper demonstrates a versatile, high-accuracy, data-acquisition electronic platform for biosensing measurements, capable of collecting minute current and voltage input signals, stemming from various types of amperometric and potentiometric biosensors. The instrument is able to process the incoming analog signals in a digital manner and export them back to the user either as an amplified analog signal or in digital format through a USB 2.0 interface. The proposed system comprises off-the-shelf IC components and a commercially available FPGA-based DSP unit. The performance of the instrumentation platform has been tested initially by means of very small ideal current and voltage signals generated by precise electronic equipments and subsequently has been validated via proof-of-concept experiments with amperometric and potentiometric sensors. The results shown in this paper exhibit potential for integrating specific sections of the proposed instrumentation board with appropriate biosensors, towards developing affordable, yet reliable Point-Of-Care (POC) diagnostic tools for sensitive biochemical measurements.


Journal of Micromechanics and Microengineering | 2013

Improved surface quality of anisotropically etched silicon {111} planes for mm-scale integrated optics

J. P. Cotter; Ioannis Zeimpekis; Michael Kraft; E. A. Hinds

We have studied the surface quality of millimeter-scale optical mirrors produced by etching CZ and FZ silicon wafers in potassium hydroxide to expose the


Applied Physics Letters | 2018

Cavity enhanced third harmonic generation in graphene

Chris Beckerleg; Thomas J. Constant; Ioannis Zeimpekis; Samuel M. Hornett; Christopher Craig; D.W. Hewak; Euan Hendry

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Kai Sun

University of Southampton

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P. Ashburn

University of Southampton

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Hywel Morgan

University of Southampton

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Chunxiao Hu

University of Southampton

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D.W. Hewak

University of Southampton

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Harold Chong

University of Southampton

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Chung-Che Huang

University of Southampton

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Katrina Morgan

University of Southampton

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