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D Gruber,
Y Li,
S Smith,
A Tiwari,
F Deng,
A. A Stokes, J.G. Terry,
A.S. Bunting,
L Mackay,
P Langridge-Smith,
A J Walton
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ABSTRACT: This paper presents a methodology together with a characterisation system for rapidly and quantitatively evaluating the lifetime and reliability of Electro-Wetting-on-Dielectric (EWOD) microfluidic devices. By studying the contact angle (CA) change when electrowetting forces are applied on the test structure, the number of times of a droplet can be switched between relaxed and actuated states can be characterised. This paper describes the development of an automated measurement system together with test structures designed to quickly characterise and optimise EWOD dielectric layer compositions. This enables the rapid determination of the driving voltage that results in the longest lifetime of the device, providing the tools to optimise both the process, architecture and the voltage driving scheme.
IEEE International Conference on Microelectronic Test Structures (ICMTS 2011); 01/2011
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Y. Li,
Y.Q. Fu,
B.W. Flynn,
W. Parkes,
Y. Liu,
S. Brodie, J.G. Terry,
L.I. Haworth,
A.S. Bunting,
J.T.M. Stevenson,
S. Smith,
A.J. Walton
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ABSTRACT: This paper presents details of the design and fabrication of test structures specifically designed for the characterisation of two distinct digital microfluidic technologies: Electro-Wetting On Dielectric (EWOD) and Surface Acoustic Wave (SAW). A test chip has been fabricated that includes structures with a wide range of dimensions and provides the capability to characterise enhanced droplet manipulation as well as other integrated functions. In particular, we detail the use of EWOD to anchor droplets while SAW excitation is applied to perform mixing.
Microelectronic Test Structures (ICMTS), 2010 IEEE International Conference on; 04/2010
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ABSTRACT: Previously reported suspended microrotating test structures designed to measure the stress in thick layers of electroplated Permalloy (NiFe alloy) have been analysed using finite element modelling and compared with experimental measurements. These results have been used to optimise a stress sensor test structure and design a new mask, with an array of test structures specifically designed to wafer map the stress of thick nickel and Permalloy films. This is the first time these structures have been employed for determining spatial variation in film stress and the results of this characterisation are reported for nickel.
Microelectronic Test Structures (ICMTS), 2010 IEEE International Conference on; 04/2010
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Y Li,
Y.Q. Fu,
B.W. Flynn,
W Parkes,
Y Liu,
S. Brodie, J.G. Terry,
L.I. Haworth,
A.S. Bunting,
J T M Stevenson,
S Smith,
A J Walton
[show abstract]
[hide abstract]
ABSTRACT: This paper presents details of the design and fabrication of test structures specifically designed for the characterisation of two distinct digital microfluidic technologies: Electro-Wetting On Dielectric (EWOD) and Surface Acoustic Wave (SAW). A test chip has been fabricated that includes structures with a wide range of dimensions and provides the capability to characterise enhanced droplet manipulation as well as other integrated functions. In particular, we detail the use of EWOD to anchor droplets while SAW excitation is applied to perform mixing.
IEEE International Conference on Microelectronic Test Structures (ICMTS 2010); 01/2010
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IEEE International Conference on Microelectronic Test Structures (ICMTS 2010); 01/2010
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Y. Li,
B.W. Flynn,
W. Parkes,
Y. Liu,
Y. Feng,
A.D. Ruthven, J.G. Terry,
L.I. Haworth,
A. Bunting,
J.T.M. Stevenson,
S. Smith,
P. Bobbili,
Y.Q. Fu,
A.J. Walton
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ABSTRACT: This paper details the first reported integration of two advanced digital microfluidic technologies where 100 mum silicon cubes are transported with electrowetting on dielectric (EWOD) and the droplet then held with EWOD while the silicon cubes are mixed with another liquid using a surface acoustic wave (SAW). Together these two technologies provide a comprehensive lab-on-a-chip combination with well developed functionalities. These include droplet generation, splitting and transportation offered by EWOD with transportation, mixing and biosensing being potentially available with SAW. The fabrication of both EWOD and SAW structures on LiNbO<sub>3</sub> substrates used low temperature Ta/Ta<sub>2</sub>O<sub>5</sub>/CYTOP layer deposition and patterning technologies, which enabled efficient transportation and mixing functions to be demonstrated.
Solid State Device Research Conference, 2009. ESSDERC '09. Proceedings of the European; 10/2009
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ABSTRACT: Suspended microrotating test structures designed to measure the stress in thin, surface micromachined films have been applied to the production of thick layers of electroplated permalloy (NiFe alloy). This process has particular significance to the production of magnetic MEMS components and devices. It is extremely important to characterise the stress in such materials, especially where these films are to be used on wafers with underlying integrated circuitry as it is well known that the matching of transistors can be affected by mechanical strains induced by interconnect features running above them. A new test chip has been designed and fabricated in order to determine the optimum dimensions for permalloy stress sensor structures.
Microelectronic Test Structures, 2009. ICMTS 2009. IEEE International Conference on; 05/2009
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Y. Mita,
Y. Li,
M. Kubota,
S. Morishita,
W. Parkes,
L.I. Haworth,
B.W. Flynn, J.G. Terry,
T.-B. Tang,
A.D. Ruthven,
S. Smith,
A.J. Walton
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[hide abstract]
ABSTRACT: A silicon swimming robot or pond skating device has been demonstrated. It floats on liquid surfaces using surface tension and is capable of movement using electrowetting on dielectric (EWOD) based propulsion. Its dimensions are 6 × 9 mm and the driving mechanism involves first trapping air bubbles within the liquid onto the hydrophobic surface of the device. The air bubbles are then moved using EWOD, which provides the propulsion. The device employs a recently reported EWOD technology enabling a driving voltage of ≈15 V, which is low enough for RF power transmission, thus facilitating wire-free movement. A wired version has been measured to move 1.35 mm in 168 ms (a speed of 8 mm s−1). This low voltage-EWOD (<15 V) device, fabricated using a CMOS compatible process, is believed to be the world’s smallest swimming MEMS device that has no mechanical moving parts. The paper also reports results of EWOD droplet operation driven by wireless power transmission and demonstrates that such a wireless design can be successfully mounted on a floating EWOD device to produce movement.
Solid-State Electronics 04/2009; · 1.40 Impact Factor
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Y Li,
B.W. Flynn,
W Parkes,
Y Liu,
Y Feng,
A.D. Ruthven, J.G. Terry,
L.I. Haworth,
A Bunting,
J T M Stevenson,
S Smith,
P Bobbili,
Y.Q. Fu,
A J Walton
Proceedings of the European Solid State Device Research Conference, 2009. ESSDERC '09.; 01/2009
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Y. Mita,
Y. Li,
M. Kubota,
W. Parkes,
L.I. Haworth,
B.W. Flynn, J.G. Terry,
T.B. Tang,
A.D. Ruthven,
S. Smith,
A.J. Walton
Solid-State Electronics 01/2009; 53:798-802. · 1.40 Impact Factor
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T B Tang,
S Smith,
B W Flynn,
J T M Stevenson,
A M Gundlach,
H M Reekie,
A F Murray,
D Renshaw,
B Dhillon,
A Ohtori,
Y Inoue, J G Terry,
A J Walton
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[hide abstract]
ABSTRACT: A wireless power transfer and communication system based on near-field inductive coupling has been designed and implemented. The feasibility of using such a system to remotely control drug release from an implantable drug delivery system is addressed. The architecture of the wireless system is described and the signal attenuation over distance in both water and phosphate buffered saline is studied. Additionally, the health risk due to exposure to radio frequency (RF) radiation is examined using a biological model. The experimental results demonstrate that the system can trigger the release of drug within 5 s, and that such short exposure to RF radiation does not produce any significant (<or= 1 degrees C) heating in the biological model. The conclusion of the work is that this system could replace a chemical battery in an implantable system, eliminating the risks associated with battery failure and leakage and also allowing more compact designs for applications such as drug delivery.
IET Nanobiotechnology 10/2008; 2(3):72-9. · 1.83 Impact Factor
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ABSTRACT: The molecular conformation of a synthetic branched, 4-way DNA Holliday junction (HJ) was electrochemically switched between the open and closed (stacked) conformers. Switching was achieved by electrochemically induced quantitative release of Mg(2+) ions from the oxidised poly(N-methylpyrrole) film (PPy), which contained polyacrylate as an immobile counter anion and Mg(2+) ions as charge compensating mobile cations. This increase in the Mg(2+) concentration screened the electrostatic repulsion between the widely separated arms in the open HJ configuration, inducing switching to the closed conformation. Upon electrochemical reduction of PPy, entrapment of Mg(2+) ions back into the PPy film induced the reverse HJ switching from the closed to open state. The conformational transition was monitored using fluorescence resonance energy transfer (FRET) between donor and acceptor dyes each located at the terminus of one of the arms. The demonstrated electrochemical control of the conformation of the used probe-target HJ complex, previously reported as a highly sequence specific nanodevice for detecting of unlabelled target [Buck, A.H., Campbell, C.J., Dickinson, P., Mountford, C.P., Stoquert, H.C., Terry, J.G., Evans, S.A.G., Keane, L., Su, T.J., Mount, A.R., Walton, A.J., Beattie, J.S., Crain, J., Ghazal, P., 2007. Anal. Chem., 79, 4724-4728], allows the development of electronically addressable DNA nanodevices and label-free gene detection assays.
Biosensors & bioelectronics 06/2008; 24(3):422-8. · 5.43 Impact Factor
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C P Mountford,
A H Buck,
C J Campbell,
P Dickinson,
E E Ferapontova, J G Terry,
J S Beattie,
A J Walton,
P Ghazal,
A R Mount,
J Crain
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ABSTRACT: This paper investigates the properties of a simple DNA-based nanodevice capable of detecting single base mutations in unlabeled nucleic acid target sequences. Detection is achieved by a two-stage process combining first complementary-base hybridization of a target and then a conformational change as molecular recognition criteria. A probe molecule is constructed from a single DNA strand designed to adopt a partial cruciform structure with a pair of exposed (unhybridized) strands. Upon target binding, a switchable cruciform construct (similar to a Holliday junction) is formed which can adopt open and closed junction conformations. Switching between these forms occurs by junction folding in the presence of divalent ions. It has been shown from the steady-state fluorescence of judiciously labeled constructs that there are differences between the fluorescence resonance energy transfer (FRET) efficiencies of closed forms, dependent on the target sequence near the branch point, where the arms of the cruciform cross. This difference in FRET efficiency is attributed to structural variations between these folded junctions with their different branch point sequences arising from the single base mutations. This provides a robust means for the discrimination of single nucleotide mismatches in a specific region of the target. In this paper, these structural differences are analyzed by fitting observed time-resolved donor fluorescence decay data to a Gaussian distribution of donor-acceptor separations. This shows the closest mean separation (approximately 40 A) for the perfectly matched case, whereas larger separations (up to 50 A) are found for the single point mutations. These differences therefore indicate a structural basis for the observed FRET differences in the closed configuration which underpins the operation of these devices as biosensors capable of resolving single base mutations.
The Journal of Physical Chemistry B 03/2008; 112(8):2439-44. · 3.70 Impact Factor
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Y Mita,
Y Li,
M Kubota,
W Parkes,
L.I. Haworth,
B.W. Flynn, J.G. Terry,
T.B. Tang,
A.D. Ruthven,
S Smith,
A J Walton
38th European Solid-State Device Research Conference, 2008. ESSDERC 2008.; 01/2008
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S Smith,
T B Tang, J G Terry,
J T M Stevenson,
B W Flynn,
H M Reekie,
A F Murray,
A M Gundlach,
D Renshaw,
B Dhillon,
A Ohtori,
Y Inoue,
A J Walton
[show abstract]
[hide abstract]
ABSTRACT: The development of an implantable system designed to deliver drug doses in a controlled manner over an extended time period is reported. Key performance parameters are the physical size, the power consumption and also the ability to perform wireless communications to enable the system to be externally controlled and interrogated. The system has been designed to facilitate wireless power transfer, which is very important for miniaturisation as it removes the need for a battery.
IET Nanobiotechnology 11/2007; 1(5):80-6. · 1.83 Impact Factor
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ABSTRACT: This paper reports the first direct experimental measurement of electromigration-induced stress in aluminum interconnects, using a series of microrotating stress sensors. The build-up of stress gradients in interconnect metallization, which is concomitant with backstress, has been previously investigated theoretically, but experimental verification using optical or X-ray techniques has proven more difficult. These initial results show a compressive-stress gradient along the line of stress sensors, consistent with that predicted by conventional mass-transport theory. Additionally, these measurements are in qualitative agreement with the mathematical model proposed by Korhonen et al. (1993), with a reduced-stress and increased-diffusion coefficient. These differences are discussed, and the causes postulated. The limited resolution of previous techniques restricts their ability to obtain a detailed characterization, whereas, in principle, this new technique can be scaled to the end of the International Technology Roadmap for Semiconductors. These preliminary findings suggest that the presented technique will provide a valuable tool for the investigation of back-end-of-line interconnect stress in the future.
IEEE Transactions on Device and Materials Reliability 07/2007; · 1.54 Impact Factor
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A.J. Walton,
J.T.M. Stevenson,
I. Underwood, J.G. Terry,
S. Smith,
W. Parkes,
C. Dunare,
H. Lin,
Y. Li,
R. Henderson,
D. Renshaw,
K. Muir,
M. Desmulliez,
D. Flynn,
M.J. MacIntosh,
W.S. Holland,
A.F. Murray,
T.B. Tang,
A. Bunting,
A.M. Gundlach
Micro Electro-Mechanical Systems, 2007. MEMS Technology. 2007 IET Seminar on; 05/2007
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A R Mount,
C P Mountford,
S A G Evans,
T-J Su,
A H Buck,
P Dickinson,
C J Campbell,
L M Keane, J G Terry,
J S Beattie,
A J Walton,
P Ghazal,
J Crain
[show abstract]
[hide abstract]
ABSTRACT: A Holliday junction (HJ) consists of four DNA double helices, with a branch point discontinuity at the intersection of the component strands. At low ionic strength, the HJ adopts an open conformation, with four widely spaced arms, primarily due to strong electrostatic repulsion between the phosphate groups on the backbones. At high ionic strength, screening of this repulsion induces a switch to a more compact (closed) junction conformation. Fluorescent labelling with dyes placed on the HJ arms allows this conformational switch to be detected optically using fluorescence resonance energy transfer (FRET), producing a sensitive fluorescent output of the switch state. This paper presents a systematic and quantitative survey of the switch characteristics of such a labelled HJ. A short HJ (arm length 8 bp) is shown to be prone to dissociation at low switching ion concentration, whereas an HJ of arm length 12 bp is shown to be stable over all switching ion concentrations studied. The switching characteristics of this HJ have been systematically and quantitatively studied for a variety of switching ions, by measuring the required ion concentration, the sharpness of the switching transition and the fluorescent output intensity of the open and closed states. This stable HJ is shown to have favourable switch characteristics for a number of inorganic switching ions, making it a promising candidate for use in nanoscale biomolecular switch devices.
Biophysical Chemistry 01/2007; 124(3):214-21. · 2.20 Impact Factor
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A. J. Walton,
J. T. M. Stevenson,
I. Underwood, J. G. Terry,
S. Smith,
W. Parkes,
C. Dunare,
H. Lin,
Y. Li,
R. Henderson,
D. Renshaw,
K. Muir,
M. Desmulliez,
D. Flynn,
M. J. MacIntosh,
W. S. Holland,
A. F. Murray,
T. B. Tang,
A. Bunting,
A. M. Gundlach
Micro Electro-Mechanical Systems, 2007. MEMS Technology. 2007 IET Seminar on; 01/2007
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C P Mountford,
A R Mount,
S A G Evans,
T-J Su,
P Dickinson,
A H Buck,
C J Campbell, J G Terry,
J S Beattie,
A J Walton,
P Ghazal,
J Crain
[show abstract]
[hide abstract]
ABSTRACT: Conformational transitions in a 4-way DNA junction when titrated with ionic solutions are studied using time-resolved fluorescence resonance energy transfer. Parameters characterising the transition in terms of critical ion concentration (c1/2) and the Hill coefficient for ion binding are obtained by fitting a simple two-state model using steady-state spectra. Data obtained from a fluorescence lifetime plate reader and analysed by fitting a single exponential to donor fluorescence lifetime decays are shown to be in good agreement with the parameters obtained from steady-state measurements. Fluorescence lifetimes, however, offer advantages, particularly in being independent of fluorophore concentration, output intensity, inhomogeneity in the excitation source and output wavelength. We demonstrate preliminary FRET-FLIM images of DNA junction solutions obtained using a picosecond gated CCD which are in agreement with results from a fluorescence lifetime plate reader. The results suggest that time-resolved FRET-FLIM is sensitive to subtle structural changes and may be useful in assays based on 4-way DNA junctions.
Journal of Fluorescence 12/2006; 16(6):839-45. · 2.11 Impact Factor
