Anthony J Walton

The University of Edinburgh | UoE · School of Engineering

The development of robust implantable sensors is important in the successful advancement of personalised medicine as they have the potential to provide in situ real-time data regarding the status of health and disease and the effectiveness of treatment. Tissue pH is a key physiological parameter and herein, we report the design, fabrication, functi...

Etch selectivity between layers is an important parameter in the fabrication of microelectronics and microsystems. This is particularly true in the case of isotropic gas/vapour etching methods used to release free standing structures through the selective etching of sacrificial layers. Commonly used structural materials have been reported to be lar...

The vapour etching of silicon sacrificial layers is often a critical process in the fabrication of micro/nanosystems. This method has a number of attractive features, in particular, high etch rates of sacrificial silicon layers and good selectivities associated with photoresist, SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="h...

This article details and compares the technology options for post-processing foundry produced CMOS at chip-scale to enable More than Moore functionality. In many cases there are attractions in using chip-based processing through the Multi-Project Wafer route that is frequently employed in research, early-stage development and low-volume production....

Hypoxia commonly occurs within tumours and is a major cause of radiotherapy resistance. Clinical outcomes could be improved by locating and selectively increasing the dose delivered to hypoxic regions. Here we describe a miniature implantable sensor for real-time monitoring of tissue oxygenation that could enable this novel treatment approach to be...

Hypoxia commonly occurs within tumours and is a major cause of radiotherapy resistance. Clinical outcomes could be improved by locating and selectively increasing the dose delivered to hypoxic regions. Here we describe a miniature implantable sensor for real-time monitoring of tissue oxygenation that could enable this novel treatment approach to be...

Nafion is a solid electrolyte polymer that can be used as a sensor membrane in microfabricated electrochemical oxygen sensors. It allows ions to be transported between the sensor electrodes and removes the need for a liquid electrolyte. Here we used a series of small square Nafion test structures, fabricated on a variety of materials using standard...

For analytical applications involving label-free biosensors and multiple measurements, i.e., across an electrode array, it is essential to develop complete sensor systems capable of functionalization and of producing highly consistent responses. To achieve this, a multi-microelectrode device bearing twenty-four equivalent 50 µm diameter Pt disc mic...

Infrared (IR) thermography was combined with simultaneous high speed flow visualisation and pressure measurements from integrated pressure sensors inside the microchannel, in order to produce two-dimensional (2D) high spatial and temporal resolution two-phase heat transfer coefficient (HTC) maps across the full domain of a polydimethylsiloxane (PDM...

The authors acknowledge support from the Innovative electronic Manufacturing Research Centre (IeMRC) through the EPSRC funded flagship project SMART MICROSYSTEMS (FS/01/02/10), Knowledge Transfer Partnership No KTP010548, EPSRC project EP/L026899/1, EP/F063865/1; EP/F06294X/1, EP/P018998/1, the Royal Society-Research Grant (RG090609) and Newton Mob...

Recently, piezoelectric thin films including zinc oxide (ZnO) and aluminium nitride (AlN) have found a broad range of lab-on-chip applications such as biosensing, particle/cell concentrating, sorting/patterning, pumping, mixing, nebulisation and jetting. Integrated acoustic wave sensing/microfluidic devices have been fabricated by depositing these...

This article presents a set of low-temperature deposition and etching processes for the integration of electrochemically deposited Ni-Fe alloys in complex magnetic microelectromechanical systems, as Ni-Fe is known to suffer from detrimental stress development when subjected to excessive thermal loads. A selective etch process is reported which enab...

This paper presents a method of electrically determining the permeability of patterned, electroplated ferromagnetic alloys and brings together the simultaneous wafer mapping of relative permeability, electrical resistivity, and mechanical strain of these electrodeposited films, as well as the layer thickness and alloy composition. The wafer mapping...

Current approaches to molecular diagnostics rely heavily on PCR amplification and optical detection methods which have restrictions when applied to point of care (POC) applications. Herein we describe the development of a label-free and amplification-free method of pathogen detection applied to Escherichia coli which overcomes the bottleneck of com...

Microelectrodes have a number of advantages over macroelectrodes for quantitative electroanalysis and monitoring, including reduced iR drop, high signal to noise and reduced sensitivity to convection. Their use in molten salts has been generally precluded by the combined materials challenges of stresses associated with thermal cycling and physical...

Microfabricated square electrodes with finely controlled highly reproducible dimensions have been developed for electrochemical analysis of high-temperature molten salt (MS). These microelectrodes have been fabricated using photolithographic techniques on silicon wafers and have been designed for operation in lithium chloride/potassium chloride eut...

Electrodeposited alloys of nickel and iron are prone to suffer from the development of undesirable-stress gradients resulting from process steps and heat treatments following deposition. As a result, the yield associated with devices using permalloy (Ni–Fe, 80%–20%) films can be severely compromised. Although electrodeposition recipes have been for...

Introduction Recently, we reported a new atmospheric pressure ionization (API) technology termed as surface acoustic wave nebulization (SAWN), which is ‘softer’ than ESI based on our previous study. (S. Heron et al. Anal. Chem. 2010, Y. Huang et al. J Am Soc Mass Spectrom. 2012). A new miniaturized standing wave (miniSW) SAWN chip has been designed...

This paper presents a method of electrically determining the permeability of patterned electroplated structures and brings together the simultaneous wafer mapping of magnetic permeability, electrical resistivity and mechanical strain of electroplated ferromagnetic films together with the thickness of the films and their composition. The wafer mappi...

Efficient nebulization of liquid sessile droplets (water and water/glycerol mixtures) was investigated using standing waves generated using ZnO/Si surface acoustic wave (SAW) devices under different RF powers, frequencies and liquid viscosity (varied glycol concentrations in water). At such high RF powers, there are strong competitions between vert...

Molten salts (MSs) are an attractive medium for chemical and electrochemical processing and as a result there is demand for MS-compatible analysis technologies. However, MSs containing redox species present a challenging environment in which to perform analytical measurements because of their corrosive nature, significant thermal convection and the...

The development and application of magnetic technologies employing microfabricated magnetic structures for the production of switching components has generated enormous interest in the scientific and industrial communities over the last decade. Magnetic actuation offers many benefits when compared to other schemes for microelectromechanical systems...

Rayleigh surface acoustic wave (SAW) devices based on 128° YX LiNbO3 and ZnO/Si substrates with different resonant frequencies from ∼62 MHz to ∼275 MHz were fabricated and characterized. Effects of SAW frequency and power on microfluidic performance (including streaming, pumping, and jetting) were investigated. SAW excitation frequency influenced t...

Electro Wetting on Dielectrics (EWOD) and Surface Acoustic Wave (SAW) device technologies were designed, fabricated and implemented into a novel digital micro-droplet Lab-on-a-Chip solution for application within intact protein measurement workflows by analytical mass spectrometry. Digital droplet actuation devices employing Electro-Wetting on Di...

A novel technique for the production of nanoscale electrode arrays that uses standard microfabrication processes and micron-scale photolithography is reported here in detail. These microsquare nanoband edge electrode (MNEE) arrays have been fabricated with highly reproducible control of the key array dimensions, including the size and pitch of the...

This report introduces a new statistical model for time-resolved photon detection in a generic single-photon-sensitive sensor array. The model is validated by comparing modelled data with experimental data collected on a single-photon avalanche diode sensor array. Data produced by the model are used alongside corresponding experimental data to calc...

Micron resolution photolithography has been employed to make microsquare nanoband edge electrode (MNEE) arrays with reproducible and systematic control of the crucial dimensional parameters, including array element size and spacing and nanoelectrode thickness. The response of these arrays, which can be reproducibly fabricated on a commercial scale,...

In this experimental study bubble growth from an isolated artificial cavity micro-fabricated on a 380 gm thick silicon wafer was investigated. The horizontally oriented boiling surface was heated by a thin resistance heater integrated on the rear of the silicon test section. The temperature was measured using an integrated micro-sensor situated on...

An MRSA assay requiring neither labeling nor amplification of target DNA has been developed. Sequence specific binding of fragments of bacterial genomic DNA is detected at femtomolar concentrations using electrochemical impedance spectroscopy (EIS). This has been achieved using systematic optimisation of probe chemistry (PNA self-assembled monolaye...

Microvolcano like surface acoustic wave (SAW) nebulization/ atomization has been realised on ZnO film based SAW devices. The SAW nebulization (SAWN) process has been observed to produce significant mist generation and ejected satellite droplets. By modifying the geometry of the interdigitated transducers to reduce the wavelengths from 400 μm to 64...

Electrodeposition of platinum metal from a chloride-based platinum electroplating bath at 35 °C onto high quality titanium nitride electrodes produced by standard microfabrication techniques has been demonstrated and characterised using electrochemical methods and scanning electron microscopy. When using a relatively simple two potential step elect...

The performance of two electrode architectures with broadly similar overall active electrode areas are examined. The first is an electrode comprising a single contiguous area (a disc) and the second is an electrode in which the cumulative electrode area is dispersed over a wide area as a 50 nm thickness platinum nanoband. A direct comparison of the...

Molten salts have proven to be an ideal medium for the development of a number of electrochemical processes. However, there is a real need in such processes for techniques to be developed which are able to sense and analyse the properties of redox active species in the extreme conditions found in molten salts. This paper reports the work undertaken...

This work describes an experimental investigation of bubble dynamics and the effect on flow boiling instabilities and heat transfer in a multiple-microchannel heat sink. In this paper, results of the experimental investigation of bubble dynamics are presented and discussed. The microchannel heat sink contained 40 parallel, rectangular channels havi...

This paper reports the development of processing methods and test structures for the characterisation and evaluation of Parylene-C as an insulating structural layer material for integration with planar micro-inductors. The process involves the filling of high aspect ratio gaps between copper structures with Parylene and subsequent chemical mechanic...

An improved bottom-up electroplating technique has been successfully developed for the fabrication of TSV arrays with 9.5:1 aspect ratios. 125,500 TSVs have been fabricated in an area of 6×6 cm with a horizontal and vertical pitch of 240 μm. A method of visually inspecting the via yield is presented, and Kelvin test structures and contact chain tes...

This paper presents the fabrication of a series of test devices designed to prove the viability of electroplated NiFe freestanding structures for use in magnetically actuated MEMS switches. Preliminary results show promising actuation responses and further release optimisation and testing will enable the quantitative measurement of the desired char...

Submillimetre Common-User Bolometer Array 2 (SCUBA-2) is an innovative 10 000 pixel bolometer camera operating at submillimetre wavelengths on the James Clerk Maxwell Telescope (JCMT). The camera has the capability to carry out wide-field surveys to unprecedented depths, addressing key questions relating to the origins of galaxies, stars and planet...

Inkjet printing is a promising additive manufacturing technology that is being increasingly used in applications such as displays, electronics and electronic packaging. Through Silicon Vias (TSVs) is an important enabling technology for advanced electronic packaging. The direct write nature of inkjet printing would also allow flexible packaging sol...

This article reports the results obtained by screen printing through a microengineered electroformed nickel screen to successfully fill TSVs and print a redistribution layer on Si wafers. Redistribution lines were deposited down to 40μm width at 70μm pitch. Straight through hole sections on the microengineered screen formed a stencil/screen hybrid...

Surface acoustic wave (SAW) nebulization/atomization has been realised on thin ZnO film based SAW devices. The surface acoustic wave nebulization (SAWN) process has been observed to produce significant mist generation and ejected satellite droplets. By modifying the geometry of the interdigitated transducers to reduce the wavelengths from 400 μm to...

We report an experimental and numerical characterization of three-dimensional acoustic streaming behavior in small droplets of volumes (1-30 μl) induced by surface acoustic wave (SAW). We provide a quantitative evidence of the existence of strong nonlinear nature of the flow inertia in this SAW-driven flow over a range of the newly defined acoustic...

Acoustic streaming of ink particles inside a water microdroplet generated by a surface acoustic wave (SAW) has been studied numerically using a finite volume numerical method and these results have been verified using experimental measurements. Effects of SAW excitation frequency, droplet volume, and radio-frequency (RF) power are investigated, and...

SCUBA-2 is a revolutionary 10,000 pixel wide-field submillimetre camera, recently commissioned and now operational at the James Clerk Maxwell Telescope (JCMT). Twin focal planes each consist of four 32 by 40 sub-arrays of superconducting Transition Edge Sensor (TES) bolometers, the largest combined low temperature bolometer arrays in operation, to...

SU-8 is an epoxy-based, negative photoresist that is widely used in the manufacturing of micromechanical systems. The polymer cross-linking that occurs during the photolithographic processing of SU-8 can result in high levels of stress in the patterned film. This has significant implications for the yield and reliability of SU-8 structures and need...

This paper presents details of the design and fabrication of test structures specifically designed for the characterization 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...

Resistive electrical test structures have been designed to enable the characterization of optical proximity correction (OPC) applied to a right-angled corner in a conducting track. The OPC consists of square serifs that are either added to the outside corner or subtracted from the inner corner. Varying degrees of OPC can be applied by changing the...

Nucleate boiling is commonly characterised as a very complex and elusive process. Many involved mechanisms are still not fully understood and more detailed consideration is needed. In this study, bubble growth from micro-fabricated artificial cavities with varied spacing on a horizontal 380 μm thick silicon wafer was investigated. The horizontally...

This paper presents integrated microfluidic lab-on-a-chip technology combining surface acoustic wave (SAW) and electro-wetting on dielectric (EWOD). This combination has been designed to provide enhanced microfluidic functionality and the integrated devices have been fabricated using a single mask lithographic process. The integrated technology use...

Surface acoustic waves (SAW) generated in a piezoelectric substrate may be used to manipulate micro-scale droplets of liquid in a digital microfluidic system for lab-on-a-chip applications. The wettability of the surface over which a droplet is driven determines the ease and speed with which the droplet is propelled. This provides the opportunity t...

This paper details the design, fabrication and characterisation of a piezoresistive membrane deflection test structure for the electrical evaluation of hermeticity in low cavity volume package. This test structure uses the 0-level silicon cap, defined in the MultiMEMS foundry service, as a deflecting membrane to electrically monitor changes in pack...

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The uncontrolled development of stress within MEMS deposited and processed films can be detrimental for both device performance and reliability. This work focuses on combining the data from previously reported strain measurements obtained from mechanical test structures with new nano-indentation measurements of Young's modulus on both micromachined...

The self-annealing properties at room temperature of electrochemically deposited copper have been investigated for the first time using test structures to simultaneously measure the spatial variation of sheet resistance and film stress with time. The phase changes associated with the self-annealing of copper on 200mm wafers have been observed over...

Using electrochemical impedance spectroscopy (EIS) the sensitive and specific detection of the antibiotic resistance gene mecA has been demonstrated. The gene sequence was obtained from clinical Staphylococcus aureus isolates. Initially a mecA specific probe was selected from hybridisation tests with a 3' and 5' version of a previously published pr...