Electronic Materials and Devices Laboratory
Nanoscale Science Laboratory
Polysilicon Thin-Film Transistors Group
Ion Beam Processing for Nanometer-Scale Devices
Microliquid Transfer Systems for Biotechnology Applications
Optic Fibre Connectors made from Silicon Nitride Microclips
Focused Ion Beam Tuning of In-plane Vibrating Micromechanical Resonators
Scanning Electron Microscopy and Transmission Electron Microscopy
Highly Integrated Electronic Systems
CUED 125th Anniversary Celebration
Power Electronic Devices and Circuits
Photovoltaic Devices and Solar Power
Vacuum Electronic Devices
Photonics and Parallel Optical Systems
3D Video and Virtual Reality Displays
Professor W.I. Milne
Dr J. Robertson
Dr F. Udrea
Research in the group continues to be centred on the deposition, characterisation and application of thin film amorphous semiconductors.
Work on Diamond Like Carbon has expanded once more and now includes a project on the development of tetrahedrally bonded amorphous carbon (ta-C) for nanolithographic applications in collaboration with Thomson CSF, France, University of Lyon and the Fraunhoffer Institute through an EU Grant "Nanolith". Work on cold cathode emitters for application in back lights for Active Matrix Liquid Crystal Displays and for the production of field emission(FE) displays themselves is also on-going(J54,J71,J72,J99,J100,J103,J132,J133, J134,J144). The back light work is carried out as part of an EU ESPRIT project in collaboration with CRL, Hayes and Sextant Avionique, Bordeaux. Recent results have indicated that electron emission from these films is from sp2 clusters embedded within an sp3 matrix. The work on FE is strongly supported by effort on the structural optical and electrical characteristic of the ta-C and hydrogenerated ta-C (ta-C:H)(J10,J11,J28,J51,J52,J53,J74,J75,J76, J77,J82,J102,J109,J110,J111,J127,J132,J143,J159,J160) , the understanding of the modelling of the growth process themselves(J24) and the plasma process during growth. The latter work is funded through collaboration with Kawasaki Heavy Industries. The use of ta-C, ta-C:H, a-CN(J110,J112,J139,J140) and C:Si as hard coatings for wear and tribological applications(J129) is also ongoing in collaboration with the Cambridge University Physics and Materials Science Departments. Scanning Probe Microscopy of ta-C and related films has also been initiated in close collaboration with the CUED Nanoscale Science group. The potential use of ta-C for TFT manufacture is also being investigated(J90,J98,J104). The interaction between the group and the School of EEE in NTU(J157) Singapore on the electrical characterisation of DLC and related materials is also continuing and a British Council funded interaction between us and the University of Barcelona, Spain on DLC films has just been initiated. Finally a collaboration with the groups in Leeds University and Milan has led to a far greater understanding of the use of both visible and UV. Raman for non-destructive testing of DLC films(J1).
Philips Research Laboratories, Redhill continue to support work on the growth and application of amorphous silicon (a-Si:H) thin films for displays. The main thrust of this work at present is to investigate the deposition of both the active layer (a-Si:H and
microcrystalline Si) and the gate insulator layer (SiOx or SiNx) for the manufacture of Thin Film Transistors (TFTs) at temperatures compatible with the use of plastic substrates. Currently, we are investigating the use of both ECR and ECWR deposition systems for this purpose. Theoretical work on the growth through STM measurements(J57,J58), and stability(J137) of Si:H based devices is also progressing and recently a project on metal-induced crystallisation has begun.
The fabrication of high voltage polycrystalline silicon (poly Si) TFTs using SIPOS field plates has been expanded to include several novel structures(J194). Work on vertical TFTs also continues in collaboration with Liverpool University.
High Dielectric constant oxides such as barium strontium titanate and tantalum pentoxide are to be used as the dielectric layer in DRAMs and ferroelectrics such as lead zironate titanate (PZT) and Strontium Bismuth Tantalate are to be used in ferroelectric non-volatile memories (FeRAMS). We have calculated the Schottky Barrier heights for these oxides and used this to model leakage in such devices(J135,J136).
Finally work on sensors has just begun(J107) and EPSRC has funded a project on SOI-based Smart MOSFET Sensors in collaboration with Professor Gardner at the University of Warwick(J59).
Dr M.E. Welland
The Nanoscale Science Laboratory is primarily concerned with developing and applying methods related to the measurement of structure and physical properties down to atomic dimensions. A substantial part of the work involves the use of scanning probe microscopy to measure surface properties down to atomic spatial resolution. A long term interest has been the use of atomic force microscopy (AFM) in tribology. Here the aim is to make quantitative measurement of local mechanical properties. To this end we have been studying the properties of the tip-surface contact in the AFM on model surfaces. Related to this is the use of forces to engineer matter at the molecular scale. In collaboration with IBM, we have developed methods to move single molecules of C60 to form patterns on the scale of 6 nm.
An important application of nanoscale engineering is in the fabrication of novel electronic optical and magnetic devices. By combining high resolution electron beam lithography and AFM, electronic devices with critical dimensions less than 20 nm have been
fabricated and tested. Such measurements give an insight into electron transport through nanometre scale structures and allow for specification of material/fabrication properties to realise a future device technology. For potential optical devices, studies of nanometre scale metallic particles have demonstrated light emission with high quantum efficiency. Such particles have potential as a new range of light emitting devices.
In the future development of information storage technology the role of patterned magnetic media will become increasingly important. We have been studying the fundamental properties of individual magnetic structures with dimensions less than 100 nm. In addition to allowing for the optimisation of shape of magnetic nanostructures for data storage, we have also been able to design simple logic circuits based purely on magnetics.
Sensor technology based on microelectronics is a rapidly expanding field. In addition to modelling the behaviour of such sensors, applications in electrochemistry and biochemistry are being pursued.
Dr P. Migliorato
The overall aim of this research is the development of the so-called "System-on-Panel", a concept expected to revolutionise the field of portable computing and instrumentation through monolithic integration of complex circuitry on glass or plastic display substrates. The most promising approach is based on low temperature Polycrystalline Silicon (Poly-Si) Thin Film Transistors (TFTs). In order to achieve a system on panel it is necessary to develop this technology to the point where TFTs can replace single crystal silicon MOSFETS not only in circuits such as display drivers but also in memories and processors. This target, which is obviously beyond the capability of a university group alone, is pursued by us in close collaboration with Seiko Epson. Epson has been funding the activity of the Polysilicon Group since 1995, for a total of over £600,000. In addition it has established the Epson Cambridge Laboratory (ECL), in September 1998, to expand its research activities in Cambridge. Presently five ECL members of staff are working with our Group in this Department. The Group's activities are organised in three main research lines: Material and Device Characterisation, Device Modelling, Circuit Testing and Modelling. The Material and Device Characterisation activity aims at developing experimental and data analysis techniques to correlate the fabrication conditions with the device performance and provide input parameters for device and circuit simulation. In the current academic year the TFT transient response has been extensively studied(J156) and correlated with
carrier generation times and floating body effects. For these measurements an in-house system has been developed, which allows to specify a variety of driving waveforms. A new topic was also started, the study of ferroelectric materials with macroscopic and nanoscopic techniques. The ferroelectric characteristics of sol-gel deposited PZT films have been correlated with material deposition parameters, texture and contacts and a model has been proposed to account for the presence of non ferroelectric boundary layers. The conduction mechanisms responsible for the leakage currents of ferroelectric capacitors are also under investigation. In collaboration with the Nanoscale Science Group (Dr Welland) a new technique for a quantitative microscopic measurement of hysteris curves has been established. This is likely to prove a powerful tool to investigate the effect of impurities and other crystallographic defects such as grain boundaries. The highlight of our device modelling work has been the incorporation in a commercial simulator (SILVACO Atlas) of our model for the off-current of Poly-Si TFTs, developed in previous years. state-of-the art equipment for circuit design and testing has been installed. Both analogue and digital TFT circuits are being developed. In particular special pixel drive architectures to accurately control light emission in organic LEDs are being studied(J156). The proprietary circuit simulation tools, described in previous reports, have been essential for this work as they yield a much higher degree of accuracy than available from existing commercial packages. Finally, the Group has been awarded a large grant from the Newton Trust for the investigation of new types of biological sensor micro-arrays in collaboration with the Cambridge Institute of Biotechnology.
Dr D.F. Moore
As device dimensions are reduced it is important to develop direct fabrication processes where this is feasible. For thin film superconducting devices using YBaCuO, it is advantageous to form Josephson junctions and other circuit components such as resistors, by locally damaging the superconductor using an ion implantation process(J17). In silicon microsystems technology, critical structures such as the readout gap in tunnel junction readout accelerometers can be directly cut using a focused ion beam(J44,J105). Related thin film technology is being rapidly developed for future nanometer electron devices(J106,J107), and there is widespread interest in developing cost effective approaches for electronic applications(J108).
Dr D.F. Moore
Dr J. Pearson
Professor W.I. Milne
Robotic systems using pin-based liquid transfer are important for preparing arrays of samples of polymerase chain reaction (PCR) products or oligonucleotides in biotechnology. In this TCD-sponsored project with BioRobotics, Cambridge, steel pins with reservoirs are microfabricated using conventional machining and copper-vapour laser micromachining to cut 20 micrometer sized capillaries and other features. A scanning electron micrograph of such a reservoir pin and microfluorescent images of arrays of transferred liquid can be seen at the www.biorobotics.co.uk website. The technology has recently been developed to the point at which it is possible to print arrays of spots with spacing down to 200 micrometer pitch, and further miniaturization should be possible using pin systems or using micromachined silicon based technology to make disposable systems(J43).
Dr D.F. Moore
Silicon microengineering technologies are being applied to make precise connections between optical components and fibres, and between optic fibres. Liquid anisotropic etching of silicon enables the accurate fabrication of V-shaped grooves to locate optic fibres. Microfabricated clips 3 micron thick are used to hold single mode fibres with a clipping force of 10 N/m. This demountable technology developed in collaboration with Cambridge Consultants Ltd enables low cost assembly without the need for active alignment(J19). The form and precision of the groove is determined by conventional optical lithography and etching of the silicon substrate, using the silicon nitride layer as both the etch mask and as the micromechanical component. The measured excess transmission loss between two single mode fibres in the same V groove is less than 0.1 dB. For connecting fibres to micromachined components, shallow V grooves are made to position the fibre core above the level of the surface of the silicon substrate(J18). This micromechanical clip technology and the kinematic location of optic fibres in silicon V-grooves, has great potential to reduce the cost and increase the performance of sensor and other systems.
Dr D.F. Moore
Vibrating resonators are important components of micro electro mechanical systems (MEMS), with applications in sensors and actuators. However, fabrication defects, material stresses and design errors can all cause resonance shifts, and tuning is typically required. In this collaboration with R. Syms of IC London, focused ion beam (FIB) micromachining is used locally to alter the suspension of a resonant mass. An electrostatic comb drive system, made using bulk silicon micromachining with a 7 micrometer thick boron doped layer, had a first resonance at an electrical drive frequency of 650 Hz(J155). Trimming was with a scanning Gallium ion beam using an acceleration voltage of 30 kV and current of 2.5 nA. After tuning the suspension by making a pair of 20 micrometer long cuts in 8 minutes, the fractional change in resonant frequency was 5%, in fair agreement with the -5.2 % change predicted theoretically. This FIB approach is very effective for delicate micromachined structures where conventional approaches are not appropriate.
Dr D.M. Holburn
Research continues into the development of knowledge-based applications for scanning electron microscopy tasks. Further progress has been made with automating the task of instrument control using the XpertEze knowledge-based system. A Web-based version of this system, named WebXpertEze, has been implemented and used to demonstrate intelligent control of remote microscopes. A preliminary design for an embedded version of XpertEze for use in production instruments has been created(J22). Future work will involve further development of the embedded XpertEze system for multiple scanning electron microscope types, and re-implementing the diagnostic expert system (FIRST AID) as an Internet-based application.
Research has continued on the development of novel methods for remote control of the scanning electron microscope, and work now centres upon applications of these techniques(J21). Considerable progress has been made in the development of a `virtual' scanning electron microscope, in which a computer program emulates the interfaces, interactions, displays and general behaviour of an SEM, using a library of stored images and appropriate software to display these in various forms reflecting different instrumental settings, illustrating changes in specimen, specimen position, magnification, focus, astigmatism and other parameters. This has aroused considerable interest at international meetings and in the industrial community.
Dr. D.M. Holburn
Work is now under way on a new project in collaboration with the Photonics Group to develop high speed optical transceivers for in-building free space data networks. Delivery of data and communications services to mobile users is regarded as a key area for development, as users increasingly demand more complex services and mobility. It is proposed that a commodity CMOS process will be used to achieve a low-cost solution. So far effort has been concentrated on design simulations to predict bandwidth, sensitivity, stability and noise characteristics. It is expected that a demonstrator unit will be based on Chiprack, an architectural approach which offers the potential to reduce designs to a small number of highly integrated silicon modules linked by means of simple, regular interconnecting structures.
The Engineering Department celebrates its 125th anniversary in 2000. To mark this occasion, a series of multimedia web-based presentations is under development. These will demonstrate some of the important milestones in the Department's contributions to engineering and technology. The complete set will be made available on the World Wide Web and as a commemorative CD-ROM. The presentations will include interactive educational simulations including a virtual scanning electron microscope, a jet engine, a car engine, and construction of a building. The web project design team is being led by Mr B.C. Breton.
Professor G.A.J. Amaratunga
Dr P.R. Palmer
Dr R.A. McMahon
Dr F. Udrea
Dr K. Sheng
The large research programme funded by Mitel Semiconductors on MOS controlled electronic devices for power switching continues to flourish. Trench gate IGBT devices(J163,J169,J173,J176) resulting from this research programme have been commercially released by Mitel. Research into extending Trench gate MOS IGBT device structures to higher voltage ratings to make them suitable for power system and traction applications is currently the focus of research(J161,J162,J172).
The EPSRC funded Power and High Voltage Microelectronics (PHIMEC) research programme is concentrated on integrated circuits suitable for power transfer and control of equipment rated up to 1kW(J9). The research at Cambridge covers two aspects. One is new and optimum device structures(J70,J168,J171) for Si technologies which allow integration of multiple power devices. The other is circuit configurations for this novel class of integrated circuits. The circuit objectives are carried out within the context of demonstrating an integrated motor control and drive chip which acts as the interface between a motor and a power supply. A new charge pump circuit has been reported in which the high side supply is derived from the switching output rather than a separate charge pump(J79) and further work is being undertaken on this type of circuit. The PHIMEC programme has industrial sponsorship from Semelab, Mitel and Philips.
Research on low voltage power devices suitable for portable and automotive application is also underway with support from industry. The particular interest is to explore new MOS based lateral device structures which have the same, or better, performance compared to vertical structures in order to increase functionality through integration. This work also encompasses MOS device structures capable of voltage power amplification at frequencies rated up to 2GHz for mobile and distributed communications.
A new research programme on examining the band-gap materials SiC and GaN in power device structures has commenced and will aim to make use of the new GaN growth facilities being set up in the Department of Materials Science.
Capsule IGBTs connected in the series have been tested for the first time. The capsule package is mechanically robust and their internal design offers performance benefits to the active gate control method(J68). The sponsor is Hill Graham Controls. Partners are sought for power systems applications.
2D computer simulation of novel vertical power semiconductor devices continues with the emphasis on single gated MOS controlled multiple mode devices (MMDs)(J124,J152,J153,J154). The study was sponsored by Siemens ZFE. It has been shown that such devices offer the user benefits both at switching and in conduction and can be designed as direct replacements for the IGBT (further partners are sought).
The modelling of various MMDs in PSPICE to assess their impact in circuits has been completed, with models based on the Ambipolar Diffusion Equation reproducing the terminal characteristics of the devices with great accuracy (EPSRC funded)(J125). Work on a comparison of IGBT models has been published in a more complete form(J67). Further research work on accurate analytical models for IGBTs and study of their high frequency performance has been carried out in collaboration with Heriott-Watt University(J73,J145,J146,J147).
Measurements regarding the performance of high current multi-chip IGBT modules continues, with Mitel Semiconductors as sponsor. The theory shows that the current sharing depends on a range of issues(J78,J123) and these are being addressed, with the intention of eliminating the problem.
Further aspects of the investigation of induction motor drives for domestic appliances have been published(J128). The calorimeter built as part of this project has been improved and is being used for measuring motor losses to a high accuracy.
Work on high phase number induction motor drives with square wave excitations has demonstrated the practicality of reducing inverter losses without degrading machine performance. Low inverter losses make this approach attractive for integrated drives(J174). High phase number drives are also being investigated for battery powered applications as a means of keeping the phase currents manageable. A new project has started on the study of the brushless doubly-fed induction motor as a variable speed drive.
Dr A.C. Metaxas
Numerical modelling in computational electromagnetics continues to be the focus of the research activity at the Electricity Utilisation Group. The basic EUG code has been used to simulate a new industrial applicator for food processing(J20) and a new version has been implemented to cover wall losses for simulating high Q-factor applicator/load configurations(J50). The basic EUG code is being extended to be able to simulate thin films in packages for processing foodstuffs. A fully explicit finite element code is currently under development for solving microwave heating problems(J69).
The simulation of radio frequency heating systems for industrial processing has been completed. A combined finite element eigenmode and circuit modelling technique has been used to simulate various tank applicator configurations for optimal design(J117,J118) and for investigating the harmonic generation from such systems(J119).
A parallel finite element package using the MPI message passage standard has been implemented. The software not only shows a scalable reduction in solution time but has also proven easily portable between different computer platforms(J91). Problems with over 1 million edge discretisations are now routinely simulated using an SGI origin 2000 supercomputer.
A finite element flux corrected transport software have been written for solving the particle continuity and Poisson equations for a needle-point to plane electrode configuration in air at atmospheric pressure. Simulations for streamers at DC(J65,J66) and coronas at radio frequencies(J63,J64) have been implemented for various parameters. A 2D version of the code has now been written for investigating the deleterious effects of corona type of discharges in industrial applicators. The addition of the coupled energy equations to the 2D code is under development and will enable the simulation of corona to arc transition.
The Group continues to be the strategic and administrative centre for the AMPERE organisation and publishes its quarterly Newsletter(J97). A keynote address has been presented at the 7th International AMPERE conference on microwave and high frequency heating in Valencia, Spain in September 1999.
Dr T.J. Flack
Ongoing research is being carried out into: the application of new finite-element techniques, such as domain decomposition, to 2-D time-domain modelling of induction motors with a view to vastly reducing the CPU time required to apply such models(J56,J83); application of this new method to the determination of stray losses, and the effects of voltage supply imbalance in induction motors; modelling, design and optimisation of brushless doubly-fed induction motors; the analysis of damper bars in stand-alone diesel-generator systems with the aim of damping speed oscillations caused by the inherent torque pulsations of diesel engines; modelling and optimisation of electromechanical shakers, under an EPSRC grant and in conjunction with Ling Dynamics Ltd; modelling and optimisation of small multiphase induction motors; development of parallel algorithms and finite-element methods for micromagnetic simulators.
Professor G.A.J. Amaratunga
Professor W.I. Milne
Dr R.A. McMahon
Dr F. Udrea
A new research programme on low cost photovoltaic solar cells for terrestrial power generation has been initiated. Reduction of the energy pay back time, that is the recovery of energy used in fabricating the cell through power generation from the cell, is the major focus. Cost and energy savings through use of Carbon based materials in combination with amorphous Si, and in all Carbon devices is being explored. Another aspect of the research programme is research on efficient power conditioning and transfer circuits for integrating solar panels to the ac mains. Integrated power circuits for solar panel interfacing is a domestic microgeneration installation are being studied in collaboration with Semelab.
Professor G.A.J. Amaratunga
Dr D.M. Garner
Field emission based vacuum electronic devices for high frequency signal amplification and power switching are being explored. For the former, a new integrated vacuum microtriode structure has been developed in the Department and experimentally demonstrated(J60). The Si microtriode research is being extended to investigate the possibility of the THz range signal generation.
A new research programme on field emission based vacuum electronic devices for switch mode power transfer has been initiated. The research is concerned with novel cathode materials and structures which can provide large current densities at low electric fields. Novel Carbon based materials suitable for this application are a particular focus of research(J2,J5,J6,J7,J8,J13). Overall vacuum device design for power switching applications is also being investigated. The research is supported by Toshiba Corporation and VATech Reyrolle.
Professor W.A. Crossland
Dr R.J. Mears
Dr T.D. Wilkinson
Dr A.B. Davey
The Photonics and Sensors Group continues its interest in highly parallel opto-electronic systems based on free-space optics, with ferroelectric liquid crystal spatial light modulators (FLC SLMs). Smart pixel systems are being designed and have been built to integrate FLC modulators on silicon VLSI backplanes.
The photonic device fabrication facility is functioning and producing high quality devices from its combined Class 100/1000 areas. These devices include single pixel structures for high-speed modulators, optically addressed structures based on amorphous silicon and custom SLMs for running research projects. We are particularly interested in very high speed liquid crystal modulators(J37,J158,J191,J192) and liquid crystal devices for manipulating phase(J40,J92).
The Group has produced a range of new devices including the fast bit plane SLM (320 x 240) pixels with a frame rate in excess of 20,000 frames per second)(J185), a similar 640 x 480 pixel device and novel phase modulated SLMs, all using silicon backplane technology. They are designed for use in filtering and switching optical signals and for applications as microdisplays(J41,J186). These devices have been the `enabling technology' for many of the applications discussed below.
Work has been widely supported by EPSRC, DTI through LINK programmes, by DERA and by industrial partners, including Nortel, British Aerospace and Thomas Swan and Co Ltd.
The initiatives commenced under the EPSRC project Parallel Optoelectronics for Telecommunications Systems (POETS) have proven to be important in the continuing research of the group.
Work is continuing to demonstrate the application of an FLC-SLM as a dynamic filter for WDM telecommunications. The pattern written on the SLM serves as a dynamic hologram to diffract the incident light and can filter, and equalise to the same power level, up to eight different wavelengths. Ongoing work aims to demonstrate the additional functionality of an add-drop multiplexer (ADM) and to reduce the filter passband width to match international telecommunications standards. A pilot project is assessing the potential application of non-linear optical polymers to faster SLM devices for light modulation, switching and WDM filtering.
As a result of the POETS project, there was a demonstration of the role of optics in asynchronous transfer mode (ATM) telecommunications systems(J183,J189). This follows on from the theoretical work into the way that optical interconnects might modify the architecture of electronic ATM switches and their role in telecommunications systems. An optically accessible silicon VLSI memory (optoRAM) was demonstrated in a packet switch structure in which 9,000 optical channels were incident on a single silicon VLSI chip. A version of this switch structure using vertical cavity surface emitting lasers is being investigated under the project `VCSEL based Very High Capacity Photonics Packet Switch' (VIVALDI), under the UK EPSRC Optical Systems Initiative.
A project which has been spawned by POETS is the DTI funded reconfigurable optical switches for aerospace and telecommunications systems (ROSES)(J39,J181). This collaboration project has built the first operational fibre to fibre switch using holographic beam steering. This is now seen by our industrial partners as a potential solution to the problems of providing large scalable optical switches for the telecoms transmission network, and is attracting commercial interest.
There is also renewed interest in the role of optics and smart pixel SLMs in neural networks. A new scheme has recently been developed to improve the learning in neural networks and how they can be applied to optical systems. Collaborative work is looking at the application of smart pixel structures to signal processing using wavelet transforms.
A new type of optical image comparator (or optical correlator) for pattern recognition has been demonstrated(J184,J187). This system is based on a single spatial light modulator using ferroelectric liquid crystals integrated with silicon VLSI. Using this technology, a complex Fourier based image processor can be squeezed inside an volume the size of a paperback novel and it does not suffer from the normal Achilles' heel of optical systems; mechanical instability. The new architecture is an attempt to successfully combine electronic and optical processing and many image processing techniques such as edge-enhancement and adaptive threshholding are being used within the system. There are many applications for this type of pattern recognition system, including industrial inspection, security system, head tracking and motion estimation for video compression.
Finally, a new class of liquid crystal display has been developed within the group, known as photo-luminescent liquid crystal display (PL-LCD)(J15,J38,J81,J175). The PL-LCD combines all the power consumption and compactness advantages of conventional flat panel LCDs with the viewing characteristics of a cathode ray tube (CRT). In collaboration with Screen Technology Ltd prototype monochrome and colour displays have been demonstrated operating at video frame rates. If developments continue at the present pace they will result in major improvements in the viewability and size of liquid crystal displays to meet the increasingly stringent requirements of the new markets that are emerging for emissive flat displays in entertainment and information technology systems.
Dr A.R.L. Travis
A video display capable of screening a three dimensional image like that of a hologram has been licensed to a local company who have now demonstrated in Japan a display with a 42" screen for the amusement arcade market. Meanwhile work continues in the department on a flat panel version of this display which comprises a screen divided into lines. One line is selected at a time, and light projected parallel to the screen is ejected at the selected line. The three dimensional image is multiplexed line by line, and since no thin film transistors are needed it should be possible to build a large screen cheaply. A wide field of view is also anticipated, and the optics for this has now been successfully tested.
Similar principles can be used to make a head mounted display which will be completely flat, so we are trying to make a virtual reality display which will be the same shape and dimensions as a pair of spectacles.
Dr R.G.S. Plumb
A combination of modelling and measurements on laser based devices, working closely with industry, continues to be productive and stimulating.
Work on general lasers with external, frequency dependent feedback now gives excellent agreement between computed and measured behaviour(J84,J85). This area has been extensively studied in the past by analytical methods, with useful results, but these were neither complete nor accurate in many cases, and our work allows numerical prediction of behaviour with accuracy comparable to that obtainable by measurement.
Time domain modelling of 4-contact tunable interrupted grating DBR lasers is still slow, but new faster computers help, and valuable results are being generated. Agreement with measured results is now excellent in broad outline(J190), and we are beginning to understand more detailed aspects of behaviour, and hence model them more precisely. One very important step is that we can now confidently model the dynamics of switching from one wavelength to another, which is crucial for expected applications.
Systematic modelling of multi-contact Fabry-Perot lasers with weak reflections between sections(J126) has confirmed that these simple devices should have good, well-behaved wavelength switching characteristics, along with narrow linewidths and high output powers. Efforts have started to construct real devices in order to confirm and strengthen our theoretical predictions.
Dr P.A. Robertson
The area of sensors research continues to be very important on an international scale with applications expanding every year. The trend of miniaturisation to improve functionality and reduce cost is common across the entire spectrum of sensor technologies. In particular, the fabrication of devices by methods compatible with integrated circuit manufacturing processes opens up the possibility of smart sensors with integrated interface electronics which are very simple to use in new products.
Research in our group has continued on micro-fluxgate magnetic sensors, fabricated by thin film processing techniques. The sensors comprise multiple patterned layers of metals and insulators, deposited on top of one another to realise a miniature three dimensional structure. These devices are connected with novel drive and signal processing electronics to give speed and noise figures an order of magnitude better than those of standard commercial Hall effect devices(J138). These sensors are being developed in conjunction with an electronics instrumentation company for use in a new product range. Potential applications include magnetic data read heads, position encoders, current probes and miniature magnetometers.
Other projects underway include a magnetic microscope imaging system, a three dimensional optical microscope system for the non-destructive measurement of feature sizes on micro-fabricated structures, and a new biochemical sensing system for monitoring chemical species in solution.
Electrical Engineering References
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Last modified: July 2000