Current Postgraduates
A. MICROWAVE DEVICES AND OPTOELECTRONIC SENSORS
These projects fall into three main areas; gallium nitride-based devices; micro-machined sensors; infrared (IR) sensors and systems. Projects in the devices area involve a combination of experimental and theoretical work. Fabrication, characterisation and/or modelling of devices from all three of the sub-areas is undertaken by the MRG.
Many of the projects involve collaborative work with international researchers from University of California at Santa Barbara (UCSB), University of Illinois at Chicago (UIC), Lakeshore Cryotronics in the USA, Vigo Systems in Poland, Raytheon Vision Systems (USA), NVESD (USA), and DRS Infrared Technologies (Dallas).
MICROWAVE DEVICES
(BD Nener, G Parish, L Faraone, J Antoszewski, G Umana Membreno, M Kocan)
This project aims to achieve reliable, manufacturable high performance III-nitride (GaN, AIN, InN and alloys) transistors for use in high power, high frequency applications such as radar and communication systems. The GaN-based FET technology offers significantly improved performance for applications in RF/microwave power amplifiers, high speed switching for power electronics, and operation in harsh electrically noise environments, such as the automotive industry, space applications, and switch mode power supplies. Despite rapid progress in performance, AlGaN/GaN-based transistors are hampered by a variety of impediments. Two particular thrusts of our research in this area are ion implantations and dielectrics. Ion implantation offers the potential to enable a reliable, commercially feasible fabrication technology for GaN-based electronic devices. Dielectric thin-film technologies are desired for gate-insulation and surface passivation layers to enhance the performance, and overcome present limitations, of GaN- and AlGaN/GaN-based microwave transistors for high power and high temperature applications. The third thrust is improvement in electronic properties of InN, which will enable even faster electronic devices due to the high mobility and peak velocity in InN compared to GaN. Projects in this area include:
A.1 AlGaN/GaN Transistor Device Reliability
What are the key limitations to AlGaN/GaN device performance? This project will involve the study of degradation effects on critical device parameters such as channel properties in AlGaN/GaN field effect transistors. In particular, understanding charge distribution and behaviour at the AlGaN/GaN interface has been identified as a crucial issue by our partners at UCSB, in the path to commercialisation of microwave GaN-based transistors.
A.2 Magneto-Transport of GaN-Based Transistor Structures
Q: What makes a transistor a HEMT (high electron mobility transistor)? A: Excellent carrier transport properties. This project will involve measurement of carrier transport in FET devices, under the influence of an applied magnetic field. Current joint projects with UCSB include investigations into the effect of passivation layers such as silicon nitride, and use of ion implantation for industrial scale processing. This project is closely related to A.1.
A.3 Modelling and Simulation of GaN Devices
The AlGaN material system exhibits many unique properties that must be carefully considered in modelling device behaviour. Furthermore, as a relatively new material system, there are many aspects and parameters that are unknown or as yet unconfirmed experimentally. This project will involve development of in-house modelling packages for GaN-based devices through adaptation of commercial packages such as Medici. Models developed will be used to simulate device behaviour and compare with measured results.
MICRO ELECTRO-MECHANICAL SYSTEMS (MEMS)
(JM Dell, J Antoszewski, CA Musca, L Faraone, A Keating)
Micro Electro-Mechanical Systems (MEMS) represent the integration of mechanical elements, sensors and actuators, with photonics and electronics on a single substrate. The application of microfabrication technology, developed for the manufacture of silicon very-large-scale-integrated (VLSI) circuits, to generate miniature three-dimensional structures such as motors, gears, accelerometers and pressure sensors on the same substrate as the associated drive and sensing electronics has dramatically changed and expanded the field of mechatronics. In addition to allowing mechanical manufacture on a micro-miniature scale, MEMS technology brings the low-cost, high-throughput techniques of VLSI technology to mechanical and sensor systems. Specific applications of MEMS include accelerometers for air-bag deployment and shock sensors, micropumps for drug delivery, pressure sensors for measuring tyre pressures. The Microelectronics Research Group is working on optical MEMS technology to make optical detectors which are only sensitive over a small, electrically tuneable wavelength range.
A.4 Design of Tunable Optical Cavity for IR Applications
This project will investigate the use of a tunable optical cavity to select specific narrow bands within the infrared region, or to enhance detector performance. Tunable detectors are the next major development in modern IR detector technology, with one of the main aims in this area being the production of a microspectrometer (a spectrometer-on-a-chip) Projects in this area include work in optics, material science and mechanical aspects of MEMS components, and are funded by Australian and US defence agencies and Australian government funding.
A.5 Design of Tunable MEMS Based Electronic Components
This project will investigate the use of MEMS for the fabrication of tunable monolithic MEMS based electronic components such as inductors. These devices can then be formed on VLSI chips, rather than using discrete devices.
INFRARED SENSORS
(J Antoszewski, JM Dell, L Faraone, CA Musca, BD Nener, R Sewell)
The ability of IR detectors to directly sense the thermal output of an object has found wide application in thermal imaging for medical diagnostics, bushfire detection, satellite remote sensing, search and rescue, thermal loss budget estimation, as well as the more traditional defence and aerospace applications. In addition, emerging applications of IR detectors are found in spectroscopic systems for mineral exploration, pipeline monitoring, pollution detection and identification, and gas monitoring systems. Specific examples include; detection of tumours and tissue damage, detecting illegal waste disposal by ships in harbours, preventative maintenance in electrical switchgear such as high voltage transformers. For the fabrication of sensitive IR detectors, the highest performance is achieved in devices using the semiconductor material mercury cadmium telluride (HgCdTe or MCT). There are a number of unique properties which give MCT an advantage over competing technologies, with the main advantage being the ability to bandgap engineer the material, for specific applications. The MRG has recently developed new detector structures that are at the leading edge of IR sensor technology. A large amount of research is being carried out to characterise and test the performance of new devices. Projects in this area will include:
A.7 Characterisation and Modelling of HgCdTe Photovoltaic Detectors
This project will undertake theoretical modelling and performance measurements of infrared photodiodes fabricated in the MRG laboratory. The junctions are formed using an in-house developed process, and are expected to deliver state-of-the-art performance. These detectors are employed in large two-dimensional arrays that are used for infrared imaging for applications such as night vision, surveillance, medical imaging and environmental applications.
A.8 Characterisation of HgCdTe Heterojunction Photodiodes
This work will investigate the performance of HgCdTe photodiodes based on bandgap engineered structures. This will involve both measurements and theoretical calculations. Bandgap engineering is one of the latest methods used to improve device performance and functionality, and involves the control of material thickness down to the atomic layer level.
A.9 HgCdTe Photoconductors
A photoconductor is a relatively simple form of device which can be used as an IR detector. This project will investigate the use of various photoconductor designs for different applications, and will also employ these devices for characterisation and understanding of the IR semiconductor material itself. HgCdTe material used in this work is either grown in-house (using Molecular Beam Epitaxy) or purchased externally. In either case, to prove the device quality of the material photoconductors are an ideal test device.
A.10 Noise in HgCdTe Based Photodetectors
The signal-to-noise ratio in photodetectors is a key performance parameter. The measurement of noise and the identification of noise mechanisms is a fundamental requirement in the improvement of performance. This project will look at theoretical noise models and measurement of noise. The project will use devices known as gated-photodiodes to measure and identify noise mechanisms.
B. SEMICONDUCTOR MATERIAL GROWTH AND CHARACTERISATION
(J Antoszewski, JM Dell, L Faraone, CA Musca, G.Parish, BD Nener, G Umana Membreno, R Sewell, M Kocan)
The MRG has some of Australia's best facilities for undertaking materials characterisation for a wide range of semiconductors, and has developed techniques that are now licensed by large semiconductor facilities around the world. A number of projects are available in this area, working on the development of new techniques, as well as using techniques we have already established to measure the properties of semiconductor layers. The data obtained from these measurements give information about the electrical, optical and structural properties of the semiconductor layers. This information will be used to design new growth processes and develop new electronic and sensor devices. Students will gain experience in high technology instrumentation, low-level signal measurement techniques, and low-noise system layout. These skills are applicable in a wide range of communications and electronics areas, as well as in the mainstream semiconductor industry.
B.1 Sensitivity of Quantitative Mobility Spectrum Analysis (QMSA) Technique
QMSA is a state-of-the-art analysis technique developed at UWA, and currently licensed to a US scientific equipment supplier, for characterising multiple hole and/or electron carrier species that often exist in modern semiconductor materials and devices. This project seeks to theoretically answer the question of how many raw experimental data points of a given experimental accuracy are required before reliable numerical values can be obtained from the analysis of the data.
B.2 Dry Etching of Compound Semiconductors
Successful, efficient fabrication of state-of-the-art compound semiconductor devices requires utilisation of a fast, anisotropic, non-damaging etch process. Projects in this area comprise unique, comprehensive investigations into low damage inductively coupled plasma reactive ion etching (ICPRIE). The study will involve both III-nitrides and HgCdTe material. Damage-free dry etching technology is currently a major impediment to the continued development of both systems, which are extremes in terms of bond strength and chemical reactivity, yet with the commonality of susceptibility to dry etch damage. The projects will involve the characterisation of processed materials using structural (SEM, AFM), optical (optical emission spectroscopy, scanning laser microscopy) and electrical (Hall, lifetime) characterisation techniques.
MERCURY CADMIUM TELLURIDE
The MRG has an established Molecular Beam Epitaxy (MBE) growth facility for mercury cadmium telluride (HgCdTe) semiconductor structures for high-performance infrared detectors. MBE, a state of the art technology for semiconductor crystal growth, allows growth of layers of different semiconductors, from as thin as a single atomic layer, to layers tens of microns thick. MBE technology is very important for fabrication and design of ultra-high performance electronics and optoelectronics devices using bandgap engineering. The Defence Science and Technology Organisation (DSTO) selected the Microelectronics Research Group to establish a university based MBE facility for the growth of mercury cadmium telluride (MCT) semiconductors, using equipment worth ~$3.5 million donated by DSTO.
Many of these projects are carried out in collaboration with University of California at Santa Barbara (UCSB), University of Illinois at Chicago (UIC), Rockwell Science Center, and La Trobe University.
B.3 Scanning Laser Microscopy (SLM) for Characterisation of HgCdTe Material
SLM is used to characterise HgCdTe semiconductor material. The SLM can be used for a number of techniques including: transient lifetime, laser beam induced current (LBIC) spatial photoresponse. Transient lifetime measurements are used to measure the lifetime of carriers in a semiconductor. Carrier lifetime is one of the most important semiconductor parameters and has a significant affect on the performance of devices fabricated from semiconductors. Transient lifetime is measured by illuminating the semiconductor with a pulsed focussed laser, and measuring the decay time of the resulting electrical signal. The LBIC technique is being investigated as a non-destructive in-process testing tool for the characterisation of IR arrays. Ideally the LBIC tests will give information about individual photodiode performance, and the overall uniformity of the arrays. Projects in this area will investigate the correlation between LBIC signature and device performance. Spatial photoresponse uses a focussed laser to stimulate carriers in a photodetector device, enabling the local response of the material to be measured. By scanning the laser in a 2-dimensional space enables the uniformity of the detector active area to a quantitatively assessed. These projects involve use of lasers, low-noise amplifiers and the measurement of extremely low signals. Once measurements are obtained various data analysis techniques are then employed determine device and material performance.
B.4 Characterisation of MBE Grown Material
Molecular Beam Epitaxy is the required semiconductor growth method for fabrication of complex multilayered device structures. The MRG runs an MBE growth facility that can grow HgCdTe. This project will look at the analysis of the grown semiconductor layers using a number of material characterisation techniques including Secondary Ion Mass Spectrometry (SIMS), LBIC, and Hall measurements and transient lifetime.
B.4.1. Characterisation of MBE grown MCT by x-ray diffraction
The X-ray diffraction facility at LaTrobe University in Melbourne has recently gone 'on-line'. Be the first to use this 'telepresence' system to make measurements on the sub-nanometer scale of the crystal structure of MCT samples grown at UWA. The results will be analysed to give information about strain and defect formation in the semiconductor layers. Control a million dollar x-ray system from your laptop!
B.4.2. Measurement of molecular fluxes in molecular beam epitaxy using Cavity ring-down spectroscopy
This project is the start of a much larger project which aims to measure very low concentrations of gases in a semiconductor crystal growth chamber using optical absorption techniques. Cavity ring-down spectroscopy is a new ultra-sensitive laser absorption spectroscopy technique that can be used to detect gas concentrations to much less than one part per billion. The student will be involved in predicting the sensitivity of various cavity ring-down experiments and constructing models of the optical absorption spectra expected during crystal growth.
B.4.3. High precision multi-channel voltmeter/data acquisition system
High performance (24 bit) analogue to digital conversion (ADC) chips are now readily available at low cost, offering the possibility of constructing a high precision / low data rate voltmeter with computer interface at a lower cost than commercial systems. This project aims to create a multi-channel data acquisition system for monitoring several process variables during semiconductor crystal growth. The system will require a PC user interface (written in LabVIEW) to communicate with a microcontroller/ADC board and low-noise input electronics.
B.5 Characterisation of Plasma Processed HgCdTe
Plasma processing via Reactive ion etching (RIE) is the technique used by the MRG to convert p-type HgCdTe to n-type and thus form an n-p junction. This project will undertake characterisation of this converted region. The methods that will be used include Hall measurements and Secondary Ion Mass Spectrometry (SIMS).
III NITRIDE
III nitride (GaN, AIN, InN and alloys) semiconductor technology is relatively immature, with significant progress in this material system only having been achieved in the last 15 years or so. Despite the many inherent advantages of nitride-based materials, significant challenges still exist in the growth and fabrication of devices. Therefore there is much to be learned regarding both the fundamental material properties of and defects within the material. Such studies are critical in enabling nitride-based technology to reach its true potential. The majority of the III nitride materials studied the in MRG are obtained as part of a long standing collaborative arrangement with the University of California at Santa Barbara. The MRG undertakes the detailed materials characterisation needed in the development of new device structures.
B.6 Optical Measurements of GaN Minority Carrier Properties
Measure an important but elusive property in nitride material. GaN material quality is directly related to its ability to emit light, which in turn is related to minority carrier lifetime. This project will use novel techniques that utilise photocurrent and photo-induced luminescence to investigate minority carrier properties in GaN material, and consequently use this information for improved materials and device performance.
B.7 Defect characterisation of GaN Based Materials
Knowledge of the defects present in material is the first step to eliminating them. Deep level transient spectroscopy (DLTS) will be used to investigate the electrical defects, and hence quality, of GaN-based structures. This is particularly critical information for our current collaborative projects with UCSB, which aim to improve material properties to enable commercially viable high power microwave (RF) AlGan/GaN transistors.
B.8 Device Processing of GaN
Help develop state-of-the-art gallium nitride processing capabilities. GaN is a desirable material partly because of its high temperature stability and chemical inertness. However, these properties also make device fabrication difficult. This topic includes investigations into etched wafers and fabricated metal contacts, both challenging but vital processing steps.
B.9 Hall/QMSA of III-nitride materials
Good transport properties (carrier concentration and mobility) of III-nitride materials are of vital importance for application of these materials into state-of-the-art devices. These projects will involve transport measurements using the powerful 12T magnet and then analysis of results using QMSA. Particular materials of interest include ion-implanted GaN, and InN.
POROUS SILICON
The MRG has recently begun a research effort in the area of porous silicon. Porous silicon is a novel nano-material with the capability to perform as a mirror, waveguide, light emitting diode, photodetector, and sensor. Porous silicon is formed by the anodisation of crystalline silicon, and can be produced with a wide range of refractive indices, varying surface area, variable energy bandgap. Furthermore a variety of materials can be infiltrated into the nanopores, including polymers, biological species, and liquid crystals. Aside from optoelectronics, other applications include: photonic bandgap structures in micro-optics, solar cells for energy conversion, gas sensing for environmental monitoring, high etch selectivity for wafer technology, highly controllable etching parameters for micromachining, biosensors, and enzyme immobilization in biotechnology.
B.10 Development of porous silicon-based devices for optoelectronics, medical and heat-exchanger applications
This area of research is relatively new within the group and hence work in this area will concentrate on the development of a process for the fabrication of porous silicon and characterisation of the material. The ultimate aim is to produce devices for optoelectronics, heat-exchanger, and medical applications. Some key parameters of porous silicon are: porosity, porous silicon depth, optical properties, homogeneity. These parameters are to be measured as a function of the formation process parameters. Porous silicon-based devices that are currently being developed within the group are: distributed Bragg reflectors (mirrors) for optical filters, anti-reflection coatings for microlenses, heat-exchangers (heatsinks) for thermoelectric cooling and water purification applications.
C. ELECTRONIC/OPTIC SYSTEMS
(CA Musca, JM Dell)
The projects in this area involve the design and production of electronic and optics systems that assist in characterising MRG devices or demonstrating the capabilities of MRG work.
C.1 Design of automated soil analysis instrumentation for agriculture.
In agriculture, the cost of inputs to production (seed, water, fertilizers, insecticides, herbicides, etc) are rapidly increasing, and returns are increasingly tied to crop quality. The ability to be able to monitor soils and target where fertilizers, herbicides etc need to be applied, and where the highest quality produce is likely to be harvested is now essential information for farmers, but is so expensive to obtain that it can only be used on a limited scale. Projects in this area are examining the instrumentation required to be able to measure key soil parameters in real time using optical techniques including infrared analysis and laser light scatter, and electrical probe measurements. Specific projects include design of optical systems to measure infrared signatures of soil, implementation of laser scattering measurements to determine particle size, use of electronic and RF probing techniques to determine moisture content, and analysis of infrared signatures to extract soil properties. Applications include wheat, rice and other grain farming, and analysis of soils for vineyard production monitoring. These projects will be undertaken in cooperation with the School of Earth and Geographical Sciences and the School of Plant Biology.
C.2 Infrared analysis of wine and grape juice
The Australian wine industry is one of the most highly automated in the world, and is becoming more like a process engineering. Rather than relying on the traditional intuitive skills of an experienced wine maker, the wine industry is looking for robust, easily used ways to monitor the entire wine making process from crushing, through fermentation and maturation, to bottling. A key technology to emerge is the use of infrared optics to measure important parameters throughout the production process. Projects in this area will investigate sampling techniques, optimum wavelength ranges for analysis, optical probe designs, and the influence of various sample parameters on the quality of the information extracted from the infrared signatures. Theses projects are being undertaken in collaboration with Houghton Wines and the School of Plant Biology.
C.3 Infrared analysis of breast milk
Breast milk is recognised as the optimum nutritional source for new born infants. However, for premature babies, it is often essential to supplement breast milk in order that essential nutrients are included in the baby's food. To determine if such supplements are needed, the mother's breast milk must be analysed, requiring often significant sample volumes, which are then not available to the baby. This project, undertaken in collaboration with Biochemistry and Molecular Biology at UWA, is examining ways in which infrared spectroscopy, microfluidics and signal processing can be combined to obtain real time measurement of key nutrients in breast milk using very small sample volumes.
D. ATMOSPHERIC PROPAGATION
(N Fowkes, BD Nener)
The ultimate performance of an EO System is determined by the atmosphere. The atmosphere can degrade the signal through scattering and absorption by aerosols, background radiation, scintillation and refraction. Projects in this area are both theoretical and/or involve experimental work. The experimental work is at sites like Rottnest measuring atmospheric parameters important to EO propagation and involves the design and installation of the instruments, and the analysis and modelling of atmospheric data and effects. The theoretical work involves mathematical and numerical modelling of atmospheric effects relevant to EO systems, particularly refraction and scintillation. Current work is funded by the Australian Department of Defence and Tenix Defence Systems Ltd (an Australian owned defence contractor). The effort is in collaboration with the UWA Department of Mathematics and Statistics; the Remote Sensing and Satellite Research Group (RSSRG) of the Physics Department of the Curtin University of Technology; CIMSS, Space Science and Engineering Center, University of Wisconsin, Madison,Wisconsin, USA, and the US Navy Space and Naval Warfare Center (SPAWAR), San Diego, USA.
D.1 Refractive Index Change in Atmosphere
Modelling of the effects on light and microwave propagation of refractive index changes due to temperature gradients in the atmosphere over the ocean; modelling of mirages and other image distortions of objects seen at large distances; scintillation.
E. VLSI DESIGN - Design of single-chip digital cameras
(F Boussaid)
The current trend in Digital Imaging Technology is towards building camera-on-a-chip imaging systems, i.e., CMOS imagers. The fully integrated product results in significant manufacturing cost savings, reduced system size, but also in lower power consumption. The unique concept of CMOS imagers offers the opportunity to integrate photo-sensing array and signal processing circuitry on a single silicon chip, enabling the development of a new generation of smart mobile imaging systems. Half the size of a small postage stamp, a CMOS imager chip can even be swallowed (pill-camera) to transmit images from inside the body. Besides biomedical, CMOS imagers have numerous commercial applications in cell phones, PC notebooks or any application for which a "micro-camera" can be requested. The MRG group is working towards integrating "human like" features and thus "intelligence" in even smaller size CMOS vision sensors. As a consequence, a CMOS vision sensor will not only "see" the outside world but also process the image, enabling in turn on-chip vision-based decision making, a key trend in machine vision research. Our approach is that of designing electronic circuits that are able to mimic part of the processing that is undertaken in biology vision systems, the ultimate trend being to mimic the human eye. To integrate such a processing power into a single chip, semiconductor industry state-of-the-art deep sub-0.25µm CMOS processes are used.
Microphotograph of a fabricated CMOS imager (3.5×3.5mm2)
Proposed final year projects may include:
E.1 Digital pixel sensors and spiking pixel architectures
E.2 Ultra-low power mega-pixel CMOS imagers
E.3 High dynamic range CMOS imagers
E.4 Development of smart CMOS imagers with on-chip processing capabilities such as face or fingerprint recognition, using the FPGA Celoxica RC300 platform.
This high-end FPGA platform will seamlessly interface with the image sensor to acquire and process data in real-time. Each project will involve design, implementation and layout of an imager circuit. If the performance of the integrated circuit is good, the chip will be fabricated and tested. This is a great opportunity to acquire expertise in the actual design of mixed-mode integrated circuits.
