This PDF file contains the front matter associated with SPIE Proceedings Volume 6800, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Electrochromic (EC) device technology can be used for modulating the transmittance of visible light and solar radiation in windows in buildings as well as for other see-through applications. This paper emphasizes the great energy savings that can be achieved in the built environment, jointly with improved indoor comfort for the users of the building. Manufacturing aspects are then considered with particular focus on potentially low-cost roll-to-roll methods. In particular the paper discusses recent work on foil-type devices embodying sputter deposited WO₃ and NiO-based films joined by a polymer electrolyte. This paper also introduces a number of new results showing that double-sided antireflection coatings based on dip coating can enhance the transmittance significantly, that tandem foils can yield a ratio between bleached-state and colored-state transmittance exceeding fifty, that solar irradiance onto the EC device can enhance its charge insertion dynamics and thereby its optical modulation, and that electromagnetic noise spectroscopy may serve for quality assessment of EC devices.

We demonstrate post-processed and reconfigurable photonic crystal double-heterostructure nanocavities via selective fluid infiltration. We experimentally investigate the microfluidic structures via evanescent probing from a tapered fiber at telecommunications wavelengths. We demonstrate a cavity with quality factor Q = 4,300. The defect-writing technique we present does not require nanometer-scale alterations in lattice geometry and may be undertaken at any time after photonic crystal waveguide fabrication.

Titanium dioxide (TiO₂) films were rendered hydrophilic through ultraviolet (UV) light irradiation (254nm) and returned to their previous hydrophobic condition when exposed to a sealed pressurized nitrogen atmosphere. UV light irradiation on TiO₂ films resulted in super-hydrophilic surfaces with water contact angles of <5°. Alternatively, exposure of the films to an N₂ environment resulted in relatively hydrophobic surfaces with water contact angles of >40°. The switching of TiO₂ surface wettability could be repeated on the same surface with little hysteresis in water contact angle values. The mechanism behind the hydrophilic and hydrophobic reversal in TiO₂ surfaces is proposed to be due to UV light mediated photocatalysis and physio- adsorption of N₂ molecules respectively. The non-intrusive control of TiO₂ surface wettability could be an attractive alternative to other wettability-based microfluidic valving strategies like electrowetting and photochromic wetting variation. The above results are discussed in terms of the potential use of the films in wettability based valving and repeated wettability patterning of TiO₂ surfaces for open and sealed microfluidic systems.

There has recently been significant interest in rubrene single-crystals grown using physical vapour transport techniques due to their application in high-mobility organic field-effect transistor (OFET) devices. Despite numerous studies of the electrical properties of such crystals, there has only been one study to date focussing on characterising and optimising the crystal growth as a function of the relevant growth parameters. Here we present a study of the dependence of the yield of useful crystals (defined as crystals with at least one dimension of order 1 mm) on the temperature and volume flow of carrier gas used in the physical vapour growth process.

The inkjet processing of water dispersable polymer carbon nanotube composite materials is reported. Single printed layers displayed good optical transparency, sheet resistance, and conductivity. It is demonstrated that an alcohol sensor based on a single printed layer of polymer carbon nanotube composite could operate at a lower voltage compared to a sensor based on a single printed layer of the polymer.

We describe the formation of hydrogen sensors by deposition of Pd clusters onto silicon dioxide coated silicon substrates with electrical contacts defined by a simple shadow masking technique. The clusters are prepared by sputtering in a gas aggregation source. The sensors are characterized by exposure to hydrogen in a simple flow chamber and by measuring the temperature dependence of the sensor resistance. Sensors with cluster coverage greater than the percolation threshold form "thin film" type sensors which exhibit a small increase in resistance on exposure to hydrogen, consistent with the increase in resistivity of bulk Pd on absorption of hydrogen. Sensors with coverage smaller than the percolation threshold form sensors which exhibit a much larger decrease in resistance on exposure to hydrogen. The response of these "percolating-tunneling" sensors is due to the absorption of hydrogen by the Pd clusters, which causes the tunnel gaps in the film to decrease in size, leading to an increase in conductance. Finally we describe tunneling sensors, where gold islands are grown on the substrate prior to cluster deposition, and which exhibit similar characteristics to the percolating-tunneling sensors.

We present a theoretical study of Zeeman spin splitting for quasi-onedimensional valence-band edges in cylindrical nanowires subject to a magnetic field parallel to the wire direction. The interplay between quantum confinement and strong spin-orbit coupling in the valence band gives rise to a controllable large variation of the effective g-factor for single wire levels. A direct correspondence is established between values for hole g-factors and characteristic spin-polarization profiles for wire-level bound states. The correlation between hole spin splittings and polarizations is mapped over the range of spin-orbit coupling strengths present in typical semiconductor materials. We propose to use nanowire subband edges as a versatile laboratory for experimental and theoretical study of the complex spin properties exhibited by quantum-confined holes.

This paper will report on the design and fabrication of a novel 3D electrostatic RF MEMS switch, which uses two movable electrodes. The concept of two movable electrodes represents a unique feature of this device and is introduced to the RF MEMS community for the first time. Since the operating principle of the switch is based on electrostatic actuation, this unique feature results in a lower operating voltage. Combining the special bulk and surface micromachining techniques has enabled the realization of this new 3D RF MEMS switch. There are two main configuration for the device structure: 1) in the first device structure all parts are made up of bulk-micromachined free-structures. 2) In the second device structure the lower part is made up of a movable bulk-micromachined cantilever and the upper section is made up of surface micromachined movable thin film structures. By applying a DC voltage between movable plates, they come in touch and provide a pass for the RF signal (on-state of the switch) and as the DC voltage is removed, electrodes will be separated and disconnect the RF signal (off-state). The substrate can be used as a third electrode to separate beams in case of stiction. The monolithic nature of this switch technology makes it possible to develop various switch configurations like SPNT, C-type, and R-type switches, and switch matrices monolithically. This switch can be used as the basic building blocks for microwave switch matrices, multiplexers / demultiplexers, and phase shifters operating at microwave frequencies. The aim is to use the new features of this switch to achieve an acceptable low switching voltage, a better RF performance and particularly reliable switching operation. In this paper design considerations, HFSS simulation and the preliminary fabrication results of the switch are demonstrated.

Contact and dispersive forces are important in the design of Micro Electro Mechanical Systems (MEMS). The influence of random surface roughness of Au films on capillary and Casimir forces is explored with atomic force microscopy in the plane-sphere geometry. In case of the Casimir force the experimental results are confronted to theoretical predictions for plane-sphere separations ranging between 20 and 200 nm. The optical response and roughness of the Au films were measured and used as input in calculations of the Casimir force. It is found that at separations below 100 nm the roughness effect manifests itself through a strong deviation from the usual scaling of the force as a function of distance. The difference with predictions based on perturbation theory can be larger than 100%. In addition, the capillary force was measured using an atomic force microscope between a gold coated sphere and gold surfaces with different roughness, i.e. from atomically flat up to 10nm rms roughness. A substantial decrease in the capillary force was observed with increasing RMS roughness up to a few nanometers. For smooth surfaces, in contact, the capillary force surpasses other force fields either the van der Waals/Casimir or the electrostatic force. For rougher films the different forces become comparable in magnitude. From these measurements two limits can be defined, i.e. a smooth limit where the whole surface interacts through the capillary force and a rough limit where only a single up to a few asperities yield a capillary contribution.

By controlling four tips independently, mechanically and electrically, in an organic manner, we can do novel measurements in nanometer scales, which are impossible by single-tip scanning tunneling microscopes (STM). The four-tip STM makes possible to measure electrical properties of nano-scale devices and materials, and also to directly image Green's function that represents propagation of electron wavefunction. We can now bring two tips as close as 20 nm to each other by using conductive carbon-nanotube tips in the four-tip STM. A new controller which drives the four tips with a single computer is another important clue for practical use of the four-tip STM.

We report a novel GaAs-based device in which I = 3/2 nuclear spins of ⁶⁹Ga, ⁷¹Ga and ⁷⁵As in a nanometer scale region can be manipulated by all-electrical means. The device comprises a quantum point contact (QPC), a narrow conduction channel in a GaAs quantum well defined by split gates, integrated with an additional metal strip on top for applying a radio-frequency (RF) pulse. With the device set in a special condition characterized by the Landau-level filling factor v = 2/3, nuclear spins in the narrow region near the QPC can be selectively polarized by driving a current through the QPC. By applying a resonant RF pulse, the polarized nuclei can be coherently manipulated, which we detect through the electrical resistance of the QPC. Different from the conventional nuclear magnetic resonance measuring the transverse component of the magnetization, our device measures the longitudinal component, which enables us to observe otherwise invisible multiple quantum coherences between states with z projection of the angular momentum differing by more than one. By appropriately tuning the length, intensity, and detuning of the RF pulse, all possible coherent superposition between two out of the four Zeeman levels can be created for each nuclide.

One-dimensional surface-relief gratings were fabricated using a direct imprinting process with a glassy carbon (GC) mold at the softening temperatures of oxide glasses. The maximum grating height attained in this study was 730 nm when the grating period was 500 nm, which could be formed by the pressing at the softening temperature of glass under constant pressure of 0.4 kN/cm². A large area glass imprinting was attempted using a GC mold with a periodic patterned area of 6 mm x 6 mm, which has the period of 500 nm and groove depth of 350 nm, respectively. Phase retardation of 0.1 λ was recognized between TE-polarized and TM-polarized lights at 600 nm wavelength. The measured values were in excellent agreement with those calculated using a rigorous coupled wave analysis.

RF voltage measurement based on electrostatic RMS voltage-to-force conversion is an alternative method in comparison to the classical thermal power dissipation method. It is based on a parallel-plate capacitor with one elastically hinged plate. By applying an AC voltage, a force proportional to its RMS value is generated between the plates, and consequently the movable plate swings to the equilibrium position between spring force and electrostatic force. For a theoretically adequate resolution and precision, the necessary geometrical dimensions of the sensor practically require the use of advanced micromachining techniques. In this contribution, we discuss a unique batch fabrication process to meet the challenge of having two very large plane-parallel surfaces separated by only a few microns. The basic design consists of an actuator made of silicon embedded between two glass wafers for electrical contacting and sealing. Each step of this hybrid process has been optimized to prevent residual liquids leading to stiction and breaking of the fragile parts of the micro-structures. Flat grooves in the silicon define the gap between the capacitor electrodes, and an anisotropic dry-etch step releases the actuator. A second glass wafer builds the top of the stack and is fixated using a patterned photo-resist. Bumpers on the bottom layer and ridges in the top wafer improve the robustness of the structure. In this paper, we present a detailed analysis of the production process, pointing out critical as well as alternative design steps towards the optimized sensor. Finally, results of working devices are shown.

A novel micro-bridge actuator that can satisfy the important requirements for optical switching has been designed, fabricated and tested. These important properties of the actuator include bi-stability, large out-of-plane movement, bi-directionality and electro-thermal actuation. The monolithic integration of a micro-mirror with this actuator is critical to demonstrate its application for optical switching in planar light circuits. In this paper, the design, simulation, fabrication and testing of the integrated system will be presented. The design and simulation issues include (i)the design of the micro-mirror that can be integrated and yet maintain the bi-stability behavior of the micro-bridge (ii) ANSYS simulations to substantiate the design (iii) the design of the dimensions of the mask lay-out of the micro-mirror to provide the desired micro-mirror size on the micro-bridge. The integrated system was fabricated on (110) oriented wafer. A vertical flat mirror, with verticality of 89.5° and a roughness of about 10nm has been obtained. The fabricated optical switch is laser diced, packaged, wire-bonded and tested. A free space optical path is established by micro-positioning optical fibers on the surface of the wafer in etched grooves to demonstrate optical switching. The optical system is actuated between the ON and OFF positions by driving 16mA and 10mA currents through the legs and bridge parts of the micro-bridge for respectively.

This paper reports the mechanical design and optimization of tunable Fabry-Perot (FP) filter structures for the development of MEMS adaptive infrared detectors using finite element modeling and experimental investigations. The results indicate that the mechanical characteristics of the FP filters are significantly influenced by the structural designs, which eventually affect the filter performance and device integrity.

We present a novel approach to enhance light emission in Si and demonstrate sub-bandgap light-emitting diodes (LED) based on the introduction of point defects. Ion implantation, pulsed laser melting and rapid thermal annealing were used to create LEDs containing self-interstitial-rich optically active regions. Procedures to fabricate LEDs on a bulk silicon substrate and on a silicon-on-insulator (SOI) wafer will be presented, and methods to improve device performances will be discussed. The control and utilization of point defects represents a new approach toward creating Si in a stable, optically active form for Si-based optoelectronics.

Electroluminescence (EL) and its temperature dependence of InAs quantum dots embedded in In_0.15Ga_0.85As quantum well [dots in a well (DWELL)] have been investigated as functions of the growth temperature of the GaAs spacer layer. The EL intensity at room temperature increases as the spacer growth temperature increases. The integrated EL intensity as a function of injection current at room temperature for all samples shows that at low currents, the gradients are superlinear but this superlinearity decreases as the spacer growth temperature is increased. From a simple analysis of the generation-recombination rate equations, it can be shown that the superlinearity stems from the nonradiative recombination being the dominant recombination process. As the spacer growth temperature is increased, this nonradiative recombination become less dominant. An Arrhenius plot of the temperature dependence of the EL intensity gives an activation energy of ~300 ± 15 meV at high temperature. The dominant loss mechanism is therefore concluded to be the electron escape from the quantum dot ground state to the GaAs barrier.

A well-known side-effect from fibre Bragg grating UV-fabrication is short wavelength attenuation, where irradiation with laser light, usually in the UV, generates both defect-induced absorption and scattering. These losses are especially problematic for high power optical fibre lasers operating at shorter wavelengths where resonant assisted coupling into the glass matrix through the rare earth ions can take place (e.g. Yb³⁺). In this, work we present a study of the relative magnitude of short wavelength attenuation in gratings written by the point-by-point method using a Ti-sapphire femtosecond laser operating at 800 nm. Such gratings are very stable and have been used as the feedback elements in fibre lasers with powers exceeding 100 W. We show that the scattering properties responsible for the attenuation are analogous to those associated with type II gratings written with UV lasers.

Mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) 1024x1024 pixel InGaAs/GaAs/AlGaAs based quantum well infrared photodetector (QWIP) focal planes have been demonstrated with excellent imaging performance. The MWIR QWIP detector array has demonstrated a noise equivalent differential temperature (NEΔT) of 17 mK at a 95K operating temperature with f/2.5 optics at 300K background and the LWIR detector array has demonstrated a NEΔT of 13 mK at a 70K operating temperature with the same optical and background conditions as the MWIR detector array after the subtraction of system noise. Both MWIR and LWIR focal planes have shown background limited performance (BLIP) at 90K and 70K operating temperatures respectively, with similar optical and background conditions. It is well known that III-V compound semiconductor materials such as GaAs, InP, etc. are easy to grow and process into devices. In addition, III-V compound semiconductors are available in large diameter wafers, up to 8-inches. Thus, III-V compound semiconductor based infrared focal plane technologies such as QWIP, InSb, and strain layer superlattices (SLS) are potential candidates for the development of large format focal planes such as 4096x4096 pixels and larger. In this paper, we will discuss the possibility of extending the infrared detector array size up to 16 megapixels.

Unintentional impurities can play a significant role in reducing the efficiency of crystalline silicon solar cells. With the advent of low-cost solar-grade silicon feedstocks, this is likely to remain the case well into the future. The purpose of this paper is to review the most important impurities in directionally-solidified ingot-grown multicrystalline silicon, their chemical states, where they come from, and the most commonly used techniques to detect them.

We have used the glancing angle deposition technique to fabricate highly porous nanostructured optical thin films that act as humidity sensors. The responsiveness and repeatability of these sensors has been investigated for samples stored under different environmental conditions. It has been found that samples stored in air have a more stable performance than those stored in a dry nitrogen environment. It has also been found that annealing impacts the responsiveness of the optical thin film sensors.

Sliver solar cells are thin, mono-crystalline silicon solar cells, fabricated using micro-machining techniques combined with standard solar cell fabrication technology. Sliver solar modules can be efficient, low cost, bifacial, transparent, flexible, shadow-tolerant, and lightweight. Sliver modules require only 5 to 10% of the pure silicon and less than 5% of the wafer starts per MW_p of factory output when compared with conventional photovoltaic modules. At ANU, we have produced 20% efficient Sliver solar cells using a robust, optimised cell fabrication process described in this paper. We have devised a rapid, reliable and simple method for extracting Sliver cells from a Sliver wafer, and methods for assembling modularised Sliver cell sub-modules. The method for forming these Sliver sub-modules, along with a low-cost method for rapidly forming reliable electrical interconnections, are presented. Using the sub-module approach, we describe low-cost methods for assembling and encapsulating Sliver cells into a range of module designs.

Photovoltaic (Pb,La)(Zr,Ti)O₃ (PLZT) films in a layered structure of different crystallographic orientations are fabricated by an optimized metalorganic deposition (MOD) method. Such films of (001) orientation exhibit a photovoltaic electrical power of approximately 20 times higher than that of random films. The anisotropic optical properties of the oriented films, including dark conductivity, photoconductivity and photovoltaic tensor surfaces, are obtained quantitatively. These results show that the photovoltaic output current and power of the oriented films are highly improved to be equal to those of semiconductors and suitable for application in the optical sensor of micro-electro-mechanical systems (MEMS).

Polyaniline (PANI) is one of the most studied conducting polymers. Obtained in its conducting form (known as "emeraldine salt") by chemical or electrochemical oxidation of aniline in aqueous acidic medium, this polymer manifests an array of attractive properties. In our work, we investigate the properties of PANI in the form of nanofibers and establish the relationship between the level of doping, optical properties and the conductivity. Two methodologies, chemical and electro-chemical polymerization were used to deposit PANI. In former, dedoped PANI was deposited as a thin film on the glass substrate which was then doped with different concentrations of hydrochloric acid (HCl) to observe the change in conductivity and color. UV-Visible spectra (transmittance and absorbance) of the films were acquired and their conductivities were measured using a four-probe setup. In the latter method, PANI in the emeraldine salt form were deposited on ITO glass using an electrolytic cell. The voltage, temperature and electrolytic environment were varied to analyze the effect of change of doping levels on the optical and electrical properties of PANI. Surface electron microscope images were also taken which showed the nanofibers possessing circular cross sections in the order of 30-60 nm.

Based on rigorous coupled mode theory, a theoretical model is established for studying the optical characteristics of long-period fiber grating (LPFG) coated with the sensing thin films. The vector components of the electric field and the local intensity curves for the lowest order cladding mode are plotted to study the field distribution of cladding mode. It is found that the transverse field components of HE₁₁ cladding mode are approximately 10² times larger about than the longitudinal field components, and the low order HE modes have a larger proportion of intensity localized in the core than the low order EH modes, just like the double-clad LPFG. Further, the influences of the sensing film optical parameters and grating structure parameters on the attenuation peak of transmission spectra are analyzed. Data simulation shows that the sensitivity to the refractive index of sensing films is predicted to be more than 10^-7. The optimal design parameters of the LPFG film sensor for higher sensitivity are ascertained by plotting the contour of the sensor sensitivity. Experimentally, the sol-gel derived SnO₂ film LPFG was prepared, and a preliminary gas-sensing test for detection of C₂H₅OH was performed. The results indicate that the LPFG film sensor with structure optimization has higher sensitivity, and the detection sensitivity is available to 10^-1ppm on the condition of optimum optical parameters. With the advantages of both film sensors and fiber sensors, the coated LPFG sensor has a wide and promising application prospect in process analytical chemistry, environmental monitoring, and biochemical sensing.

We show that integrated optical star couplers can be useful characterization devices to measure the sidewall roughness-induced scattering losses of planar waveguides. We describe the detailed fabrication processes of these star couplers on the silicon-on-insulator (SOI) platform and the process improvements implemented to reduce the waveguide sidewall roughness and scattering loss. We report the main process challenges, particularly to assure a clear gap between any adjacent waveguides of the dense and closely spaced output waveguide array. These challenges are addressed by optimizing the exposure dose of the resist and adding an oxygen ashing treatment to eliminate waveguide footings. We demonstrate further improvement on the waveguide profile and sidewall roughness through the use of a thin Cr hardmask for the dry plasma etching. This optimized fabrication process is capable of producing approximately a 3 nm root-mean-square sidewall roughness, measured using both scanning electron microscopy (SEM) and atomic force microscopy (AFM). Using the fabricated star couplers, we manage to measure the relative scattering losses of various waveguides with the width varying from 0.2 to 2.0 μm in a single measurement, and show that the measured losses agree with the measured sidewall roughness.

This study presents a new concept that combines microtechnology with solar thermal energy to provide a free portable energy source. A water-methanol mixture flows through an array of parallel microchannels which are fabricated into a silicon matrix using conventional micro-fabrication techniques. A vacuum layer is interposed between the channels and the external surface to thermally insulate the channels from the ambient temperature. A selective coating is deposited on one of the vacuum walls to absorb the short wavelength incoming radiation and reduce the long wavelength radiation, hence reducing the heat losses. A geometry and material optimization is still being developed in order to obtain the highest possible efficiency for the micro-heater, while keeping a low pressure drop in the micro-channels. The methanol outlet temperature is predicted to be higher than 250°C. This temperature is required for hydrogen production in a methanol reforming micro-reactor. Therefore, it is envisaged that the micro-solar heater will supply the thermal energy needed for hydrogen generation, that can later be used as fuel for microfuel cells. Both technologies can be integrated in a portable device.

This paper presents the fabrication and test of a flexible luminous device using hollow cathode discharge. The discharge device consists of three layers which are a thin anode layer, an insulation layer and a hollow cathode layer. The device has an array of 10 x 10 holes for the emission. The hole diameter and depth are 100 μm and 120 μm, respectively. The hollow cathode discharge occurs between two electrodes. The hollow cathode discharge usually has the characteristics of the high current density. The discharge device is fabricated by micromachining technology. The anode and the cathode are aluminum and nickel, respectively. Polyimide is chosen as an insulating material because of an excellent dielectric property and a good mechanical stability. The anode of aluminum is deposited by thermal evaporator. Polyimide is spin coated and the hollow cathode is fabricated by nickel electroplating. The thickness of the flexible luminous device is about 150 μm and total size of the device is 20 mm x 10 mm. The discharge test was performed in argon gas chamber at room temperature for various pressures. The current is measured during the discharge to various applied voltages. Current-voltage characteristics of the device were obtained for the operation voltage ranging from 250 to 300 V. The discharge appears at the applied voltage of 260 V in 360 torr. The discharge is also observed at the atmospheric pressure. Compared with a macro discharge device, this device operates at much higher pressure, even at 1 atm. The discharge test confirms that the fabricated device is feasible for a flexible display operating at the atmospheric pressure.

Self-assembled amphiphile systems are utilized in a wide variety of applications including drug delivery and energy storage. Nano-scale physical and chemical interactions govern the packing of self-assembled amphiphilic molecules, resulting in thermodynamically stable phases of defined geometries. Possible phases include micellar, hexagonal, cubic, lamellar and sponge phases. The internal nano-structure of the amphiphile self assembly materials play an important role in the properties of these systems and their application. To date small angle x-ray scattering (SAXS) has been the most common technique used to characterise their structure. Positron annihilation lifetime spectroscopy (PALS) offers a possible alternative technique as it is sensitive to both the internal cavities and the intermolecular forces and in combination with SAXS, may provide more detailed structural information such as trends with composition and temperature variations. The phase behaviour of a bulk phytantriol sample, consisting of 33 % w/w water was explored using PALS, and it was found that PALS was sensitive to phase transitions from bicontinuous cubic (Pn3m) to reversed hexagonal (H₂) to reversed micellar (L₂) phases. These boundaries agreed well with SAXS data. Trends observed for the PALS parameters ι3 and I3 as a function of temperature largely supports the concept that the ortho-positronium is annihilating in the organic regions of the self-assembled structure. However, further investigation is required. We have also developed an innovative data analysis technique to analyse PALS spectra for pore information, with the aim of minimising operator bias and error, which leads to better quantitative comparison of PALS results between laboratories.

Surface photovoltage (SPV) transient provides a non-destructive, contact-free method for characterization of semiconductor surfaces. Here we study SPV-transients of differently cleaned, heavily doped epiready GaAs wafers. After a rapid initial part the transient shows a very slow decay taking place in 100 - 1000 s time scale. Chemical NH₄OH:H₂O₂:H₂O cleaning and atomic hydrogen UHV cleaning are applied. SPV-transients are measured by Kelvin probe in normal atmospheric conditions. A large signal surface trapping model is developed which includes both majority and minority carrier processes and covers the whole light on, steady state, light off sequence. Model fitting allows band bending, energy and density of surface states as well as electron and hole capture cross-sections to be extracted. The results show that the traps are electronic states in thin oxide layer covering the samples. This conclusion is based on the finding that the capture cross-sections are very small, in the range 10^-19 - 10^-26 cm², which calls tunneling for explanation. This indicates that after cleaning the oxide layer is rapidly re-grown in laboratory atmosphere in less than 30 min. Typical band bendings are 0.6 - 0.8 eV, trap energies are slightly above the mid-gap and the density of occupied trap states is around 5×10¹² cm^-2 at thermal equilibrium.

For propose of achieving the high coherent quantum dots or the expected spectral emission, we have proposed the epitaxial method solved by using self-organized grown on the In_xGa_1-xAs relaxed layer and the mis-orientated GaAs substrates. In this study, using extra slow growth rate of 0.075ML/sec to grow the quantum dot matrix under the temperature of 500°C by the general Riber 32P solid-source MBE system, the high surface density and uniformity in size of two-stacked of quantum dot (QD) matrix have been established. The temperature dependences of the full widths at half-maximum (FWHM) and the positions of photoluminescence (PL) bands are studied experimentally by adding In_0.1Ga_0.9As surfactant layer and using mis-orientated substrate, respectively. The 3-dimensional QD images using atomic force microscopy (AFM) well agree with the results of above mentioned. Therefore, a systematic estimate is given of the QD structures grown on different epitaxial conditions.

One-dimensional nanostructures, such as nano-wires and nano-belts, offer a high degree of interest for furthering the current state of nanotechnology research and development. Higher aspect ratio, diameter dependent band-gap, and increased surface scattering for electrons are some of the more significant features in which nano-wires differ from their normal counterparts, which exhibit bulk properties. Many methods for the fabrication of nano-wires, nano-rods and nano-tubes have been developed including lithographic and non-lithographic techniques. Among them Template synthesis (non-lithographic technique) is a versatile, flexible and simple approach to the fabrication of metallic nano-wires and nano-tubes. We have successfully fabricated arrays of Cu-Se 5μm, 1μm, 100nm, 40nm hetero structures using a non-lithographic technique of filling cylindrical pores of track-etch membranes with Cu and Se materials. These were then analyzed by scanning electron microscope. I-V curves of deposited Cu-Se hetero structures of varying diameters were also recorded which show increase of negative differential resistance with decrease in diameters of these hetero-structures. The effect of thermal annealing at different temperatures causing thermal stress on these synthesized structures was also studied.

We present a novel method of etching lithium niobate during the Ti diffusion process. A hypothesis for this etching process is explained by defining the kinetics of the Ti diffusion process as an electrochemical reaction. The Ti ions diffuse into the X cut LiNbO₃ crystal by swapping with Nb ions generating an electric field. Investigations were carried out by placing a bare LiNbO₃ wafer on top of the Ti patterned LiNbO₃ substrate during the diffusion process in a wet oxygen atmosphere. The built-in electric field during the Ti diffusion process is neutralised with the bare LiNbO₃ placed on top and is evident from the material removal that takes place from the top bare substrate and deposited on the bottom substrate were Ti is diffused. Hence the bare substrate is etched in the regions where Ti is present on the bottom substrate. Features can be arbitrarily defined (using Ti etching) and can have dimensions of 1 micron or smaller. Etch depths of the order of 1 micron have been demonstrated while maintaining smooth surfaces. The crystalline nature of the etched surface is analysed using X-ray diffraction techniques. The refractive index measurement and the surface roughness of the etched surface are also presented.

In this paper we present a detailed analysis of charged impurity scattering for two-dimensional electron systems in high quality GaAs heterostructures, using both first order perturbation theory and a more complex self-consistent multiple scattering theory. We calculate scattering due to both homogeneous background impurities and remote ionised impurities in modulation doped heterostructures. We consider both the quantum scattering time τ_q (important for quantum effects and devices) and the more conventional momentum relaxation time τ_t. Whereas the total scattering time gives an indication of the magnitude of the disorder, the ratio of τ_t / τ_q gives an indication as to the origin of the disorder.

Electrodeposition is a versatile technique combining low processing cost with ambient conditions that can be used to prepare metallic, polymeric and semiconducting nano/micro structures. In the present work, track-etch membranes (TEMs) of makrofol (KG) have been used as templates for synthesis of ZnS nanowalled microtubules using electrodeposition technique. The morphology of the microtubules was characterized by scanning electron microscopy. Size effects on the band gap of tubules have also been studied by UV-visible spectrophotometer.

ZnO/p-Si hetero-structure photodiodes have been fabricated by ion beam sputtering technique. The sputtered ZnO films were identified to be polycrystalline nature with wurtzite structure of ZnO and n-type electrical conductivity. Several single and bi-layer metal contacts were produced on both sides of hetero-junction and IV characteristics were measured. It was found that Ni-Au bi-layer contacts were ohmic and best for the diode measurements, having high linearity and low resistivity on both p-Si and ZnO. The IV curve of the hetero-junction indicate that all of the samples have low forward resistance, around 30 ohms and a leakage current around 1 milliamp at 4 volts reverse bias. The photo response of these diodes was tested by shining an 8mW, 780-nm diode laser on to the diodes and measuring the resulting photo current. The responsivity of the hetero-junction was measured as 0.3A/W. This is a quantum efficiency of 48% at 780-nm. Measurement of the ZnO absorption at 780-nm and estimates of the first surface reflectivity of these samples suggests that quantum efficiencies up to 85% are achievable. This is comparable with the best silicon diodes reported in the literature to date which has quantum efficiencies up to 32% and responsivities up to 0.18A/W.

Surface plasmon resonance (SPR) is a very important metrology in biology detection. Phase modulation is one of the SPR detection technologies and the sample changes can be recognized from the phase variation. It is able to detect very tiny bio sample variation due to its high sensitivity. In this study, the optical system design based on a paraboloidal lens-based surface plasmon resonance instrument will be used to control the SPR critical angle. The charge coupled device camera (CCD camera) will be used to record the images of the bio-reaction and (5,1) phase-shifting algorithm will be adopted to retrieve the phase fringes of the whole spot from the intensity maps. The combination of the angle control SPR system and the (5,1) phase-shifting algorithm will expand the whole spot detection ability from the intensity to phase modulation because the intensity maps are going to be recorded for the (5,1) phase-shifting algorithm calculation. The difference between (5,1) phase-shifting algorithm and Five-Step Algorithm¹ is that (5,1) phase-shifting algorithm only needs one image map at one time during the bio reaction and Five-Step Algorithm requires five image maps. Therefore, (5,1) phase-shifting algorithm will reduce the process of experiment and the requirement of the memory. The different concentration alcohols were measured by the optical system to verify the (5,1) phase-shifting algorithm applied in SPR phase modulation measurement and to prove the idea is workable and successful.

We have succeeded in fabricating a needle array of polycarbonate by using a three-dimensional LIGA process. The diameter of the bottom of the needle was about 50 μm, and the height was 135 μm. Although a usual LIGA process has been employed to form structure only with vertical sidewalls, it has now become possible to fabricate needle shape structure by employing a technology that combines X-ray gray mask with the LIGA process. The X-ray gray mask was composed of Si X-ray absorbers and a SU-8 membrane. The sidewall of the X-ray absorber was diagonally processed by Si tapered-trench-etching technology where the transmission intensity of X-rays could be varied locally. An X-ray lithography experiment was executed by using the X-ray gray mask on a beamline BL-4 in TERAS synchrotron radiation facility at AIST. Using this technology a PMMA resist master with three-dimensional structures was made. A Pt layer was sputter deposited as a seed layer on the PMMA resist master, and a Ni mold was fabricated by an electroforming technology. In addition, needle arrays of polycarbonate (PC) and of polymethyl methacrylate (PMMA) were produced by hot embossing technology. Thus, we succeeded in extending the LIGA process to a three-dimensional process capability by employing X-ray gray mask.

SiC is widely recognized as an ideal candidate for electronics and sensors required to operate at extremely high temperatures. Cubic SiC (3C-SiC) is preferred to the hexagonal polytypes for the fabrication of mechanical devices due to its lower cost (a film is deposited on a Si substrate) and greater ease of fabrication. As the deposited SiC film is normally quite thin, some traditional designs of devices are not suitable. The Capacitive Ring-Electrode Accelerometer (CREA) introduced in this paper offers much greater design flexibility. Featuring a central boss of un-prescribed thickness, the value of its seismic mass can be set over a wide range, independently of the sensing capacitance. The latter is realized between a SiC electrode, which surrounds and moves together with the boss, and the underlying substrate. The CREA design was extensively analysed in a FE environment and prototypes were fabricated. Pressure sensors based on the deformable membrane principle and piezoresistive pickup have also been designed, fabricated and tested. The dependence of apex displacement on pressure was used to extract the Young's modulus and the residual stress of the SiC film (bulge test). The membrane was investigated by optical profilometry at various values of pressure and at temperatures between 300 K and 800 K. The shape of the membrane was compared with the FE predictions with a positive outcome.

Capacitive microphones (condenser microphones) work on a principle of variable capacitance and voltage by the movement of its electrically charged diaphragm and back plate in response to sound pressure. There has been considerable research carried out to increase the sensing performance of microphones while reducing their size to cater for various modern applications such as mobile communication and hearing aid devices. This paper reviews the development and current performance of several condenser MEMS microphone designs, and introduces a microphone with spring supported diaphragm to further improve condenser microphone performance. The numerical analysis using Coventor FEM software shows that this new microphone design has a higher mechanical sensitivity compared to the existing edge clamped flat diaphragm condenser MEMS microphone. The spring supported diaphragm is shown to have a flat frequency response up to 7 kHz and more stable under the variations of the diaphragm residual stress. The microphone is designed to be easily fabricated using the existing silicon fabrication technology and the stability against the residual stress increases its reproducibility.

We proposed one novel MEMS-based thermometer with low power-consumption for animal/human health-monitoring network application. The novel MEMS-based thermometer was consisted of triple-beam bimorph arrays so that it could work in a continuous temperature range. Neither continuous electric supply nor A/D converter interface is required by the novel thermometer owing to the well-known deflection of bimaterials cantilever upon temperature changes. The triple-beam structure also facilitated the novel thermometer with excellent fabrication feasibility by conventional microfabrication technology. The parameters of the triple-beam bimorph arrays were determined by finite element analysis with ANSYS program. Low stress Au and Mo metal films were used as top and bottom layer, respectively. The deflection of the triple-beam bimorphs were measured on a home-made heating stage by a confocal scanning laser microscopy. The novel bimorphs had temperature responses similar to traditional single-beam bimorphs. Initial bend of the prepared triple-beam bimorphs were dominantly determined by their side beams. The sensitivity of the novel thermometer was as high as 0.1°C. Experimental results showed that the novel thermometer is attractive for network sensing applications where the power capacity is limited.

Paper reports improved results in the fabrication of 45° micromirrors using low concentration of TMAH with NCW-601A surfactant. 45° micro mirror is an essential component for obtaining 90° out-of-plane reflection of the optical beam. TMAH anisotropic wet etching on (100) silicon wafer with features aligned to the flat so that 45° slope is formed on (110) plane. This requires the etch rate of <110> planes to be lower than <100> planes. Etching rate selectivity depends on: temperature, concentration, and additives. Substantial undercutting of mask needs to be taken into consideration during the design. TMAH concentrations ranging from 2.5% to 10% with different concentrations of surfactant have been studied to achieve improved smoothness of the micromirror surface and better selectivity. SEM/AFM measurement show the roughness of mirror is less than 1nm. Results also show that the surface roughness varies along the 45° slope with the roughest portion at the top of the mirror. This paper will describe the techniques to reduce the size of the rough portion of the mirror.

Deep reactive ion etching (DRIE) is an important tool in MEMS fabrication to achieve three-dimensional structures. However, the etching profiles are not yet perfect. We had etching test samples fabricated in three MEMS foundries and measured the etching rates, sidewall angles, mask selectivity, and sidewall roughness against the line and space of 2 to 5000 μm. We also performed similar DRIE processes using our system and compared our samples and the samples from the foundries. The measurement results revealed the typical fabrication results in the MEMS foundries and their differences. The data were included in the database of MemsONE, a newly developed MEMS design software, and can be used for the process emulations.

Mechanical quality factor (Q-factor) is essential to detect-limitation of a resonant based mass sensor because it determines signal to noise ratio. This paper studies the effects of different energy dissipation mechanisms, including air damping, support loss and thermoelastic damping (TED), on Q-factor of a microcantilever under atmospheric pressure conditions. The contribution of each mechanism was analyzed at various cantilever geometry. And the precondition to Z.Hao's model, which describes the support loss effect by elastic wave theory, was discussed. It was found that in 5 μm-thick silicon cantilevers, air damping was the predominant reason to energy dissipation when cantilever length was larger than 140 μm. The support loss and TED became noteworthy at shorter cantilevers when cantilever length to thickness ratio (L/t) was less than 20. Q-factor of a microcantilever thus can be improved by increasing the cantilever thickness to suppress air damping, but not infinitely because the support loss became comparable to air damping when cantilever thickness was increased. Moreover, it was found that the Q-factor of a multi-layered microcantilever was degraded markedly with the increase of layer numbers.

A novel sensing gap reconfigurable capacitive type MEMS accelerometer with high sensitivity and high resolution is designed, fabricated and characterized. The present MEMS accelerometer is fabricated by using simple SOI process-DRIE. However, conventional Silicon on Insulator (SOI) process is hard to make patterns which is smaller than 1 um because of its high aspect ratio and ICP etching error such as loading-effect and under-cutting. So we have adopted a simple idea of the MEMS actuator-stopper system to modulate the sensing gap precisely. Unlike previous capacitive type MEMS accelerometer which has an anchored reference comb electrodes, the proposed accelerometer has a movable reference comb with MEMS electrostatic actuators and stoppers. By simply applying DC bias to MEMS actuators, the reference comb electrode is moved to the sensing comb structure until the actuators contacting the stoppers. The gap between sensing comb fingers and reference comb fingers is reduced by the gap between actuators and stoppers. In this paper, the initial sensing gap is 1.5um and it reduced to 0.5um, when working. Then, the overall capacitance and sensitivity is simple increased. The capacitance is increased from 3.47pF at the OFF state to 5.35pF at the ON state by applying 2V DC bias.

An electrostatically actuated in-situ measuring method for average stress gradient of a MEMS film was proposed based on pull-in voltages of a set of cantilevers. The key of the measuring method is to realize accurate calculation of pull-in voltages of the cantilevers. To increase the accuracy of the measurement, bending of the cantilevers along the width direction due to the stress gradient was considered. Actual simulations indicate that the calculating speed and the accuracy of the measuring method are ideal, and the method can be applied to in-situ measurement.

This paper reports on the design and simulation of a new valve-less pump for use in microfluidic applications. The simple-structure micropump comprises a piezoelectric Pb(Zr,Ti)O₃ (PZT) - Si diaphragm and flow channels which are fabricated using silicon micromachining techniques. The silicon diaphragm (5×5×0.05mm³) is driven by the PZT (45-μm thick) actuator that has quick response time and large driving force with low power consumption. A key technology to realize the pump diaphragm is the PZT-Si bonding process using a thin gold film as an intermediate layer. Under fabrication conditions of 550°C and 0.8 MPa, the strength of the bonding was experimentally validated to be 13 MPa. The maximum displacement of the diaphragm was measured to be 3 μm_0-P with driving voltage of 30 V_p-p at resonance frequency of 10 kHz. Structural analysis of the diaphragm was done in terms of three-dimensional model using commercial software ANSYS. The flow channels are easily fabricated by silicon etching process. Design of flow channels focused on a cross junction formed by neck of the pump chamber, one outlet and two opposite inlet channels. This structure allows a difference in fluidic resistance and fluidic momentum to be created inside the channels during each pump vibration cycle. Two designs of the devices which have different channel depths, namely type A and type B, was investigated. Flow simulation was done by numerical transient model (using ANSYS-Fluent), in which only the measured deformation of the PZT diagram is applied and therefore no other assumptions are required. The results showed that the mass flow rate of the type A is 0.129×10^-6 kg/s (mean flow rate of 6.3 ml/min) and that of type B is 1.65×10^-6 kg/s (mean flow rate of 80.8 ml/min).

One main obstacle that reduces the yield in RF MEMS technology is the variation of the residual stress resulting from fabrication. Residual stress can occur across the wafer, from the wafer to another wafer, or from one batch of fabrication to another one, and is more pronounced in cantilever bean type switches. For the present paper we have used new sets of dimples to reduce the sensitivity of the structure to the stress level. The SEM pictures of the proposed configuration and those of the conventional beam switch fabricated on the same wafer are analyzed sufficiently. The comparison amply proves soundness of our method. The high actuation voltage is another main issue that requires considerable investigation, and is generally higher in clamped-clamped beam type switches. In order to reduce the actuation voltage, we have designed, fabricated and tested several configurations with different supporting beams. The actuation voltage of as low as 10 volts is achieved and all switches exhibit excellent RF performance. At 40GHz the insertion loss of the switches varies ranging from 0.35dB to 0.7dB. It is evident that at a lower frequency ranges this becomes even better. At 40GHz, the return loss for all switches measured -24dB. Lastly, isolation is better than 20dB to 30dB for all the frequency band of interest.

A road map has been proposed for the design methodology of a RF MEMS switch. The design methodology for RF MEMS is often an interactive process which involves continuous adjustments for the specifications, structure and the fabrication steps. This helps in defining and obtaining the required RF microwave specifications. A novel RF MEMS D shape capacitive shunt switch is proposed. The switch structure is fabricated on a high resistive silicon substrate. This structure consists of coplanar waveguide transmission line, a D shape lower electrode with thin dielectric layer on top and suspended membrane bridge. The lower electrode of the switch is fabricated in D shape using high viscosity and high conductive adhesives. The switch RF path is fabricated on top of silicon dioxide using a thick coplanar waveguide transmission line. The thick transmission line metal connects to the lower electrode and the dielectric material to form the through path of a shunt switch. The suspended metal membrane spans the two coplanar ground lines. With no applied actuation voltage the residual tensile stress keeps the membrane suspended above the RF path. By applying an electrostatic field between membrane and the lower electrode an attractive force causes the floating membrane to pull down and make contact with the lower electrode and dielectric surface to form a low impedance RF path to ground. Main area to which the development aims is lowering the actuation voltage to levels compatible with mainstream IC technologies, while maintaining the RF performance. Proposed switch has shown satisfactory performance between 0-40 GHz frequency range. Paper will present simulation and theoretical results. Experimental results of conductive epoxy fabrication are also presented. This switch could have an important application in the telecommunication network like switching networks.

Material removal at the sub-micron level has been a topic of interest in the past few years, particularly with respect to the fabrication of miniaturized devices. While numerous techniques have been developed and refined from their larger mesoscale counterparts (e.g. microEDM, micromilling), most have inherent limitations such as tool dimensions restricting the minimum feature which can be produced. In this work, we are proposing a novel technique of using the electrokinetic phenomenon for precise material removal at rates in the order of nanometers/min. An AC electric field with a DC offset is applied to a flowing fluid containing suspended particles which will then collide with the workpiece material causing material wear and tear and thus material removal. Results showed that the technique was feasible in achieving sub-micron material removal in micro-channels up to a depth of several hundred nanometers. With no chemicals involved in the process, the technique offers the further attraction of being a benign nano-manufacturing process with potential usage in the biochip and microfluidics areas.