Simon S. Ang

Quantum Dots as a Novel Immunofluorescent Detection System for Cryptosporidium parvum and Giardia lamblia

ABSTRACT Semiconductor quantum dot-conjugated antibodies were successfully developed to label Cryptosporidium parvum and Giardia lamblia. This novel fluorescence system exhibited superior photostability, gave 1.5- to 9-fold-higher signal-to-noise ratios than traditional organic dyes in detecting C. parvum, and allowed dual-color detection for C. parvum and G. lamblia.

Digital control of a voltage-mode synchronous buck converter

A digital control algorithm capable of separately specifying the desired output voltage and transient response for a synchronous buck converter operating in voltage mode was developed. This algorithm is based on superimposing a small control signal onto a voltage reference at each switching cycle to cancel out the perturbations. A zero steady-state error in the output voltage can be obtained with the aid of additional dynamics to allow the controller to track a load change and update the reference to a new load state. The specifications of the control algorithm are achieved by pole placement using complete state feedback. The control algorithm was implemented on a digital signal processor (DSP)-controlled synchronous buck converter.

Fabrication and characterization of sputtered-carbon microelectrode arrays

This paper describes a robust and reliable process for fabricating a novel sputter-deposited, thin-film carbon microelectrode array using standard integrated circuit technologies and silicon micromachining. Sputter-deposited carbon films were investigated as potential candidates for microelectrode materials. The surface properties and cross section of the microelectrode arrays were studied by atomic force microscopy and scanning electron microscopy, respectively. Electrical site impedance, crosstalk, and lifetime (dielectric integrity) of microelectrodes in the array were characterized. Electrochemical response of the microelectrodes to hexaammineruthenium(III) chloride and dopamine were investigated by fast-scan cyclic voltammetry and high-speed, computer-based chronoamperometry; results show that thin-film carbon microelectrodes are well-behaved electrochemically. The thin carbon films offer extremely good electrical, mechanical, and chemical properties and thus qualify as viable candidates for various electroanalytical applications, particularly acute neurophysiological studies.

Transient Liquid Phase Die Attach for High-Temperature Silicon Carbide Power Devices

Recently, silicon carbide power devices have been receiving attention for applications above 300 °C. For high-temperature applications, the die attached for these devices has to withstand the maximum operating temperature. In this paper, a transient liquid phase (TLP) die attach technique was demonstrated for two binary alloy systems, Ag-In and Au-In, on Si3N4 substrates. A nearly void-free joint was developed using the Ag-In alloy. Two inter-metallic phases of Agln2 and Ag2ln, along with pure Ag were identified. After annealing at 400 °C, the silver appears to be more evenly spread to form a silver-rich Ag-In alloy with a Ag composition of 70-75 wt.%, even though a nearly pure silver phase is still found in the region where the silver was initially deposited on the Si3N4 substrate. For the Au-In system, there was no indication of bonding degradation at the interface after annealing at 400 °C for 100 h in air. Two inter-metallic phases, Auln and Auln2, along with pure gold, were identified in the Au-In TLP joint. After annealing, the bonding interface became a more Au-rich Au-In alloy. The die attach pull strength, after thermal annealing, increased to approximately twice the minimum strength. The uniformity of the bonds improves and they become more homogeneous because the formation of intermetallic phases continues during thermal annealing.

Microfluidic device as a new platform for immunofluorescent detection of viruses

A bead-based microfluidic device was developed and demonstrated to achieve rapid and sensitive enzyme-linked immunosorbent assay (ELISA) with quantum dots as the labeling fluorophore for virus detection. In comparison to standard ELISA performed on the same virus, the minimal detectable concentration of the target virus was improved from 360 to 22 ng mL-1, the detection time was shortened from >3.25 h to <30 min, and the amount of antibody consumed was reduced by a factor of 14.3.

Development of a solid propellant microthruster with chamber and nozzle etched on a wafer surface

The development of a novel solid propellant microthruster is presented. The solid propellant microthruster is an excellent micropropulsion system for high-accuracy station keeping, attitude control, speed adjustment, gravitation compensation and orbit adjustment of microspacecraft. The design and fabrication using microfabrication technologies for the microthruster are demonstrated. Moreover, the experiments for microcombustion and thrust testing are described in detail. Initial tests, using gunpowder and potassium perchlorate as the main components of the solid propellant, have produced 9.11 × 10−5–1.52 × 10−4 N ⋅ s of total impulse at sea level.

Development of a low-temperature co-fired ceramic solid propellant microthruster

Low-temperature co-fired ceramic (LTCC) technology has been first successfully employed for the realization of a solid propellant microthruster. The microthruster has potential applications in microspacecraft as an excellent micropropulsion system for high-accuracy station keeping, attitude control, drag compensation and orbit adjust. The design, fabrication and experimental investigation of LTCC microthrusters are reported. Results from experiments on microcombustion, and thrust and impulse measurements both at sea level and in vacuum are presented. Initial tests employing gunpowder-based solid propellant have produced 3.81 × 10−5–1.27 × 10−4 N s of total impulse and 5.55–14.41 s of specific impulse at sea level, and 1.31 × 10−4–2.79 × 10−4 N s of total impulse and 19.05–31.55 s of specific impulse in vacuum. The performance of the LTCC solid propellant microthruster is also compared with that of a silicon-based solid propellant microthruster.

A multi-loop voltage feedback filterless class-D switching audio amplifier using unipolar pulse-width-modulation

Voltage feedback is frequently used in class-D switching audio power amplifiers. This paper discusses the design and implementation of a low-cost filterless class-D, unipolar pulse-width modulation switching audio amplifier having a multi-loop voltage feedback scheme. Classical frequency-compensation techniques are used to design and stabilize the three voltage feedback loops implemented in this application. This design method proves to be a cost-effective solution for designing high-fidelity (hi-fi) audio amplifiers. The cost is reduced because no output filter is used, the required switching frequency is half of the one needed if bipolar PWM was used, and no current sensor is needed for feedback purposes. The output impedance is extremely low due to the reduction of the successive voltage loops, making the amplifier less load dependent. Simulation results show that a total harmonic distortion (THD) of 0.005% can be achieved using this topology, as well as a flat frequency response, free of phase distortion in the audio band. Experimental results show the feasibility of this control scheme, since a THD of 0.05% was achieved with a laboratory prototyped amplifier. A comparison of the performance of this audio amplifier with that of some commercial class-D audio amplifiers, reveals that our design can seriously compete with some of the ICs leading the market at a lower cost.

Electrical characterization of the interconnected mesh power system (IMPS) MCM topology

A significant decrease in MCM substrate production cost can be achieved by reducing the number of substrate layers from the conventional four or five (power, ground, X signal, Y signal, pad) to two or three. Besides reducing direct processing steps, yield will also increase as defect producing operations are eliminated. This paper describes the Interconnected Mesh Power System (IMPS), a new interconnection topology which leverages the production technologies of fine line lithography and batch via generation to allow planar power and ground distribution, and dense signal interconnection, on only two metal layers. Several possible implementations of the topology in MCM-D and MCM-L are described. The design of a test vehicle which characterizes both the signal transmission and power distribution properties of the IMPS topology is discussed. The test vehicle has been built in an aluminum/polyimide on silicon process developed at HiDEC. Results of signal transmission measurements (impedance, delay, and crosstalk) for various signal/power/ground configurations are presented. Power distribution characteristics (DC drops and AC noise) are presented and compared with measurements on a test vehicle implemented with solid power and ground planes. From the measured characteristics of the test vehicle, the applicability (clock frequency, power, etc.) for the IMPS topology has been determined. Most MCM applications can benefit from the substrate cost reduction enabled by IMPS. >

A comparison of mechanical lapping versus chemical-assisted mechanical polishing and planarization of chemical vapor deposited (CVD) diamond

Abstract Polishing and planarization of CVD diamond substrates are essential steps in the processing of synthetic diamond for applications in the semiconductor industry. Using the methods of mechanical lapping and chemical-assisted mechanical polishing (CAMP), CVD diamond samples were polished against a cast-iron scaife and an alumina plate, respectively, using the same pressure on the samples. A diamond slurry was used in the mechanical lapping process, and a heated liquid chemical was used in a patented chemical-assisted mechanical polishing and planarization (CAMPP) process. The diamond samples were analyzed at several time intervals during the lapping and polishing processes, and during a combination of the two processes in which mechanical lapping preceded CAMPP. The polishing rate and surface characteristics of the diamond samples were the primary analytical measurements made, and the data were used to compare the relative lapping/polishing efficiencies of the two processes in an effort to develop an optimized process for producing highly polished CVD diamond substrates.