Fred Barlow

Bio: Fred Barlow is an academic researcher from University of Idaho. The author has contributed to research in topics: Power module & Fourier transform. The author has an hindex of 19, co-authored 88 publications receiving 1368 citations. Previous affiliations of Fred Barlow include Virginia Tech & Metropolitan State University of Denver.

Design and fabrication of embedded resistors in LTCC for high frequency applications

Abstract: This work was aimed at the RF performance of embedded resistors in LTCC, with tight tolerance, and low variation in resistance value, as basic required properties. In order to conduct this performance evaluation, two test vehicles were designed; one to evaluate the effect of physical design on embedded resistors, the other for characterization at high frequencies. DuPont 951 Green Tapes and CF021 resistor paste (100Ω/sq.) were employed to fabricate the substrates that were cofired at 875°C for 15 minutes. A four-probe Kelvin contact method and the HP-4263 LCR meter were used for the direct current (DC) resistance measurement, and an HP network analyzer was used for impedance measurements. It was found that although the majority of resistors had a 3a tolerance of 20∼30%, resistors less than lOmil wide or one square in aspect ratio had much higher tolerance and variation than the others. For the 2 to 5 square resistors in a certain width, the tolerance varied little. The apparent sheet resistivity demonstrated negative variation for resistors under 2 square and positive for over 2 square in aspect ratio. In a substrate with two resistor layers, the tolerance of most resistors on the upper layer was less than 15%, half of that on the lower layer, while their variation of apparent sheet resistivity were similar. Unlike the resistor width and aspect ratio, the overlap and extension had little influence on the tolerance and variation due to the short diffusion distance between termination and resistor. It is recommended that for low tolerance and low variation design, the preferred options are 20mil to 35mil width for one (1) to five (5) square aspect ratio, 10mil overlap and 5mil extension, and most importantly, no other embedded passives on the layers just over or under the resistors. With this design and the regular LTCC fabrication process, a tolerance less than 15% and variation no more than ± 5% have been achieved repeatedly in this work.

Z-axis interconnections for high density processors, Part 1

Abstract: Three-dimensional packaging has been considered by many the best path towards smaller, lighter, faster and less expensive electronics; however, interconnections and efficient thermal transfer have been stumbling blocks towards achieving that goal. Focusing on one of these challenges, this paper examines commercially available z-axis interconnection media, with advantages, disadvantages and selection criteria for the intended system. After an initial down selection based on published data, several connector styles will be tested for life cycle integrity and overall effectiveness for system integration. The primary specifications for the z-axis interconnections are 0.5-mm pitch, area array, high reliability in harsh military environments, and minimal contact force to simplify the external compression structure. This paper also describes the critical nature of the overall structural design and tolerance control, for reliable assemblies and continuous operation; with over two thousand interconnects between each of the five layers in the 3D stack-up.

Investigation of wirebonds on insulated-metal substrate for multichip power module applications

Abstract: One of the most common reliability problems for multichip power modules is wirebond lifting or wirebond failure. Thus, it is important to investigate the bonding of aluminum bond wire to copper, nickel-plated, and gold/nickel-plated surfaces on insulated-metal substrates (IMS) for multichip power module applications. Due to the high power requirements in multichip power modules, the aluminum bond wires usually carry high currents. As such, it is important to understand the high current effects on these aluminum wirebonds. Wirebonding of aluminum bond wire is an inherent destructive process to its structural properties due to the ultrasonic energy required to form the wedge bonds. It was found that the bond strength of the aluminum bond wire to copper, nickel-plated, and gold/nickel-plated on the insulated-metal substrate depends on the current carrying conditions and the thermal annealing of the aluminum bond wires. In general the bond pull strength of the aluminum bond wires on copper and nickel-plated IMS boards increases upon carrying a current large enough to cause a significant thermal annealing. Low temperature thermal annealing is found to improve the wire strength itself but degrade the bond strength slightly probably due to interfacial change or intermetallic formation at the bonding interface. Wire strength was measured based on elongation and tensile strengths. The paper will present data on the bond strength and interfacial change of the aluminum bond wire on IMS boards after carrying high currents and upon low temperature thermal annealing. These wirebonds were subjected to shear test and pull test according to MIL-STD-883E to evaluate the integrity of the wirebonds. The paper will provide measurements data of bond strength for copper, nickel, and gold surfaces on IMS boards, after current and annealing testing, and a comparison of these different surfaces. The paper will also address the possibility of interfacial change or intermetallic formation due to the passing of high current through the wirebonds.

Miniaturization of power supplies with emphasis on integrated passive components

Abstract: This paper addresses miniaturization of power supplies with emphasis on thick film passive components integration. Three key issues need to be addressed; electrical simulation and characterization, thermal analysis, simulation and verification, and materials characterization; therefore, these issues are examined in this work. Thick film passive components (capacitors and resistors) have been evaluated for use in the miniaturization of power electronic circuits. Also, guidelines for the design implementation and steps necessary to integrate these passive components on prefired Alumina (Al 2 O 3 ) and Aluminum Nitride (AIN) ceramic surfaces have been generated. Thick film capacitors on the order of 120pF/mm 2 with breakdown voltage ratings of 250V have been fabricated on prefired Aluminum Nitride, as well as stable resistors ranging in value from a few ohms to several Megaohms have been also evaluated in this work. The use of Aluminum Nitride, as a high performance ceramic substrate, and the resulting issues concerning compatible thick film pastes, have also been investigated and the thermal properties of these components have been studied. Since a sizable amount of heat is generated by power electronic circuits, the integrated components are analyzed with respect to tolerance and degeneration over a wide temperature range.

Advanced Laser Diode Cooling Concepts

Abstract: A new, patent-pending method of cooling high-power laser diode arrays has been developed which leverages advances in several areas of materials science and manufacturing. This method utilizes multi-layer ceramic microchannel coolers with small (100’s of microns) integral water channels to cool the laser diode bar. This approach is similar to the current state-of-the-art method of cooling laser diode bars with copper microchannel coolers. However, the multi-layer ceramic coolers offer many advantages over the copper coolers, including reliability and manufacturing flexibility. The ceramic coolers do not require the use of deionized water as is mandatory of high-thermal-performance copper coolers. Experimental and modeled data is presented that demonstrates thermal performance equal to or better than copper microchannel coolers that are commercially available. Results of long-term, high-flow tests are also presented to demonstrate the resistance of the ceramic coolers to erosion. The materials selected for these coolers allow for the laser diode bars to be mounted using eutectic AuSn solder. This approach allows for maximum solder bond integrity over the life of the part.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

A Survey of Wide Bandgap Power Semiconductor Devices

Abstract: Wide bandgap semiconductors show superior material properties enabling potential power device operation at higher temperatures, voltages, and switching speeds than current Si technology. As a result, a new generation of power devices is being developed for power converter applications in which traditional Si power devices show limited operation. The use of these new power semiconductor devices will allow both an important improvement in the performance of existing power converters and the development of new power converters, accounting for an increase in the efficiency of the electric energy transformations and a more rational use of the electric energy. At present, SiC and GaN are the more promising semiconductor materials for these new power devices as a consequence of their outstanding properties, commercial availability of starting material, and maturity of their technological processes. This paper presents a review of recent progresses in the development of SiC- and GaN-based power semiconductor devices together with an overall view of the state of the art of this new device generation.

Overview of Dual-Active-Bridge Isolated Bidirectional DC–DC Converter for High-Frequency-Link Power-Conversion System

Abstract: High-frequency-link (HFL) power conversion systems (PCSs) are attracting more and more attentions in academia and industry for high power density, reduced weight, and low noise without compromising efficiency, cost, and reliability. In HFL PCSs, dual-active-bridge (DAB) isolated bidirectional dc-dc converter (IBDC) serves as the core circuit. This paper gives an overview of DAB-IBDC for HFL PCSs. First, the research necessity and development history are introduced. Second, the research subjects about basic characterization, control strategy, soft-switching solution and variant, as well as hardware design and optimization are reviewed and analyzed. On this basis, several typical application schemes of DAB-IBDC for HPL PCSs are presented in a worldwide scope. Finally, design recommendations and future trends are presented. As the core circuit of HFL PCSs, DAB-IBDC has wide prospects. The large-scale practical application of DAB-IBDC for HFL PCSs is expected with the recent advances in solid-state semiconductors, magnetic and capacitive materials, and microelectronic technologies.

Eliminate Reactive Power and Increase System Efficiency of Isolated Bidirectional Dual-Active-Bridge DC–DC Converters Using Novel Dual-Phase-Shift Control

Abstract: This paper proposes a novel dual-phase-shift (DPS) control strategy for a dual-active-bridge isolated bidirectional DC-DC converter. The proposed DPS control consists of a phase shift between the primary and secondary voltages of the isolation transformer, and a phase shift between the gate signals of the diagonal switches of each H-bridge. Simulation on a 600-V/5-kW prototype shows that the DPS control has excellent dynamic and static performance compared to the traditional phase-shift control (single phase shift). In this paper, the concept of ldquoreactive powerrdquo is defined, and the corresponding equations are derived for isolated bidirectional DC-DC converters. It is shown that the reactive power in traditional phase-shift control is inherent, and is the main factor contributing to large peak current and large system loss. The DPS control can eliminate reactive power in isolated bidirectional DC-DC converters. In addition, the DPS control can decrease the peak inrush current and steady-state current, improve system efficiency, increase system power capability (by 33%), and minimize the output capacitance as compared to the traditional phase-shift control. The soft-switching range and the influence of short-time-scale factors, such as deadband and system-level safe operation area, are also discussed in detail. Under certain operation conditions, deadband compensation can be implemented easily in the DPS control without a current sensor.

Wearable Electrochemical Sensors and Biosensors: A Review

Abstract: This article reviews recent advances and developments in the field of wearable sensors with emphasis on a subclass of these devices that are able to perform highly-sensitive electrochemical analysis Recent insights into novel fabrication methodologies and electrochemical techniques have resulted in the demonstration of chemical sensors able to augment conventional physical measurements (ie heart rate, EEG, ECG, etc), thereby providing added dimensions of rich, analytical information to the wearer in a timely manner Wearable electrochemical sensors have been integrated onto both textile materials and directly on the epidermis for various monitoring applications owing to their unique ability to process chemical analytes in a non-invasive and non-obtrusive fashion In this manner, multi-analyte detection can easily be performed, in real time, in order to ascertain the overall physiological health of the wearer or to identify potential offenders in their environment Of profound importance is the development of an understanding of the impact of mechanical strain on textile- and epidermal (tattoo)-based sensors and their failure mechanisms as well as the compatibility of the substrate employed in the fabrication process We conclude this review with a retrospective outlook of the field and identify potential implications of this new sensing paradigm in the healthcare, fitness, security, and environmental monitoring domains With continued innovation and detailed attention to core challenges, it is expected that wearable electrochemical sensors will play a pivotal role in the emergent body sensor networks arena