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Author

Jeremy Junghans

Bio: Jeremy Junghans is an academic researcher from University of Arkansas. The author has contributed to research in topic(s): Laser diode & JFET. The author has an hindex of 8, co-authored 21 publication(s) receiving 234 citation(s).

Papers
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Journal ArticleDOI
TL;DR: In this article, the authors describe the fabrication process used to create the precise channel and jet structures used in these LTCC-based coolers, as well as some of the challenges associated with these processes, including the erosion of the copper coolers by the coolant, a requirement for the use of deionized water within the system, and a significant CTE mismatch between the diode bar and the metal cooler.
Abstract: A number of emerging applications of low-temperature co-fired ceramic (LTCC) require embedded fluidic structure within the co-fired ceramic and or precise external dimensional tolerances. These structures enable the control of fluids for cooling, sensing, and biomedical applications, and variations in their geometry from the design can have a significant impact on the overall performance of the devices. One example of this type of application is a multilayer cooler developed recently by the authors for cooling laser diode bars. In many laser systems, laser diodes are the primary emitters, or assemblies of these diode bars are used to pump traditional laser crystals such as Nd:YLF. Assemblies of these diodes require large amounts of electrical current for proper operation, and the device operating temperature must be carefully controlled in order to avoid a shift in the output wavelength. These diodes are packaged into water-cooled assemblies and by their nature dissipate enormous amounts of heat, with waste heat fluxes on the order of 2000 W/cm2. The traditional solution to this problem has been the development of copper multilayer coolers. Assemblies of laser diodes are then formed by stacking these diode bars and coolers. Several problems exist with this approach including the erosion of the copper coolers by the coolant, a requirement for the use of deionized water within the system, and a significant CTE mismatch between the diode bar and the metal cooler. Diodes are bonded to these metal structures and liquid coolant is circulated through the metal layers in order to cool the diode bar. In contrast, the coolers developed by the authors utilize fluid channels and jets formed within LTCC as well as embedded cavity structures to control the flow of a high-velocity liquid and actively cool the laser diode bars mounted on the surface of the LTCC.† The dimensional tolerances of these cooler assemblies and complex shapes that are used to control the fluid can have a significant impact on the overall performance of the laser system. This paper describes the fabrication process used to create the precise channel and jet structures used in these LTCC-based coolers, as well as some of the challenges associated with these processes.

35 citations

Journal ArticleDOI
TL;DR: The experimental results show that the device can operate at 450°C, which is impossible for conventional Si devices, but the current capability of the SiC JFET diminishes with rising temperatures, and the saturation current becomes 20% at450°C with respect to the value at the room temperature.
Abstract: This paper reports on the measured dc characteristics of a SiC JFET device from room temperature up to 450°C in order to evaluate the device's capability for high-temperature operation. The authors packaged SiC JFET bare die into a dedicated high-temperature package to be able to perform experiments under extremely high ambient temperatures. The experimental results show that the device can operate at 450°C, which is impossible for conventional Si devices, but the current capability of the SiC JFET diminishes with rising temperatures. For example, the saturation current becomes 20% at 450°C with respect to the value at the room temperature.

26 citations

Proceedings ArticleDOI
TL;DR: In this paper, a next-generation microchannel cooler has been developed for packaging laser diode arrays, which eliminates many of the problems associated with typical copper-based cooling designs and provides excellent thermal performance.
Abstract: A next-generation microchannel cooler has been developed for packaging laser diode arrays th at eliminates many of the problems associated with typical copper-based cooling designs. † The coolers are built on well-established Low-Temperature Cofired Ceramic technology and provide excellent thermal performance. They do not require the use of deionized water. This work highlights the strengths of the new cooler technology. The results of a long-term, high-flow-rate test which demonstrates the excellent erosion resistance of these coolers are presented. Three devices have been tested for 2500 hours at a flow rate of 0.25 GPM and show minimal signs of erosion. This data is compared to a similar test conducted with copper coolers. Several design parameters are also addressed for the ceramic coolers. The available form and fit characteristics are addressed, as is the custom-configurable nature of the devices. Keywords: laser diode, microchannel, cooling, diode array, LTCC, ceramic, deionized water, erosion

25 citations

Journal ArticleDOI
TL;DR: The authors packaged SiC JFET and Schottky diodes in thermally stable packages and built a high-temperature inductor to demonstrate the suitability of the SiC devices for high-Temperature power converter applications.
Abstract: This paper reports on SiC devices operating in a dc-dc buck converter under extremely high ambient temperatures. To this end, the authors packaged SiC JFET and Schottky diodes in thermally stable packages and built a high-temperature inductor. The converter was tested at ambient temperatures up to 400°C. Although the conduction loss of the SiC JFET increases slightly with increasing temperatures, the SiC JFET and Schottky diode continue normal operation because their switching characteristics show minimal change with temperature. This work further demonstrates the suitability of the SiC devices for high-temperature power converter applications.

25 citations

Proceedings ArticleDOI
16 Jun 2005
TL;DR: In this article, the capability of SiC devices for operation under extremely high ambient temperatures was evaluated in a DC-DC buck converter, and the experimental results showed that the device can operate at 450 degC, which is impossible for conventional Si devices, but the current capability of the SiC JFET diminishes with rising temperatures.
Abstract: This paper evaluates the capability of SiC devices for operation under extremely high ambient temperatures. To this end, the authors packaged SiC JFET and Schottky barrier diodes (SBD) in thermally stable packages and built a high-temperature inductor to be evaluated in a DC-DC buck converter. The DC characteristics of the SiC JFET devices were first measured at ambient temperatures ranging from room temperature up to 450 degC. The experimental results show that the device can operate at 450 degC, which is impossible for conventional Si devices, but as expected the current capability of the SiC JFET diminishes with rising temperatures. A DC-DC converter was then designed and built in accordance with the static characteristics of the SiC JFETs that were measured under extremely high ambient temperatures. The converter was tested up to an ambient temperature of 400 degC. The conduction loss of the SiC JFET increases slightly, as predicted from its DC characteristics, but its switching characteristics hardly change with increasing temperatures. Thus, SiC devices are well suited for operation in harsh temperature environments

24 citations


Cited by
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Journal ArticleDOI
TL;DR: It is shown that this solid oxide “skin” enables many new applications for liquid metals including soft electrodes and sensors, functional microcomponents for microfluidic devices, self-healing circuits, shape-reconfigurable conductors, and stretchable antennas, wires, and interconnects.
Abstract: Gallium and several of its alloys are liquid metals at or near room temperature. Gallium has low toxicity, essentially no vapor pressure, and a low viscosity. Despite these desirable properties, applications calling for liquid metal often use toxic mercury because gallium forms a thin oxide layer on its surface. The oxide interferes with electrochemical measurements, alters the physicochemical properties of the surface, and changes the fluid dynamic behavior of the metal in a way that has, until recently, been considered a nuisance. Here, we show that this solid oxide “skin” enables many new applications for liquid metals including soft electrodes and sensors, functional microcomponents for microfluidic devices, self-healing circuits, shape-reconfigurable conductors, and stretchable antennas, wires, and interconnects.

392 citations

Journal ArticleDOI
TL;DR: In this article, a power converter operating at temperatures above 200 °C has been demonstrated, but work is still ongoing to design and build a power system able to operate in harsh environment (high temperature and deep thermal cycling).
Abstract: High temperature power electronics has become possible with the recent availability of silicon carbide devices. This material, as other wide-bandgap semiconductors, can operate at temperatures above 500 °C, whereas silicon is limited to 150-200 °C. Applications such as transportation or a deep oil and gas wells drilling can benefit. A few converters operating above 200 °C have been demonstrated, but work is still ongoing to design and build a power system able to operate in harsh environment (high temperature and deep thermal cycling).

221 citations

Journal ArticleDOI
TL;DR: In this paper, the authors describe emerging methods to pattern metals that are liquid at room temperature, including injection, injection, subtractive, additive, and additive techniques, which can be divided into four categories: (i) patterning enabled by lithography, (ii) injection, (iii) subtractive and (iv) additive techniques.
Abstract: This highlight describes emerging methods to pattern metals that are liquid at room temperature. The ability to pattern liquid metals is important for fabricating metallic components that are soft, stretchable, conformal, and in some cases, shape-reconfigurable. Applications include electrodes, antennas, micro-mirrors, plasmonic structures, sensors, switches, and interconnects. Gallium (Ga) and its liquid metal alloys are attractive alternatives to toxic mercury. This family of alloys spontaneously forms a surface oxide that dominates the rheological and wetting properties of the metal. These properties pose challenges using conventional fabrication methods, but present new opportunities for patterning innovations. For example, Ga-based liquid metals may be injected, imprinted, or 3D printed on either soft or hard substrates. The use of a liquid metal also enables rapid and facile room temperature processing. The patterning techniques organize into four categories: (i) patterning enabled by lithography, (ii) injection, (iii) subtractive techniques, and (iv) additive techniques. Although many of these approaches take advantage of the surface oxide that forms on Ga and its alloys, some of the approaches may also be suitable for patterning other soft-conductors (e.g., conductive inks, pastes, elastomeric composites).

206 citations

Journal ArticleDOI
TL;DR: The current state of wide bandgap device technology is reviewed and its impact on power electronic system miniaturization for a wide variety of voltage levels is described in this article, followed by an outline of the applications that stand to be impacted.
Abstract: The current state of wide bandgap device technology is reviewed and its impact on power electronic system miniaturization for a wide variety of voltage levels is described. A synopsis of recent complementary technological developments in passives, integrated driver, and protection circuitry and electronic packaging are described, followed by an outline of the applications that stand to be impacted. A glimpse into the future based on the current technological trends is offered.

157 citations

Journal ArticleDOI
TL;DR: In this paper, a review of efforts to increase ηE is presented and it is shown that for well-optimized structures, the residual losses are dominated by the p-side waveguide and nonideal internal quantum efficiency.
Abstract: High-power broad-area diode lasers are the most efficient light sources, with 90-μm stripe GaAs-based 940-980 nm single emitters delivering > 10 W optical output at a power conversion efficiency ηE(10 W) > 65%. A review of efforts to increase ηE is presented here and we show that for well-optimized structures, the residual losses are dominated by the p -side waveguide and nonideal internal quantum efficiency ηi . The challenge in measuring efficiency to sufficient precision is also discussed. We show that ηE can most directly be improved using low heat sink temperature THS with ηE(10 W) reaching > 70% at THS = -50 °C. In contrast, increases in ηE at THS = 25 °C require improvements in both material quality and design, with growth studies targeting increased ηi and reduced threshold current and design studies seeking to mitigate the impact of the p-side waveguide. “Extreme, double asymmetric” (EDAS) designs are shown to substantially reduce p-side losses, at the penalty of increased threshold current. The benefit of EDAS designs is shown here using diode lasers with 30-μm stripes, (in development as high beam quality sources for material processing). Efficiency increases of ~ 10% relative to conventional designs are demonstrated at high powers.

149 citations