Characterization of Nanomaterials for Thermal Management of Electronics

Recently, there has been a growing interest in flexible electronic devices as they are light, highly flexible, robust, and use less expensive substrate materials. Such devices are affected by thermal management issues that can reduce the device’s performance and reliability. Therefore, this work is focused on the study of the thermal properties of nanomaterials and the methods to address such issues. The goal is to enhance the effective thermal conductivity by adding nanomaterials to the polymer matrix or by structural modification of nanomaterials. The thermal conductivity of copper nanowire/polydimethylsiloxane and copper nanowire/polyurethane composites were measured and showed more than threefold enhancement compared to the thermal conductivity values of the neat polymers. Furthermore, identical heat sources were used on the neat polymer as well as the composite samples, and the resulting thermal images were taken, which showed that the resulting hot spot was significantly less severe for the composite sample, demonstrating the potential of copper nanowire/polymer composite as a substrate for flexible electronics with better heat spreading capability. In addition, the thermal properties of cellulose nanocrystals-poly (vinyl alcohol) composite films with different structural configurations of cellulose nanocrystals (such as isotropic and anisotropic configurations) were investigated as an alternative to commonly used petroleum-based materials for potential application in the thermal management of flexible electronic devices. Also, the in-plane thermal conductivity of the anisotropic composite film was as high as ~ 3.45 W m-1 K-1 in the chain direction. Moreover, the composite films showed ~ 4-14 fold higher in-plane thermal conductivity than most polymeric materials used as substrates for flexible electronics. A high degree of cellulose nanocrystal orientation and the inclusion of poly (vinyl alcohol) were the reasons for such improvements. In addition, thermal images showed that the cellulose nanocrystals-poly (vinyl alcohol) composite films had better heat dissipation capability compared to the neat poly (vinyl alcohol) films, indicating its potential application for flexible electronic devices. In another study, thermal properties of nanodiamond films obtained through a solution-based directed covalent assembly were studied as a low-cost and greener alternative to the nanodiamond films grown via chemical vapor deposition method for thermal management of electronics. The results obtained showed cross-plane thermal conductivity as high as 3.50 +/- 0.54 W m-1 K-1 for nanodiamond film of 139.1 +/- 19.5 nm thick. Such a low cross-plane thermal conductivity value can be attributed to higher porosity and poor interface quality compared to that of the nanodiamond films grown via chemical vapor deposition method. Hence, there is still more room for improvement for such nanodiamond films. The above chapters were focused on the study of the thermal properties of various types of nanomaterials for thermal management of electronic devices. In the next chapter, a technique for the fabrication of a device, that is capable of performing characterization nanomaterials was presented. In this work, suspended beam microdevices for electrothermal characterization of nanomaterials were fabricated through a standard photolithography technique that is less time-consuming, less expensive and much simpler than the methods used by other research groups in the past. The agreement of the measured in-plane thermal conductivity of the suspended central silicon nitride bare bridge with the literature validated the microdevice, setup, and the experimental procedure. Furthermore, these microdevices can be used to measure other important thermoelectric properties of nanomaterials such as the Seebeck coefficient, electrical conductivity, and thermoelectric figure of merit

From carbon nanostructures to new photoluminescence sources: an overview of new perspectives and emerging applications of low pressure PECVD

13 pages, 9 figures.Low-pressure, plasma-enhanced (PE)CVD is a powerful and versatile technique that has been used for thin-film deposition and surface treatment since the early 1960s. However, it is only recently that it has been used in applications other than the different stages of microelectronic circuit fabrication. Now, PECVD is being used in emerging applications due to new materials and process requirements in a wide variety of areas, such as biomedical applications, solar cells, fuel cell development, fusion research, or the synthesis of silicon nanocrystals showing efficient photoluminescence, useful for future solid-state light sources. These new scenarios have stimulated further development of novel PECVD diagnostic techniques, together with fundamental experimental and theoretical studies aimed at a better understanding of some of the basic processes underlying the plasma/surface interaction. This paper gives an overview of some new research areas where PECVD is finding promising applications.FJGV acknowledges partial financial support from CSIC-CAM (Project No. 200550M016 and 200650M016) and MEC (Projects No. MAT2006-13006-C02-01 and ENE2006-14577-C04-03), VJH and IT acknowledge funding from MEC (Projects No. FTN-2003-08228-C03-03, FIS2004-00456 and ENE2006-14577-C04-03).Peer reviewe

Energy Transport in Organic Photovoltaics.

Organic photovoltaics (OPV) have the potential to be a flexible and low-cost form of carbon-neutral energy production. However, many of the underlying physical mechanisms that dictate the behavior of OPVs remain frustratingly obscure in comparison to the well-understood physics of inorganic semiconductors. This dissertation centers around the development of new techniques to characterize the behavior of excitons in organic semiconductors, both in the bulk and at interfaces. We first examine the method of spectrally-resolved photoluminescence quenching (SR-PLQ), the most convenient and powerful current technique for measuring the exciton diffusion length (LD) of organic semiconductors, and extend it to work with optically thin films. This allows for its application to a much wider range of materials and physical systems. The second part of the dissertation presents a further extension of the method of PL quenching to characterize non-ideal interfaces, those which block or quench only a fraction of incident excitons. This is used to understand the operation of a novel fullerene:wide energy gap material buffer in OPVs. In combination with charge transport and morphological studies, it is shown that the mixed buffer shows disproportionate benefits from the two materials; blocking excitons superlinearly with wide energy gap material concentration and still conducting charges efficiently even at very small (10%) fullerene concentration. Finally, we extend the principles of PL quenching to characterize arbitrary interfaces, including those between materials with identical energy levels but different LD and exciton lifetime, and those between materials with small (~20 meV) energy offsets. These techniques allow us to finally resolve the ambiguity in the spin state of the exciton which serves as the primary source of photocurrent in C60, one of the most important materials in current efficient OPVs.PhDPhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/113547/1/kjberg_1.pd

Diode laser modules based on laser-machined, multi-layer ceramic substrates with integrated water cooling and micro-optics

This thesis presents a study on the use of low temperature co-fired ceramic (LTCC) material as a new platform for the packaging of multiple broad area single emitter diode lasers. This will address the recent trend in the laser industry of combining multiple laser diodes in a common package to reach the beam brightness and power required for pumping fibre lasers and for direct-diode industrial applications, such as welding, cutting, and etching. Packages based on multiple single emitters offer advantages over those derived from monolithic diode bars such as higher brightness, negligible thermal crosstalk between neighbouring emitters and protection against cascading failed emitters. In addition, insulated sub-mounted laser diodes based on telecommunication standards are preferred to diode bars and stacks because of the degree of assembly automation, and improved lifetime. At present, lasers are packaged on Cu or CuW platforms, whose high thermal conductivities allow an efficient passive cooling. However, as the number of emitters per package increases and improvements in the laser technology enable higher output power, the passive cooling will become insufficient. To overcome this problem, a LTCC platform capable of actively removing the heat generated by the lasers through impingement jet cooling was developed. It was provided with an internal water manifold capable to impinge water at 0.15 lmin-1 flow rate on the back surface of each laser with a variation of less than 2 °C in the temperature between the diodes. The thermal impedance of 2.7°C/W obtained allows the LTCC structure to cool the latest commercial broad area single emitter diode lasers which deliver up to 13 W of optical power. Commonly, the emitters are placed in a “staircase” formation to stack the emitters in the fast-axis, maintaining the brightness of the diode lasers. However, due to technical difficulties of machining the LTCC structure with a staircase-shaped face, a novel out-plane beam shaping method was proposed to obtain an elegant and compact free space combination of the laser beam on board using inexpensive optics. A compact arrangement was obtained using aligned folding mirrors, which stacked the beams on top of each other in the fast direction with the minimum dead space

NASA SBIR abstracts of 1991 phase 1 projects

The objectives of 301 projects placed under contract by the Small Business Innovation Research (SBIR) program of the National Aeronautics and Space Administration (NASA) are described. These projects were selected competitively from among proposals submitted to NASA in response to the 1991 SBIR Program Solicitation. The basic document consists of edited, non-proprietary abstracts of the winning proposals submitted by small businesses. The abstracts are presented under the 15 technical topics within which Phase 1 proposals were solicited. Each project was assigned a sequential identifying number from 001 to 301, in order of its appearance in the body of the report. Appendixes to provide additional information about the SBIR program and permit cross-reference of the 1991 Phase 1 projects by company name, location by state, principal investigator, NASA Field Center responsible for management of each project, and NASA contract number are included

Wide Bandgap Based Devices

Emerging wide bandgap (WBG) semiconductors hold the potential to advance the global industry in the same way that, more than 50 years ago, the invention of the silicon (Si) chip enabled the modern computer era. SiC- and GaN-based devices are starting to become more commercially available. Smaller, faster, and more efficient than their counterpart Si-based components, these WBG devices also offer greater expected reliability in tougher operating conditions. Furthermore, in this frame, a new class of microelectronic-grade semiconducting materials that have an even larger bandgap than the previously established wide bandgap semiconductors, such as GaN and SiC, have been created, and are thus referred to as “ultra-wide bandgap” materials. These materials, which include AlGaN, AlN, diamond, Ga2O3, and BN, offer theoretically superior properties, including a higher critical breakdown field, higher temperature operation, and potentially higher radiation tolerance. These attributes, in turn, make it possible to use revolutionary new devices for extreme environments, such as high-efficiency power transistors, because of the improved Baliga figure of merit, ultra-high voltage pulsed power switches, high-efficiency UV-LEDs, and electronics. This Special Issue aims to collect high quality research papers, short communications, and review articles that focus on wide bandgap device design, fabrication, and advanced characterization. The Special Issue will also publish selected papers from the 43rd Workshop on Compound Semiconductor Devices and Integrated Circuits, held in France (WOCSDICE 2019), which brings together scientists and engineers working in the area of III–V, and other compound semiconductor devices and integrated circuits

Micro- and Nanotechnology of Wide Bandgap Semiconductors

Owing to their unique characteristics, direct wide bandgap energy, large breakdown field, and excellent electron transport properties, including operation at high temperature environments and low sensitivity to ionizing radiation, gallium nitride (GaN) and related group III-nitride heterostructures proved to be enabling materials for advanced optoelectronic and electronic devices and systems. Today, they are widely used in high performing short wavelength light emitting diodes (LEDs) and laser diodes (LDs), high performing radar, wireless telecommunications, as well ‘green’ power electronics. Impressive progress in GaN technology over the last 25 years has been driven by a continuously growing need for more advanced systems, and still new challenges arise and need to be solved. Actually, lighting industry, RF defene industry, and 5G mmWave telecommunication systems are driving forces for further intense research in order to reach full potential of GaN-based semiconductors. In the literature, there is a number of review papers and publications reporting technology progress and indicating future trends. In this Special Issue of Electronics, eight papers are published, the majority of them focusing materials and process technology of GaN-based devices fabricated on native GaN substrates. The specific topics include: GaN single crystalline substrates for electronic devices by ammonothermal and HVPE methods, Selective – Area Metalorganic Vapour – Phase Epitaxy of GaN and AlGaN/GaN hetereostructures for HEMTs, Advances in Ion Implantation of GaN and Related Materials including high pressure processing (lattice reconstruction) of ion implanted GaN (Mg and Be) and III-Nitride Nanowires for electronic and optoelectronic devices

Single-photon detectors integrated in quantum photonic circuits

Toward photonic circuits for quantum computer

Advances in Middle Infrared Laser Crystals and Its Applications

In the last twenty years, there has been a growing interest in middle infrared (mid-IR) laser crystals and their application to achieve mid-IR laser radiations, which has benefited from the development of novel mid-infrared crystals and the improving quality of traditional mid-IR crystals. Moreover, these works have promoted the development of related technical applications. This Special Issue of the journal Crystals focuses on the most recent advances in mid-IR laser crystals, from materials to laser sources and applications. It aims to bring together the latest developments in novel mid-IR crystals, improvements in the quality of mid-IR crystals, mid-IR non-linear crystals and mid-IR lasers, as well as the application of mid-IR technology in spectroscopy, trace gas detection and remote sensing, optical microscopy and biomedicine. Aspiring authors are encouraged to submit their latest original research, as well as forward-looking review papers, to this Special Issue