Ultra-wide band gap semiconductor devices based on β-phase gallium oxide (Ga2O3) offer the potential to achieve higher switching performance and efficiency and lower manufacturing cost than that of today's wide band gap power electronics. However, the most critical challenge to the commercialization of Ga2O3 electronics is overheating, which impacts the device performance and reliability. We fabricated a Ga2O3/4H-SiC composite wafer using a fusion-bonding method. A low-temperature (≤600 °C) epitaxy and device processing scheme was developed to fabricate MOSFETs on the composite wafer. The low-temperature-grown epitaxial Ga2O3 devices deliver high thermal performance (56% reduction in channel temperature) and a power figure of merit of (∼300 MW/cm2), which is the highest among heterogeneously integrated Ga2O3 devices reported to date. Simulations calibrated based on thermal characterization results of the Ga2O3-on-SiC MOSFET reveal that a Ga2O3/diamond composite wafer with a reduced Ga2O3 thickness (∼1 μm) and a thinner bonding interlayer (<10 nm) can reduce the device thermal impedance to a level lower than that of today's GaN-on-SiC power switches.

Ulta-wide bandgap semiconductors based on β-Ga_2O_3 offer the potential to achieve higher power switching performance, efficiency, and lower manufacturing cost than today's wide bandgap power semiconductors. However, the most critical challenge to the commercialization of Ga_2O_3 electronics is overheating, which impacts the device's performance and reliability. We fabricated a Ga_2O_3/4H-SiC composite wafer using a fusion-bonding method. A low temperature (≤ 600 ^∘C) epitaxy and device processing approach based on low-temperature (LT) metalorganic vapor phase epitaxy is developed to grow a Ga_2O_3 epitaxial channel layer on the composite wafer and subsequently fabricate into Ga_2O_3 power MOSFETs. This LT approach is essential to preserve the structural integrity of the composite wafer. These LT-grown epitaxial Ga_2O_3 MOSFETs deliver high thermal performance (56 reduction in channel temperature), high voltage blocking capabilities up to 2.45 kV, and power figures of merit of ∼ 300 MW/cm^2, which is a record high for any heterogeneously integrated Ga_2O_3 devices reported to date. This work is the first realization of multi-kilovolt homoepitaxial Ga_2O_3 power MOSFETs fabricated on a composite substrate with high heat transfer performance which delivers state-of-the-art power density values while running much cooler than those on native substrates. Thermal characterization and modeling results reveal that a Ga_2O_3/diamond composite wafer with a reduced Ga_2O_3 thickness (∼ 1 μm) and thinner bonding interlayer (< 10 nm) can reduce the device thermal impedance to a level lower than today's GaN-on-SiC power switches.

A standard paradigm of localization microscopy involves extension from two to three dimensions by engineering information into emitter images, and approximation of errors resulting from the field dependence of optical aberrations. We invert this standard paradigm, introducing the concept of fully exploiting the latent information of intrinsic aberrations by comprehensive calibration of an ordinary microscope, enabling accurate localization of single emitters in three dimensions throughout an ultrawide and deep field. To complete the extraction of spatial information from microscale bodies ranging from imaging substrates to microsystem technologies, we introduce a synergistic concept of the rigid transformation of the positions of multiple emitters in three dimensions, improving precision, testing accuracy, and yielding measurements in six degrees of freedom. Our study illuminates the challenge of aberration effects in localization microscopy, redefines the challenge as an opportunity for accurate, precise, and complete localization, and elucidates the performance and reliability of a complex microelectromechanical system.

β-phase gallium oxide (Ga2O3) is an emerging ultrawide bandgap (UWBG) semiconductor (EG ∼ 4.8 eV), which promises generational improvements in the performance and manufacturing cost over today's commercial wide bandgap power electronics based on GaN and SiC. However, overheating has been identified as a major bottleneck to the performance and commercialization of Ga2O3 device technologies. In this work, a novel Ga2O3/4H-SiC composite wafer with high heat transfer performance and an epi-ready surface finish has been developed using a fusion-bonding method. By taking advantage of low-temperature metalorganic vapor phase epitaxy, a Ga2O3 epitaxial layer was successfully grown on the composite wafer while maintaining the structural integrity of the composite wafer without causing interface damage. An atomically smooth homoepitaxial film with a room-temperature Hall mobility of ∼94 cm2/Vs and a volume charge of ∼3 × 1017 cm-3 was achieved at a growth temperature of 600 °C. Phonon transport across the Ga2O3/4H-SiC interface has been studied using frequency-domain thermoreflectance and a differential steady-state thermoreflectance approach. Scanning transmission electron microscopy analysis suggests that phonon transport across the Ga2O3/4H-SiC interface is dominated by the thickness of the SiNx bonding layer and an unintentionally formed SiOx interlayer. Extrinsic effects that impact the thermal conductivity of the 6.5 μm thick Ga2O3 layer were studied via time-domain thermoreflectance. Thermal simulation was performed to estimate the improvement of the thermal performance of a hypothetical single-finger Ga2O3 metal-semiconductor field-effect transistor fabricated on the composite substrate. This novel power transistor topology resulted in a ∼4.3× reduction in the junction-to-package device thermal resistance. Furthermore, an even more pronounced cooling effect is demonstrated when the composite wafer is implemented into the device design of practical multifinger devices. These innovations in device-level thermal management give promise to the full exploitation of the promising benefits of the UWBG material, which will lead to significant improvements in the power density and efficiency of power electronics over current state-of-the-art commercial devices.

Some of the most exciting recent advancements in heat conduction physics have been motivated, enabled, or achieved by the thermal management community that ITherm serves so effectively. In this talk we highlight the resulting renaissance in basic heat conduction research, which is linked to cooling challenges from power transistors to portables. Examples include phonon transport and scattering in nanotransistors, engineered high-conductivity composites, modulated conductivity through phase transitions, as well as the surprising transport properties of low-dimensional (1D and 2D) nanomaterials. This work benefits strongly from decades of collaboration and leadership from the semiconductor industry. Dr. Kenneth E. Goodson chairs the Mechanical Engineering Department, and holds the Davies Family Provostial Professorship and a courtesy appointment in Materials Science at Stanford University. His lab has graduated 40 PhDs, nearly half of whom are professors at schools including MIT, Stanford, and UC Berkeley. Honors include the Kraus Medal, the Heat Transfer Memorial Award, the AIChE Kern Award, the SRC Technical Excellence Award, the InterPACK Achievement Award, and Fellow grade with ASME, IEEE, APS, and AAAS. Goodson co-founded Cooligy, which built computer heat sinks and was acquired by Emerson in 2006. At Stanford, serving as Mechanical Engineering Chair and Vice Chair since 2008, Goodson led two strategic plans and launched hiring of 15 faculty members who are transforming the department’s scholarship and diversity. ITherm 2018, May 29 June 1, 2018 Sheraton Hotel & Marina, San Diego, CA, USA 17 Final Conference Program CONFERENCE KEYNOTES Ravi Kuppuswamy Sean Ross Paolo Petagna Intel ARFL CERN K-1: FPGAS: THE ACCELERATOR OF CHOICE FROM THE EDGE TO THE CLOUD Presenter: Ravi Kuppuswamy (Intel) Wednesday, May 30, 9:00-10:00 AM, Bel Aire Abstract: The computing landscape is dynamically evolving and changing on a real-time basis. With the surge of mobile devices, network infrastructure requirements, edge and data center applications, the need to manage our data-centric connected world is exploding. FPGAs play a critical role in managing and accelerating hardware and software workloads across platforms, efficiently meeting the needs of customers to deliver rapid innovation in their markets. In particular, we’re just now scratching the surface of what’s possible with Artificial Intelligence (AI). From self-driving cars to precision medicine to military defense, AI is poised to impact every industry and facet of life. It has the potential to dramatically improve and even save lives for people in every part of the world. But before we can harness AI for the greater good of humanity, we’ll need to turn theory into practice, bring machine learning models out of training, and put them to the test. In short, we need to understand how to make AI work in the field. This Conference keynote will cover how FPGAs help in deploying AI and accelerating the new ecosystem needed to support these applications. The computing landscape is dynamically evolving and changing on a real-time basis. With the surge of mobile devices, network infrastructure requirements, edge and data center applications, the need to manage our data-centric connected world is exploding. FPGAs play a critical role in managing and accelerating hardware and software workloads across platforms, efficiently meeting the needs of customers to deliver rapid innovation in their markets. In particular, we’re just now scratching the surface of what’s possible with Artificial Intelligence (AI). From self-driving cars to precision medicine to military defense, AI is poised to impact every industry and facet of life. It has the potential to dramatically improve and even save lives for people in every part of the world. But before we can harness AI for the greater good of humanity, we’ll need to turn theory into practice, bring machine learning models out of training, and put them to the test. In short, we need to understand how to make AI work in the field. This Conference keynote will cover how FPGAs help in deploying AI and accelerating the new ecosystem needed to support these applications. Ravishankar (Ravi) Kuppuswamy is vice president and general manager of the Engineering in the Programmable Solutions Group at Intel. He is responsible for product engineering, organizational development, business-enabling operations, and innovation initiatives inside the FPGA business. Kuppuswamy served previously as vice president in the Intel Platform Engineering Group and director of Many Integrated Core and Intel® Xeon® processor product development. He first joined Intel in 1996 as an analog design engineer, and subsequently held various technical and management positions spanning five generations of Intel lead process technology microprocessors. In 2006, he relocated to Bangalore, India, to lead execution on the 6-core Intel Xeon processor for servers, formerly codenamed “Dunnington.” In 2008, India’s National Association of Software and Services Companies bestowed its Innovation of the Year Award on the Dunnington program. From 2008 to 2010, Kuppuswamy served as design manager for the 10-core Intel Xeon processor for servers, formerly code-named “Eagleton.” Before assuming his current role in 2014 and relocating to Oregon, he spent 3 years in the Intel Architecture Group as director of microprocessor and graphics product development in India. A frequent speaker and industry contributor in verylarge-scale integrated circuit development, Kuppuswamy has two patents and several published papers in the field. He earned his bachelor’s degree in electrical engineering and master’s degree in chemistry, both from Birla Institute of Technology and Science in Pilani, India. He also holds a master’s degree in electrical engineering from Arizona State University. ITherm 2018, May 29 June 1, 2018 Sheraton Hotel & Marina, San Diego, CA, USA Final Conference Program 18 K-2: TRANSITIONING DIRECTED ENERGY WEAPONS FROM THE LABORATORY TO THE TACTICAL EDGE: THE THERMAL INTERFACE Presenter: Sean Ross (Air Force Research Laboratory) Thursday, May 31, 9:00-10:00 AM, Bel Aire Abstract: Healthy systems engineering begins with an examination of the impact of the operating requirements on the components and interfaces of the proposed system. Thermal management leads the list of challenges to the integration of high energy laser systems on weight and volume constrained platforms, especially smaller aircraft. This presentation will introduce the generic architectures of High Energy Lasers and High Power Microwaves and cover the major issues and trades involved and summarize some current efforts to mature the Directed Energy system thermal management interface. Healthy systems engineering begins with an examination of the impact of the operating requirements on the components and interfaces of the proposed system. Thermal management leads the list of challenges to the integration of high energy laser systems on weight and volume constrained platforms, especially smaller aircraft. This presentation will introduce the generic architectures of High Energy Lasers and High Power Microwaves and cover the major issues and trades involved and summarize some current efforts to mature the Directed Energy system thermal management interface. Dr. Sean Ross has worked at the Air Force Research Laboratory, Directed Energy Directorate, since 1994. Currently, he is the directed energy deputy at the office of the Deputy Assistant Secretary of the Air Force for Science, Technology and Engineering. Dr. Ross is a board member of the Directed Energy Professional Society. He is the author of “Laser Beam Quality Metrics” textbook and frequently teaches courses on the subject. Dr. Ross led the creation of the Environmental Laser Test Facility to test high-energy laser systems and components in simulated flight environments prior to flight testing. He has been involved in power, thermal, structural and other high-energy laser integration issues for over a decade. Dr. Ross holds a BS and MS in Physics from Brigham Young University, and a PhD in Optical Science and Engineering from the Center for Research and Education in Optics and Lasers (CREOL), College of Optics and Photonics, University of Central Florida. K-3: DETECTOR THERMAL MANAGEMENT WITH CO2 BOILING SYSTEMS AT CERN Presenter: Paolo Petagna (CERN) Friday, June 1, 9:00-10:00 AM, Bel Aire Abstract: For the thermal management of silicon detectors in the next generation of particle physics experiments, total powers well in excess of 100 kW with volumetric densities up to 100 W/dm 3 must be removed from sealed volumes, where the detectors are organized in convoluted surfaces. In order to ensure their required operational life of 10 years, the silicon sensors, submitted to high radiation levels, must be maintained at temperatures well below 0 °C. Furthermore, the mass of the support structures and ancillary systems must be minimized, while large temperature gradients, both in time and space, should be avoided. The most demanding applications already implement boiling flows of CO2 in small diameter evaporators: CO2 presents extremely favorable thermo-physical properties, is radiation hard and environmentally friendly. The typical geometry of a silicon detector’s CO2 evaporator is a few meters long pipe, 1.0 to 2.5 mm in I.D. However, after a recent successful application of silicon micro-structured cold plates in liquid phase, one experiment will implement for the first time in 2019 a cooling system based on CO2 boiling in silicon micro-channels. The talk will review the achievements and the ongoing R&D at CERN on both the local evaporators and global system design. For the thermal management of silicon detectors in the next generation of particle physics experiments, total powers well in excess of 100 kW with volumetric densities up to 100 W/dm 3 must be removed from sealed volum

We make use of the intrinsic aberrations of an optical microscope to track single particles in three dimensions, and we combine information from multiple particles on a rigid body of a microelectromechanical system to measure its motion in six degrees of freedom. Our tracking method provides an extraordinary amount of information from an ordinary imaging system, revealing unintentional motion of the microsystem due to fabrication tolerance and nanoscale clearance between parts in sliding contact. Our work facilitates quantification and study of the actuation performance and reliability of complex microsystems.

The β-gallium oxide (Ga 2 O 3 ) material system offers the potential to dramatically improve the electrical performance and cost-effectiveness of next-generation power electronics. This is because of its ultra-wide bandgap (~4.8 eV) and the availability of high-quality single-crystal bulk substrates. However, the low thermal conductivity of Ga 2 O 3 (11-27 W/m-K) implies that significant thermal challenges need to be overcome to commercialize Ga 2 O 3 devices. In the present work, a single crystal (010) Ga 2 O 3 wafer was integrated with a 4H-SiC substrate via fusion bonding to address this concern of poor thermal conductivity. A differential steady-state thermoreflectance method was established to measure the thermal boundary resistance at the Ga 2 O 3 /SiC interface (100 m 2 K/GW), which has yet to be reported due to the limited probing depth of conventional frequency- and time-domain thermoreflectance techniques.

HVPE growth of [beta]-Ga2O3 films for devices on bulk and thermally enhanced [beta]-Ga2O3 composite substrates was recorded at Photonics West 2020 in San Francisco, California.

Ultra-wide bandgap β-gallium oxide (Ga2O3) devices are of considerable interest with potential applications in both power electronics and radio frequency devices. However, current Ga2O3 device technologies are limited by the material's low intrinsic electron mobility and thermal conductivity. The former problem can be addressed by employing modulation-doped β-(AlxGa1−x)2O3/Ga2O3 heterostructures in the device architecture. In this work, (AlxGa1−x)2O3/Ga2O3 modulation-doped field effect transistors (MODFETs) have been investigated from a thermal perspective. Thermoreflectance thermal imaging was used to characterize the self-heating of the MODFETs. The (Al0.18Ga0.82)2O3 thermal conductivity (3.1–3.6 W/mK) was determined using a frequency domain thermoreflectance technique. Electro-thermal modeling was used to discern the effect of design parameters such as substrate orientation and channel length on the device self-heating behavior. Various thermal management schemes were evaluated using the electro-thermal device model. From an electro-thermal co-design perspective, the improvement in electrical performance followed by the mitigation of self-heating was also studied. For example, by employing a Ga2O3-on-SiC composite wafer, which was fabricated in this work, a 50% increase in power handling capability can be achieved as compared to a homoepitaxial device. Furthermore, flip-chip heterointegration and double-sided cooling approaches can lead to more than 2× improvement in the power handling capability. Using an augmented double-sided cooling design that includes nanocrystalline diamond passivation, a 5× improvement in the power handling capability can be accomplished, indicating the potential of the technology upon implementation of a suitable thermal management scheme.

A standard paradigm of localization microscopy involves extension from two to three dimensions by engineering information into emitter images, and approximation of errors resulting from field dependence of optical aberrations. We invert this standard paradigm, introducing the concept of fully exploiting the latent information of intrinsic aberrations by complete calibration of an ordinary microscope, enabling accurate localization of single emitters in three dimensions across an ultrawide and deep field. To complete the extraction of spatial information from microscale bodies ranging from imaging substrates to microsystem technologies, we introduce a synergistic concept of the rigid transformation of the positions of multiple emitters in three dimensions, improving precision and yielding measurements in six degrees of freedom. Our study provides new insight into the challenge of aberration effects in localization microscopy, redefines the challenge as an opportunity for accurate, precise, and complete localization, and elucidates the performance and reliability of a complex microsystem.

Microelectromechanical systems (MEMS) that require contact of moving parts to implement complex functions exhibit limits to their performance and reliability. Here, we advance our particle tracking method to measure MEMS motion in operando at nanometer, microradian, and millisecond scales. We test a torsional ratcheting actuator and observe dynamic behavior ranging from nearly perfect repeatability, to transient feedback and stiction, to terminal failure. This new measurement capability will help to understand and improve MEMS motion.

The common assumption that precision is the limit of accuracy in localization microscopy and the typical absence of comprehensive calibration of optical microscopes lead to a widespread issue—overconfidence in measurement results with nanoscale statistical uncertainties that can be invalid due to microscale systematic errors. In this article, we report a comprehensive solution to this underappreciated problem. We develop arrays of subresolution apertures into the first reference materials that enable localization errors approaching the atomic scale across a submillimeter field. We present novel methods for calibrating our microscope system using aperture arrays and develop aberration corrections that reach the precision limit of our reference materials. We correct and register localization data from multiple colors and test different sources of light emission with equal accuracy, indicating the general applicability of our reference materials and calibration methods. In a first application of our new measurement capability, we introduce the concept of critical-dimension localization microscopy, facilitating tests of nanofabrication processes and quality control of aperture arrays. In a second application, we apply these stable reference materials to answer open questions about the apparent instability of fluorescent nanoparticles that commonly serve as fiducial markers. Our study establishes a foundation for subnanometer localization accuracy in widefield optical microscopy.

We fabricate and test subresolution aperture arrays as calibration devices for optical localization microscopy. An array pitch with a relative uncertainty of approximately three parts in ten thousand enables localization with subnanometer accuracy.

Cross-sensitivity matrices are used to translate the response of three-axis accelerometers into components of acceleration along the axes of a specified coordinate system. For inertial three-axis accelerometers, this coordinate system is often defined by the axes of a gimbal-based instrument that exposes the device to different acceleration inputs as the gimbal is rotated in the local gravitational field. Therefore, the cross-sensitivity matrix for a given three-axis accelerometer is not unique. Instead, it depends upon the orientation of the device when mounted on the gimbal. We define nine intrinsic parameters of three-axis accelerometers and describe how to measure them directly and how to calculate them from independently determined cross-sensitivity matrices. We propose that comparisons of the intrinsic parameters of three axis accelerometers that were calculated from independently determined cross-sensitivity matrices can be useful for comparisons of the cross-sensitivity-matrix measurement capability of different institutions because the intrinsic parameters will separate the accelerator-gimbal alignment differences among the participating institutions from the purely gimbal-related differences, such as gimbal-axis orthogonality errors, z-axis gravitational-field alignment errors, and angle-setting or angle-measurement errors.

Gallium-Nitride (GaN) MMIC circuits have been developed that achieve much greater RF power density compared to GaAs based predecessors. Even greater power densities are possible from these wideband gap devices. However, the requirement to maintain reliable junction temperatures limits both linear and areal power densities. Under the DARPA-sponsored NJTT and ICECool Applications programs, chip-scale thermal management solutions are being developed that combine GaN-on-Diamond with microchannel embedded cooling solutions that enable reliable MMIC operation at heat flux levels of >1kW/cm2 .

Mechanical linkages are fundamentally important for the transfer of motion through assemblies of parts to perform work. Whereas their behavior in macroscale systems is well understood, there are open questions regarding the performance and reliability of linkages with moving parts in contact within microscale systems. Measurement challenges impede experimental studies to answer such questions. In this study, we develop a novel combination of optical microscopy methods that enable the first quantitative measurements at nanometer and microradian scales of the transfer of motion through a microelectromechanical linkage. We track surface features and fluorescent nanoparticles as optical indicators of the motion of the underlying parts of the microsystem. Empirical models allow precise characterization of the electrothermal actuation of the linkage. The transfer of motion between translating and rotating links can be nearly ideal, depending on the operating conditions. The coupling and decoupling of the links agree with an ideal kinematic model to within approximately 5%, and the rotational output is perfectly repeatable to within approximately 20 microradians. However, stiction can result in nonideal kinematics, and input noise on the scale of a few millivolts produces an asymmetric interaction of electrical noise and mechanical play that results in the nondeterministic transfer of motion. Our study establishes a new approach towards testing the performance and reliability of the transfer of motion through assemblies of microscale parts, opening the door to future studies of complex microsystems.

The concept of localization precision, which is essential to localization microscopy, is formally extended from optical point sources to microscopic rigid bodies. Measurement functions are presented to calculate the planar pose and motion of microscopic rigid bodies from localization microscopy data. Physical lower bounds on the associated uncertainties - termed centroid precision and orientation precision - are derived analytically in terms of the characteristics of the optical measurement system and validated numerically by Monte Carlo simulations. The practical utility of these expressions is demonstrated experimentally by an analysis of the motion of a microelectromechanical goniometer indicated by a sparse constellation of fluorescent nanoparticles. Centroid precision and orientation precision, as developed here, are useful concepts due to the generality of the expressions and the widespread interest in localization microscopy for super-resolution imaging and particle tracking.

A new device-first low-temperature bonded gallium nitride (GaN)-on-diamond high-electronic mobility transistor (HEMT) technology with state-of-the-art, radio frequency (RF) power performance is described. In this process, the devices were first fabricated on a GaN-on-silicon carbide (SiC) epitaxial wafer and were subsequently separated from the SiC and bonded onto a high-thermal-conductivity diamond substrate. Thermal measurements showed that the GaN-on-diamond devices maintained equivalent or lower junction temperatures than their GaN-on-SiC counterparts while delivering more than three-times higher RF power within the same active area. Such results demonstrate that the GaN device transfer process is capable of preserving intrinsic transistor electrical performance while taking advantage of the excellent thermal properties of diamond substrates. Preliminary step-stress and room-temperature, steady-state life testing shows that the low-temperature bonded GaN-on-diamond device has no inherently reliability limiting factor. GaN-on-diamond is ideally suited to wideband electronic warfare (EW) power amplifiers as they are the most thermally challenging due to continuous wave (CW) operation and the reduced power-added efficiency obtained with ultra-wide bandwidth circuit implementations.