Query: Near-junction cooling for next-generation power electronics

Candidate papers:

abstract: Abstract This article focuses on chip scale single phase cooling for high heat flux and high temperature power device operation. This technology is focused on future wide band gap semiconductors, which are expected to survive harsh environments. To this end, strategies for near junction cooling of vertical current power electronics devices are briefly reviewed, and two chip scale coolers are experimentally investigated. Using single phase water at an inlet temperature of 50 degC, a 40 mm x 20 mm straight microchannel (quantity 200, 38 mm x 313 mm) cooling chip is shown to dissipate up to 127.5 W/cm2 over a 1 cm2 area with a pressure drop of 40.2 kPa at 100 ml/min. A second 75% downsized 20 mm x 10 mm cooling chip based on a unique 500 mm x 500 mm unit cell microchannel plus jet impingement array architecture is then introduced. At the same inlet temperature and in single phase operation, this chip scale cooler is shown to dissipate up to 1.02 kW/cm2 over a 0.25 cm2 area. A maximum average heat transfer coefficient of 120.2 kW/m2K and a pressure drop of 81.2 kPa is further established at a 450 ml/min fluid flow rate. The unit cell jet impingement based design is shown to additionally support average heater temperatures of 177.1 degC. Such technologies are anticipated to enable a 5 to 10 fold reduction in power package size when compared with traditional remote cooling strategies.
author_names: Feng Zhou

Shailesh Joshi

Yanghe Liu

Ercan M Dede
title: Near junction cooling for next generation power electronics
venue: International Communications in Heat and Mass Transfer
year: 2019

abstract: Rapid miniaturization alongwith increasing heat loads in power electronics devices like insulated gate bipolar transistors (IGBTs) have necessitated the need for advanced thermal management technologies in the packaging of these devices. This study quantifies the benefits of key advanced thermal management solutions for packaging of power electronics packages. Thermal resistance network modeling is used to estimate the maximum heat flux that can be dissipated by an IGBT package, while maintaining the junction temperature below 125 degC and 200 degC for silicon and silicon carbide (wide bandgap material) devices, respectively. While the model is completely analytical, it does address important complexities associated with heat flow in packages via the use of a sub model to account for thermal spreading. The advanced cooling technologies evaluated in this study include the use of high thermal conductivity polymer heat sinks, double sided heat sinking of packages, liquid cooling (single and two phase) jet impingement and spray cooling. Additionally, combinations of these cooling technologies are evaluated as well. The heat dissipation achievable from these technologies is compared with that from an air cooled copper heat sink (baseline) The results of this study provide insights and a starting point for selecting thermal management technologies (or combinations) based on the heat dissipation requirements of power electronics packages.
author_names: Palash V Acharya

Vaibhav Bahadur

Robert E Hebner

Abdelhamid Ouroua

Shannon Strank
title: Assessing the Performance of Advanced Cooling Techniques on Thermal Management of Next Generation Power Electronics
venue: ASME 2019 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems
year: 2019

author_names: Palash V Acharya
title: Assessing polymeric nanocomposites and advanced cooling techniques for thermal management of next generation power electronics
year: 2019

abstract: Abstract Large transverse output voltage of transverse thermoelectric film devices is key for their important applications. Currently, the transverse output voltage is only several to tens of mV*K 1 due to the great challenge that multilayer films with a nanometer scale thickness are tilted in transverse thermoelectric film devices. Herein, a novel misaligned mask method is developed to low costly fabricate artificially tilted thermoelectric film devices (ATTFDs) with excellent transverse power generation and cooling performances through accurately controlling the tilted arrangement of nanometer scale multilayer films. The huge transverse output voltage of 300 mV K 1 and cooling temperature gradient of 68 K*mm 1 are obtained for the first time in Bi/Bi0.5Sb1.5Te3 ATTFDs, which are comparable to those from expensive superlattice based thermoelectric devices. Our work demonstrates that ATTFDs can be narrow space applied to high efficient film refrigerators in next generation electronics and optoelectronics, high sensitive thermal response sensors, thermoelectric driven inorganic LED film devices.
author_names: Xin Mu

Wanting Zhu

Wenyu Zhao

Hongyu Zhou

Zhigang Sun

Cuncheng Li

Shifang Ma

Ping Wei

Xiaolei Nie

Jihui Yang

Qingjie Zhang
title: Excellent transverse power generation and cooling performances of artificially tilted thermoelectric film devices
year: 2019

abstract: An innovative arrangement for the electrothermal integration of power electronics and motor in a high power drive systems is presented within this paper with a focus on automotive traction applications. Important challenges which needed to be overcome within this research work consist firstly of the coupling of the thermal design of the switching power modules and of the permanent magnet (PM) electric motor and secondly, the integration of high speed switching devices into the motor housing, without compromising the performance of the transistors. To provide a solution to these challenges, an integrated liquid cooling system for both the stator windings and the power devices has been designed. A bespoke power module has been designed and manufactured in order to meet the specific requirements of this packaging approach. The control structure of the drive system is also highlighted together with initial commissioning results.
author_names: Liliana de Lillo

Behzad Ahmadi

Lee Empringham

Mark Johnson

Jordi Espina

Robert Abebe
title: Next Generation Integrated Drive, NGID: A Novel Approach to Thermal and Electrical Integration of High Power Density Drives in Automotive Applications
venue: 2018 IEEE Energy Conversion Congress and Exposition (ECCE)
year: 2018

abstract: This thesis sets out a series of new techniques to improve the thermal management of power electronics. The work is motivated by the increasing impetus to design smaller, more energy efficient electronic power systems for a range of applications, notably electric vehicles. Thermal management is an increasingly important tool which can facilitate improvements in power density through better monitoring and control of system temperatures. This thesis seeks to deliver improvements in implementing this strategy. A review of the state of the art in thermal management is reported, focussing on temperature measurement, thermal characterisation and system modelling techniques. In addition, novel techniques for arbitrary dissipation control and die temperature measurements in semiconductor devices are presented. A novel analysis of the limitations of low order thermal models is also described. Improvements and applications of these techniques form the basis of this thesis. The pseudorandom binary sequence (PRBS) technique for system identification is applied throughout the thesis to characterise thermal systems. A mathematical analysis is provided, together with a novel technique to determine the minimum gain which can be identified by PRBS techniques in the presence of noise. A novel improvement to the PRBS technique for typically ten times more noise resilient measurements is then developed based on mathematical mixing of different frequency PRBS signals. In parallel, a novel technique is formulated to estimate the temperature throughout a multiple device system using digital IIR filters and PRBS thermal characterisation, which achieves errors of 3 5% when demonstrated practically. By combining these techniques, a comprehensive temperature estimation and control methodology is implemented for a multiple device system under active cooling. Finally, the expansion of the proposed methodologies to steady state die temperature estimation is presented with comparable accuracy to surface temperature measurements, increasing the usefulness of the developed techniques in a practical setting.
author_names: Jonathan N Davidson
title: Advanced thermal modelling and management techniques to improve power density in next generation power electronics
year: 2015

abstract: Abstract The global tendency towards miniaturization driven by the micro electronics industry is pushing system density and packaging towards unprecedented values of thermal design power, with a dramatic reduction of the surface area of the devices.As such, the thermal management of these systems requires novel and smarter cooling methods, in particular in view of the next generation of 3D integrated circuits.On chip two phase cooling represents a very attractive long term solution to this problem.Two phase flow boiling in a micro pin fin heat sink is experimentally studied here for this cooling process.The micro evaporator tested has a heated area of 1 cm 2 consisting of 66 rows of cylindrical in line micro pin fins with a diameter, height and pitch of respectively 50 m m, 100 m m and 91.7 m m .An infrared temperature measurement technique is coupled with high speed flow visualization to investigate the fluid dynamics and heat transfer associated with flow boiling in the micro evaporator.Time dependent features of the flow, operational maps, pressure drop and heat transfer performance in stable flow conditions under a range of heat flux and mass flux of, respectively, 20 44 W cm 2 and 750 1750 kg m 2 s 1 and a constant outlet saturation temperature of 25 deg C are experimentally investigated.The fluid used is the dielectric refrigerant R134a.This study shows that R134a exhibits a very stable flow boiling behavior under a wide range of flow conditions.Low amplitude temperature oscillations with frequencies in the range of 14 22 Hz are detected and the high speed videos demonstrate that these are related to the bubble nucleation process.The heat transfer coefficient trends along the test section are strongly dependent on the vapor quality, with local values as high as 50 kW m 2 K 1 measured in the proximity of the flow area exit. This dependency is attributed to the impact of the two phase flow patterns which develop along the channels, i.e. slug and annular flow. The heat transfer performance enhances significantly with the applied heat, while mass flux exhibits a minor influence.
author_names: Chiara Falsetti

Mirco Magnini

John Richard Thome
title: Hydrodynamic and thermal analysis of a micro pin fin evaporator for on chip two phase cooling of high density power micro electronics
year: 2018

abstract: The paper will discuss the integration of 3D printing and inkjet printing fabrication technologies for microwave and millimeter wave applications. With the recent advancements in 3D and inkjet printing technology, achieving resolution down to 50 um, it is feasible to fabricate electronic components and antennas operating in the millimeter wave regime. The nature of additive manufacturing allows designers to create custom components and devices for specialized applications and provides an excellent and inexpensive way of prototyping electronic designs. The combination of multiple printable materials enables the vertical integration of conductive, dielectric, and semi conductive materials which are the fundamental components of passive and active circuit elements such as inductors, capacitors, diodes, and transistors. Also, the on demand manner of printing can eliminate the use of subtractive fabrication processes, which are necessary for conventional microfabrication processes such as photolithography, and drastically reduce the cost and material waste of fabrication. The utilization of 3D and inkjet printing to fabricate integrated circuits interconnects and antennas is an interesting avenue for research due to the customized nature of certain applications such as automotive radar and 5G wireless solutions. This paper will explore different ways of interfacing with monolithic microwave integrated circuits (MMICs) using additive manufacturing methods including printed vias, ramp interconnects, and wire bonds. With these structures, microwave properties such as matching and losses can be improved due to the ease of printing tailored interfaces that match with each individual device. It will also include demonstration of fully additively manufactured antennas exhibiting excellent bandwidth and circular polarization, something that is expensive and difficult to achieve with traditional manufacturing methods. Finally, the paper will also introduce future directions for additively manufactured electronics, including the packaging of high power devices, cooling functionality, and using exotic materials for electromagnetic interference shielding and flexibility. INTRODUCTION Additive manufacturing has been gaining a lot of traction in the past decade as it promises very fast prototyping and low cost manufacturing. Components that typically have month long lead times can be fabricated in mere days or even hours. Every year, additional 3D printable materials are being introduced to the market, and with that 3D printing can be utilized for new applications. One area of additive manufacturing is inkjet printing, which is a drop on demand method of printing large areas of devices with high accuracy, where metal, dielectric and semiconducting inks can be deposited quickly on almost all surfaces. Inkjet printing is extremely fast and low cost and can be utilized for applications at mm wave frequencies allowing for fast prototyping and roll to roll manufacturing [1] Additionally, the drop on demand nature of inkjet printing facilitates a low temperature <200C) process as the metal is directly deposited on top of the substrate instead of using high temperature PVD systems. With this, flexible substrates are easily metallized without any bending or warping. Another area of additive manufacturing is 3D printing. 3D printers utilize a 3D model and a slicer to slice the model into very thin layers and recreates the model using these layers. Traditionally 3D prints were fabricated using fused deposition model (FDM) where a polymer filament, usually PLA or ABS plastics, was melted and extruded to make the model layer by layer. However new stereolithography (SLA) systems, where the model is built onto a platform in a photoactive resin bath, are generally able to achieve very high (10um) resolution print layers. Another big benefit of SLA printing is its surface roughness, which is on the order of hundreds of nanometers [2] These two factors allow for 3D SLA printed parts to be utilized in high frequency mm wave applications. This paper will delve into several topics in high frequency designs using both 3D and inkjet printing. Designs for fully inkjet printed RF passive components such as capacitors and inductors will be presented. These devices are critical to RF systems and are used in various ways including impedance matching and DC/RF chokes. These devices can be easily manufactured in the same process, in the same inkjet printer, saving time and cost. Other passive devices such as die interconnects will be discussed. These fully additive manufactured interconnects, which replaces wire bonding, are a revolutionary way of designing smart packaging, the inclusion of many different functionality in one smart package. Next advanced 3D printed antennas are presented. These specific antennas demonstrate complex structures that are difficult or impossible to fabricate using traditional manufacturing techniques and drastically reduce the time of prototype to production. These antennas introduce advantageous features, such as high bandwidth or ease of integration with other components. Finally, the paper will explore future topics for research. INKJET PRINTED PASSIVE COMPONENTS Typically, in an RF system, baluns, capacitors and inductors are utilized as in signal conditioning, impedance matching, coupling/choking applications. These devices are critical to RF applications and should have low loss and high quality (Q) factor. Typically, lumped components in standard surface mount packages, such as 0603, are placed and soldered onto circuit boards. However, these packages are tall and bulky and can snap off when bent on flexible substrates. Inkjet printed capacitors and inductors are planar structures, conformal, and low loss which can withstand bending when printed on flexible substrates such as LCP. Additionally, components which generally take many fabrication steps, such as metallization and dielectric deposition can be completed in one inkjet printing process. The additive, drop on demand aspect of fabrication is also low waste, which can save drastic costs when printing in massive quantities. Metal Insulator Metal Capacitors Metal insulator metal (MIM) capacitors are the most basic single layer capacitors. These capacitors are two metal electrodes separated by a dielectric, both of which can be inkjet printable. For metal conductive layers, silver nano particle (SNP) was printed and for dielectric insulator layers, polyvinylpyrrolidone(PVP) was printed for thin films >0.5m) or production epoxy based negative photo resist for thick films(>3m) These allow for various controls of capacitance values, as printing thicker or thinner dielectrics or changing the electrode area, granting full control of design specifications based on the end application. Flexible MIM capacitors fabricated on polyimide substrates show self resonance frequency(SRF) of >1GHz[3] while MIM capacitors with 1.6m 1.8m thick PVP dielectric and SNP metal electrodes were fabricated on silicon substrate as shown in Fig.1 has SRF of 1.2GHz, a maximum Q factor of 25, with a capacitance per area of 33pF/mm [4] Fig. 1. Inkjet printed MIM capacitors on silicon wafers Baluns and Inductors Inductors and baluns are similar spiral structures. Baluns are usually used in signal conditioning applications to change balanced signals into unbalanced and vice versa. Transformer based baluns incorporate three windings in 5 layer structures as shown in Fig. 2a and b respectively [5] The transformer balun demonstrates the complex structures that can be fabricated using additive inkjet printing. Inductors have a similar winding structure since they require long conductive traces to get appreciable inductance values. 1.5 turn inductors were fabricated with SNP ink as the conductive metal and epoxy based negative photo resist ink as the dielectric layer separators and shows a Q factor of 21 at 1 GHz [6] Both applications are inherently multilayer structures, but these demonstrations show the ease of inkjet printing multilayer RF components which can operate at high frequencies and the level of integration that can be achieved by utilizing inkjet printing to reduce processing steps. Fig 2. Inkjet printed 5 layer RF balun schematic (a) and fabricated sample on LCP (b) (a) (b) INTERCONNECTS Interconnects are essential packaging components for the practical implementation of any microelectronic device in a functional electronic system. Specifically, first level interconnects are responsible for interconnecting a microelectronic chip, or die, with its packaging substrate. In a modern wireless system, this packaging substrate can take the form of a metallic leadframe for traditionally packaged off the shelf components, a laminate based interposer for signal fanout and redistribution, or a printed circuit board (PCB) where a chip is integrated directly with other packaged components on the primary host substrate. These packaging methods typically achieve first level interconnection through bond wire or flip chip technologies depending on several design factors, including signal pad location, thermal path management, and the routing of signals below an interconnected device. Wire and ribbon bonding are rapid, low cost, and mature methods for realizing these chip to board interconnects, however increased parasitics and mechanical stability are highlighted concerns that must be considered in a practical setting [7] With the recent growth of additive manufacturing technologies for the development of wireless components, packages, and systems, the first level interconnect is a prime candidate for investigating the integration of inkjet and 3D printing fabrication methods to realize fully printed 3D RF interconnect transitions. The use of additive manufacturing technologies for the interconnection process has the potential to offer several improvements from traditional wire bonding soluti
author_names: Xuanke He

Bijan Tehrani

Ryan A Bahr

Manos M Tentzeris
title: Additive Manufacturing for Next Generation Microwave Electronics and Antennas
year: 2019

abstract: The objective of this research was to investigate the performance of two phase spray cooling with HFC 134a and HFO 1234yf refrigerants using practical enhanced heat transfer surfaces. Results of the study were expected to provide a quantitative spray cooling performance comparison with working fluids representing the current and next generation mobile air conditioning refrigerants, and demonstrate the feasibility of this approach as an alternative active cooling technology for the thermal management of high heat flux power electronics (i.e. IGBTs) in electric drive vehicles. Potential benefits of two phase spray cooling include achieving more efficient and reliable operation, as well as compact and lightweight system design that would lead to cost reduction. The experimental work involved testing of four different enhanced boiling surfaces in comparison to a plain reference surface, using a commercial pressure atomizing spray nozzle at a range of liquid flow rates for each refrigerant to determine the spray cooling performance with respect to heat transfer coefficient (HTC) and critical heat flux (CHF) The heater surfaces were prepared using dual stage electroplating, brush coating, sanding, and particle blasting, all featuring "practical" room temperature processes that do not require specialized equipment. Based on the obtained results, HFC 134a provided a better heat transfer performance through higher HTC and CHF values compared to HFO 1234yf at all tested surfaces and flow rates. While majority of the tested surfaces provided comparable HTC and modestly higher CHF values compared to the reference surface, one of the enhanced surfaces offered significant heat transfer enhancement.
author_names: Sulaiman Saleh Altalidi
title: Two Phase Spray Cooling with HFC 134a and HFO 1234yf for Thermal Management of Automotive Power Electronics using Practical Enhanced Surfaces
year: 2017

abstract: The aircraft industry demands a significant increase in terms of efficiency and gravimetric power density of power converters for next generation aerospace applications. Between the two minimum targets, i.e. an efficiency 98% and a gravimetric power density 10 kW/kg, the specification concerning the converter weight is the most challenging to fulfill. Since cooling systems and magnetic components dominate the weight breakdown of conventional converter concepts, multi cell topologies, enabling improved semiconductors performance and reduced filtering requirements, are foreseen as promising solutions for the power electronics on board of More Electric Aircraft. On the other hand, the necessary simultaneous operation of a high number of cells inevitably limits the reliability of multi cell converters if redundancy is not provided. In this paper, a favorable scaling trend of power density with respect to reliability, aiming to guarantee fault tolerant operation without affecting the performance figures, is identified in modular multi cell converters. Thus, a 45 kW weight optimized modular multi cell three phase inverter featuring a redundant power stage is optimized, achieving an efficiency of 99% and a gravimetric power density of 22.8 kW/kg.
author_names: Mattia Guacci

Dominik Bortis

Johann Walter Kolar
title: High Efficiency Weight Optimized Fault Tolerant Modular Multi Cell Three Phase GaN Inverter for Next Generation Aerospace Applications
venue: 2018 IEEE Energy Conversion Congress and Exposition (ECCE)
year: 2018