Analyzing Losses Using Junction Temperature of 300V 2.4kW 96% efficient, IMHz GaN Synchronous Boost Converter Brian Hughes, James Lazar, Stephen Hulsey, Austin Garrido, Daniel Zehnder, Marcel Musni, Rongming Chu, Karim Boutros  Laboratories LLC, Malibu, CA, USA, bhughes@hrl.com Abstract- New techniques for measuring and analyzing losses in GaN power converters are presented. A 2.4kW synchronous boost converter, switching 300V at IMHz with normally-off, AIN-base gate, AIGaN/GaN HFETs [ I], serves as a vehicle to substantiate the results. An infrared camera is utilized to accurately measure temperatures of the upper and lower switches, as a function of switched current. These temperature measurements are correlated to loss in the respective switches, utilizing temperature data obtained via DC loss measurements. The higher temperature observed in the lower switch results from the switching loss in that switch, and is clearly evident in the thermal images. Analysis of the temperature dependence exposes the loss due to dynamic on-resistance and the switching loss. The extracted parameters accurately model both the efficiency and junction temperatures versus switching current. I. INTRODUCTION GaN-on-Si devices are outstanding candidates for ture high-efficiency power eleconic applications [2,3,4,5]. The high breakdown field and high elecon mobility of GaN's 2- Dimensional-Elecon-Gas (2DEG) results in high breakdown voltage, low on-resistance and low switching charge. GaN devices switch efficiently at much higher equencies than Si devices of the same voltage rating, enabling smaller passive components in switching converters, and reduced converter size. GaN devices manufactured in a high volume Si fab, on GaN epitaxially grown on large Si wafers, are cost "The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency - Energy (ARPA-E), U.S. Department o f Energy, under Award Number DE-ROOOO I 1 7 . " "The information, data, or work presented herein was funded in part by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of y information, apparatus, product, or process disclosed, or represents that its use would not ininge privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof" competitive with Si devices. Noally-off GaN HFETs are preferred for reasons of safety and fast switching. GaN-on-Si HFETs have demonstrated efficient high voltage switching at equencies up to IMHz [6,7]. A precise understanding of the loss mechanisms in GaN power converters is necessary to predict and optimize performance. It is inherently difficult to directly measure GaN switching loss owing to switching speeds of only a few nanoseconds. Furthermore, the conduction loss calculation is complicated by dynamic on-resistance, which depends on switching conditions. New techniques for exacting these parameters are presented here. II. GAN DEVICES AIGaN/GaN heterojunction field effect ansistors, HFETs, are fabricated on Si subsates [ 1 ,8]. The gate length is 1 flm and the gate width is 40mm. The GaN devices are normally- off with a threshold voltage of 1 .4 V, as shown in Fig. 1 . The high positive threshold voltage and low gate hysteresis are atibuted to the high quality of the AIN based gate insulator.  DielC  A1GaN Barrier Gate Insulator � chann - (a) 0.30  0 . 25 V,.=10V 0 . 20 E � 0.15 _ °0 . 1 0 0.05  0.00.  Vo, (V) (b) Figure I . 600V GaN-on-Si HFE.T (a) Device cross-section showing field plates for high breakdown and low dynamic Ron, (b) Transfer curves showing threshold voltage of 1 .4 V. 978-1-4799-1194-3 1 13/$3 l .00 ©20 13 IEEE 13 1