UNIVERSITY OF CALIFORNIA Santa Barbara InP HBT Power Amplifier MMICs toward 0.4W at 220GHz A Dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Electrical and Computer Engineering by Thomas Benjamin Reed Committee in charge: Professor Mark Rodwell, Chair Professor Emeritus Stephen Long Professor Robert York Doctor Zach Griffith March 2013 The dissertation of Thomas Benjamin Reed is approved. _____________________________________________________ Zach Griffith _____________________________________________________ Stephen Long _____________________________________________________ Robert York _____________________________________________________ Mark Rodwell, Committee Chair March 2013 InP HBT Power Amplifier MMICs toward 0.4W at 220GHz Copyright © 2013 by Thomas Benjamin Reed iii ACKNOWLEDGEMENTS This work relied on the countless contributions of those that came before. Prof. Mark Rodwell is a driven visionary for the future of electronics. He has been a highly generous advisor. Zach Griffith has a wealth of knowledge in high frequency device, circuit technology, and life. His advice has saved many headaches. Thank you for all your time and hard work to make this SSPA effort successful. I acknowledge committee members Prof. Stephen Long and Prof. Robert York for their valuable experience and expertise. UCSB Rodwell Group Members, including Vibhor Jain, Ashish Baraskar, Evan Lobisser, Andy Carter, Saeid Daneshgar, Hyunchul Park, Johann Rode, Hanwei Chiang, Prateek Choudhary are great colleagues. Ken Ota, Serra Hoagland, and other non-engineers have helped me remain grounded. My family has been a source of strength throughout graduate school. DARPA MTO has provided the funding resources through the HiFIVE pro- gram to pursue these power amplifier MMICs at 220GHz. Finally, Sarah, my wife is a joy. She lightens the loads of life and has been there for me through the best and worst parts of this experience. iv VITA OF THOMAS BENJAMIN REED March 2013 Education Dec. 2009 – Present University of California Santa Barbara Santa Barbara, CA Ph.D. in Electrical Engineering (Estimated March 2013 Graduation) Sept. 2008 – Dec. 2009 University of California Santa Barbara Santa Barbara, CA M.S. in Electrical Engineering Sept. 2002 – April 2008 Brigham Young University Provo, UT BS in Electrical Engineering, Minor in Mathematics PRoFESSionaL Ex PERiEncE Aug. 2008 – Mar. 2013 Graduate Student Researcher Santa Barbara, CA Department of Electrical and Computer Engineering, UCSB Jan. 2012 – Mar. 2012 Laboratory Teaching Assistant Santa Barbara, CA Department of Electrical and Computer Engineering, UCSB June 2011 – Aug. 2011 Electrical Engineering Student Intern Albuquerque, NM Microsystems, Organization 1711, Sandia National Laboratories Sept. 2007 – April 2008 Teaching Assistant Provo, UT Department of Electrical Engineering, Brigham Young University June 2007 – Aug. 2007 Electrical Engineering Internship Seattle, WA ASIC Design Group, Cray, Inc. PuBLicationS Griffith, Z.; Reed, t.; Rodwell, M.; Field, M., “A 220GHz Solid-State Power Amplifier MMIC with 26.8dB S21 Gain, and 55.5mW P at 17.0dB Compressed Gain,” Microwave Symposium OUT Digest (MTT), 2013 IEEE MTT-S International, pp. 1-4, 2-7 June 2013. Reed, t.B.; Rodwell, M.J.W.; Griffith, Z.; Rowell, P.; Urteaga, M.; Young, A.; Field, M., “A 220GHz InP HBT Solid-State Power Amplifier MMIC with 90mW P at 8.2dB Com- OUT pressed Gain,” Compound Semiconductor Integrated Circuit Symposium (CSICS), 2012 IEEE, pp.1-4, 14-17 Oct. 2012 H. Park, M. Lu, E. Bloch, t. Reed, Z. Griffith, L. Johansson, L. Coldren, and M. Rodwell, “40Gbit/s Coherent Optical Receiver Using a Costas Loop,” European Conference and Exhi- bition on Optical Communication, OSA Technical Digest (Optical Society of America, 2012), paper Th.3.A.2. Reed, t.B.; Rodwell, M.J.W.; Griffith, Z.; Rowell, P.; Field, M.; Urteaga, M., “A 58.4 Solid-State Power Amplifier at 220 GHz using InP HBTs,” Microwave Symposium Digest (MTT), 2012 IEEE MTT-S International, pp. 1444-1446, 17-22 June 2012. v Bloch, E.; Park, H.; Lu, M.; Reed, t.; Griffith, Z.; Johansson, L.; Coldren, L.; Ritter, D.; Rodwell, M. J., “A 1-20 GHz InP HBT Phase-Lock-Loop IC for Optical Wavelength Synthesis,” Mi- crowave Symposium Digest (MTT), 2012 IEEE MTT-S International, pp. 1492-1494, 17-22 June 2012. Reed, t.B.; Rodwell, M.J.W.; Griffith, Z.; Rowell, P.; Urteaga, M.; Field, M.; Hacker, J., “48.8 mW Multi-Cell InP HBT Amplifier with On-Wafer Power Combining at 220 GHz,” Compound Semiconductor Integrated Circuit Symposium (CSICS), 2011 IEEE, pp. 196-199, 16-19 Oct. 2011. Hacker, J.; Munkyo Seo; Young, A.; Griffith, Z.; Urteaga, M.; Reed, t.; Rodwell, M.; , “THz MMICs based on InP HBT Technology,” Microwave Symposium Digest (MTT), 2010 IEEE MTT-S International, pp.1126-1129, 23-28 May 2010. FiELd oF Study Major Field : Studies in High Frequency Circuit Design with Professor Mark Electronics/Photonics Rodwell and Zach Griffith, Ph.D. vi ABSTRACT InP HBT Power Amplifier MMICs toward 0.4W at 220GHz by Thomas Benjamin Reed RF power amplification above 200GHz has become more critical as higher frequency bands are sought for radar and space applications. At 220GHz, a low-loss free-space propagation window is very alluring for potential systems, however, a single transis- tor cannot produce sufficient output power requisite for a wireless system. This work demonstrates solid-state power amplifier MMICs targeting up to 0.4W at 220GHz. Power amplifier cells are designed using four 6μm-long common emitter and common base InP HBTs to form a cascode. Single InP HBTs with 250nm-wide emit- ters and have shown a peak f of 700GHz and peak f of 400GHz. The cascode cell MAX T shows above 15dB of small signal available gain at 220GHz. Non-inverted microstrip IC interconnects shield the InP substrate and provide a low-loss environment for impedance tuning and power combining. Multiple levels of power combining are performed on wafer to reach a high overall saturated output power at 220GHz. Exper- iments were designed to find the limits of transistor density, the optimal Class A load line, the optimal number of power combining levels and gain stages, the maximum physical size, and the maximum possible DC power consumption at the IC level. In the first attempt, a 4-Cell SSPA was reported to have 48.8mW of saturated output power at 220GHz with a compressed gain of 4.5dB. On a second maskset, a vii 2-stage, 8-Cell SSPA had 90mW of saturated 220GHz output power at 8.2dB of com- pressed gain. A third set of designs demonstrates a 4x increase in output HBT periph- ery over the 8-Cell SSPAs in Tapeouts 1 and 2. In full-thickness RF power measure- ments, 180mW of saturated power was observed at 214GHz when air cooled. When heat removal by wafer thinning and mounting is complete, power levels may be close to the 400mW shown in simulation. viii Contents ACKNOWLEDGEMENTS iv VITA OF THOMAS BENJAMIN REED v ABSTRACT vii LIST OF FIGURES xii 1 INTRODuCTION TO SSPA DESIGN 1-A Introduction 1 1-B Design Challenges at 220 GHz 2 1-C Noteworthy Results 5 1-D Novel Methods In 220GHZ PA Design 6 1-E InP HBT Technology Description 8 2.1 MICROWAVE POWER AMPLIFIER DESIGN 2.1-A Linear Amplfiers 15 2.1-B Transistor Amplifier Topologies 17 2.1-C Bandwidth Considerations and Parasitics 21 2.1-D RF Power Amplifiers 22 2.1-E Class A Power Amplifiers 25 2.1-F Other Power Amplifier Classes 26 2.1-G Power Amplifier Tuning 28 2.1-H Transmission Lines 30 2.1-I Impedance Matching 34 2.1-J Impedance Transformation 37 2.1-K Using Smith Charts 37 2.1-L Smith Chart Impedance Matching Networks 41 2.1-M Transistor Impedance Matching 42 2.1-N Stability Factor and Stability Measure 44 2.2 220GHz SSPA DESIGN 2.2-A Adjusting Microwave Methods for 220GHz 49 2.2-B 220GHz PA MMIC Specifications & Technology 51 ix 2.2-C 220GHz PA Cell Design 53 2.2-D PA Cell DC Design 56 2.2-E Matching and Tuning Networks 59 2.2-F Circuit, Layout, and EM Simulation 66 2.2-G 2:1 Combiner Design 68 2.2-H 4:1 Combiner Design 70 2.2-I Off-Wafer Combiners For Larger Power 72 2.2-J PA MMIC Synthesis 74 2.2-K Efficiency Accounting In an 8-Cell PA MMIC 78 2.3 SSPA MEASuREMENT AND CALIBRATION 2.3-A Description of S-parameters 81 2.3-B VNA Setup & Calibration 82 2.3-C Calibration Tolerances 86 2.3-D VNA Calibration Methods 87 2.3-E Power Sweep Testing 90 2.3-F Power Sweep 92 2.3-G Calibration of the Power Bench 93 3 RESuLTS OF HIFIVE PA MMICS 3.1-A Results of HiFIVE 1 PA MMICs 95 3.1-B Load Line comparison & 2 Cell PA 95 3.1-C 4-Cell Amplifiers 96 3.1-D 8-Cell Amplifiers 98 3.1-E Tapeout 1 Conclusions 99 3.2-A Results of HiFIVE 2 PA MMICs 99 3.2-B 4-Cell Multi-Stage PAs 100 3.2-C 8-Cell Multi-Stage PAs 102 3.2-D Tapeout 2 Conclusions 105 3.3-A Results of HiFIVE 3 PA MMICs 105 3.3-B 16-Cell PA 106 3.3-C 8-Cell PA using new 8x6μm HBT 108 3.3-D 16-Cell PA using new 8x6μm HBT 109 3.3-E Tapeout 3 Conclusions 111 x