Ray Pengelly, Cree RF and Microwave Products, Research Triangle Park, NC October 21, 2010

Transcription

1 Ray Pengelly, Cree RF and Microwave Products, Research Triangle Park, NC October 21, 2010

2 Agenda GaN HEMT Transistor Structures High Power Densities Blessing or Curse? Thermal Management CW, Pulsed and Linear Operation Wideband General Purpose Amplifiers Linear and Efficient Telecommunication Amplifiers Doherty and Envelope Tracking Approaches GaN HEMT MMICs Packaging Improvements to device structures and package materials Device Reliability Trends Applications and Higher Frequencies

3 Strengths of GaN HEMTs High breakdown voltage V DD large; R L high easier to match; lower losses High sheet charge density; n s = 1 x Current density is large Device area can be reduced Large Watts/mm of gate periphery High saturated drift velocity High saturation current density and W/mm Small device area per watt lower capacitances Low drain-source capacitance Easier to match More suitable for switch-mode amplifiers

4 Attributes of GaN HEMTs High Voltage Operation High power densities 4 to 8 watts/mm at 28 and 50 volt operation respectively both a blessing and a curse! High Frequency Performance present Cree process has f T of 27 GHz High Efficiency Low Quiescent Current High Native Linearity Low capacitance per peak watt (12% of LDMOS and 21% of GaAs MESFET) supports broad bandwidths Enable new amplifier architectures Highly correctable under DPD (digital pre-distortion) Almost constant C DS as a function of V DS great for Drain Modulation

5 GaN versus Si, GaAs and SiC Concept Si GaN on SiC Band Gap (ev) Thermal Conductivity (W/Kcm) Breakdown Field (10 6 V/cm) Saturated Electron Velocity (peak) (10 7 cm/s) Relative Permittivity Si GaAs 4H-SiC GaN (1) 1 (2.1) 2 (2) 1.5 (2.7) DPD Doherty LINC EER Class F/E/J High thermal time constant Moderate bandwidth Low off-state impedance High output capacitance Large non-linear output capacitance Poor amplitude to phase modulation conversion Moderate bandwidth Low f T Moderate breakdown Low thermal time constant Large bandwidth High off-state impedance Low output capacitance Small non-linear output capacitance Good amplitude to phase modulation conversion Large bandwidth High f T High breakdown Material properties of major semiconductors Impact of GaN on power amplifier concepts 5

6 GaN HEMT Structures Without field plate With field plate Field plate is connected to gate Increases breakdown voltage Reduces dispersion, depletion of channel by surface traps

7 Field Plate Operation

8 Improved I-V with Field Plated Devices

9 Typical Power Performance of Field Plated HEMTs

10 Blessings and Curses of High Power Density At 28 volts, Cree GaN HEMTs have an RF power density of 4 watts per millimeter of gate periphery At 48 volts, the same transistors have an RF power density of 8 watts per millimeter At 65 volts, the same transistors have an RF power density of 11 watts per millimeter With high operating voltages and power densities the design engineer has to be very aware of thermal management e.g. A CGH21120F transistor operating at 48 volts will generate 220 watts of CW RF power and at P SAT have a drain efficiency of 65% Dissipated heat is 118 watts T RISE is 177 O C Needs de-rating The same device can operate at 35 volts producing 150 watts of CW power with 70% drain efficiency Dissipated heat is 64 watts T RISE is 90 O C T CASE can be >100 O C

11 Blessings and Curses of High Power Density Pulsed Operation Pulses need to be shorter than 100 s of microseconds to make substantial reductions in channel temperature Good news is that the effective pulse widths for modern digital modulation schemes such as W-CDMA and WiMAX with 5 to 20 MHz channel bandwidths are < 100 nsec Linear Operation Operating GaN HEMTs at high drain voltages impacts backed-off (linear region) operating temperatures e.g. At 28 volts a CGH27120 delivers 16 watts average power under WiMAX at a drain efficiency of 25% Dissipated heat is 48 watts with a T RISE of 82 O C NO derating At 48 volts a CGH27120 delivers > 30 watts average power under WiMAX at a drain efficiency of 25% Dissipated heat is >90 watts with a T RISE of 153 O C Needs derating to T CASE of 72 O C

12 General Purpose Application Insertions for GaN HEMTs Emphasis usually on P1dB or saturated power, wide bandwidth and best efficiency Applications include Wideband, noisy, jammers Software defined radios Tactical communications Phased array systems Test instrumentation Medical applications e.g. ablation Exciter applications e.g. lighting

13 Gain (db) Input Return Loss (db) Power Out (dbm) Drain Efficiency (%) 0.5 to 2.5 GHz Reference High Power Amplifier Performance using Cree CGH40045F CGH40045F - Output Power and Drain Efficiency versus Frequency Power Out (dbm) Drain Efficiency (%) Frequency (GHz) 30 > 50 watts CW power over 5:1 frequency range 55 to 65% drain efficiency CGH40045F Gain and Input Return Loss versus Frequency S21 S Frequency (MHz) -15 pg. 13

14 Performance of Push-Pull Power Amplifier for 0.5 to 2.5 GHz using Cree CGH40090PP Gain (db) Power Out (dbm) Drain Efficiency (%) Drain Efficiency (%) 60 CGH40090PP -Output Power and Drain Efficiency versus Frequency Power Out (dbm) Drain Efficiency (%) CGH40090PP Gain and Drain Efficiency vs Output Power 0.5 GHz Gain 1.0 GHz Gain 1.5 GHz Gain 2.0 GHz Gain 2.5 GHz Gain 0.5 GHz DE 1.0 GHz DE 1.5 GHz DE 2.0 GHz DE 2.5 GHz DE Frequency (GHz) 50 Drain Efficiency is 50% Power Out (dbm)

15 CGH40045F under Pulsed Stimulus at Output Power (dbm) Drain Efficiency (%) Gain (db) 50V drain voltage 70.0 CGH40045 Pulse Transfer Vds=50V, 40uS Pulse 10% Duty Cycle, F=2.5GHz 100 watt Pout Drain Efficiency Gain Input Power (dbm) The CGH40045F GaN HEMT was originally designed for 28 volt operation - Works well at 50 volts within thermal constraints pg. 15

16 Performance of CGH40180PP in Demonstration Amplifier CW Output Power (W) Gain (db) Drain Efficiency Drain Efficiency 260 Power and Efficiency vs Frequency 100.0% % % % % % % 30.0% 22 Gain and Drain Efficiency vs Output Power 80.0% % Frequency (MHz) % 60.0% 50.0% % % % % % Output Power (dbm)

17 GaN HEMT MMICs and Foundry Services Range of custom MMICs completed successfully for top tier DoD contractors Power Amplifiers Low noise amplifiers Switches Limiters Complete transceivers First COTS GaN MMICs released in June 2008 Both SiC MESFET and GaN HEMT Foundry services are available DC to 18 GHz

18 Gain (db) Input/Output Return Loss (db) Power Output (dbm) Power Added Efficiency (%) CMPA F Typical Performance 40 CMPA F -Output Power and Power Added Efficiency versus Frequency 50% % 40% 37 35% 36 30% % 20% 33 15% PSat_48V 32 10% PAE_48V 31 5% 30 0% Frequency (GHz) x 0.5 Package CMPA F -S21, S11 & S22 versus Frequency 0 Wide bandwidth: 20 MHz to 6 GHz 3 watts typical Power Output 20% efficiency 17 db Small Signal Gain 28 volt operation Small 0.25 sq. inch footprint S21_48V S11_48V S22_48V Frequency (GHz) pg. 18

19 Gain (db) Input/Output Return Loss (db) Saturated Power Output (dbm) Power Added Efficiency (%) CMPA F Typical Performance 50 Saturated Power Output and Power Added Efficiency versus Frequency 50% Typical Psat (dbm) PAE at 44 dbm (%) 45% 40% 35% 46 30% 45 25% 44 20% % 10% 5% 0.5 x 0.5 Package 40 0% Frequency (GHz) 30 CMPA F -S21, S11 & S22 versus Frequency 0 Wide bandwidth: 2.5 to 6 GHz 25 watts typical Power Output 30% efficiency 24 db Small Signal Gain 28 volt operation Small 0.25 sq. inch footprint (S21) (S11) (S22) Frequency (GHz) pg. 19

20 Telecommunication Insertions for GaN HEMTs Emphasis usually on linearity and efficiency under relatively high peak to average ratio signals Applications include WiBro and WiMAX at 2.3, 2.6, 3.5 and 5.5 GHz W-CDMA LTE (Long Term Evolution) DVB (Digital Video Broadcast) Multi-Carrier GSM Secure COFDM Links

21 Efficiencies for Doherty and ET Power Amplifiers in 2.11 to 2.17 GHz UMTS Band (meeting 3GPP SEM) DC to RF Efficiency, % 8 watts Doherty WiMAX PAR=11.2dB Delft/Cree GaN 2 watts HEER PAR=8.5dB 50% Postech/Cree GaN 20 watts Doherty W-CDMA 57% Delft/Cree GaN 16 watts Doherty W-CDMA 49% Postech/Cree GaN 37 watts ET W-CDMA 50% UCSD/Nitronex GaN 40 watts ET W-CDMA 43% Cree GaN PAR of 7.6 db (unless otherwise stated) 42 watts ET W-CDMA 58% UCSD/Triquint GaAs HVHBT 50 watts Doherty W-CDMA 43% NXP Si LDMOSFET 70 watts Doherty W-CDMA 40% Freescale Si LDMOSFET 90 watts Doherty W-CDMA 53% CREE GaN HEMT Average Power, Watts

22 Basic Doherty Amplifier Configuration Main Amp RF Input 0 o Class AB Bias Quarter-Wave Line (~ 50 Ohms, Z TBD) 90 o Peaking Amp Class C-like Bias Quarter-Wave Output Transformer (~35 Ohms) RF Output The Doherty amplifier configuration is becoming more and more popular as a means of improving overall DC to RF conversion efficiency Up to certain input power levels the carrier amplifier saturates earlier than a conventional Class A/B Amplifier because of the load impedance it sees the peaking amplifier is still OFF Above a certain input power level the peaking amplifier turns ON and contributes power as well as altering the load line to the carrier amplifier pg. 22

23 CDPA21480 UMTS Band Doherty Amplifier Wilkinson Splitter Energy Storage Capacitors 90 O Line RF Input RF Output 90 O Line 2.5 x 3.5 inches pg. 23

24 Measured Single-Channel W-CDMA ACLR & Efficiency vs. RF Average Output Power ACLR (dbc) Drain Efficiency CGH21240DD WCDMA Transfer with & without DPD Single Channel WCDMA, 6.8 db PAR with CFR Vds=50V, Idsq=600 ma, Frequency=2.14 GHz ACLR-5 ALT-10 ACLR-5 (PD) ALT-10 (PD) ACLR+5 ALT+10 ACLR+5 (PD) ALT+10 (PD) 55% 50% 45% 40% -35 Drain Effic (PD) 35% % % % % % -65 5% -70 0% WCDMA Average Output Power (dbm)

25 How Envelope Tracking (ET) Works pg. 25

26 Switch Mode GaN HEMT ET HPA Summary Single Carrier W - CDMA Peak to Average Ratio 7.6 db Average Output Power> 14 watts Gain > 15 db EVM < 2% Overall Efficiency > 50% DAC Envelope amplifier Application of GaN Class E Amplifers in EER/ET Amplifier Systems D. Kimball 1, J. Jeong 1, C. Hsia 1, P. Draxler 1,2, P. Asbeck 1, D. Choi 3, W. Pribble 4 and R. Pengelly 4 1 ECE Department, UCSD, La Jolla CA Qualcomm, San Diego, CA DSP Signal generation, Decresting/ detroughing, pre-distortion, time alignment LPF Upconverter Envelope BPF RF Driver RF HPA 3 Nokia Research, San Diego, CA 4 Cree, Durham, NC ADC LPF Downconverter pg. 26

27 CGH21120F under compressed Class A/B under Envelope Tracking (multi-carrier WCDMA) pg. 27

28 Pout (W), Gain (db) PAE, N Gain (db), Pout (W) PAE, N GaN HEMT Class F Amplifier provides 86% PAE at 17 watts at 2 GHz V D bias Z 6, 6 Z 5, 5 Z L bw R 1 R 2 C 1 C 2 4 4, 4 L bw Z drain Z1, 1 4 L bw Z 2, 2 C ds Z R 3 L Performance vs. Drain Voltage 805B_N1, 2 GHz Gain (db) Pout (W) M axpae Drain Efficiency 86% PAE 17 W B_N1, Vdd = 42.5 V Pout(W) Gain(dB) PAE N Pin (dbm) Vdd (v) Data provided by S. Long and D. Schmelzer, UCSB

29 Effect of Efficiency on Transistor Operating Temperature

30 Packaging of High Power Density Transistors TiPtAu 80%Au20%Sn? Package flange material needs to have high thermal conductivity but also have a coefficient of expansion that is close to SiC Unfortunately there a limited number of choices to get both right simultaneously!

31 Properties of Relevant Materials Material Structure Thermal Conductivity W/mK Coefficient of Thermal Expansion ppm/k Cu Pure Diamond Silicon SiC 4H-SI AlSiC 63%SiC > W90Cu 90% W W75Cu 75% W Mo70Cu 70% Mo Mo50Cu 50% Mo CuMoCu 1:4: CuMoCu 1:1: Cu/Mo70Cu/Cu 1:4:1 laminate 340 8

32 Thermal Improvements At the transistor level New power transistor layouts to reduce junction temperature at constant power density Present layout At the package level New flange materials with higher thermal conductivity and CTE match to SiC Present CuW is ~200 W/mK New SuperCMC is 350 W/mK New Layout provides 20% reduction in operating temperatures Combined lowers 175 C junction temperature to 123 C Aluminum diamond is 550 W/mK T J decreases by 10% T J decreases by further 15%

33 Robustness Robustness falls into several categories Voltage and Current overload Voltage and Current withstand due to output load mis-match Pulsed energy withstand at transistor input Electro-static discharge withstand Radiation (total dose) withstand Self-generated heating Shockley, Brattain and Bardeen, 1947 For many military applications, the output load mis-match withstand is critical. Normally specified to a minimum of 10:1 VSWR simulates disconnected antenna! If in a Class A/B amplifier peak drain voltage is 96 volts (assuming 48 volt rail) then at worst case phase with 80% of power being reflected back the peak drain voltage will be 134 volts Hence the need for Vbd s of at least 150 volts for GaN HEMTs when operating at 48 volts!

34 Reliability - Cree GaN vs. other GaN Suppliers Cree GaN devices are the most reliable in the industry Cree GaN Supplier T GaN GaN on Si Temperature ( deg. C) GaN on Si under DC operation E a = 2.0 ev GaN on SiC E a = 1.3 ev Cree GaN on SiC E = 1.6 ev a MTTF (hours) 580 million Cree device hours in the field

35 Higher Frequencies Switches, LNA s etc.

36 MMIC Switches Separate RF and Control Ports No need for Chokes Takes no control current PIN diode replacement High Power Operation Wideband Operation

37 Low Noise Amplifiers X-Band Measured and Modeled Two-Stage LNA s-parameters Two-Stage X-Band MMIC Low Noise Amplifier Measured Two-Stage noise figure parameters A maximum input power level of 23 dbm is reached at a 7 db compression level without any sign of short term degradation D. Krause et al, 2004

38 Other Wide Bandgap Device Applications Other circuits using Wide Bandgap devices include Mixers (both FET and diode) Multipliers Limiters DC/DC Converters Phase Shifters Attenuators analog and digital Oscillators

39 90 nm GaN HEMT Technology for mm-waves

40 Performance of GaN HEMTs at mm-waves (passivated higher capacitance)

41 Acknowledgements I would like to acknowledge the assistance of my Cree colleagues in preparing this presentation Ulf Andre Don Farrell Don Gajewski Chris Harris Jim Milligan Brad Millon Carl Platis Art Prejs Bill Pribble Scott Shephard Simon Wood