GaN MMIC PAs for MMW Applicaitons

GaN MMIC PAs for MMW Applicaitons Miroslav Micovic HRL Laboratories LLC, 311 Malibu Canyon Road, Malibu, CA 9265, U. S. A. mmicovic@hrl.com

Motivation for High Frequency Power sources 6 GHz 11 GHz Frequency Spectrum High Data Rate Wireless Links (1 Gbits/s) Commercial Bands (E-band radio) 71 GHz 76 GHz, 81 GHz 86 GHz, 92 GHz 95 GHz Inter-Satellite 59.3 GHz 64 GHz Active Millimeter-Wave Imaging 94 GHz SAR, Phase Array Radar (Space based W-band radar for earth studies.) RF Sources for THz Multiplier Diodes Fundamental Power for THz Space Array Spectroscopy Power Required Watts Available Sources < 2 mw GaN MMIC 3 W at 95 GHz

Microwave and Millimeter-wave Solid State Sources 1 Pulsed mode Estimated CW GaN limit 1 Pout [W] 1 Estimated CW LDMOS limit Estimated CW GaAs limit HRL GaN 28 1 Symbols: LDMOS catalog items GaAs catalog items GaN reported data HRL GaN 26 HRL GaN 27.1.1 1 1 1 Frequency [GHz] Output power per single die.

HRL W-band GaN Roadmap Output Power (mw) 3,5 3, 2,5 2, 1,5 1, 5 26 26 HRL HRL IEDM IEDM paper paper HRL HRL IR&D IR&D 27 27 Q3 Q3 28 28 Plan Plan..2.4.6.8 1. 1.2 1.4 1.6 1.8 Gate Width (mm) Extrapolate >3 >3 W! W! Q4 Q4 28 28 Plan Plan Best Best GaAs GaAs phemt phemt and and InP InP HEMT HEMT Disruptive W-band W GaN Power MMICs 8X higher power density than mmw GaAs phemt

Cost trade-off estimate for 3 Watt W-band SSPA GaAs phemt SSPA GaN SSPA 8-way waveguide combining Number of WR-1 power modules Number of MMIC s per module 8-way splitter and 8 way combiner required 8 3 (Attenuator, Phase Shifter, Power Amplifier) Power combining not required 1 1 (Power Amplifier only) Hand-tuning to obtain phase and amplitude match for combining Combiner arms tuned manually No tuning 3 Watt 95 95 GHz GaN SSPA is is Cost Effective

W-band GaN MMIC Device Passivation Source Ohmic n + GaN AlGaN Schottky barrier GaN T-gate device AlGaN buffer SiC substrate Gate Lg =.12 µm Drain Ohmic n + GaN N+ layer facilitates fabrication of ohmic contacts. Double Heterojunction Structure Low ohmic contact resistance <.2 Ω/mm. Comparable to GaAs phemt s and InP HEMT s. Smooth ohmic metal edges. Recessed gate Bi-layer e-beam gate litho Lg =.12 µm for Ka-band SiN passivation and capacitor dielectric 2 µm Source-Drain separation TaN 5 Ω/Square resistor Epi resistors

Short Channel Effects - Buffer Isolation Electrostatic Potential [ev] 2 1-1 -2-3 Ec Ef Ev Conventional HEMT Al.26 Ga.74 N SHFET GaN -4 2 4 6 8 1 Position [Angstroms] 1 2 1 18 1 16 1 14 1 12 1 1 Electron Concentration [cm -3 ] Electrostatic Potential [ev] 2 1-1 -2-3 Ec Ef Al.3 Ga.7 N Ev DHFET GaN Al.4 Ga.96 N -4 2 4 6 8 1 Position [Angstroms] Techniques used to improve backside confinement and buffer isolation Doping Fe doped buffer layer; Y.-F. Wu et al., El. Dev. Lett., Vol. 25, pp 117-119 C doped buffer layer; S. Rajan et al., El. Dev. Lett., Vol. 25, pp 247-249 Polarization Engineering GaN DHFET structure; M. Micovic et al., IEDM 24 Digest, pp 87-81 InGaN back barrier; T. Palacios et al., El. Dev. Lett., Vol. 27, pp 13-15 1 2 1 18 1 16 1 14 1 12 1 1 Electron Concentration [cm -3 ]

Short Channel Effects - Buffer Isolation 1 Transfer curves of GaN DHFET (blue) and SHFET (red); Both wafers have field plate gate structure; Vds=1V Transfer curves of Lg =.12 µm GaN HEMTs Conventional (Red), DHFET (Blue) 1 Ids [ma/mm] 1 1 1.1 >1x Leakage Reduction Vds=1V Ids DHFET Idss SHFET.1.1-5 -4-3 -2-1 1 2 Vg [V] DHFET Structure: -Improved Back-Channel Confinement, -Reduced sub-threshold drain leakage current.

Uniformity Better than 1% over 3 Wafer Epi Thickness.9 % AlGaN %.68 % Sheet resistance.46 % Uniformity = Std. Dev. / Mean No edge exclusion

Individual Source Vias 3x3 vertical wall vias in 5 µm substrate Enables microstrip MMICs Low source inductance < 1 ph Critical for high power W-band power amp performance

DC Device Characteristics L g =.1 µm, W g = 4 x 37.5 µm GaN HFET Id [ma] 14 Vgs = to -4 V Vgs = 12 Step = -.5 V -.5 V 1-1. V 8-1.5 V 6-2. V 4-2.5 V 2-3. V 2 4 6 8 1 12 14 Vds [V] Id ss = 9 ma/mm Ids [ma/mm] 1 9 8 7 6 5 4 3 2 1 Ids gm -4.5-4 -3.5-3 -2.5-2 -1.5-1 -.5 Vgs [V] g m of 36 ms/ mm at V ds = 12 V 5 45 4 35 3 25 2 15 1 5 gm [ms/mm]

Small Signal RF Performance 35 3 25 MSG H21 f T = 9 GHz f max = 2 GHz Gain [db] 2 15 1 5 1 1 1 Frequency [GHz] L g =.1 µm, W g = 4 x 37.5 µm GaN HFET V ds = 1 V, I ds = 45 ma.

5 mw 7 GHz GaN MMIC PA 7 GHz MMIC Chip Layout Size 3.4 mm x 1.3 mm Operating Voltage = 15 V Measured Gain > 15 db Small Signal Gain, Return Loss [db] 2 1-1 12 GHz Bandwidth, Gain > 15 db, Gain Ripple <.5 db Measured frequency response of 7 GHz GaN PA 7.4 GHz 15.46 db 71.2 GHz 15.42 db 76.13 GHz 16.29 db 82.3 GHz 16.16 db -2 6 7 8 9 Frequency (GHz) Measured small signal gain of 7 GHz 5 mw GaN MMIC PA. Performance meets design goal.

Output power of 7 GHz MMIC measured at a frequency of 76 GHz Pout (dbm), Gain (db), PAE (%) 3 25 2 15 1 5 Pout (dbm) Gain (db) PAE (%) 1 2 3 4 5 6 7 8 9 1 11 12 13 14 15 Pin (dbm) P sat = 5 mw PAE = 17% P 1dB = 24 dbm Vds = 15 V

Comparison of 7 GHZ MMIC Performance with the best commercial phemt Parameter Gain 7 GHz GaN MMIC PA >14 db Commercial GaAs phemt > 5 db P 1dB 24 dbm 2 dbm Psat 27 dbm 22 dbm PAE Input return loss Output return loss 16.5 % < -8 db < - 8 db < -4 db < -2 db The The most powerful MMIC reported to to date at at 7 7 GHz

5 mw 8 GHz GaN MMIC PA 2 15 GHz Bandwidth, Gain > 11 db Measured frequency response of 8 GHz GaN PA 8 GHz MMIC Chip Layout Size 3.4 mm x 1.3 mm Operating Voltage = 15 V Measured Gain > 11 db Small Signal Gain, Return Loss [db] 1-1 76.37 GHz 14.97 db 82.721 GHz 14.5 db 86.62 GHz 12.7 db -2 6 7 8 9 1 Frequency (GHz) Measured small signal gain of 8 GHz 5 mw GaN MMIC PA. MMIC Designed for for E-band E Radio Band

Output power of 8 GHz MMIC measured at a frequency of 83 GHz Pout, Gain, PAE [dbm, db, %] 3 25 2 15 1 5 Pout Gain PAE 27 dbm 17 % 12 db P sat = 5 mw PAE = 17% P 1dB = 24 dbm Vds = 15 V -1-5 5 1 15 2 Power modules using 26 GaN SR parts used as a power source. Pin [dbm] Highest Output Power and and Efficiency reported for for a solid state source at at this this frequency.

Comparison of 8 GHZ MMIC Performance with the best commercial phemt Parameter Gain 8 GHz GaN MMIC PA >11 db Commercial GaAs phemt > 5 db P 1dB 24 dbm 2 dbm Psat 27 dbm 22 dbm PAE Input return loss Output return loss 17 % < -7 db < - 7dB < -4 db < -2 db The The most powerful MMIC reported to to date at at 8 8 GHz

5 mw 9 GHz GaN MMIC PA Flat Response over 92 GHz- 95 GHz frequency band. 9 GHz Measured Bandwidth, frequency Return response Loss of 95 GHz < -1 GaN dbpa 2 9 GHz MMIC Chip Layout Size 2.4 mm x 1.3 mm Operating Voltage = 15 V Measured Gain > 15 db Small Signal Gain, Return Loss [db] 1-1 -2 88.865 GHz 14.52 db 9.884 GHz 14.88 db 97.451 GHz 14.22 db 8 9 1 11 Frequency (GHz) Measured small signal gain of 9 GHz 5 mw GaN MMIC PA. Performance Meets Design Goals

Output Power of 9 GHz GaN MMIC measured at a frequency of 94.75 GHz Pout, Gain, PAE [dbm, db, %] 25 2 15 1 5 P o u t [d B m ] G a in [d B ] PAE [% ] P.5dB = 23 dbm Linear Gain = 14.4 db 23 db m 13.8 db 9 % -2 2 4 6 8 1 Pin [dbm ] Output power limited by available input drive, circuit less than.5 db compressed. HRL is building a power source using GaN MMIC to test the power.

Comparison of 9 GHZ MMIC Performance with best commercial GaAs phemt Parameter Gain HRL 9 GHz GaN MMIC PA >14 db GaAs phemt > 1 db Gain Ripple <.5 db < 1 db P 1dB >23 dbm 2 dbm Psat To be measured 23 dbm PAE Input return loss Output return loss To be measured < -1 db < - 1dB < -8 db < -8 db

25 mw 1 GHz GaN MMIC PA 2 Measured frequency response of 1 GHz GaN PA 1 GHz MMIC Chip Layout Size 2.4 mm x 1.3 mm Operating Voltage = 15 V Measured Gain > 15 db Small Signal Gain, Return Loss [db] 1-1 -2 95.912 GHz 15.19 db 1.3 GHz 15.72 db 12.13 GHz 15.23 db 8 9 1 11 Frequency (GHz) Measured performance of the first 1 GHz GaN MMIC chip. Fastest GaN MMIC Circuit Near Term Potential for for 15 15 GHz 22 22 GHz

Summary GaN MMIC technology will dominate high frequency > 5 GHz solid state RF power technology. Key challenges for MMW GaN: Ohmic Contacts Short gate lengths Device Structure GaN MMICs exceeding power of best GaAs and InP MMICs at 95 GHz demonstrated. GaN MMICs with 5 x power of the best InP MMICs are on the road map for 29. MMW GaN MMIC technology enables new systems, applications and services.