40 GHz MMIC Power Amplifier in InP DHBT Technology Y.Wei, S.Krishnan, M.Urteaga, Z.Griffith, D.Scott, V.Paidi, N.Parthasarathy, M.Rodwell Department of Electrical and Computer Engineering, University of California tel: , fax

Outline LEC 2002UCSB Introduction Transferred-Substrate Power DHBT Technology Circuit Design Results Conclusion

IntroductionLEC 2002 Applications for power amplifiers in Ka band  satellite communication systems  wireless LANs  local multipoint distribution system  personal communications network links and digital radio MMIC Amplifiers in this frequency band Kwon et. al., IEEE MTT, Vol.48, No. 6, June stage HEMT, class AB, Pout=1 W, Gain=15 dB, PAE=28.5%, size=9.5 mm 2 This Work: Single stage cascode InP DHBT, class A, Pout=50 mW, Gain=7 dB, PAE=12.5% size=0.42 mm 2

Transferred-Substrate HBT MMIC fabrication

MBE DHBT layer structure Band profile at V be =0.7 V, V ce =1.5 V InP 8E17 Si 300 Å emitter InGaAs 1E19 Si 500 Å Grade 1E19 Si 200 Å InP 1E19 Si 900 Å Grade 8E17 Si 233 Å Grade 2E18 Be 67 Å InGaAs 4E19 Be 400 Å Grade 1E16 Si 480 Å InP 2E18 Si 20 Å InP 1E16 Si 2500 Å Multiple stop etch layers Buffer layer 2500 Å base collector substrate 400 Å InGaAs base 3000 Å InP collector

Small-area T.S. DHBTs have high cutoff frequencies. UCSB Sangmin Lee BV CEO = 8 V at J E = 0.4 mA/  m 2 f max = 462 GHz, f t = 139 GHz V ce(sat) ~1 V at 1.8 mA/  m 2

Design difficulties with large-area power DHBTs UCSB Yun Wei ARO MURI Thermal instability further increases current non-uniformity Ic Temperature collector SiN emitter contact basepoly BCB Metal strip Au Via Steady state current and temperature distribution when thermally stable base feed sheet resistance:  s = 0.3  / significant for > 8 um emitter finger length Large Area HBTs: big C cb, small R bb,  even small excess R bb substantially reduces f max 0.08  m Emitter contact Metal1 Base contact Current hogging in multi-finger DHBT: Distributed base feed resistance: Ic Temperature K<1 for thermal stability → must add emitter ballast resistance Initial current and temperature distribution thermal feedback further increases current non-uniformity

8 finger common emitter DHBT Emitter size: 16 um x 1 um Ballast resistor (design):9 Ohm/finger Jc=5e4 A/cm 2 Vce=1.5 V First Attempt at Multi-finger DHBTs: Poor Performance Due to Thermal Instability thermally driven current instability  collapse UCSB low f max due to premature Kirk effect (current hogging) excess base feed resistance ARO MURI Yun Wei

Large Current High Breakdown Voltage Broadband InP DHBT UCSB 8 -finger DHBT 8 x (1  m x 16  m emitter ) 8 x (2  m x 20  m collector ) Key Improvements 8 Ohm ballast per emitter finger 2nd-level base feed metal Device Performance f max >330 GHz, V brceo >7 V, J max >1x10 5 A/cm mA, 3.6 Volt device 2nd-level base feed metal Ballast resistor emitter collector Flip chip Yun Wei ARO MURI

UCSB HBT power amplifier-why cascode? ARO MURI Yun Wei I B1 * R. Ramachandran and A.F. Podell "Segmented cascode HBT for microwave-frequency power amplifiers" Advantages: common-base stage has large V ce → large output power common-emitter-stage has low V ce → small R ballast required → maintains large available power gain Disadvantage inductance of base bypass capacitor even small L greatly degrades gain V ce1 V ce I E1 R ballast I E2 radial stub capacitor

UCSB InP TS DHBT Power Amplifier Design ARO MURI Yun Wei Optimum admittance match Input match Low frequency stabilization 8 finger cascode Inter-stage DC bias /4

40 GHz 128  m 2 power amplifier UCSB cascode PA 0.6mm x 0.7 mm, A E =128  m 2 ARO MURI f 0 =40 GHz BW 3dB =16 GHz G T =7 dB P 1dB =14 dBm P sat =17 4dB gain Yun Wei

UCSB Yun Wei common base PA 0.5mm x 0.4 mm, A E =128  m 2 ARO MURI Bias: I c =78 mA, V ce =3.6 V f 0 =85 GHz BW 3dB =28 GHz G T =8.5 dB P 1dB =14.5 dBm P sat =16dBm, associated gain: 4.5 dB Y. Wei et al, 2002 IEEE MTT-S symposium W band power amplifiers in TS InP DHBT technology

UCSB Yun Wei cascode PA 0.5mm x 0.4 mm, A E =64  m 2 ARO MURI Bias: I c =40 mA, V ce =3.5 V f 0 =90 GHz BW 3dB =20 GHz G T =8.2 dB P 1dB =9.5 dBm P sat =12.5 dBm, associated gain: 4 dB Y. Wei et al, 2002 IEEE MTT-S symposium

Continuing work Higher-current DHBTs for increased mm-wave output power 250 GHz f max, I c,max =240 mA, thermally stable at 200 mA bias at V ce =3.2 Volts → suitable for W-band ~150 mW power amplifiers W-band DHBT power amplifiers designs for > 100 mW saturated output power now being tested Results to be reported subsequently… UCSB Yun Wei LEC 2002

Conclusions 40 GHz MMIC power amplifier in InP DHBT technology 7 dB power gain and 14 dBm output power at 1 dB compression. 17 dBm (50 mW) saturated output power 12.5% peak power added efficiency Future work: higher power DHBT power amplifiers at W-band and above lumped 4-finger topology, longer emitter fingers, power combining G-band ( GHz) DHBT power amplifiers Acknowledgement Work funded by ARO-MURI program under contract number PC UCSB Yun Wei LEC 2002