A Robust AlGaN/GaN HEMT Technology for RF Switching Applications Michael D. Hodge1,2, Rama Vetury1, Jeff Shealy1, and Ryan Adams2 1) RF Micro Devices, Charlotte, NC 2) University of North Carolina at Charlotte, Charlotte, NC DPBU Outline • Advantages of GaN Materials for RF Switching • Background on GaN reliability • OFF-State Step Stress Experiment • Conclusion DPBU GaN Material Advantages Ruggedness Power Handling Low Loss, Low Noise UNREALIZED Potential DPBU Why GaN for RF Switches ? High Power RF Switch Technologies Si P-i-N GaAs FET GaN FET Loss Isolation Power Handling Speed Linearity Operating Efficiency Engineering Complexity • GaN-on-SiC • Engineer COFF, low Ron • high BKDN • high ID,max • Low RTH • High Max TCH • Si PP-i-N: – Drive Current Dependence • GaAs pHEMT: – BKDN vs RON Trade DPBU Device Design - GaN RF switch LGCFP LG-O Source Connected FP Gate Gate SiN SiN Source Drain PA FET Path Control FET S/D S/D LG Switch FET HPA • Symmetric Operation Switch Power Amp/Switching FET • Non-symmetric Operation LNA DPBU GaN High Temperature Reliability Test Tch (C) GaN High Temperature Reliability Test 10 10 GaN1 GaN 2 High Power High Linearity 10 325 300 275 250 Total Devices 10 Wafers 10 Fab Lots 10 200 175 150 RFMD GaN1 8 High Power 6 4 2 0 18 19 20 21 10 350 8 RFMD GaN2 22 23 1/kT Epi Vendors 24 25 26 27 28 Tch (C) 10 Number of Temperatures 10 GaN1 High Power GaN2 300 275 250 225 200 175 150 High Linearity 6 10 High Linearity 325 MTTF Results 225 MTTF Sample Size 350 10 4 10 MTTF Hrs Ea eV TCHANNEL ºC VDS V 2 10 0 10 18 19 20 21 22 23 1/kT 24 25 26 27 28 DPBU Reliability Concerns in GaN HEMTs Inverse Piezoelectric Effect (IPE) Hot Electron Induced Degradation (HEI) • Requires • Requires • High electric field • High electric field • Observed to have no time dependence • Carriers • Impact • Physical crystal defect • Symptoms • Parametric degradation • Ron, Idmax, Idss • Increased gate leakage • Time dependent • Impact • Hot electrons induce traps in buffer and/or barrier layers • Symptoms • Parametric degradation • Ron, Idmax, Idss 7 DPBU Inverse Piezoelectric Related Literature Study Stress Conditions Critical Voltage (V) Total Stress Time (Mins) Technology Notes (1) Joh 2006 Vds=0V, Vgs=-15V to -34V 17-34V 100 GaN-on-SiC Lg dependent (2) Joh 2008 Vds=0V, Vg=-10V to -50V 27V (2T) 38V (3T) 40 GaN-on-SiC 2T stress harsher than 3T Vgs=-8V, Vd=10V to 50V (3) Demirtas 2009 Vds=0V, Vgs=-1V to –20V 37V GaN-on-SiC 70V GaN-on-Si 20 GaN-on-SiC GaN-on-Si Vcrit of GaN-on-Si > GaN-on-SiC (4) Makaram 2010 Vg=-7V, Vd=8V to 50V 150C base 20V 42 GaN-on-SiC Metal etch to reveal pits Vg=-7V, Vd=50V 150C base 10 and 1000 • Failure Within Minutes of Stress • 20-100 minutes • 2T is the most stressful • Critical Voltage • 17-38V (GaN-on-SiC) DPBU Step Stress Test Conditions Designed to replicate IPE literature stress test conditions2 Lds = 4.25um Device A 200 200 150 150 100 100 50 50 0 0 Base Temp Conditions 1&2 = 25C Conditions 3&4 = 85C Vgs (V) Vds = 0V Vds (V) Vgs = -8V Device A - Condition 1&3 Device B - Condition 1&3 Device A - Condition 2&4 -50 -50 -100 -100 -150 -150 -200 Device B - Condition 2&4 -200 0 10 20 30 40 50 60 Time (mins) 2 .J. Joh and J. A. del Alamo, “Critical Voltage for Electrical Degradation of GaN High-Electron Mobility Transistors,” IEEE Electron Device Lett., vol. 29, no. 4, pp. 287-289, Apr. 2008. Lds = 3.1um Vbd = 110V Device B Lds = 4.5um Vbd = 200V DPBU Switch Stress Test Results – Device A Device A - Condition 13 2 4 5 ΔRon (%) 0 -5 A1 -10 A2 A1 A3 A2 A4 -15 -20 A5 -25 0 10 20 30 40 50 60 70 Stress Voltage (V) 80 90 100 Tbase= 25C, to -100V 85C, Vds= 0V, 0 toVgs= 100V,0Vgs= -8V • No degradation of Ron up device breakdown • No degradation in Idss and Idmax observed • Any degradation is <1% from initial • Device B shows the same trends 2T Stress Base 25C 1 3T Stress 2 Base 85C 3 4 DPBU Step Stress Test Results – Device A • No degradation of Id • Negative threshold shift • Indicates enhancement of channel carriers DPBU Step Stress Test Results – Device A • Longer term stress • Held at most stressful condition according to literature • Vds=0V, Vgs= -100V • No further parametric change after 6 and 60 hours. DPBU Summary of Step Stress • Comprehensive OFF-state stress test • Multiple bias configurations • 2 Terminal • 3 Terminal • Multiple base temperatures • 25C • 85C • Devices stressed just before catastrophic breakdown • No parametric degradation observed • Ron • Idss • Idmax DPBU Conclusions • No degradation observed in the OFF-state stress • No IPE related degradation observed in AlGaN/GaN switch FETs • AlGaN/GaN technology robust for RF switching applications DPBU Acknowledgements • The authors would like to thank for their support and discussions • AFRL • Dr. John Blevins • Dr. Chris Bozada • ONR • Dr. Paul Maki DPBU Appendix DPBU Stress Study Results – PA – OFF-State No crystal defect Test Condition Base Temp (°C) Vds (V) Approx Id (mA/mm) Pdiss (W/mm) Vgs (V) 1 245 60 0.03 0.0018 -10 2 245 100 2 0.2 -10 • RFMD GaN Power Amplifier • No difference over extended time • 300 hours and 1016 hours overlays DPBU Constant Stress Test Result • OFF-State – No degradation observed • Results are inconsistent with IPE related degradation