Time Evolution of Electrical Degradation under High-Voltage Stress - PowerPoint PPT Presentation

Time Evolution of Electrical Degradation under High-Voltage Stress in GaN HEMTs Jungwoo Joh and Jesús A. del Alamo Microsystems Technology Laboratories, MIT Acknowledgements: ARL (DARPA WBGS program) ONR (DRIFT-MURI) TriQuint Semiconductor

Purpose • GaN HEMT Reliability: big concern – RF power degradation – I D ↓ , R D ↑ , I G ↑ , ∆ V T … • Goal: understand degradation mechanism 0 -0.2 ∆ P out (dB) -0.4 -0.6 RF stress 10 GHz,V D =28 V -0.8 I DQ =150 mA/mm -1 P in =23 dBm 0 5 10 15 P out =33.7 dBm 2/20 Time (hr)

Outline • Background • Project goal • Experimental – Procedure – Results • Discussion • Conclusions 3/20

High Voltage Degradation in GaN HEMTs 1.2 1.E+01 OFF-state, V GS =-10 V V DS 1.15 1.E+00 V GS =-10 V I Dmax /I Dmax (0), R/R(0) 1.1 1.E-01 R D |I Goff | (A/mm) G S D R S 1.05 1.E-02 AlGaN 1 1.E-03 2DEG 0.95 1.E-04 I Dmax I Goff 0.9 1.E-05 GaN V crit 0.85 1.E-06 Joh, EDL 2008 10 20 30 40 50 V DGstress (V) I Dmax : V DS =5 V, V GS =2 V I Goff : V DS =0.1 V, V GS =-5 V I D , R D , and I G start to degrade beyond critical voltage (V crit ) (+ trapping behavior – current collapse) Common physical origin in I D and I G degradation 4/20

Structural Degradation Cross-section Plan-view 1. V stress ~V crit : Gate SiN Groove formation in GaN cap AlGaN GaN 2. V stress >V crit : Pit formation in AlGaN barrier 3. V stress >>V crit : Pit growth (to AlGaN/GaN interface) and merge + crack formation 5/20 Joh, MR 2010 Makaram, APL 2010

Trapping vs. Permanent stress recovery 1 V DS =0 V GS = ‐ 30 V permanent degradation I Dmax /I Dmax (0) total (apparent) 0.9 degradation 0.8 trapping degradation 0.7 88 days 0 30 60 recovery Time (min) 13 % permanent degradation + 15 % trapping degradation 6/20

Project Goal • Investigate time evolution of degradation and correlate with structural degradation 7/20 Meneghesso, IJMWT 2010 Marcon, IEDM 2010

Experimental Procedure • Detrapping step to flush trapped START electrons quickly • Benign device characterization: Detrapping • Full I D -V DS , I D -V GS curves Full Characterization (DC, CC) • I D transient measurement: T base =3 0°C current collapse, detrapping time Electrical Stress constant T stress • Performed at 30 °C End? • Stress conditions: NO YES • OFF-state: V DS =40 V, V GS =-7 V END: detrapping + • T stress =75–200 °C Full characterization 8/20

Gate Current and V T -4 -4 0.25 0.25 10 10 Stress: V GS = ‐ 7 V and V DS =40 V Stress: V GS = ‐ 7 V and V DS =40 V 125 °C 125 °C 0.2 0.2 -5 -5 10 10 I Goff  I Goff  0.15 0.15 |I Goff | (A) |I Goff | (A) |  V T | (V) |  V T | (V) -6 -6 10 10 0.1 0.1  | Δ V T |  | Δ V T | -7 -7 10 10 0.05 0.05 -8 -8 0 0 10 10 -4 -4 -2 -2 0 0 2 2 4 4 6 6 10 10 10 10 10 10 10 10 10 10 10 10 Initial Initial Stress time (s) Stress time (s) • Very fast I Goff and V T degradation (<10 ms)  E-field driven oxide punch-through? Electrochemical etching? • Degradation saturates after 10 4 s. 9/20

I D Transient Measurement trapping pulse ( 1 s V GS = ‐ 10 V, V DS =0 V) trapping pulse ( 1 s V GS = ‐ 10 V, V DS =0 V) @ t=0 - @ t=0 - uncollapsed I Dlin (fresh) uncollapsed I Dlin (fresh) 10 10 stress time=0-1 s stress time=0-1 s permanent permanent degradation degradation 10 10 uncollapsed I Dlin (stressed) uncollapsed I Dlin (stressed) 9 9 100 100 I Dlin (mA) I Dlin (mA) 8 8 1000 1000 current collapse : current collapse : trapping trapping 7 7 degradation degradation After 10ks After 10ks 6 6 collapsed I Dlin (stressed) collapsed I Dlin (stressed) -3 -3 -2 -2 -1 -1 0 0 1 1 2 2 3 3 10 10 10 10 10 10 10 10 10 10 10 10 10 10 uncol. I Dlin – col. I Dlin t (sec) t (sec) CC= uncollapsed I Dlin • After electrical stress: Permanent degradation + trapping related degradation 10/20

Detrapping Time-constant Spectrum Stress time Stress time -4 -4 0x 10 0x 10 <1s <1s 10s 10s -0.2 -0.2 Amplitude (A.U.) Amplitude (A.U.) 100s 100s -0.4 -0.4 1000s 1000s -0.6 -0.6 V DS =0 pulse V DS =0 pulse >10ks >10ks 1s, V GS = ‐ 10 V 1s, V GS = ‐ 10 V -0.8 -0.8 T a =30 °C T a =30 °C DP1 DP1 -1 -1 -3 -3 -2 -2 -1 -1 0 0 1 1 2 2 3 3 10 10 10 10 10 10 10 10 10 10 10 10 10 10 Detrapping time constant (sec) Detrapping time constant (sec) • Sharp increase in DP1 (E a =0.56 eV) + long time constant slow traps beyond incubation time. 11/20

Drain Current Degradation 6 6 35 35 Permanent I Dmax Degradation (%) Permanent I Dmax Degradation (%) Stress: V GS = ‐ 7 V and V DS =40 V Stress: V GS = ‐ 7 V and V DS =40 V 30 30 5 5 125 °C 125 °C Current collapse (%) Current collapse (%) 25 25 Current collapse  Current collapse  4 4 20 20 3 3 15 15 2 2 Incubation 10 10 time  I Dmax  I Dmax 1 1 5 5 degradation degradation 0 0 0 0 -4 -4 -2 -2 0 0 2 2 4 4 6 6 10 10 10 10 10 10 10 10 10 10 10 10 Initial Initial uncol. I Dlin – col. I Dlin Stress time (s) Stress time (s) CC= uncollapsed I Dlin • For current collapse and permanent I Dmax degradation, incubation time is observed. 12/20

Temperature Dependence: I G 4 10 Stress: V GS = ‐ 7 V and V DS =40 V 125 °C 3 75 °C Normalized |I Goff | 10 |I Goff /I Goff (0)| 150 °C 2 10 100 °C 1 10 0 10 -4 -2 0 2 4 6 10 10 10 10 10 10 0 Stress Time (s) • Weak temperature dependence 13/20

Temperature Dependence: V T 0 0 -0.05 -0.05 150 °C 150 °C -0.1 -0.1 125 °C 125 °C 100 °C 100 °C  V T (V)  V T (V) -0.15 -0.15 -0.2 -0.2 -0.25 -0.25 75 °C 75 °C Stress: Stress: -0.3 -0.3 V GS = ‐ 7 V and V DS =40 V V GS = ‐ 7 V and V DS =40 V -0.35 -0.35 -4 -4 -2 -2 0 0 2 2 4 4 6 6 10 10 10 10 10 10 10 10 10 10 10 10 0 0 Stress Time (s) Stress Time (s) • No dependence during initial negative V T shift • Positive turn-around seems to occur earlier at high T 14/20

Permanent I Dmax Degradation 1.02 1.02 1 1 75 °C 75 °C I Dmax (norm) I Dmax (norm) 0.98 0.98 100 °C 100 °C 0.96 0.96 0.94 0.94 125 °C 125 °C Stress: Stress: 150 °C 150 °C V GS = ‐ 7 V and V DS =40 V V GS = ‐ 7 V and V DS =40 V 0.92 0.92 -4 -4 -2 -2 0 0 2 2 4 4 6 6 10 10 10 10 10 10 10 10 10 10 10 10 0 0 Stress Time (s) Stress Time (s) • Shorter incubation time at high T • No saturation behavior up to >10 5 s 15/20

Current Collapse 40 40 150 °C 150 °C V GS = ‐ 7 V and V DS =40 V V GS = ‐ 7 V and V DS =40 V 125 °C 125 °C Current collapse (%) Current collapse (%) 30 30 100 °C 100 °C 75 °C 75 °C 20 20 10 10 0 0 -4 -4 -2 -2 0 0 2 2 4 4 6 6 10 10 10 10 10 10 10 10 10 10 10 10 Stress Time (s) Stress Time (s) • Shorter incubation time at high T • More degradation at high T 16/20

Temperature Acceleration of Incubation Time 15 Permanent I Dmax degradation 10 E a =1.12 eV ln(  inc ) (s) Current collapse 5 E a =0.59 eV 0 I Goff , E a =0.17 eV -5 28 30 32 34 36 1/kT (eV -1 ) • Different level of temperature acceleration for incubation time. • E a for permanent I Dmax degradation is similar to life test data * . 17/20 * Saunier, DRC 2007; Meneghesso, IJMWT 2010

Discussion: Time Evolution of Structural Degradation V DS =0, V GS =-40 V, T base =150 °C Joh, IWN 2010 • Very fast groove formation (10 s) on gate edge.  Related to gate current degradation • Pit density/size gradually increase with time. 18/20

Electrical vs. Structural Degradation 2 10 10000 Stress: 150 °C V GS = ‐ 7 V and V DS =40 V 125 °C Average Pit Area (nm 2 ) Current collapse (%) 100 °C 75 °C 1 10 1000 Pit area~t 1/4 Slope=0.22 100 0 10 -4 -2 0 2 4 6 10 10 10 10 10 10 1 10 100 1000 10000 0 Stress Time (s) Stress Time (s) Joh, IWN 2010 Similar time dependence in current collapse and pit formation. 19/20

Conclusion • Investigated time evolution of electrical degradation in GaN HEMTs • Fast I G degradation ~ 10-100 ms – Weak temperature dependence – Oxide punch through / groove formation? • Current collapse degradation ~ 10-100 s – Related to pit formation • Permanent I D degradation >100 s – Strong thermal activation (E a =1.1 eV) 20/20