Trapping vs. Permanent D Degradation in GaN HEMTs d ti i G N HEMT - PowerPoint PPT Presentation

Trapping vs. Permanent D Degradation in GaN HEMTs d ti i G N HEMT Jungwoo Joh and Jesús A. del Alamo Massachusetts Institute of Technology Acknowledgements: TriQuint Semiconductor ARL (DARPA WBGS program) ONR (DRIFT ‐ MURI program)

Motivation Motivation • GaN HEMT reliability: big concern GaN HEMT reliability: big concern • Performance degradation at high voltage: – Trapping ‐ related (recoverable) T i l t d ( bl ) – Permanent (non ‐ recoverable) G S D _ _ _ _ _ _ _ _ AlGaN _ _ _ _ _ _ _ _ GaN

Experimental: GaN HEMT Experimental: GaN HEMT Gate Gate Source Drain SiN GaN Cap AlGaN 2DEG GaN SiC Substrate Standard device with integrated field plate : • L =0 25 um W=2x25 um • L G =0.25 um, W=2x25 um • Fabricated by TriQuint Semiconductor 3

Electrical Stress and Characterization Electrical Stress and Characterization START Comprehensive but fast: Coarse characterization (<15 sec) Fine characterization (~30 sec) Characterization Trap analysis (30 min) Frequent : I Dmax , R S , R D , I Goff , V T … Coarse characteri ation e er 1 2 mins Coarse characterization: every 1 ‐ 2 mins Trapping Analysis Fine characterization: before and after stress and at important ponits Benign : Benign : Electrical Stress l l Both sets of measurements to produce a V DS , V GS (or I D ) change smaller than 2% on any extracted parameter after 100 executions 4

Permanent vs. Trapping Permanent vs. Trapping stress recovery 1 V =0 V DS =0 V GS = ‐ 30 V permanent degradation (0) total (apparent) 0.9 Dmax /I Dmax degradation 0 8 0.8 I D t trapping i degradation I Dmax : V DS =5 V V GS =2 V 0 7 0.7 88 days 0 30 60 recovery Time (min) 13 % permanent degradation + 15 % trapping degradation 5

OFF ‐ state Stress @ 100 C OFF state Stress @ 100 C V GS = ‐ 5 V, V DS =40 V @ 100 C 1.2 1 2 1 E+03 1.E+03 100 C V DS 1.E+02 V GS R/R(0) R D 1.1 1.E+01 mm) G S D R S ax /I Dmax (0), R S I Goff | (mA/m AlGaN 1.E+00 1 1.E-01 2DEG I Goff 1.E-02 1 E-02 Goff I Dma 0.9 0 9 | GaN 1.E-03 I Dmax 0.8 1.E-04 0 500 1000 1500 2000 2500 At these points, Time (min) I Goff : V DS =0.1 V trapping analysis was V GS = ‐ 5 V performed at 25 C. Fast and sharp I G degradation Slower I Dmax & R D degradation 6

Transient after V DS =0 pulse Transient after V DS 0 pulse trapping pulse ( 1 s V GS = ‐ 10 V, V DS =0 V) @ t=0 - @ 9 5 9.5 uncollapsed I Dlin (before) stress time=0 min permanent 9 degradation 5 5 uncollapsed I Dlin (after) uncollapsedI (after) 8.5 8 5 I Din (mA) 15 8 35 current collapse : 7.5 75 7 5 trapping degradation 155 7 25 C After 315 min 6 5 6.5 collapsed I Dlin (after) -3 -2 -1 0 1 2 3 10 10 10 10 10 10 10 t (sec) I Dlin (V GS =1, V DS =0.5 V) transient after applying trapping pulse Current collapse increases up to 300 min and saturates. 7

Trapping & Permanent Degradation Trapping & Permanent Degradation 30 1 zed) (normaliz apse (%) trapping degradation 20 0.98 rrent colla psed I Dlin permanent 10 0.96 Permanent degradation: degradation Uncollap uncollapsed I Dlin ll d I Cu Trapping degradation: 0 0.94 Current collapse p 0 500 1000 1500 2000 2500 uncol. I Dlin – col. I Dlin = Time (min) uncollapsed I Dlin Trapping degradation mostly saturates after 300 min. Permanent degradation keeps increasing. 8

Impact of Temperature Impact of Temperature OFF ‐ state (100 C) ( ) OFF ‐ state (150 C) ( ) 40 1 40 1 normalized) trapping degradation pse (%) n (norm) pse (%) trapping 0.98 0.98 30 30 degradation llapsed I Dlin (n Current collap 0 96 0.96 0 96 0.96 Current collap collapsed I Dlin 20 20 0.94 permanent 0.94 permanent degradation 10 degradation 10 0.92 0.92 C C Unc Unco 0 0.9 0 0.9 0 500 1000 1500 2000 2500 0 500 1000 1500 Time (min) Time (min) More degradation in trapping & permanent at higher T  Both degradations are thermally activated. Increase in current collapse saturates faster than at 100 C. 9

Hot ‐ electron Stress Hot electron Stress V GS =0, V DS =40 V (I D ~800 mA/mm) Room T (T j 235 C) Room T (T j ~235 C) V DS R D V GS G S D AlGaN 2DEG R S Hot electrons! I Goff Goff GaN I Dmax Much less degradation in I G 10

OFF ‐ state vs. Hot ‐ electron Stress OFF state vs. Hot electron Stress OFF ‐ state (100 C) Hot ‐ electron (RT, T j ~235 C) 30 1 (normalized) 30 1 trapping I Dlin (norm) degradation apse (%) apse (%) 20 0.95 20 0.95 p permanent Current colla Current colla Uncollapsed ollapsed I Dlin permanent degradation degradation 10 0.9 10 0.9 Unco trapping degradation t i d d ti 0 0.85 0 0.85 0 500 1000 1500 2000 2500 0 1000 2000 3000 4000 5000 Time (min) Time (min) More permanent degradation than OFF ‐ state. Less current collapse increase for V DS =0 pulse.  less trap formation in high ‐ power stress 11

Summary Summary • During all stress modes: During all stress modes: 1. Very fast I G degradation (few minutes) 2. Trapping ‐ related degradation mostly saturates in pp g g y a short time (few hours) 3. Permanent degradation keeps increasing over time • OFF ‐ state: – More trapping degradation – Faster & more degradation at higher T. • Hot ‐ electron stress: – More permanent degradation 12