Anomalous Source-side Degradation of InAlN/GaN HEMTs under ON-state Stress

Transcription

1 Anomalous Source-side Degradation of InAlN/GaN HEMTs under ON-state Stress Yufei Wu, Jesús A. del Alamo Microsystems Technology Laboratories, Massachusetts Institute of Technology October 04, 2016 Sponsor: NRO Contract No. DII NRO000-13C0309 Collaborator: Jose Jimenez (Qorvo) 1

2 Outline 1. Motivation 2. Source-side degradation under ON-stress 3. Gate leakage current and its temperature dependence 4. Positive gate stress 5. Conclusions 2

3 Motivation: InAlN as barrier Al 0.2 Ga 0.8 N/GaN ln 0.17 Al 0.83 N/GaN In 0.17 Al 0.83 N Δ P 0 (e cm -2 ) 6.5 x x P piezo (e cm -2 ) 5.3 x P total (e cm -2 ) 1.2 x x [J. Kuzmik, EDL 2001] High spontaneous polarization in InAlN high 2DEG density InAlN thickness scaling gate length scaling W- and V-band applications [M. A. Laurent, JAP 2014] In 0.17 Al 0.83 N lattice matched to GaN Potentially better reliability! 3

4 Motivation: InAlN as barrier InAlN/GaN HEMTs W-band E-mode Four gate geometries: W g = 8 X 25 µm W g = 8 X 50 µm W g = 2 X 25 µm W g = 2 X 50 µm Thermal models available [Saunier, CSICS 2014] 4

5 High-V DS -high-i D stress Stress and characterization conditions: V DS,stress = 25 V, I Dstress = 400 ma/mm (V G ~ 1.5 V), 5 mins, RT (T j ~ 136 C) 25 C after thermal detrapping I D (ma/mm) V GS = 2 V V DS Permanent degradation: I D (ma/mm) before stress after stress Significant I Dmax degradation ΔV T > 0 Significant I Doff degradation V DS = 0.1 V V GS 5

6 High-V D -high-i D stress After thermal detrapping, gate current degradation: 10-1 I G, I S after stress 10-3 Large increase in I G after stress 10-5 I D after stress After stress: I G = I S >> I D in forward and I (A) 10-7 reverse bias 10-9 I G before stress I S before stress Source-side damage unexpected! Uncommon but previously observed in V DS = 0 V I D before stress AlGaN/GaN HEMTs [J. Joh, IEDM 2010] V G S 6

7 Temperature dependence of I G and I D T-dependence of I -1 G : T-dependence of I D : 10-3 After stress 10-3 T = -50 C I G (A) Before stress V DS =0 T = -50 C T = -25 C T = 0 C T = 25 C T = 50 C T = 75 C T = 100 C T = 125 C T = 150 C T = 175 C T = 200 C I D (A) Before stress V DS =0 After stress T = -25 C T = 0 C T = 25 C T = 50 C T = 75 C T = 100 C T = 125 C T = 150 C T = 175 C T = 200 C V G S V G S Before stress: For moderate V GS, negative T coefficient thermionic emission limited current I S behaves similar to I G After stress: Significantly reduced T dependence for I G and I S I D less affected degradation on source side 7

8 HRTEM of a virgin device Virgin device drain side Virgin device source side Gate metal Gate metal passivation passivation InAlN AlN AlN InAlN GaN GaN Residual oxide? Gate recessed to the AlN interlayer 8

9 HRTEM of stressed device Stressed device drain side Stressed device source side Gate metal Gate metal passivation passivation InAlN GaN AlN AlN InAlN GaN Disordered region in GaN channel at gate edge on source side 9

10 Hypothesis for Damage High V DS,stress + high I Dstress high I Gstress too high I GS high T j high electric field across AlN barrier on source side Conditions favor defect formation in AlN barrier on source side I GS Also, gate sinking ΔV T >0 10

11 Positive V G step-stress-recovery experiment Stress and characterization conditions: V GS,stress = V, V DS,stress = 0 V, step = 0.1 V, RT (T j ~ 48 C) 25 C after thermal detrapping I D (ma/mm) V GS = 2 V V DS Permanent degradation: I D (ma/mm) Significant I Dmax degradation ΔV T > 0 Significant I Doff degradation before stress after stress, detrapped V DS = 4 V V GS 11

12 Time evolution of I Dmax and I Goff Stress conditions: V DS,stress = 0 V, V GS,stress = V in 0.1 V steps stress time = recovery time = 150 s; characterization every 15 s RT I Goff (ma/mm) stress 10 1 recovery V Gstress I V GS = -2 V, V DS = 0.1 V 1.7 V final detrapped time (s) I Dmax (ma/mm) V Gstress I V GS = 2 V, V DS = 4 V stress recovery V 2.5 final detrapped time (s) I Goff starts to increase from V GS,stress ~ 1.7 V trap generation in AlN I Dmax starts to severely degrade from V GS,stress ~ 2.3 V gate sinking 12

13 Time evolution of I Gstress Stress conditions: V DS,stress = 0 V, V GS,stress = V in 0.1 V steps stress time = recovery time = 150 s; characterization every 15 s RT I Gstress (ma/mm) V GStress time (s) I Gstress (ma/mm) V GStress time (s) 2.3 V I Gstress increase becomes significant for V GS,stress 2.3 V 13

14 Gate current degradation After thermal detrapping, gate current degradation: I G After stress 10-5 I G I S, I D I (A) 10-7 I S, I D 10-9 Before stress V DS = V G S Symmetric degradation: I S I D I G /2 Reproduced degradation signature of high-v DS -high-i D stress: high forward V G leads to increase in I G 14

15 HRTEM of stressed device Stressed device drain side Stressed device source side Gate metal Gate metal Gate metal passivation InAlN InAlN AlN GaN GaN Disordered region in GaN channel at gate edge on drain side Disordered region in GaN channel at gate edge on source side 15

16 Conclusions Permanent degradation after High-V DS -high-i D stress: o I Goff Defect formation in AlN barrier on source side o ΔV T > 0, I Dmax Gate sinking o Affects source side Positive gate stress: o Reproduced degradation signature of high-v DS -high-i D stress: I Goff, ΔV T > 0, I Dmax o I S ~ I D ~ I G /2 Symmetric degradation on source and drain side 16

17 Thank you & Questions? 17