THz I I I -V HEMT Technology J. A. del Alamo Microsystems Technology Laboratories, MIT I nternational Wireless Symposium 2013 Workshop on THz Material Growth, Device Fabrication and Modeling Beijing, April 14, 2013 Acknowledgements: Dae-Hyun Kim, Jianqiang Lin, Tae-Woo Kim, Niamh Waldron Sponsors: FCRP-MSD, Intel, SRC, ARL Labs at MIT: MTL, SEBL, NSL
Outline 1. High ‐ frequency III ‐ V HEMTs: megatrends 2. State ‐ of ‐ the ‐ art InGaAs HEMTs and f T analysis 3. The path to THz operation 2
1. I I I -V HEMT: record f T vs. time f T =710 GHz, f max =478 GHz Current record: Chen APEX 2013 f T =688 GHz f max =800 GHz Kim IEDM 2011 (Teledyne/MIT) (and MHEMT) Chen • For >20 years, record f T obtained on InGaAs ‐ channel HEMTs • InGaAs ‐ channel HEMTs offer record balanced f T and f max 3
Record f T I I I -V HEMTs: megatrends • Over time: L g ↓ , In x Ga 1 ‐ x As channel x InAs ↑ • L g , x InAs saturated no more progress possible? 4
Record f T I I I -V HEMTs: megatrends • Over time: t ch ↓ , t ins ↓ t ch , t ins saturated no more progress possible? • 5
2. State-of-the-art I nGaAs HEMT L g =40 nm InGaAs Metamorphic HEMT • In 0.7 Ga 0.3 As QW channel o t ch = 10 nm o µ n,Hall > 10,000 cm 2 /V ‐ sec • In 0.52 Al 0.48 As barrier + In 0.7 Al 0.3 As spacer (Kim, EL 2011) Dual Si ‐ doping (Kim, IEDM 2010) • • Pt (3 nm)/Ti/Pt/Au Schottky o t ins =4 nm • InP etch stop (t InP =6 nm) • L side =100 nm • Gate stem > 250 nm GaAs substrate • Mo ‐ based S/D with 2 µm S ‐ D spacing Kim, IEDM 2011 6
TEM cross section Au Pt G S D Ti HEMT Epi Graded Buffer Buried Pt GaAs Substrate 7
Output and transfer characteristics Kim, IEDM 2011 1.2 3 L g =40 nm L g =40 nm V GS = 0.6 V 0.8 V 0.8 2 0.5 V I D [mA/ m] g m [mS/ m] 0.4 1 0.2 V V DS = 0.1 V 0.0 0 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 V DS [V] V GS [V] • Large current drive: I D >1 mA/µm at V DS =0.8 V • High transconductance: g mpk = 2.75 mS/ μ m at V DS =0.8 V • V T ≈ 0 V, R ON =280 Ω . μ m 8
High-frequency characteristics V DS =0.6 V, V GS =0.4 V 4 h 21 V DS =0.6 V, V GS =0.4 V 40 f T = 688 GHz 3 MSG f max = 800 GHz Gains [dB] 2 Stability Factor (k) U g 20 1 k 0 0 9 10 11 12 10 10 10 10 Frequency [Hz] • Only transistor of any kind with both f T and f max > 680 GHz • Obtained at same bias point, V DS =0.6 V Kim, IEDM 2011 9
f T vs. f max 300 600 700 = f avg = f f 1500 m ax Kim, IEDM 2010 (f max =1.25 GHz) 1000 f max [GHz] TSC/MIT Kim, IEDM 2011 (This work) MIT/TSC HEMT 500 Fujitsu HEMT NGAS HEMT SNU HEMT UCSB HBT UIUC HBT TSC HBT HRL HBT 0 ETH HBT 0 200 400 600 800 1000 f T [GHz] • Record f T FET Best ‐ balanced f T and f max transistor • 10
f t analysis G S D C gs C gd g mi v gs R S R D g oi • First ‐ order f T expression for HEMT: 11
Break out extrinsic capacitances G S D • Capacitance components: 12
Delay time analysis • Delay time: • Components of delay time: Intrinsic delay (transit time) Extrinsic delay Parasitic delay 13
Extraction of parasitic capacitances • Need devices with different L g • Bias them at same V GS overdrive around peak f T point • Extract small ‐ signal equivalent circuit models • Study L g scaling behavior of C gs and C gd V DS = 0.6 V V GS - V T = 0.3V 2000 C gs C gs , C gd [fF/mm] C gs_ext 1000 C gd_ext C gd 0 0 100 200 L g [nm] Kim, IEDM 2011 14
Delay components of L g = 40 nm I nGaAs HEMT Delay time from f T : ~231 fs yields <v e >=5x10 7 cm/s • Intrinsic delay: ~81 fs • Extrinsic delay: ~99 fs most significant • Parasitic delay: ~50 fs • Unaccounted: ~9 fs Kim, IEDM 2011 15
Scaling of delay components 600 V DS = 0.6 V Transit V GS - V T = 0.3V 400 Delays [fs] 200 ext par 0 0 100 200 L g [nm] ext and par do not scale, become dominant for L g < 50 nm 16
Scaling of small-signal components V DS = 0.6 V V GS - V T = 0.3V 2000 C gs C gs , C gd [fF/mm] C gs_ext 1000 C gd_ext C gd 0 0 100 200 L g [nm] As L g ↓: do not scale do not scale ↑ ↓ 17
3. The path to THz operation • Intrinsic delay ↓ L g ↓ • Extrinsic delay ↓ : C gsext , C gdext ↓ gate engineering g mi ↑ harmonious scaling • Parasitic delay ↓ : R S +R D ↓ S/D engineering g oi /g mi ↓ harmonious scaling 18
How to reach f t = 1 THz? 1200 30% reduction 1 THz 1000 in all the parasitics 800 600 f T [GHz] V DS = 0.6 V 400 Measured f T Modeled f T Model Projection 200 100 30 L g [nm] f T = 1 THz feasible by: scaling to L g ≈ 25 nm ~30% parasitic reduction 19
Approach to R S + R D ↓ : self-aligned process Kim, IEDM 2010 Waldron, TED 2010 1.0 VGS = 0.5 V L g =50 nm L side =100 nm 0.4 V 0.8 0.3 V 0.6 I D [mA/ m] 0.2 V 0.4 0.1 V 0.2 0 V 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 V DS [V] • Dry ‐ etched Mo contacts: R c = 7 Ω . μ m • L g =50 nm, R ON =290 Ω . μ m, g mpk =2.2 mS/ μ m @ V DS =0.5 V 20
L g = 60 nm self-aligned I n 0.7 Ga 0.3 As HEMT L g =60 nm 4 Measured data Modeled data V GS = 0.2 V, V DS = 0.6 V H 21 40 H 21 , MAG/MSG and U g [dB] 3 f T =595 GHz f max =680 GHz U g 2 K 20 MAG/MSG 1 K 0 0 1 10 100 1000 Frequency [GHz] Kim, IEDM 2010 Highest f T and f max of any FET at L g 60 nm 21
L g = 30 nm self-aligned I nGaAs MOSFET with L side ~ 30 nm Lin, IEDM 2012 V gs = -0.2 to 0.5 V in 0.1 V step 600 R on =475 m (at V gs =0.7 V) L g = 30 nm I d ( A/ m) 400 200 0 0.0 0.1 0.2 0.3 0.4 0.5 V ds (V) L side ~30 nm g mpk =1.4 mS/ μ m R ON =475 Ω .µm access region design critical! 22
Regrown source and drain regions L ch =55 nm InGaAs MOSFET: R ON =199 Ω .µm Egard, IEDM 2011 L ch =30 nm InGaAs MOSFET: R ON =133 Ω .µm Zhou, EDL 2012 23
Harmonious scaling: aspect ratio of record f t devices Channel Aspect Ratio: L g /t ch Insulator Aspect Ratio: L g /t ins Dimensions verified by XTEM • Channel AR: 3 ~ 4 For L g =25 nm: t ch ~ 7 nm, t ins ~ 3 nm • Insulator AR: 7 ~ 10 24
I ssues in channel scaling Deep channel thickness scaling degrades performance: R S ↑ f T ↓ InAs HEMT, L side = 80 nm, t ins = 5 nm Noticeable mobility degradation: t ch =10 nm µ e =13,500 cm 2 /V.s t ch =5 nm µ e =9,950 cm 2 /V.s Kim, IPRM 2010 25
v inj - impact of channel thickness 4 VDS = 0.5 V 2 /V-s n ~ 13,000 cm t ins = 4 nm & t ch = 10 nm 2 /V-s n ~ 9,950 cm 3 Kim, IEDM 2009 t ins = 3 nm & t ch = 5 nm 7 cm/s] 2 v inj [10 Strain-Si 1 Si nFETs (VDS = 1.1 ~ 1.3 V) 0 10 100 L g [nm] In thin ‐ channel devices: • Long L g : v inj decreases right along with e (~23%) • Short L g : v inj relatively unaffected consistent with near ballistic transport 26
Channel transport enhancement through strain engineering InAs 300 K quantum ‐ well mobility vs. lattice constant: InAs InSb InP AlSb Independent control of channel strain and composition: new possibilities for channel design 27
I ssues in barrier scaling Want to scale L g without degrading g m or g o In 0.7 Ga 0.3 As HEMTs t ch =13 nm, L side =150 nm Kim, TED 2008 For harmonious scaling: as L g ↓ t ins ↓ 28
Limit to HEMT barrier scaling: gate leakage current InAlAs/InGaAs HEMTs L g =40 nm V DS =0.5 V At L g =40 nm, modern HEMTs are at the limit of scaling! 29
Limit to HEMT barrier scaling: gate leakage current InAlAs/InGaAs HEMTs 10 ‐ 5 x! Al 2 O 3 (3 nm)/InP (2 nm)/InGaAs L g =40 nm MOSFET V DS =0.5 V V DS =0.5 V Need high ‐ K gate dielectric: HEMT MOSFET! 30
I I I -V MOSFET: deep scaling possible InP (1 nm) + Al 2 O 3 (0.4 nm) + HfO 2 (2 nm) EOT ~ 0.9 nm [ vs. 4 nm InAlAs EOT = 1.3 nm] Equivalent oxide thickness should bring us to L g =20 nm V ds =0.5 and 0.05 V -6 10 L g = 300 m Long ‐ channel -7 10 I d (A/ m) In 0.53 Ga 0.47 As MOSFET -8 10 μ e ≈ 2700 cm 2 /V.s -9 10 S=69 mV/dec -10 10 Lin, IEDM 2012 -11 10 -0.2 0.0 0.2 0.4 0.6 V gs (V) S=69 mV/dec Low D it at MOS interface demonstrated 31
High-frequency I nGaAs MOSFETs L g =60 nm InGaAs MOSFET with L side ~5 nm, EOT=1.2 nm Kim, APL 2012 L g =60 nm V DS =0.5 V f t =370 GHz, R ON =220 Ω .µm, g m =2.0 mS/µm, S=110 mV/dec 32
THz MOSFETs: possible designs n + n + Etched S/D QW ‐ MOSFET Regrown S/D QW ‐ MOSFET Gate ‐ all ‐ around FinFET nanowire FET 33
Conclusions • THz III-V FETs just around the corner need to reduce parasitics need to scale harmoniously • Exploding interest on III-V CMOS: huge opportunity for THz III-V electronics! fast technology progress new processes and tools fundamental research on transport, interface, etc. Si as substrate for THz electronics 34
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