l = 40 nm in0.7ga0.3as mhemts - massachusetts … slides.pdf · 14 balance in f t and f max 0 200...
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1
fT = 688 GHz and fmax = 800 GHz in
Lg = 40 nm In0.7Ga0.3As MHEMTs
with gm_max > 2.7 mS/m
D.-H. Kim, B. Brar and *J. A. del Alamo,Teledyne Scientific Company, *MIT
IEDM December-6th, 2011
III-V HEMT: record fT vs. time
2
Current record:ft=660 GHzLeuther IPRM 2011 (Fraunhofer Inst.)
(and MHEMT)
For >20 years, record fT obtained on InGaAs-channel HEMTs.
Well balanced devices:ft=644 GHz, fmax=680 GHz at same bias pointKim EDL 2010(MIT)
InGaAs-channel HEMTs offers record balanced fT and fmax.
RON ~ 420 Ohm-m
Strategy to improve fT
3
• In typical HEMTs: – RON: 350 ~ 450 Ω-m– T-Gate: Stem height = ~ 150 nm
Kim, EDL 2008
0 10 20 30 40 50 60-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
Electron density [cm-3]
CB
Pro
file
[eV]
Vertical depth [nm]
Single delta doping
Zero bias
0
2
4
ns = 3 x 1012 /cm2
EC and n incross section
x 1018
Lg = 30 nm
Cgext
4
Contents
1. Introduction
2. Device Technology
3. DC and RF Characteristics
4. Analytical fT Model
5. Conclusions
5
- SiO2 assisted T-gate
Lg = 40 nm Gate-stem > 250 nm
- Two-step recess (InP = 6 nm)
- Pt (3 nm)/Ti/Pt/Au Schottky
- QW: 10 nm In0.7Ga0.3As n,Hall > 10,000 cm2/V-s
- *In0.52Al0.48As/In0.7Al0.3As spacer
- **Dual Si -doping
Device Technology
S
Cap
D
Etch stopper
Barrier
Channel
Buffer
tins
OxideLside
tch
Stem
Buried Pt
100 mm InP Substrate
KIM, *Electron Lett 2011 ** IEDM 2010
6
TEM Images
- Mo-based S/D with 2 m
- Gate Stem > 250 nm
GaAs Substrate
Graded Buffer
HEMT Epi
- Lg = 40 nm, Lside = 100 nm
- tins = ~ 4 nm
Buried Pt
Ti
Pt
Au
SG
D
7
DC of Lg = 40 nm InGaAs MHEMTs
- Maximum ID > 1 mA/m- RON = 280 Ω-m
- gm > 2 mS/m @ VDS = 0.3 V- gm_max = 2.75 mS/m
@ VDS = 0.8 V
0.0 0.2 0.4 0.6 0.8 1.00.0
0.4
0.8
1.2
0.5 V
I D [m
A/
m]
VDS [V]
VGS = 0.6 V
0.0 0.2 0.4 0.60
1
2
30.8 V
0.2 V
g m [m
S/m
]
VGS [V]
VDS = 0.1 V
- Output characteristics - - gm characteristics -
-0.2 0.0 0.2 0.4 0.610-10
10-9
10-8
10-7
10-6
10-5
10-4
10-3
VDS = 0.05 V
VDS = 0.8 V ID
I D, I
G [A
/m
]
VGS [V]
IG
8
Subthreshold characteristics- Lg = 40 nm - - gm_max scalability-
gm saturates.
1001000
1500
2000
2500
3000tins = ~ 4 nm
VDS = 0.5 V
In0.7Ga0.3As MHEMTs [This work] In0.7Ga0.3As PHEMTs [IEDM-10] InAs PHEMTs [IEDM-08]
g m,m
ax [
S/m
]
Lg [nm]
- VT = 0.02 V @ VDS = 0.5 V- S = 100 mV/dec., DIBL = 105 mV/V
As Lg ↓,
This work
109 1010 1011 10120
20
40
Frequency [Hz]
Gai
ns [d
B]
0
1
2
3
4
k
Ug
MSG
Stability Factor (k)
h21
fT = 602 GHz
9
fT & fmax: Lg = 40 nm, Wg = 2 x 20 mCalibration: LRRM, De-embedding: OPEN/SHORT
- fT already approaches to 600 GHz @ VDS = 0.35 V.
- VGS/VDS = 0.4/0.35 V -
109 1010 1011 10120
20
40
Frequency [Hz]
Gai
ns [d
B]
0
1
2
3
4
fT = 688 GHz
ID = 0.4 mA/mk
Ug
MSG
Stability Factor (k)
h21
- Record fT = 688 GHz @ VDS = 0.6 V.
- VGS/VDS = 0.4/0.6 V -
Gummel technique for fT extraction
10101010
In one-pole system:
Then:
Slope gives fT
Gummel, Proc IEEE 1969
109 1010 1011 10120
20
40
Frequency [Hz]
Gai
ns [d
B]
VDS = 0.6 VID = 0.4 mA/m
k
Ug
MSG
h21
0.0 20.0G 40.0G 60.0G0.00
0.04
0.08
0.12
Imag
(h21
-1)
Frequency [Hz]
1/slope = fT= 690 GHz
11111111
109 1010 1011 10120
20
40
Frequency [Hz]
Gai
ns [d
B]
VDS = 0.6 VID = 0.4 mA/m
k
Ug
MSG
h21
Different measurement systemfor fT extraction
0.0 20.0G 40.0G 60.0G0.00
0.04
0.08
0.12
Imag
(h21
-1)
Frequency [Hz]
- 8510C @TSC: 1 ~ 50 GHz
109 1010 1011 10120
20
40
Frequency [Hz]
Gai
ns [d
B]
- PNA @UCSB: 1 ~ 67 GHz
691 GHz0.0 20.0G 40.0G 60.0G
0.00
0.04
0.08
0.12
Imag
(h21
-1)
Frequency [Hz]
1/slope = fT= 690 GHz
12
Small-signal model for fT extraction
109 1010 1011 10120
20
40
Frequency [Hz]
Gai
ns [d
B]
0
1
2
3
4
VDS = 0.6 VID = 0.4 mA/m
k
Ug
MSG
Stability Factor (k)h21
109 1010 1011 10120
20
40
Frequency [Hz]
Gai
ns [d
B]
0
1
2
3
4Stability Factor (k)
freq (1.000GHz to 67.00GHz)
S11
S21/5
S22
5xS12
- Excellent agreement, modeled fT = 680 GHzfmax = 800 GHz
Summary on fT measurements
13131313
Measurements in two different test benches:
All measurements at same bias point: VGS=0.4 V, VDS=0.6 V
Kim, EDL 2010
8510C@TSC
PNA@UCSB
fT
[GHz]
From H21 688 688
From Gummel’s approach 690 691
From Small-signal model 680
fmax [GHz] 800
14
Balance in fT and fmax
0 200 400 600 800 10000
500
1000
1500
MIT/TSC HEMT Fujitsu HEMT NGAS HEMT SNU HEMT UCSB HBT UIUC HBT TSC HBT HRL HBT ETH HBT
max ff
f max
[GH
z]
fT [GHz]
300 600 700 = favg =
TSC/MIT(This work)
→ Best-balanced fT and fmax transistor→ Record fT FET
Lai, IEDM08Kim, IEDM10
Urteaga, DRC11
15
Contents
1. Introduction
2. Device Technology
3. DC and RF Characteristics
4. Analytical fT Model
5. Conclusions
17
Break out ‘extrinsic’ capacitances
• Capacitance components [fF/mm]:
Cgs = Cgsi + Cgsext
= Cgsi_areal × Lg + Cgsext
Cgd = Cgdi + Cgdext
= Cgdi_areal × Lg + Cgdext
[fF/m2] [fF/m2]
18
Delay time analysis
• Delay time:
• Components of delay time:
18
Intrinsic delay (transit time)
Extrinsic delay Parasitic
delay
(Cgsi_areal + Cgdi_areal) Lggmi
19
Lg-dependent model parameters
0 100 2000
1000
2000
Cgs_ext
Cgs
, Cgd
[fF/
mm
]
Lg [nm]
VDS = 0.6 VVGS - VT = 0.3V
Cgs
Cgd
Cgd_ext
1000.1
1
10
VDS = 0.6 VVGS - VT = 0.3V
goi
Lg [nm]g m
i, goi [m
S/m
]
gmi
- Linearly proportional to Lg
- Cgs_ext > Cgd_ext
← |Vgs| < |Vgd|
- gmi saturates at Lg = ~ 60 nm- goi continues to increase
As Lg↓,
→ gmi/goi ↓
1
Cgsi_areal
20
Delay components of Lg=40 nm InGaAs MHEMT
20
Delay time from ft: ~231 fs• Intrinsic delay: ~81 fs• Extrinsic delay: ~ 99 fs• Parasitic delay: ~50 fs• Unaccounted: ~9 fs
least significant, yields ve=5 x107 cm/s
most significant
42.08%2.52%
33.84%
21.56%
accounted
Transit
ext
par
34 %
42 %
22 %
2 %
21
Scaling of delay components
0 100 2000
200
400
600VDS = 0.6 VVGS - VT = 0.3V
Del
ays
[fs]
Lg [nm]
Transit
ext
par
ext and par do not scale, become dominant for Lg < ~ 60 nm.
100
200
400
600
800
1000
VDS = 0.6 V VDS = 0.5 V VDS = 0.4 V
f T [GH
z]
Lg [nm]
• Intrinsic delay:
Lg ↓ (without degrading gmi), ve ↑ channel engineering
• Extrinsic delay:
Cgsext, Cgdext ↓, or alternatively gmi ↑ (harmonious scaling)
22
Options to improve fT
22
• Parasitic delay:
RS+RD ↓, increase electrostatic integrity: goi/gmi↓
23
100200
400
600
800
1000
1200
VDS = 0.6 V
30% reductionin all the parasitics
Measured fT
Modeled fT
Model Projection
f T [GH
z]
Lg [nm]
1 THz
Model Projection
fT = 1 THz is feasible at Lg = ~ 25 nm.
24
Summary
40-nm In0.7Ga0.3As MHEMTs on GaAs substrate
- RON = 280 Ω-m, gm_max > 2.7 mS/m @ VDS = 0.8 V
- S = 100 mV/dec., DIBL = 105 mV/V
- Measured fT = 688 GHz (Record in any FET)
- fT/fmax = 688/800 GHz (Best-balanced transistor)
Analytical fT Model- Excellent description of fT behavior in III-V HEMTs
- Guidance to improve fT beyond 1 THz