D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017
Denis Flandre, Valeriya Kilchytska, Cecilia Gimeno, David Bol, Babak Kazemi Esfeh, Jean-Pierre Raskin
Measurement and modelling of specific behaviors in 28nm FD SOI UTBB MOSFETs of importance for
analog / RF amplifiers
ICTEAM Institute, Université catholique de Louvain Louvain-la-Neuve, Belgium
D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017
Context
q VT adjustment q Improved SCE control (suppression of SUB depletion)
FD-SOI: Unique Analog design opportunity
• New design opportunity by controlling analog device characteristics through back gate biasing techniques © Courtesy Ph. Flatresse, ST M, confidential
No pocket implant
Total dielectric isolation
No channel doping
FD-SOI
Body Bias: 85mV/V VTh adjust in FD-SOI
2
UTBB
→ Also better other analog performances ? And are they correctly modeled ?
D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017
Outline
ü Context
ü Analog / RF Figures of Merit :
from device assessment to circuit design at low frequency
ü UTBB specificities & challenges
Back gate biasing & FoM variation with frequency
ü Wideband RF amplifier
Non-linear performance
ü Conclusions
3
D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017
Analog / RF figures of merit
q Transconductance gm q Drive current, Id q Output conductance, gd q Early voltage, VEA (VEA=Id/gd) q gm/Id ratio q Gate capacitance, Cgg q Parasitics (C, R)
Key-factors @ MOSFET-level Ø fT = gm/(2·π·Cgg) Ø fmax α fT, Rg Ø Av0 = gm/gd = (gm/Id)·VEA ≠ const ( f )
@ IC (amplifier)-level Ø GBW = gm/(2·π·CL) = = (gm/Id) ·(Id /(2·π·CL))
ð depends on
4
D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017
Methodology : device assessment & circuit design
q independent on VT q independent on L (except SCE) q independent on Vsub
Allow fair comparison of different devices & at different conditions
L=30nmL=30nm
WI: ~1/SWI: ~1/S
SI: SI: µµ, n, n
10-12 10-10
Gm
/I d, V
-1
0
Normalized drain current, Id/(W/L), A10-8 10-6 10-4
10
20
30
RRsdsdvvsatsat
Vsub = - 2 → 2 V
Baseband applications (High gain, High precision)
High Frequency applications (High drive current)
V. Kilchytska et al. SSE 2012
L=30nmL=30nm
WI: ~1/SWI: ~1/SWI: ~1/SWI: ~1/S
SI: SI: µµ, n, n
10-12 10-10
Gm
/I d, V
-1
0
Normalized drain current, Id/(W/L), A10-8 10-6 10-4
10
20
30
RRsdsdvvsatsat
Vsub = - 2 → 2 V
Baseband applications (High gain, High precision)
High Frequency applications (High drive current)
V. Kilchytska et al. SSE 2012
√(2µCox/nIdnorm)
gm / Id vs Id,norm gm - Av Analog Metric
Intrinsic gain, Av0
g m/W
Vd=1 VVg=VTh+0.6 V
Intrinsic gain, Av0
g m/W
Vd=1 VVg=VTh+0.6 V
ShortShort--LL
LongLong--LL
SCE, Rsd
Intrinsic gain, Av0
g m/W
Vd=1 VVg=VTh+0.6 V
Intrinsic gain, Av0
g m/W
Vd=1 VVg=VTh+0.6 V
ShortShort--LL
LongLong--LL
SCE, Rsd
q analogue of Ion– Ioff digital metric q very visual q independent of VT
5
D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017
Comparison of UTBB vs bulk
x 1.1 in SOI → (n/µ) / 1.2
6
gm / Id gd
gm/Id ~ 10 – 20 % and gd ~ 2 – 10 x better in UTTB than bulk
depending on length, bias, temperature and frequency conditions
D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017
Circuit validation at low frequency and power A Fully-Differential OTA in 28 nm UTBB FDSOI CMOS Harikumar et al, ECCTD 2015
DC open-loop gain (dB)40 50 60 70 80 90
Tota
l bia
s cu
rrent
(A)
10 -6
10 -5
BulkFD SOI
Harikumar
SPICE simulations
7
D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017
q Vsub → “+” ð Id norm↑ of 5-10% (sign of µ ↑)
q Vsub → “–” ð VEA ↑ (as a result of DIBL improvement) ð Gm/Id ↑ ↑ (at low Vg=Vd) (result of VT shift) ð one can win ~ 5 dB (in max Av range)
UTBB Specificities (1) : Effect of Vsub
V. Kilchytska et al. SSE 2012
⇒ Choice of Vsub “+” or “-” depends on targeted applications (either Id ↑ or Av ↑)
Vsub → “–” : S↓, DIBL↓, but VT ↑ ð Ion↓
Vsub → “+”: µ ↑ ð Gm max & Ion ↑ Trade-off for analog FoM ???
Vbg=0 V
Vbg=+1 V
Vbg=-1 V Vbg+ Vbg-
AV0 (dB) 20 24 28 32 36
g m/W
(mS/µm
)
0
0.4
0.8
1.2
1.6
↑↑↑↑↑↑↓↓--
↓↓↓↓↓↓↑↑++
AAv0v0ggmm/I/IddVVEAEAIIdd, g, gmmVVbgbg
↑↑↑↑↑↑↓↓--
↓↓↓↓↓↓↑↑++
AAv0v0ggmm/I/IddVVEAEAIIdd, g, gmmVVbgbg
8
D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017
gd (f) & gm (f) ⇒ Gain (f)
⇒ Performance prediction from DC data is insufficient ⇒ Quest for wide-f characterization ⇒ gm – Av analogue metric is strongly f-dependent:
gm ↑, gd ↑ ↑, Av ↓ with f↑
Frequency-dependent effects: Floating body, self-heating, substrate coupling, …
f↑
f↑
L↑ S parameters
VNA 40 kHz → 4 GHz
de-embedding
Sij → Yij conversion
gd = Re(Ydd)
S parametersVNA 40 kHz → 4 GHz
de-embedding
Sij → Yij conversion
gd = Re(Ydd)
S. Makovejev et al. ULSI 2014
9
UTBB Specificities (2) : Effect of frequency
D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017
⇒ GP allows to suppress SUB-related gd (f) variation ⇒ SH is the main reason of gd(f) variation
p-substrate
n n
G
pBOX
S D
SUB
p-substrate
n n
G
pBOX
S D
SUB
GP
gd(f) = gintr + Δgd_FB(f) + Δgd_SH(f) + Δgd_SUB(f)
noGP
with GP
S. Makovejev et al. ULSI 2014
10
UTBB Specificities (3) : Effect of self-heating (SH)
D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017 11
SH extraction using RF (S-param) method
• Rth in bulk lower than in FDSOI • Cth higher in bulk than in FDSOI due to larger Si volume available for generated heat • Temperature rise due to self-heating up to
~32 K in bulk and ~87 K in FDSOI
• In spite of stronger SH effect, FDSOI outperform bulk in terms of Analog FoM in entire frequency range • While thermal effects are stronger in FDSOI, their influence on device parameters is limited
gm - Av analogue metric
S. Makovejev et al. EuroSOI-ULIS 2015
( ) addLFdd
SHdth dTdIVgI
gR
_
_
+
Δ=
ddth VIRT =Δ
S. Makovejev et al. ULIS 2014
FDSOI
bulk
SH and its effect on Analog FoM in 28 FDSOI vs bulk
0 0.25 0.5 Power, mW/µm
D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017
Outline
12
ü Context
ü Analog / RF Figures of Merit :
from device assessment to circuit design at low frequency
ü UTBB specificities & challenges
Back gate biasing & FoM variation with frequency
ü Wideband RF amplifier
Non-linear performance
ü Conclusions
D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017
Wideband LNA
13
Crucial for efficient low-power multi-standard applications such as - UWB (Ultra-Wide Band) - SDR (Software-Defined Radio)
High gain up to 6 - 10 GHz + • impedance matching • noise figure • linearity • low area (inductorless)
D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017
Wideband inductor-less LNA
14
UTBB FD-SOI versus Bulk
Noise-cancelling Inductor-less architecture
With high linearity For 6 - 10 GHz
Software-Defined Radios In 28nm CMOS
!
G. De Streel et al. IEEE S3S Conf. 2015
C. Gimeno et al. IMS Conf. 2017
D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017
Non-linearity figures of merit
15
Noise floor
Pout
PinIIP3
OIP3
Pin, 1dB
1 dBPout, 1dB
Dyn
amic
rang
e (D
R)
Y = g1X + g2X2 + g3X
3Considering IIP3 of an amplifier in open loop is proportional to while in feedback
(g1 / g3)1/2
g3 − 2g22 / g1
with
Considering a memoryless circuit excited by a sinusoidal signal with AC amplitude A
D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017
Transconductance : Bulk vs UTBB SOI
16
q Advantage of FDSOI is very clear in below–around – VTh
q Vg >VTh+0.2 V ⇒ Bulk curves stretch out w.r.t FDSOI to higher Id and higher gm1
q Contrarily FDSOI curves quasi-saturate with Vd↑
Normalized Drain Current, Id/(W/L) (µA) 0
10
20
30
40
50
Nor
mal
ized
Tra
nsco
nduc
tanc
e, g
m1/(
W/L
) (µ
S)
0 10 20 30
Vd=
Bulk
FDSOI Vd = 50 mV … 1 V
Rsd effect ???
q RF measurements give : Rsd_FDSOI <Rsd_bulk
q Id-Vd curves do not indicate higher Rsd in FDSOI
⇒ Not related to Rsd L=30 nm; W= 48.6 µm
V. Kilchytska et al. EUROSOI-ULIS 2017
D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017
Second-derivative gm2 : Experiments vs SPICE
17
q Difference in the Vd behavior of FDSOI and Bulk devices is not well reproduced by Spice simulations
q At low Vd: Spice curves agree well for both Bulk and FDSOI devices q With Vd ↑: discrepancy is rather strong in FDSOI device q “Stretching” of bulk curves is well reproduced, but not “saturation” of FDSOI ones,
which in Spice simulations behave in the same way as bulk
Measurements Spice simulations
D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017 18
Silvaco ATLAS simulations : with SH or not
Normalized Drain Current, Id/(W/L) (µA) 0
10
20
30
40
50
Nor
m. T
rans
cond
ucta
nce,
gm
1/(W
/L)
(µS)
0 10 20
Vd=
noSH
SH Vd = 50 mV … 1 V
SH – solid lines noSH – dashed lines
Normalized Drain Current, Id/(W/L) (µA) 0 10 20
Vd=
noSH
SH
Vd = 50 mV … 1 V
SH – solid lines noSH – dashed lines
0
-5⋅10-5
5⋅10-5
1⋅10-4
Nor
mal
ized
2nd
I d d
eriv
ativ
e, g
m2/(
W/L
) strongly suggests that the experimental difference
in FDSOI vs Bulk is (at least partially) due to SH
V. Kilchytska et al. EUROSOI-ULIS 2017
Preliminary RF experiments show similar trend
D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017
Impact of back-gate bias on non-linearities
19
B. Kazemi et al. ESSDERC 2017 DC :
RF :
D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017
Wideband LNA SPICE simulations
20
Back-bias improvement also obtained in simulations over large process and temperature variations
C. Gimeno et al., IEEE S3S Conf. 2017
D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017 21
Conclusions ü Analog / RF FoM are excellent in FDSOI to design high-performance amplifiers (gain, bandwidth, power consumption) but specificities require cautious modeling (back bias, frequency, self-heating)
ü Non-linearities in FDSOI and Bulk MOSFETs compared by measurements and simulations :
Minimization at lower biases in FDSOI w.r.t bulk, which is beneficial for LP applications
Application of a positive back-gate (or body) bias in FDSOI allows for further non-linearity reduction
ü Next : noise ? (see L. Van Brandt ’s presentation in this workshop)
D. Flandre, UCL / ICTEAM MOS-AK Workshop, Leuven, 11 Sept. 2017
ACKNOWLEDGEMENTS
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Research projects & Major partners : STM, LETI, IMEC…
WELCOME Characterization Platform (ELEN/ICTEAM/UCL):
https://sites.uclouvain.be/welcome/index.php