Nanoelectronic Biosensor Modelling, Design and
Characterization
PhD student: Paolo Scarbolo, Tutor: Luca Selmi
Thanks to: Federico Pittino, Andrea Bandiziol, Pierpaolo Palestri, Enrico Accastelli and Carlotta Guiducci
Dipartimento di Ingegneria Elettrica Gestionale e Meccanica (DIEGM), Università degli Studi di Udine
1. NANOELECTRONIC BIOSENSORS
2. TCAD MODELS OF pH SENSORS
H+
Field Effect Transistor (FET)-based biosensors are
investigated as pH-meters or high sensitivity detectors of
specific targets such as DNA strands, proteins and viruses.
The sensor operates as a standard FET where the gate
1,2
terminal is replaced with a liquid electrolyte solution
.
OH2+ OH OH2+ O
-
OH
-
OXIDE
OH
NANOWIRE
OH
CROSS SECTION
OH2+
OH
O
1) Surface processes at the oxide/electrolyte
interface such as protonation and deprotonantion of the oxide surface sites,
generate a pH-dependent surface charge.
SiOH ⇄ SiO-+ H+
SiOH2+⇄ SiOH + H+
+
σS=q([SiOH2 ]-[SiO ])
(de-protonation)
(protonation)
(surface charge)
2) Models for realistic multi-ion electrolyte
and surface processes have been integrated in
a commercial TCAD (Sentaurus) and used to
simulated the response of nanowire (NW)
devices in contact with electrolytes.
1
TCAD Simulations
0
10
−1
1.8
10
1.5
10
1.2
10
0.9
10
0.6
10
−2
−3
−4
−5
pH
pH
pH
pH
pH
0.3
Chip provided by CEA-LETI (Grenoble, FR) and measurement equipement (microfluidic environment,
solution and semiconductor parameter analyzer) provided by EPFL (Lausanne, SW)
age [V]
3. NANOWIRE DESIGN AND DEVICE LAYOUT
0.5
= 11
=9
=7
=5
=3
Drain Current [μA]
Drain Current [μA]
2.1
10
−6
10
3) The pH-dependent surface charge
modulates the NW surface potential,
thus affecting the current flow in the
channel and shifting the Drain
Current - Gate Voltage characterisitic
along the x-axis.
−7
10
2
1
1.5
Front Gate Voltage [V]
4. EXTRACTION OF PARASITICS
NANOWIRE
3
10
Drain Current [µA]
The SOI-based Silicon Nanowire
(SiNW) devices were fabricated at
CEA LETI with a top-down process,
with SiO2 as gate-oxide in contact
with the electrolyte solution. The NW
width ranges from 50 nm and 1 μm.
3.5e+07
2.3e+06
1.6e+05
1.1e+04
7.5e+02
5.1e+01
3.5e+00
Slope 1
Measured (With RSD)
Measured (No RSD)
VG-VT=0.3V
VG -VT =0.5V
2
10
1
10
Large series resistances (RSD) are
present due to non-metallic PAD1
source and drain connections.
Current Density in the cross section of the NR (above
threshold). The inversion layer is concentrate to the
three sides in contact with the electrolyte.
10
75
10
50
10
0
−1
−2
25
10
0
2
3
4
Back Gate Voltage [V]
Measurement
Simulation
age [V]
3
10
2
10
1
200
10
150
10
100
10
0
−1
−2
50
−3
10
5
Simulations show a thin inversion
layer (yellow/green) on the NW sides
in contact with the solution, leading
to a current scaling proportional to
W+2∙H.
0
0.8
10
−3
1.2
1.6
Front Gate Voltage [V]
10
2
The developed TCAD model with the extracted series resistance
values and trap charges at the NW-oxide/NW-channel interface,
reproduces measurements with good accuracy in both dry and
wet environment.
7. FUTURE WORK
1) Verify the dependence of the sensitivity
to the design parameters.
2) Explore AC operation of nanowires.
Contacts: e-mail: scarbolo.paolo@spes.uniud.it, Tel: +393400020870
Measurement
0.6
1B05 W=140nm
1B06 W=170nm
9
7.5
0.5
0.4
0.3
0.2
H
p
V/ pH
m V/
3
. m
5
4 .7
5
0 49
B
1 06
1B
6
pH pH
/
V /
m mV
47 .2
5 51
0
1B 06
1B
0.1
0
200
pH=7
pH=6
300
Simulations
W=170nm
60
Measurements 10.5
pH=5
400
time [s]
4.5
3
1.5
pH=4
500
600
Sensitivity ∂VFG/∂pH [mV/pH]
100
250
Wet Environment
Drain Current
) [μA]
FG>VT[nA]
Drain(V
Current
1
70
PAD3
Drain Current [nA]
2
10
10
W+2∙H [ µm]
6. pH SENSOR RESPONSE
300
Drain Current [nA]
Drain Current [nA]
125
0.6
Drain Current (VFG<VT) [nA]
Measurement
Simulation
10
Drain Current [nA]
150
3
0.2
Series resistance compensation is
fundamental to observe the
expected scaling of the drain
current with the NW dimensions.
5. CHARACTERIZATION
Dry Environment
W
0
−1
PAD4
H
10
10
PAD2
Current Density [A/cm-2]
50
40
30
ID@ 1 nA
ID@ VT
ID@ 700 nA
20
10
3
5
7
pH
9
11
Measurements and simulations show no dependence of the
voltage sensitivity on the drain current.
The measured voltage sensitivity (pH≥4) is in good agreement
with the one predicted by the simulations (red circles).
Acknowledgements: EPFL, CEA-LETI. This research is partially supported by the Progetto Vinci –
Università Italo-Francese / Université Franco-Italienne.
1. Toumazou, Christofer, et al. "Simultaneous DNA amplification and detection using a pH-sensing
semiconductor system." Nature methods 10.7 (2013): 641-646.
2. Merriman, B., R&D Team, I. T. and Rothberg, J. M. (2012), Progress in Ion Torrent semiconductor
chip based sequencing. ELECTROPHORESIS, 33: 3397–3417. doi: 10.1002/elps.201200424