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Conductive or insulating substrate ?
How resolution and accuracy is affected by the substrate material (silicon, quartz or plastic)
Marco SampietroHIGH RESOLUTION ELECTRONIC MEASUREMENTS IN NANO-BIO SCIENCE
Marco.Sampietro@polimi.it
AmplifierContact pad
Experimental area
Conductiveelectrolyte (PBS, …)
Connecting strip
Experiments with cartridges in liquid
CE
Marco.Sampietro@polimi.it
Affinity biosensors
Binding detection Proximity detection
Electric field lines
Free channel
Cell detection
Electric field lines
Low Impedance
High Impedance
Advantages:• No need for optical instrumentation• Label-free technique
ElectrodeS S
O OH
SS
O OH
S S
O OH
S S
O OH
S S
O OH
S S
O OH
S S
O OH
S S
O OH
Enzyme
molecule
Counter electrode
Marco.Sampietro@polimi.it
IMPEDANCE MEASUREMENT
Rf
)(tvi
DUT )(tvo
Cp2Cp1
)(tii
)()(
SISVZ
i
iDUT =
In phase ⇒ resistance
In quadrature ⇒ capacitance
Transimpedance amplifier
vi(t)
Marco.Sampietro@polimi.it
Experiments with cartridges in liquid
Rf
+ -
VCE
Vout
- Absolute error !
Insulating substrate
Electrolyte
200 nm
SignalCE
Spurious signal
The thicker the better
Marco.Sampietro@polimi.it
AmplifierContact pad
Experimental area
Connecting strip covered by insulator
Good and spurious signals – top view
CE
Signal
Spurious signal
Marco.Sampietro@polimi.it
Practical tips
∅ 5 µm
C = 3 pF
1 cm x 100µm
C = 330 pF
2 mm x 3 mm
f
+ -
Vout
C = 3 pFC = 3 pF
f
+ -
Vout
10µm1 mm
Y
∆=2%
∆=0.02%Y
∆=2%
∆=1%
Marco.Sampietro@polimi.it
Beware of conductive substrate !
Rf
+ -
VCE
Vout
SiO2
Electrolyte
200 nm
CE
Conductive
C very big (short circuit)
ADDITIONALspurious signal.
Very big !
Marco.Sampietro@polimi.it
Amplifier
Contact pad
Experimental area
Contact pad contributes !
CE
Signal
All metal deposited on the chip contributes
Marco.Sampietro@polimi.it
Comparison btwn QUARTZ & SILICON
Rf
CE
Measurement of at various frequency
V
I
CIV
ω1
=
Marco.Sampietro@polimi.it
Comparison btwn QUARTZ & SILICON
Electrolyte
CE
Insulator
Electrolyte
CE
Conductive
Conductive
Marco.Sampietro@polimi.it
Comparison btwn QUARTZ & SILICON
With a silicon cartridge:
10% modulation of Cdl
(∆Cdl=0.8pF)
350ppm modulation of the total signal (0.8pF/2.2nF)
Difficult to be measured !
M. Carminati et al., Sensors and Actuators B, Chemical, vol.174 (2012) 168– 175
Marco.Sampietro@polimi.it
Conductive substrate held to GND
Rf
+ -
VCE
Vout
SiO2
200 nm
CE
Conductive
Silicon substrate connected to GROUND
Much easier to be measured !
Marco.Sampietro@polimi.it
SiO2
200 nm
CE
Insulating
NOISE EFFECT : quartz substrate
Electrolyteis at ground
Rf
+ -
Vout
Small sensor capacitance small noise
Csensor = ?
Marco.Sampietro@polimi.it
SiO2
200 nm
CE
Conducting
NOISE EFFECT : silicon substrate
Electrolyteis at ground
Rf
+ -
Vout
Big sensor capacitance big noise
Csensor = ?
Also the pad contributes !
Marco.Sampietro@polimi.it
Comparison Quartz vs Silicon : Noise
M. Carminati et al., Sensors and Actuators B, Chemical, vol.174 (2012) 168– 175
Marco.Sampietro@polimi.it
Current sensing : molecules through nanopore
DNA Molecule
Low-Pass Filter
(160Hz)
Low-Pass Filter
(160Hz)
Ag/AgCl
Ag/AgCl
Headstage
A
Si
Nanopore Device
Amplifier
Amplifier
Ionic Current
Tunneling Current
V1
V3
V4
V2
iTUN
iION
Cstray
Tunneling Electrodes
D. Branton et al., Nature biotechnology, 2008, 26, 1146-53. T. Albrecht et al., Nature Communications, 2012, 3, 829.
DNA sequencing
A. Ivanov et al., Nano letters, 2011, 11, 279-85.
Marco.Sampietro@polimi.it
Noise in nanopore on conductive Silicon
Lg=1mm
Lm=50µm
SiN (t=20 nm)
Si Si
gasket
Cm
gasket
electrolyte
electrolyte
Condition B=10kHz B=100kHzCm = 5pF 2.3pA 7.3pACm+ (CSI in series with CSiN) = 3.3 nF 133pA 1.5nA
pF5t
LxLC mmSiNm =ε≅
CSi
CSiN
nF3.3CCCxCC
SiNSi
SiNSistray ≅
+≅
(Idc= 100pA; Camp = 1pF)
Insulating substrate
Conductive substrate !J.K.Roosenstein et al. «Integrated nanopore sensing platform with
sub-microsecond temporal resolution», Nature 2012
Marco.Sampietro@polimi.it
Microfluidic system … on top of a microelectronic system
Ways through in Microfluidics
Experiments on the microfluidic gasket can interferewith the reading of microelectrodes elsewhere ?
Marco.Sampietro@polimi.it
Rf
+ -
VCE
Vout
SiO2
Electrolyte
200 nm
CE
Conductive
ADDITIONALspurious signal.
Very big !
Beware of conductive substrate !
THINGS to REMEMBER (1)
Conductive substrate promotes additional path for spurious signal (BAD)
Marco.Sampietro@polimi.it
THINGS to REMEMBER (2)
Accuracy and resolution can be affected very hard (bad)
SiO2
200 nm
CE
Conducting
Electrolyteis at ground
Rf
+ -
Vout
Cdetvery BIG
Also the pad contributes !
Beware of conductive substrate !
BIG noise
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