Post on 20-Mar-2018
Fabrication and Sensing Properties of Nanowire FET Arrays
NanowireSensor RTD 2009
Nanowire field effect transistor (FET) arrays are developed as a platform for an ion and (bio)-chemical sensor that enables an electrical and label-free detection of charged particles. The sensing mechanism is based on the modification of the conductance through the silicon nanowire due to the adsorption of the target ions or molecules. To enable the specific detection of (bio-) analytes, the surface of the nanowire has to be functionalised with appropriate receptors.
1Paul Scherrer Institut, Villigen PSI, Switzerland2University of Basel, Department of Physics, Basel, Switzerland
1K. Bedner*, 1V. A. Guzenko, 2A. Tarasov, 2M. Wipf, 1R. A. Minamisawa, 2O. Knopfmacher, 2D. Just, 2R. L. Stoop, 2J. Brunner, 2W. Fu, 1C. David, 2M. Calame, 1J. Gobrecht, 2C. Schönenberger
MOTIVATION RESULTS
1 10 10010-12
10-11
10-10
10-9
10-8
10-7
SV (
V2 rm
s/Hz)
f (Hz)
4.3MΩ 9.2MΩ 15.4MΩ 25.8MΩ 39.6MΩ 90.7MΩ
Vbg
=-4V
Vds
=0.09V
1/f
width=100nm
pH 7
R
OUTLOOK
Analysis of noise measurements:- signal-to-noise ratio- detection limit- operating range- influence of the nanowire width
Vbg
Vref
Vlg
V
Vsd
A
A
0 200 400 600 800 10000
10
20
30
40
50
60
70
Wtop
(nm)
HfO2
Al2O
3
sens
itivi
ty (
mV
/pH
)
Sensitivity
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.510-10
10-9
10-8
10-7
10-6
10-5
10-4
Vref
(V)
W(top)
=100nm
W(top)
=1µm
pH = 4, 7, 10
G (
S)
Vsd
=0.1V
Vbg
=0V
HfO2
Transfer Curves(subthreshold regime)
Wbottom
Wtop Wside
silicon
SiO2
signal: transfer curves shift withchanging pH value
3 4 5 6 7 8 9 10 11
-1.3
-1.2
-1.1
-1.0
-0.9
-0.8
-0.7
W(top)
=100nm
W(top)
=150nm
W(top)
=200nm
W(top)
=200nm
Vre
f (V
) at
20n
S
pH
Vds
=0.1 V, Vbg
=0 V
HfO2
61 mV/pH
pH Response (subthreshold regime)
pH-response: linear, negligiblehysteresis, ideal sensitivity
comparison of different nanowirewidths: transfer curves have tobe normalized by Weff=2Wside+Wtop
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.50.0
0.5
1.0
1.5
2.0
2.5
3.0 W(top)
=100nm
W(top)
=1µm
pH = 4, 7, 10
G/ W
eff (
S/m
)
Vref
(V)
HfO2
Vds
= 0.1V
Vbg
= 0V
Transfer Curves(linear regime)
Weff = 2Wside+ W top
0 200 400 600 800 10000
1
2
3
4
5
6
7
HfO2 10nm
HfO2 20nm
Al2O
3 20nm
-gm /
Wef
f (S
/Vm
)
W top
(nm)
Vds
= 0.1V
Vbg
= 0V
Transconductance g m
normalized transconductance gmis similar for different nanowirewidths: sensitivity is indepen-dent of nanowire widths
ideal sensitivity of 60mV/pH at 300K sensitivity indendent of nanowire widths same sensitivity for Al2O3 and HfO2
sensitivity is a surface property
KatpHmVV
pHpHq
TkV pzc
B
300/60
)(3.2
max =∆
−−=∆ α
V
Ggm ∆
∆=
∆V
∆G
gm
INFLUENCE OF THE NANOWIRE WIDTH
• Vsd drives current through the nanowire• Vbg modulates the conductivity• Vlg is swept to measure transfer curves• Vref measures the potential in the liquidanalyte: pH buffer solutions
-0.5 0.0 0.5 1.0 1.5 2.00
2
4
6
8
Vsd
=0.1V
NW 1 NW 2
G (
µS)
Vref
(V)
Vbg
=-6V
pH 7
10-10
10-9
10-8
10-7
10-6
10-5
width =1µm
G
(S
)
120mV/dec
Al2O
3
Transfer Curves
• reproducible electrical characteristics• negligible hysteresis• no leakage currents
EXPERIMENT SUMMARY
• successful fabrication of silicon nanowire sensors: - nanowire widths: 100nm to 1µm
• ideal pH-sensitivity : - Al2O3 and HfO2 as detection surface
• sensitivity is independent of nanowire width (subthreshold & linear regime) feasible to use nanowire FET arrays for multiplexed detection
Measurement Set-up
SENSOR FABRICATION
liquidelectrode
sourcecontacts
draincontact
liquidchannel
backgatecontact
PMMA
metal
silicon
silicon oxide resist
metalALD oxide
epoxy
HfO2,Al2O3
100 nm
5µm
lithography wet and dry etching ion implantationof contacts
ALD deposition contact metallization
40µm
100µm
10x10mm
bonding, microfluidicfunctionalization
SU-8/PDMS
• 48 nanowires per sample• nanowire width: 100nm – 1µm• nanowire length: 6µm