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Low-Frequency Noise in Field-Effect Devices 
Functionalized with Dendrimer/Carbon-
Nanotube Multilayers 
Ferdinand V. Gasparyan, Arshak Poghossian, Svetlana A. Vitusevich, Mykhaylo V. Petrychuk, 
Viktor A. Sydoruk, Jose R. Siqueira Jr., Osvaldo N. Oliveira Jr., Andreas Offenhäusser, and 
 Michael J. Schöning 
 
Abstract—Low-frequency noise in an electrolyte-insulator-
semiconductor (EIS) structure functionalized with multilayers of 
polyamidoamine (PAMAM) dendrimer and single-walled carbon 
nanotubes (SWNT) is studied. The noise spectral density exhibits 
1/fγ dependence with the power factor of γ ≈ 0.8 and γ = 0.8 - 1.8 for 
the bare and functionalized EIS sensor, respectively. The gate-
voltage noise spectral density is practically independent of the pH 
value of the solution, and increases with increasing gate voltage or 
gate-leakage current. It has been revealed that functionalization of an 
EIS structure with a PAMAM/SWNTs multilayer leads to an 
essential reduction of the 1/f noise. To interpret the noise behavior in 
bare and functionalized EIS devices, a gate-current noise model for 
capacitive EIS structures based on an equivalent flatband-voltage 
fluctuation concept has been developed. 
 
Index Terms—Low-frequency noise, field-effect sensor, carbon 
nanotube, dendrimer. 
 
I. INTRODUCTION 
The functionalization of electrolyte-gate field-effect devices 
(FED), like ion-sensitive field-effect transistors (ISFET), 
capacitive electrolyte-insulator-semiconductor (EIS) structures 
and light-addressable potentiometric sensors, with nano- and 
biomaterials is one of the most attractive approaches for the 
development of (bio-)chemical sensors and biochips. Since 
FEDs are charge-sensitive devices, each (bio-)chemical 
reaction leading to chemical or electrical changes at the gate 
insulator/electrolyte interface can be detected by coupling the 
gate with respective chemical or biological recognition 
elements. These devices have been shown to be versatile tools 
for detecting pH, ion concentrations, enzymatic reactions [1]–
[3], charged macromolecules (DNA (deoxyribonucleic acid), 
proteins, polyelectrolytes) (see e.g., [4]–[6]), cellular 
metabolisms and action potentials of living cells [7], [8]) as 
well as for designing biocomputing logic gates [9]. More 
recently, nanoparticles [10]–[12], silicon nanowires [13], [14] 
and carbon nanotubes [15] have attracted significant interest 
as a promising material for novel nanoscale bioelectronic 
devices, due to their excellent electronic and chemical 
properties, leading to an enhanced sensor performance. 
 
Manuscript received Februar 9, 2010. 
 F. V. Gasparyan is with the Yerevan State University, 1 Alex Manoogian 
St., 0025 Yerevan, Armenia (e-mail:fgaspar@ysu.am). 
 A. Poghossian and M. J. Schöning are with the Institute of Nano- and 
Biotechnologies, Aachen University of Applied Sciences, Ginsterweg 1, 
52428 Jülich, Germany, and Jülich-Aachen Research Alliance for Future 
Information Technology (JARA-FIT), Forschungszentrum Jülich, 52425 
Jülich, Germany (e-mail: a.poghossian@fz-juelich.de; m.j.schoening@fz-
juelich.de). 
S. A. Vitusevich, V. A. Sydoruk, and A. Offenhäusser are with the Institute 
of Bio- and Nanosystems, Jülich-Aachen Research Alliance for Future 
Information Technology (JARA-FIT), Forschungszentrum Jülich, 52425 
Jülich, Germany (e-mail: s.vitusevich@fz-juelich.de; v.sydoruk@fz-
juelich.de; a.offenhaeusser@fz-juelich.de). 
M. V. Petrychuk is with the Taras Shevchenko National University, 01033 
Kyiv, Ukraine (e-mail: pmichail@mail.ru). 
J. R. Siqueira Jr. and O. N. Oliveira Jr. are with the Physics Institute of São 
Carlos, University of São Paulo, 369, São Carlos, Brazil (e-mail: 
junior@ifsc.usp.br; chu@ifsc.usp.br). 
The study of noise spectroscopy can give additional insight 
into the detection mechanism and detection limit of 
biosensors. An investigation of a signal/noise ratio in FEDs is 
especially important in case of an application of FEDs for the 
measurement of low analyte concentrations, for the detection 
of biomolecules by their intrinsic molecular charge [4]–[6], as 
well as for the monitoring of action potentials of living cells, 
where the sensor output signal can be very small [7], [8]. On 
the other hand, noise measurements could be a very sensitive 
method for the analysis of the semiconductor/metal interface 
quality as well as for the quantitative determination of an 
analyte concentration as it has been shown for H2 gas sensors 
in [16], [17]. While the noise has been extensively studied in 
MOSFETs (metal-oxide-semiconductor field-effect transistor) 
and related devices [18], [19], so far, the noise investigation in 
electrolyte-gate FEDs has been limited to transistor structures. 
For instance, low-frequency (LF) noise of a drain current of 
Al2O3-gate pH-sensitive ISFETs was studied in [20], [21]. 
More recently, drain current noise in ISFETs modified with 
DNA molecules [22] and in electrolyte-gate carbon-nanotube 
transistors [23], [24] as well as Nyquist noise of cell adhesion 
in a neuron-transistor hybrid [25] has been investigated. In 
contrast, very little is known about the noise in field-effect 
capacitive structures [26]. 
In this work, LF noise in a capacitive field-effect EIS 
structure functionalized with polyamidoamine (PAMAM) 
dendrimer/SWNT (single-walled carbon nanotube) 
multilayers has been investigated and compared with noise in 
a bare EIS device. In contrast to transistor structures, 
mailto:a.poghossian@fz-juelich.de
mailto:m.j.schoening@fz-juelich.de
mailto:m.j.schoening@fz-juelich.de
mailto:s.vitusevich@fz-juelich.de
mailto:a.offenhaeusser@fz-juelich.de
mailto:junior@ifsc.usp.br
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capacitive EIS sensors are simple in layout and cost-effective 
in fabrication (usually, no photolithographic process steps or 
complicated encapsulation procedures are required). In 
addition, it has been reported that functionalization of FEDs 
with carbon nanotubes incorporated into layer-by-layer (LbL) 
prepared dendrimer films enhances their biosensor 
performance [27], [28]. As it will be demonstrated below, the 
functionalization of an EIS structure with a PAMAM/SWNT 
multilayer leads to an essential reduction of LF noise. 
II. FABRICATION AND FUNCTIONALIZATION OF EIS 
STRUCTURES 
Capacitive Al-p-Si-SiO2-Ta2O5 structures with a 30 nm 
thermally grown SiO2 and a 55 nm Ta2O5 layer were 
fabricated. The Ta2O5 layer has been prepared via electron-
beam evaporation of 30 nm Ta followed by thermal oxidation 
at 515 °C for about 30 min [29]. As contact layer, a 300 nm 
Al film was deposited on the rear side of the Si wafer and 
then, the wafer was cut into single chips of 10 mm x 10 mm 
size. The EIS sensor was mounted into a home-made 
measuring cell and sealed by an O-ring to protect the side 
walls and backside contact of the chip from the electrolyte 
solution. The contact area of the EIS sensor with the solution 
was about 0.5 cm2. 
The LbL assembly technique has been recognized as a very 
attractive tool for fabricating functional hybrid materials and 
nanostructured films, because it offers fine control over film 
thickness and architecture at the nanoscale. The 
PAMAM/SWNT multilayers were obtained via consecutive 
dropping of the respective PAMAM (for 5 min) and SWNT 
(for 10 min) solutions onto the sensor surface, followed by 
rinsing and drying steps. These procedures were repeated until 
the required number of bilayers was achieved (in this study 3-
bilayers). Fourth generation G4 PAMAM dendrimers and 
SWNTs functionalized with carboxylic groups were 
purchased from Aldrich Co. In aqueous solution, carboxylic 
groups of the SWNTs deprotonate to carboxylate anions 
(COO-), yielding negatively charged SWNTs. Since at the pH 
values of the solutions used the surface of aTa2O5 layer is 
negatively charged, we started the formation of the LbL 
multilayers with the positively charged PAMAM dendrimers. 
Fig. 1 shows the schematic of the EIS structure functionalized 
with a multilayer of PAMAM/SWNT (a) and the chemical 
structure of the materials employed (b). For the details of LbL 
formation of PAMAM/SWNT multilayers, see e.g., [27], [28]. 
The morphology of the prepared PAMAM/SWNT films has 
been studied with an atomic force microscope (AFM) BioMat 
Workstation (JPK Instruments, Germany). Fig. 2 illustrates a 
tapping mode liquid-cell AFM image of the functionalized 
sensor surface. The scan size was 5 µm x 5 µm. The prepared 
LbL film represents an interconnected network structure with 
randomly oriented SWNTs. The presence of deprotonated 
carboxylic groups on the nanotubes facilitates their 
electrostatic interaction with the positively charged PAMAM 
molecules. The film has a high porosity due to the 
interpenetration of the SWNT network into the dendrimer 
layers. 
III. RESULTS AND DISCUSSION 
A. C-V characteristics and pH sensitivity of bare and 
functionalized EIS sensors 
The adsorption of each PAMAM or SWNT layer was 
monitored by means of capacitance-voltage (C–V) method at a 
frequency of 120 Hz using an impedance analyser (Zahner 
Elektrik, Germany). The measurements have been performed 
in a pH 7 buffer solution in a Faraday cage at room 
temperature. For experiments, a DC (direct current) 
polarization voltage is applied via the reference electrode 
(conventional liquid-junction Ag/AgCl electrode, Metrohm) 
and a small AC (alternating current) voltage (20 mV) is 
applied to the system in order to measure the capacitance of 
the sensor (see Fig. 1a). All potential values are referred to the 
Ag/AgCl reference electrode. 
The total capacitance of the EIS structure functionalized 
with PAMAM/SWNT layers, C, can be described as a series 
connection of the space-charge capacitance of the 
semiconductor, Csc, the capacitance of the gate insulator, Ci,, 
and the effective capacitance of the PAMAM/SWNT 
multilayer, CML: 
MLisc CCCC
1111
++= . (1) 
Csc, and therefore C, is among others a function of the gate 
voltage (Vg) applied to EIS structures and the potential at the 
gate insulator/electrolyte interface after the PAMAM/SWNT 
adsorption. Fig. 3a shows typical C-V curves for the EIS 
structure before and after each step of functionalization. 
Similar to the bare EIS structure, dependent on the magnitude 
and polarity of the applied gate voltage, three regions in the C-
V curves can be distinguished: accumulation (Vg<-1 V), 
depletion (-0.6 V<Vg<0 V) and inversion (Vg>0.2 V). As it can 
be seen, after the adsorption of three bilayers of 
PAMAM/SWNT, the maximum capacitance in the 
accumulation range of the C-V curves remains nearly 
unchanged. Taking into account that the maximum 
capacitance in the accumulation range of the C-V curve is 
approximately equal to the gate capacitance, i.e., Cmax=Ci and 
Cmax(PAMAM/SWNT)=CiCML/(Ci+CML) for the bare and 
PAMAM/SWNT-covered EIS structure, respectively, it can be 
concluded that the CML is much higher than Ci. 
On the other hand, relatively large shifts (20 mV after the 
adsorption of the first PAMAM1 layer, and about 10 mV after 
the adsorption of further SWNT or PAMAM layers) have 
been registered along the voltage axis in the depletion range of 
the C-V curves. These shifts can clearly be recognized from 
the zoomed graph in the depletion region at ~60% of the 
maximum capacitance (see Fig. 3b). This indicates that the 
adsorption of a PAMAM or SWNT layer induces an 
interfacial potential change at the electrolyte side and/or gate-
insulator side of the layer that is in series to the applied gate 
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voltage Vg. The direction of the shift along the voltage axis 
depends on the sign of the charge of the adsorbed dendrimer 
molecules or SWNTs. In case of the adsorption of the 
positively charged PAMAM, the potential shifts in the same 
direction as for the case of an additional positive charging of 
the Ta2O5 surface. Consequently, the direction of the potential 
change after adsorption of negatively charged SWNTs 
corresponds to the case as if the Ta2O5 surface would have 
been additionally negatively charged. Similar effects were 
reported for a polyelectrolyte multilayer formation onto a p-
Si-SO2 [30], [31] and a p-Si-SO2-diamond [32] capacitive EIS 
sensor. 
Before the noise experiments, the gate-leakage current and 
the pH sensitivity of bare and functionalized p-Si-SiO2-Ta2O5 
sensors have been examined. The gate-leakage current in the 
accumulation range was higher (~2-6 nA) than in the 
depletion and inversion range (~0.2-0.4 nA). In addition, in 
the accumulation region the gate-leakage current for a bare 
EIS structure was 2-3 times higher than in case of a 
functionalized EIS sensor. This could be attributed to the 
blocking of some of the current paths across the gate area 
covered with the PAMAM/SWNT multilayer. The EIS 
sensors with a bare Ta2O5 gate insulator show a pH sensitivity 
of about 56-57 mV/pH in the range from pH 3 to pH 11, 
which is in good agreement with values typically reported for 
a Ta2O5 layer [33], [34]. The presence of the PAMAM/SWNT 
film did not affect significantly the pH sensitivity of the EIS 
structure (54.5 mV/pH). This behavior could be attributed to 
the high porosity of the PAMAM/SWNT film allowing the 
penetration of H+- or OH--ions to the Ta2O5 surface. 
B. Low-frequency noise in bare and functionalized EIS 
structures 
Noise spectra of bare and functionalized EIS sensors were 
recorded in a frequency range from 0.06 to 100 Hz using the 
experimental setup shown in Fig. 4. A voltage from battery E 
was applied to the EIS structure via a load resistance (R=10 
MΩ) and an Ag/AgCl liquid-junction reference electrode. The 
noise signal from the EIS sensor was amplified using a home-
made ultra-low-noise preamplifier and a low-noise amplifier 
(LNA) ITHACO 1201. The LNA output was connected to an 
HP 35670A dynamic signal analyzer, which records the noise 
signal and transforms it into a frequency spectrum using the 
FFT (Fast Fourier Transform). The measuring cell with the 
EIS sensor, reference electrode and LNA were placed in a 
shielding box for protection from external electromagnetic 
influences. Before the noise experiments in EIS structures, the 
internal noise level in the measuring system (without EIS 
sensor) was checked. The noise level from the circuits, 
preamplifier and amplifier were several orders of magnitude 
lower than noise in EIS structures under test. 
The LF noise spectra were measured in buffer solutions of 
pH 3, pH 7, and pH 11 in accumulation, depletion and 
inversion regions of the C-V curve by applying different gate 
voltages. We have observed that the pH value of the buffer 
solution did not significantly influence the noise spectral 
density. This is in agreement with results obtained on pH 
ISFETs [20], [21]. It has been reported that the gate-referred 
1/f noise of the channel current of pH ISFETs is also 
independent of the pH, and the origin of LF noise in these 
ISFETs is the trapping/detrapping of carriers at the Si-SiO2 
interface [20], [21]. Moreover, it has been discussed that the 
ionic strength of the solution does not affect the noise 
magnitude of liquid-gated SWNT transistors [23]. These 
results suggest that the interface between the solution and the 
gate insulator does not or not significantly contribute to the 1/f 
noise. 
Fig. 5 depicts the gate-voltage noise-power spectral density 
(NSD), SV, as a function of frequency for the bare (a) and 
functionalized EIS structure (b), recorded in a pH 7 buffer 
solution at applied gate voltages of -1.5, -1.2, -0.4, 0, and 0.5 
V, respectively. As can be seen, the measured NSD exhibits 
an 1/fγ dependence, whereas the amplitude of the NSDdepends on both the applied gate voltage and the frequency 
range. At frequencies of f<1 Hz, the power factor estimated 
from Fig. 5 was approximately γ ≈ 0.8 and γ = 0.8 - 1.8 for the 
bare and functionalized EIS sensors, respectively. The noise in 
the bare EIS structure shows a strong dependence on the 
applied gate voltage (see Fig. 5a). Moreover, the LF noise is 
much higher in the accumulation region of the C-V curve at 
applied voltages of -1.5 and -1.2 V. Similar effects have been 
observed for Al-SiO2-n-Si MOS capacitors showing RTS 
(random telegraphic signals) noise [35]. However, in our 
structures no RTS noise behavior was registered. In contrast 
to the bare EIS structure, the gate voltage related effects in the 
LF noise of the functionalized EIS sensor are suppressed (Fig. 
5b) which could be attributed to the presence of the 
PAMAM/SWNT multilayer. 
Surprisingly, at frequencies of f <10 Hz and negative applied 
voltages, the noise-reduction effect has been revealed in the 
functionalized EIS structure. This effect depends on both the 
applied gate voltage and the frequency, and is stronger in the 
accumulation regime. As an example, Fig. 6 shows the noise 
spectral density for the bare and functionalized EIS structures 
as a function of the applied gate voltage evaluated from Figs. 
5a and 5b at a frequency of 1 Hz. As can be seen from Fig. 6, 
the presence of the additional PAMAM/SWNT multilayer 
leads to the essential reduction (by the factor of up to 100 in 
the accumulation range) of the 1/f noise in comparison to the 
bare EIS structure. 
C. Noise model for EIS structures 
Several different theories have been proposed to explain the 
physical origin of noise in FEDs. These include the carrier 
number fluctuation theory originally developed by 
McWorther, the mobility fluctuation or Hooge model as well 
as various unified models (see e.g., [18], [19], [36], [37] and 
references there). In addition, recently, a charge fluctuation 
model has been proposed to explain the noise behavior of 
MOS capacitors [26] and carbon nanotubes [23]. Usually, 
low-frequency noise in FEDs is measured in the channel 
current of transistor structures. Typically, 1/f noise in 
MOSFETs has a spectrum with a slope that varies between 0.7 
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and 1.3 [37]. It has been generally accepted that at low 
frequencies, 1/f noise is the dominant source of noise in 
MOSFETs and trap-related processes (due to the 
trapping/detrapping of carriers in traps located in the gate 
oxide, near or at the Si/SiO2 interface) are the major cause of 
1/f fluctuations. The origin of low-frequency noise in the 
channel current of ISFETs has been also explained by the 
trapping/detrapping of carriers at the Si-SiO2 interface in 
according to the carrier-number fluctuation model [20]–[22]. 
In addition, it has been reported that the gate-referred 1/f noise 
(caused by the capacitive coupling between the channel and 
gate) in ISFETs is independent of the gate bias [20]. 
A simple adoption of the carrier-number fluctuation model 
to capacitive EIS structures, however, does not allow to 
completely explain the experimentally observed effects such 
as the dependence of the equivalent gate voltage (or gate 
current) NSD on a gate-voltage or the noise-reduction effect 
in functionalized EIS structures. The noise investigations in 
AlGaN/GaN heterostructure field-effect transistors [38] and in 
MOS devices with ultrathin gate oxides [39]–[42] show that 
one of the possible reasons for the dependence of low-
frequency noise on the gate bias is the contribution of the 
gate-leakage current noise to the output noise. In leaky 
dielectrics, besides the channel current noise, gate-leakage 
current in the gate oxide of MOS devices should be 
considered as an important low-frequency noise source. 
To interpret the results of noise experiments for bare and 
functionalized EIS structures, we describe a gate-current noise 
model for capacitive EIS structures based on an equivalent 
flatband-voltage fluctuation concept that is also used in the 
carrier-number fluctuation noise model for the drain-current 
noise in transistor structures [42]. In general, the flatband 
voltage (a voltage by which the energy bands in the 
semiconductor continue horizontally up to the surface and the 
net-charge density in the semiconductor is zero) of an EIS 
system is given by [4], [43], [44]: 
 
i
iS
solreffb C
Q
q
WEV −−+−= χϕ , (2) 
where Eref is the potential of the reference electrode, ϕ is the 
electrolyte/gate insulator interfacial potential (which can be a 
function of the pH, ion or analyte concentration as well as 
charge of adsorbed molecules), χsol is the surface-dipole 
potential of the solution, WS is the work function of the 
electrons in the semiconductor, q is the elementary charge, 
and Qi is the total insulator charge per unit area including the 
charges located within the gate oxide as well as trapped in 
surface and interface states. Similarly, the flatband voltage of 
the EIS device covered with the dendrimer/SWNT multilayer 
can be defined as: 
 
ML
ML
i
iS
solMLreffbML C
Q
C
Q
q
WEV −−−+−= χϕ , (3) 
where ϕML is the electrolyte/gate insulator interfacial potential 
after the multilayer adsorption, the term QML/CML represents 
the potential drop across the multilayer, and QML is the total 
charge in the dendrimer/SWNT multilayer per unit area, 
which is pH-dependent because of protonation/deprotonation 
of both amino- and carboxylic groups of dendrimers and 
SWNTs, respectively. 
The theoretical modeling of the noise in functionalized 
FEDs is very complicated due to the presence of an 
organic/inorganic hybrid structure. For uncorrelated noise 
sources, the total NSD of a system can be considered as the 
sum of the individual power densities and should include 
noise caused from the reference electrode, electrolyte, 
multilayer of PAMAM/SWNT, oxide/electrolyte and 
multilayer/electrolyte interfaces, and the solid-state device 
itself. As it has been reported previously, the gate-related 1/f 
noise in ISFETs [20], [21] and electrolyte-gated carbon 
nanotube transistors [23] is independent on the pH. Our 
experiments in different pH buffer solutions also show that the 
pH value does not affect significantly the NSD of both bare 
and functionalized EIS structures. Therefore, it can be 
suggested that the interface between the solution and the gate 
insulator as well as charge fluctuations in the 
PAMAM/SWNT multilayer due to the 
protonation/deprotonation processes do not distinctly 
contribute to the 1/f noise. Thus, if the fluctuations in ϕ , ϕML, 
and QML can be ignored, and if the reference electrode and 
electrolyte solution generate no noise, then the flatband-
voltage fluctuations will be associated with the fluctuations of 
the number of trapped charges in the gate insulator: 
 
i
i
fbfbML C
QVV δδδ =~ . (4) 
The spectral density of the gate-current fluctuations (SIg) is 
related to the spectral density of the flatband-voltage 
fluctuations (Sfb) by [42]: 
)(
)(
)( 22
22 fSg
C
fS
gSgfS V
i
Qi
fbIg ≡== , (5) 
where g=δIg/δVg is the gate conductance, Ig is the gate current, 
SV is the spectral density of the voltage fluctuations, and SQi (f) 
is the spectral density of the trapped charge fluctuations. The 
detailed expression for the gate-current (or gate voltage) noise 
spectral density will be defined by the mechanism of current 
transport in a capacitive EIS structure (in this work, an 
electrolyte-Ta2O5-SiO2-Si-Al structure). For a metal-Ta2O5-
SiO2-Si-Al structure, the hopping conduction and tunneling 
were elucidated to be the dominant conduction mechanisms in 
the SiO2 layer and Poole-Frenkel field-assisted emission in the 
Ta2O5 layer [45]. It has been observed that the gate current 
noise in MOS capacitors[39] and MOSFETs [40]–[42] with 
thin gate oxides is increased with increasing gate voltage or 
leakage current, similar to the noise behavior of the capacitive 
EIS structures investigated in this work. This has been 
attributed to the more slow-trap states available for a trap-
assisted tunneling with increasing gate voltage [39]–[42]. 
Noise investigations in Ta-Ta2O5-MnO2 capacitors also show 
a clear dependence of the noise spectral density on the leakage 
current [46]. From the standpoint of gate-leakage current 
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mechanisms and similarities of gate-current noise behavior in 
MOSFETs and EIS structures, it seems that as in MOSFETs, 
the trap-related processes are the most likely cause of low-
frequency gate-current noise in capacitive EIS devices, 
because traps or slow states in oxides can result in a low-
frequency fluctuation-dissipation in the conductance of gate 
oxides [39]. Thus, the gate noise will be proportional to the 
total amount of traps that can be charged/discharged in the 
dielectric. The gate voltage-dependent changes in the 
occupancy of the oxide trap levels will result in a modulation 
of the conductivity of current paths or charge carriers passing 
through the device, which could explain the experimentally 
observed gate-voltage dependence of the noise in capacitive 
EIS structures. In addition, since the EIS devices work in a 
liquid environment, the possible micro- and nanopores or 
pinholes in the gate insulator will be filled with electrolyte 
solution, thus, decreasing the effective thickness of the gate 
insulator in pore regions and generating new current paths. As 
a result, the gate current and therefore, the gate-current noise 
in EIS structures is expected to be higher than in MOS 
structures with the same gate insulator. 
The above proposed noise model might allow also to explain 
the experimentally observed noise-reduction effect in an EIS 
structure functionalized with a PAMAM/SWNT multilayer. 
Although the PAMAM/SWNT multilayer can be considered 
as a porous structure allowing the penetration of solution to 
the Ta2O5 surface, nevertheless, it will screen or block some 
of the current paths across the gate area, thus, decreasing the 
leakage current and the gate-current noise as well as 
suppressing the gate-voltage dependence of the NSD, that in 
fact, has been observed in experiments with a functionalized 
EIS structure. Another possible reason for the observed noise-
reduction effect could be electrochemical processes at the 
Ta2O5/PAMAM and electrolyte/PAMAM/SWNT interface as 
well as the charge redistribution in the PAMAM/SWNT 
multilayer itself. As it has been demonstrated in [27], [28], the 
PAMAM/SWNT multilayer could act as a “stabilizer” 
providing a smaller drift and a more stable sensor signal. 
IV. CONCLUSION 
LF noise in a capacitive field-effect Al-p-Si-SiO2-Ta2O5 EIS 
structure functionalized with a PAMAM/SWNT multilayer 
has been investigated and compared with the noise in a bare 
EIS device. The noise spectral density exhibits an 
1/fγ dependence with the power factor of γ ≈ 0.8 and γ = 0.8 - 
1.8 for the bare and functionalized EIS sensors, respectively. 
The gate-voltage noise spectral density was practically 
independent on the pH value of the solution and is increased 
with increasing gate voltage or gate-leakage current. It has 
been revealed that the existence of the PAMAM/SWNTs 
multilayer leads to considerable reduction of the 1/f noise. The 
gate-current noise behavior in bare and functionalized EIS 
devices has been modeled using the flatband-voltage 
fluctuations concept. The experimentally observed gate-
voltage dependence of the noise in capacitive EIS structures 
can be explained by the gate-voltage-dependent changes in the 
occupancy of the oxide trap levels resulting in a modulation of 
the conductivity of current paths or charge carriers passing 
through the EIS structure. The detailed mechanism of current 
transport in field-effect capacitive electrolyte-
(SWNT/PAMAM)-Ta2O5-SiO2-Si-Al and electrolyte-Ta2O5-
SiO2-Si-Al structures as well as the microscopic origin of the 
noise-reduction effect requires further investigations. 
ACKNOWLEDGMENT 
The authors thank M. Bäcker for the AFM image. Financial 
support from CAPES (Brazil) is gratefully acknowledged. 
F.V. Gasparyan is grateful to German Academic Exchange 
Service (DAAD) for financial support. 
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[12] J. Gun, M. J. Schöning, M. H. Abouzar, A. Poghossian, and E. Katz, 
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Ferdinand V. Gasparyan was born in Yerevan, Armenia, in 1950. He 
received the MSc degree as physics-engineer from Yerevan Polytechnic 
Institute, Yerevan, Armenia, in 1972, the PhD 
degree in 1981, and the Dr. Sci. degree in 1995. He 
is full professor with the Department of Physics of 
Semiconductors and Microelectronics, Yerevan State 
University. He has authored and co-authored more 
than 120 scientific papers and 6 books. His current 
research interests include physical properties and 
internal noises of semiconductors and p-i-n 
structures, IR and UV photodiodes, and 
photoelectrical conversion of solar energy. 
 
 
Arshak Poghossian received his PhD degree in solid-state physics from 
Leningrad Electrotechnic Institute (Russia) in 1978 
and the Dr. Sci. (Engineering) degree in solid-state 
electronics and microelectronics from the State 
Universtity of Yerevan (Armenia) in 1995. After 
being an associate professor at State Engineering 
University of Armenia and director of Microsensor 
Ltd. (Yerevan) from 1991 to 1996, he has been a 
professor at the University of Management and 
Information (Yerevan). Since 1998, he has been 
with the Institute of Thin Films and Interfaces 
(now, Institute of Bio- and Nanosystems) at the 
Research Centre Jülich, and since 2004, he joined the Institute of Nano- and 
Biotechnologies at Aachen University of Applied Sciences, Germany. In 
2008, he has been appointed as Honorary Professor. His research interests are 
solid-state chemical sensors and biosensors, sensor materials, nano-devices, 
microsystem technology, nano- and biotechnology. 
 
 
Svetlana A. Vitusevich received the MSc in radiophysics and electronics, 
Kiev State University, Ukraine, in 1981 and the PhD 
degree in physics and mathematics from Institute of 
Semiconductor Physics (ISP), Kyiv, Ukraine, in 1991. 
From 1981 to 1997, she was with the ISP, Kyiv, 
Ukraine, as researcher (1981), scientific researcher 
(1992), and senior scientific researcher (1994). From 
1997 to 1999, she was Alexander von Humboldt 
Research Fellow at theInstitute of Bio- and 
Nanosystems (former Institute of Thin Films and 
Interfaces) at Forschungszentrum Jülich (FZJ), 
Germany. Since 1999, she is senior scientific researcher at FZJ. She received 
Dr. habil. degree in 2006. Her research interests include transport and noise 
properties of different materials for advanced electronic devices and circuits. 
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Her achievements include more than 110 papers in scientific journals and 7 
patents, among them two for semiconductor functional transformer. 
 
 
Mykhaylo V. Petrychuk received the PhD degree 
(1993) in semiconductor physics from the Institute 
of Semiconductor Physics NAS, Ukraine. He is a 
senior research scientist of the Radio-Engineering 
Department at the National Taras Shevchenko 
University of Kyiv, Ukraine. His primary area of 
expertise is the physics of low-frequency noise in 
semiconductors and devices. His research interests 
include studing of fundamental origin of 1/f noise. 
He has been involved in the investigation of noise 
in low-dimensional quantum structures since 2002. 
He has made a significant contribution to the 
discovery and understanding of non-equilibrium low-frequency noise in GaN-
based structures with two-dimensional conducting channels. He has published 
over 80 journal/conference papers. 
 
 
Viktor A. Sydoruk received the B.S. degree and 
the MSc degree in radiophysics and electronics 
from the National Taras Shevchenko University of 
Kyiv, Ukraine, in 2006 and 2008, respectively. He 
is currently working towards the PhD degree as a 
Graduate Research Assistant under the direction of 
Dr. habil. Svetlana Vitusevich at the Research 
Centre Jülich, Germany. His research focuses on the 
design and characterization of nanostructures, 
understanding the electrical transport in the 
structures using noise spectroscopy and supporting 
instrumentation for study of biosensors. 
 
José R. Siqueira Jr. received his B.S. degree in 
Physics at the Universidade Federal de São Carlos 
in 2004. His MSc and PhD degrees were received in 
Materials Science and Engineering from the Instituto 
de Física de São Carlos at the Universidade de São 
Paulo, Brazil, in 2006 and 2010, respectively. His 
research focuses on the processing and 
characterization of nanostructured films using 
nanomaterials such as carbon nanotubes, 
nanoparticles and dendrimers to develop specific 
units for biosensing within a platform exploiting 
electrochemical measurements in field-effect devices. 
 
Prof. Osvaldo N. Oliveira Jr. is a physics professor 
at the Instituto de Física de São Carlos, Universidade 
de São Paulo, Brazil. He received his PhD from the 
University of Wales, Bangor (UK), in 1990. His 
research interests include nanostructured films, 
especially for applications in sensing and biosensing, 
and natural language processing. He has supervised 
over 30 PhD and MSc. students, authored ca. 330 
papers in refereed journals and filed 7 patents. He is 
currently associate editor for the Journal of 
Nanoscience and Nanotechnology. In 2006 he 
received the Elsevier Scopus Award as one of the most productive Brazilian 
scientists in terms of number of publications and citations. 
 
Andreas Offenhäusser graduated in physics 
(Diplom) from the University of Ulm in 1985 and 
completed his PhD at the University of Ulm in 1989. 
From 1990 to 1992 he worked as an engineer at 
Robert Bosch GmbH, Reutlingen. From 1992 to 1994 
he joined the Frontier Research Program, RIKEN, 
Japan. From 1994 to 2001, he worked at the Max 
Planck Institute for Polymer Research, Mainz, as a 
group leader. In 2000, he received his “habilitation“. 
He moved to the Forschungszentrum Jülich in 2001 
where he is presently director at the Institute of Bio- and Nanosystems (IBN-
2). He is professor for experimental physics at the Rheinisch-Westfälische 
Technische Hochschule (RWTH) Aachen, Germany. The focus of his work is 
the functional coupling of sensory cells and neurons with microelectronic 
devices, signal processing in biological neuronal networks, electronic DNA-
Chips, and biophysics of lipid bilayers and membrane receptors. 
 
 
Michael J. Schöning received his diploma degree in electrical engineering 
(1989) and his PhD in the field of semiconductor-
based microsensors for the detection of ions in 
liquids (1993), both from the Karlsruhe University 
of Technology. In 1989, he jointed the Institute of 
Radiochemistry at the Research Centre Karlsruhe. 
Since 1993, he has been with the Institute of Thin 
Films and Interfaces (now, Institute of Bio- and 
Nanosystems) at the Research Centre Jülich, and 
since 1999 he was appointed as full professor at 
Aachen University of Applied Sciences, Campus 
Jülich. Since 2006, he serves as a director of the 
Institute of Nano- and Biotechnologies (INB) at the 
Aachen University of Applied Sciences. His main research subjects concern 
silicon-based chemical and biological sensors, thin-film technologies, solid-
state physics, microsystem and nano(bio-)technology. 
 
SWNT PAMAM
a) b)
RE
Impedance
analyzer
V=bias
Electrolyte
V~
 
 
Fig. 1. Schematic of the EIS structure functionalized with a multilayer of 
PAMAM/SWNT (a) and chemical structure of the materials employed (b); 
RE: reference electrode. 
 
 
 
Fig. 2. Tapping mode liquid-cell AFM image of the EIS sensor surface 
functionalized with a PAMAM/SWNT multilayer. 
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Fig. 3. C-V curves for a bare pSi-SiO2-Ta2O5 EIS structure and EIS sensor 
functionalized with a PAMAM/SWNT multilayer measured in a buffer 
solution of pH 7 (a), and zoomed C-V curves for the different layers in the 
depletion range (b). 
 
Fig. 5. Voltage noise spectral density (SV) vs. frequency for a bare (a) and 
functionalized (b) EIS structure measured at various Vg: (1) -1.5 V, (2) -1.2 V, 
(3) -0.4 V, (4) 0 V, and (5) 0.5 V. 
 
 
 
 
Fig. 4. Experimental setup for noise measurements. E: battery; R: load 
resistance; DUT: device under test; LNA: low-noise current amplifier; FFT-
analyzer: Fast Fourier Transform analyzer. 
Fig. 6. Noise spectral density for bare and functionalized EIS structures as a 
function of the applied gate voltage evaluated from Figs. 5a and 5b at a 
frequency of 1 Hz. 
	I. INTRODUCTION
	II. FABRICATION AND FUNCTIONALIZATION OF EIS STRUCTURES 
	III. RESULTS AND DISCUSSION
	IV. Conclusion