The paper presents the creation of well aligned, vertically oriented, single crystal, high aspect ratio zinc oxide nanorods
(ZnO NRs) for the purpose of gas detection in a chip based sensor. It is hypothesized that the best sensor functionality
will be observed when the ZnO NRs are uniform and well controlled in their growth. The resulting process will
maximize aspect ratio and attempt to find an optimal NR density for surface gas absorption.
Solar cells currently used are silicon based because they have higher efficiency than cells from other materials, but the
manufacturing cost is high. Though, cheaper cells can be fabricated using organic materials because it solution
processable, the efficiency is very low. Hybrid solar cells have improved the efficiency of organic solar cells. Hybrid
solar cells with ZnO nanorods as the inorganic and P3HT (poly 3-hexylthiophene) and PCBM ((6, 6)-phenyl C61 butyric
acid methyl ester) as the active layer reported in literature is usually prepared by spin coating. The major drawback of
using spin coating technique is that large area fabrication is not possible and material wastage makes this technique
uneconomical. Large scale production is feasible if these cells can be prepared by spray coating. Here we will discuss the
fabrication and characterization of hybrid solar cells by spray coating technique.
Detectors currently used for UV detection are Si based and photomultiplier tubes, but these are bulky and less sensitive.
ZnO based detector is an alternative to silicon and photomultiplier tubes due to its high sensitivity to UV light and can be
fabricated cheaply and compactly. Here we attempt to increase the sensitivity of ZnO based detector by using electrode
design that resembles a Wheatstone bridge and the detector has metal-semiconductor-metal structure. This new
improved design enhances the collection of carriers and also miniaturization of the detector. The nanorods for the
detector were grown by solution growth technique and the response of the detector on the length of the interdigitated
fingers and spacing between the interdigitated fingers were also studied.49518
ZnO nano rods were grown by aqueous chemical growth technique over ZnO seeds in mesh form deposited on ITO
coated glass substrate. The structural and morphological analysis of the seed layer and the nano rods were studied, both
the seed and the nano rods are crystalline in nature and majority of the planes are oriented along the C-axis. Over the
nano rods layer P3HT (poly 3-hexylthiophene)/PCBM ((6, 6)-phenyl C61 butyric acid methyl ester) blend, PEDOT: PSS
(Poly ethylenedioxythiophene doped with poly styrene sulphonic acid) were successively spin coated and Gold was
coated as the top electrode by electron beam evaporation. The Current (I) vs. Voltage (V) characteristics of the device
was measured without illumination and with illumination. The device showed an ohmic behavior instead of rectifying
behavior.
Potassium ion monitoring, in human body, is important for diagnostic and therapeutic purposes. The
dynamic response of potassium selective ISFET sensors is instrumental in formulating calibration schema
and signal compensations to correct systematic errors. In the research reported here, response
characteristics of potassium selective ISFETs were studied. The range of detection was set between 1mM
and 25mM to cover all the physiological potassium concentrations. The signals were obtained from an
array of sensors, with different aspect ratios, by varying potassium ion concentrations in a time dependent
fashion. Normalization of the drain current was used to compensation for variance in order of magnitude
observed in different sensors. Sensor response time and linear response range were analyzed, in relation to
difference in aspect ratios. Probable modifications in calibration scheme and compensation technique,
subjective to the findings, have been suggested.
Ion Sensitive Field Effect Transistors (ISFETs) for sensing change in ionic concentration in biological
systems can be used for detecting critical conditions like Myocardial Ischemia. Having the ability to yield
steady signal characteristics can be used to observe the ionic concentration gradients which mark the onset
of ischemia. Two ionic concentrations, pH and [K+], have been considered as the indicator for Myocardial
Ischemia in this study. The ISFETs in this study have an organic
semi-conductor film as the electronically
active component. Poly-3 hexylthiophene was chosen for its compatibility to the solution processing, which
is a simple and economical method of thin film fabrication. The gate electrode, which regulates the current in the active layer, has been employed as the sensor element. The devices under study here were fabricated on a flexible substrate PEN. The pH sensor was designed with the Tantalum Oxide gate dielectric as the ion selective component. The charge accumulated on the surface of the metal oxide acts as the source of the effecter electric field. The device was tested for pH values between 6.5 and 7.5, which comprises the variation observed during ischemic attack. The potassium ion sensor has got a floating gate electrode which is functionalized to be selective to potassium ion. The device was tested for potassium ion concentration between 5 and 25 mM, which constitutes the variation in extra cellular potassium ion concentration during ischemic attack. The device incorporated a monolayer of Valinomycin, a potassium specific ionophore, on top of the gate electrode.
In this paper, gate-induced pentacene semiconductor strain sensors based on hybrid-gate dielectrics using poly-vinylphenol
(PVP) and high-K inorganic, Ta2O5 are fabricated on flexible substrates, polyethylene naphthalate (PEN).
The Ta2O5 gate dielectric layer is combined with a thin PVP layer to obtain very smooth and hydrophobic surfaces which improve the molecular structures of pentacene films. The PVP-Ta2O5 hybrid-gate dielectric films exhibit a high dielectric capacitance and low leakage current. The sensors adopting thin film transistor (TFT)-like structures show a significantly reduced operating voltage (~6V), and good device characteristics with a field-effect mobility of 1.89 cm2/V•s, a threshold voltage of -0.5 V, and an on/off ratio of 103. The strain sensor, one of the practical applications in large-area organic electronics, was characterized with different bending radii of 50, 40, 30, and 20 mm. The sensor output signals
were significantly improved with low-operating voltages.
Ion-sensitive Field-Effect Transistors (ISFETs) have been applied for in vitro and online detection for clinical purposes
such as concentration of urea, penicillin-G and potassium ion (K+). They have proven to be highly sensitive, shown less
response time, reproducible and smaller than the piecewise assembled conventional biosensors. Materials like p3HT,
Tantalum Oxide and PVA-SbQ have show their merit as components of various FETs fabricated on silicon substrate.
This paper discusses the feasibility of using them together along with design enhancements such as zigzag inter-digitated
electrode. The results hitherto obtained have been analyzed and conclusions are drawn to set future course of
experimentation to develop the ISFET for sensor applications.
Design and fabrication of Organic Thin Film Transistor (OTFT) based miniaturized piezoelectric sensor is presented in
this investigation. The device is fabricated on flexible polyethylene naphthalate (PEN) film, using the small-molecule
hydrocarbon pentacene as the semiconductor layer and solution-processed polyvinylphenol as the gate dielectric. Field
effect mobility of the OTFT is greater than 0.01 cm2/Vs, Ion/Ioff current ratio greater than 105. The piezoelectric polymer,
Polyvinylidene Fluoride (PVDF) is used as the sensor layer that is attached over the extended gate metal electrode of the
OTFT. OTFT, which is in close proximity with sensor, serves as the amplifier to amplify the signal generated by
piezoelectric sensor.
In this study, strain sensors consisting of a pentacene-carbon nanotubes (CNTs) composite layer are fabricated on
flexible substrates, Kapton polyimide films, employing Wheatstone bridge configuration. The sensors were characterized
with bending at 45° with respect to the bridge bias direction for two different bending radii of 50, and 40mm that
corresponds to strains of 1, and 1.25 %, respectively. It was noted that the output signal of the sensors is substantially
enhanced with the addition of CNTs, resulting from the improvement in conductivity of the sensing active layer. This
strain sensor using CNTs-organic semiconductor matrix composite as the active layer fabricated on flexible substrates is
expected to possess better reliability as compared with conventional metallic foils and inorganic semiconductor strain
sensors because of their low Young's modulus (~5GPa). For instance, the high Young's modulus of micro crystalline
silicon (~200GPa) limits its applications for sensors when fabricated on polymeric substrates due to the large modulus
mismatch between them.
Organic semiconductors, such as pentacene, are particularly interesting because of its potential for various applications
including thin film transistors (TFTs), electronic papers, radio frequency identification cards (RFIDs), and sensors. In
this paper, we review recent progress in organic electronics with emphasis on their applications for sensing devices, and
investigate the morphologies of pentacene films deposited on SiO2 and Si surfaces at different substrate temperatures.
Scanning electron microcopy (SEM) micrographs from a nominally 50nm-thick pentacene film on SiO2 indicate that the
grain sizes of pentacene film increase with an increase in substrate temperature. In addition, the grain size on clean
silicon grown at a substrate temperature of 100 degrees C is markedly larger that on SiO2, ranging 10~20μm. Based on this
morphological investigation on pentacene films, various types of organic sensors and devices with conjunction with
interdigitated, gated and ungated structures are presented.
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