Abstract:
Organic electronics is a rapidly growing technology that is expected to compete
with conventional microelectronics in the near future. Organic active materials
based devices such as junction diodes, sensors, FETs, solar cells, OLEDs,
RFIDs and memories will enable future generations of electronics products that
may ultimately enter the mainstream electronics market. The interest of
researchers and industry in organic electronics is mainly for its advantages of
offering
inexpensive,
environmental friendly
flexible
and
large
manufacturing
area
processes.
electronic
In
the
devices with
research work
undertaken in this dissertation, methyl-red (MR), 5,10,15,20-Tetrakis(3’,5’-di-tert-
butylphenyl) porphyrinatocopper(II) (TDTPPCu) and polymethylsilsesquioxane
(PMSSQ) nanocomposite are investigated as active materials for their potential
applications in organic electronics. These organic materials belong to the families
of azo dyes, macrocyclic compounds and polymer nanocomposites. Employing
these materials, sensors, a field effect transistor and non-volatile memory cells
are fabricated and characterized.
Using methyl-red thin film based metal/organic/metal structures are investigated.
The potential applications of methyl-red for organic rectifying junctions and
humidity sensors are demonstrated successfully. The methyl-red based surface-
type diodes fabricated with different electrodes exhibited high rectification ratio.
In the case of Au/methyl-red/Ag surface-type diode, the rectification ratio of the
order of 105 is achieved, which is the 2nd highest rectification ratio ever attained
for organic diodes. Various electrical parameters of these methyl-red based
devices have been determined using conventional current-voltage (I-V) method,
Abstract
Cheungs' functions and modified Norde’s function. The electrical parameters
obtained using different techniques are found in reasonable agreement. The
humidity-dependent-characteristics of methyl-red are also studied in the surface-
type capacitive and resistive sensors. Significant changes in the capacitance and
resistance of the sensors are observed under the effect of different relative
humidity
(RH)
levels.
The
methyl-red
based
sensors
exhibit
fast
response/recovery time and very small hysteresis. All these interesting features
make methyl-red a promising material for electronics applications.
To determine the potential of TDTPPCu for electronics applications, n-
Si++/TDTPPCu/Al device is fabricated and its electrical properties are
investigated. The current-voltage characteristics of the device are observed
nonlinear and asymmetric. Using these characteristics, the junction parameters
are calculated. Subsequently, TDTPPCu is studied as an active material for
multifunctional capacitive sensors and photo-field effect transistor (photo-FET).
The TDTPPCu based light, humidity and temperature sensors are studied in
surface-type structures. The capacitance of the photo sensor is increased by 4.7
times from the dark condition under an illumination of 3850 lx. In the case of the
humidity sensor the capacitance of the sensor changed 9.5 times with the
increase in relative humidity (RH) from 30% to 95%. No change in capacitance
appeared in the temperature sensor below 120 °C. Based on the experimental
results, a mathematical model for the multifunctional sensors has been
developed which explains the basic sensing mechanisms of the sensors. The
sensors are simulated using this model. The simulated results match well with
the experimental results. The effect of light on the output characteristics of a very
simple and novel structured photo-FET is also investigated. The transistor is
fabricated by employing the TDTPPCu as a channel material. Light, instead of
the gate voltage, is used for controlling the drain-source current. Significant
Abstract
change in the drain-source current is observed under illumination. The photo-
FET structure might lead to advancement in the understanding of photo-physics
and electronic processes in organic semiconductors that can direct to efficient
devices, modified to the specific requirement without the limitations imposed by
conventional semiconductor technology.
Employing a nanocomposite of PMSSQ non-volatile memory (NVM) cells are
fabricated for the first time. The electrical behavior of PMSSQ nanocomposite
thin films and possibility of nano-traps formation and charge storage in the films
have been studied. Later, a nano-trapped NVM using the nanocomposite is
investigated. Capacitance-voltage (C-V) analysis is performed to examine the
memory effect. A wide clockwise hysteresis window of 12 V is observed, which
indicates the high charge storage capability of the nanocomposite film. A model
for charge trapping mechanism and potential distribution in the NVM cells have
been proposed which elucidates the charge trapping and detrapping mechanism
in the composite. The programmed/erased characteristics of the composite
based memory cells show the great potential of this nanocomposite for practical
applications. The proposed model will help in further understanding in the charge
trapping and detrapping mechanism in the nanocomposite based memories.