This work demonstrates a novel surface scanning method for the quantitative determination of the local pyroelectric coefficient in ferroelectric thin films. Such films find application in flexible and large-area printed ferroelectric sensors for gesture-controlled non-touch human-machine interface devices.
The method is called Pyroelectric Scanning Probe Microscopy (PyroSPM)[1] and allows generating a map of the pyroelectric response with very high spatial resolution. In domains of previously aligned dipole moments small heat fluctuations are achieved by laser diode excitation from the bottom side thus inducing changes in the surface potential due to the pyroelectric effect. Simultaneously, the surface potential variations are detected by scanning surface potential microscopy thus forming the base for the pyroelectric coefficient map. The potential of the method is demonstrated on the basis of ferroelectric semi-crystalline copolymer thin films yielding local maxima of the pyroelectric coefficients around 40µC/m2K. Another promising feature of PyroSPM is the ability to visualize “screened” polarization thus enabling in-depth profiling of polarization distributions and domain formation and to study the composition dependence and the time and frequency behavior of ferroelectric nano-domains.
Michael Mühlberger, Hannes Fachberger, Iris Bergmair, Michael Rohn, Bernd Dittert, Rainer Schöftner, Thomas Rothländer, Dieter Nees, Ursula Palfinger, Anja Haase, Alexander Fian, Martin Knapp, Claudia Preininger, Gerald Kreindl, Michael Kast, Thomas Fromherz
The NILaustria research project cluster consists of 8 individual research projects and aims to improve nanoimprint
lithography in an application driven approach. The cluster is presented as well as highlights from the projects, e.g. the
replication of 12.5nm half pitch features using working stamp copies, topics from organic electronics, metamaterials and
SiGe technology. An outlook on the new activities is given.
Martin Sagmeister, Bernhard Lamprecht, Elke Kraker, Anja Haase, Georg Jakopic, Stefan Köstler, Harald Ditlbacher, Nicole Galler, Tobias Abel, Torsten Mayr
We present an integrated optical sensor platform suitable for the parallel detection of multiple parameters in an array
format. This sensor technology combines fluorescent sensor layers with ring-shaped thin-film organic photodiodes
(OPDs), serving as integrated fluorescence detectors. The sensing layers are deposited by screen-printing on the upper
side of a PET substrate, which is exposed to an analyte, whereas the ring-shaped photodiodes are monolithically
integrated, by vapour phase deposition, on the backside of the transparent substrate, in correct alignment to the sensing
layers. The monolithic integration of sensor layers and detectors on one common substrate as well as the special ring
shaped form of the photodiodes guarantees that a maximum of the fluorescent light emitted from the sensor layers is
collected. A key advantage of the above described sensor geometry is the straightforward potential to realise sensor
arrays for the parallel detection of multiple parameters: different sensor spots are illuminated by commercial LEDs or
alternatively with one large area OLED, and are read-out by individual integrated organic photodiodes, surrounding the
respective sensor layers. Three different sensing principles including absorption, fluorescence and surface plasmon
resonance can be applied in the same basic sensor platform. The functionality of the concept is demonstrated by an
integrated oxygen sensor. Sensor schemes for the analytical parameters carbon dioxide, temperature and ammonia, are
proposed. Efficient front end electronics enabling intensity and time domain detection of sensor signals for the testing
and characterisation of the integrated sensor devices have been developed.
A compact, integrated photoluminescence based oxygen sensor, utilizing an organic light emitting device
(OLED) as the light source and an organic photodiode (OPD) as the detection unit, is described. The detection
system of the sensor array consists of an array of circular
screen-printed fluorescent sensor spots surrounded by
organic photodiodes as integrated fluorescence detectors. The OPD originates from the well-known Tang
photodiode, consisting of a stacked layer of copper phthalocyanine (CuPc, p-type material) and perylene
tetracarboxylic bisbenzimidazole (PTCBi, n-type material). An additional layer of tris-8-hydroxyquinolinatoaluminium
(Alq3, n-type material) was inserted between the PTCBi layer and cathode. An ORMOCERR layer
was used as encapsulation layer. For excitation an organic light emitting diode is used. The sensor spot and the
detector are processed on the same flexible substrate. This approach not only simplifies the detection system by
minimizing the numbers of required optical components - no optical filters have to be used for separating the
excitation light and the luminescent emission-, but also has a large potential for low-cost sensor applications.
The feasibility of the concept is demonstrated by an integrated oxygen sensor, indicating good performance.
Sensor schemes for other chemical parameters are proposed.
Here we report on the fabrication and detailed characterization of flexible low-voltage organic thin-film transistors
directly integrated with pyro- and piezoelectric sensors. The functional layer of the capacitive sensors is a ferroelectric
fluoropolymer. The transistors on the other hand are based on a high-k nanocomposite gate dielectric and on pentacene
as the organic semiconductor and can be operated well below 5V. It is shown, that the transistors can be fabricated on the
fluororpolymer layer. Since the control of parameter spread is a very important topic in large area electronics, it was
attempted to investigate the homogeneity of a significant set of devices by individual assessment of the layer
composition and thickness, the pentacene morphology, the actual geometry and the electrical parameters. It turned out
that starting from the measured device parameters such as layer thickness, capacitance, channel dimension, grain size
and threshold voltage, the drain current can be calculated with high accuracy in a specified operation point. In addition, it
is shown that the main influence on the parameter spread originates from the variations in the threshold voltage. Storage
in air destroys the transistors on the long term, whereas bias stress measurements under inert conditions reveal that the
interfaces are very stable.
Solid state lighting offers a lot of novel prospects for tomorrows customized lighting solutions. None the less, to compete
with and to surpass the performance of the traditional lighting systems, design and development of LED light sources is
still facing the necessity of further improvements, in particular with respect to device efficiency and light control. In this
contribution we discuss recent developments and novel strategies in order to improve the light extraction efficiency as
well as to affect the directionality of the light emitted from high power LEDs. In order to be up to characterize these
modifications with high spatial resolution, novel characterization techniques, like the implementation of a confocal
principle into the measurement set-up are discussed.
ITO (tin doped indium oxide) coatings with a sheet resistance of 2 to 3 kΩ(square) were produced by gravure printing process
on PET and PEN foil. The printing paste consisted of ITO nanoparticles which were dispersed in a solvent by using a
surfactant. The dispersion was mixed with a binder and a photo initiator before printing. The printed films were hardened
under UV-irradiation at low temperatures (< 130°C). The sheet resistance could be decreased by heat treatment at 120°C
under forming gas atmosphere (N2/H2) to 1.5 kΩ(square). The transmission of the ITO coated PET and PEN foils is more than
80 % in the visible range.
The ITO films were directly used as the bottom electrode in an organic photodiode (OPD). The setup of the OPD
originates from the well known Tang photodiode, consisting of a stacked layer of copper phthalocyanine (p-type
material) and perylene tetracarboxylic bisbenzimidazole (n-type material). The photodiodes are characterised via current-voltage
(I-V) characteristics. The performance of the photodiodes with printed ITO on plastic substrates could be
improved by the deposition of a PEDOT/PSS layer (Baytron(R) P) on the ITO coated foils and was then comparable to the
performance of photodiodes with semi-transparent gold as anode on PET substrates. These results demonstrate the
suitability of the printed ITO layers as anode for organic photodiodes.
A compact, integrated photoluminescence based oxygen and pH sensor, utilizing an organic
light emitting device (OLED) as the light source and an organic photodiode (OPD) as the
detection unit, is described. The main challenge in such an integrated sensor is the suppression
of the excitation light at the detector, which is typically by many orders of magnitude higher in
intensity than the emitted fluorescence. In our approach we refrain from utilizing edge filters
which require narrowband excitation sources and dyes with an adequate large stoke shift. We
developed an integrated sensor concept relying on two polarizers to separate the emission and
excitation light. One polarizer is located right after the OLED, while the other one, oriented at 90°
to the first, is placed in front of the OPD. The main advantage of this solution is that any
combination of excitation and emission light is acceptable, even if the two signals overlap
spectrally. This is especially important for the use of OLEDs as the excitation sources, as these
devices typically exhibit a broad spectral emission.
Due to its outstanding carrier transport capabilities the aromatic hydrocarbon pentacene is still one of the most promising out of all organic semiconducting materials investigated so far. Pentacene appears in several polymorphic structures that significantly differ with respect to the d(001) spacing. It is shown, that precise control of the epitaxial growth process of thin films enables not only to adjust the formation of the polymorphic phases, but also to influence grain size and shape. The relative volume fraction of the pentacene polymorphs is determined by several parameters which are substrate material, deposition rate, film thickness and substrate temperature. A comparison of X-ray diffraction and Raman measurements reveals that the phase with the smaller layer-by-layer spacing grows on top of the other]. Moreover, there is a strict correlation between evaporation rate and maximum grain size. In addition to structural we also investigated the electrical properties of pentacene thin films focussing on polymorphism and its influence on the transport properties. Apart from the fact that the charge carrier mobility is strongly influenced by the grain size it turned out that the bulk phase is related to a lower intrinisic mobility than the thin film phase.
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