Roll-to-roll UV nanoimprint lithography (R2R-UV-NIL) gains increasing industrial interest for large-area nano- and microstructuring of flexible substrates. It combines the possibility of multi length scale and 2.5D patterning of a functional resist with a square meter per minute productivity.
The fabrication of micro- and nanooptic elements and systems nowadays can be named a classical application of batch NIL. However, large-area application fields like display, photovoltaics or solar cell markets ask for upscaling possibilities with respect to active area and throughput. The combination of direct laser lithography, step+repeat imprinting for shim fabrication and R2R reproduction even offers a much higher diversity of application fields. Free form lenses and mirrors, waveguiding units or complex light manipulating systems add new possibilities for customized photonic systems, security features or large area high-end decoration.
Within this talk we will present the possibilities of combining greyscale laser lithography and roller-based imprinting with functionalized high-k imprint resins and see how to produce meters-per-minute 2.5D optical features on flexible substrates.
In this work we present our most advanced technology node of organic thin film transistors (OTFTs) manufactured with a channel length as short as 2 μm by contact photolithography and a self-alignment process directly on a plastic substrate. Our process design kit (PDK) is described with P-type transistors, capacitors and 3 metal layers for connections of complex circuits. The OTFTs are composed of a double dielectric layer with a photopatternable ultra thin polymer (PNDPE) and alumina, with a thickness on the order of 100 nm. The organic semiconductor is either Pentacene or DNTT, which have a stable average mobility up to 0.1 cm2/Vs. Finally, a polymer (e.g.: Parylene-C) is used as a passivation layer.
We describe also our design rules for the placement of standard circuit cells. A “plastic wafer” is fabricated containing 49 dies. Each die of 1 cm2 has between 25 to 50 devices, proving larger scale integration in such a small space, unique in organic technologies.
Finally, we present the design (by simulations using a Spice model for OTFTs) and the test of analog and digital basic circuits: amplifiers with DC gains of about 20 dB, comparators, inverters and logic gates working in the frequency range of 1-10 kHz.
These standard circuit cells could be used for signal conditioning and integrated as active matrices for flexible sensors from 3rd party institutions, thus opening our fab to new ideas and sophisticated pre-industrial low cost applications for the emerging fields of biomedical devices and wearable electronics for virtual/augmented reality.
Roll-to-Roll-UV-nanoimprint lithography (R2R-UV-NIL) enables high resolution large area patterning of flexible substrates and is therefore of increasing industrial interest. We have set up a custom-made R2R-UV-NIL pilot machine which is able to convert 10 inch wide web with velocities of up to 30 m/min. In addition, we have developed self-replicable UV-curable resins with tunable surface energy and Young’s modulus for UV-imprint material as well as for polymer working stamp/shim manufacturing. Now we have designed test patterns for the evaluation of the impact of structure shape, critical dimension, pitch, depth, side wall angle and orientation relative to the web movement onto the imprint fidelity and working shim life time. We have used female (recessed structures) silicon masters of that design with critical dimensions between CD = 200 nm and 1600 nm, and structure depths of d = 500 nm and 1000 nm - all with vertical as well as inclined side walls. These entire master patterns have been transferred onto single male (protruding structures) R2R polymer working shims. The polymer working shims have been used for R2R-UV-NIL runs of several hundred meters and the imprint fidelity and process stability of the various test patterns have been compared. This study is intended as a first step towards establishing of design rules and developing of nanoimprint proximity correction strategies for industrial R2R-UV-NIL processes using polymer working shims.
Ferroelectric material supports both pyro- and piezoelectric effects that can be used for sensing pressures on large, bended surfaces. We present PyzoFlex, a pressure-sensing input device that is based on a ferroelectric material (PVDF:TrFE). It is constructed by a sandwich structure of four layers that can easily be printed on any substrate. The PyzoFlex foil is sensitive to pressure- and temperature changes, bendable, energy-efficient, and it can easily be produced by a screen-printing routine. Even a hovering input-mode is feasible due to its pyroelectric effect. In this paper, we introduce this novel, fully printed input technology and discuss its benefits and limitations.
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.
We demonstrate the printing of a complex smart integrated system using only five functional inks: the fluoropolymer
P(VDF:TrFE) (Poly(vinylidene fluoride trifluoroethylene) sensor ink, the conductive polymer PEDOT:PSS (poly(3,4
ethylenedioxythiophene):poly(styrene sulfonic acid) ink, a conductive carbon paste, a polymeric electrolyte and SU8 for
separation. The result is a touchless human-machine interface, including piezo- and pyroelectric sensor pixels (sensitive
to pressure changes and impinging infrared light), transistors for impedance matching and signal conditioning, and an
electrochromic display. Applications may not only emerge in human-machine interfaces, but also in transient
temperature or pressure sensing used in safety technology, in artificial skins and in disposable sensor labels.
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.
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.
We describe Raman-scattering experiments in copper-oxide superconductors with transition temperatures between 12 and 90 K as a function of temperature and polarization. The broad continuum observed in all compounds in both the normal and the superconducting state is attributed predominantly to electronic excitations and will be interpreted in terms of charge- carrier fluctuations. The effect of impurities is studied systematically. The limitations of the present theoretical approach as well as possible generalizations are discussed.
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