Barbara Stadlober

Influence of grain sizes on the mobility of organic thin-film transistors

A mobility model for organic thin-film transistors (OTFTs) has been considered that fully accounts for the effect of grains and grain boundaries of the organic layer. The model has been applied to a top contact pentacene OTFT. Comparison between simulation results and experimental data shows a strong dependence of mobility as a function of grain size. The field-effect-extracted mobility is not linearly related to the grain size, but presents a rather abrupt reduction for a grain size smaller than 2μm.

An All‐Printed Ferroelectric Active Matrix Sensor Network Based on Only Five Functional Materials Forming a Touchless Control Interface

An All-Printed Ferroelectric Active Matrix Sensor Network Based on Only Five Functional Materials Forming a Touchless Control Interface

Flexible active-matrix cells with selectively poled bifunctional polymer-ceramic nanocomposite for pressure and temperature sensing skin

A monolithically integrated bifunctional frontplane is introduced to large area electronics. The bifunctional frontplane element is based on a composite foil of piezoelectric ceramic lead titanate nanoparticles embedded in a ferroelectric poly(vinylidene fluoride trifluoroethylene) polymer matrix. Bifunctionality to pressure and temperature changes is achieved by a sequential, area selective two-step poling process, where the polarization directions in the nanoparticles and the ferroelectric polymer are adjusted independently. Thereby, sensor elements that are only piezoelectric or only pyroelectric are achieved. The frontplane foil is overlaid on a thin-film transistor backplane. Our work constitutes a step toward multifunctional frontplanes for large area electronic surfaces.

High-mobility pentacene organic field-effect transistors with a high-dielectric-constant fluorinated polymer film gate dielectric

High-performance pentacene organic thin-film transistors with double layers of the terpolymer electret poly(vinylidene fluoride/tetrafluoroethylene/hexafluoropropylene) and the polymer poly(vinyl cinnamate) as a gate dielectric are reported. The electret is a high-k dielectric polymer with a static dielectric constant of e=14. The transistors show an intrinsic field-effect mobility in the range of μi=1cm2∕Vs and an on- to off-current ratio of about 105. High-k polymer gate dielectrics seem promising for organic nonvolatile memory and sensor field-effect transistors.

Fabrication of n‐ and p‐Type Organic Thin Film Transistors with Minimized Gate Overlaps by Self‐Aligned Nanoimprinting

[∗] U. Palfi nger , C. Auner , H. Gold , A. Haase , J. Kraxner , G. Jakopic , J. R. Krenn , B. Stadlober Institute of Nanostructured Materials and Photonics Joanneum Research GmbH Franz-Pichlerstrasse 30, A-8160 Weiz (Austria) Fax: 0043-316-876-2710 Telephone: 0043-316-876-2721 E-mail: barbara.stadlober@joanneum.at T. Haber , M. Sezen , W. Grogger Institute for Electron Microscopy Graz University of Technology Steyrergasse 17, A-8010 Graz (Austria) G. Domann Fraunhofer-Institut für Silicatforschung ISC Neunerplatz 2, D-97082 Würzburg (Germany)

PyzoFlex: printed piezoelectric pressure sensing foil

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. It is constructed with a sandwich structure of four layers that can be printed easily on any material. We use this material in combination with a high-resolution Anoto-sensing foil to support both hand and pen input tracking. The foil is bendable, energy-efficient, and it can be produced in a printing process. Even a hovering mode is feasible due to its pyroelectric effect. In this paper, we introduce this novel input technology and discuss its benefits and limitations.

Tuning the threshold voltage in organic thin-film transistors by local channel doping using photoreactive interfacial layers.

In recent years, organic thin-film transistors (OTFTs) have attracted a great deal of attention due to their potential applications in low cost sensors,1 memory cards,2 and integrated circuits.3 Great efforts are under way to design OTFTs with high performance, high stability, high reproducibility, and low cost.4 Two of the most crucial device parameters are the charge carrier mobility and the threshold voltage (VTh). Concerning the mobility, the main goals for most applications is its maximization.5 For VTh, the situation is more complex: for example, for integrated circuits it would be desirable to tune VTh over a broad range,6 e.g., for inverter applications. In silicon technology, complementary circuits that consist of p-channel and n-channel transistors are typically used.7 There have been many attempts to adapt this technology to OTFTs and fabricate organic complementary inverters.2,8,9 They, however, suffer from poor n-type transistor performance and/or air instability of n-type semiconductor materials. An alternative approach is the adaptation of unipolar depletion-load inverters enabling simplified processing, even if they do not provide the low power consumption and the simple circuit design intrinsic to complementary logic.10,11 Depletion-load inverters consist of an enhancement-mode driver transistor and a depletion-mode load transistor and can be realized using only p-type OTFTs. So far there have been attempts to achieve this target by using a level shifter12,13 or a dual gate structure.14 The main objective is to find a reproducible method to realize driver and load transistors with equivalent device characteristics (in particular mobilities), but different VTh values.

Submicron pentacene-based organic thin film transistors on flexible substrates

The authors demonstrate the fabrication of organic thin film transistors (OTFTs) based on pentacene with submicron channels on flexible substrates. Nanoimprint lithography is used for the patterning of the source and drain electrodes and processed directly on the spin-on gate dielectric, the structured gate electrode, and the flexible substrate. The use of sub-100-nm thin organic gate dielectrics enables full drain current saturation for devices with channel lengths down to 500nm. The submicron OTFTs exhibit negative threshold voltages with an absolute value well below 5V and have subthreshold swings around 0.5V/decade. This demonstrates the possibility to fabricate fully structured and miniaturized OTFTs operating at low voltages and paves the way for a low-cost fabrication of downscaled high performance organic electronic circuits.

Sexithiophene films on clean and oxidized Si(111) surfaces: Growth and electronic structure

The growth and the electronic properties of sexithiophene thin films on silicon surfaces have been studied by angle resolved ultraviolet photoelectron spectroscopy while morphology and crystalline order have been assessed by atomic force microscopy and x-ray diffraction. The influence of the surface modification of the substrate as well as of the growth temperature and the growth rate were investigated in ultrahigh vacuum through controlled multistep growth sequences ranging from (sub)monolayer coverage up to thick films. Depending on the preparation, two electronically distinct sexithiophene (6T) films could be produced, as revealed by their ionization potentials which differed by ∼0.7eV. The evolution of the electronic energy levels with film thickness is considered in terms of the concepts of interface dipole and band bending, with the latter being argued to be inappropriate. Irrespective of substrate or growth conditions the thick 6T films were found to all have the same work function of ∼0.4eV, which...

Detailed simulation of structural color generation inspired by the Morpho butterfly

The brilliancy and variety of structural colors found in nature has become a major scientific topic in recent years. Rapid-prototyping processes enable the fabrication of according structures, but the technical exploitation requires a profound understanding of structural features and material properties regarding the generation of reflected color. This paper presents an extensive simulation of the reflectance spectra of a simplified 2D Morpho butterfly wing model by utilizing the finite-difference time-domain method. The structural parameters are optimized for reflection in a given spectral range. A comparison to simpler models, such as a plane dielectric layer stack, provides an understanding of the origin of the reflection behavior. We find that the wavelength of the reflection maximum is mainly set by the lateral dimensions of the structures. Furthermore small variations of the vertical dimensions leave the spectral position of the reflectance wavelength unchanged, potentially reducing grating effects.