Ute Zschieschang

Max Planck Institute for Solid State Research, Stuttgart, Baden-Württemberg, Germany

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Publications (140)717.61 Total impact

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    ABSTRACT: A dense array of 500 organic TFTs with two different threshold voltages arranged in a checkerboard pattern has been fabricated. The threshold voltages were defined by preparing self-assembled monolayers (SAMs) of either an alkyl or a fluoroalkylphosphonic acid on the gate-oxide surface of each TFT, using a combination of microcontact printing from an elastomeric stamp and dipping into a solution. The threshold voltages are −1.01 ± 0.15 V for the TFTs with the fluoroalkyl SAM and −1.28 ± 0.23 V for the TFTs with the alkyl SAM. ToF-SIMS analysis shows that the two SAMs can be patterned with a pitch of 10 μm and without significant cross-contamination. Cross-sectional TEM and NEXAFS characterization of the SAMs indicate that the properties of the SAMs prepared by microcontact printing and dipping are essentially identical.
    11/2015; 26:239-244. DOI:10.1016/j.orgel.2015.07.031
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    ABSTRACT: A detailed understanding for the mechanisms that control degradation of the electrical performance of organic thin-film transistors (TFTs) during exposure to various environments, such as oxygen and humidity, is still developing. This is particularly true for n-channel organic TFTs. Here we present an investigation of the long-term stability of n-channel TFTs based on the small-molecule organic semiconductor N,N′-bis(2,2,3,3,4,4,4-heptafluorobutyl-1,7-dicyano-perylene-(3,4:9,10)-tetracarboxylic diimide (PDI-FCN2) during storage in dry nitrogen, dry air, wet nitrogen and ambient air. By monitoring the electrical characteristics of the TFTs over a period of six weeks, we are able to show that the degradation of the electrical parameters (charge-carrier mobility and the simultaneous shift of the threshold voltage) is caused by two distinct mechanisms with different time constants. Exposure to oxygen or nitrogen (in the absence of humidity) causes the carrier mobility to drop by a factor of two and the threshold voltage to shift towards more positive values within 20 days, possibly due to a slight rearrangement of the conjugated molecules within the semiconductor layer. Storing the TFTs in saturated water vapor or in ambient air causes the threshold voltage and the carrier mobility to change much more rapidly, within just one day. The observed degradation in ambient air can be explained by an electrochemical instability of the radical anion of the organic semiconductor.
    Organic Electronics 11/2015; 26:340-344. DOI:10.1016/j.orgel.2015.07.060 · 3.83 Impact Factor
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    ABSTRACT: A detailed study on the effects of core halogenation of tetraazaperopyrene (TAPP) derivatives is presented. Its impact on the solid structure, as well as the photophysical and electrochemical properties, has been probed by the means of X-ray crystallography, UV/Vis and fluorescence spectroscopy, high-resolution electron energy loss spectroscopy (HREELS), cyclic voltammetry (CV), and DFT modeling. The aim was to assess the potential of this approach as a construction principle for organic electron-conducting materials of the type studied in this work. Although halogenation leads to a stabilization of the LUMOs compared to the unsubstituted parent compound, the nature of the halide barely affects the LUMO energy while strongly influencing the HOMO energies. In terms of band-gap engineering, it was demonstrated that the HOMO-LUMO gap is decreased by substitution of the TAPP core with halides, the effect being found to be most pronounced for the iodinated derivative. The performance of the recently reported core-fluorinated and core-iodinated TAPP derivatives in organic thin-film transistors (TFTs) was investigated on both a glass substrate, as well as on a flexible plastic substrate (PEN). Field-effect mobilities of up to 0.17 cm(2) Vs(-1) and on/off current ratio of >10(6) were established.
    Chemistry - A European Journal 10/2015; DOI:10.1002/chem.201503484 · 5.73 Impact Factor
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    ABSTRACT: The mechanisms behind the threshold-voltage shift in organic transistors due to functionalizing the gate dielectric with self-assembled monolayers (SAMs) are still under debate. We address the mechanisms by which SAMs determine the threshold voltage, by analyzing whether the threshold voltage depends on the gate-dielectric capacitance or not. We have investigated transistors based on five oxide thicknesses and two SAMs with rather diverse chemical properties, using the benchmark organic semiconductor dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene. Unlike several previous studies we have found that the dependence of the threshold voltage on the gate-dielectric capacitance is completely different for the two SAMs. In transistors with an alkyl SAM, the threshold voltage does not depend on the gate-dielectric capacitance and is determined mainly by the dipolar character of the SAM, whereas in transistors with a fluoroalkyl SAM, the threshold voltages exhibit linear dependence on the inverse of the gate-dielectric capacitance. Kelvin probe force microscopy measurements indicate this behavior is attributed to an electronic coupling between the fluoroalkyl SAM and the organic semiconductor.
    ACS Applied Materials & Interfaces 09/2015; 7(41). DOI:10.1021/acsami.5b02747 · 6.72 Impact Factor
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    ABSTRACT: Two p-type semiconducting azapyrenoacene materials, quinoxalino[2′,3′:9,10]phenanthro[4,5-abc]phenazine (TQPP) and 6,7,15,16-tetramethylquinoxalino[2′,3′:9,10]phenanthro[4,5-abc]phenazine (TQPP-[CH3]4), were characterized and were found to display high thermal stability and planar molecular geometry as revealed by single-crystal X-ray analysis. In bottom-gate p-channel organic thin-film transistors, field-effect mobilities of 2.5 × 10−3 cm2/V s and 7.5 × 10−5 cm2/V s were measured in ambient air for TQPP and TQPP-[CH3]4, respectively. Computational results of reorganization energies and electronic couplings indicate larger inter and intra-columnar couplings for TQPP-[CH3]4 in comparison to TQPP and predict the suitability of both semiconductors for hole as well as electron transporters.
    Journal of Molecular Structure 08/2015; 1093. DOI:10.1016/j.molstruc.2015.03.057 · 1.60 Impact Factor
  • Ute Zschieschang · Hagen Klauk ·
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    ABSTRACT: Abstract Organic thin-film transistors were fabricated directly on the surface of commercially available cleanroom paper using the vacuum-deposited small-molecule semiconductor dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT). A thin, high-capacitance gate dielectric that allows the TFTs to be operated with low voltages of 2 V was employed. The TFTs have a charge-carrier mobility of 1.6 cm2/Vs, an on/off current ratio of 106, and a subthreshold slope of 90 mV/decade. In addition, the TFTs also display a very large differential output resistance, which is an important requirement for applications in analog circuits and active-matrix displays.
    Organic Electronics 07/2015; 25:340-344. DOI:10.1016/j.orgel.2015.06.038 · 3.83 Impact Factor
  • Sibani Bisoyi · Shree Prakash Tiwari · Ute Zschieschang · Hagen Klauk ·
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    ABSTRACT: In this paper, the influence of gate-source and drain-source bias on the bias-stress stability and lifetime of pentacene-based low-voltage (-3 V) organic thin-film transistors (TFTs) built on plastic substrate has been investigated. The 10%-current-decay lifetime is used for analyzing the influence of applied bias on the bias-stress stability of TFTs, and to compare various biasing conditions. Our results show a 3 to 4 times higher 10%-current-decay lifetime when magnitude of gate-source and drain-source voltage are equal and less than 2.5 V during bias stress, compared to that when drain-source voltage is kept at -3.0 V.
  • Deyu Tu · Kazuo Takimiya · Ute Zschieschang · Hagen Klauk · Robert Forchheimer ·
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    ABSTRACT: In this paper, we present a consistent model to analyze the drain current mismatch of organic thin-film transistors. The model takes charge fluctuations and edge effects into account, to predict the fluctuations of drain currents. A Poisson distribution for the number of charge carriers is assumed to represent the random distribution of charge carriers in the channel. The edge effects due to geometric variations in fabrication processes are interpreted in terms of the fluctuations of channel length and width. The simulation results are corroborated by experimental results taken from over 80 organic transistors on a flexible plastic substrate.
    Journal of Display Technology 06/2015; 11(6):1-1. DOI:10.1109/JDT.2015.2419692 · 2.24 Impact Factor
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    ABSTRACT: We have synthesized crystals of two-dimensional layered tin disulfide (SnS 2) by chemical vapor transport and fabricated field-effect transistors based on mechanically exfoliated SnS 2 multilayer platelets. We demonstrate that the threshold voltage of these transistors can be modified by passivating the gate-oxide surface with a self-assembled monolayer of an alkylphosphonic acid, affording transistors with desirable enhancement-mode characteristics. In addition to a positive threshold voltage and a large on/off current ratio, these transistors also have a steep subthreshold swing of 4 V/decade.
    Journal of Applied Physics 03/2015; 117(10):104509. DOI:10.1063/1.4914488 · 2.18 Impact Factor
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    ABSTRACT: The electronic properties of chemically synthesized graphene nanoribbons (GNRs) are investigated in a field-effect transistor (FET) configuration. The FETs are fabricated by dispersing GNRs into an aqueous dispersion, depo­siting the GNRs onto an insulating substrate, and patterning of metal contacts by electron-beam lithography. At room temperature, the GNR FET shows a large drain current of 70 μA, very good charge injection from the contacts, saturation of the drain current at larger drain-source voltages, and an on/off current ratio of 2. The small on/off current ratio can be explained by either the unfavorable transistor geometry or by the unintentional agglomeration of two or more GNRs in the channel. Furthermore, it is demonstrated that, by quantum-chemical calculations, the bandgap of a GNR dimer can be as small as 30% of the bandgap of a GNR monomer.
    02/2015; 1(3). DOI:10.1002/aelm.201400010

  • 01/2015;
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    ABSTRACT: The bias-stress stability of low-voltage organic p-channel and n-channel thin-film transistors (TFTs) based on five promising organic semiconductors and fabricated on flexible polyethylene naphthalate (PEN) substrates has been investigated. In particular, it has been studied to which extent the bias-stress-induced decay of the on-state drain current of the TFTs is affected by the choice of the semiconductor and by the gate-source and drain-source voltages applied during bias stress. It has been found that for at least some of the organic p-channel TFTs investigated in this study, the bias-stress stability is comparable to that of a-Si:H and metal-oxide TFTs, despite the fact that the organic TFTs were fabricated at significantly lower process temperatures, which is important in view of the fabrication of these devices on plastic substrates.
    Organic Electronics 11/2014; 15(11):3173-3182. DOI:10.1016/j.orgel.2014.08.057 · 3.83 Impact Factor
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    ABSTRACT: A process for the fabrication of bottom-gate, top-contact (inverted staggered) organic thin-film transistors (TFTs) with channel lengths as short as 1 μm on flexible plastic substrates has been developed. The TFTs employ vacuum-deposited small-molecule semiconductors and a low-temperature-processed gate dielectric that is sufficiently thin to allow the TFTs to operate with voltages of about 3 V. The p-channel TFTs have an effective field-effect mobility of about 1 cm2/Vs, an on/off ratio of 107, and a signal propagation delay (measured in 11-stage ring oscillators) of 300 ns per stage. For the n-channel TFTs, an effective field-effect mobility of about 0.06 cm2/Vs, an on/off ratio of 106, and a signal propagation delay of 17 μs per stage have been obtained.
    Design Automation and Test in Europe; 09/2014
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    ABSTRACT: Organic thin-film transistors (TFTs) have potential as pixel drivers in flexible active-matrix organic light-emitting diode displays [1]. Hence it is essential to analyze the charge-carrier injection and extraction dynamics of organic TFTs to gain a better understanding of the trapping and detrapping at the TFT interfaces. From the current-voltage characteristics of the TFTs, many important parameters can be extracted, such as carrier mobility, threshold voltage, on/off ratio, subthreshold slope and transconductance. But to quantitatively evaluate the trapping and detrapping dynamics, displacement current measurements on two-terminal long-channel capacitors (LCCs) are far more useful [2, 3]. The cross-section and the layout of an LCC are schematically shown in Fig. 1. Unlike a TFT, an LCC has only one contact, so that carriers are injected into and extracted from the semiconductor through the same contact. To increase the signal-to-noise ratio, a very large channel length (up to 6 cm) is employed. While Liang et al. have performed displacement current measurements on pentacene-based LCCs [2,3], we report here on displacement current measurements on LCCs based on four different organic semiconductors: pentacene, dinaptho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT), 2,9-didecyl-DNTT (C10-DNTT) and diphenyl-DNTT (DPh-DNTT). In TFTs, these semiconductors show hole mobilities ranging from 1 to 7 cm2/Vs. The goal of the displacement current measurements reported here is to study how the choice of the semiconductor affects the trapping and detrapping dynamics in organic TFTs.
    2014 72nd Annual Device Research Conference (DRC); 06/2014
  • Ute Zschieschang · Tanja Holzmann · Bettina V. Lotsch · Hagen Klauk ·
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    ABSTRACT: Tin disulfide (SnS2) is a layered metal dichalcogenide semiconductor [1]. Its crystal structure and many of its electrical, optical and catalytic properties are similar to those of molybdenum disulfide (MoS2) [2] which has received significant attention due to the large electron mobilities of over 500 cm2/Vs that have been measured in monolayer MoS2 field-effect transistors (FETs) [3]. A potential advantage of SnS2 over MoS2 is its larger bandgap (2.3 eV for bulk SnS2 [1], compared to 1.2 eV for bulk MoS2 [2]), which may translate into smaller leakage currents and larger on/off ratios in FETs, especially when the channel length is small and the applied drain-source voltage is large. Recently, Song et al. reported an electron mobility of 50 cm2/Vs for FETs based on mechanically exfoliated SnS2 monolayers [4]. These monolayer FETs showed a subthreshold swing of 10 V/decade and a promising on/off ratio of 105, but similar to many metal dichalcogenide FETs reported in the literature, this large on/off ratio was obtained only when the applied drain-source voltage was very small (0.01 V). In addition, the FETs had a negative threshold voltage. However, for many applications, such as active-matrix displays and low-power logic circuits, positive threshold voltages and large on/off ratios at large drain-source voltages are more desirable. Here we demonstrate FETs based on mechanically exfoliated SnS2 multilayers with a thickness of several hundred nanometers that have relatively small field-effect mobilities (0.04 cm2/Vs), but provide a steep subthreshold swing (4 V/decade) and a large on/off ratio (106) even when the applied drain-source voltages are quite large (10 V).
    2014 72nd Annual Device Research Conference (DRC); 06/2014
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    ABSTRACT: This paper presents analysis of the charge storage behavior in organic thin-film transistors (OTFTs) by means of admittance characterization, compact modeling, and 2-D device simulation. The measurements are performed for frequencies ranging from 100 Hz to 1 MHz and bias potentials from zero to -3 V on top-contact OTFTs that employ air-stable and high-mobility dinaphtho-thieno-thiophene as the organic semiconductor. It is demonstrated that the dependence of the intrinsic OTFT gate-source and gate-drain capacitances on the applied voltages agrees very well with Meyer's capacitance model. Furthermore, the impact of parasitic elements, including fringe current and contact impedance, is investigated. The parameters used for the simulation and modeling of all the dynamic characteristics correspond closely to those extracted from static measurements. Finally, the implications of the admittance measurements are also discussed relating to the OTFTs dynamic performance, particularly the cutoff frequency and the charge response time.
    IEEE Transactions on Electron Devices 01/2014; 61(1):98-104. DOI:10.1109/TED.2013.2292390 · 2.47 Impact Factor
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    ABSTRACT: The small-molecule organic semiconductor 2,9-di-decyl-dinaphtho-[2,3-b:2′,3′-f]-thieno-[3,2-b]-thiophene (C10-DNTT) was used to fabricate bottom-gate, top-contact thin-film transistors (TFTs) in which the semiconductor layer was prepared either by vacuum deposition or by solution shearing. The maximum effective charge-carrier mobility of TFTs with vacuum-deposited C10-DNTT is 8.5 cm2/V s for a nominal semiconductor thickness of 10 nm and a substrate temperature during the semiconductor deposition of 80 °C. Scanning electron microscopy analysis reveals the growth of small, isolated islands that begin to coalesce into a flat conducting layer when the nominal thickness exceeds 4 nm. The morphology of the vacuum-deposited semiconductor layers is dominated by tall lamellae that are formed during the deposition, except at very high substrate temperatures. Atomic force microscopy and X-ray diffraction measurements indicate that the C10-DNTT molecules stand approximately upright with respect to the substrate surface, both in the flat conducting layer near the surface and within the lamellae. Using the transmission line method on TFTs with channel lengths ranging from 10 to 100 μm, a relatively small contact resistance of 0.33 kΩ cm was determined. TFTs with the C10-DNTT layer prepared by solution shearing exhibit a pronounced anisotropy of the electrical performance: TFTs with the channel oriented parallel to the shearing direction have an average carrier mobility of (2.8 ± 0.3) cm2/V s, while TFTs with the channel oriented perpendicular to the shearing direction have a somewhat smaller average mobility of (1.3 ± 0.1) cm2/V s.
    Organic Electronics 12/2013; 14(12):3213–3221. DOI:10.1016/j.orgel.2013.09.003 · 3.83 Impact Factor
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    ABSTRACT: In the late 1960s, a new concept was proposed for an infrared absorbing device called a “rectenna” that, combining an antenna and a nanoscale metal-insulator-metal diode rectifier, collects electromagnetic radiation in the terahertz regime, with applications as detectors and energy harvesters. Previous theories hold that the diode rectifies the induced terahertz currents. Our results, however, demonstrate that the Seebeck thermal effect is the actual dominant rectifying mechanism. This new realization that the underlying mechanism is thermal-based, rather than tunneling-based, can open the way to important new developments in the field, since the fabrication process of rectennas based on the Seebeck effect is far simpler than existing processes that require delicate tunnel junctions. We demonstrate for the first time the fabrication of a rectenna array using an efficient parallel transfer printing process featuring nearly one million elements.
    IEEE Transactions on Nanotechnology 11/2013; 12(6):1144-1150. DOI:10.1109/TNANO.2013.2281373 · 1.83 Impact Factor
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    ABSTRACT: Organic thin-film transistors (TFTs) are prepared by vacuum deposition and solution shearing of 2,9-bis(perfluoroalkyl)-substituted tetraazaperopyrenes (TAPPs) with bromine substituents at the aromatic core. The TAPP derivatives are synthesized by reacting known unsubstituted TAPPs with bromine in fuming sulphuric acid, and their electrochemical properties are studied in detail by cyclic voltammetry and modelled with density functional theory (DFT) methods. Lowest unoccupied molecular orbital (LUMO) energies and electron affinities indicate that the core-brominated TAPPs should exhibit n-channel semiconducting properties. Current-voltage characteristics of the TFTs established electron mobilities of up to μn = 0.032 cm2 V−1 s−1 for a derivative which was subsequently processed in the fabrication of a complementary ring oscillator on a flexible plastic substrate (PEN).
    Advanced Functional Materials 08/2013; 23(31). DOI:10.1002/adfm.201203600 · 11.81 Impact Factor
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    ABSTRACT: Low-operating-voltage flexible organic thin-film transistors with high thermal stability using DPh-DNTT and SAM gate dielectrics are reported. The mobility of the transistors are decreased by 23% after heating to 250 °C for 30 min. Furthermore, flexible organic pseudo-CMOS inverter circuits, which are functional after heating to 200 °C.
    Advanced Materials 07/2013; 25(27). DOI:10.1002/adma.201300941 · 17.49 Impact Factor

Publication Stats

7k Citations
717.61 Total Impact Points


  • 2006-2015
    • Max Planck Institute for Solid State Research
      Stuttgart, Baden-Württemberg, Germany
  • 2010
    • The University of Tokyo
      Tōkyō, Japan
  • 2009
    • Technische Universität Chemnitz
      • Department of Electrical Engineering and Information Technology
      Karl-Marx-Stadt, Saxony, Germany
  • 2008
    • Friedrich-Alexander Universität Erlangen-Nürnberg
      • Department of Materials Science and Engineering
      Erlangen, Bavaria, Germany
  • 2007
    • Universität Stuttgart
      Stuttgart, Baden-Württemberg, Germany
  • 2002-2006
    • Infineon Technologies
      München, Bavaria, Germany
  • 2005
    • Technische Universität Bergakademie Freiberg
      Freiburg, Saxony, Germany