Ute Zschieschang

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

Are you Ute Zschieschang?

Claim your profile

Publications (133)673.82 Total impact

  • [Show abstract] [Hide abstract]
    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
  • [Show abstract] [Hide abstract]
    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 · 1.69 Impact Factor
  • [Show abstract] [Hide abstract]
    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 · 2.19 Impact Factor
  • [Show abstract] [Hide abstract]
    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;
  • [Show abstract] [Hide abstract]
    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
  • [Show abstract] [Hide abstract]
    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
  • [Show abstract] [Hide abstract]
    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
  • [Show abstract] [Hide abstract]
    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; 01/2014
  • [Show abstract] [Hide abstract]
    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 · 2.36 Impact Factor
  • [Show abstract] [Hide abstract]
    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
  • [Show abstract] [Hide abstract]
    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 · 1.62 Impact Factor
  • [Show abstract] [Hide abstract]
    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
  • [Show abstract] [Hide abstract]
    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 · 15.41 Impact Factor
  • Advanced Materials 07/2013; 25(27):3617-3617. DOI:10.1002/adma.201370173 · 15.41 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Air-stable bottom-gate, top-contact n-channel organic transistors based on a naphthalene diimide exhibiting electron mobilities up to 0.8 cm2/Vs at low voltages were fabricated. Transistors with channel lengths of 1 μm show a transconductance of 60 mS/m, but are significantly limited by the contact resistance. Transmission line measurements in combination with contact resistance models were applied to investigate this influence. Both contact resistance and contact resistivity are proportional to the inverse gate overdrive voltage. Organic complementary ring oscillators were fabricated on a flexible plastic substrate showing record signal delays down to 17 μs at a supply voltage of 2.6 V.
    Applied Physics Letters 06/2013; 6(6). DOI:10.1063/1.4811127 · 3.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Bottom-gate, top-contact (inverted staggered) organic thin-film transistors with a channel length of 1 μm have been fabricated on flexible plastic substrates using the vacuum-deposited small-molecule semiconductor 2,9-didecyl-dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (C10-DNTT). The transistors have an effective field-effect mobility of 1.2 cm2/V s, an on/off ratio of 107, a width-normalized transconductance of 1.2 S/m (with a standard deviation of 6%), and a signal propagation delay (measured in 11-stage ring oscillators) of 420 ns per stage at a supply voltage of 3 V. To our knowledge, this is the first time that megahertz operation has been achieved in flexible organic transistors at supply voltages of less than 10 V.
    Organic Electronics 06/2013; 14(6):1516–1520. DOI:10.1016/j.orgel.2013.03.021 · 3.83 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents S-parameter characterization and a corresponding physics-based small-signal equivalent circuit for organic thin-film transistors (OTFTs). Furthermore, the impact of misalignment between the source/drain contacts and the patterned gate on the dynamic TFT performance is explored and a simple method to estimate the misalignment from the measured S-parameters is proposed. An excellent fit between theoretical and experimental S-parameters is demonstrated. For this study, OTFTs based on the air-stable organic semiconductor dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) having a channel length of 1 μm and a gate-to-contact overlap of 5 or 20 μm and being operated at a supply voltage of 3 V are utilized. The intentional asymmetry between gate-to-source and gate-to-drain overlaps is precisely controlled by the use of high-resolution silicon stencil masks.
    Organic Electronics 05/2013; 14(5):1318–1322. DOI:10.1016/j.orgel.2013.02.014 · 3.83 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This letter presents the first comprehensive experimental studies on the frequency response of staggered low-voltage organic thin-film transistors (OTFTs) using S-parameter measurements. The transistors utilize air-stable dinaphtho-thieno-thiophene as the organic semiconductor with various channel lengths and gate overlaps. A peak cutoff frequency of 3.7 MHz for a channel length of 0.6 $mu{rm m}$, gate overlap of 5 $mu{rm m}$, and a supply voltage of 3 V is achieved. In view of the low supply voltage and air-stability, this result marks a record achievement in OTFT technology. The channel length dependence of the cutoff frequency is described in a compact model and a close correspondence to the measured data of OTFTs with variable device dimensions is shown. Moreover, the cutoff frequencies at different gate biases are found to be proportional to the dc transconductance.
    IEEE Electron Device Letters 04/2013; 34(4):520-522. DOI:10.1109/LED.2013.2246759 · 3.02 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We measure the gap density of states and the Fermi level position in thin-film transistors based on pentacene and dinaphtho[2,3-b:2^{'},3^{'}-f]thieno[3,2-b]thiophene (DNTT) films grown on various surfaces using Kelvin probe force microscopy. It is found that the density of states in the gap of pentacene is extremely sensitive to the underlying interface and governs the Fermi level energy in the gap. The density of gap states in pentacene films grown on bare silicon dioxide (SiO_{2}) was found to be larger by 1 order of magnitude compared to that in pentacene grown on SiO_{2} treated with hexamethyldisilazane and larger by 2 orders of magnitude compared to that of pentacene grown on aluminum oxide (AlO_{x}) treated with a self-assembled monolayer (SAM) of n-tetradecylphosphonic acid (HC_{14}-PA). When DNTT was grown on HC_{14}-PA-SAM-treated AlO_{x}, the gap density of states was even smaller, so that the Fermi level pinning was significantly reduced. The correlation between the measured gap density of states and the transistor performance is demonstrated and discussed.
    Physical Review Letters 01/2013; 110(3):036803. DOI:10.1103/PhysRevLett.110.036803 · 7.51 Impact Factor

Publication Stats

6k Citations
673.82 Total Impact Points

Institutions

  • 2006–2015
    • Max Planck Institute for Solid State Research
      Stuttgart, Baden-Württemberg, Germany
  • 2011
    • Technische Universität München
      • Institute of Nanoelectronics
      München, Bavaria, Germany
  • 2010
    • The University of Tokyo
      Tōkyō, Japan
    • McMaster University
      • Department of Electrical and Computer Engineering
      Hamilton, Ontario, Canada
  • 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