| 1. |
- Smits, Edsger C. P., et al.
(author)
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Bottom-up organic integrated circuits
- 2008
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In: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 455:7215, s. 956-959
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Journal article (peer-reviewed)abstract
- Self- assembly - the autonomous organization of components into patterns and structures(1) - is a promising technology for the mass production of organic electronics. Making integrated circuits using a bottom- up approach involving self- assembling molecules was proposed(2) in the 1970s. The basic building block of such an integrated circuit is the self- assembled- monolayer field- effect transistor ( SAMFET), where the semiconductor is a monolayer spontaneously formed on the gate dielectric. In the SAMFETs fabricated so far, current modulation has only been observed in submicrometre channels(3-5), the lack of efficient charge transport in longer channels being due to defects and the limited intermolecular pi-pi coupling between the molecules in the self-assembled monolayers. Low field- effect carrier mobility, low yield and poor reproducibility have prohibited the realization of bottom- up integrated circuits. Here we demonstrate SAMFETs with long- range intermolecular pi - pi coupling in the monolayer. We achieve dense packing by using liquid- crystalline molecules consisting of a pi- conjugated mesogenic core separated by a long aliphatic chain from a monofunctionalized anchor group. The resulting SAMFETs exhibit a bulk- like carrier mobility, large current modulation and high reproducibility. As a first step towards functional circuits, we combine the SAMFETs into logic gates as inverters; the small parameter spread then allows us to combine the inverters into ring oscillators. We demonstrate real logic functionality by constructing a 15- bit code generator in which hundreds of SAMFETs are addressed simultaneously. Bridging the gap between discrete monolayer transistors and functional self-assembled integrated circuits puts bottom- up electronics in a new perspective.
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| 2. |
- Mathijssen, Simon G. J., et al.
(author)
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Manipulating the local light emission in organic light-emitting diodes by using patterned self-assembled monolayers
- 2008
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In: Advanced Materials. - : Wiley-VCH Verlag. - 0935-9648 .- 1521-4095. ; 20:14, s. 2703-
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Journal article (peer-reviewed)abstract
- Patterned organic light-emitting diodes are fabricated by using microcontactDrinted self-assembled monolayers on a gold anode (see background figure). Molecules with dipole moments in opposite directions result in an increase or a decrease of the local work function (foreground picture), providing a direct handle on charge injection and enabling local modification of the light emission
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| 3. |
- Asadi, Kamal, et al.
(author)
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Organic ferroelectric opto-electronic memories
- 2011
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In: Materials Today. - : ELSEVIER SCI LTD. - 1369-7021 .- 1873-4103. ; 14:12, s. 592-599
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Research review (peer-reviewed)abstract
- Organic electronics have emerged as a promising technology for large-area micro-electronic applications, such as rollable displays(1), electronic paper(2), contactless identification transponders(3,4), and smart labels(5). Most of these applications require memory functions; preferably a non-volatile memory that retains its data when the power is turned off, and that can be programmed, erased, and read-out electrically.
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| 4. |
- Gholamrezaie, Fatemeh, et al.
(author)
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Charge Trapping by Self-Assembled Monolayers as the Origin of the Threshold Voltage Shift in Organic Field-Effect Transistors
- 2012
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In: Small. - : Wiley-VCH Verlag. - 1613-6810 .- 1613-6829. ; 8:2, s. 241-245
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Journal article (peer-reviewed)abstract
- The threshold voltage is an important property of organic field-effect transistors. By applying a self-assembled monolayer (SAM) on the gate dielectric, the value can be tuned. After electrical characterization, the semiconductor is delaminated. The surface potentials of the revealed SAM perfectly agree with the threshold voltages, which demonstrate that the shift is not due to the dipolar contribution, but due to charge trapping by the SAM.
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| 5. |
- Kemerink, Martijn, et al.
(author)
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The operational mechanism of ferroelectric-driven organic resistive switches
- 2012
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In: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 13:1, s. 147-152
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Journal article (peer-reviewed)abstract
- The availability of a reliable memory element is crucial for the fabrication of plastic logic circuits. We use numerical simulations to show that the switching mechanism of ferroelectric-driven organic resistive switches is the stray field of the polarized ferroelectric phase. The stray field modulates the charge injection from a metallic electrode into the organic semiconductor, switching the diode from injection limited to space charge limited. The modeling rationalizes the previously observed exponential dependence of the on/off ratio on injection barrier height. We find a lower limit of about 50 nm for the feature size that can be used in a crossbar array, translating into a rewritable memory with an information density of the order of 1 Gb/cm(2). (C) 2011 Elsevier B. V. All rights reserved.
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| 6. |
- Lenz, Thomas, et al.
(author)
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Microstructured organic ferroelectric thin film capacitors by solution micromolding
- 2015
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In: Physica Status Solidi (a) applications and materials science. - : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 212:10, s. 2124-2132
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Journal article (peer-reviewed)abstract
- Ferroelectric nanostructures offer a promising route for novel integrated electronic devices such as non-volatile memories. Here we present a facile fabrication route for ferroelectric capacitors comprising a linear array of the ferroelectric random copolymer of vinylidenefluoride and trifluoroethylene (P(VDF-TrFE)) interdigitated with the electrically insulating polymer polyvinyl alcohol (PVA). Micrometer size line gratings of both polymers were fabricated over large area by solution micromolding, a soft lithography method. The binary linear arrays were realized by backfilling with the second polymer. We investigated in detail the device physics of the patterned capacitors. The electrical equivalent circuit is a linear capacitor of PVA in parallel with a ferroelectric capacitor of P(VDF-TrFE). The binary arrays are electrically characterized by both conventional Sawyer-Tower and shunt measurements. The dependence of the remanent polarization on the array topography is explained by numerical simulation of the electric field distribution.
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| 7. |
- Sharma, A., et al.
(author)
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Bias-stress effect and recovery in organic field effect transistors: Proton migration mechanism
- 2010
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In: ORGANIC FIELD-EFFECT TRANSISTORS IX. - : Society of Photo-optical Instrumentation Engineers (SPIE). - 9780819482747
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Conference paper (peer-reviewed)abstract
- Organic field-effect transistors exhibit operational instabilities when a gate bias is applied. For a constant gate bias the threshold voltage shifts towards the applied gate bias voltage, an effect known as the bias-stress effect. We have performed a detailed experimental and theoretical study of operational instabilities in p-type transistors with silicon-dioxide gate dielectric. We propose a mechanism in which holes in the semiconductor are converted into protons in the presence of water and a reversible migration of these protons into the gate dielectric to explain the instabilities in organic transistors. We show how redistribution of charge between holes in the semiconductor and protons in the gate dielectric can consistently explain the experimental observations. Furthermore, we explain in detail the recovery of a pres-stressed transistor on applying zero gate bias. We show that recovery dynamics depends strongly on the extent of stressing. Our mechanism is consistent with the known aspects of bias-stress effect like acceleration due to humidity, constant activation energy and reversibility.
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| 8. |
- van de Ruit, Kevin, et al.
(author)
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The Curious Out-of-Plane Conductivity of PEDOT:PSS
- 2013
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In: Advanced Functional Materials. - : Wiley-VCH Verlag. - 1616-301X .- 1616-3028. ; 23:46, s. 5787-5793
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Journal article (peer-reviewed)abstract
- For its application as transparent conductor in light-emitting diodes and photovoltaic cells, both the in-plane and out-of-plane conductivity of PEDOT:PSS are important. However, studies into the conductivity of PEDOT:PSS rarely address the out-of-plane conductivity and those that do, report widely varying results. Here a systematic study of the out-of-plane charge transport in thin films of PEDOT:PSS with varying PSS content is presented. To this end, the PEDOT:PSS is enclosed in small interconnects between metallic contacts. An unexpected, but strong dependence of the conductivity on interconnect diameter is observed for PEDOT:PSS formulations without high boiling solvent. The change in conductivity correlates with a diameter dependent change in PEDOT:PSS layer thickness. It is suggested that the order of magnitude variation in out-of-plane conductivity with only a 3-4-fold layer thickness variation can quantitatively be explained on basis of a percolating cluster model.
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| 9. |
- Andringa, Anne-Marije, et al.
(author)
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Localizing trapped charge carriers in NO2 sensors based on organic field-effect transistors
- 2012
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In: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 101:15
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Journal article (peer-reviewed)abstract
- Field-effect transistors have emerged as NO2 sensors. The detection relies on trapping of accumulated electrons, leading to a shift of the threshold voltage. To determine the location of the trapped electrons we have delaminated different semiconductors from the transistors with adhesive tape and measured the surface potential of the revealed gate dielectric with scanning Kelvin probe microscopy. We unambiguously show that the trapped electrons are not located in the semiconductor but at the gate dielectric. The microscopic origin is discussed. Pinpointing the location paves the way to optimize the sensitivity of NO2 field-effect sensors. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4758697]
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| 10. |
- Bobbert, Peter A., et al.
(author)
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Operational Stability of Organic Field-Effect Transistors
- 2012
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In: Advanced Materials. - : Wiley-VCH Verlag. - 0935-9648 .- 1521-4095. ; 24:9, s. 1146-1158
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Journal article (peer-reviewed)abstract
- Organic field-effect transistors (OFETs) are considered in technological applications for which low cost or mechanical flexibility are crucial factors. The environmental stability of the organic semiconductors used in OFETs has improved to a level that is now sufficient for commercialization. However, serious problems remain with the stability of OFETs under operation. The causes for this have remained elusive for many years. Surface potentiometry together with theoretical modeling provide new insights into the mechanisms limiting the operational stability. These indicate that redox reactions involving water are involved in an exchange of mobile charges in the semiconductor with protons in the gate dielectric. This mechanism elucidates the established key role of water and leads in a natural way to a universal stress function, describing the stretched exponential-like time dependence ubiquitously observed. Further study is needed to determine the generality of the mechanism and the role of other mechanisms.
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