Efficient charge injection from a high work function metal in high mobility n-type polymer field-effect transistors

Caironi, Mario; Newman, Christopher R.; Moore, Jennifer; Natali, Dario; Yan, He; Facchetti, Antonio; Sirringhaus, Henning

doi:10.1063/1.3424792

Cited by 75 publications

(83 citation statements)

References 17 publications

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“…This is in agreement with previous studies on P(NDI2OD-T2)-based OTFTs with Au contacts, [ 38 ] where it was demonstrated that injectionwhich dominates over transport across y -axis thanks to the high bulk mobility of P(NDI2OD-T2)-is a highly non-linear phenomenon because the reverse-biased source/semiconductor junction is subject to the Schottky barrier-lowering effect. When L is down-scaled while keeping V DS constant, the channel resistance gets smaller, the voltage drop across R y C TOT gets larger and carrier injection is super-linearly enhanced.…”

supporting

confidence: 81%

“…It is known that for P(NDI2OD-T2)-based transistors metal to semiconductor carrier injection dominates over transport across the bulk andbeing a non-linear phenomenon-results in a dependence of contact resistance on the drain to source voltage. [ 38 ] Here we have quantitatively investigated the impact of this phenomenon on the injection length, which turns out to depend on the channel length, going from about 10 μm for L = 40 μm down to about 2 μm for L = 5 μm. Consequently, when scaling L at constant drain to source voltage, it is possible-to a certain degree-to scale L OV as well without sizeably compromising the relative weight of contact resistances.…”

Section: Discussionmentioning

confidence: 99%

“…Our methodology allows to rationalize and to generalize this result, which is valid for all staggered transistors where the electrode-semiconductor injection process is dominating over the semiconductor bulk contribution. [ 38 ] This fi nding provides a clear guideline for the development of high performance and downscaled OTFTs, underlining the importance of developing π-conjugated materials with enhanced bulk transport properties.…”

Section: Introductionmentioning

confidence: 99%

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Injection Length in Staggered Organic Thin Film Transistors: Assessment and Implications for Device Downscaling

Natali

Chen

Maddalena

et al. 2016

Adv Elect Materials

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of organic semiconductors show carrier mobility in excess of 5 cm 2 V −1 s −1 when employed as active materials in long (>10 μm) channel organic thin fi lm transistors (OTFT). [2][3][4][5][6][7][8][9][10][11][12] Therefore by scaling the channel length down to 10-1 μm, in principle OTFTs should be able to operate at relatively high (1-10 MHz) frequencies at reasonable (<10 V) applied voltages. [ 13 ] In practice, apart from some reports, [13][14][15][16][17][18][19][20][21][22] this is often not easy to achieve because of injection issues: [ 23,24 ] contact resistances tend to become dominant over the channel resistance in short channel transistors reducing the expected improvement of device performances. [ 25 ] This situation is severely limiting the range of applications for OTFTs. [ 26 ] Indeed contact resistances arise from contact/semiconductor interface properties hence they are not expected to scale with the transistor channel length. To address this issue not only suitable modifi cations of the contact/semiconductor interface aimed at enhancing the contact injecting properties have to be implemented, [ 27 ] but also the device topology has to be considered. Staggered OTFTs, where the contacts and the transistor channel do not lie in the same plane, are usually characterized by lower contact resistances than coplanar ones: [ 28 ] while in these latter the injection area is limited by the accumulated channel depth (few nanometers), in the former the overlap between gate and source/drain contacts (many micrometers or even tens of micrometers) can be exploited, as shown in Figure 1 . The gate/contact overlapping length has to be suitably engineered: on the one hand it should be large enough to accommodate the injected current and to minimize contact resistances; but on the other hand it should not be too large because overlapping areas not effectively involved in injection solely result in additional parasitic capacitances that deteriorate the device speed. [ 13,29 ] It is therefore important to quantify the injection length, which is the length over which sizeable carrier injection occurs. [ 30,31 ] Despite the large number of studies on contact effects in OTFTs, [ 24,32 ] few of them discuss the effect of the gate to contact overlap: Xu et al. found a relationship between the optimal contact length and the semiconductor thickness in staggered OTFT. [ 33 ] Park et al. found that threshold voltage, fi eld effect mobility and contact resistances are affected by the contact length in staggered OTFT; [ 34 ] Wang et al. simulated the effect of contact length scaling. [ 35 ] Ante et al. studied the effect of contact In staggered thin fi lm transistors, the injection length is the fraction of the gate to contact overlap that is effectively involved in current injection. Its assessment is important to properly downscale device dimensions. In fact, in order to increase transistor operation speed, the whole device footprint should be downscaled, which means both the gate to contact overlap and the channel length, as ...

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supporting

confidence: 81%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Injection Length in Staggered Organic Thin Film Transistors: Assessment and Implications for Device Downscaling

Natali

Chen

Maddalena

et al. 2016

Adv Elect Materials

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“…DPPT-TT thin films spin-coated that O 2 -plasma-treated gold has a work function in the range of 5.0-5.5 eV, while photolithographically patterned gold electrodes without O 2 plasma treatment have a work function in the range of 4.7-4.9 eV. [33][34][35] We therefore expected an energy offset of around 0.9-1.4 eV (Figure 1b), leading to an energy barrier for electron injection existing between the LUMO of the DPPT-TT and the work function of the gold electrodes cleaned by a standard procedures after photolithography (cleaned with acetone, isopropyl alcohol and O 2 plasma treatment, referred to as "O 2 -plasma-cleaned gold"). This energy offset and the electron-injection barrier could be reduced if no O 2 plasma treatment was used (using gold cleaned with acetone and isopropyl alcohol in air, referred to as "solventcleaned gold").…”

Section: Doi: 101002/adma201102786mentioning

confidence: 99%

High‐Performance Ambipolar Diketopyrrolopyrrole‐Thieno[3,2‐b]thiophene Copolymer Field‐Effect Transistors with Balanced Hole and Electron Mobilities

et al. 2011

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Ambipolar OFETs with balanced hole and electron field-effect mobilities both exceeding 1 cm(2) V(-1) s(-1) are achieved based on a single-solution-processed conjugated polymer, DPPT-TT, upon careful optimization of the device architecture, charge injection, and polymer processing. Such high-performance OFETs are promising for applications in ambipolar devices and integrated circuits, as well as model systems for fundamental studies.

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“…Analogously with previous reports on PNDI2OD-T2, the two distinctive peaks observed can be attributed to a π-π* transition and an intramolecular transition with charge transfer character between the electron-donating unit and the electronacceptor unit, respectively. [63][64][65][66][67] With respect to the analogue NDI copolymer with the thienylene moiety instead of the selenophene, PNDI-SVS UV-vis absorption maxima are 30 nm red shifted owing to the introduction of a slightly stronger electron donor unit. Correspondingly, the optical band gap of PNDI-SVS, estimated at the onset of absorption maxima, is 1.31 eV, slightly narrower than the bandgap of PNDI-TVT.…”

Section: Synthesis and Density Functional Theory Calculationmentioning

confidence: 99%

High‐Mobility Naphthalene Diimide and Selenophene‐Vinylene‐Selenophene‐Based Conjugated Polymer: n‐Channel Organic Field‐Effect Transistors and Structure–Property Relationship

Sung

Luzio

Park

et al. 2016

Adv Funct Materials

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Interdependence of chemical structure, thin-film morphology, and transport properties is a key, yet often elusive aspect characterizing the design and development of high-mobility, solution-processed polymers for large-area and flexible electronics applications. There is a specific need to achieve >1 cm 2 V −1 s −1 field-effect mobilities (μ) at low processing temperatures in combination with environmental stability, especially in the case of electron-transporting polymers, which are still lagging behind hole transporting materials. Here, the synthesis of a naphthalene-diimide based donor-acceptor copolymer characterized by a selenophene vinylene selenophene donor moiety is reported. Optimized field-effect transistors show maximum μ of 2.4 cm 2 V −1 s −1 and promising ambient stability. A very marked film structural evolution is revealed with increasing annealing temperature, with evidence of a remarkable 3D crystallinity above 180 °C. Conversely, transport properties are found to be substantially optimized at 150 °C, with limited gain at higher temperature. This discrepancy is rationalized by the presence of a surface-segregated prevalently edge-on packed polymer phase, dominating the device accumulated channel. This study therefore serves the purpose of presenting a promising, high-electron-mobility copolymer that is processable at relatively low temperatures, and of clearly highlighting the necessity of specifically investigating channel morphology in assessing the structure-property nexus in semiconducting polymer thin films.

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Efficient charge injection from a high work function metal in high mobility n-type polymer field-effect transistors

Cited by 75 publications

References 17 publications

Injection Length in Staggered Organic Thin Film Transistors: Assessment and Implications for Device Downscaling

Injection Length in Staggered Organic Thin Film Transistors: Assessment and Implications for Device Downscaling

High‐Performance Ambipolar Diketopyrrolopyrrole‐Thieno[3,2‐b]thiophene Copolymer Field‐Effect Transistors with Balanced Hole and Electron Mobilities

High‐Mobility Naphthalene Diimide and Selenophene‐Vinylene‐Selenophene‐Based Conjugated Polymer: n‐Channel Organic Field‐Effect Transistors and Structure–Property Relationship

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