Contact Resistance as an Origin of the Channel-Length-Dependent Threshold Voltage in Organic Field-Effect Transistors

Weis, Martin; Lee, Keanchuan; Taguchi, Dai; Manaka, Takaaki; Iwamoto, Mitsumasa

doi:10.1143/jjap.51.100205

Cited by 8 publications

(10 citation statements)

References 18 publications

(23 reference statements)

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“…For positive V GS and V DS voltages, we did not observe transistor operation. Additionally, the low values of the measured drain–source current ( I DS ) may be explained by two reasons, firstly it may be due to the high energy mismatch between the Fermi level of the metal electrode (Au = 5.1 eV) and HOMO of the organic semiconductor (HOMO = 4.4 eV) . The other reason may be related to the molecular conformation close to the dielectric interface .…”

Section: Resultsmentioning

confidence: 99%

Hole‐mobility limits for the Zn(OC)₂ organic semiconductor obtained by SCLC and field‐effect measurements

Landi

Tunç

Sio

et al. 2016

Physica Status Solidi (a)

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The hole mobility of a semiconducting film with a new type of small molecule has been determined by electrical characterization with two different device geometries. The small molecule, namely Zn(OC)2, consists of oxadiazole groups (O), that act as electron conductor and blue emitter, and carbazole groups (C), that are hole conductors, which are arranged around a central Zn‐atom. This disordered organic material has in principal ambipolar conduction properties. In both the organic devices investigated, that is, a vertical diode and a bottom‐gate organic field effect transistor, the transport is dominated by holes. In the diode structure, the charge carrier transport shows a dependence from the electric field with a space charge limited current characteristic. The hole mobility value is several orders of magnitude higher as compared to the one extracted from the characteristics of the organic transistor. This large difference in the charge carrier transport properties for the two different device configurations is due to the strong influence of the dielectric/semiconductor interface which degrades the hole transport in the organic field effect transistor.

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Section: Resultsmentioning

confidence: 99%

Hole‐mobility limits for the Zn(OC)₂ organic semiconductor obtained by SCLC and field‐effect measurements

Landi

Tunç

Sio

et al. 2016

Physica Status Solidi (a)

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“…Subsequently, a semi-logarithmic relationship between V T and φ b is yielded (Figure 5d), being associated with the statement that contact resistance is exponentially proportional to φ b , [73,75] and collaterally affects the threshold voltage. [71,76] In brief, M created lower energetic states for electron injection in the blends, thus reducing the voltage required to overcome the injection barrier.…”

Section: Ofet Characteristicsmentioning

confidence: 99%

Regulate the Electron Mobility and Threshold Voltage of P(NDI2OD‐T2)‐Based Organic Field‐Effect Transistors by the Compatibility Principle

Yang

Lai

2021

Adv Elect Materials

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Blending has been used extensively to meet the requirements for high‐mobility organic field‐effect transistors (OFETs), involving various combinations of (non‐)conjugated polymers and (non‐)conjugated molecules. Nonetheless, the collaborative effects of conjugated polymer and its structurally analogous molecule on charge‐transport properties have rarely been reported. In this work, P(NDI2OD‐T2) and N,N′‐bisbutyl‐2,6‐bis([2,2′]bithiophenyl‐5‐yl)‐1,4,5,8‐naphthalene diimide (M), are synthesized and blended with each other. M is designed to resemble the monomeric unit of P(NDI2OD‐T2) on the basis of the premise that structural similarity would promote their compatibility in the blends. This compatibility preserves electronic coupling through intermolecular interaction and establishes charge‐transport pathways as well. Overall, the thin‐film morphology of the blends could be prudently regulated through controlling the blending fraction, resulting in raising electron mobility up to ≈0.3 cm2 V−1 s−1. More importantly, this approach reduces threshold voltage by 50%, originating from lowering the injection barrier. These findings are well rationalized and the promising capabilities of the compatibility principle in OFETs are strongly supported.

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“…For instance, the all‐important charge accumulated channel forms within a few nanometers of the OSC/dielectric interface . Also, the dielectric influences numerous OTFT parameters, such as operating voltage, threshold voltage, on–off current, subthreshold swing/slope, hysteresis, mobility, and operational stability . However, the relationship between the dielectric and R C is rarely considered.…”

Section: Introductionmentioning

confidence: 99%

“…[9] In principle, these requirements can be met by reducing R C . [27,28] Also, the dielectric influences numerous OTFT parameters, such as operating voltage, [29] threshold voltage, [30,31] on-off current, [32] subthreshold swing/slope, [33] hysteresis, [34] mobility, [35] and operational stability. The largest contributor to R C is the potential energy difference between the metal contact and the OSC.…”

mentioning

confidence: 99%

Impact of the Gate Dielectric on Contact Resistance in High‐Mobility Organic Transistors

Paterson

Mottram

Faber

et al. 2019

Adv Elect Materials

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the greatest focus placed on improving the charge-carrier mobility (µ). [1][2][3][4][5] However, these successful improvements in µ will be in vain unless other important operating parameters are also improved. One particularly weak point in OTFTs that use undoped, wide-bandgap organic semiconductors (OSCs) is contact resistance (R C ). Not only are the µ values reported for OTFTs suffering from R C at a high risk of being overestimated or underestimated, [1,6,7] but a large R C can also prevent OTFT miniaturization. [8] These points are important if OTFTs are ever to be used in integrated circuits (ICs), where IC operating frequencies can be increased by reducing the channel length and improving µ. [9,10] Indeed, Hagen Klauk recently calculated two key requirements for OTFTs to be used in GHz frequency applications for the "internet of things": i) R C less than 100 Ωcm and ii) channel dimensions either equal to or less than 1 µm. [9] In principle, these requirements can be met by reducing R C . Although R C is extracted as a single value from the OTFT output characteristics, its magnitude encompasses different aspects of OTFT operation. The largest contributor to R C is the potential energy difference between the metal contact and the OSC. In OTFTs, this energetic difference typically creates a Schottky barrier, which reduces how efficiently charge carriers are injected into/extracted from the OTFT channel. [11,12] Therefore, much research has focused on techniques that improve this energetic mismatch, such as contact doping, [13][14][15] alternative contact materials, OSC doping, [4,16,17] injection layers, [18,19] and self-assembled monolayer (SAM) treatments. [20,21] However, there are a number of additional factors that influence the magnitude of R C , including the OSC microstructure, [22,23] charge trapping at the metal/OSC interface, [24] as well as the type of dielectric materials employed [25,26] and the microstructure they create at the OSC/dielectric interface.The dielectric layer in OTFTs has attracted significant attention over the years for a variety of reasons. For instance, the all-important charge accumulated channel forms within a few nanometers of the OSC/dielectric interface. [27,28] Also, the dielectric influences numerous OTFT parameters, such as operating voltage, [29] threshold voltage, [30,31] on-off current, [32] subthreshold swing/slope, [33] hysteresis, [34] mobility, [35] and operational stability. [36,37] However, the relationship between the The impact of the gate dielectric on contact resistance in organic thin-film transistors (OTFTs) is investigated using electrical characterization, biasstress stability measurements, and bandgap density of states (DOS) analysis. Two similar dielectric materials, namely Cytop and poly[4,5-difluoro-2,2bis(trifluoromethyl)-1,3-dioxole-co-tetrafluoroethylene] (Teflon AF2400), are tested in top-gate bottom-contact OTFTs. The contact resistance of Cytopbased OTFTs is found to be greater than that of the AF2400-based devices, even though the metal/OSC...

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Contact Resistance as an Origin of the Channel-Length-Dependent Threshold Voltage in Organic Field-Effect Transistors

Cited by 8 publications

References 18 publications

Hole‐mobility limits for the Zn(OC)₂ organic semiconductor obtained by SCLC and field‐effect measurements

Hole‐mobility limits for the Zn(OC)₂ organic semiconductor obtained by SCLC and field‐effect measurements

Regulate the Electron Mobility and Threshold Voltage of P(NDI2OD‐T2)‐Based Organic Field‐Effect Transistors by the Compatibility Principle

Impact of the Gate Dielectric on Contact Resistance in High‐Mobility Organic Transistors

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Contact Resistance as an Origin of the Channel-Length-Dependent Threshold Voltage in Organic Field-Effect Transistors

Cited by 8 publications

References 18 publications

Hole‐mobility limits for the Zn(OC)2 organic semiconductor obtained by SCLC and field‐effect measurements

Hole‐mobility limits for the Zn(OC)2 organic semiconductor obtained by SCLC and field‐effect measurements

Regulate the Electron Mobility and Threshold Voltage of P(NDI2OD‐T2)‐Based Organic Field‐Effect Transistors by the Compatibility Principle

Impact of the Gate Dielectric on Contact Resistance in High‐Mobility Organic Transistors

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Hole‐mobility limits for the Zn(OC)₂ organic semiconductor obtained by SCLC and field‐effect measurements

Hole‐mobility limits for the Zn(OC)₂ organic semiconductor obtained by SCLC and field‐effect measurements