Principal goals in organic thin‐film transistor (OTFT) gate dielectric research include achieving: (i) low gate leakage currents and good chemical/thermal stability, (ii) minimized interface trap state densities to maximize charge transport efficiency, (iii) compatibility with both p‐ and n‐ channel organic semiconductors, (iv) enhanced capacitance to lower OTFT operating voltages, and (v) efficient fabrication via solution‐phase processing methods. In this Review, we focus on a prominent class of alternative gate dielectric materials: self‐assembled monolayers (SAMs) and multilayers (SAMTs) of organic molecules having good insulating properties and large capacitance values, requisite properties for addressing these challenges. We first describe the formation and properties of SAMs on various surfaces (metals and oxides), followed by a discussion of fundamental factors governing charge transport through SAMs. The last section focuses on the roles that SAMs and SAMTs play in OTFTs, such as surface treatments, gate dielectrics, and finally as the semiconductor layer in ultra‐thin OTFTs.

A series of 0−3 metal oxide−polyolefin nanocomposites are synthesized via in situ olefin polymerization, using the following single-site metallocene catalysts: C 2-symmetric dichloro[rac-ethylenebisindenyl]zirconium(IV), Me2Si( t BuN)(η5-C5Me4)TiCl2, and (η5-C5Me5)TiCl3 immobilized on methylaluminoxane (MAO)-treated BaTiO3, ZrO2, 3-mol %-yttria-stabilized zirconia, 8-mol %-yttria-stabilized zirconia, sphere-shaped TiO2 nanoparticles, and rod-shaped TiO2 nanoparticles. The resulting composite materials are structurally characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), 13C nuclear magnetic resonance (NMR) spectroscopy, and differential scanning calorimetry (DSC). TEM analysis shows that the nanoparticles are well-dispersed in the polymer matrix, with each individual nanoparticle surrounded by polymer. Electrical measurements reveal that most of these nanocomposites have leakage current densities of ∼10−6−10−8 A/cm2; relative permittivities increase as the nanoparticle volume fraction increases, with measured values as high as 6.1. At the same volume fraction, rod-shaped TiO2 nanoparticle−isotactic polypropylene nanocomposites exhibit significantly greater permittivities than the corresponding sphere-shaped TiO2 nanoparticle−isotactic polypropylene nanocomposites. Effective medium theories fail to give a quantitative description of the capacitance behavior, but do aid substantially in interpreting the trends qualitatively. The energy storage densities of these nanocomposites are estimated to be as high as 9.4 J/cm3.

New carbonyl-functionalized quaterthiophenes, 5, 5' ''-diheptanoyl-2,2':5',2' ':5' ',2' ''-quaterthiophene (DHCO-4T), 5, 5' ''-diperfluorohexylcarbonyl-2,2':5',2' ':5' ',2' ''-quaterthiophene (DFHCO-4T), and 2,7-[bis-(5-perfluorohexylcarbonylthien-2-yl)]-4H-cyclopenta[2,1-b:3,4-b']-dithiophen-4-one (DFHCO-4TCO) have been synthesized and characterized. Field-effect transistors fabricated with these materials exhibit high electron mobilities both in a vacuum (up to 0.6 cm2 V-1 s-1) and in air (up to 0.02 cm2 V-1 s-1) and very high Ion:Ioff currents ratios (>107). DHCO-4T is the first organic material exhibiting excellent ambipolar transport (mue/muh up to 0.1/0.01 cm2 V-1 s-1, (Ion:Ioff)e/(Ion:Ioff)h up to 107/108 for the same device) over a broad range of deposition temperatures. These materials are therefore promising for organic complementary circuits.

Aluminum oxide encapsulated high-permittivity (ε) BaTiO 3 and ZrO 2 core-shell nanoparticles having variable Al 2 O 3 shell thicknesses were prepared via a layer-by-layer methylaluminoxane coating process. Subsequent chemisorptive activation of the single-site metallocene catalyst [rac-ethylenebisindenyl]zirconium dichloride (EBIZrCl 2 ) on these Al 2 O 3 -encapsulated nanoparticles, followed by propylene addition, affords 0-3 metal oxide-isotactic polypropylene nanocomposites. Nanocomposite microstructure is analyzed by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, differential scanning calorimetry, atomic force microscopy, and Raman spectroscopy. The in situ polymerization process yields homogeneously dispersed nanoparticles in a polyolefin matrix. Electrical measurements indicate that as the concentration of the filler nanoparticles increases, the effective permittivity of the nanocomposites increases, affording ε values as high as 6.2. The effective permittivites of such composites can be predicted by the Maxwell-Garnett formalism using the effective medium theory for volume fractions (ν f ) of nanoparticles below 0.06. The nanocomposites have leakage current densities of ∼10 -7 -10 -9 A/cm 2 at an electric field of 10 5 V/cm, and very low dielectric loss in the frequency range 100 Hz-1 MHz. Increasing the Al 2 O 3 shell thickness dramatically suppresses the leakage current and high field dielectric loss in these nanocomposites.

The 0−3 metal oxide−isotactic polypropylene nanocomposites are synthesized via in situ propylene polymerization using the C 2-symmetric metallocene catalyst dichloro[rac-ethylenebisindenyl]zirconium(IV) (EBIZrCl2) immobilized on methylaluminoxane (MAO)-treated barium titanate (BaTiO3) or titanium dioxide (TiO2) nanoparticles. The composite materials are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and 13C nuclear magnetic resonance (NMR) spectroscopy. It is shown that the nanoparticles are homogeneously dispersed in the polyolefin matrices. Electrical measurements reveal nanocomposite leakage current densities of ∼10-6 to 10-9 A/cm2, permittivities as high as 6.1, and breakdown strengths of ∼4 MV/cm. Energy densities are estimated to be as high as 9.4 J/cm3.