Polymer electronic memories: Materials, devices and mechanisms

2.2. Interface Trapping Effects 211 3. High-k Dielectric Materials for OFETs 212 3.1. Inorganic Dielectrics 212 3.1.1. Aluminum Oxide 213 3.1.2. Tantalum Oxide 215 3.1.3. Titanium Dioxide 216 3.1.4. Hafnium Dioxide 217 3.1.5. Zirconium Dioxide 218 3.1.6. Cerium Dioxide 218 3.2. Organic Dielectrics 218 3.2.1. Polymer Dielectrics 218 3.2.2. Self-Assembled Monoand Multilayers 225 3.3. Hybrid Dielectrics 227 3.3.1. Polymeric-Nanoparticle Composites 227 3.3.2. Inorganic-Organic Bilayers 232 3.3.3. Hybrid Solid Polymer Electrolytes 235 4. Summary 235 5. Acknowledgments 236 6. References 236

High-k organic, inorganic, and hybrid dielectrics for low-voltage organic field-effect transistors.

With the advent of devices based on single crystals, the performance of organic field-effect transistors has experienced a significant leap, with mobility now in excess of 10 cm2 V−1 s−1. The purpose of this review is to give an overview of the state-of-the-art of these high-performance organic transistors. The paper focuses on the problem of parameter extraction, limitations of the performance by the interfaces, which include the dielectric–semiconductor interface, and the injection and retrieval of charge carriers at the source and drain electrodes. High-performance devices also constitute tools of choice for investigating charge transport phenomena in organic materials. It is shown how the combination of field-effect measurements with other electrical characterizations helps in elucidating this still unresolved issue.

High-Performance Organic Field-Effect Transistors

We have investigated the paraelectric-to-ferroelectric phase transition of various sizes of nanocrystalline barium titanate (BaTiO3) by using temperature-dependent Raman spectroscopy and powder X-ray diffraction (XRD). Synchrotron X-ray scattering has been used to elucidate the room temperature structures of particles of different sizes by using both Rietveld refinement and pair distribution function (PDF) analysis. We observe the ferroelectric tetragonal phase even for the smallest particles at 26 nm. By using temperature-dependent Raman spectroscopy and XRD, we find that the phase transition is diffuse in temperature for the smaller particles, in contrast to the sharp transition that is found for the bulk sample. However, the actual transition temperature is almost unchanged. Rietveld and PDF analyses suggest increased distortions with decreasing particle size, albeit in conjunction with a tendency to a cubic average structure. These results suggest that although structural distortions are robust to cha...

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Crystal structure and the paraelectric-to-ferroelectric phase transition of nanoscale BaTiO3.

A new type of nonvolatile ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) memory based on an organic thin-film transistor (OTFT) with a single crystal of tri-isopropylsilylethynyl pentacene (TIPS-PEN) as the active layer is developed. A bottom-gate OTFT is fabricated with a thin P(VDF-TrFE) film gate insulator on which a one-dimensional ribbon-type TIPS-PEN single crystal, grown via a solvent-exchange method, is positioned between the Au source and drain electrodes. Post-thermal treatment optimizes the interface between the flat, single-crystalline ab plane of TIPS-PEN and the polycrystalline P(VDF-TrFE) surface with characteristic needle-like crystalline lamellae. As a consequence, the memory device exhibits a substantially stable source–drain current modulation with an ON/OFF ratio hysteresis greater than 103, which is superior to a ferroelectric P(VDF-TrFE) OTFT that has a vacuum-evaporated pentacene layer. Data retention longer than 5 × 104 s is additionally achieved in ambient conditions by incorporating an interlayer between the gate electrode and P(VDF-TrFE) thin film. The device is environmentally stable for more than 40 days without additional passivation. The deposition of a seed solution of TIPS-PEN on the chemically micropatterned surface allows fabrication arrays of TIPS-PEN single crystals that can be potentially useful for integrated arrays of ferroelectric polymeric TFT memory.

Non-volatile Ferroelectric Poly(vinylidene fluoride-co-trifluoroethylene) Memory Based on a Single-Crystalline Tri-isopropylsilylethynyl Pentacene Field-Effect Transistor

The authors report on a solution-processed composite film based on poly(vinylidene fluoride/trifluoroethylene) copolymer and barium titanate (BT) nanopowder, to be used as ferroelectric high-κ gate insulation in organic field-effect transistors (OFETs) Flexible films of up to 50vol% BT powder content are produced by preparing homogeneous dispersion of the powder in the polymer solutions The films exhibited high specific volume resistivities combined with dielectric constants of up to 515 at 1kHz Low-voltage OFETs with ferroelectric hysteresis and good memory retention properties were demonstrated by using the composite films

Spin-cast composite gate insulation for low driving voltages and memory effect in organic field-effect transistors

Gate insulators and interface effects in organic thin-film transistors

Physics-based models of organic field-effect transistors (OFETs) which can be used for computer-aided simulation of organic integrated circuits were investigated. For this purpose hybrid OFETs with poly(3-hexylthiophene-2,5-diyl) as the semiconductor were fabricated and characterized. The differential drain-source resistance reveals the need for a unified consideration of a gate-voltage-dependent mobility and of the depletion effect. We avoid neglecting the capacitance of the insulator and the semiconductor which would have otherwise introduced restrictions. The analytic modeling yields a compact static equivalent circuit diagram.

Static model for organic field-effect transistors including both gate-voltage-dependent mobility and depletion effect

We report a low-temperature process to manufacture an all polymer thin-film transistor avoiding curing and annealing temperatures higher than 80°C. This aspect of energy efficiency directly supports the low-cost feature of organic devices in fabrication. The process is being demonstrated by using commercially available polymers such as poly(ethylenedioxythiophene)/polystyrenesulfonate dispersion representing the source, drain and gate electrode, Norland optical adhesive NOA 75 as the gate-dielectric and regioregular poly(3-hexylthiophene-2,5-diyl) as the semiconducting polymer - all on a polyvinyl chloride substrate. Functional devices with a channel length of 25 μm and a channel width of 1 mm to 5 mm have been realized.

R. R. Schliewe

Papers

Spin-cast composite gate insulation for low driving voltages and memory effect in organic field-effect transistors

Gate insulators and interface effects in organic thin-film transistors

Static model for organic field-effect transistors including both gate-voltage-dependent mobility and depletion effect

Low-Temperature Process for Manufacturing All Polymer Thin-Film Transistors