Novel Electrical Properties of Nanoscale Thin Films of a Semiconducting Polymer:  Quantitative Current-Sensing AFM Analysis

Abstract

Thin films (20-150 nm thickness) of poly(o-anthranilic acid) with various doping levels were prepared on silicon substrates with deposited indium tin oxide, and their topography and current-voltage (I-V) characteristics were quantitatively investigated using current-sensing atomic force microscopy with a platinum-coated tip. The films were found to have a surface morphology like that of orange peel, with a periodic modulation and a surface roughness. The films exhibited nonuniform current flows and I-V characteristics that depended on the doping level as well as on the film thickness. Films with a high doping level were found to exhibit Zener diode switching behavior, whereas the films with a very low doping level (or that were dedoped) exhibited no current flow at all, and so are insulators. Interestingly, self-doped films (which are at an intermediate doping level) were found to have a novel electrical bistability, i.e., a switching characteristic like that of Schottky diodes, and increasingly insulating characteristics as the film thickness was increased. The films with thickness < or =62 nm, which exhibited this novel and stable electrical bistability, can potentially be used in the fabrication of high-density, stable, high-performance digital nonvolatile memory devices based only on transistors. The measured current images and I-V characteristics indicate that the electrical switching and bistability of the films are governed by local filament formation and charge traps.

Electrical memory devices based on inorganic/organic nanocomposites

“…As in copper-ion memories, [73][74][75] mobile metallic ions from the electrodes or the nanoparticles can migrate to form a conductive filament between the two electrodes when a high enough voltage is applied to the device. It has been observed using a current-sensing atomic force microscope [76][77][78][79] and an infrared microscope 80 that only the switching occurred in localized areas of the devices. Highly conductive spots are created after the device is switched to the low conductive state.…”

Novel Rewritable, Non‐volatile Memory Devices Based on Thermally and Dimensionally Stable Polyimide Thin Films

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] However, such organic materials are mostly insoluble and thus require more elaborate and more expensive fabrication processes such as vacuum evaporation and deposition than are commonly used in the fabrication of inorganic materials. [1][2][3][4][5] Moreover, deposited organic layers have relatively low boiling points and low chemical resistances, which means that they are susceptible to damage during the processing required by the fabrication of memory devices.…”

Organic nonvolatile memory transistors with self-doped polymer energy well structures

“…19,20 The intrinsic viscosity (Z) of the SD-PARA polymer product was determined to be 0.11 dl g À1 in N-methyl-2-pyrrolidinone at 25.0 1C using an Ubbelohde capillary viscometer (Fungilab, Sant Felin de Vogregat, Barcelona, Spain). Poly(3-hexylthiophene; P3HT; M w (weight-average molecular weight) ¼ 6.0 Â 10 4 ; polydispersity index ¼ 2.0; regioregularity ¼ 95%) was supplied from Lumtec (Science-Based Industrial Park, Hsin-Chu, Taiwan), whereas poly(vinyl phenol; PVP, M w ¼ 2.5 Â 10 4 ) and methylated poly(melamine-coformaldehyde; MMF, M w ¼ 432) were purchased from the Sigma-Aldrich Co. (St Louis, MO, USA).…”

“…In this study, we used a self-doped polyaniline derivative (selfdoped poly(o-anthranilic acid; SD-PARA)) 19,20 as a partially charged interlayer because the SD polymer is resistant to any possible deterioration of the device performances by the migration of guest dopant molecules that are doped into polymers when external guest dopants are used (note that polar dopant molecules can be mobile under high electric fields for writing operation). For fabricating the PEW-OFET devices, we specifically attempted to use relatively cheap silver (Ag) source and drain electrodes rather than the expensive gold electrodes that have typically been used in previous reports 18 because the use of gold electrodes is one of the primary hurdles for the commercialization of organic memory devices.…”