A Study on Defects in Organic Semiconductors for Field Effect Transistors

2012 - 2013The understanding and the modeling of mechanisms involved in organic semiconductors are the aims of this Ph.D. thesis. In particular, the document focuses the attention on the role played by organic semiconductor defectson the electrical performance of organic-based field effect transistors. Critical issues are, indeed, the localized states related to the presence of structural defects and chemical impurities. They dominate the charge carrier transport in organic semiconductors and define the quality of interfaces occurring in the transistors... [edited by author]XII n.s

Light- and bias-induced effects in pentacene-based thin film phototransistors with a photocurable polymer dielectric

In this work, pentacene-based thin film phototransistors were fabricated with a photocurable polymer insulator and their electrical stability was monitored when the devices were exposed to light sources at different wavelengths. The magnitude of the photocurrent induced by illumination was found to be the result of two distinct factors: a direct photocurrent, related to electron–hole pair generation, and a current enhancement caused by a threshold voltage shift. The direction of threshold translation is attributed to the nature of trap states, specifically those located in the pentacene film near the interface with the polymer, and is affected by a measurement-induced effect, so that the photosensitivity can be modulated by a persistent gate bias during illumination. The equations for these two contributions were developed to study the light effects on material structure, the trapping process of electrons at the insulator–semiconductor interface and the photoconductive efficiency in the organic semiconductor

Processing–Structure–Performance Relationship in Organic Transistors: Experiments and Model

In this paper, organic thin film transistors with different configurations are fabricated, and the effect on their performance when tailoring the semiconductor/insulator and semiconductor/contact interfaces through suitable treatments is analyzed. It is shown that the admittance spectroscopy used together with a properly developed electrical model turns out to be a particularly appropriate technique for correlating the performance of devices based on new materials in the manufacturing methods. The model proposed here to describe the equivalent metal–insulator–semiconductor (MIS) capacitor enables the extraction of a wide range of parameters and the study of the physical phenomena occurring in the transistors: diffusion of mobile ions through the insulator, charge trapping at the interfaces, dispersive transport in the semiconductor, and charge injection at the metal contacts. This is necessary to improve performance and stability in the case, like this one, of a novel organic semiconductor being employed. Atomic force microscopy images are also exploited to support the relationship between the semiconductor morphology and the electrical parameters

Multiplier-less Stream Processor for 2D Filtering in Visual Search Applications

A new 2D convolution-based filter is presented specifically designed to improve Visual Search applications. It exploits a new radix-3 partitioning method of integer numbers, derived from the weight partition theory, which allows substituting multipliers with simplified floating-point adders, working on 32 bits floating point filter coefficients. The memory organization allows elaborating the incoming data in raster scan order, as those directly provided by an acquisition source, without frame buffers and additional aligning circuitry. Compared to the existent literature, build around conventional arithmetic circuitry, the proposed design achieves state-of-the-art performances in the reduction of the mapped physical resources and elaboration velocity, achieving a critical path delay of about 4.5 ns both with a Xilinx Virtex 7 FPGA and CMOS 90nm std_cells

Simulation and fabrication of polarized organic photodiodes

Several important applications rely today on the detection of polarized light, as demonstrated by the wide range of sensing devices exploited over the years. Nevertheless, the miniaturization of such systems has been little explored. In this work, a possible solution towards the direct integration of the sensing optics within an electronic device has been established, utilizing a wire-grid polarizer in conjunction with a photodetector realized with organic semiconductors. The optical and electronic properties of the device have been studied and optimized using physically based numerical simulations. Consequently, a proof of concept of the photodetector has been demonstrated, having a polarization extinction ratio of 50 at a wavelength of 550 nm

Type 1 narcolepsy in anti-Hu antibodies mediated encephalitis: a case report

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