Ahmed Nejim

Bio: Ahmed Nejim is an academic researcher. The author has contributed to research in topics: Logic gate & Transistor. The author has an hindex of 4, co-authored 9 publications receiving 191 citations.

Current Status and Opportunities of Organic Thin-Film Transistor Technologies

Abstract: Attributed to its advantages of super mechanical flexibility, very low-temperature processing, and compatibility with low cost and high throughput manufacturing, organic thin-film transistor (OTFT) technology is able to bring electrical, mechanical, and industrial benefits to a wide range of new applications by activating nonflat surfaces with flexible displays, sensors, and other electronic functions. Despite both strong application demand and these significant technological advances, there is still a gap to be filled for OTFT technology to be widely commercially adopted. This paper provides a comprehensive review of the current status of OTFT technologies ranging from material, device, process, and integration, to design and system applications, and clarifies the real challenges behind to be addressed.

Modelling of organic field-effect transistors for technology and circuit design

Abstract: As organic field-effect transistors (OFETs) are preparing to take a key role in the flexible and low cost electronics applications, there is a pressing need for predictive device models to support technology optimization and circuit design. This paper focuses on the specific OFET features that challenge current modelling approaches. The presented modelling techniques range from the fundamental semiconductor equations to compact device model representations as required for implementation in advanced TCAD and EDA commercial tools. The models are verified with measured characteristics of advanced OFET device structures.

Parametrization of the Gaussian Disorder Model to Account for the High Carrier Mobility in Disordered Organic Transistors

Abstract: Correct parameterization of the Gaussian disorder model (GDM) on spatially random sites is necessary for a complete description of charge transport in disordered materials and concomitant device characteristics Because the GDM on spatially random sites considers both energetic and spatial disorder, it is superior to the GDM on a cubic lattice However, analytical arguments and experimental evidence are still lacking for correct parameterization of the model over a wide range of model parameters, energetic and spatial disorder, and electric fields We show that the model requires a set of parameters to correctly account for high mobility and its charge density dependence, and we develop such a model The model is implemented in a numerical simulation tool for comparison with the measured device characteristics Accurate agreement with experimental data, particularly with the high mobility values in organic field-effect transistors, is achieved throughout a wide range of temperature by adjusting both the localization length and the attempt-to-escape frequency

Parameter Extraction and Evaluation of UOTFT Model for Organic Thin-Film Transistor Circuit Design

Abstract: In this paper, we report a systematic approach to extract parameters from organic thin film transistors (OTFTs) that are used for compact Spice models. The universal organic thin-film transistor (UOTFT) model and Silvaco's Smartspice platform are utilized for simulations whereas experimental data are collected from Plastic Logic's (PL) thin-film transistors that are processed on flexible plastic substrates. The parameter extraction procedure is outlined where both current-voltage and capacitance-voltage measurements are employed. This is then followed by simulations of inverters and ring oscillators to assess the results against simple logic circuits.

New Compact Modeling Solutions for Organic and Amorphous Oxide TFTs

Abstract: We review recent compact modeling solutions for Organic and Amorphous Oxide TFTs (OTFTs and AOS TFTs, respectively), which were developed, under the framework of the EU-funded project DOMINO, to address issues specifically connected to the physics of these devices. In particular, using different approaches, analytical equations were formulated to model the Density of States (DOS), different transport mechanisms, trapping/de-trapping, drain current, stress, capacitances, frequency dispersion and noise. The final TFT models were, after implementation in Verilog-A, validated by means of the design and simulation of test circuits.

Charge transport in high-mobility conjugated polymers and molecular semiconductors

Abstract: Conjugated polymers and molecular semiconductors are emerging as a viable semiconductor technology in industries such as displays, electronics, renewable energy, sensing and healthcare. A key enabling factor has been significant scientific progress in improving their charge transport properties and carrier mobilities, which has been made possible by a better understanding of the molecular structure–property relationships and the underpinning charge transport physics. Here we aim to present a coherent review of how we understand charge transport in these high-mobility van der Waals bonded semiconductors. Specific questions of interest include estimates for intrinsic limits to the carrier mobilities that might ultimately be achievable; a discussion of the coupling between charge and structural dynamics; the importance of molecular conformations and mesoscale structural features; how the transport physics of conjugated polymers and small molecule semiconductors are related; and how the incorporation of counterions in doped films—as used, for example, in bioelectronics and thermoelectric devices—affects the electronic structure and charge transport properties. Organic semiconductors are making their way into applications ranging from display technology to flexible electronics and biomedical applications. This Review discusses current understanding of charge carrier transport in these materials and strategies to improve their performance.

Current versus gate voltage hysteresis in organic field effect transistors

Abstract: Research into organic field effect transistors (OFETs) has made significant advances—both scientifically and technologically—during the last decade, and the first products will soon enter the market. Printed electronic circuits using organic resistors, diodes and transistors may become cheap alternatives to silicon-based systems, especially in large-area applications. A key parameter for device operation, besides long term stability, is the reproducibility of the current–voltage behavior, which may be affected by hysteresis phenomena. Hysteresis effects are often observed in organic transistors during sweeps of the gate voltage (V GS). This hysteresis can originate in various ways, but comparative scientific investigations are rare and a comprehensive picture of “hysteresis phenomena” in OFETs is still missing. This review provides an overview of the physical effects that cause hysteresis and discusses the importance of such effects in OFETs in a comparative manner.