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Thin Film Transistors
Published in Juan Bisquert, The Physics of Solar Energy Conversion, 2020
A thin film transistor (TFT) is a three-terminal device, formed by a thin active film deposited on top of an insulating (normally a metal-oxide) layer that separates the bottom electrode (the gate G) from the active film, which is denoted as the channel; see Figure 14.1. The active film has two contacts, the source (S) and the drain (D). The application of bias voltage Vds between these contacts allows us to measure the current along the channel. The fundamental advantage of the three-contact structure is that the carrier density in the film is controlled by the voltage applied below the substrate, the gate voltage, with respect to the source contact, Vgs, denoted simply Vg; see Figure 14.1. The conductivity of the channel can be changed by orders of magnitude, from an “off” state below a given threshold voltage Vt in which there is no conduction at all, to a highly conducting state. We have already observed in Section 8.5 that the properties of organic conductors can vary widely, from intrinsic and insulating to highly doped, from crystalline to disordered, or formed by a polymer and even a blend of electron and hole conductor materials. To analyze the main features of transistor operation, we will consider two types of situations.
Clinical Radiographic Units
Published in Paolo Russo, Handbook of X-ray Imaging, 2017
Flat panel detectors have integrated readout mechanisms based on a thin film of transistors (TFT). The TFT (Figure 26.22) enables the adjacent coupling of the readout electronics and the pixels within the flat panel, and is built into a sheet of glass positioned along with the amorphous silicon and phosphors: the phosphors on the uppermost layer; the amorphous silicon in the middle; and the readout TFT on the lower level. The TFT is created through a process of microfabrication, where the parts of the thin film are created using photolithography. This uses light to transfer a geometric pattern to the substrate. This enables the new material for the thin film transistors to be deposited inside the photolithographic geometry (Neudeck and Pierret 2002).
Thin Film Transistors
Published in Juan Bisquert, Nanostructured Energy Devices, 2017
A thin film transistor (TFT) is a three-terminal device, formed by a thin active film deposited on top of an insulating (normally a metal-oxide) layer that separates the bottom electrode (the gate G) from the active film, which is denoted as the channel; see Figure 5.1. The active film has two contacts, the source (S) and the drain (D). The application of bias voltage Vds between these contacts allows us to measure the current along the channel. The fundamental advantage of the three-contact structure is that the carrier density in the film is controlled by the voltage applied below the substrate, the gate voltage, with respect to the source contact, Vgs, denoted simply Vg; see Figure 5.1. The conductivity of the channel can be changed by orders of magnitude, from an “off” state below a given threshold voltage Vt in which there is no conduction at all, to a highly conducting state. We have already observed in Section ECK.8.5 that the properties of organic conductors can vary widely, from intrinsic and insulating to highly doped, from crystalline to disordered, or formed by a polymer and even a blend of electron and hole conductor materials. To analyze the main features of transistor operation, we will consider two types of situations.
Topological structure and COVID-19 related risk propagation in TFT-LCD supply networks
Published in International Journal of Production Research, 2023
Xiongping Yue, Dong Mu, Chao Wang, Huanyu Ren, Pezhman Ghadimi
TFT-LCD supply networks warrant a dedicated investigation because TFT-LCD panels are used in many applications, such as TVs, laptops, smartphones, and monitors. Most previous studies have investigated technical improvements and operational management in the TFT-LCD panel industry. However, none of these studies investigated TFT-LCD supply network topologies. Moreover, the hidden risky sources in TFT-LCD supply networks have not been clarified, which inspired our research. Therefore, TFT-LCD supply network topologies are investigated from a dynamic perspective. First, in contrast to the static analysis of characteristics, the evolution of TFT-LCD supply network topologies from 2015 to 2020 is examined by forming weighted and undirected supply networks. Second, the hidden risky sources in TFT-LCD supply networks due to the COVID-19 pandemic are revealed by risk propagation models. The results can support managers in optimising the supply network structure and mitigating adverse shocks. The main results and implications are presented in the following.
A high-gain two-stage amplifier using low-temperature poly-si oxide thin-film transistors with a Corbino structure
Published in Journal of Information Display, 2022
Dong-Hwan Jeon, Won-Been Jeong, Jeong-Soo Park, Hoon-Ju Chung, Seung-Woo Lee
Currently, various backplane technologies have been used in display applications. For instance, thin-film transistors (TFTs) made of n-type hydrogenated amorphous silicon (a-Si:H) have been widely used in liquid crystal display panels. TFTs made of low-temperature polycrystalline silicon (LTPS) exhibit high mobility, thereby allowing for high-speed operation. N-type amorphous indium-gallium-zinc oxide TFTs, also known as oxide TFTs, have extremely low leakage currents and uniform device performance. LTPS and oxide TFT technologies have been widely used in mobile and large area displays, respectively. Recently, low-temperature poly-Si oxide (LTPO) TFT technologies have been actively studied for mobile applications [1]. The low leakage current of oxide TFT contributes to the realization of a variable refresh rate and low power consumption in display applications. As a result, various studies adopting the LTPO technology have been conducted, such as pixel circuits for displays using organic light-emitting diodes [2–5], liquid crystals [6–9], and micro-light-emitting diodes [10]. In addition to pixel circuits, LTPO technology has been studied in display circuits, such as gate drivers [2,11–13], level shifters [14], and inverters [15–19].
Flexible distributed Bragg reflectors as optical outcouplers for OLEDs based on a polymeric anode
Published in Journal of Information Display, 2021
Carmela Tania Prontera, Marco Pugliese, Roberto Giannuzzi, Sonia Carallo, Marco Esposito, Giuseppe Gigli, Vincenzo Maiorano
In 1987, Tang and his co-workers demonstrated the first organic light emitting diode (OLED) that used an organic material as an emitter in a thin film electroluminescent device [1]. Since then, this kind of optoelectronic device has been extensively developed in both the academic and industrial fields for display and lighting applications. Indeed, OLEDs are dominating the display market, thanks to their multiple advantages: improved image quality (better contrast, higher brightness, wide viewing angle, wide color range, and fast refresh rate); low power consumption; and simple design that enables, in principle, the fabrication of thin, flexible, and even bendable displays [2,3]. Moreover, high-performance displays can be obtained by combining a pixelated matrix of OLEDs with a thin transistor layer that controls the switching of the individual pixels (active-matrix OLED or AMOLED) [4]. Usually, the opaque thin film transistor (TFT) array is manufactured on the substrate before the deposition of the materials of the OLED. For this reason, a top-emitting OLED (TOLED) is preferable for AMOLED structures [5,6]. Furthermore, in the top-emission architecture, the light is not trapped in the substrate with advantages in the light outcoupling [7–10]. The top-emitting structure also represents a solution for the integration of OLED devices in textiles, with interesting prospects for the development of wearable displays [11]. For all the mentioned reasons, TOLEDs are an ideal candidate for easy integration and engineering for the evolution of next-generation flexible displays.