-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.

Thin-film, self-aligned source-gated transistors (SGTs) have been made in polysilicon.The very high output impedance of this type of transistor makes it suited to analog circuits.Intrinsic voltage gains of greater than one thousand have been measured at particular drain voltages. The drain voltage dependence of the gain is explained based on the device physics of the source-gated transistor and the fact that pinch-off occurs at both the source and the drain. The results obtained from these devices, which are far from optimal, suggest that, with proper design, the source-gated transistor is well suited to a wide range of analog applications.

-A physical description for low-field behavior of a Schottky source-gated transistor (SGT) is outlined where carriers crossing the source barrier by thermionic emission are restricted by JFET action in the pinch-off region at the drain end of the source. This mode of operation leads to transistor characteristics with low saturation voltage and high output impedance without the need for field relief at the edge of the Schottky source barrier and explains many characteristics of the SGT observed experimentally. Two-dimensional device simulations with and without barrier lowering due to the Schottky effect show that transistors can be designed so that the current is independent of source length and thickness variations in the semiconductor. This feature, together with the fact that the current in an SGT is independent of source-drain separation, hypothesizes the fabrication of uniform current sources and other large-area analog circuit blocks with repeatable performance even in imprecise technologies such as high-speed printing.

Ultra-large-scale integrated (ULSI) circuits have benefited from successive refinements in device architecture for enormous improvements in speed, power efficiency and areal density. In large-area electronics (LAE), however, the basic building-block, the thin-film field-effect transistor (TFT) has largely remained static. Now, a device concept with fundamentally different operation, the source-gated transistor (SGT) opens the possibility of unprecedented functionality in future low-cost LAE. With its simple structure and operational characteristics of low saturation voltage, stability under electrical stress and large intrinsic gain, the SGT is ideally suited for LAE analog applications. Here, we show using measurements on polysilicon devices that these characteristics lead to substantial improvements in gain, noise margin, power-delay product and overall circuit robustness in digital SGT-based designs. These findings have far-reaching consequences, as LAE will form the technological basis for a variety of future developments in the biomedical, civil engineering, remote sensing, artificial skin areas, as well as wearable and ubiquitous computing, or lightweight applications for space exploration.

-Source-gated transistors (SGTs) have potentially very high output impedance and low saturation voltages, which make them ideal as building blocks for high performance analog circuits fabricated in thin-film technologies. The quality of the saturation is greatly influenced by the design of the field-relief structure incorporated into the source electrode. Starting from measurements on self-aligned polysilicon structures, we show through numerical simulations how the field plate design can be improved. A simple source field plate around 1µm long situated several tens of nm above the semiconductor can increase the low-voltage intrinsic gain by more than two orders of magnitude and offers adequate tolerance to process variations in a moderately scaled thin-film SGT.