For the past ten years, organic materials have been extensively investigated as an electronic material for thin film transistor (TFT) devices. Organic materials have great promise in terms of properties, processing and cost effectiveness. Organic thin-film transistors (OTFT) can be fabricated at reduced temperature and at lower cost compared to hydrogenated amorphous silicon thin-film transistors. The combination of low-temperature processing and flexible substrates may enable a large-scale low-cost continuous manufacturing process, resulting in a greatly reduced cost per unit area. Organic thin-film transistor (OTFT) is a promising alternative to amorphous silicon devices. They are the fundamental building blocks for basic analytical circuits, such as amplifiers, as well as the key elements for digital combinational logic circuits, such as adders, shifters, inverters, and arithmetic logic units, and are used to build sequential logic circuits, such as flip-flops. Moreover, organic transistors are essential for modern memory devices, integrated circuits, and microprocessors used in personal computers and laptops.
Figure 1. Basic schematic of a field-effect transistor
Applications
Radio frequency identification (RFID): There has been enormous interest in the development of RFID tags for item-level tracking of individual consumer's goods. Such tags are expected to dramatically improve inventory control, automation, and purchasing and checkout operations. Several approaches have been developed to realize item-level RFID. In most conventional approach, low-cost silicon RFID tags were developed. But their usages are restricted in water- and metal-contaminated environments. Moreover, silicon based RFIDs are not bendable, which limits their applicability in general flexible items. In contrast, organic electronic devices find wide applications in replacing flexible RFIDs. To realize low cost individual RFID tags, efforts have been made for development of item level RFID tags by using organic transistors and printed electronics technologies. Organic RFID tags are generally one to three orders of magnitude cheaper than silicon technology per unit area. RFID devices are usually deployed in different frequency bands to execute the required tasks. Operating range of most low-cost RFID technologies is likely to be limited by power delivered from the reader to the passive tag.
Displays system: An organic LED is a thin film device whose emissive layers are made of organic compound and does not require any back light function. In these displays, generation and combination of electron hole pairs produces photons in emissive layer. When current passes through a thin multi-layer organic material, it should be efficiently converted into light. Many OLEDs together on a screen make up a picture. OLEDs require no backlighting, so they have high luminous efficiency. They have also shown promise for brighter backgrounds, sharper images, better color quality, larger viewing angles, and lower voltage and faster switching time in the order of nano seconds. OLEDs are used in mobile phones, televisions and display systems. Organics have potential advantages in displays, where TFTs are implemented as switches to activate individual pixels. Hand-held devices with ultrathin displays can achieve higher resolution and information content, while new technologies, such as flexible displays and electronic paper, are potential revolutionary advancements. It has been demonstrated that organic light emitting diode (OLED) pixels are switched by integrating smart pixels with an OTFT.
Sensors: Because reliable devices for sensitive and selective chemical and biological assays are required in a variety of fields, miniaturized electronic analytical systems capable of fast, high-throughput and cost-effective multiplex sample screening are highly desirable. Operating OTFTs as responsive devices in a sensing circuit configuration should be a viable option. The strategic use of the gate bias can result in improved sensing performance. The remarkable response repeatability can be obtained by applying a reverse gate bias pulse after exposing the OTFT to analyte. OTFT opens the door to an organic-based sensor with good reliability.
