**Organic Field-Effect Transistor: Device Physics, Materials, and Process**

Jingjing Chang, Zhenhua Lin, Chunfu Zhang and Yue Hao

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.68215

#### Abstract

Organic field-effect transistors have received much attention in the area of low cost, large area, flexible, and printable electronic devices. Lots of efforts have been devoted to achieve comparable device performance with high charge carrier mobility and good air stability. Meanwhile, in order to reduce the fabrication costs, simple fabrication conditions such as the printing techniques have been frequently used. Apart from device optimization, developing novel organic semiconductor materials and using thin-film alignment techniques are other ways to achieve high-performance devices and functional device applications. It is expected that by combining proper organic semiconductor materials and appropriate fabrication techniques, high-performance devices for various applications could be obtained. In this chapter, the organic field-effect transistor in terms of device physics, organic materials, device process, and various thin-film alignment techniques will be discussed.

Keywords: organic field-effect transistors, device physics, organic semiconductor materials, device process, thin-film alignment

#### 1. Introduction

Organic field-effect transistors (OFETs) have received much attention for plastic electronics due to their good solution processability, low temperature deposition, low cost, and compatibility with large-area printing technology. Although the conventional amorphous silicon-based semiconductors have achieved much progress with charge carrier mobility around 1.0 cm2 V<sup>1</sup> s 1 , the thin-film deposition of conventional semiconductor usually needs high temperature process and dustless conditions which significantly increase the fabricating cost. Most importantly, the silicon-based materials are rare to be processed on flexible substrates due to their poor stretching characteristics. Nevertheless, compared to the conventional silicon-based semiconductors, the organic-based semiconductors exhibit low cost, good processibility and can be fabricated on

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flexible substrates. Hence, using organic semiconducting materials has become an important topic in the development of low-cost, large area, flexible, and lightweight devices.

Organic-based semiconductors have various applications as key components of numerous electronic and optoelectronic devices, including field-effect transistors (FETs), photovoltaics (PVs), and light-emitting diodes (LED). Especially for the field-effect transistor, a lot of efforts have been done to develop new organic materials to improve device performance with high charge carrier mobility and good air stability. Anyhow, OFETs have been considered as a key component of organic integrated circuits for application in flexible smart cards, low-cost radio frequency identification (RFID) tags, sensor devices, organic active matrix displays, and so on [1–6]. However, it is still far from satisfactory for practical applications. The focus of recent attention has been devoted to improving device performance and stability, reducing the fabrication cost, exploring new applications, and developing simple fabrication techniques. Overcoming these challenges relies on the novel organic semiconductor development and device optimization.

In this chapter, organic field-effect transistors will be discussed from three aspects: the device physics, device materials, and device processing. The first section will talk about the charge transport and related mechanisms in organic semiconductor materials and the techniques used to characterize the charge carrier mobility, such as time of flight, field-effect transistor, and space-charge limited current (SCLC) technique. In the second section, we discuss the organic field-effect transistor from basic principle, device structure, and the main parameters, such as charge carrier mobility, current on/off ratio, threshold voltage, subthreshold voltage, and the corresponding influence factors in the OFET. The third section will talk about the organic materials selection, including mostly used aromatic p-type semiconductors and n-type semiconductors. The forth section will discuss the fabrication techniques in the organic field-effect transistors, including vapor deposition, solution deposition, and some thin-film alignment methods.
