ABSTRACT
CHAPTER 3 Thin-Film Transistors Thin-film transistors (TFTs) were proposed by Weimer 1 , 2 in 1961. The semiconductor layer and gate insulator of the original TFTs were made of cadmium sulfide and silicon monoxide, respectively. These thin-film layers were deposited in vacuum by evaporation. In spite of the complexity of fabricating TFTs in a vacuum chamber, they obtained both depletion-type and enhancement-type TFTs with good saturation-current characteristics. At first, they applied these TFTs to thin-film logic circuitry and built circuits such as flip-flops, AND gates, and NOR gates for computer applications. Soon after this, the application of TFTs to liquid-crystal displays was also proposed and various materials have been studied for this purpose. Among them, CdSe TFTs 3 , 4 have been intensively studied, and TFT-addressed liquid-crystal panels of up to 6"×6" in size have been fabricated. Such panels are typically made with Al or Au as metallization, CdSe as the semiconductor, and SiO2 or Al2O3 as the insulator. Their applicability to alphanumeric and video displays has been demonstrated on a 180×180 pixel panel.
