Oxide-Channel Ferroelectric-Gate Thin Film Transistors with Nonvolatile Memory Function

In this chapter, principle and progress of oxide-channel ferroelectric-gate transistors are reviewed. At first, it is pointed out that ferroelectric-gate insulator can induce large charge density because of the remanent polarization, in addition to non-volatile memory function. Next, using this feature of ferroelectric gate insulator, it is shown that even conductive oxide, such as indium-tin-oxide (ITO), can be used as a channel if its thickness is thin enough. Good transistor performance is demonstrated for ITO-channel ferroelectric-gate thin film transistors (TFTs). In particular, a large on-current can be obtained in such devices, because large charge density is utilized even though the channel mobility is not so high. Furthermore, transparent devices were demonstrated using ITO for both channel and electrodes. In addition, ITO channel TFTs without nonvolatile memory function are demonstrated using high-dielectric constant (high-k) material as a gate insulator.