Promising Solution Processed Lanthanide Films as High-k Gate Insulators for Low Voltage-Driven Oxide Thin Film Transistors

Abstract

Low power-operated oxide thin film transistors (TFTs) were successfully obtained using high-k lanthanides produced via a simple solution process. Sol-gel derived high-k thin films exhibit the dielectric constant in the range of 11-15 with breakdown field as high as 3.5 MV cm À1 . Among the representative lanthinides, the Gd-based oxide acts as an effective gate insulator operating the TFTs properly. It might be induced by the uniform nucleation density followed by finer nanocrystalline grains with high Gd content.In general, high capacitance in thin film transistors (TFTs) plays an important role in increasing the capacitive coupling between the gate and active layer, leading to enhancement of the subthreshold swing and the operation voltage range. High-k lanthanides have attracted much attention as potential gate insulators to replace SiO 2 for next generation TFTs. 1,2 Offering high capacitance with low leakage current and good thermal/chemical stability with respect to various substrates, they are superior to other high capacitive materials such as HfO 2 , ZrO 2 .Recently, oxide TFTs have attracted much attention as promising large-area backplane electronics for upcoming displays, including transparent display devices currently under development. 3 The development of high-performance amorphous metal oxide semiconductors has been actively carried out to date, while there has been only limited research on the use of alternative dielectrics as gate insulators. 4-6 Much effort has been dedicated to reducing power consumption for the realization of mobile and portable applications using oxide-based TFTs with a high-k gate dielectric. Very recently, Liu et al. first investigated the characteristics of a ZnO-based TFT with a gate oxide of Gd 2 O 3 fabricated at room temperature via a pulsed laser deposition method. 7 While the aforementioned advantages using high-k materials as gate insulators are well documented, one of the major problems associated with the introduction of high-k films is a dramatic lowering of the channel mobility. The exact reason for the observed decrease has not been identified, although a number of possible scattering mechanisms have been proposed, including the following: remote phonons, fixed charges, and interfacial dipoles. 8,9 Thus, the proper selection of semiconductors and gate insulators and in-depth studies of high-k/oxide semiconductor systems are important undertakings in the quest for improving the performance of oxide TFTs.Additionally, given recent advances in vacuum-deposited oxide semiconductors, stable and complementary solution-processed alloxide devices offer a new approach. Moreover, direct patterning can be accomplished through ink-jet printing, imprinting, and roll-toroll processes without a complex photolithography process. Operational solution-processed oxide TFTs represent a vital part of this vision, and the stringent requirements on film quality and electrical characteristics make the realization of such TFTs a challenging goal and a key development milestone. 10,11 ...

Independent control of phases and defects in TiO2 thin films for functional transistor channels

“…On the other hand, TiO 2 has not seriously been considered as a transistor channel, although the TiO 2 channel carries a potential of modulating various surface properties by electrostatic back gating. It is partially because the previously fabricated TiO 2channel thin film transistors (TFTs) only showed a limited value of field effect mobility (m FE ) below 1 cm 2 V À1 s À1 in TFTs [3][4][5][6][7][8][9]. This m FE is one-order lower than indium gallium zinc oxide (IGZO) channel, which is used in TFTs for displays due to its relatively high electron mobility >10 cm 2 V À1 s À1 and spatial uniformity [10].…”

“…In the past literature, TiO 2 -channel TFTs were fabricated with several different gate insulators: SiO 2 [4,[6][7][8][9]16], LaAlO 3 [3], and Y 2 O 3 [5]. The low m FE in these devices was sometimes attributed to electronic traps or scattering centers at the gate-channel interface [8].…”

Low-Voltage-Operating Transistors and Logic Circuits Based on a Water-Driven ZrGdOx Dielectric with Low-Cost ZnSnO

“…Among these high-κ materials, ZrO x has attracted more attention because of its appropriate band alignment and high dielectric constant of 22. Currently, some researchers have been enthusiastic about improving ZrO x -based or GdO x -based TFTs and have gained obvious progress by spin-coating. − Liu et al even fabricated ZnO/Gd 2 O 3 TFTs at room temperature via pulse laser deposition . By combining ZrO 2 and Gd 2 O 3 together, it is possible to design a kind of excellent ternary gadolinium zirconium oxide dielectric film with respective advantages.…”