Interfacial Oxidized Gate Insulators for Low-Power Oxide Thin-Film Transistors

Abstract

Low power consumption is essential for wearable and internet-of-things applications. An effective way of reducing power consumption is to reduce the operation voltage using a very thin and high-dielectric gate insulator. In an oxide thin-film transistor (TFT), the channel layer is an oxide material in which oxygen reacts with metal to form a thin insulator layer. The interfacial oxidation between the gate metal and In–Ga–Zn oxide (IGZO) was investigated with Al, Ti, and Mo. Positive bias was applied to the gate metal for enhanced oxygen diffusion since the migration of oxygen is an important factor in interfacial oxidation. Through interfacial oxidation, a top-gate oxide TFT was developed with low source–drain voltages below 0.5 V and a gate voltage swing less than 1 V, which provide low power consumption.

High-Performance Self-Aligned Top-Gate Amorphous InGaZnO TFTs With 4 nm-Thick Atomic-Layer-Deposited AlOx Insulator

“…The capacitance-voltage (C-V) characteristics stay almost constant in a wide frequency range from 1 kHz to 500 kHz, indicating the absence of common hydrogen-related mobile ions or dipoles in high-k dielectrics [11], [14], [22]. Both current and capacitance measurements verify the excellent insulating properties of the 4-nm-thick ALD AlO x , being better than the reported high-k candidates [9]- [14], [16]- [21].…”

“…In comparison to aforementioned high-k dielectrics, AlO x has a relatively larger band offset with a-IGZO [1], [15]. This is beneficial to suppress the gate leakage current (I g ) and bias instabilities, thus making AlO x a more favorable candidate for the ultrathin GI of AOS TFTs [16]- [21]. The AlO x GI of AOS TFT has been thinned down to 5 nm by using the atomic layer deposition (ALD) [17].…”

Improved Electron Transport Properties of Zn-Rich In–Ga–Zn–O Thin-Film Transistors

“…Next, we fabricated IGZO m -TFTs on ITO-AlO x glass insulator substrates and measured their transistor characteristics. Compared to the other high- k dielectrics, AlO x has a relatively larger band offset with IGZO m . , Therefore, we expected that the gate leakage current and bias instabilities would be suppressed by the use of AlO x gate insulator for IGZO m -TFTs. Figure a shows the typical transfer characteristics of IGZO m -TFTs at room temperature.…”

Near-Ideal Top-Gate Controllability of InGaZnO Thin-Film Transistors by Suppressing Interface Defects with an Ultrathin Atomic Layer Deposited Gate Insulator

“…However, the self-aligned top-gate (SATG) AOS TFT with smaller parasitic capacitance and better scalability , is preferred by the advanced applications, wherein the post-AOS GI deposition places a daunting challenge on realizing ultrathin top-gate (TG) EOT with ALD high- k dielectrics. The associated ALD processes with chemically reactive species often induced abundant defect states at the GI/channel interface − and in the AOS channel. , These defect states can result in the increased off-state current ( I off ), a reduced on/off ratio, poor subthreshold swing (SS), and a negative threshold voltage ( V th ) shift, , while the defect-sensitive stabilities could deteriorate even more severely. , Therefore, it is highly desired to clarify the interaction mechanism between the top AlO x GI and the bottom a-IGZO channel, in order to direct the suppression of defect generation during the ALD process and thus enable the high performance and reliability of ultrathin-EOT SATG AOS TFTs.…”

“…In order to enhance the gate controllability in short-channel AOS transistors, various high- k dielectrics deposited by atomic layer deposition (ALD) have been investigated to considerably reduce the equivalent oxide thickness (EOT) of the GI, such as HfO x , − LaAlO 3 , HfAlO x , and AlO x . − However, the conduction band offset (Δ E c ) between the AOS channel and high- k GI is lower than that between AOS and SiO 2 , which can arise the risk of charge injection to the conduction band of GI. , Among these dielectrics, AlO x has the largest Δ E c with a-IGZO, , which makes AlO x the most favorable high- k GI for AOS TFTs.…”