Review Article: Atomic layer deposition for oxide semiconductor thin film transistors: Advances in research and development

Abstract

This article is a review of recent research and development advances in oxide thin film transistors (TFTs) fabricated by atomic layer deposition (ALD) processes. The ALD process is remarkable as it offers accurate control of film thickness and composition as well as the ability to achieve excellent uniformity over large areas at relatively low temperatures. Firstly, an introduction to n-type oxide TFTs is provided with a focus on the development of active-layer material combinations from binary oxide active layers, like zinc oxide and indium oxide, to ternary and quaternary oxide active layers formed by doping with elements such as gallium or tin to achieve high mobility and high device stability for TFTs. Secondly, ALD p-type channel oxide TFTs are also introduced, which are required for the realization of many types of low-power circuits, such as complementary metal oxide semiconductor devices.

Low-Voltage Hf-ZnO Thin Film Transistors With Ag Nanowires Gate Electrode and Their Application in Logic Circuit

“…The O-deficiency of Hf-ZnO is smaller than that of ZnO. Oxygen deficiency leads to higher carrier concentration, which moves the Fermi level upwards [17], [26]. The relative area of O-H for all thin films is very small, implying the ALD processed thin films have a high density [27].…”

“…Before coated, the 20 nm ALD-Al 2 O 3 was grown on the polyimide (PI) at 100 • C as the buffer layer of TFT devices. The buffer layer has two functions: (1) to decrease the rootmean-squared (RMS) and improve the surface quality of substrate; and (2) to reduce the water vapor transmission rate (WVTR) of substrate [15]- [17]. The Ag NWs dispersed in isopropyl alcohol (IPA), whose diameter is about 30 nm and length is about 100 μm.…”

Amorphous InGaZnO and metal oxide semiconductor devices: an overview and current status

“…In most cases this has taken the form of solution processing methods such as spin coating, inkjet printing, or spray pyrolysis [137][138][139][140] . There is also a growing body of work using spatial atomic layer deposition (S-ALD) that began in 2015 with work from Illiberi et al 141 and has expanded to several research groups in the last few years [142][143][144][145] . in large area and roll-to-roll processing, it remains very much a developing area with significant challenges, and is partially reviewed in the recent work from Sheng et al 145 .…”

“…There is also a growing body of work using spatial atomic layer deposition (S-ALD) that began in 2015 with work from Illiberi et al 141 and has expanded to several research groups in the last few years [142][143][144][145] . in large area and roll-to-roll processing, it remains very much a developing area with significant challenges, and is partially reviewed in the recent work from Sheng et al 145 . For solution processing routes these challenges are mostly in terms of the material properties, as solution processed a-IGZO has a significantly lower density than the sputtered material, which leads to reduced device performance in terms of carrier mobility, threshold control, and device stability (see section 4 for discussion of the link between density, defects, and device performance).…”

Temperature Gradient ZnO Deposited via ALD for High-Performance Transistor Applications

“…For the deposition technique of the ZnO, atomic layer deposition (ALD) is different from the traditional physical and chemical vapor deposition techniques [7], [8]. Physical vapor deposition techniques, such as magnetron sputtering, usually lead to poor film composition consistency and reproducibility, which is not ideal for making high-performance films [9].…”