Structural, Optical, and Electrical Properties of InO_x Thin Films Deposited by Plasma-Enhanced Atomic Layer Deposition for Flexible Device Applications

Abstract

Indium oxide (InO x ) thin films have attractive carrier transport properties for oxide semiconductors because of the large isotropic 5 s orbital overlap. In this study, InO x films were deposited by plasma-enhanced atomic layer deposition (PEALD). We evaluated the effects of the ALD process conditions such as the process temperature, plasma power, and plasma duration time on the microstructure, physical, chemical, and electrical properties of the as-deposited InO x films. The InO x film deposited at an even growth temperature of 100 °C exhibited a polycrystalline structure without impurities. As the growth temperature increased, the (222) orientation became favorable and the surface morphology of the as-deposited films improved. In addition, staggered-bottom gate structure thin-film transistors (TFTs) were fabricated to examine the feasibility of the ALD-processed InO x film as a channel material for TFTs. As the growth temperature increased from 100 to 250 °C, the mobility increased from 3.4 to 12.6 cm2/V s and the hysteresis value decreased from 1.85 to 0.94 V due to increasing carrier concentrations and decreasing defect states, respectively. Finally, a flexible device was fabricated on a polyethylene naphthalate substrate; the device parameters of V th and μsat were determined to be 2.21 V and 16.6 cm2/V s, respectively. These results demonstrate the potential for fabricating flexible TFT applications using PEALD.

High-Performance Thin-Film Transistor with Atomic Layer Deposition (ALD)-Derived Indium–Gallium Oxide Channel for Back-End-of-Line Compatible Transistor Applications: Cation Combinatorial Approach

“…The device with the In 2 O y channel layer showed high μ FE value of 59.45 ± 1.37 cm 2 /(V s) and a low SS value of 78.4 mV/decade and a great I ON/OFF ratio. This performance corresponds to the state-of-the-art characteristics, compared to those for the In 2 O 3 FETs reported in the literature. ,, The transistors with sputtered In 2 O 3 channel layer are known to suffer from the large leakage current (>1 nA) and thus low I ON/OFF ratio (<10 6 ), which is attributed to the high free carrier density due to the facile formation of V O . ALD-derived In 2 O y transistors had better performance than that of sputtered In 2 O 3 transistor, which can be explained by the conformal uniformity of ultrathin channel layer (<10 nm) and less gap-state density, because of its higher mass density stemming from self-limiting behavior.…”

“…), which is attributed to the high free carrier density due to the facile formation of V O . 28 ALD-derived In 2 O y transistors had better performance than that of sputtered In 2 O 3 transistor, which can be explained by the conformal uniformity of ultrathin channel layer (<10 nm) and less gap-state density, because of its higher mass density stemming from self-limiting behavior. It is important to understand the cause for the behavior of the fabricated In 2 O y transistor produced in this study, which exhibits the superior performance, in terms of mobility and steep subthreshold slope.…”

“…This performance corresponds to the state-of-the-art characteristics, compared to those for the In 2 O 3 FETs reported in the literature. 28,45,58 The transistors with sputtered In 2 O 3 channel layer are known to suffer from the large leakage current (>1 nA) and thus low…”

“…18,27 Although the highest Hall mobility is expected in the crystalline In 2 O 3 , the random polycrystalline nature and huge concentration of shallow oxygen vacancy (V O ) defects of In 2 O 3 allow the resulting TFTs to suffer from unacceptable leakage current and V TH nonuniformity. 28,29 Tailoring the crystal structure and electron concentration in the bixbyite In 2 O 3 is an essential process, which can be achieved by the proper introduction of Ga 2 O 3 during ALD growth. In this paper, the ALD-growth of In 2(1−x) Ga 2x O y films and its application in TFTs are examined as grown by plasmaenhanced ALD (PEALD).…”

“…Among various O/S systems, the ternary IGO substance is promising in terms of high mobility due to the low effective electron mass. Unlike IGZO, Zn-free IGO can exhibit an amorphous state or cubic bixbyite crystal structure, depending on the cation composition and processing temperature. , Although the highest Hall mobility is expected in the crystalline In 2 O 3 , the random polycrystalline nature and huge concentration of shallow oxygen vacancy ( V O ) defects of In 2 O 3 allow the resulting TFTs to suffer from unacceptable leakage current and V TH nonuniformity. , Tailoring the crystal structure and electron concentration in the bixbyite In 2 O 3 is an essential process, which can be achieved by the proper introduction of Ga 2 O 3 during ALD growth.…”