Cation Composition-Dependent Device Performance and Positive Bias Instability of Self-Aligned Oxide Semiconductor Thin-Film Transistors: Including Oxygen and Hydrogen Effect

Abstract

Amorphous oxide semiconductor transistors control the illuminance of pixels in an ecosystem of displays from largescreen TVs to wearable devices. To satisfy application-specific requirements, oxide semiconductor transistors of various cation compositions have been explored. However, a comprehensive study has not been carried out where the influence of cation composition, oxygen, and hydrogen on device characteristics and stability is systematically quantified, using commercial-grade process technology. In this study, we fabricate self-aligned topgate structure thin-film transistors with three oxide semiconductor materials, InGaZnO (In/Ga/Zn = 1:1:1), In-rich InGaZnO, and InZnO, having mobility values of 10, 27, and 40 cm 2 /V•s, respectively. Combinations of varied amounts of oxygen and hydrogen are incorporated into each transistor by controlling the fabrication process to study the effect of these gaseous elements on the physical nature of the channel material. Electrons can be captured by peroxy linkage (O 2 2− ) or undercoordinated In (In* to become In + ), which are manifested in the extracted subgap density-of-states profile and first-principles calculations. Energy difference between electron-trapped In + and O 2 2− σ* is the smallest for IGZO, and In + −O 2 2− annihilation occurs by electron excitation from the subgap In + state to the O 2 2− σ*. Furthermore, characteristic time constants during positive bias stress and recovery reveal the various microscopic physical phenomena within the transistor structure between different cation compositions.

Improvement in Short-Channel Effects and Bias-Stress Stability of Vertical Thin-Film Transistors Using Atomic-Layer-Deposited In–Ga–Sn–O Channels

“…Notwithstanding, VTFTs fabricated using IGTO channel layers with different cationic compositions exhibited excellent NBS stability, resulting in Δ V TH smaller than 0.5 V. The Δ V TH values under the PBS conditions were estimated to be +2.32, +1.54, and +0.87 V for Dev-A, Dev-B, and Dev-C, respectively. It has been reported as a general trend that the oxide channel TFTs typically experience a larger positive Δ V TH under PBS with increasing In content within the conventional IGZO channels . These results have previously been suggested to result from a higher degree of electron trapping events under PBS owing to a higher concentration of conduction carriers in the channel layers.…”

“…It has been reported as a general trend that the oxide channel TFTs typically experience a larger positive ΔV TH under PBS with increasing In content within the conventional IGZO channels. 22 These results have previously been suggested to result from a higher degree of electron trapping events under PBS owing to a higher concentration of conduction carriers in the channel layers. Contrarily, it was interesting to note that the obtained values of ΔV TH under PBS showed an anomalous decreasing trend with an increase in In content within the IGTO channel.…”

“…In other words, this interesting result demonstrates that the bulk trap density might be mainly influenced by the structural factors featured for the VTFTs rather than by the simple variations in the channel composition. These insights verified for the VTFTs were suggested be totally different from the case of conventional planar TFTs, in which bulk and interface trap densities at front channel between the active and GI interface generally exhibit an increasing trend with increasing the In content included in the channel due to a higher concentration of oxygen vacancies …”

“…These insights verified for the VTFTs were suggested be totally different from the case of conventional planar TFTs, in which bulk and interface trap densities at front channel between the active and GI interface generally exhibit an increasing trend with increasing the In content included in the channel due to a higher concentration of oxygen vacancies. 22 Alternatively, even for the VTFTs, typical events of electron trapping may also be initiated at the front channel between the active and GI interface under PBS, apart from the generation of additional free carriers due to the Sn localization. In this regard, it can be the important case that the localization of Sn and generation of additional carriers in the IGTO channel may compensate for + ΔV TH typically induced by the electron trapping due to an increase in channel conductance under PBS.…”

Investigation on Atomic Bonding Structure of Solution-Processed Indium-Zinc-Oxide Semiconductors According to Doped Indium Content and Its Effects on the Transistor Performance

“…Among them, in the studies focusing on the atomic composition ratio, the field-effect mobilities in the range 0.5–10.0 cm·V −1 s −1 were controlled by varying the ratio of In:Zn or In:Zn:Ga, and the thickness, roughness, and crystallinity of the semiconductor film were investigated relative to the atomic ratio [ 14 , 15 , 16 ]. Furthermore, a field-effect mobility of over 10 cm·V −1 s −1 was demonstrated using various dopant materials [ 17 , 18 , 19 , 20 ], and a mobility improvement of approximately ten times was achieved by applying chemical treatment or post-treatment [ 21 , 22 ]. In certain cases, the electrical characteristics of the TFT were significantly enhanced via the passivation process [ 23 ].…”