Developing Subthreshold-Swing Limit of PEALD In–Sn–Ga–O Transistor via Atomic-Scaled Sn Control

Abstract

The In−Sn−Ga−O (ITGO) thin-film transistor (TFT) is promising in that it possesses enhanced electrical characteristics and stability because the tin (Sn) has large spherical s orbitals and a high binding energy with oxygen (O). Recently, there have been several reports of ITGO material fabricated via sputtering. Therefore, studies that control Sn composition to achieve unique characteristics and obtain conformal films have been limited. For these reasons, we evaluated plasma-enhanced atomic layer deposition (PEALD)-derived ITGO materials with varied Sn composition. The electrical characteristics are enhanced with the Sn subcycle ratio from 1 to 5 in the ITGO films (carrier concentration: 6.4 × 10 20 to 2.2 × 10 21 cm −3 , resistivity: 8.6 × 10 −4 to 6.1 × 10 −4 Ω cm). These results are due to carrier generation by the Sn, a decrease in oxygen-related defects (22.9% to 19.5%), and suppressed indium-oxide (In 2 O 3 ) crystallinity. To demonstrate their applicability to practical devices, the ITGO films were applied to TFTs as active channel layers. The ITGO TFTs with increasing Sn content show a decrease then increase of subthreshold swing (S.S.) characteristics, while the field-effect mobility (μ FE ) slightly increases. In addition, the ITGO TFTs show improved negative bias illumination stress (NBIS) stability with increasing Sn content, while the turnaround point is observed in the Sn 5 subcycle. As a result, the ITGO TFT with the Sn 3 subcycle shows an extremely low S.S. of 64.8 ± 1.9 mV/decade and an NBIS result of −0.5 V. The outstanding performance of the ITGO TFT with Sn 3 subcycle is attributed to its low number of oxygen-related defects, amorphous structure, and low valence band maximum (VBM) level. Therefore, the ITGO TFTs with optimized Sn content have the advantages of low power consumption and resistance to an environment with illumination.

Thermally Activated Defect Engineering for Highly Stable and Uniform ALD-Amorphous IGZO TFTs with High-Temperature Compatibility

“…Particularly, the device with the GI grown at 400 °C showed an SS of 61 ± 1 mV/decade, which is comparable to the theoretical minimum value of 60 mV/decade. An extremely low SS indicates that defects in the active layer and interface between the active layer and GI were minimized by the GI deposition temperature after high-temperature annealing. , In addition, μ FE gradually increased from 17.2 to 27.6 cm 2 /Vs with increasing GI deposition temperatures. Several researchers have reported that the increase in μ FE and on-current ( I on ) is closely related to the tail state of the conduction band .…”

Atomic layer deposition for nanoscale oxide semiconductor thin film transistors: review and outlook

“…With the growing interest in ALD, studies on materials using ALD have also rapidly increased, as shown in the table, which will be discussed in this review. In particular, superior electrical performances have been recently reported, including a remarkable mobility of over 100 cm 2 V −1 s −1 [43,46], an exceptionally low subthreshold swing under 100 mV/decade [64,66,80,83], and highly improved stability using a stack structure [14]. However, the main benefits of employing ALD for oxide semiconductor channel TFTs have not been clearly suggested.…”

“…Using table 1, we determined that studies of indium-based oxide semiconductors have greatly increased since 2021. Not only binary In 2 O 3 [42][43][44][45][46][47][48][49], but also a ternary as IGO [59][60][61][62], IZO [62,63], In-Al-O (IAO) [64,65] and ITO [66], quaternary as IGZO [4,30,[71][72][73][74][75][76][77][78][79][80], ITAO [81,82], and ITGO [83] have been introduced. Also, compared to other materials in table, the precursors for indium oxide are variously used.…”

Optimal Aluminum Doping Method in PEALD for Designing Outstandingly Stable InAlZnO TFT

“…Conversely, only one atomic layer is deposited by one cycle of plasma-enhanced atomic layer deposition (PEALD), [28] and it is very easy to finetune the composition ratio of the oxide thin film. [14,29,30] In particular, the super-cycle PEALD method, in which each atomic layer is deposited alternately, can control the ratio of elements in the thin film by adjusting the ratio of the number of cycles of the atomic layer. Therefore, PEALD can provide an excellent method to inject Al into IAZO and control its amount.…”