Solution-Grown Homojunction Oxide Thin-Film Transistors - ACS

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Solution-Grown Homojunction Oxide Thin-Film Transistors Junhee Lee,† Jinwon Lee,† Jintaek Park,† Sung-Eun Lee,† Eun Goo Lee,† Changik Im,† Keon-Hee Lim,*,†,‡ and Youn Sang Kim*,†,§ †

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Program in Nano Science and Technology, Graduate School of Convergence Science and Technology, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea ‡ Department of Mechanical Science and Engineering, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States § Advanced Institutes of Convergence Technology, 145 Gwanggyo-ro, Yeongtong-gu, Suwon 16229, Republic of Korea S Supporting Information *

ABSTRACT: Growing attention has been given to low temperature, solution-processed metal oxide thin-film transistors because they can be applied in the emerging sector of flexible and large-scale electronics. However, major obstacles of solution-grown devices, such as their relatively low field-effect mobility and the difficulty of controlling carrier concentration, limit the further advancement of the electronics. Here, we overcome these constraints through a newly renovated structure, called a “homojunction”, consisting of double-stacked semiconductors with same material. The homojunction oxide thin-film transistor has remarkable electrical performance with controllability, for example, tunable turn-on voltage (−80 V to −8 V) and high average field-effect mobility (∼50 cm2/V·s) are obtained via a low annealing temperature process (250 °C). Furthermore, notable achievements associated with stability, reliability, and uniformity are verified. These results are attributed to the unique phenomena of solution-grown thin films: the change of both chemical and physical properties of thin films. Our findings highlight that the thin films of high quality can be yielded through the solution process at low annealing temperatures, and thus solution-grown transistors hold great promise for widespread industrial applications. KEYWORDS: homojunction, oxide thin-film transistor, solution process, high field-effect mobility, turn-on voltage

1. INTRODUCTION Oxide semiconductors (OSs) have been regarded as a promising candidate for active material of thin-film transistors (TFTs), an integral component of future transparent and flexible electronics because of their high optical transparency, tunable energy band, high carrier mobility (>10 cm2/V·s), and deposition process versatility.1−7 Currently, oxide TFTs are generally fabricated through vacuum processes among other various methods to deposit OSs. Because the vacuum process produces OS films of high density and low defects, vacuumprocessed oxide TFTs exhibit outstanding electrical performance and long-term stability.6,7 However, vacuum processes are inevitably of high costs because of their equipment and complicated processes of generating TFTs such as photolithography. This throws light on the necessity of introducing inexpensive and manageable methods to develop oxide TFTs.5,8 Solution deposition techniques have been considered to be a substitute for vacuum procedures, given their low costs and ease of processing under ambient conditions. Particular attention has been paid to solution processes with a low annealing temperature which helps to manufacture oxide TFTs on a flexible and transparent substrate and is also appropriate © XXXX American Chemical Society

for a continuous and large-scale deposition processing, an essential condition for a future industry such as roll-to-roll process.8−11 Many researchers have thus attempted to produce low-temperature, solution-grown oxide TFTs of high performance with a focus on eliminating impurities which are barely removed by a low annealing temperature. It has been argued that solution-processed oxide TFTs with few impurities can be developed through diverse methods such as developing precursors, ultraviolet (UV) annealing, and combustion methods.12−15 Although they demonstrate better electrical performance than ones from a typical sol−gel procedure, solution-processed oxide TFTs still display inferior electrical performance as compared to vacuum-processed oxide TFTs. The dominant reason is believed to be that a small amount of orbital overlap derived from both porous structures and voids left after impurities are removed during the annealing procedure.12,16 This indicates that there is a limitation to replace solution-processed oxide TFTs with ones from vacuum processes. However, recent studies have Received: October 22, 2018 Accepted: January 3, 2019 Published: January 4, 2019 A

DOI: 10.1021/acsami.8b18422 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces

Figure 1. Device structure and electrical characteristics of homojunction transistors. (A) Schematic architecture of homojunction TFTs. (B) Transfer curves measured in the linear regime (VD = 1 V) for a single-layered amorphous In2O3, a poly-crystalline In2O3, and a homojunction TFT. (C) Comparison of an average field-effect mobility between the heterojunction, homojunction, and the single-layered In2O3 TFTs. The channel width W and length L were 300 and 300 μm, respectively, for all devices; the inclination of homojunction TFTs for (D) μFE and (E) Von according to the modification of a channel layer; and the tendency of homojunction transistors toward (F) μFE and (G) Von depending on diverse CEMLs.

solution-grown devices that have superior electrical characteristics such as high μFE, suitable Von, and long-term stability. Herein, we newly suggest a renovated structure called a “homojunction” consisting of double-stacked semiconductors with same material, which are named as a channel layer and a channel-electron modulation layer (CEML), respectively. Not only do the solution-grown homojunction oxide TFTs display superior electrical performance comparable to that of state-ofthe-art solution-processed devices, but their marked characteristics are also adjusted to obtain adequate Von. For instance, the solution-grown In2O3/In2O3 homojunction TFTs show the highest μFE (∼50 cm2/V·s) with Von regulated from −80 to −8 V. Moreover, the solution-grown In2O3/In2O3 homojunction TFTs are produced at a low annealing temperature (250 °C), and they present notable accomplishments related to stability, reliability, and uniformity in spite of a solution process. On the basis of the results from various analyses and on controllable electrical characteristics of TFTs, we argue that such superior electrical characteristics of the homojunction transistors are attributed to the unique phenomena of solution-grown thin films: chemical alternations of surface traps of a channel layer because of the existence of a CEML, and variations of carrier concentration according to the state of the controlled homojunction. This study contends that the homojunction

suggested that various techniques, including doping of foreign atoms, high-pressure annealing, and structure with two different materials, can help to overcome such drawbacks of solution-grown TFTs.16−21 Specifically, solution-processed oxide TFTs with doublelayered structures seem to hold great promise as an alternative of state-of-the-art vacuum-processed oxide TFTs. For example, heterojunction oxide TFTs consisting of two different OSs have been proposed to achieve high electrical properties in terms of field-effect mobility (μFE).20,21 The heterojunction oxide TFTs obtain a high average μFE of 30 cm2/V·s via solution processes at a low annealing temperature, comparing favorably to cutting-edge vacuum-processed TFT characteristics. Also, low temperature, solution-processed TFTs with a bilayered dielectric structure show high average μFE, 24 cm2/V· s.18 Although this method helps to achieve notable improvement of μFE, the research studies on the double-stacked structure are still in the initial stage because there are numerous unresolved issues such as unsuitable operating characteristics and controversial operation mechanism. Moreover, little has been known in terms of the exact role of each layer and the impacts of properties of solution-grown films on electrical performance. Thus, this indicates the need of additional studies on double-stacked TFTs to produce B


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Figure 2. Analyses of single-layered films with respective molar ratios and homojunctions. (A) XRD characteristics of In2O3 films annealed at 250 and 200 °C. (B) HR-TEM cross-section images of Si/SiO2/In2O3 (0.1 M)/In2O3 (0.1 M) homojunction TFT. (C) Properties of In2O3 films with diverse molar ratios measured by AFM and XRR. (D) Elemental depth profile of the thick single-layered In2O3 film (∼14 nm) stack on the Si/SiO2 substrate.

single-layered In2O3 TFTs (Figure 1B). Examining transfer characteristics of the In2O3/In2O3 homojunction and singlelayered In2O3 TFTs shows that μFE of the In2O3/In2O3 homojunction TFTs is 48 cm2/V·s, and that of the polycrystalline (amorphous) single-layered In2O3 TFTs is 8.3 (2.7) cm2/V·s. All single-layered In2O3 and In2O3/In2O3 homojunction TFTs exhibit a conventional n-channel behavior with on/off ratios of above 106. Polycrystalline and amorphous single-layered In2O3 TFTs have their own electrical properties depending on the molar concentration of precursors (Figure S1), in accordance with previous work.22 Analysis of electrical characteristics in Figure 1B reveals that μFE of the In2O3/In2O3 homojunction TFTs surpasses other reported performance of various TFTs including the heterojunction oxide TFTs (Figure 1C).21 The μFE of the solution-grown In2O3/In2O3 homojunction TFTs exhibits nearly 6 times higher than polycrystalline single-layered In2O3 TFTs and at least a factor of 1.5 higher than the cutting-edge, high-performing solution-grown heterojunction oxide TFTs with an average μFE of 30 cm2 V−1 s−1.21 The tendencies for electrical performance of the solutiongrown In2O3/In2O3 homojunction TFTs with diverse conditions are represented from Figure 1D to 1G. Interestingly, the systems, where channel layers are altered with 0.05, 0.1, 0.15, 0.2, and 0.25 M and CEML is fixed in 0.1 M, obtain unexpected results in the area of μFE (Figure 1D). Similar μFE should have been procured when the same material is used for the channel because free electrons accumulated near the semiconductor/dielectric interface dominated the mobility.23,24 However, the thicker a film was, the poorer its electrical performance was achieved because of the difference in film quality except for 0.05 M, which we will discuss later. Other structures, where the channel layer was anchored in 0.1 M In2O3 and CEMLs were switched with 0.05, 0.1, 0.15, 0.2, and 0.25 M, displayed different inclinations that μFE was

oxide TFTs pave the way for applying solution-processed OS thin films to advanced transistor channels.

2. RESULTS AND DISCUSSION As shown in Figure 1A, our device structure is a bottom-gate and top-contact transistor with a solution-grown In2O3/In2O3 homojunction where each layer is named as a channel layer and a CEML, respectively. We used a highly boron-doped silicon wafer as a gate electrode and a substrate. A silicon dioxide (SiO2) with 200 nm thickness was thermally oxidized on the wafer as a gate dielectric. The solution-grown In2O3/ In2O3 homojunction layers were fabricated on the SiO2 layer via spin-coated sequential depositions of In2O3 precursors under 5% humidity which is a critical factor to develop thin films by using a single solution process.22 The solution-grown In2O3 layers consisting of the homojunction oxide TFTs are produced by utilizing different molar ratios of In 2 O 3 precursors. Diverse film thicknesses are formed by using the different precursors and the material phase of thin films are controlled through adjustment of annealing temperature, both of which result in changing carrier concentration of each thin film.34 These methods of handling carrier density in the films contribute to having outstanding electrical characteristics of solution-grown homojunction transistors. For source and drain electrodes, the channel width and length of thermally evaporated aluminum are 300 and 300 μm, respectively. The details are represented in the Experimental Section. One of the outstanding results of our structure is that the solution-grown In2O3/In2O3 homojunction TFTs can modulate its Von, while maintaining their high μFE, through controlling a channel layer and a CEML. By optimizing process conditions of each layer, we acquire the oxide TFTs sustaining significantly larger currents without largely shifting Von, most likely because of the enhanced electron channel mobility, than solution-grown polycrystalline and amorphous C


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Figure 3. Influences of a surface charge effect and defects on single-layered transistors and homojunction TFTs. Schematic diagrams and electrical hysteresis of (A) high-quality single films under 11 nm, (B) low-quality single films above 11 nm, (C) homojunction TFTs with amorphous CEML (a-In2O3), and (D) homojunction TFTs with crystalline CEML (C-In2O3). (E) Causes of μFE degradation in single-layered In2O3 films. (F) Explanations of having various electrical performances.

from the ones with polycrystalline CEML, which have been mentioned above. To further investigate the microstructure of the In2O3/In2O3 homojunction, HR-TEM analysis was carried out. The HRTEM data provided direct evidence that In2O3 was nanocrystalline with a lattice spacing of 0.41 nm and that the interfaces among dielectric, channel-layer, and CEML were atomically sharp (Figure 2B). Because the results indicated a low interface roughness of the channel and provided a clue of the respective layers not affecting each other, the electrical performance of the solution-grown In2O3/In2O3 homojunction TFTs was considered to be influenced by not other external factors but the channel layer. To determine the effect of a single layer itself, we analyzed single-layered In2O3 films through AFM. We found that film thicknesses had a linear relationship with molar concentrations, and its root-mean-square roughness (RRMS) showed atomically smooth topography for each film (Figure 2C). These outcomes corresponded to the HR-TEM data showing a sharp interface between the channel layer and the CEML. In addition, the chemical status of each In2O3 single layer is well in agreement with previous work.22 Although the properties of films such as the phase, RRMS, and thicknesses depending on the molar concentration of precursors were identified, neither were the extraordinary electrical characteristics sufficiently

preserved regardless of CEML conditions (Figure 1F). A high μFE of above 45 cm2 V−1 s−1 was acquired at Von near −20 V, whereas state-of-the-art works of the heterojunction oxide TFTs showed their average μFE at a Von of −40 V.20,21 The In2O3/In2O3 homojunction TFTs with amorphous CEML showed the analogous trend of polycrystalline CEML, slightly decreasing their average μFE of 25 cm2 V−1 s−1 (Figure 1G). To elucidate the origin of these unusual results from the solution-grown In2O3/In2O3 homojunction TFTs of diverse combinations, a wide range of analyses such as X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), atomic force microscopy (AFM), Xray photoelectron spectroscopy (XPS), and X-ray reflectivity (XRR), were performed. First, we conducted XRD analysis to see if the phase of materials influences the properties of the In2O3/In2O3 homojunction TFTs. Polycrystalline thin films were produced when the annealing temperature was at 250 °C, whereas other thin films annealed at 200 °C exhibited an amorphous phase (Figure 2A). Although thin films were formed in different states depending on the annealing temperature, no significant disparities were found in the phases of films derived from precursors of different molar concentrations. The phases seemed to have an impact on the solution-grown In2O3/In2O3 homojunction TFTs as their electrical performance with amorphous CEML was different D


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Figure 4. Reliability and uniformity of homojunction TFTs and performances of a solution-processed homojunction NMOS inverter. (A) Electrical performances of homojunction lasting more than 50 days. (B) Histogram plot of high μFE by 25 devices of In2O3 (0.1 M)/In2O3 (0.1 M) from two different wafers fabricated in parallel. (C) Voltage transfer characteristics of a solution-processed NMOS inverter at different supply voltages.

explained nor significant physical and chemical changes in films were observed. We thus conducted XPS and XRR analyses to reveal any potential distinctions between various types of films. The results of XPS did not display considerable differences in surface binding energy among layers developed from precursors of diverse concentration. When we measured the depth-resolved elemental composition of a thick In2O3 film via successive XPS spectra at differing etching times (depth), notable discrepancies were nonetheless detected (Figure 2D). The small amount of Si was identified at the bulk region because of the escape depth of the Si 2p photoelectrons, leading to the presence of Si at an etching time of ∼100 s. The XPS data showed that nitrogen gradually increased as etching time went by. This might be caused by indium nitrate we used for precursors. It is expected that the dense film of surface formed by oxidation prevented nitrate components in the bulk region from escaping out of films (Figure S6). This phenomenon was corroborated by a previous study that informed intermittent enclosure of solvent and precursor residues in the bulk of the layer caused by a faster curing of the surface areas.25 Despite providing further evidence of impurities being trapped, the causes of a difference in curing speed have little been known, and these studies have mainly performed indirect approaches to validate this difference. Our work suggest oxidation, verified through O 1s XPS spectra (Figure S6), resulted in forming the dense surface region, and nitrogen components are not eliminated during annealing because of rapid reaction on the surface. Further research related to the exact mechanism of this phenomenon is being conducted as a future work. Furthermore, the increased nitrogen component toward the bulk region seemed to lower the electrical characteristics of the In2O3/In2O3 homojunction TFTs because the nitrogen constituents acting as impurities impeded the coordination of indium and oxygen. In OSs, the bonding between metal and oxygen form percolated charge-transport pathways.1,5,31 The oxide TFTs show outstanding electrical performance when the arrangements of these atomic components in their own periodic structure are referred to as high density. On the other hand, when impurities replace the positions for the constituents, it produces deformed structures, point defects or dislocations, all of which contribute to hindering the percolated carrier transportation in OSs.12,16,25 Therefore, the higher the rate of impurities exists in the film, the lower the film densities obtain. The OS films of low density induce inferior electrical characteristics of the oxide TFTs, which is in agreement with the electrical data of the In2O 3/In2O 3 homojunction TFTs.

We further examined single-layered In2O3 films by utilizing XRR to estimate the density of films in diverse conditions (Figure 2C). As expected, the surface densities of all films were similar to 7.14 g/cm3 while an ideal indium oxide density is 7.31 g/cm3.30 On the contrary, the density of the bulk region became lower as the depth went deeper. We thus calculated the film density by adding the respective density of the bulk and surface and dividing it by the total thickness of each film. The fascinating results have been achieved in which solutionprocessed films under 6 nm obtained a density above 7.1 g/ cm3, whereas ones above 6 nm showed a lower density (Figure 2C). Our finding indicates that the oxidation process at ambient conditions was disturbed when the layers were thicker than 6 nm, proposing that solution-grown thin films should be developed under 6 nm for a high-quality layer. Based on the above analyzed data, we summarized the influences on electrical characteristics of solution-grown singlelayered In2O3 and the In2O3/In2O3 homojunction TFTs. The oxide TFTs with single-layered In2O3 films under 11 nm showed inferior electrical characteristics because of a surface charge effect (Figure 3A). The surface effect is triggered by charges trapped near the surface, and they affect flowing electrons at the interface of the semiconductor/insulator by Coulomb forces.26,27 This leads to the repulsion and attraction of charge carriers inside the channel. Hence, the surface to channel distance at least has to be larger than 7 nm to inhibit blocking of repulsion or trapping process by surface charges.26 In the case of the oxide TFTs with single-layered In2O3 films above 11 nm, which is thick enough to prevent the surface charge effect, inferior electrical performance was inherited from the impurities inside the bulk region (Figure 3B). The hysteresis of single-layered In2O3 TFTs also supported our claim because Von of the In2O3 TFTs with few defects, where In2O3 is under 11 nm, barely changed while that of the highly defective In2O3 TFTs, where In2O3 is above 11 nm, varied significantly (Figure 3B). The solution-grown In2O3/In2O3 homojunction TFTs consisting of two high-quality films, a channel layer and CEML (∼6 nm), showed excellent hysteresis characteristics and were not affected by the surface effect (Figure 3C,D). The Fermi level alignment happens in amorphous CEML because amorphous In2O3 tends to have a higher work function than the polycrystalline In2O3. When two different phases of films are combined, the electrons move from crystal to amorphous materials. This results in lowering the carrier concentration in the channel and hence the mobility of the structure because a conduction mechanism of OSs is the percolation and multiple trapping-and-release models (Figure 3F).1,5,31,32 On the E


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double-stacked TFTs have not been reported yet, long-term stability of homojunction would be considered as one of major advantages, considering the fact that atom diffusion happens when the two different materials are combined in other fields such as solar cell.33 Overall, the solution-grown homojunction oxide TFTs developed in this work have a huge potential for further exploitation in the semiconductor industry. It also indicates that in the near future, solution-grown OSs could compare favorably to mature semiconductor technologies if produced at a lower cost.

contrary, the Fermi level alignments and the surface effect were not found in the In2O3/In2O3 homojunction TFTs with crystalline CEML, generating superior electrical performance. The influences of surface effect or film quality on single-layered In2O3 are illustrated in Figure 3E. Not only did we achieve highest μFE through the homojunction oxide TFTs, but we also demonstrated the durability of their electrical performance even in long-term storage. The solution-grown In2O3/In2O3 homojunction TFTs preserved their superior electrical characteristics more than 50 days under ambient conditions, with both the μFE and Von barely changed (Figure 4A). A further advantage of the solution-grown In2O3/In2O3 homojunction TFTs was the small μFE variation between devices. The uniformity of the In2O3/In2O3 homojunction TFTs was explained by Figure 4B where the mobility of the system for 25 different transistors was plotted as a function of product number. All solutiongrown In2O3/In2O3 homojunction TFTs displayed little variation between devices and mobility with an average μFE of 46.5 cm2 V−1 s−1, which is a considerable progressive performance as compared to previous works. We also utilized these less defective thin films to create an inverter which is one of the important logic gates in logic circuits. An n-type metal OS (NMOS) inverter of depletion mode was formulated by integrating the solution-grown In2O3/In2O3 homojunction TFTs. A classical inverter performance was achieved where an output voltage in diverse voltage conditions changed from logic 1 to 0 with a swept input voltage (Figure 4C). This indicated that these gates would also be appropriate for assembling complex logic circuits.

4. EXPERIMENTAL SECTION 4.1. Precursor Solution Synthesis and Deposition Techniques. Indium nitrate hydrate [In(NO3)3·H2O] (99.999%, SigmaAldrich) was dissolved in deionized (DI) water to formulate In2O3 precursor solutions (0.05, 0.1, 0.15, 0.2, and 0.25 M) and then the precursors were stirred at 500 rpm for three days. To produce thin films, we used the spin-coating deposition method where parameters were 5000 rpm for 30 s at a humidity under ∼5%. The humidity represents the relative humidity at 25 °C. A 0.22 mm syringe filter PTFE (DISMIC 13HP020AN, Advantec, Japan) was used to filter the In2O3 precursor. As-deposited polycrystalline (amorphous) films were soft-baked at 250 (200) °C for 1 min, and then subjected into the tube furnace to anneal for 4 (8) h at 250 (200) °C. All chemicals were used as received. 4.2. Transistor Fabrication and Characterization. Transistors were constructed in the bottom-gate, top-contact structure on highly B-doped Si wafers with a thickness of 200 nm thermally developed layer of SiO2 as a role of the gate electrode and the gate dielectric, respectively. The wafers were cleansed by subsequent ultrasonication in detergent for 15 min, DI water rinsing for 1 h, ultrasonication in acetone, and isopropanol for 15 min each, followed by UV/ozone treatment for 20 min. Deposition procedure of the In2O3 layers was carried out using the methods described above. An Agilent 4155B semiconductor parameter analyzer measured the transfer and output characteristics of homojunction TFT under dark conditions. The field-effect mobility of homojunction TFTs was evaluated by the linear formula, which is stated in the Supporting Information section (Figure S9). 4.3. Material Characterization Techniques. The roughness and thickness of In2O3 films were investigated using AFM (XE100, PSIA). We utilize XRR (SmartLab, Rigaku Co.) to obtain the density of In2O3 films with Cu Kα radiation (λ = 1.54 Å) at 45 kV and 200 mA. GlobalFit program is used to acquire XRR fitting data. To determine the phase of materials, XRD (D8 Advance, Bruker Co.) was executed with Cu Kα radiation (λ = 1.54 Å) at 40 kV and 150 mA (6 kW) and grazing-incidence mode. The XPS spectra were acquired in a AXIS Supra (Kratos, U.K.) system equipped with a monochromic Al Kα X-ray source. Depth profile analysis was performed by mild, destructive in situ sputter etching using an Ar+ beam of 5 kV to achieve the required depth resolution. The samples for HR-TEM observation were prepared by ion-beam processing techniques through Quanta 3D FEG. A platinum-plated layer with a thickness of 15 nm was deposited via sputter before TEM sample preparation to make its surface more conductive. The HR-TEM images were all obtained by a JEM-2100F field emission electron microscope from JEOL Ltd.

3. CONCLUSIONS For the first time, homojunction oxide TFTs consisting of solution-grown In2O3 thin films have been proposed by adopting simplicity and low-temperature nature of the growth process. Despite employing the solution-processed OS films, the solution-grown oxide TFTs presented in this study achieved a higher electrical performance than other reported solution-grown oxide TFTs such as single-layered In2O3 and heterojunction oxide TFTs. The study further provides evidence on the performance of solution-grown In2O3/In2O3 homojunction TFTs, which is even comparable to that of stateof-the-art vacuum-processed devices.5,28,29 The outstanding electrical performance of the solution-grown In2O3/In2O3 homojunction TFTs is attributed to three main factors: (i) the capability to develop high quality thin film via a single solution process under ambient conditions, (ii) the functions of CEML layers to prevent the influence of surface space charges, and (iii) the ability to control the charge concentration in the channel and thus manipulate Von. The high-quality In2O3 film utilized for the channel layer is a critical factor to achieve high μFE in which low-defected thin films provide charge carrier paths, channel, of few hindrances where charge carriers would easily flow. In addition, the presence of CEML plays a significant role in the solution-grown homojunction oxide TFTs because it helps to avoid the degradation of electrical performance originated from surface charge effect. Moreover, adjusting the phase and the thickness of CEML realizes a semiconductor of high mobility and tunable Von. Furthermore, other device traits such as uniformity and reliability are validated, and the solutiongrown homojunction oxide TFTs show long-term storage stability under ambient conditions. Although stability of other

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b18422. Detailed electrical characteristics of solution-grown homojunction TFTs. XRR characterization and fitting line of In2O3. Information for both thickness and RMS of single-layered In2O3 films depending on different molar concentration of precursor solution and that the F


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comparison between the electrical characteristics of the In2O3 TFTs after one day and after 50 days later. OM image of patterned homojunction TFT exists and the reason why we use field-effect mobility in linear region are written (PDF)

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*E-mail: [email protected] (K.-H.L.). *E-mail: [email protected] (Y.S.K.). ORCID

Youn Sang Kim: 0000-0002-4580-2037 Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT of Korea (MSIT) (2017R1A2B3005482).

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REFERENCES

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