1. Introduction

In the modern society, advances in nanotechnology have caused a boom in the semiconductor industry. Researchers are expending efforts to improve integrated circuits and to devise methods for preparing high-quality nanostructures on different substrates for the advancement of technologies. Toward this end, various techniques such as e-beam lithography [1,2], focused ion-beam [3,4], and UV lithography [5,6] are being studied in industry and academia. However, these existing techniques have the disadvantage of being time-consuming and costly [7]. To overcome these shortcomings, researchers have studied various alternative techniques. One such technique is nanoimprint lithography (NIL) [8–10], which is an effective technique for the fabrication of nanostructures through pattern transfer; this technique usually involves thermal curing or UV curing [11–13]. In the case of UV curing, it has the advantages of high throughput and low cost [14]. In particular, several identical nanostructures can be produced in a short time, and this technique is used in various fields such as LED patterning [15], quantum dot devices [16], solar cells [17], and color filters [18].

The rubbing method is widely used in the display industry owing to its low cost and high speed; furthermore, it can be used for large areas and mass production [19,20]. However, the rubbing method causes friction scratches. Moreover, the formation of debris particles is a major disadvantage. In particular, inorganic materials with excellent properties are required to develop a simpler and defect-free manufacturing method. Various deposition techniques, including atomic layer deposition [21] and sputter methods [22], require high vacuum equipment, which is expensive and the use of which is time-consuming. However, the sol-gel method is cheap and easy to use for coating areas with different shapes [23,24]. Furthermore, the method is attractive owing to its high purity, solution concentration, and homogeneity and since it is easy to control the doping concentration.

For high-quality electronics, including liquid crystal (LC) applications, the choice of materials and the manufacturing method are important. Transparent conducting oxides (TCOs) are used in various applications to improve electrical performance because of their high transparency and electrical conductivity [25,26]. Among the various TCO materials, zinc oxide is a group II to VI n-type inorganic semiconductor material that is utilized in most research fields [27]. ZnO is an oxide semiconductor with a wide direct band gap (∼3.37 eV) and large exciton binding energy (60 meV), which has applications in electronic, optoelectronic, and information technology device platforms due to its electrical and optical properties [28–30]. Moreover, ZnO is an interesting material for use in new light-emitting devices such as TCOs [31], solar cells [32], and photocatalysis due to its excellent transparency in the visible region, high electron mobility, and chemical and photochemical stability properties. Notably, high-quality LC devices can be realized by improving the electro-optical performance. Currently, alternatives to the polyimide layer are being sought to improve the performance of LCDs. Inorganic alignment materials with a high dielectric constant (high-k) are optically transparent and insulating, show excellent adhesion to various surfaces, and have high chemical stability and resistance and excellent dielectric properties [33–35]. Hence, they have attracted the attention of researchers. SiO_x [36], Al₂O₃ [37], diamond-like carbon [38], Ta₂O₅/TiO₂ [39–41], and MoO₃ [42,42] are promising materials for thin films because of their outstanding chemical stability, high refractive index, high UV absorptivity, and dielectric properties. In particular, compared with these materials, InSnO thin films prepared using the sol-gel process show better quality, porosity, and lower resistivity [43]. The resistivity of InSnO thin films is close to the standard values of thin films produced by sputtering, which are around 10⁻⁴ Ω·cm. Such a thin film has low sheet resistance and high projection simultaneously. Owing to these advantages, InSnO thin films are a popular research topic in industry and academia. In this study, we formed an alignment layer through UV-NIL by using an indium-tin oxide (InSnO) thin film, which is a representative high-k material, with a sol-gel method. Furthermore, to increase the resolution of the pattern, we prepared a solution by mixing the InSnO sol-gel solution with a UV curing agent. The pattern replication showed a difference according to the UV exposure time, and a state change of the LCs was used to confirm changes in the anisotropic and van der Waals forces in the alignment layer.

2. Experiments

2.1 Preparation of solution

Indium(III) nitrate hydrate (InN₃O₃·xH₂O)/tin(II) chloride (SnCl₂)

To prepare a solution with doping photosensitive polymer, we mixed 0.1 mol L⁻¹ indium(III) nitrate hydrate (InN₃O₃·xH₂O, Sigma-Aldrich, St. Louis, MO, USA) and 0.1 mol L⁻¹ tin(II) chloride (SnCl₂, Sigma-Aldrich, St. Louis, MO, USA) in a ratio of 5:5 and dissolved the mixture in 2-methoxyethanol (2ME), as shown Fig. 1(a). The resulting solution was stirred at 70°C for 1 h and aged for at least one day. After the solution was thoroughly mixed, a photocurable polymer was added and the solution was stirred for 30 min to make solution. The solution was then mixed with a UV photocuring polymer in a volume ratio of 10:1. To intuitively see the combination of tin and indium molecules, illustrated the bonding model and molecular structure of indium and tin in Fig. 1(b, c). The UV photocuring polymer (Irgacure 2959; Sigma-Aldrich, Ciba) comprised three components (Fig. 1(d, e, f)). First, dipentaerythritol hexaacrylate (DPHEA), a hexafunctional monomer, was used to produce a transparent hard coating to prevent static electricity. The second component was tripropylene glycol diacrylate (TPGDA), a trifunctional monomer, that was used to increase the gelation stability at high temperatures with high T_g, low viscosity, and high curing speed. The last component was 2-hydroxyethyl acrylate (2HEA), a hydroxy-functional acrylic monomer that can be used in a variety of ways to produce resins that are useful in high-performance coating applications. As shown in Fig. 1(b), absolute bonding between indium and tin molecules could be achieved.

 

Fig. 1. Schematic of the solution blending process used for the preparation of a nanopatterned thin film. (a) Sol-gel process. The InSnO solution was prepared by mixing 0.1 mol of SnO and 0.1 mol of InO and dissolving the mixture in 2ME in a ratio of 5:5. (b) Oxidation bond model of SnO and InO molecules with the photocurable polymer. Chemical structures of (c) indium and tin, (d) dipentaerythritol hexaacrylate (DPHEA), (e) tripropylene glycol diacrylate (TPGDA), and (f) 2-hydroxyethyl acrylate (2HEA).

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2.2 Fabrication of polydimethysiloxane replica sheet for NIL

To fabricate a polydimethylsiloxane (PDMS) replica sheet, first, a nanoscale periodic line pattern structure was made on a Si wafer through deep-ultraviolet laser interference lithography. The PDMS sheet was fabricated by mixing an elastomer base and a curing agent in a ratio of 10:1. The mixture was poured onto a Si wafer and trapped air bubbles in PDMS were removed using a vacuum chamber. Subsequently, the periodic structure of the Si master was transferred to PDMS (Sylgard-184, Dow Corning) as shown in Fig. 2(a). On the other hand, during peeling of the imprint mold from the resist, the patterned PDMS may be damaged or distorted due to adhesion and friction between the PDMS mold and the resist. Therefore, heat the PDMS at 70 degrees for 2 hours on a hot plate to completely cure it, and then cool it at room temperature for 1 hour to harden it. Lastly, in order to minimize delamination between the PDMS and Si wafers, high-precision electronic tweezers (Nano (Lotus effect) tweezers) are used to separate the nanopatterns from top to bottom along the groove direction. This separated PDMS was used as a sheet for the NIL process. PDMS was used in the NIL process since a flexible mold is more advantageous for multiple processes than a hard mold.

 

Fig. 2. (a) Fabrication process of polydimethylsiloxane (PDMS) sheets on silicon wafer and transfer of the nanostructure on InSnO thin films for nanoimprint lithography (NIL) process. (b) Schematic configuration of ultraviolet (UV) irradiation equipment.

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2.3 NIL process with UV irradiation for replication of periodic line pattern on thin films

To deposit the solution, we cleaned ITO glass (Samsung Corning 1737; standard 32 mm × 22 mm × 1.1 mm; sheet resistance: 10 Ω sq⁻¹) substrates through repeated ultrasonication in isopropyl alcohol and acetone, and the prepared solution was then spin-coated on the substrates for 30 s at 3000 rpm. After attaching the finished PDMS sheet to the coated InSnO thin films, the two materials were exposed to 356 nm UV light for 1, 3, and 5 min. The structure of the UV irradiation equipment is shown in Fig. 2(b). First, a 1 kW mercury lamp was used as the UV radiation source and the energy density was set to 7.9 mW/cm². During UV irradiation, the thin film was cured, and the 1D nanostructure was transferred. After exposure, the PDMS sheet was peeled off the surface, leaving behind a nanostructured thin film.

2.4 Fabrication of LC cell and analysis of InSnO thin films replicated with aligned nanopatterns

A nanopatterned thin film was used as an LC alignment layer to produce an antiparallel cell. The cell gap was maintained as 60 µm and positive LCs (Δn = 0.111, n_e = 1.595, n_o = 1.484, Δɛ = 10.3, T_c = 81.8°C; IAN-5000XX T14, JNC Co.) were injected into the antiparallel cell gap via capillary force. The polarized optical microscopy (POM; BXP51, Olympus) measurement method was used to check the LC alignment, and the pretilt angle was measured via the crystal rotation method (TBA 107, Autronic) to determine the orientation alignment of LCs.

2.4 Analysis of surface properties of nanopatterned InSnO thin films

AFM was performed to investigate the shape change of the surface of nanopatterned InSnO thin films exposed to UV irradiation. The noncontact mode and a scan rate of 0.5 Hz were used. Furthermore, the nanopattern height, amplitude, and pitch of the thin films were compared with those of the Si wafer’s pattern via line profiling (XEI software, Park Systems). Additionally, the variation of the chemical composition of the thin films with the exposure time to UV radiation was analyzed through x-ray photoelectron spectroscopy (XPS; K-Alpha, Thermo VG, UK), and the optical transmittance of the thin films at 380–800 nm (visible region) was measured at room temperature using an ultraviolet-visible (UV-vis) near-infrared scanning spectrophotometer (UV–3101PC, Shimadzu).

3. Results and discussion

Chemical bonding of surface molecules creates structural mismatches when creating nanopatterns. Because replicated nanopatterns are affected by chemical bonds, it is necessary to observe changes in the chemical composition of the thin film depending on UV irradiation time. We conducted a compositional investigation with Intensity change according to binding energy of the photocurable-polymer-doped InSnO via XPS analysis (Fig. 3). The variation of the intensity with the binding energy of tin and indium is shown in Fig. 3(a) and (b). First, the intensity of Sn3d5/2 for UV irradiation times of 1, 3, and 5 min was measured to be 10655.6, 20824.7, and 15315.4 at 486.18 eV, respectively. The rate of change of the Sn3d5/2 intensity increased significantly to 95.43% when the irradiation time increased from 1 to 3 min, and it decreased by 26.46% for a further increase in the irradiation time from 3 to 5 min. For irradiation times of 1, 3, and 5 min, the intensity of Sn3d3/2 was 7615.5, 14068.2, and 10495.3 at 494.68 eV, respectively. Moreover, the Sn3d3/2 intensity increased by 87.7% when the irradiation time increased from 1 to 3 min and decreased by 25.41% when the irradiation time increased from 3 to 5 min. Second, the intensity of In3d5/2 for UV irradiation times of 1, 3, and 5 min was measured to be 12416.5, 20851.2, and 16561.7 at 444.68 eV, respectively. The In3d5/2 intensity increased significantly to 67.93% when the irradiation time increased from 1 to 3 min and decreased by 20.57% when the irradiation time further increased from 3 to 5 min. The intensity of In3d3/2 for irradiation times of 1, 3, and 5 min was 8336.7, 14134.4, and 11181.7 at 452.28 eV, respectively. Moreover, the In3d3/2 intensity increased to 69.54% when the irradiation time increased from 1 to 3 min, and it decreased by 20.89% when the irradiation time increased from 3 to 5 min. As evident from the trend of the molecular intensities of tin and indium, when the UV irradiation time increased from 1 to 3 min, the molecular bond between SnO and InO became considerably more active. However, when the UV irradiation time further increased from 3 to 5 min, the intensity decreased, indicating that the bonds of strongly bound molecules were broken. The intensity of each binding energy of carbon for different UV irradiation times is shown in Fig. 3(c). C—C bonding appears at 284.28 eV, which is about 44897.8 for irradiation for 1 min, whereas it is about 46387.4 when irradiated for 3 min, which is a 3.32% increase. However, when the UV irradiation time is increased to 5 min, it is reduced by 3.78% to about 44631.7. Furthermore, C—OH bonding appears at 285.78 eV, which is about 18880.1 for irradiation for 1 min, whereas it is about 15620.4 for 3 min of irradiation, which is a 17.3% reduction. However, if the UV irradiation time is increased to 5 min, it increases by 8.33% to about 16922.2. On the other hand, C=O bonding appears at 288.28 eV and shows a steadily decreasing trend with an increase in the UV irradiation time. For irradiation times of 1, 3, and 5 min, it decreases by 2.34% and 3.73% from 14227.6 to 13895.6 and further to 13377.2, respectively. In Fig. 3(d), the intensity of O1s shows a significant decrease 3 min. For UV irradiation times of 1, 3, and 5 min, the intensity is 58988.3, 51134.1, and 51542.7, and when the time was increased from 1 to 3 min, the intensity decreased by 13.31%. This is consistent with the decrease for the C=O bond and the increase in the case of the C-C bond as the depletion layer was greatly reduced. The InSnO sol-gel film doped with solution-processed UV curable polymer is covered with a PDMS sheet, and the sol is transferred to the empty space of the nanopattern by capillary driving force. Then, the light and heat energy applied due to UV irradiation enables radiation and curing of the film's negative pattern. During UV irradiation, various deformations occur due to drying and shrinkage of sol-gel, gas permeation and demolding of PDMS. As a result, when the modified film was UV irradiated for 3 minutes, the Sn metal (486.6 eV) and In metal (444.0 eV) peaks increased the most, indicating that it was a well-formed metal oxide [44]. Consequently, the photocurable-polymer-doped InSnO thin film was well-formed from the polymer and metal oxide mixture for UV irradiation for 3 min. As a result, the photocurable-polymer-doped InSnO thin film was formed with the least structural mismatch under UV irradiation for 3 minutes.

 

Fig. 3. Graph of changes in the chemical composition spectrum of the InSnO thin films obtained through X-ray photoelectron spectroscopy analysis. The X-ray source used monochromate AI Kα with an ultimate energy resolution of 0.50 eV full width at half maximum (FWHM) of the Ag3d intensity curve and an ion source energy range of 100 V to 3 keV. (a) Sn3d_5/2 and Sn3d_3/2 intensity, (b) In3d5/2 and In3d3/2 intensity, (c) C1s (C—C, C—OH, C=O bonding) intensity, and (d) O1s intensity.

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We conducted structural observations through AFM measurements to verify the XPS analysis results. Figure 4 shows a comparison of graphical AFM images of the surface of the InSnO thin films with the photocuring polymer between different UV exposure times. The PDMS sheet was filled with a liquid thin film containing a solution that filled the depressions of the nanopattern. However, after imprinting the PDMS sheet under UV exposure, the InSnO solution with the photocuring polymer solidified and the pattern on the PDMS sheet was transferred onto the thin films. These observations showed that a linear nanopattern could be used to direct the alignment of LC molecules. Priority, the patterned structure of the PDMS sheet had an average line pattern period of 750 nm, a width of 450 nm, a spacing of 300 nm, and a height of 30 nm. Therefore, when the NIL process was properly performed, one-dimensional nanostructures fabricated on a film of a certain width and height could be visually confirmed via surface analysis. It was confirmed that the reverse shape of the PDMS mold was transferred to the film surface. For a UV exposure time of 1 min, the nanostructure pattern was reproduced uniformly, as shown in Fig. 4(a). Even when the UV exposure time was set to 3 min, the PDMS mold had a clear periodic uniform pattern with nearly constant height and width, as shown in Fig. 4(b). However, Fig. 4(c) shows AFM images of inferior quality surfaces. Such inferior quality results when the UV irradiation exposure time is too long; the thin films melt and stick to the PDMS sheet. The fact that the thin films in the three-dimensional image are skewed to one side indicates that the thin films come up in the direction in which the PDMS sheet is peeled off. To accurately confirm that the nanopattern was completely replicated on the InSnO thin films, we performed line profiling to compare the cases of UV irradiation times of 1 and 3 min; the line profiles are shown in Fig. 4(d). For 1 min, the line pattern periodicity was about 700 nm, the width was 230 nm, the spacing was 350 nm, and the height was 41 nm. However, for 3 min, the line pattern periodicity was about 700 nm, the width was 230 nm, and the spacing was 350 nm, similar to the case of 1 min. However, the height was 49 nm. This indicates that the pattern was more suitable for the PDMS sheet as the thin film grew with an increase in the UV irradiation time. As the InSnO crystals successfully bonded and grew, the van der Waals interaction was observed to act strongly on the thin films, as expressed by the following equation:

The transparency of a thin film is an important factor when determining its suitability for use in a display device, and hence, the UV–vis transmittance of the InSnO thin film in the visible range of 380–780 nm was measured, and it is shown in Fig. 5. The transmittance of the thin film for UV exposure times of 1, 3, and 5 min was 87.61, 86.42 and 84.90, respectively; thus, the transmittance increased with the exposure time. In comparison, the conventional PI-coated glass has an average transmittance of 83.23% [45]. Thus, all the fabricated thin films had about 2p% higher transmittance than commercially available display thin films. The transmittance was measured using a JASCO V-650 UV-vis spectrophotometer, and the calculation formulas are as follows:

Light energy is proportional to the wavelength, as shown in the Eq. (2), and it absorbs visible light with a wavelength different from that of UV light, with the wavelength absorbed depending on the energy required for transition [46,47]. E is the energy of light, h is Frank’s constant, and v is the frequency. The Beer–Lambert law in Eq. (3) describes the linear relationship between the absorption concentration of electromagnetic waves and the absorption values; P and P₀ are the intensity of radiation of light energy per 1 cm² area of the detector per second, A is the absorbance, T is the transmittance, a is the absorption coefficient, b is the passage of radiation, c is the concentration of the absorbing species and ɛ is the molar extinction coefficient [48]. On the basis of the waveguide mode theory of periodic nanopatterning on a surface, photons from the visible region light were trapped and light loss occurred, resulting in a decrease in the transmittance of the thin film. Despite the inclusion of nanopatterns, the InSnO thin film is suitable for use in devices because the transmittance is higher than that of the PI thin film using the commercially available rubbing method.

 

Fig. 4. AFM images (using noncontact mode and topography from Z-position sensor) in three and two dimensional of pattern transferred on InSnO mixed with UV-cured polymer thin films for UV irradiation times of (a) 1 min, (b) 3 min, and (c) 5 min. (d) Results of line profile analysis conducted on the horizontal axis for 1, 3, and 5 min to analyze the accuracy of the copying of line patterns.

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Fig. 5. UV-vis transmittances of the InSnO thin films for UV irradiation times of 1 min, 3 min, and 5 min. The measured wavelength range was 250–900 nm, and the visible region was 380–780 nm.

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To confirm the applicability of the thin film, we applied LC applications according to the characteristics of the thin film through uniform LC alignment. To confirm the alignment of the LCs, after preparing the antiparallel LC cell, when uniform LC alignment was achieved, we blocked light passing through the LC cell between the orthogonal analyzer and the polarizing plate, and a dark POM image was observed [49–51]. The LC cells fabricated under UV irradiation through nanopattern transfer onto InSnO layers showed uniformly aligned LC states. Figure 6. (a), (b), and (c) show images of UV irradiation for 1, 3, and 5 min, respectively. A clear dark image appeared at 1 and 3 min, indicating perfect alignment of the LCs. Under the well-transferred nanopattern conditions, the LCs were aligned in a single direction parallel to the surface pattern, which served as a guide. LC molecules around the surface were confined to the nanopatterned intersperse, and because of the collective behavior of LCs, the anisotropic molecules moved to the bulk and were aligned in a single direction. Furthermore, the action of van der Waals forces between the LCs and InSnO thin film helped determine the alignment direction according to the anisotropy of the LCs (Fig. 6(h) and (i)). When an external force was applied to change the LC molecules in contact with the surface, changes in the polar deformation and azimuthai deformation occurred. The elastic energy generated in the LCs because of the fine groove reached the minimum value when the direction of the LCs was parallel to the groove. In other words, free energy (F) represents the energy of perpendicular to the groove, and the increase in free energy because of the torsion phenomenon is given by the following equation:

Here, K is the modulus of elasticity, a is the depth of the groove, and q is the wave number. Thus, the LCs were uniformly aligned according to the groove theory and on the basis of van der Waals force in the nanopatterned thin films. As mentioned, positive LCs were used during fabrication, and the direction of the long axis (n_o) was perpendicular to the thin film. The principle of anisotropy is consistent with the results of periodicity of the well-transferred nanopattern, which is the result of AFM analyzed earlier. The principle of the POM is illustrated in (d). When the nanopattern is parallel to one axis of the cross-polarization plate, light propagates in a straight line through a parallel LC molecule and is blocked by the cross-polarization plate of the upper substrate. If the LCs are evenly aligned and the cells are rotated by 45°, light transmission through the cross-polarizing plate is maximized. Thus, it was confirmed that LC cell rotation under the cross polarizer resulted in uniform alignment. The direction of the nanopattern was between the polarizer's direction and the polarizer intersecting at an angle of 45°. Therefore, we checked the uniformly aligned LCs in the nanopattern. The LCs’ arrangement state could be confirmed from the pretilts determined by the crystal rotation method [52,53]. Figure 6(e), (f), and (g) show the pretilt angle measurement results for UV irradiation times of 1, 3, and 5 min, respectively. The experimental blue curve and the simulated red curve can calculate angle of LC molecules. The blue curve was determined on the basis of well-aligned LCs by using birefringence information, and it indicates that LC molecules were well aligned along a single direction and that the pretilt angle was calculated with high reliability. The formula for pretilt angle calculation is given by the Eq. (5).

 

Fig. 6. Fabrication of TN (Twisted Nematic) liquid crystal (LC) cells using replicated nanostructures after InSnO thin film deposition on general glass substrates. Polarized optical microscopy (POM) images for irradiation times of (a) 1 min, (b) 3 min, and (c) 5 min. (d) Principle of light passing through according to alignment and non-alignment of the LCs in POM. Incident angle - transmittance measurements were performed under latitudinal rotation using the crystal rotation method on InSnO thin films at (e) 1 min, (f) 3 min, and (g) 5 min. (h) Schematic of groove theory in which the pattern of nanostructure affects the orientation of LCs. (i) Alignment principle according to the influence of LCs and surface force in the nanostructure on the thin film.

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As evident in Fig. 7(e), (f), and (g), the most uniform average pretilt angle was 1.06727° and 0.7496687° at 1 and 3 min. Notably, the pretilt angle value was consistent with the previously discussed analysis based on XPS, AFM, and POM and confirmed the characteristics of the InSnO thin films. Figures 6(h) and (i) show the principle of arrangement of LC molecules according to changes in the chemical properties of the surface and the replicated nanopatterns. According to the aforementioned groove theory, the polarity deformation and azimuth angle change when an external force is applied. The groove on the surface contributes to the alignment according to the size of the substrate volume based on the center of the liquid crystal molecule. It contributes to the polar direction, which is the LCs’ cell thickness direction, and shows order by molecular concentration, Boltzmann constant, temperature, and length in the horizontal orientation.

4. Conclusion

We studied an alignment layer through UV-NIL; an indium-tin oxide (InSnO) by sol-gel method were used in the preparation of the alignment layer. To increase the resolution of the pattern, we used a solution prepared by mixing a solution with a UV curing agent. High-resolution 1-D nanostructure replication showed dependence on the UV exposure time, and XPS and AFM analysis were used to confirm that the dependence. The state change of the LCs was used to confirm changes in the anisotropic and van der Waals forces of the alignment layer. In XPS analysis, an important observation was that the intensities of InO and SnO increased significantly. On the other hand, increasing the exposure time to UV irradiation from 3 min to 5 min slightly reduced the indium tin molecule. AFM images showed superior patterned grooves for the UV exposure time of 3 min. Thus, the nanostructured patterns on the films acted as alignment guides for the LC molecules on the surface. In particular, the most similar groove pattern was observed at 3 min of UV exposure time. However, if the UV exposure time was set to 5 min or more, the nanostructure was not replicated properly. This was consistent with the intensity trend of XPS analysis and implies that the molecules of the thin film dissolved in the PDMS sheet and adhered. The highest resolution nanostructure was achieved at 3 min of UV exposure time, which was therefore the most suitable condition in the UV-NIL process for highly efficient pattern transfer onto the thin film. Furthermore, LCs were aligned, confirming the performance of the nanopatterned structure of the surface, and the interrelationship between the surface of the thin film and the movement of LCs was determined on the basis of the van der Waals force, anisotropic, and groove theory and through POM and pretilt angle measurements. The NIL technique is also suitable for large-area processes and can be used in both soft organic and rigid inorganic layer alignment methods. Through embossing, SnO solutions combined with InO can be reproduced on a large scale, and various modifications can be made by changing the exposure time of UV irradiation according to the needs of consumers. Thus, tin-doped indium thin films are proposed as future alternatives to device materials.