Indium Gallium Zinc Oxide Films Research Articles

Effects of deposition method and conditions for IGZO film and thermal annealing on composite film quality, surface roughness, microstructural defects, and electrical properties of Ti/IGZO/graphene/polyimide specimens

The depositions of a thin graphene as the inter layer of the indium gallium zinc oxide (IGZO) film and polyimide substrate and a Ti film bellow the IGZO layer to induce the IGZO crystallizations have been reported by the authors' study [1] to have a significant reduction in the electrical resistivity (R) and increases in carrier mobility (Mb) and concentration (Cc) via the annealing as compared to those created in the specimens without graphene. In the present study, Ti/IGZO/graphene/polyimide specimens were fabricated using Ti as the top layer, with the IGZO film prepared using e-beam evaporation and radio-frequency magnetron sputtering, in order to compare the ability of preserving the structure integrity of graphene after the IGZO deposition. When sputtering was used, the thicknesses of the Ti and IGZO films were controlled by the deposition power; when e-beam evaporation was used, the thicknesses were controlled by the deposition time. Rapid thermal annealing (RTA) was further applied to some specimens to investigate the combined effects of the IGZO deposition method and heat treatment on the microstructure defects, electrical and mechanical properties, and surface morphology of the specimens. The quantities of bulges and microvoid defects increase after the RTA, and become the governing factors for increasing surface roughness (Ra). The X-ray photoelectron spectroscopy spectra for O1s were deconvoluted to evaluate the peak intensity ratio, IRO2, defined for the evaluation of the oxygen vacancies in the microstructure. When sputtering was used, IRO2 increased after RTA; in contrast, when e-beam evaporation was used, IRO2 decreased after RTA. For all specimens without RTA, an increase in either the deposition power or time of IGZO has decreased IRO2. TiO2, ZnO, and Ga2O3 are the three oxides created in the specimens. The ways of increasing the TiO2 grains result in a rise of IRO2. The electrons released from the TiO2 formations are available to raise the quantity of ZnO. The peak intensity (PIZnO) of ZnO is lowered by annealing, irrespective of the IGZO deposition method. With sputtering and without RTA, increasing the IRO2 value increased the carrier mobility (Mb), but decreased the resistivity (R) and carrier concentration (Cc), irrespective of the deposition power. After the RTA, carrier concentration and resistivity are lowered, and carrier mobility is risen. With e-beam evaporation and without RTA, the vague interface between Ti and IGZO films and the void defects in IGZO make these electrical properties more complicated in behavior and dependent on IGZO deposition time. Specimen's resistivity was lowered and carrier concentration was elevated by applying the RTA. The deposition of the Ti film as top layer can result in a much bigger reduction of R and further increases in Mb and Cc for these two IGZO deposition methods as compared to those shown in Ref. [1].

(Invited) Oxide TFT Fabrication with Various Low Temperature Techniques

Oxide thin film transistors (TFTs) have attracted much attention for next-generation electronics because of their superior performance compared with conventional a–Si TFTs such as high mobility and optical transmittance in the visible light.1 Some display manufacturing companies have already manufactured oxide TFTs based products, but there are some issues remained for oxide TFTs to be used for flexible displays. One of the issues is the high-temperature annealing process (> 300°C). Due to low thermal durability, flexible substrates cannot be processed in high temperatures.2-3 In this study, we propose various researches to lower the processing temperatures in oxide TFTs: photocatalytic reactions of titanium dioxide (PRT) and rotating magnetic field (RMF) treatment. In addition, we suggest ethyl cyanoacrylate (ECA) based instant glue (IG) as a new material for the passivation layers of oxide TFTs with low processing temperature. Photocatalytic Reaction of Titanium Dioxide (PRT) In this study, we fabricate indium–zinc oxide (IZO) TFTs using PRT. The hydroxyl radicals are generated by reaction between titanium dioxide (TiO2) and water molecules during UV irradiation. These hydroxyl radicals decompose the 2-methoxyethanol (2ME; one of the representative solvents) into smaller organic molecules. The decomposed 2ME has low boiling points and molar masses compared with non-PRT treated 2ME. Therefore, PRT treatment not only provides superior electronic devices caused by less defect sites in the oxide channel layers, but also allows low temperature process at 230°C. Additionally, since TiO2 particles can generate hydroxyl radicals permanently under UV irradiation, the PRT treated IZO TFTs show improved electrical characteristics even after four times recycling of TiO2. Rotating magnetic field (RMF) treatment In this work, we fabricate indium–gallium–zinc oxide (IGZO) TFTs by RMF treatment at a low temperature of 150°C. For RMF treatment, IGZO films are exposed to periodically rotating magnetic field and thermal energy of 150°C. The magnetic field and thermal energy simultaneously facilitate the interaction and attraction of metal and oxygen atoms leading to formation of M–O bonds in IGZO films. As a result, RMF treated IGZO TFTs exhibited improved electrical performances and positive bias stress (PBS) characteristics compared with those of IGZO TFTs treated by only thermal annealing process at 300°C. Instant Glue (IG) Passivation We introduce IG as a novel material for the passivation layer of IGZO TFTs. The ECA-based IG is a moisture-curing adhesive, which is liquid at room temperature and cures rapidly by reacting with moisture in atmosphere. As it is solidified rapidly at room temperature, it has shorter process time than that of conventional organic materials; the IG passivation layer is prepared successfully just for 1 min at 150°C. The IG passivation layer can modify the chemical stoichiometry of IGZO films and prevent any interaction between the back surface of the IGZO TFT and ambient gas. Therefore, the IGZO TFTs with an IG passivation layer show improved electrical characteristics and reliability compared to those without passivation layer. References Jae Won Na, You Seung Rim, Hee Jun Kim, Jin Hyeok Lee, Seonghwan Hong, and Hyun Jae Kim, ACS Appl. Mater. Interfaces 9, 35, 29849 (2017).Hua Xu, Dongxiang Luo, Min Li, Miao Xu, Jianhua Zou, Hong Tao, Linfeng Lan, Lei Wang, Junbiao Peng, and Yang Cao, J. Mater. Chem. C 2, 7, 1255 (2014).Seonghwan Hong, Sung Pyo Park, Yeong-gyu Kim, Byung Ha Kang, Jae Won Na, and Hyun Jae Kim, Scientific Reports 7, 1, 16265 (2017). Figure. Schematics of various techniques to lower the processing temperatures for oxide TFTs, (a) photocatalytic reaction of titanium dioxide, (b) rotating magnetic field treatment, (c) instant glue passivation. Figure 1

Improvement of electrical characteristics and stability of IGZO TFT through surface single crystallization of IGZO film at room temperature

The electrical characteristics and stability of indium gallium zinc oxide (IGZO) thin film transistors (TFTs) are improved through surface single crystallization of IGZO film by Cs ions adsorption at room temperature. The experimental results show that the Cs ions can bond with the oxygen ions in IGZO film, changing surface structure of IGZO film from amorphous to a single crystalline. The electrical properties and stability of surface single crystalline IGZO and a-IGZO based thin film transistors were investigated, respectively. With the introduction of the surface single crystalline of the IGZO film, the electrical properties of TFT were greatly improved, showing that the carrier mobility improved from 5.28 cm2 V−1s−1 to 8.84 cm2 V−1s−1, and the threshold voltage deceased from 7.6 V to 2.3 V, accompanied with a leakage current below 10−15 A. The stability of Vth shifts in surface single crystalline IGZO based TFT was 6.3 V under VGS = 20 V for 5000 s, improved by ∼32% compared with that of a-IGZO TFT.

Employment of rapid thermal annealing for solution-processed InGaZnO thin film transistors

We employed rapid thermal annealing (RTA) as a novel approach to anneal indium–gallium–zinc–oxide films for thin film transistor (TFT) applications. We analyzed the binding states of the elements presented in the films annealed with RTA and hot plate based on X-ray photoelectron spectroscopy data. The investigation confirmed that the RTA samples underwent sol–gel reactions at a low temperature of 180 °C. We also acquired the transfer curves of the TFTs incorporated with the samples. The RTA samples exhibited a high on-current level, whereas the hot plate sample annealed at the same temperature demonstrated nearly no current flow. The data manifested that RTA generated both photonic and thermal energies, thus efficiently facilitating sol–gel reactions at a low temperature. Furthermore, we investigated on the energy band structures of the annealed films based on reflection electron energy loss spectroscopy and ultraviolet photoelectron spectroscopy analyses, discovering that the annealing atmosphere significantly affected the band structure of the film.

A Barrier Structure for Photoelectrode of Dye-Sensitized Solar Cell for Enhancing Efficiency

In this letter, the indium–gallium–zinc oxide (IGZO) had been applied to the photoelectrode for reducing dark reaction. According to the experimental results, the IGZO film formed an energy barrier to retard the recombination between photo-generated electron in active layer and hole ( $I_{3}^{-}$ ) in electrolyte. It contributes an enhancement of electron lifetime, decrease in dark reaction, and improvement in the short-circuit current density ( $J_{\text {SC}}$ ). Consequently, the photovoltaic conversion efficiency of dye-sensitized solar cell is enhanced from 3.34% to 5.47%. This enhancement has the potential to expand an electron device of photocatalyst.

Effects of hydrogen impurities on performances and electrical reliabilities of indium-gallium-zinc oxide thin film transistors

The influences of hydrogen impurities on the performances of indium-gallium-zinc oxide (IGZO) thin film transistors (TFT) are summarized in this article. Firstly, the sources of hydrogen impurities in the IGZO channels of the TFTs are proposed, which could originate from the residual gas in the deposition chamber, the molecules absorbed on the sputtering target surface, the neighbor films that contain abundant hydrogen elements, doping during annealing processes, etc. The hydrogen impurities in the IGZO films can exist in the forms of hydroxyl groups and metal hydride bonds, respectively. The former originates from the reaction between H atoms and the O2- ions. This reaction releases free electrons, leading to a rise of the Fermi level of IGZO, and thus enhancing the mobilities of IGZO TFTs. The latter incurs negative charges on H atoms, and thus changing the distribution of the subgap density of states, hence improving the negative bias (or illumination) stabilities of IGZO TFTs. Subsequently, various methods are also proposed to characterize hydrogen elements in IGZO, such as secondary ion mass spectroscopy, thermal desorption spectroscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Finally, the effects of hydrogen impurities on the electrical characteristics of the IGZO TFTs, such as the field effect mobilities, subthreshold swings, threshold voltages, on/off current ratios as well as the positive and negative bias stress stabilities, are discussed. The results indicate that hydrogen element concentration and process temperature are two key factors for the device performances. With the increase of hydrogen element concentration in the IGZO channels, the TFTs exhibit higher electron mobilities, lower subthreshold swings and better reliabilities. However, annealing at too high or low temperatures cannot improve the device performance, and the most effective annealing temperature is 200-300℃. It is anticipated that this review could be helpful to the IGZO TFT researchers in improving the device performances and understanding the underlying mechanism.

Ultra-High Sensitivity to Low Hydrogen Gas Concentration With Pd-Decorated IGZO Film

To enhance the performance of semiconducting metal oxides, as hydrogen (H2) sensor, we introduced a high carrier concentration ( ${N}_{d}$ ) metal oxide, indium-gallium–zinc oxide (IGZO), combined with palladium (Pd) catalysis. This allowed the detection of low concentrations of H2 at room temperature. The base current level was linearly increased with the Pd thickness. As a result, a high sensor sensitivity of $6.1 \times 10^{6}$ % at 5% H2 concentration was obtained using a 1-nm-thick Pd-decorated IGZO film. Comparative studies with a zinc oxide (ZnO) counterpart showed that the ${N}_{d}$ of IGZO ( $8 \times 10^{18}$ cm $^{-3}$ ) is significantly higher than that of ZnO ( $2 \times 10^{16}$ cm $^{-3}$ ), indicating a closer location for the Fermi level of IGZO to the conduction band. Therefore, a relatively small amount of electron-donating H2 was required to overcome the energy barrier in IGZO. Consequently, the 1-nm-thick Pd-decorated IGZO sensor responded to a gas level as low as 0.01% (100 ppm) and demonstrated a 70-fold higher sensitivity compared with ZnO sensor at all H2 concentrations.

Radio-frequency oxygen-plasma-enhanced pulsed laser deposition of IGZO films

We demonstrate the crystalline structures, optical transmittance, surface and cross-sectional morphologies, chemical compositions, and electrical properties of indium gallium zinc oxide (IGZO)-based thin films deposited on glass and silicon substrates through pulsed laser deposition (PLD) incorporated with radio-frequency (r.f.)-generated oxygen plasma. The plasma-enhanced pulsed laser deposition (PEPLD)-based IGZO thin films exhibited a c-axis-aligned crystalline (CAAC) structure, which was attributed to the increase in Zn-O under high oxygen vapor pressure (150 mTorr). High oxygen vapor pressure (150 mTorr) and low r.f. power (10 W) are the optimal deposition conditions for fabricating IGZO thin films with improved electrical properties.

Tribology Properties of IGZO Films by the Sliding Contacts of Reciprocating Motion

In the present study, sliding tribo tests with reciprocating motion were carried out to simulate the thumb-driven wear arising in indium gallium zinc oxide (IGZO) specimens prepared at five inclination angles during film deposition. Frictional and normal forces, Fx and Fy, and vibrations were used to analyze energy dissipation (ΔW) and composite mean force fluctuation intensities (IFSS). Friction coefficient is lowered by decreasing the mean surface roughness (Ra); its increase can raise ΔW. The friction coefficients of samples prepared with a nonzero inclination angle were lower than that of the IGZO_0° specimen.

Effects of deposition power of IGZO film and graphene layer in IGZO/graphene + Ni/SiO2/Si wafer specimens on the mechanical and electrical properties in tribotests

In the present study, indium gallium zinc oxide (IGZO) films were deposited onto graphene+Ni/SiO2/Si wafer specimens with deposition powers of 60-, 80-, and 100-W, respectively. The effects of deposition power on the microstructure and vacancy defects formed in the graphene+Ni layer are evaluated based on the electrical and mechanical properties of as-received specimens. The role and behavior of the graphene+Ni film on the electrical resistance of the IGZO film with microcracks were evaluated using a tribotester. The variations of the acceleration, ay, in the direction normal to specimen contact surface and the morphology of worn surface and the friction coefficient in a stroke are provided us to identify their wear styles including seizure, stick-slip motion, and running-in instability. After applying a number of swing cycles, the turning angle of the Ni crystalline with respect to the graphene orientation increases with increasing the number of cycles. The mean microcrack length increases with increasing the turning angle. However, the electrical resistance of specimen is not elevated by increasing the microcrack length so long as the connection of the graphene layer with the IGZO film is sustained. Increase in the deposition power promotes the growth of hillocks in the graphene+Ni layer. These hillocks make the graphene+Ni layer convex with an uneven film thickness and lead to void defects in the graphene+Ni layer, they also cause the IGZO film with relatively large mean surface roughness and high friction coefficient.

Effects of graphene layers in IGZO / graphite-like +Ni/SiO_2/Si wafer specimens on electrical and optical properties in tribotests

In the present study, graphite-like +Ni/SiO2/Si wafer specimens were prepared using a co-sputtering system. Then, indium gallium zinc oxide (IGZO) films were deposited onto the graphite-like +Ni/SiO2/Si wafer specimens at deposition powers of 60, 80, and 100 W, respectively. The effects of IGZO deposition power on the specimen’s microstructure and the vacancy defects in the graphite-like +Ni layer are evaluated in terms of the electrical and mechanical properties of the as-prepared specimens. The effects of the graphite-like +Ni film on the electrical resistance of the IGZO film with microcracks is evaluated using a tribotester. The quantity and mean size of microcracks and variations of electrical resistance of the IGZO/graphite-like +Ni/SiO2/Si wafer specimens with time are used to evaluate the role of the graphite-like +Ni layer as an alternate conductor of electric current when the IGZO film is degraded by microcracks. The growth of hillocks in the graphite-like +Ni layer can be enhanced by increasing the IGZO deposition power. These hillocks cause the graphite-like +Ni layer to be convex and have an uneven film thickness, and lead to vacancy defects in the graphite-like film. The O atoms of IGZO were incorporated into graphene in the graphite-like layer as substitutional impurities. The effects of these impurities on the electrical structure with a characteristic of superconductors occur intermittently in the tribotests, resulting in a sharp reduction in the electrical resistance of a specimen. An increase in the intensity ratio, IRO2, related to oxygen vacancies, increases the peak intensities (PIs) of elemental Ga and the Ga-O bond, and decreases that of the Ga-Ga bond. In the IGZO/Glass specimens, a small reduction of the average transmittance is created in the specimens prepared by increasing the deposition power from 60 W to 100 W. The behavior of reflection is exactly opposite to that of transmittance. An increase in deposition power is favorable for the rise of optical band gap (Eg). Increasing the concentration of Zn2p3/2 or Zn2p1/2 increases PIGreen in photoluminescence profiles. Reductions in either In atoms or C-C and C-O bonds increase PIOrange. PIRed and can be increased by either increasing PIGa-Ga or decreasing the values of PIGa2p3/2, PIGa2p1/2, and PIGa-O.

Blade-coated sol-gel indium-gallium-zinc-oxide for inverted polymer solar cell

The inverted organic solar cell was fabricated by using sol-gel indium-gallium-zinc-oxide (IGZO) as the electron-transport layer. The IGZO precursor solution was deposited by blade coating with simultaneous substrate heating at 120 °C from the bottom and hot wind from above. Uniform IGZO film of around 30 nm was formed after annealing at 400 °C. Using the blend of low band-gap polymer poly[(4,8-bis-(2-ethylhexyloxy)-benzo(1,2-b:4,5-b’)dithiophene)-2,6-diyl-alt- (4-(2-ethylhexanoyl)-thieno [3,4-b]thiophene-)-2-6-diyl)] (PBDTTT-C-T) and [6,6]-Phenyl C71 butyric acid methyl ester ([70]PCBM) as the active layer for the inverted organic solar cell, an efficiency of 6.2% was achieved with a blade speed of 180 mm/s for the IGZO. The efficiency of the inverted organic solar cells was found to depend on the coating speed of the IGZO films, which was attributed to the change in the concentration of surface OH groups. Compared to organic solar cells of conventional structure using PBDTTT-C-T: [70]PCBM as active layer, the inverted organic solar cells showed significant improvement in thermal stability. In addition, the chemical composition, as well as the work function of the IGZO film at the surface and inside can be tuned by the blade speed, which may find applications in other areas like thin-film transistors.

Improvement of TFT Characteristics for Low-Temperature Solution-Processed Oxide Semiconductors with Hydrogen Injection and Oxidation Process

Thin-film transistors (TFTs) using oxide semiconductors have attracted much attention for switching and driving devices in large-screen, high-resolution liquid crystal display (LCD) and organic light-emitting diode (OLED) displays because of their high mobility1-3. As an advanced oxide TFT fabrication method, the solution-process is widely researched due to advantages such as its low process cost, large-scale fabrication capacity, and the simplicity of the process. However, several drawbacks of the solution-process must be addressed for display applications. One of the key points is the trade-off between the processing temperature and the TFT characteristics. From previous research on solution-processed oxide TFTs, it has been reported that low-temperature-processed TFTs are generally inactive below 400 °C due to a lack of metal-oxide-metal bond formation and decomposition of the residual species4,5. However, a low-temperature process is strongly required for application to plastic substrates for flexible displays and flexible electronics devices.In addition, a low-temperature process is important to achieve low fabrication costs. Here, we demonstrate improvement of the TFT characteristics by application of a hydrogen injection and oxidation (HIO) process for low-temperature solution-processed oxide TFTs. From a technical standpoint, we consider that the important factor is how to efficiently decompose the residual species. The solution-processed oxide TFTs exhibit inferior device performance when a few residual species remain. Therefore, a reduction reaction is initiated by a hydrogen injection process to decompose the residual spices. The characteristics of a TFT based on indium gallium zinc oxide (IGZO) were evaluated, such as the field effect mobility and the threshold voltage (Vth) shift under positive and negative bias stress. The maximum temperature for the entire fabrication process was as low as 300 °C. Solution-processed IGZO thin films were fabricated by a spin-coating method onto 200 nm thick thermally oxidized SiO2/n+-Si substrates and annealing at 300 °C for 1 h. The IGZO precursor was prepared from 0.3 M solutions of indium nitrate hydrate (In(NO3)3·xH2O), gallium nitrate hydrate (Ga(NO3)3·xH2O), and zinc nitrate hydrate (Zn(NO3)2·xH2O) in pure water. The composition ratio for In:Ga:Zn was set to 4:1:1. Hydrogen plasma treatment was adopted for the hydrogen injection process with subsequent annealing at 300 °C for 1 h. After fabrication of the IGZO film, the active area of the IGZO film was defined using a conventional photolithography method. Patterned source/drain (S/D) electrodes (Mo) were formed on the IGZO thin films using a shadow mask. Figure 1 shows the transfer characteristics of the IGZO TFT with and without the HIO process. The transfer characteristics of these IGZO TFTs for gate voltages (Vg) ranging from -30 to 30 V were measured at a fixed drain voltage (Vd) of 30 V. After the HIO process for the IGZO TFTs, the field effect mobility was significantly improved from 2.1 cm2/Vs to 4.8 cm2/Vs. Figure 2 shows the results for the threshold voltage shift (ΔVth) under a positive gate bias stress (PBS) of 20 V and a negative gate bias stress (NBS) of -20 V, with and without the HIO process. The stress time was set to 1 h at the maximum. Improvement of the reliability was confirmed: the Vth shift was less than 0.25 V for PBS and -2 V for NBS. The trap sites of any residual species or defect states in active channels were thus efficiently suppressed by the hydrogen injection process. In addition, the oxidation process may enhance the metal-oxide-metal bond formation. In conclusion, the HIO process as a combination of hydrogen reduction reaction and oxidation was demonstrated as effective for the improvement of solution-processed oxide TFTs. Improvement of the TFT characteristics was confirmed in terms of the field effect mobility and the Vthshift under PBS and NBS. Therefore, we consider that this new approach will lead to the development of high-performance solution-processed oxide TFTs in future. 1K. Nomura, H. Ohta, A. Takagi, T. Kamiya, M. Hirano, and H. Hosono, Nature 432, 488 (2004). 2K. Nomura, H. Ohta, K. Ueda, T. Kamiya, M. Hirano, and H. Hosono, Science 300, 1269 (2003). 3L. Wang, M. Yoon, G. Lu, Y. Yang, A. Facchetti, and T.J. Marks, Nature materials 5, 893 (2006). 4 M. G. Kim, M. G. Kanatzidis, A. Facchetti, and T. J. Marks, Nature materials 5, 382 (2011) 5 S. Jeong, Y. G. Ha, J. Moon, A. Faccchetti, T. J. Marks, Advanced materials 22, 1346 (2010) Figure 1

Low-Temperature Photochemically Activated Amorphous Indium-Gallium-Zinc Oxide for Highly Stable Room-Temperature Gas Sensors.

We report on highly stable amorphous indium-gallium-zinc oxide (IGZO) gas sensors for ultraviolet (UV)-activated room-temperature detection of volatile organic compounds (VOCs). The IGZO sensors fabricated by a low-temperature photochemical activation process and exhibiting two orders higher photocurrent compared to conventional zinc oxide sensors, allowed high gas sensitivity against various VOCs even at room temperature. From a systematic analysis, it was found that by increasing the UV intensity, the gas sensitivity, response time, and recovery behavior of an IGZO sensor were strongly enhanced. In particular, under an UV intensity of 30 mW cm(-2), the IGZO sensor exhibited gas sensitivity, response time and recovery time of 37%, 37 and 53 s, respectively, against 750 ppm concentration of acetone gas. Moreover, the IGZO gas sensor had an excellent long-term stability showing around 6% variation in gas sensitivity over 70 days. These results strongly support a conclusion that a low-temperature solution-processed amorphous IGZO film can serve as a good candidate for room-temperature VOCs sensors for emerging wearable electronics.

Effects of ZnO composition on structure, optical and electrical properties of cosputtering In2O3–Ga2O3–ZnO films

This study investigated the impacts of structure, optical and electrical properties of indium–gallium–zinc oxide (IGZO) film with varied ZnO deposition powers on glass substrates by using cosputtering system with two radio-frequency (RF) (ZnO and Ga2O3) and one direct-current (DC) (In2O3) magnetron. The average transmittance decreased obviously from 86.37 to 81.44 % and the optical energy gap decreased from 3.56 to 3.29 eV when ZnO deposition power increases. Results are ascribed to facts that the content of Zn in IGZO films was increased and the fitting extinction coefficient near the wavelength in the range of 370–450 nm obviously increased with increase of ZnO deposition power; the fitting refractive index of IGZO films was noticeably increased and surface morphology displayed a dense structure. The crystallinities of IGZO films reveal from an amorphous structure with a content of Zn less than 50 at.% to a polycrystalline phase of IGZO film with a content of Zn around 70.5 at.%. The residual stress of the indium gallium oxide (IGO) films with undoped ZnO content significantly changed from a tensile stress to a compressive stress with an increased annealing temperature. When the ZnO composition incorporated into the IGO film, variations of the residual stress in the films gradually become smaller. The optimum process condition of cosputtering IGZO films with a ZnO deposition power at 100 W and an annealing temperature at 300 °C showed the largest film mobility, smallest surface roughness, and a lower residual stress.

Effects of e-beam deposited gate dielectric layers with atmospheric pressure plasma treatment for IGZO thin-film transistors

Abstract In this report, indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) performances were improved using atmospheric pressure plasma treatment on e -beam deposited silicon dioxide gate dielectric layers. The impact on the electrical properties of the IGZO-TFTs with different plasma powers at fixed N 2 gas flow rate on the SiO 2 dielectric surface has been investigated. The performances of the IGZO TFTs showed improvement at high power of 300 W and 400 W treatments. The amorphous IGZO films on SiO 2 /ITO glass achieved transmittance higher than 90% in the wavelength range of 350–1000 nm, and it could be further enhanced with increasing plasma treatment power. The reduced surface roughness in the SiO 2 gate dielectric layer from increased plasma power would affect the performance of IGZO TFTs, especially by higher current on/off ratio, enhanced electron mobility, reduced sub-threshold swing voltage and interfacial trap charge density, and decreased threshold voltage. The amorphous IGZO TFTs with plasma treatment power at 400 W exhibited the field effect mobility, sub-threshold swing, on-current to off-current ratio, interfacial trap density and threshold voltage of 33.5 cm 2 /V s, 0.10 V/dec, 10 7 , 1.2 × 10 12 cm − 2 eV − 1 and 0.77 V, respectively. In addition, the high mobility of 33.5 cm 2 /V s was achieved using simple and cost-effective atmospheric pressure plasma treatment on e-beam deposited SiO 2 gate dielectrics.

Ultraviolet photodetector and gas sensor based on amorphous In-Ga-Zn-O film

In this study, amorphous indium gallium zinc oxide (IGZO) thin films with thickness ranges from 13 to 160nm were deposited on glass. The energy gap of the IGZO measured through transmission spectroscopy was approximately 3.45eV. When irradiated by ultraviolet (UV) light the transition efficiency (ΔI/Idark) of the 115-nm-thick IGZO films were found approximately as 23,924.The IGZO thin films were also tested for use as gas sensors. When attached by ozone molecules, the resistance of the film altered as a result of electron transfer from the film to the gas molecules. The fabricated IGZO films can detect ozone to the ppb level. Our results showed that IGZO thin films were capable of sensing both ozone gas and UV light with high sensitivity.

Crystallization behavior of amorphous indium–gallium–zinc-oxide films and its effects on thin-film transistor performance

Amorphous indium–gallium–zinc oxide (a-IGZO) films were deposited by DC magnetron sputtering and post-annealed in air at 300–1000 °C for 1 h to investigate the crystallization behavior in detail. X-ray diffraction, electron beam diffraction, and high-resolution electron microscopy revealed that the IGZO films showed an amorphous structure after post-annealing at 300 °C. At 600 °C, the films started to crystallize from the surface with c-axis preferred orientation. At 700–1000 °C, the films totally crystallized into polycrystalline structures, wherein the grains showed c-axis preferred orientation close to the surface and random orientation inside the films. The current–gate voltage (Id–Vg) characteristics of the IGZO thin-film transistor (TFT) showed that the threshold voltage (Vth) and subthreshold swing decreased markedly after the post-annealing at 300 °C. The TFT using the totally crystallized films also showed the decrease in Vth, whereas the field-effect mobility decreased considerably.

Activation of sputter-processed indium-gallium-zinc oxide films by simultaneous ultraviolet and thermal treatments.

Indium–gallium–zinc oxide (IGZO) films, deposited by sputtering at room temperature, still require activation to achieve satisfactory semiconductor characteristics. Thermal treatment is typically carried out at temperatures above 300 °C. Here, we propose activating sputter- processed IGZO films using simultaneous ultraviolet and thermal (SUT) treatments to decrease the required temperature and enhance their electrical characteristics and stability. SUT treatment effectively decreased the amount of carbon residues and the number of defect sites related to oxygen vacancies and increased the number of metal oxide (M–O) bonds through the decomposition-rearrangement of M–O bonds and oxygen radicals. Activation of IGZO TFTs using the SUT treatment reduced the processing temperature to 150 °C and improved various electrical performance metrics including mobility, on-off ratio, and threshold voltage shift (positive bias stress for 10,000 s) from 3.23 to 15.81 cm2/Vs, 3.96 × 107 to 1.03 × 108, and 11.2 to 7.2 V, respectively.

Correlation between crystallinity and oxygen vacancy formation in In–Ga–Zn oxide

We study the effect of indium–gallium–zinc oxide (IGZO) crystallinity on oxygen vacancies that play an important role in the characteristics of IGZO-based devices. Optical and electrical measurements revealed that deep defect levels due to oxygen vacancies are largely eliminated in c-axis-aligned crystal IGZO (CAAC-IGZO), which has increased crystallinity without clear grain boundaries. In this study, the correlation between crystallinity and oxygen vacancy formation has been examined by first-principles calculations to investigate the effect of oxygen vacancies in IGZO. Furthermore, the likelihood of oxygen vacancy formation at an edge portion of single-crystal IGZO has been verified by observations of oxygen atoms at the edge region of the IGZO film by annular bright-field scanning transmission electron microscopy (ABF-STEM). Experimental and calculation results show that the high crystallinity of IGZO is important for the inhibition of oxygen vacancies.