Solution-processed Metal Oxide Semiconductors Research Articles

The impact of nickel doping on metal-oxide network in solution-processed indium zinc oxide transistors

Solution-processed nickel zinc oxide (IZO) thin-film transistors (TFTs) are of great interest as core elements for future display technology based on the low-cost manufacture. It still remains a challenge to ensure stability in the off-current state of IZO using a dopant that is more resource-friendly than Ga in solution processing. In this study, we suggest a solution-based doping process of the IZO semiconductors with a Ni carrier suppressor and investigated the effects of Ni on their transistor operation. Owing to similar size of Ni2+ to Zn2+, an appropriate concentration of Ni partially substituted Zn sites and the strong bonding force of Ni with O reduces hydroxide groups on the surface bonded to Zn, whereas excess Ni addition rather inhibited the formation of smooth thin film. The resulting Ni-doped IZO TFT devices from an optimized Ni concentration exhibited higher performances with significantly reduced off-state currents while maintaining high on-state currents, compared to IZO TFTs. This approach enriches the current family of solution-processed metal oxide semiconductors by providing another option for resource-friendly carrier suppressor, which can contribute to the inexpensive and simple solution process for fabricating TFTs.

High-k and high-temperature-resistant polysilsesquioxane: Potential for solution-processed metal oxide semiconductor transistors operating at low voltage

High-k and high-temperature-resistant polysilsesquioxane: Potential for solution-processed metal oxide semiconductor transistors operating at low voltage

High-K and High-Temperature-Resistant Polysilsesquioxane: Potential for Solution-Processed Metal Oxide Semiconductor Transistors Operating at Low Voltage

High-K and High-Temperature-Resistant Polysilsesquioxane: Potential for Solution-Processed Metal Oxide Semiconductor Transistors Operating at Low Voltage

Flexible, solution-processed, indium oxide (In2O3) thin film transistors (TFT) and circuits for internet-of-things (IoT)

Over the last decade, novel approaches to explore low voltage flexible devices and low power flexible circuits are being widely researched by the scientific community. To realize the true potential of energy thrifty Internet-of-Things (IoT) objects, low power circuits and hence their low-voltage operating devices are a paramount prerequisite, especially when their power is constrained by autonomous energy scavenging. At present, through advanced manufacturing processes, silicon-based semiconductor devices are powering the modern electronics industry. However, processing temperatures are inhibiting them from flexible and printed electronics, as well as being too costly for scalability to the trillions of IoT objects anticipated. Therefore, development of solution-processed metal oxide semiconductors creates huge opportunities for IoT and wearables. Here, flexible solution-processed indium oxide (In2O3) thin film transistors (TFT) and inverter circuits with low operating voltage are reported. The operating voltage of the TFTs is ≤ 3 V with threshold voltage (Vth) 0.82 V, on/off ratio 105 and extracted mobility (μ) in saturation regime is 14.5 cm2/V·s. The gain of the inverter at VDD 1, 2 and 3 V was determined to be 10, 22 and 32 respectively. Furthermore, measured transconductance (gm) and subthreshold swing (S) are found to be 140 μS and 0.22 V/dec, respectively.

Surface Passivation Treatment to Improve Performance and Stability of Solution-Processed Metal Oxide Transistors for Hybrid Complementary Circuits on Polymer Substrates.

Hybrid integration of n‐type oxide with p‐type polymer transistors is an attractive approach for realizing high performance complementary circuits on flexible substrates. However, the stability of solution‐processed oxide transistors is limiting the lifetime and reliability of such circuits. Oxygen vacancies are the main defect degrading metal oxide transistor performance when ambient oxygen adsorbs onto metal oxide films. Here, an effective surface passivation treatment based on negative oxygen ion exposure combined with UV light is demonstrated, that is able to significantly reduce surface oxygen vacancy concentration and improve the field effect mobility to values up to 41 cm2 V−1 s−1 with high on–off current ratio of 108. The treatment also reduces the threshold voltage shift after 2 days in air from 5 to 0.07 V. The improved stability of the oxide transistors also improves the lifetime of hybrid complementary circuits and stable operation of complementary, analog amplifiers is confirmed for 60 days in air. The suggested approach is facile and can be widely applicable for flexible electronics using low‐temperature solution‐processed metal oxide semiconductors.

High-performance solution-processed flexible Cu2O photodetector via UV-irradiation

Solution processing of metal oxide semiconductors (MOS) is widely used for electronic and optoelectronic applications. However, the high-temperature annealing process that is required for device-quality films is incompatible with a flexible substrate because plastics can be thermally damaged. This study fabricates a p-type Cu2O flexible photodetector (PD) with a metal-semiconductor-metal structure on a polyethylene terephthalate (PET) substrate by irradiating a preheated precursor film with ultraviolet (UV) light. High-quality Cu2O crystals are formed on PET substrates by the charge transfer transition that is excited by the UV-irradiation at room temperature. An extremely high photo-to-dark current ratio (PDCR) of 1590 is achieved for a solution-processed Cu2O flexible PD. This flexible PD exhibits a relatively fast photoresponse (~0.2 s) and folds reproducibly after repeated bending for 500 cycles. This process does not require conventional high-temperature thermal annealing and is applicable to other solution-processed MOS, particularly those that are used for flexible electronic applications.

Sol-Gel Drived Novel Hafnium-Indium-Zinc Oxide (HIZO)-Based Gas Sensor for Nitrogen Dioxide Detection

Introduction Nitrogen dioxide (NOX) is a toxic gas which can cause inflammation of respiratory system and increase the risk of asthma even at low concentration [1]. The metal oxide semiconductor (MOS) is one of the most popular gas sensing materials because of their high sensitivity, fast response and low-cost fabrication. Recently, various types of metal oxide nano-structures such as nanospheres, nanowires and nanosheets are studied to enhance sensing properties by maximizing the surface-to-volume-ratio [2-3]. However, these materials have several requirements of complex synthetic processes, such as high temperature, vacuum processes, and so on. To overcome the limitations, solution-processed MOSs as the sensing materials are could be other options due to their simple fabrication process. In the present work, for the first time, we fabricated gas sensor using sol-gel drived novel hafnium-indium-zinc oxide (HIZO) which has good sensitivity and selectivity toward low concentration of NOX gas through a solution process. This study also investigates the effect of hafnium additions on IZO to enhancements in the gas response toward NOX. Method The 0.25 M HIZO sol-gel (from Merck) solutions were prepared by dissolving indium nitrate hydrate, zinc nitrate hydrate, and hafnium chloride in DI-water with a various composition ratio. The atomic ratio of In:Zn was fixed at 6.8:2.2 and the atomic percentages of Hf of the total amounts were 0, 5, 9, 15, 20 and 30 at. %. The prepared solutions were stirred thoroughly at 70 °C for 12 h. To fabricate interdigitated electrodes, platinum was sputtered on Si/SiO2 substrate with 10 μm distance. The sol-gel solutions were drop-coated on the interdigitated electrodes and dried at 100 °C. The samples were finally annealed at 350 °C for 2 h in air to evaporate impurities and densify films. Sensing measurements were done in a gas sensing system varying operating temperatures in the range of 100 °C through 250 °C using a power supply. The gas concentrations were controlled diluting target gases with dry air. We tested gas responses by monitoring changes in resistances of Rg/Ra, where Rg is a resistance during exposure to the target gas, and Ra is a resistance in air, respectively. Results and Conclusions Figure 1 (a) shows gas responses of IZO with and without 15 %-hafnium as varying temperature from 50 to 250 °C. The sensor of hafnium-added IZO exhibited a higher response (61.4) toward 1.6 ppm of NOX gas than that of IZO without hafnium especially at 100 °C. It might be attributed to oxygen vacancies increase due to addition of hafnium. Figure 1 (b) and (c) illustrate oxygen 1s spectrum acquired from XPS analysis for the IZO and hafnium-added IZO, respectively. The amount of oxygen vacancies increases with an incorporation of hafnium as can be compared in figure (b) and (c). The sensor also showed excellent sensitivity toward NOX gas until 16 ppb, selectivity toward NOX gas among various gas species such as hydrogen, acetone, and toluene, and stability to continuous measurements for a month. We successfully fabricated solution-processed HIZO-based gas sensors capable of detecting low concentrations of NOX gas operating at low temperatures. Acknowledgments J.-S. Park was partially supported by the Project (No. P0006858) of KIAT and MOTIE in Korea.

Fabrication of cupric oxide‐based transistors by sol–gel technique

Solution-processed metal-oxide semiconductors are a great challenge for advanced electronic devices. Here we report the fabrication of field-effect transistor with a cupric oxide (CuO) films prepared by the sol–gel technique. The X-ray diffraction and optical spectroscopy confirmed the presence of polycrystalline cupric oxide film with an energy gap of 1.0 eV. The field-effect transistor proved semiconductor behaviour with p-type conductivity and the charge mobility of 0.034 cm2/V s and On/Off ratio of 104, that makes the sol–gel technique a suitable low-cost alternative of sputtering technique.

High-Performance Thin-Film Transistors Enable By Metal Oxide Semiconductor with Polyaniline Doing in the Channel Layer

Thin-film transistors(TFTs) using metal oxide-based semiconductors have attracted much attention because of their high carrier mobility, excellent optical transparency, low process temperature and solution process. In particular, indium oxide(InO x ) is capable of aqueous routes for environmentally friendly and shows excellent carrier transport due to high carrier concentrations. Despite these advantages, pristine InO x films are generally polycrystalline structures, making it difficult to apply to flexible electronics, and it is necessary to adjust the carrier density to improve stability. Moreover, such a polycrystalline thin film does not exhibit uniform threshold voltage and field-effect mobility, making it difficult to enlarge the device. To address this problems, InO x was doped with inorganic materials such as Ga, Zn, Sn and Sc. Since the thin film transistors using these amorphous metal oxide semiconductor lowers the carrier density, it adversely affects carrier mobility.In order to solve the doping problem of the conventional inorganic material that lowers the carrier mobility, we proposed solution-processed polyaniline doping in the channel layer of metal oxide semiconductors. As a result, depending on the polymer concentration inside the metal oxide semiconductor, the crystallinity of the InO x film decreases and the carrier concentration is controlled, affecting electrical properties such as field-effect mobility, on / off ratio, onset voltage and hysteresis. These results show the possible applicability to the industrial field as well as a significant meaning in improving the properties with polymer doping in the solution-processed metal oxide semiconductor at low temperatures.

Flexible Metal Oxide Semiconductor Devices Made by Solution Methods.

For the fabrication of next-generation flexible metal oxide devices, solution-based methods are considered as a promising approach because of their potential advantages, such as high-throughput, large-area scalability, low-cost processing, and easy control over the chemical composition. However, to obtain certain levels of electrical performance, a high process temperature is essential, which can significantly limit its application in flexible electronics. Therefore, this article discusses recent research conducted on developing low-temperature, solution-processed, flexible, metal oxide semiconductor devices, from a single thin-film transistor device to fully integrated circuits and systems. The main challenges of solution-processed metal oxide semiconductors are introduced. Recent advances in materials, processes, and semiconductor structures are then presented, followed by recent advances in electronic circuits and systems based on these semiconductors, including emerging flexible energy-harvesting devices for self-powered systems that integrate displays, sensors, data-storage units, and information processing functions.

Impact of fluorine doping on solution-processed In–Ga–Zn–O thin-film transistors using an efficient aqueous route

Simple and facile solution-processed thin-film transistors (TFTs) using metal-oxide semiconductors are promising for producing large-area electronics. To achieve a high-performance solution-processed metal-oxide TFT at a low processing temperature, simple fluorine doping was performed for obtaining a solution-processed metal-oxide semiconductor through efficient metal aqua complexation. The TFTs fabricated using conventional IGZO and fluorine-doped IGZO (IGZO:F) precursors were evaluated. The IGZO:F fabricated TFT demonstrated higher mobility, better switching characteristics, and enhanced overall TFT performance. This simple, low-temperature fluorine doping technique improved the solution-processed TFT for future scalable and low-cost TFTs.

Metal oxide heterojunctions for high performance solution grown oxide thin film transistors

With the continuous development of the next generation display technique, solution-processed thin-film transistors based on metal oxide semiconductors attract researchers’ more and more attentions. Both forming oxide alloys and multi-layer heterojunctions are facilitated to further improve the device performances. Here, employing low temperature and solution processed technique, we alternately stacked InZnO oxide alloy and In2O3 high mobility oxide to form heterojunction transistors. Results showed that the heterojunction device performances depend on the individual oxide layer position in the device structure and the layer number of heterojunctions since they were significantly modulated by the interfacial dipole, gate insulator effect of TFT device, and hall carrier concentrations of heterojunction films. In2O3/IZO heterojunction transistors demonstrated the highest saturation field-effect mobility of 31 cm2 V−1·s−1 which was much higher than those of transistors based on individual In2O3, IZO, and ZnO. Apart from that, a 10 V threshold voltage and a 107 on/off current ratio were achieved for the In2O3/IZO heterojunction transistors. These findings provide a powerful strategy on designing high performance metal oxide channel and a scientific basis for the application of solution processed metal oxide semiconductor heterojunctions in the next generation of electronic devices.

Sol-Gel Drived Novel Hafnium-Indium-Zinc Oxide (HIZO)-Based Gas Sensor for Nitrogen Dioxide Detection

Introduction Nitrogen dioxide (NOX) is a toxic gas which can cause inflammation of respiratory system and increase the risk of asthma even at low concentration [1]. The metal oxide semiconductor (MOS) is one of the most popular gas sensing materials because of their high sensitivity, fast response and low-cost fabrication. Recently, various types of metal oxide nano-structures such as nanospheres, nanowires and nanosheets are studied to enhance sensing properties by maximizing the surface-to-volume-ratio [2-3]. However, these materials have several requirements of complex synthetic processes, such as high temperature, vacuum processes, and so on. To overcome the limitations, solution-processed MOSs as the sensing materials are could be other options due to their simple fabrication process. In the present work, for the first time, we fabricated gas sensor using sol-gel drived novel hafnium-indium-zinc oxide (HIZO) which has good sensitivity and selectivity toward low concentration of NOX gas through a solution process. This study also investigates the effect of hafnium additions on IZO to enhancements in the gas response toward NOX. Method The 0.25 M HIZO sol-gel (from Merck) solutions were prepared by dissolving indium nitrate hydrate, zinc nitrate hydrate, and hafnium chloride in DI-water with a various composition ratio. The atomic ratio of In:Zn was fixed at 6.8:2.2 and the atomic percentages of Hf of the total amounts were 0, 5, 9, 15, 20 and 30 at. %. The prepared solutions were stirred thoroughly at 70 °C for 12 h. To fabricate interdigitated electrodes, platinum was sputtered on Si/SiO2 substrate with 10 μm distance. The sol-gel solutions were drop-coated on the interdigitated electrodes and dried at 100 °C. The samples were finally annealed at 350 °C for 2 h in air to evaporate impurities and densify films. Sensing measurements were done in a gas sensing system varying operating temperatures in the range of 100 °C through 250 °C using a power supply. The gas concentrations were controlled diluting target gases with dry air. We tested gas responses by monitoring changes in resistances of Rg/Ra, where Rg is a resistance during exposure to the target gas, and Ra is a resistance in air, respectively. Results and Conclusions Figure 1 (a) shows gas responses of IZO with and without 15 %-hafnium as varying temperature from 50 to 250 °C. The sensor of hafnium-added IZO exhibited a higher response (61.4) toward 1.6 ppm of NOX gas than that of IZO without hafnium especially at 100 °C. It might be attributed to oxygen vacancies increase due to addition of hafnium. Figure 1 (b) and (c) illustrate oxygen 1s spectrum acquired from XPS analysis for the IZO and hafnium-added IZO, respectively. The amount of oxygen vacancies increases with an incorporation of hafnium as can be compared in figure (b) and (c). The sensor also showed excellent sensitivity toward NOX gas until 16 ppb, selectivity toward NOX gas among various gas species such as hydrogen, acetone, and toluene, and stability to continuous measurements for a month. We successfully fabricated solution-processed HIZO-based gas sensors capable of detecting low concentrations of NOX gas operating at low temperatures. Acknowledgments J.-S. Park was partially supported by the Project (No. P0006858) of KIAT and MOTIE in Korea.

Flexible low-power source-gated transistors with solution-processed metal-oxide semiconductors.

Source-gated transistors (SGTs) with Schottky barriers have emerged as extraordinary candidates for constructing low-power electronics by virtue of device simplicity, high gain, and low operation voltages. In this work, we demonstrate flexible low-power SGTs with solution processed In2O3 channels and Al2O3 gate dielectrics on ultrathin polymer substrates, exhibiting light area density (0.56 mg cm-2), low subthreshold swing (102 mV dec-1), low operation voltage (<2 V), fast saturation behaviors (0.2 V), and low power consumption (46.3 μW cm-2). These achievements pave the way for employing the unconventional SGTs in wearable applications where low-power dissipation and high mechanical flexibility are essential.

Wearable 1\u2009V operating thin-film transistors with solution-processed metal-oxide semiconductor and dielectric films fabricated by deep ultra-violet photo annealing at low temperature

Amorphous metal-oxide semiconductors (AOSs) such as indium-gallium-zinc-oxide (IGZO) as an active channel have attracted substantial interests with regard to high-performance thin-film transistors (TFTs). Recently, intensive and extensive studies of flexible and/or wearable AOS-based TFTs fabricated by solution-process have been reported for emerging approaches based on device configuration and fabrication process. However, several challenges pertaining to practical and effective solution-process technologies remain to be resolved before low-power consuming AOS-based TFTs for wearable electronics can be realized. In this paper, we investigate the non-thermal annealing processes for sol-gel based metal-oxide semiconductor and dielectric films fabricated by deep ultraviolet (DUV) photo and microwave annealing at low temperature, compared to the conventional thermal annealing at high temperature. A comprehensive investigation including a comparative analysis of the effects of DUV photo and microwave annealing on the degree of metal-oxide-metal networks in amorphous IGZO and high-dielectric-constant (high-k) aluminum oxide (Al2O3) films and device performance of IGZO-TFTs in a comparison with conventional thermal annealing at 400 °C was conducted. We also demonstrate the feasibility of wearable IGZO-TFTs with Al2O3 dielectrics on solution-processed polyimide films exhibiting a high on/off current ratio of 5 × 104 and field effect mobility up to 1.5 cm2/V-s operating at 1 V. In order to reduce the health risk and power consumption during the operation of wearable electronics, the operating voltage of IGZO-TFTs fabricated by non-thermal annealing at low temperature was set below ~1 V. The mechanical stability of wearable IGZO-TFTs fabricated by an all-solution-process except metal electrodes, against cyclic bending tests with diverse radius of curvatures in real-time was investigated. Highly stable and robust flexible IGZO-TFTs without passivation films were achieved even under continuous flexing with a curvature radius of 12 mm.

A low-temperature and short-annealing process for metal oxide thin film transistors using deep ultraviolet light for roll-to-roll processing

Solution-processed metal oxide semiconductors have superior electron mobility and stability than solution-processed organic semiconductors. However, their fabrication requires a very-high-temperature and long-time annealing process. In this study, we utilized deep ultraviolet (DUV) light to decrease both the temperature and time of the annealing process. High external energy is required to break the organic bonds in a metal oxide film, which is generally supplied by a high-temperature annealing process carried out for a long duration.Alternatively, the required high energy can be supplied more efficiently by irradiating the metal oxide film with DUV light for a shorter duration. In this work, we used DUV light whose peaks at 172 nm instead of the generally used mercury lamp, peaking at 254 and 185 nm. Owing to this difference, thin film transistors (TFTs) could be fabricated on silicon wafers at a lower temperature and shorter duration as compared to the conditions used in previous studies. Various conditions, such as the heating temperature, duration of DUV irradiation, and N2 flow rate, were optimized to control the heating temperature so as to achieve a mobility of 4.44 cm2/V·s and on–off ratio of 2 × 107, which are much higher than those of a transistor annealed at 300 °C for 30 min (mobility, 1.31 cm2/V·s and on–off ratio, 7 × 105).

Effect of strontium doping on indium zinc oxide thin film transistors fabricated by low-temperature solution process

Solution-processed metal oxide semiconductors for thin film transistors (TFTs) require high-temperature annealing to improve the electrical performance. On the other hand, a high-temperature process cannot be applied to flexible substrates, which is an obstacle preventing the application of MOS films to flexible devices. This paper reports a simple method for improving the electrical characteristics of low-temperature solution-processed indium zinc oxide (IZO) TFTs with strontium (Sr)-doping and vacuum annealing. The addition of Sr to the IZO thin film decreased the density of oxygen vacancies due to the strong bonding energy of Sr with oxygen ions and improved the electrical stability of the IZO TFTs. On the other hand, vacuum annealing increased the number of oxygen vacancies in the IZO film resulting from the low oxygen partial pressure, which led to an increase in carrier concentration. By combining these two methods, Sr-doped IZO TFTs with a high field-effect mobility of 8.75 cm2 V−1 s−1 at 2 mol. % of Sr doping were fabricated.

Investigation of the Electrical Characteristics of Bilayer ZnO/In₂O₃ Thin-Film Transistors Fabricated by Solution Processing.

Metal-oxide thin-film transistors (TFTs) have been developed as promising candidates for use in various electronic and optoelectronic applications. In this study, we fabricated bilayer zinc oxide (ZnO)/indium oxide (In2O3) TFTs by using the sol-gel solution process, and investigated the structural and chemical properties of the bilayer ZnO/In2O3 semiconductor and the electrical properties of these transistors. The thermogravimetric analysis results showed that ZnO and In2O3 films can be produced by the thermal annealing process at 350 °C. The grazing incidence X-ray diffraction patterns and X-ray photoemission spectroscopy results revealed that the intensity and position of characteristic peaks related to In2O3 in the bilayer structure were not affected by the underlying ZnO film. On the other hand, the electrical properties, such as drain current, threshold voltage, and field-effect mobility of the bilayer ZnO/In2O3 TFTs obviously improved, compared with those of the single-layer In2O3 TFTs. Considering the energy bands of ZnO and In2O3, the enhancement in the TFT performance is explained through the electron transport between ZnO and In2O3 and the formation of an internal electric field in the bilayer structure. In the negative gate-bias stress experiments, it was found that the internal electric field contributes to the electrical stability of the bilayer ZnO/In2O3 TFT by reducing the negative gate-bias-induced field and suppressing the trapping of holes in the TFT channel. Consequently, we suggest that the bilayer structure of solution-processed metal-oxide semiconductors is a viable means of enhancing the TFT performance.

P-1.10: Solution-processed metal oxide semiconductors fabricated with oxygen radical assisting perchlorate aqueous precursors through a new low-temperature reaction route

P-1.10: Solution-processed metal oxide semiconductors fabricated with oxygen radical assisting perchlorate aqueous precursors through a new low-temperature reaction route

Low-temperature, high-mobility, solution-processed metal oxide semiconductors fabricated with oxygen radical assisted perchlorate aqueous precursors.

In this report, a simple and general chemical route for fabricating MO semiconducting films at a relatively low temperature without any fuel additives or special annealing steps was demonstrated. The precursor, which consisted of perchlorate, nitrate, and water, is easily converted into In2O3 at an annealing temperature of 250 °C due to oxygen radical assisted decomposition and generation of a large amount of heat. It is found that perchlorate salt can decompose and form an oxide film with high quality at a lower temperature when assisted by nitrate salt. The optimized In2O3-TFT fabricated via this precursor exhibits a saturation mobility of 14.5 cm2 V-1 s-1. Furthermore, this approach has been expanded to the fabrication of ZnO films and attained improved performance, indicating its universality.