Solution-processed Indium Oxide Research Articles

Effects of iodine doping on structural and electrical characteristics of solution-processed indium oxide thin-film transistors and its potential application for iodine sensing

Effects of iodine doping on structural and electrical characteristics of solution-processed indium oxide thin-film transistors and its potential application for iodine sensing

Effect of the gas flow rate in the focused-oxygen plasma treatment of solution-processed indium oxide thin film transistors

In2O3 is a transparent semiconductor layer due to its transparency, high mobility, and solution processability. In this paper, we study the effect of focused oxygen plasma treatment on solution processed indium oxide films annealed at 250 °C and analyze the effect of the gas flow rate. Thin film transistor devices were prepared based on pristine In2O3 films and films treated with oxygen plasma using flow rates of 3, 6, and 9 sccm. The results show that controlling the plasma flow rate can be used to finetune the device characteristics, and the selecting the optimal flow rate is important to improve the electron mobility, threshold voltage, on/off current ratio, and the electrical stability of the devices. The In2O3 TFTs treated at 6 sccm showed the best performance with mobility of 2.19 cm2V−1s−1, threshold voltage of of 4.25 V, and on/off current ratio of 2.13 × 106. The successful fabrication of high-performance, low-temperature solution deposited indium oxide transistors using the focused oxygen plasma treatment for electrical device applications demonstrates the practical potential of this treatment method for future transparent electronics.

具有大电导动态范围和多级电导态的铁电Hf0.5Zr0.5O2栅控突触晶体管

Benefiting from the nonvolatile and fast programming operations of ferroelectric materials, ferroelectric synaptic transistors (FSTs) are promising in neuromorphic computing. However, it is challenging to realize conductance with a large dynamic range (Gmax/Gmin) and multilevel states simultaneously under low energy consumption. Here, solution-processed indium oxide (In2O3) synaptic transistors gated by ferroelectric Hf0.5Zr0.5O2 (HZO) are proposed for the first time to address the above problems. Excellent synaptic characteristics were realized through the delicately regulated ferroelectric phase and good inhibition of charge injection in ferroelectric bulk and ferroelectric/semiconductor interface. Long-term potentiation/depression (LTP/D) up to 101 effective conductance states and excellent endurance (>1000 cycles) with large Gmax/Gmin = 32.2 were successfully mimicked under a low energy consumption of 490 fJ per spike event. Besides, the simulation achieved 96.5% recognition accuracy of handwriting digit, which is the highest record for existing FSTs. This work provides a new pathway for developing low-cost, high-performance, and energy-efficient FSTs.

Oxide TFTs with S/D-contacts patterned by high-resolution reverse-offset printed resist layers

Besides the metal oxide thin film transistors (TFTs) in flat-panel displays that are fabricated using vacuum-processes, there is a growing interest in the fabrication of metal oxide TFTs by means of scalable, low-cost solution and printing processes for applications such as flexible displays and biosensors. Although devices with printed semiconductor and gate insulator can exhibit good electrical performance, source/drain-contacts (S/D) printed from silver (Ag) nanoparticles (NPs) typically suffer from deteriorated electrical characteristics and stability problems. On the other hand, metals providing good contacts, such as aluminum (Al), titanium (Ti) and molybdenum (Mo), cannot be formed as air-stable NPs. To overcome these issues, we have developed a patterning method based on high-resolution reverse-offset printing (ROP) of a sacrificial polymer resist layer. ROP delivers patterns with micrometer-level resolution and steep sidewalls, which are ideal for patterning vacuum-deposited metal contacts at high resolution via lift-off process. Solution-processed indium oxide (In2O3) TFTs were successfully fabricated by using ROP lift-off process for patterning of gate and S/D-electrodes using Al. The fabricated In2O3-based TFTs with Al S/D-contacts exhibit good uniformity, constant mobility (μ sat) ∼ 2 cm2 (V s)−1 over a wide range of width/length-ratios (W/L) and almost zero turn-on voltage (V on) ∼ −0.2 V. TFTs down to 5 µm channel lengths were successfully patterned. Further development of the fabrication process could lead to flexible fully-print-patterned high-resolution TFT backplanes for flexible displays, biosensors, photosensors and x-ray detectors.

Low-temperature crystallization of indium oxide thin films with a photoactivable additive

In this study, we report a simple route to the low-temperature crystallization of solution-processed indium oxide thin films by introducing ammonium nitrate in the sol–gel metal oxide precursor solution as photoactivable additive and applying deep ultraviolet (DUV) irradiation onto the as-spun oxide films in an inert atmosphere. Thermal and structural analyses revealed that the initial temperatures for condensation and crystallization were reduced down to 130 and 200 °C, respectively, by the in situ generation of reactive chemical species enabled by DUV-assisted nitrate photolysis. Furthermore, transmission electron microscopy confirmed that the degree of indium oxide film crystallinity was gradually enhanced as the amount of nitrate in the precursor solution was increased. Finally, electrical characterizations showed that carrier mobility, threshold voltage, subthreshold swing, and threshold voltage shift under the positive bias stress of sol–gel indium oxide thin-film transistors were improved from 0.21 to 5.03 cm2/V s, from 4.18 to 1.64 V, from 1.33 to 0.72 V/dec, and from 6.44 to 4.04 V, respectively, by combining ammonium nitrate and DUV photoactivation.

Humidity effect on electrical performance and bias stability of solution-processed In2O3 thin film transistor

ABSTRACT Relative humidity (RH) in storage environment has a great impact on the electrical performance of thin film transistors (TFTs), and the RH is critical for semiconductor manufacturing and device packaging. In this work, solution-processed indium oxide (In2O3) TFT is fabricated, and the electrical performance of the device is investigated after being exposed to various RH conditions. It is found that the threshold voltage (Vth) and the mobility of In2O3 TFT exhibit clear responses to the RH ranging from 23% to 85%. The inherent mechanism about the humidity effect on the electrical performance is elaborated, and this is due to the “donor effect” from the absorbed water molecules. In addition to the effect on Vth and mobility, RH also exhibits a significant effect on the electrical stability of the TFT. The experimental result indicates that the In2O3 TFT exposed to RH <50% exhibits excellent stability with an applied positive bias stressing for 2000s.

O2 and H2O Barrier-Based High Reliability and Stability Using Polytetrafluoroethylene Passivation Layer for Solution Processed Indium Oxide Thin Film Transistors

The excellent chemical stability and hydrophobicity of Polytetrafluoroethylene (PTFE) polymer lead to its applicability in high-performance flexible electronic appliances. Though the detailed investigation for PTFE passivated metal oxide thin-film transistors (TFTs) is still lacking. Here, we report the highly stable oxygen barrier based on the PTFE passivation layer (PVL) spin-coated upon the lowtemperature solution-processed indium oxide (In₂O₃) TFTs. Particularly, by using the solution-process method, fabrication cost and multiple time-consuming steps are eliminated in the counterpart of the radio frequency magnetron sputtering. The PTFE PVL can significantly suppress the adsorption of surrounding moisture and oxygen from environments owing to its most chemically robust carbon-fluorine bond. In addition, the comprehensive electrical performance in terms of the saturation mobility, on-off current ratio, threshold voltage, subthreshold swing, and interface trap density of the In₂O₃ TFTs passivated with different weight ratios of PTFE are compared. The results show that 1 wt.&#x0025; PTFE passivated In2O3 TFT demonstrates a drastically reduced threshold voltage and highest stability under constant bias. Consequently, oxygen barrier-based PTFE is a promising PVL material for various emerging electronic devices.

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.

Zirconium-aluminum co-doping on solution-processed indium oxide thin film and deceives measured by a novel nondestructive method

Solution-processed co-doped indium oxide (In₂O₃) have broad application prospects in the display industry. In this paper, zirconium-aluminium co-doped indium oxide (InxZryAl1-x-yO) thin films and thin film transistors (TFTs) are prepared by the solution method. Doping ratio of Zr-Al is 1:0, 2:1, 1:1, 1:2 and 0:1, respectively, and the total atomic ratio of Zr-Al doping is 10 at.%. A novel nondestructive method, microwave photoconductivity decay (µ-PCD) is used to evaluate the quality of thin films by simply measuring their response under laser irradiation. The result shows that doping Zr-Al can reduce the defects in In₂O₃ thin films effectively. The addition of Zr can effectively reduce oxygen vacancies, and the addition of Al can inhibit the crystallization of In₂O₃ thin films. The optimal InxZryAl1-x-yO thin film with minimum defects is obtained with doping ratio of Zr:Al = 2:1. The roughness of thin films is below 0.37 nm, and possess exceptional transmittance (>95%) in the visible range. The optimized TFT exhibits mobility of 2.3 cm2µV−1µs−1, an on/off current ratio of 2.0 × 104, a threshold voltage of 2.29 V and a subthreshold swing of 1.61 Vµdec−1 with doping ratio of Zr:Al = 2:1.

Multimode Operation of Organic-Inorganic Hybrid Thin-Film Transistors Based on Solution-Processed Indium Oxide Films.

Solution-processed metal oxide (MO) thin films have been extensively studied for use in thin-film transistors (TFTs) due to their high optical transparency, simplicity of fabrication methods, and high electron mobility. Here, we report, for the first time, the improvement of the electronic properties of solution-processed indium oxide (InOx) films by the subsequent addition of an organic p-type semiconductor material, here 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene), yielding organic-inorganic hybrid TFTs. The addition of TIPS-pentacene not only improves the electron mobility by enhancing the charge carrier percolation pathways but also improves the electronic and temporal stability of the IDS(VG) characteristics as well as reduces the number of required spin-coating steps of the InOx precursor solution. Very interestingly, the introduction of 10 nm TIPS-pentacene films on top of 15 nm InOx layers allows the fabrication of either enhancement- or depletion-mode devices with only minimal changes to the fabrication process. Specifically, we find that when the TIPS-pentacene layer is added on top of the source/drain electrodes, resulting in devices with embedded source/drain electrodes [embedded electrode TFTs (EETFTs)], the devices exhibit an enhancement-mode behavior with an average mobility (μ) of 6.4 cm2 V-1 s-1, a source-drain current ratio (Ion/Ioff) of around 105, and a near-zero threshold voltage (VTH). When on the other hand the TIPS-pentacene layer is added before the source-drain electrodes, i.e., in top-contact electrode TFTs (TCETFTs), a very clear depletion mode behavior is observed with an average μ of 6.3 cm2 V-1 s-1, an Ion/Ioff ratio of over 105, and a VTH of -80.3 V. Furthermore, a logic inverter is fabricated combining the enhancement (EETFTs)- and depletion (TCETFTs)-mode transistors, which shows a potential for the construction of organic-inorganic hybrid electronics and circuits.

Enhancement of electrical properties of solution-processed oxide thin film transistors using ZrO2 gate dielectrics deposited by an oxygen-doped solution

Solution deposition of high-quality dielectric films is one of the big challenges in achieving excellent electrical performance of bi-layer solution-processed metal oxide (MO) thin film transistors (TFTs). Using an oxygen-doped precursor solution (ODS), we successfully deposited high-quality zirconium oxide (ZrO2) dielectric films by a solution process. The ODS-ZrO2 films show low leakage current density (10−7 A cm−2 at 2 MV cm−1), high breakdown electric field (7.0 MV cm−1) and high permittivity (19.5). Consequently, solution-processed indium oxide (In2O3) TFTs with ODS-ZrO2 film as the gate dielectric show excellent electrical performance, for example high carrier mobility up to 62.02 cm2 V s−1, a large on/off drain current ratio of 3.0 × 106, a small subthreshold swing of 0.14 V and excellent bias stress stability. Our work demonstrates the critical role of the dielectric film in the electrical performance of MO-TFTs. More importantly, we reveal that high dielectric constant (κ) dielectric film deposited with ODS should be an effective way to significantly increase the electrical properties of MO-TFTs for future low-cost, high-performance applications.

The effect of post-metal annealing on the electrical performance and stability of two-step-annealed solution-processed In2O3 thin film transistors

In this work, solution-processed indium oxide (In2O3) thin film transistors (TFTs) were fabricated by a two-step annealing method. The influence of post-metal annealing (PMA) temperatures on the electrical performance and stability is studied. With the increase of PMA temperatures, the on-state current and off-state current (Ion/Ioff) ratio is improved and the sub-threshold swing (SS) decreased. Moreover, the stability of In2O3 TFTs is also improved. In all, In2O3 TFT with post-metal annealing temperature of 350°С exhibits the best performance (a threshold voltage of 4.75 V, a mobility of 13.8 cm2/V, an Ion/Ioff ratio of 1.8 × 106, and a SS of 0.76 V/decade). Meanwhile, the stability under temperature stress (TBS) and positive bias stress (PBS) also show a good improvement. It shows that the PMA treatment can effectively suppress the interface trap and bulk trap and result in an obviously improvement of the In2O3 TFTs performance.

Anodization-induced ZrOx/AlOx stacked films for low-temperature, solution-processed indium oxide thin-film transistors

In this study, anodization is introduced to induce dehydroxylation and condensation of solution-processed ZrOx films as well as growth of AlOx films. The anodization-induced ZrOx/AlOx stacked films are systematically studied in structure, surface morphology, density, chemical composition, dielectric and electrical properties. X-ray diffraction and atomic force microscopy reveal that anodization-induced ZrOx/AlOx stacked films exhibit amorphous structure and smooth surface roughness (<1 nm). X-ray reflectivity and x-ray photoelectron spectroscopy reveal that the solution-processed ZrOx films exhibit a higher density and a lower content of hydroxyl groups after anodization, suggesting the anodization can induce dehydroxylation and condensation for the ZrOx films. The synergistic effect of collision inducing dissociation and the self-heating from anodization of Al film is proposed to explain the dehydroxylation of the ZrOx films. Dielectric and electrical measurements illustrate that the anodization-induced ZrOx/AlOx stacked films exhibit a lower leakage current, a higher breakdown voltage and a slighter capacitance dispersion on frequency comparing with that of solution-processed ZrOx films without anodization. To verify the possible applications of anodization-induced ZrOx/AlOx stacked films as the gate dielectric in metal-oxide (MO) thin-film transistors (TFTs), they were integrated in low-temperature, directly photopatternable InOx TFTs. Remarkably, with a low process temperature of 200 °C, the InOx TFTs based on the optimized ZrOx/AlOx dielectrics exhibit an average mobility of 8.94 cm2 V−1 s−1, an I on/I off of large than 105 and negligible hysteresis in transfer curves. These results demonstrate the potential application of anodization-induced solution-processed MO dielectric films for low-temperature TFTs.

Impact of NH3 plasma treatment for solution-processed indium oxide thin-film transistors with low thermal budget

The challenges associated with low-temperature solution-processed metal oxide thin-film transistors (TFTs) have hindered the realization of flexible oxide electronics at temperatures lower than 200 °C. NH3 plasma treatment is embarked upon as a route to effectively transform the chemical precursors to semiconducting metal oxides with high electrical quality. NH3 plasma-activated indium oxide (InOx) TFTs with saturated mobility 2.48 cm2V−1s−1 have been obtained at temperature as low as 150 °C. The low-temperature activation mechanism of NH3 plasma treatment for InOx films and the role of post-annealing in the fabrication process of InOx TFTs have been explored. Research shows that NH3 plasma treatment activates InOx films based on plasma bombardment, radicals doping and radical reactions; then, unreacted radicals and interstitial radicals were effectively removed by extra thermal energy from post-annealing. In comparison to thermal annealing, NH3 plasma treatment with moderate post-annealing is capable of achieving high degrees of condensation and densification reactions for InOx film and modulating the carrier concentration in a manner suitable for high-performance semiconducting behavior with low thermal budget. However, The InOx film after NH3 plasma treatment exhibited a non-uniform geometry due to the effect of plasma-induced damage in the local regions of InOx film, which restricts its commercial application. Some strategies were reported to eliminate the effect of plasma-induced damage by changing plasma conditions or pre-annealing temperature. The results demonstrated that changing plasma conditions by decreasing the plasma chamber temperature or the plasma power can eliminate plasma-induced damage, but attenuate the electrical performance of InOx TFT; nevertheless, changing pre-annealing temperature to 30 °C not only effectively eliminate plasma-induced damage, but also further improve the electrical performances of InOx TFT. These results provide a way for fabricating low-temperature oxide circuitry and supply an effective idea for avoiding plasma-induced damage.

The Effect of Zirconium Doping on Solution-Processed Indium Oxide Thin Films Measured by a Novel Nondestructive Testing Method (Microwave Photoconductivity Decay)

Solution-processed indium oxide is an ideal transparent semiconductor material with wide band gap. Zirconium is an element characterized by a strong binding ability to oxygen which can inhibit the formation of oxygen vacancies and reduce the surface defect state. In this paper, zirconium doped indium oxide (InxZryO) thin films were prepared by the solution method, with indium oxide being doped with zirconium in order to tune the relative number of oxygen vacancies. The influence of the Zr doping concentration and the post-annealed temperature on the properties of the InxZryO thin films was investigated. The results show that the doping process improves the crystallinity and relative density of the obtained films. A novel nondestructive method named microwave photoconductivity decay (μ-PCD) was used to evaluate the quality of InxZryO thin films by simply measuring their response under laser irradiation. The relative number of oxygen vacancies and the minority carrier concentration achieved minimum values at 10 at.% Zr doping concentration. Furthermore, InxZryO thin films with optimal properties from an electrical point of view were obtained at 10 at.% Zr doping concentration, annealed at 400 °C. Characterized by an average transmittance above 90% in the visible range, the obtained InxZryO thin films can be used as active layer materials in the fabrication of high-performance thin film transistor (TFT) devices.

Raman spectroscopy study of solution-processed In2O3 thin films: effect of annealing temperature on the characteristics of In2O3 semiconductors and thin-film transistors

We investigate the effect of annealing temperature on the characteristics of solution-processed indium oxide (In2O3) films. From thermogravimetric analysis of the precursor solution, annealing temperatures of 150, 350, and 450 °C are adopted. The In2O3 films are analyzed by ultraviolet/visible spectroscopy, atomic force microscopy, grazing incidence X-ray diffraction, and Hall-effect measurement. Raman spectroscopy is used to examine the crystal polymorphism of the solution-processed films. Experimental results suggest that the optimal annealing temperature can be 350 °C. The transistor with the In2O3 semiconductor annealed at 350 °C exhibits the field-effect mobility of 1.4 V/cm2 and on/off ratio of 2.1 × 106.

Role of gallium and yttrium dopants on the stability and performance of solution processed indium oxide thin-film transistors

We study the effect of gallium and yttrium doping on both the electrical performance and the stability of indium based metal-oxide thin-film transistors (MOTFTs) at varied concentrations.

Electrical stability of solution-processed indium oxide thin-film transistors under illumination stress

ABSTRACTWe investigated the variation in the electrical characteristics of solution-processed indium oxide (In2O3) thin-film transistors (TFTs) under monochromatic illumination conditions at different wavelengths of 1240, 800, 600, 500, 400, and 350 nm. In our results, there was no discernible difference between the characteristics of the TFT measured in the dark state and those obtained under light illumination at the wavelengths of 1240 nm and 800 nm. On the other hand, the TFT performance was remarkably changed when light having a wavelength of 600 nm or less was illuminated. It is found that the photon energy, which causes the characteristic degradation in the solution-processed In2O3 TFTs, is much lower than the direct band gap energy of In2O3. Consequently, illumination-induced instability in the performance of solution-processed In2O3 TFTs can be explained with the transition phenomena of neutral oxygen vacancies to ionized ones in the In2O3 semiconductor film.

Low temperature solution processed indium oxide thin films with reliable photoelectrochemical stability for efficient and stable planar perovskite solar cells

Low temperature, solution processed indium oxide thin films act as the electron transport layer in planar perovskite solar cells (PSCs), which result in high efficiency and reliable stability.

Solution-processed indium oxide electron transporting layers for high-performance and photo-stable perovskite and organic solar cells.

Interface engineering is considered the key to improving the device performance and stability of solar cells. In particular, TiO2 nanostructures, when used as electron transporting layers (ETLs) in metal halide perovskite solar cells (PSCs), led to excellent power conversion efficiencies (PCEs) of over 20%. They effectively transferred charge carriers from the perovskite and suppressed charge recombination at the interfaces. However, the photocatalytic effect of TiO2 on the perovskite can significantly degrade the device performance under ultraviolet illumination. Therefore, other classes of n-type metal oxides with a wide band gap should be developed to improve their photo-stability. Herein, we demonstrate the development of In2O3 thin films by a solution process and their application as ETLs in PSCs and organic solar cells (OSCs). Pin hole-free In2O3 ETLs obtained by the thermal decomposition of an In precursor thin film exhibit high conductivity (2.49 × 10-4 S cm-1) and low surface roughness (7.33 nm). This leads to impressive PCEs of 14.63% and 3.03% for the PSC and the inverted OSC, respectively. Furthermore, the In2O3-PSC shows better photo-stability than the TiO2-PSC by virtue of the wider band gap of In2O3, which leads to a PCE retention of 74% and 46%, relative to the initial PCE values of the PSC and the inverted OSC, respectively.