Layer In Thin Film Transistors Research Articles

High-Performance and Radiation-Hardened Solution-Processed ZrLaO Gate Dielectrics for Large-Area Applications.

Radiation hardness is important for electronics operating in harsh radiation environments such as outer space and nuclear energy industries. In this work, radiation-hardened solution-processed ZrLaO thin films are demonstrated. The radiation effects on solution-processed ZrLaO thin films and InOx/ZrLaO thin-film transistors (TFTs) were systemically investigated. The Zr0.9La0.1Oy thin films demonstrated excellent radiation hardness with negligible roughness, composition, electrical property, and bias-stress stability degradation after radiation exposure. The metal-oxide-semiconductor capacitors (MOSCAPs) based on Zr0.9La0.1Oy gate dielectrics exhibited an ultralow flat band-voltage (VFB) sensitivity of 0.11 mV/krad and 0.19 mV/krad under low dose and high dose gamma irradiation conditions, respectively. The low dose condition had a 103 krad (SiO2) total dose and a 0.12 rad/s low dose rate, whereas the high dose condition had a 580 krad total dose and a 278 rad/s high dose rate. Furthermore, InOx/Zr0.9La0.1Oy thin-film transistors (TFTs) exhibited a large Ion/Ioff of 2 × 106, a small subthreshold swing (SS) of 0.11 V/dec, a small interface trap density (Dit) of 1 × 1012 cm-2, and a 0.16 V threshold shift (ΔVTH) under 3600 s positive bias-stress (PBS). InOx/Zr0.9La0.1Oy TFT-based resistor-loaded inverters demonstrated complete swing behavior, a static output gain of 13.3 under 4 V VDD, and an ∼9% radiation-induced degradation. Through separate investigation of the radiation-induced degradation on the semiconductor layer and dielectric layer of TFTs, it was found that radiation exposure mainly generated oxygen vacancies (Vo) and increased electron concentration among gate oxide. Nevertheless, the radiation-induced TFT instability was mainly related to the semiconductor layer degradation, which could be possibly suppressed by back-channel passivation. The demonstrated results indicate that solution-processed ZrLaO is a high-potential candidate for large-area electronics and circuits applied in harsh radiation environments. In addition, the detailed investigation of radiation-induced degradation on solution-processed high-k dielectrics in this work provided clear inspiration for developing novel flexible rad-hard dielectrics.

Enhancement-mode thin film transistor using amorphous phosphorus-doped Indium–Zinc–Tin-Oxide channel layer

In this research, we investigated optical properties of amorphous Phosphorus-doped Indium–Zinc–Tin-Oxide (a-IZTO:P) thin films and their feasibility as the channel layer for thin film transistors (TFTs). The a-IZTO:P TFT with bottom-gate top-contact structure was prepared on silicon substrates by radio frequency (RF) magnetron sputtering at room temperature. After annealing in air at 350 °C, the IZTO:P films kept amorphous and showed good optical transmittance of over 80% within the visible range. The a-IZTO:P TFT operated in enhancement-mode and exhibited promising electrical performance with saturation mobility (μSAT) of 34.6 cm2/V∙s, threshold voltage (VTH) of 0.8 V, subthreshold swing (SS) of 0.53 V/decade and on/off current ratio (ION/IOFF) of 4.88 × 108. In addition, the stability of a-IZTO:P TFTs was also investigated.

Chemically Tunable Organic Dielectric Layer on an Oxide TFT: Poly(p-xylylene) Derivatives.

Inorganic materials such as SiOx and SiNx are commonly used as dielectric layers in thin-film transistors (TFTs), but recent advancements in TFT devices, such as inclusion in flexible electronics, require the development of novel types of dielectric layers. In this study, CVD-deposited poly(p-xylylene) (PPx)-based polymers were evaluated as alternative dielectric layers. CVD-deposited PPx can produce thin, conformal, and pinhole-free polymer layers on various surfaces, including oxides and metals, without interfacial defects. Three types of commercial polymers were successfully deposited on various substrates and exhibited stable dielectric properties under frequency and voltage sweeps. Additionally, TFTs with PPx as a dielectric material and an oxide semiconductor exhibited excellent device performance; a mobility as high as 22.72 cm2/(V s), which is the highest value among organic gate dielectric TFTs, to the best of our knowledge. Because of the low-temperature deposition process and its unprecedented mechanical flexibility, TFTs with CVD-deposited PPx were successfully fabricated on a flexible plastic substrate, exhibiting excellent durability over 10000 bending cycles. Finally, a custom-synthesized functionalized PPx was introduced into top-gated TFTs, demonstrating the possibility for expanding this concept to a wide range of chemistries with tunable gate dielectric layers.

36.1: Invited Paper: High Performance PrIZO Oxide TFTs and the Target Fabrication

Praseodymium‐doped indium zinc oxide (PrIZO) has been employed as the channel layer of thin film transistors (TFTs). The TFTs with Pr doping exhibit a remarkable suppression of the light induced instability. A negligible photo‐response and remarkable enhancement in negative gate bias stress under illumination (NIBS) are achieved in the PrIZO TFTs. Meanwhile, the PrIZO TFTs show reasonable characteristics with a high field effect mobility of 26.3 cm2/Vs, SS value of 0.28V/decade, and Ion/Ioff ratio of 109. A prototype of fully transparent AMOLED display is successfully fabricated to demonstrate the potential of Pr‐doping TFTs applied in transparent devices. The G4.5 target of PrIZO has been fabricated for the future mass production.

Dimensional structure regulation of organic–inorganic hybrid perovskite and its application in thin film transistors

The effects of dimensional structure on the properties of lead iodide perovskite (C8H9NH3)2(CH3NH3) n−1Pb n I3n+1 were investigated. Furthermore, perovskite thin films with different dimensionalities were applied as the channel layer of thin film transistors (TFT). The electrical performance and stability of TFT devices were significantly improved through the regulation of dimensional microstructure of the perovskites. As a result, the quasi-2D (n = 6) perovskite TFTs achieved a field-effect mobility (μ FE) of 3.90 cm2 V−1 s−1, with 104 on-off current ratio and −1.85 V threshold voltage, which can be maintained well after 4 days without degradation at 30% ambient humidity. Moreover, the electrical performance of the TFTs based on Pure-2D and Quasi-2D perovskite also exhibited a good bias stability.

Effects of Oxygen Injection Rates on a-IGZO Thin-film Transistors with Oxygen Plasma Treatment

In this study, investigate the influence of oxygen plasma treatment on the oxide channel layer of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors based on the amount of oxygen gas injected. The a-IGZO channel layer thin-film transistors (TFTs) were fabricated with plasma treatment of zero, three, six, or nine standard cubic centimeters per minute (sccm) of oxygen gas injection into the a-IGZO channel layer using gun-type plasma cells from a molecular beam epitaxy system after the post-annealing process. In this experiment, oxygen plasma treatment on the a-IGZO channel layer improved the electrical and surface-area performance. Of all the treatment conditions, the a-IGZO channel layer TFT treated with plasma from an injection of 6 sccm of oxygen gas showed excellent transfer characteristics. They include saturation mobility of 14.4 cm²/Vs, a threshold voltage of 4.5 V, an on/off current ratio of 1.1 × 10<SUP>8</SUP>, and an inverse subthreshold slope of 0.7 V/dec. Surface morphology analyses confirmed that increases in the oxygen gas injection rate decreased. A dynamic inverter test was conducted by configuring the logic circuit for the a-IGZO channel layer TFT, which verified the possibility for future application of the backplane device in active-driven displays.

Fabrication of Amorphous ZnO TFT with Tunable Channel Length

The paper discusses the fabrication of amorphous zinc oxide (a:ZnO)-top gate top contact (the gate is situated on the top and the contacts are taken from the top) thin-film transistor (TFT) using spin-spray pyrolysis (SSP) unit. The solutions of ZnO and poly-vinyl-alcohol (PVA) are synthesized separately by the sol–gel method. The ZnO and PVA solution are coated over glass substrate using the SSP unit and drop-cast technique, respectively. These films are characterized using an optical profilometer, X-ray diffractometer, energy dispersive X-ray analysis, ultraviolet–visible spectrophotometry and Keithley measurement system. The XRD and EDAX measurement confirm the amorphous nature and composition respectively. The thickness of the ZnO and PVA film are 460 nm and 600 nm, respectively. The resistance of ZnO film is 100 KΩ. Using the absorption spectrum, we calculate the bandgap of ZnO and PVA thin film samples which are 3.05 eV and 3.9 eV respectively. The metal–insulator–metal (MIM) structure is fabricated using fluorine-doped tin oxide, PVA and silver paste. The MIM structure is characterized for the electrical parameters such as capacitance and dielectric constant $$(\upvarepsilon r)$$ which is found to be 0.4 μF and 8 respectively at 40 Hz frequency. The TFT is fabricated by depositing the aluminium as electrode, ZnO as channel layer and and PVA as insulator layer of TFT with different W/L ratios. The TFT parameters such as threshold voltage (Vth), on/off current ratio (Ion/off) and mobility are studied and presented. The results confirm that Vth decreases with the shrinking of channel length. Current ratio Ion/off increases with the reduction of the channel length due to the increase in on-current value.

EHD-jet patterned MoS2 on a high-k dielectric for high mobility in thin film transistor applications

Solution synthesis of MoS2 precursor followed by direct printing could be an effective way to make printed electronic devices. A linear MoS2 pattern was obtained by an electrohydrodynamic (EHD)-jet printer with a sol-gel system without chemical vapor deposition. The morphology of the MoS2 after a transfer process was maintained without wrinkles or cracking, resulting in a smooth surface compared with that of spin-coated films. EHD-jet printed MoS2 was transferred onto high-k dielectric Al2O3 and used as a semiconductor layer in thin film transistor (TFT) devices. The printed MoS2 TFT has relatively good electrical characteristics, such as a linear field effect mobility, current ratio, and low subthreshold swing of 47.64 2.99 cm2 V−1 s−1, 7.39 0.12 × 106, and 0.7 0.05 V decade−1, respectively. This technique may have promise for future applications.

Analysis of low frequency noise characteristics of praseodymium doped indium gallium oxide thin film transistor

Metal oxide thin film transistors (MOTFTs) have been extensively investigated in the display industry because of their attractive characteristics, including high performances, low processing temperatures, and simple fabrication. However, under the actual working condition, the characteristics of TFTs are easily affected by the light irradiation caused the negative gate bias stress (NBIS). Therefore, the NBIS stability of MOTFT is a crucial issue that must be solved before their commercialization into an optoelectronic device. In this article, praseodymium-doped indium gallium oxide (PrIGO) is employed as the channel layer of thin film transistor (TFT). The TFTs with Pr doping exhibit a remarkable enhancement in NBIS stability. The structure and chemical composition of PrIGO film are analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. Besides, to further explore the mechanism for the improvement of NBIS stability, the low-frequency noise characteristics of IGO-TFT device and PrIGO-TFT device are studied. According to the low frequency noise characterization and analysis results, the correspondence between the normalized drain current noise power spectral density(&lt;inline-formula&gt;&lt;tex-math id="Z-20210823100314-1"&gt;\begin{document}$ S_{\rm ID}/I_{\rm DS}^2 $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20210368_Z-20210823100314-1.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20210368_Z-20210823100314-1.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;) and frequency shows 1/&lt;i&gt;f&lt;sup&gt;γ&lt;/sup&gt;&lt;/i&gt; (&lt;i&gt;γ&lt;/i&gt; ≈ 0.8) low frequency noise behavior for IGO-TFT device and PrIGO-TFT device. In addition, by studying the influences of different channel lengths on the low frequency noise of the IGO-TFT and PrIGO-TFT devices, it can be concluded that the low frequency noise of the device comes mainly from the channel region rather than from the source/drain contact region. In the linear region of the IGO-TFT device and PrIGO-TFT device, according to the linear fitting of the &lt;inline-formula&gt;&lt;tex-math id="Z-20210823100337-1"&gt;\begin{document}$ S_{\rm ID}/I_{\rm DS}^2 $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20210368_Z-20210823100337-1.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20210368_Z-20210823100337-1.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; versus the overdrive voltage (&lt;i&gt;V&lt;/i&gt;&lt;sub&gt;GS &lt;/sub&gt;– &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;th&lt;/sub&gt;), it is proved that the low frequency noise of the IGO-TFT device and the PrIGO-TFT device are mainly affected by the carrier number fluctuation model. Finally, based on the carrier number fluctuation model, the defect state density at the interface between active layer and gate insulating layer is extracted to be 7.76 × 10&lt;sup&gt;17&lt;/sup&gt; cm&lt;sup&gt;–3&lt;/sup&gt;·eV&lt;sup&gt;–1&lt;/sup&gt; and 9.55 × 10&lt;sup&gt;17&lt;/sup&gt; cm&lt;sup&gt;–3&lt;/sup&gt;·eV&lt;sup&gt;–1&lt;/sup&gt; for IGO-TFT and PrIGO-TFT devices, respectively. We speculate that the Pr element can induce defect states in the IGO system, and the trap states induced by Pr ions facilitate the capture of free electrons by positively charged oxygen vacancies, which lead the photo-induced carrier in conduction band to be suppressed.

Application of Taguchi arrays using DOE for optimizing processing and understanding sputtered coated ZnO TFTs

This study applies the Taguchi orthogonal array (OA) to improve and optimize the performance of ZnO thin-film transistors (TFT). Radiofrequency (RF) sputtering method was used to deposit the active layer of TFTs. The annealing temperature, environmental conditions, sputter rate, and thin-film thickness were the parameters whose impact on output parameters like mobility was analyzed in the process optimization using design of experiment (DOE). The ZnO TFTs show state-of-the-art performance features, including high saturation mobility (0.83c), high Ion/Ioff ratio (104). The optimal configuration was found to be high annealing temperature 450 °C under N2 atmosphere, low sputter rate. This paper presents a method that can empower the fast optimization of metal oxide TFTs for future developments in the manufacturing process. If a full factorial design had been implemented, 64 tests would have been necessary, however in this work, we have reduced the number of tests to 9 only using Taguchi method.

(Invited) Amorphous Zinc Oxysulfide Thin Films: Synthesis, Physical Properties, and TFT Application

Amorphous oxide semiconductors (AOSs) have been under extensive research during recent years. Because of their high electron mobility even under amorphous state, they have been widely used as key materials for flat panel displays and flexible electronics devices, especially as channel layer of thin film transistor (TFT). Recently, it has been reported that an amorphous mixed-anion semiconductor consisting of only earth-abundant elements, zinc oxynitride (a-ZnON), shows high electron mobility and capability to TFT application [1]. However, a-ZnON is unstable in air due to weak chemical bonds between Zn and N [2]. To overcome this drawback, we synthesized another earth-abundant amorphous mixed-anion semiconductor, amorphous zinc oxysulfide (a-ZnOS) thin films and found that their electron mobility is comparable to those of conventional AOSs (~15 cm2V-1s-1), in addition to good chemical stability under ambient conditions [3]. Successively, a-ZnOS based TFTs were fabricated with bottom-gate and top contact configuration. a-ZnOS thin films with S/(S+O) = ~0.30 shows obvious TFT performance in the pristine states, although their field effect mobility (μ FE) was moderate (μ FE <1 cm2V−1s−1). μ FE increased with the decrease of S/(S+O), but the carrier density became too large for TFT operation. By annealing these films in vacuum at 150 °C for 10 min, their TFT performance was significantly improved; on/off ration over 104 and μ FE over 10 cm2V−1s−1.[1] Kim et al., Sci. Rep. 3, 1459 (2013).[2] Lee et al. Appl. Phys. Lett. 107, 122105 (2015)[3] Y.Zhu et al., Adv. Electron. Mater. 6, 1900602 (2019).

Ultra-High Mobility Transistors Via Metal Induced Conductive Region

The amorphous oxide semiconductors (AOSs) such as In-Ga-Zn-O (IGZO) and Zn-Sn-O (ZTO) have been extensively studied as the active layers for thin film transistors (TFTs) in display backplanes due to its high mobility (>10cm2/Vs), transparency, low process temperature and large area uniformity. However, many studies on AOSs have reported that there is trade-off relationship between electrical performance and device stability. Generally, the mobility increases with increasing indium or tin content, while the stability is degraded simultaneously. Furthermore, because the indium is a rare metal and expensive, incorporating indium in active materials is one of the critical reasons for increasing overall process costs. For this reason, the development of an indium-free oxide semiconductor materials with high mobility and stability is continuously required.Recently, (Zn1-xBax)SnO3 (ZBTO) has been reported to be a very stable oxide semiconductor with high electron mobility results from its small effective mass and less defective structure. Based on these desirable material properties, it has been adopted as an active material for cost-effective and high-performance TFTs. Also, in order to improve electrical performance dramatically, an additional metal layers are introduced.The metal capping layers have been reported to improve the performance of TFTs by various mechanisms, including the elimination of the scattering/trapping centers, low-temperature crystallization, and electron injection. However, although many research have been performed to demonstrate the origin of the mobility enhancement by the metal capping layer, the exact mechanism has not been confirmed. Also, former reports of this method showed several drawback such as the induced crystallization and need for stabilization time, which may limit its application on large-area displays.To investigate the effect of metal capping layer, the device was fabricated using In-free active material. The ZBTO active layer were deposited via RF magnetron sputtering on the p++ Si/SiOx substrate. All sample was annealed at 350℃ for 1 hour in air ambient, and patterned using shadow masks. The channel width (W) and length (L) were 800 and 200 μm, respectively. In case of metal capped device, 20 nm-thick Al or Ti metal layer was sputtered selectively between the source/drain electrodes with dimensions W/L = 1300/100 μm.In this work, the formation of conductive region in active layer induced by metal capping layer was suggested as new mechanism of the mobility improvement. Due to the strong oxidation power of Al metal, oxygen deficiency is easily induced in active layer near the interface between Al and ZBTO during Al oxidation. This conductive region in active layer generates free electrons, which can be transported without serious scattering owing to the low defect density of ZBTO. These phenomena were confirmed by TEM and XPS results. As a result, the ZBTO TFTs with an Al metal layer exhibited significantly improved field-effect mobility from 20.8 cm2/Vs to 153.4 cm2/Vs without degradation of other transfer parameters. Furthermore, the ZBTO TFTs showed far superior mobility improvement compared to other conventional oxide TFTs. The carrier transport mechanisms was investigated by 1/f noise measurements, which indicated that carrier transport of ZBTO TFTs with the Al capping layer is enhanced by the reduced bulk trap sites. Moreover, reliability tests including NBS, PBS indicated that the front channel of ZBTO active layer was relatively less affected. Our results indicate that adopt of stable active material with small defect density, in this case ZBTO, is a key factor in the fabrication of metal-assisted TFTs capable of ultra-high performance.

Flexible Oxide Thin-Film Transistors Fabricated at Room Temperature By Introducing Polymer Dielectric and Microwave Annealing

Amorphous oxide semiconductors (AOSs) have attracted considerable attention as an active layer material for thin-film transistors (TFTs), due to their many advantages such as high field effect mobility and large area uniformity compared to amorphous Si counterparts. In particular, amorphous indium gallium zinc oxide (a-IGZO) have widely studied for high performance TFTs which require high mobility, high on/off ratio, low leakage current and room temperature fabrication. Even if, a-IGZO TFTs can be deposited at room temperature, additional thermal treatment is still required in order to obtain satisfactory electrical characteristic and stability.Organic materials can be used for dielectrics of flexible TFTs because of their flexible mechanical properties. Generally, organic dielectric films are fabricated by solution process like spin-coating. Spin coating process can be easy and cheap method, however, the quality of films is not as good as the one with vacuum process because of the residual impurities and thermal damage to the substrate during post-coating bake. Poly(chloro para-xylylene) (Parylene C) can be fabricated via pyrolysis-CVD process at room temperature, which lead to unique characteristics of pinhole-free nature. Also, electrical properties of parylene C films are quite enough to utilize as dielectric layer of TFTs. Moreover, parylene C can act as passivation layer due to their remarkable chemical resistance.In this work, microwave annealing and parylene C are adopted to IGZO TFTs to reduce overall process temperature. Microwave can selectively heat target material by conversion of electromagnetic energy to thermal energy inside of the target material. Finally, flexible IGZO TFTs were realized on PET substrate owing to low process temperature of microwave annealing and parylene C deposition.Transfer and output characteristics were measured in order to investigate the possibility of parylene C as an insulator on oxide TFTs. The device exhibit typical output characteristics with a clear pinch-off, current saturation and no current crowding. When the applied gate voltage bias was 20 V, the saturation drain current was around 230 μA at drain voltage of 20 V. From transfer curve, fully room temperature fabricated IGZO TFTs exhibit mobility, Vth, S.S and hysteresis of 12.9 cm2/Vs, 0.796 V, 0.651 V/dec and 0.62 V. Flexible IGZO TFTs were fabricated using PET substrate which shows low glass transition temperature. The device was well operated which indicate microwave annealing and parylene C deposition process is suitable for low glass transition temperature substrate. The electrical stability of the IGZO TFTs with parylene C gate dielectric under bending stress was evaluated. After bending 15,000 times, switching characteristics was still remained. Mobility and S.S were hardly deteriorated, however, Vth shows small negative shift of near -1 V. In this work, IGZO TFTs were fabricated at room temperature by introducing microwave annealing and room temperature deposited gate dielectric, parylene C. By combining microwave annealing and room temperature fabricated parylene C, the process temperature was decreased enough to utilize flexible substrate with low glass transition temperature. Fabricated flexible IGZO TFTs was shown to withstand harsh 15,000 bending test. Figure 1

Deep level defects and their instability in PLD-grown IGZO (In2Ga2Zn5O11) thin films studied by thermally stimulated current spectroscopy

InGaZnO (IGZO) is an excellent semiconductor material for thin-film transistors (TFTs) used in direct-current and radio-frequency (RF) switching applications, especially since it can be grown at low temperatures on a wide variety of substrates. IGZO thin films with a composition of InGaZnO4 have been deposited and used as channel layers in TFTs for many applications to date; however, IGZO compositions can also be easily changed to vary their properties. These different compositions of IGZO may have different defect properties. In this study, we report the growth of IGZO with composition of In2O3:Ga2O3:5ZnO (In2Ga2Zn5O11) by pulsed laser deposition (PLD) and its electronic defects studied by thermally stimulated current (TSC) spectroscopy. It was found that the as-grown sample has a DC activation energy of 0.62 eV, and four major traps with activation energies between ∼0.16–0.50 eV and one at ∼0.90 eV. Electrical properties and the deep traps of PLD-grown IGZO thin film were found to be varied by post-processing conditions such as thermal history and measurement conditions such as the bias and light exposure applied to the samples. The instabilities induced by these conditions can be explained by structural and stoichiometric features—the ZnO4 tetrahedra and GaO6 octahedra in the structure may become distorted, caused by oxidation or reduction, so that the different defect states could be changed and/or lattice energy variations from the distortion can be observed. This work demonstrates that current-based trap emission, such as that associated with TSC, can effectively reveal electronic defects in highly-resistive semiconductor materials, especially those that are not amenable to capacitance-based techniques, such as deep-level transient spectroscopy, and provide an effective manner to study the trap instabilities in IGZO.

Transmission Line Method Analysis on the Electrical Properties of Bi-Layer Channel Oxide Thin Film Transistors with Oxide-Metal-Oxide Electrodes

Amorphous oxide thin film transistors (TFTs) is designed with bi-layer channel structure of SiInZnO/SiZnSnO (SIZO/SZTO). Bi-layer TFTs has excellent characteristics, such as high mobility, excellent on/off ratio, and low sub-threshold swing compared with the single layer TFTs. In the bi-layer structure, electrical properties were improved by the bottom layer of SIZO film with high carrier concentration and the SZTO film of the top layer could improve stability. Source and drain (S/D) electrodes adopt oxide-metal-oxide (OMO) of SiInZnO/Ag/SiInZnO (SIZO/Ag/SIZO) structure to manufacture high performance TFTs. The sheet resistance ( $$R_{sh}$$ ) and contact resistance ( $$R_{c}$$ ) of single layer TFTs and bi-layer TFTs were obtained using transmission line method (TLM), and the bi-layer TFTs exhibited low $$R_{sh}$$ and $$R_{c}$$ resistances with OMO electrodes. The low $$R_{sh}$$ was found to be advantageous to lowering the $$R_{c}$$ at the S/D electrodes when the OMO structure was applied to a TFTs as revealed in the outstanding device performances. OMO electrodes provide potential possibility to improve oxide TFT with excellent characteristics.

Direct Patterned Zinc-Tin-Oxide for Solution-Processed Thin-Film Transistors and Complementary Inverter through Electrohydrodynamic Jet Printing.

The solution-processed deposition of metal-oxide semiconducting materials enables the fabrication of large-area and low-cost electronic devices by using printing technologies. Additionally, the simple patterning process of these types of materials become an important issue, as it can simplify the cost and process of fabricating electronics such as thin-film transistors (TFTs). In this study, using the electrohydrodynamic (EHD) jet printing technique, we fabricated directly patterned zinc-tin-oxide (ZTO) semiconductors as the active layers of TFTs. The straight lines of ZTO semiconductors were successfully drawn using a highly soluble and homogeneous solution that comprises zinc acrylate and tin-chloride precursors. Besides, we found the optimum condition for the fabrication of ZTO oxide layers by analyzing the thermal effect in processing. Using the optimized condition, the resulting devices exhibited satisfactory TFT characteristics with conventional electrodes and conducting materials. Furthermore, these metal-oxide TFTs were successfully applied to complementary inverter with conventional p-type organic semiconductor-based TFT, showing high quality of voltage transfer characteristics. Thus, these printed ZTO TFT results demonstrated that solution processable metal-oxide transistors are promising for the realization of a more sustainable and printable next-generation industrial technology.

Effects of P-Type SnOx Thin-Film Transistors with N₂ and O₂ Ambient Furnace Annealing.

Recently oxide-based thin-film transistors (TFTs) are investigated for emerging applications of the next generation display devices and other electronic circuits (Fortunato, E., et al., 2012. Oxide semiconductor thin-film transistors: A review of recent advances. Advanced Materials, 24, pp.2945-2986). Despite of the great success in n-type oxide semiconductors with high transparency and high field-effect mobility, high performance P-type oxide TFTs are so highly desired that complementary circuits can be realized with low power and high performance (Ou, W.C., et al., 2008. Anomalous P-channel amorphous oxide transistors based on tin oxide and their complementary circuits. Applied Physics Letters, 92, p.122113). There are some oxides such as SnO, CuO, Cu₂O and NiO are regarded as promising P-type semiconductor materials. In this investigation, tin oxide SnOx is fabricated to be active layer for TFTs device, and furnace annealing with several combinations of nitrogen and oxygen ambient is compared to enhance the electrical characteristics of P-type SnOx TFTs (Park, K.S., et al., 2009. High performance solution-processed and lithographically patterned zinc-tin oxide thin-film transistors with good operational stability. Electrochemical and Solid-State Lett., 12, pp.H256-H258). The results show that with N₂+O₂ ambient, 30 minutes furnace annealing, the P-type SnOx TFTs device shows better performance with mobility (μFE) 0.883 cm²/V · S, threshold voltage (VT) -4.63 V, subthreshold swing (SS) 1.15 V/decade, and Ion/Ioff ratio 1.01×10₃.

Enhancement on carrier mobility in amorphous indium tin oxynitride (ITON) thin films

Indium tin oxynitride (ITON) thin films were deposited by reactive DC magnetron sputtering technique. The samples were deposited onto glass and silicon (100) substrates at room temperature. For this purpose, the sputtering reactive atmosphere was composed of different argon and nitrogen concentrations, to modify the structural, optical and electrical properties of obtained ITON thin films. Energy dispersive spectroscopy (EDS) was used in order to know the chemical composition of the different deposited samples, the nitrogen incorporation in the indium tin oxide structure was verified in all ITON analyzed samples. Additionally, through an infrared absorption spectroscopy study of the deposited films, it was possible to confirm the nitrogen incorporation in the ITO structure for the samples deposited under nitrogen presence. Several absorption bands corresponding to In–N, N–N, In–O, and Sn–O bonds were detected. As the effect of nitrogen incorporation, both crystalline structure and surface morphology are widely affected. On the other hand, the nitrogen presence in the structure leads to increase the carrier mobility reaching a value above 1100 cm2/Vs for the sample deposited in a higher nitrogen flux concentration, this result of high mobility raises ITON thin films a promising candidate to be used as an active layer in thin film transistors. The band gap values were calculated using the Tauc parabolic band model from the absorption spectra and it resulted in values near to 4.0 eV. Finally, the obtained transmission values were in the order of 75–80% in the visible region.

Mechanochemical and Thermal Treatment for Surface Functionalization to Reduce the Activation Temperature of In-Ga-Zn-O Thin-film Transistors.

Amorphous indium-gallium-zinc oxide (a-IGZO) films, which are widely regarded as a promising material for the channel layer in thin-film transistors (TFTs), require a relatively high thermal annealing temperature to achieve switching characteristics through the formation of metal-oxygen (M-O) bonding (i.e., the activation process). The activation process is usually carried out at a temperature above 300 °C; however, achieving activation at lower temperatures is essential for realizing flexible display technologies. Here, a facile, low-cost, and novel technique using cellophane tape for the activation of a-IGZO films at a low annealing temperature is reported. In terms of mechanochemistry, mechanical pulling of the cellophane tape induces reactive radicals on the a-IGZO film surface, which can give rise to improvements in the properties of the a-IGZO films, leading to an increase in the number of M-O bonds and the carrier concentration via radical reactions, even at 200 °C. As a result, the a-IGZO TFTs, compared to conventionally annealed a-IGZO TFTs, exhibited improved electrical performances, such as mobility, on/off current ratio, and threshold voltage shift (under positive bias temperature and negative bias temperature stress for 10,000 s at 50 °C) from 8.25 to 12.81 cm2/(V·s), 2.85 × 107 to 1.21 × 108, 6.81 to 3.24 V, and -6.68 to -4.93 V, respectively.

Enhancement on the performance of eco-friendly solution-processed InO/AlO thin-film transistors via lithium incorporation

Solution-processed fabrication of thin-film transistors (TFTs) has low cost and roll-to-roll capability. Indium oxide is one of the promising materials for the metal oxide semiconductor layer in TFTs. Early works used high temperature (∼700 °C) anneal, which is not suitable for flexible substrates. The toxic solvents, such as 2-methoxyethanol (2-Me), have been widely used in the preparation of precursor solutions. To overcome these challenges, we propose a low temperature (≤250 °C) and an eco-friendly process through the incorporation of lithium. Both X-ray photoelectron spectroscopy and electrical characterizations were carried out to optimize the process. The best result was obtained with 10 at.% lithium incorporation. The high field-effect mobility, averaged over 30 devices, is 21.6 cm2 V−1 s−1, which is 380% higher than the groups without lithium incorporation and is higher than or comparable with those reported by early works for the low-temperature solution prepared InO films. They were used to build an inverter successfully. Moreover, the bias stability of the transistors was also proved to be improved through lithium doping. This eco-friendly solution process has the potential for low-cost fabrication of TFTs on the flexible substrate.