High-performance Oxide Thin-film Transistors Research Articles

Temperature dependence and functionalization of solution processed high-k hybrid gate insulators for high performance oxide thin-film transistors

We demonstrate a solution processed gate insulator (GI) with high dielectric constant (high-k) of up to ∼8.9 for high performance and low voltage operation amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs). High mobilities of up to ∼30 cm2 V s−1, threshold voltage of <0.5 V, and low off current (∼10−12 A) can be achieved through the combination of high-k BaTiO x (BTO) nanoparticles and a polysiloxane (PSX) polymer matrix. This combination enables a lower process temperature of 300 °C from 650 °C while ensuring enhanced performance and low gate leakage current. We also show the tunability of the high-k hybrid BTO/PSX through fluorination and addition of a photosensitive property to further reduce the leakage current and inhibit dry etching related degradation. High-k hybrid BTO/PSX GI is a promising candidate for high performance and low-voltage operation oxide TFTs.

InSnZnO Thin-Film Transistors With Nitrogenous Self-Assembled Multilayers Passivation

Nitrogenous octadecylamine (ODA) self-assembled multilayers (SAMs) are prepared as passivation layers by the vapor-phase process for amorphous InSnZnO (ITZO) thin-film transistors (TFTs). The vapor-phase proposed ODA SAMs show excellent properties as a barrier against the atmosphere and serve as an effective nitrogen doping (N doping) source. After the self-assembled process, the distribution of the oxygen vacancies is modified by N-doping in the channel of the ITZO TFTs, wherefore the ITZO TFTs with ODA SAMs demonstrate an improvement of electrical properties. In addition, the oxygen and water adsorption/desorption reactions at the back channel are suppressed by the atmosphere isolation and N-doping effect, leading to an improvement of the positive bias stability. These results indicate that the nitrogenous ODA SAMs can be likely passivation layers for high-performance oxide TFT devices.

Low-temperature and high-performance ZnSnO thin film transistor activated by lightwave irradiation

Ultra-high-resolution and flexible display applications require high-performance oxide thin film transistors (TFTs) fabricated at low temperatures. This study fabricated low-temperature and solution-processed high-mobility ZnSnO (ZTO) thin films and TFTs by a lightwave-activation annealing process. The effect of Sn content on the microstructures and electrical properties of lightwave-activated ZTO (LW-ZTO) films and TFTs was investigated. The lightwave-activation process triggered the efficient decomposition of chloride-based precursors and enhanced the performance of ZTO TFTs at a low temperature (230 °C). The optimized ZTO TFTs exhibited excellent electrical properties, including a high saturation mobility of 45.1 cm2/Vs and an on-current/off-current ratio of 105-106 at a low operating voltage of 3 V. Furthermore, the LW-ZTO devices demonstrated high operational stability with a small Vth shift of 0.231 V under bias stress for 5400 s. The performance of the ZTO TFTs was attributed to the low-temperature lightwave-activation process, stemming from the synergic effects of light and heat. These promising results highlight the potential applications of low-temperature lightwave-activated oxide transistors in next-generation cost-effective and low-power flexible electronics.

High-Performance Oxide TFTs With Co-Sputtered Indium Tin Oxide and Indium-Gallium-Zinc Oxide at Source and Drain Contacts

Amorphous indium-gallium-zinc oxide (IGZO) thin-film transistors (TFTs) have shown significant potential for applicationin transparent and flexible electronicdevices. However, the source and drain (S/D) electrodesof IGZO TFTs with indium tin oxide (ITO) thin films can cause Schottkylike behavior in the output characteristics owing to the formation of a potential barrier between the IGZO and ITO thin films. In this study, we designed and fabricated TFTs by applying a novel ITO S/D electrode layer (375 nm) with co-sputtered IGZO and ITO thin films (125 nm) deposited at room temperature. The proposed TFT exhibits superior electric characteristics (μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> = 35.4 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs) compared to those of TFTs with conventional ITO electrodes (μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> = 9.1 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs) owing to its lower contact and channel resistance and the generation of a surface reaction between S/D and channel layers, creating additional oxygen vacancies at the IGZO channel region. The proposed S/D electrode could be fabricated on a glass substrate at low temperatures (below 200 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> C). The excellent electrical properties of the proposed IGZO TFT are expected to promote the application of TFTs in advanced displays.

Low Temperature Solution Processed Hybrid Gate Insulators for High Performance Oxide Thin-Film Transistors

Low Temperature Solution Processed Hybrid Gate Insulators for High Performance Oxide Thin-Film Transistors

Enhanced contact properties of spray-coated AgNWs source and drain electrodes in oxide thin-film transistors

Facile patterning of electrodes is required for various electronic applications, particularly in solution-processed oxide thin-film transistors (TFTs). In this study, source and drain electrodes were prepared from silver nanowires (AgNWs) using spray-coating and hot press techniques. Although spray coating allowed production of AgNW patterns, which could function as electrodes in oxide TFT, the as-sprayed films did not provide a sufficient physical contact with oxide semiconductors and formed interspaces that impeded electron injection. At the same time, hot press technique produced denser AgNW networks that had a tight contact with the oxide semiconductors. As a result, hot-pressed films were considered as satisfactory source and drain electrodes for high-performance oxide TFTs, as they provided an easy electron injection. Finally, the prepared oxide TFTs with hot-pressed AgNW electrodes exhibited average field-effect mobility of 4.75 ± 1.5 cm2/V, significantly higher than that of the TFTs with as-sprayed AgNW electrodes (0.08 ± 0.05 cm2/V).

Aqueous Solution-Processed Boron-Doped Gallium Oxide Dielectrics for High-Performance Thin-Film Transistors

In this paper, we report aqueous solution-processed boron-doped gallium oxide dielectric thin films for high-performance oxide thin-film transistors. The role of B incorporation on the microstructu...

Multifunctional, Room-Temperature Processable, Heterogeneous Organic Passivation Layer for Oxide Semiconductor Thin-Film Transistors.

In recent decades, oxide thin-film transistors (TFTs) have attracted a great deal of attention as a promising technology in terms of next-generation electronics due to their outstanding electrical performance. However, achieving robust electrical characteristics under various environments is a crucial challenge for successful realization of oxide-based electronic applications. To resolve the limitation, we propose a highly flexible and reliable heterogeneous organic passivation layer composed of stacked parylene-C and diketopyrrolopyrrole-polymer films for improving stability of oxide TFTs under various environments and mechanical stress. The presented multifunctional heterogeneous organic (MHO) passivation leads to high-performance oxide TFTs by: (1) improving their electrical characteristics, (2) protecting them from external reactive molecules, and (3) blocking light exposure to the oxide layer. As a result, oxide TFTs with MHO passivation exhibit outstanding stability in ambient air as well as under light illumination: the threshold voltage shift of the device is almost 0 V under severe negative bias illumination stress condition (white light of 5700 lx, gate voltage of -20 V, and drain voltage of 10.1 V for 20 000 s). Furthermore, since the MHO passivation layer exhibits high mechanical stability at a bending radius of ≤5 mm and can be deposited at room temperature, this technique is expected to be useful in the fabrication of flexible/wearable devices.

High-Performance Thin-Film Transistors with Aqueous Solution-Processed NiInO Channel Layer

We report the aqueous-solution-processed Ni-doped In2O3 (NixIn2–xO3, NiInO) thin-film transistors (TFTs) for the first time. The effect of Ni doping on In2O3 microstructure, oxygen defects, and the electron transport properties are investigated by extensive characterization techniques. Analyses indicate that the oxygen vacancies in NiInO are suppressed as the Ni-doping concentration increases, leading to a lower off-state current and a positive shift in threshold voltage. The optimized NiInO TFTs exhibit a high mobility of 17.71 cm2/(V s), on/off current ratio > 106, threshold voltage of 4.21 V, and superior bias stress stability. The success of Ni doping could be attributed to the small ion radius of Ni, large Lewis acid value, and strong Ni–O bond strength. Therefore, the fabricated NiInO TFT provides a bright path for the development of high-performance oxide TFTs.

Nanostructured High-Performance Thin-Film Transistors and Phototransistors Fabricated by a High-Yield and Versatile Near-Field Nanolithography Strategy.

Thin-film transistors (TFTs) and field-effect transistors (FETs) are basic units to build functional electronic circuits and investigate transport physics. In conventional TFTs or FETs, performance in terms of current level, on-off ratio, and the sensitivity of detection is limited by homogeneous semiconducting layers. In this paper, we develop TFTs with submicron heterostructures by using a strategy based on near-field photolithography. We use an array of total-reflective polydimethylsiloxane pyramids or trenches as a soft photomask in photolithography to induce multiple reflections and diffractions to focus the light. The textured feature enables the generation of gaps, dots, and grids at the nanoscale, with dimensions as small as sub-100 nm on substrates at the centimeter scale. We demonstrated the very high performance oxide TFTs on the nanoscale and periodic degenerately doped heterojunctions, and they yielded a nearly 20-fold increase in transconductance and apparent device mobility. The on-off ratio was higher than 109, with notably enhanced output current and clear scaling effect with channel length. We also built nanostructured wide-gap/narrow-gap heterojunctions to balance the high on-off ratio and sensitive photoresponse in a unidirectional phototransistor. This study shows the viability of programming a variety of nanoscale submicron patterns or interfaces in TFTs and FETs to significantly enlarge the scope of research on multifunctional TFTs and FETs.

High-performance Zinc-Tin-Oxide thin film transistors based on environment friendly solution process

Zinc-Tin-Oxide (ZTO) thin films were fabricated using a simple and eco-friendly sol-gel method and their application in thin film transistors (TFTs) was investigated. Annealing temperature has a crucial influence on the structure and electrical properties of sol-gel ZTO thin films. The ZTO thin films annealed at 300–600 °C revealed smooth and uniform surfaces with amorphous state, in addition, a high optical transparency over 90% of the ZTO films in the visible range was obtained. The electrical performance of ZTO TFTs showed obvious dependence on annealing temperature. The ZTO TFTs annealed at 500 °C showed a high carrier mobility of 5.9 cm2/V, high on/off current ratio (Ion/off) of 106-107, and threshold voltage (Vth) of 1.03 V. To demonstrate the application of sol-gel ZTO films in low-power display fields, we also fabricated ZTO TFTs with a solution-processed high-permittivity (high-k) ZrTiOx dielectric layer. The ZTO/ZrTiOx TFTs showed high mobility of 17.9 cm2/V and Ion/off of 105-106 at a low operation voltage of 3 V, indicating that Indium-free ZTO thin films would be potential candidates for low cost, high performance oxide TFT devices.

Development of high-resolution active matrix spatial light modulator

We developed a high-resolution active matrix spatial light modulator on a glass substrate. To integrate a switching device on the glass substrate, we designed a high-performance oxide thin-film transistor with a minimum channel length of 1 μm and a maximum processing temperature of 380°C. To drive a large number of data lines, we used multiple source drivers and data drivers as well. For an optical modulation, we optimized a liquid crystal of a high anisotropic refractive index of 0.25 with a cell gap of 2.5 μm, which was effectively operated until pixel pitch is 1.6 μm. Hologram was successfully reconstructed by fabricated SLM with 7-μm pixel pitch. For the other approach for a high-resolution spatial light modulator, we tested a phase change material of Ge2Sb2Te5 [GST]. The variation of refractive index between a polycrystalline phase and an amorphous phase of the GST film is used for a hologram reconstruction. By optimizing the underlying oxide thickness, we can show a color hologram without color filters.

High-performance oxide thin film transistor fully fabricated by a direct rheology-imprinting

Operation of all oxide thin-film transistors fully fabricated by a direct rheology-imprinting technique was demonstrated. In the device, a highly conductive amorphous La-Ru-O (8 × 10−3 Ω cm) was used as the gate and source/drain electrodes. Indium oxide and amorphous La-Zr-O were utilized as the semiconducting channel and gate insulator, respectively. Silsesquioxane-based SiO2 was used both as a mask and as a passivation layer for the channel. The obtained “on/off” current ratio, field-effect mobility, threshold voltage, and subthreshold swing factor were approximately 107, 8.4 cm2 V−1 s−1, −0.18 V, and 80 mV/decade, respectively.

Low-temperature, nontoxic water-induced high-k zirconium oxide dielectrics for low-voltage, high-performance oxide thin-film transistors

High-performance n- and p-type metal-oxide thin-film transistors are fabricated on ZrOx high-k dielectrics via a nontoxic water-inducement method.

Facile and environmentally friendly solution-processed aluminum oxide dielectric for low-temperature, high-performance oxide thin-film transistors.

We developed a facile and environmentally friendly solution-processed method for aluminum oxide (AlOx) dielectrics. The formation and properties of AlOx thin films under various annealing temperatures were intensively investigated by thermogravimetric analysis-differential scanning calorimetry (TGA-DSC), X-ray diffraction (XRD), spectroscopic ellipsometry, atomic force microscopy (AFM), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), impedance spectroscopy, and leakage current measurements. The sol-gel-derived AlOx thin film undergoes the decomposition of organic residuals and nitrate groups, as well as conversion of aluminum hydroxides to form aluminum oxide, as the annealing temperature increases. Finally, the AlOx film is used as gate dielectric for a variety of low-temperature solution-processed oxide TFTs. Above all, the In2O3 and InZnO TFTs exhibited high average mobilities of 57.2 cm(2) V(-1) s(-1) and 10.1 cm(2) V(-1) s(-1), as well as an on/off current ratio of ∼10(5) and low operating voltages of 4 V at a maximum processing temperature of 300 °C. Therefore, the solution-processable AlOx could be a promising candidate dielectric for low-cost, low-temperature, and high-performance oxide electronics.

Growth of IZO/IGZO dual-active-layer for low-voltage-drive and high-mobility thin film transistors based on an ALD grown Al2O3 gate insulator

We successfully integrated the high-performance oxide thin film transistors with novel IZO/IGZO dual-active-layers. The results showed that dual-active-layer (IZO/IGZO) TFTs, compared with single active layer IGZO TFTs and IZO TFTs, exhibited the excellent performances; specifically, a high field effect mobility of 14.4cm2/Vs, a suitable threshold voltage of 0.8V, a high on/off ratio of more than 107, a steep sub-threshold swing of 0.13V/dec, and a substantially small threshold voltage shift of 0.51V after temperature stress from 293K to 353K. In order to understand the superior performance, the density-of-states (DOS) were investigated based on the temperature-dependent transfer curves. The superior electric properties were attributed to the smaller DOS and higher carrier concentration. The proposed IZO/IGZO-TFT in this paper can be used as driving devices in the next-generation flat panel displays.

Self-formed copper oxide contact interlayer for high-performance oxide thin film transistors

Oxide thin film transistor employing copper source/drain electrodes shows a small turn on voltage and reduced hysteresis. Cross-sectional high-resolution transmission electron microscopy image confirmed the formation of ∼4 nm CuOx related interlayer. The lower bond-dissociation energy of Cu-O compared to Si-O and In-O suggests that the interlayer was formed by adsorbing oxygen molecules from surrounding environment instead of getting oxygen atoms from the semiconductor film. The formation of CuOx interlayer acting as an acceptor could suppress the carrier concentration in the transistor channel, which would be utilized to control the turn on voltage shifts in oxide thin film transistors.

Artificial semiconductor/insulator superlattice channel structure for high-performance oxide thin-film transistors

High-performance thin-film transistors (TFTs) are the fundamental building blocks in realizing the potential applications of the next-generation displays. Atomically controlled superlattice structures are expected to induce advanced electric and optical performance due to two-dimensional electron gas system, resulting in high-electron mobility transistors. Here, we have utilized a semiconductor/insulator superlattice channel structure comprising of ZnO/Al2O3 layers to realize high-performance TFTs. The TFT with ZnO (5 nm)/Al2O3 (3.6 nm) superlattice channel structure exhibited high field effect mobility of 27.8 cm2/Vs, and threshold voltage shift of only < 0.5 V under positive/negative gate bias stress test during 2 hours. These properties showed extremely improved TFT performance, compared to ZnO TFTs. The enhanced field effect mobility and stability obtained for the superlattice TFT devices were explained on the basis of layer-by-layer growth mode, improved crystalline nature of the channel layers, and passivation effect of Al2O3 layers.

Synergistic Approach to High-Performance Oxide Thin Film Transistors Using a Bilayer Channel Architecture

We report here a bilayer metal oxide thin film transistor concept (bMO TFT) where the channel has the structure: dielectric/semiconducting indium oxide (In2O3) layer/semiconducting indium gallium oxide (IGO) layer. Both semiconducting layers are grown from solution via a low-temperature combustion process. The TFT mobilities of bottom-gate/top-contact bMO TFTs processed at T = 250 °C are ~5tmex larger (~2.6 cm(2)/(V s)) than those of single-layer IGO TFTs (~0.5 cm(2)/(V s)), reaching values comparable to single-layer combustion-processed In2O3 TFTs (~3.2 cm(2)/(V s)). More importantly, and unlike single-layer In2O3 TFTs, the threshold voltage of the bMO TFTs is ~0.0 V, and the current on/off ratio is significantly enhanced to ~1 × 10(8) (vs ~1 × 10(4) for In2O3). The microstructure and morphology of the In2O3/IGO bilayers are analyzed by X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy, revealing the polycrystalline nature of the In2O3 layer and the amorphous nature of the IGO layer. This work demonstrates that solution-processed metal oxides can be implemented in bilayer TFT architectures with significantly enhanced performance.

The status and perspectives of metal oxide thin-film transistors for active matrix flexible displays

The purpose of this paper is to give an overview of the state-of-the-art of metal oxide thin-film transistors (TFTs). First, the question of how to achieve high-performance oxide TFTs is addressed, including the exploration of new channel materials, the realization of low-resistance ohmic contacts and the implementation of high-k dielectric materials as the gate insulator. The electrical instability of the oxide TFTs is also discussed, which is critical for their application in flexible backplane electronics: special attention is given to the understanding of the degradation mechanism of oxide TFTs against bias thermal stress (BTS) and light illuminated BTS. Finally, the recent application of oxide TFTs in active matrix displays, such as electronic paper, liquid crystal displays and organic light-emitting diodes, is addressed.