Transparent Thin-film Transistors Research Articles

Dielectric properties of hafnium oxide film prepared by HiPIMS at different O2/Ar ratios and their influences on TFT performance

High-k hafnium oxide (HfO2) film was prepared by high power impulse magnetron sputtering (HiPIMS). The influences of oxygen supply on the plasma state, film properties and TFT performance were investigated. The films are near-stoichiometric and preferentially (−1 1 1)-orientated. When the oxygen supply increased from 1% to 3%, the excitation/ionization rate of the plasma species increased, leading to higher crystallinity, higher density, and lower oxygen vacancy defect concentration of the film, therefore improving the dielectric properties of the film. When the oxygen supply further increased to 5%, the excitation/ionization rate decreased, thereby leading to lower crystallinity, lower density, and higher oxygen vacancy defect concentration of the film, therefore deteriorating the dielectric properties of the film. The film deposited at 3% oxygen supply exhibited the best dielectric properties with the highest k value of 24 and the highest breakdown-electric field (4.7 MV/cm), which should be attributed to the high crystallinity, high density and low oxygen vacancy defect concentration of the film. Finally, transparent thin film transistors (TFTs) with ITO gate electrode, HfO2 gate dielectric layer and indium-gallium-zinc oxide channel were fabricated on flexible colorless polyimide substrate at full room temperature by all HiPIMS process. The fixed positive charges and k value of HfO2 film have significant effects on the TFT performance. The best TFT exhibited good electrical performance, featuring a remarkably low subthreshold swing of 0.13 V/decade. It also exhibited fair stability against bending and gate bias stress.

Modification of Indium Tin Oxide Electrodes by Fluorinated Silanes for Transparent Organic Thin-Film Transistors

Modification of Indium Tin Oxide Electrodes by Fluorinated Silanes for Transparent Organic Thin-Film Transistors

Facile diffusion of sulfur and fluorine into a-IGTO thin films for high-performance and reliability of transparent amorphous oxide semiconductor thin-film transistors

Facile diffusion of sulfur and fluorine into a-IGTO thin films for high-performance and reliability of transparent amorphous oxide semiconductor thin-film transistors

High transparent and stability indium praseodymium oxide thin-film transistors with tungsten doping by solution method

Indium-oxide-based thin-film transistors are widely investigated and exhibit higher carrier mobility than amorphous silicon. Lanthanide-doped Indium oxide TFTs show relatively high negative bias illumination stress (NBIS) stability but at the cost of mobility. To improve the NBIS stability by the solution method, we doped Tungsten (W) into Praseodymium-doped Indium oxide (InPrO) and fabricated InPrWO TFT. We proposed that W doping could densify the films and suppress oxygen vacancy. With the increase of W doping concentration from 0 to 3 mol%, the contact angle of precursor solutions first decreased and then increased, reaching minimums of ∼13° at 1 mol%. When the W doping concentration increased from 0 to 1 mol%, the density of films increased from 6.155 to 6.479 g/cm3. While doping concentration increased from 1 to 3 mol%, the density of films decreased. Transmittance of InPrWO films was higher than 90 % from 300 to 800 nm. The localized defects of InPrWO films were investigated by μ-PCD. With 1 mol% W doping, deep-level and shallow-level defects were relatively the least. XPS result revealed that W was successfully doped into the films. Besides, the oxygen vacancy ratio first decreased and then increased when the W doping concentration increased. InPrWO film with 1 mol% W doping had the least oxygen vacancy ratio, resulting in the highest stability. The TFT fabricated with optimal 1 mol% W doped InPrWO film showed excellent electrical characteristics (μsat = 5.4 cm2/Vs, Vth = -0.3 V, Ion/Ioff = 8.0 × 105, and SS = 0.30 V/dec). With the W doping concentration increased, the NBIS stability first increased and then decreased, having minimum shift ΔVth = -2.1 V at 1 mol%. We improved the quality of films and NBIS stability of TFT by doping W into InPrO and appropriate post-processing, satisfying the development trend of high transparency and high stability TFTs for future displays.

Transparent and flexible zinc oxide-based thin-film diodes and thin-film transistors: A review

Electronics today has evolved significantly, including its application in transparent and flexible devices. Flexible electronics offers new product concepts, including low production cost, low energy consumption, and sustainable and environmentally friendly materials. This concept leads to the development of novel materials that realize today’s requirements. Incorporating optically transparent and flexible thin-film-based devices into the electronic circuitry helps in maintaining high conductivity along with achieving the similar electronic behavior of the conventional electronic gadgets. Thin-film diodes (TFDs) and thin-film transistors (TFTs) are the core materials to be incorporated as building blocks for flexible devices. Among them, oxide-based thin films have been marked to be significant because of their efficient electrical performance, low temperature processing, and device flexibility. The present article reviews the concepts and application of zinc oxide (ZnO) as the semiconducting material for flexible thin-film devices. We also review flexible and transparent TFDs and TFTs that are based prominently on ZnO as the semiconducting material. Furthermore, the present issues have also been addressed.

Enhancement in Performance and Reliability of Transparent IGZO Thin-Film Transistors by ITO/Ti Stacked Source/Drain Contacts

Enhancement in performance and reliability of transparent IGZO thin-film transistor (TFT) was achieved by adopting a laminated structure with a thin ITO layer and an ultrathin Ti layer as the source/drain (S/D) contacts. Compared with the transparent TFT with pure ITO S/D contacts, the transparent TFT with the ITO/Ti S/D contacts showed three times of enhancement in field-effect mobility from 4.75 to 12.10 cm2/Vs, two times of enhancement in on/off current ratio from 7.0 × 107 to 1.54 × 108, three times of reduction in contact resistance from 15.74 to 4.64 kΩ, and a decrease in threshold voltage from 3.11 V to 2.80 V. The TFT with the ITO/Ti S/D contacts also maintained an extremely low leakage current at zero gate bias (for the device with channel width/channel length of 40 μm/5 μm, the leakage current was ∼1 × 10−13 A). In addition, the TFT with the ITO/Ti S/D contacts showed a hump-free transfer curve and a smaller shift in threshold voltage under negative bias illumination stress. The enhancement in performance and reliability makes the transparent TFT with the ITO/Ti S/D contacts very promising in transparent display applications.

Improved Performance of Transparent MoS2 Thin-Film Transistor with IZO Electrodes by Air Thermal Annealing

Improved Performance of Transparent MoS2 Thin-Film Transistor with IZO Electrodes by Air Thermal Annealing

Preparation and electrical characteristics of transparent thin film transistors with sputtered aluminum and phosphorus co-doped indium-zinc-oxide channel layer

Thin film transistors (TFTs) with aluminum and phosphorus co-doped indium-zinc-oxide (IZO:Al,P) channel layer were fabricated by the radio frequency (RF) magnetron sputtering. The IZO:Al,P films were amorphous and highly transparent with exceed 80% transmittance in visible region. High performance IZO:Al,P TFTs have been observed due to the incorporation of Al and P, which serve as an inhibitor against oxygen vacancies and carrier. The electrical properties of IZO:Al,P TFTs were investigated as function of annealing temperatures. The IZO:Al,P TFTs have achieved superior performance (threshold voltage (VTH) of 0.8 V, on-state current (ION) of 1.6 × 10-3 A, off-state current (IOFF) of 2.2 × 10-12 A, µSAT of 39.2 cm2/V∙s and subthreshold swing (S.S.) of 0.68 V/dec.) under the annealing temperature as low as 300 °C.

Transparent and conformable organic light-emitting diodes for skin-attachable invisible displays

A skin-attachable invisible display offers a new opportunity in next-generation electronic application, such as smart contact lenses, human-machine health monitoring interfaces and soft electronic skins. In response to this trend, transparent organic light-emitting diodes (OLEDs) offer enormous advantages in future skin-attachable invisible displays, including excellent flexibility and superior efficiency. Although several approaches reported recently attempt to manufacture transparent and flexible OLEDs, it is still a tremendous challenge to simultaneously meet the desired optical and mechanical properties. Herein, we develop a feasible strategy to achieve transparent and conformable OLEDs (TC-OLEDs). Benefiting from the intrinsic high transparency and outstanding deformability of our electrodes, the whole device shows high transmittance up to 85.0% at a wavelength of 400 nm and high mechanical flexibility with skin-like conformability. More strikingly, the resulting device maintains excellent photoelectric performance with a maximum current efficiency (CE) of 56.8 cd/A and external quantum efficiency (EQE) of 17.1%. Based on the versatile TC-OLEDs, we also report an all-organic and all-conformable invisible display driven by transparent and conformable organic thin film transistors (TC-OTFTs) for the first time. This work offers a meaningful guidance for the construction of TC-OLEDs and the development of skin-attachable invisible displays.

Homojunction structure amorphous oxide thin film transistors with ultra-high mobility

Amorphous oxide semiconductors (AOS) have unique advantages in transparent and flexible thin film transistors (TFTs) applications, compared to low-temperature polycrystalline-Si (LTPS). However, intrinsic AOS TFTs are difficult to obtain field-effect mobility (μ FE) higher than LTPS (100 cm2/(V·s)). Here, we design ZnAlSnO (ZATO) homojunction structure TFTs to obtain μ FE = 113.8 cm2/(V·s). The device demonstrates optimized comprehensive electrical properties with an off-current of about 1.5 × 10–11 A, a threshold voltage of –1.71 V, and a subthreshold swing of 0.372 V/dec. There are two kinds of gradient coupled in the homojunction active layer, which are micro-crystallization and carrier suppressor concentration gradient distribution so that the device can reduce off-current and shift the threshold voltage positively while maintaining high field-effect mobility. Our research in the homojunction active layer points to a promising direction for obtaining excellent-performance AOS TFTs.

Investigation of Contact Resistance Between Sputter-Deposited ITO and Mist-CVD-Deposited InSnZnO for Transparent Thin-Film Transistors Applications

The transparent thin-film transistors based on InSnZnO are investigated in this study. The Al2O3 and InSnZnO thin films deposited using mist chemical vapor deposition (mist CVD) are respectively used as the gate insulating and channel layers. The indium tin oxide (ITO) thin films deposited using the radio frequency (RF) sputtering method are served as the source/drain and gate electrodes. When the RF power of 45 W is used to deposit the ITO film, the lowest specific contact resistance of 9.7 × 10−3 Ω-cm2 and high optical transmittance of 72.4% are obtained. Furthermore, the thin-film transistor with ITO as the source/drain electrodes exhibits more stable electrical characteristics than the one with Al.

Numerical simulation of Transparent Gate Thin-Film Transistor (TG-TFT) with varied gate materials for high-performance applications

This work presents the performance evaluation of Transparent Gate Thin-Film Transistor (TG-TFT) with the relative analysis of numerous materials such as Aluminum (Al), Gold (Au), Indium Tin Oxide (ITO), Zinc Oxide (ZnO), and Titanium Nitride (TiN). This work also aims to find the best suitable gate material on the TFT for high-performance applications through a solid thin film. It is observed from the outcomes that TG-TFT performance improves significantly with TiN gate in terms of mobility (∼4 times), switching ratio (ION/IOFF) by 46.42 %, and electric field by ∼ 29 % as compared to conventional gate material (Au). Further, surface potential and energy band profile have been shown. Therefore, the examination shows the perspective of TiN as gate materials that can be reused for requests in nanoelectronics tools and designing of IC boards owing to the better conductivity, robustness, and cheap nature of TiN along with proven results it can be used as a gate material.

Low-temperature solution-processed nanoparticle-doped nickel oxide thin-film transistor

Developing p-type oxide thin-film transistors (TFTs) is an essential path for further application in complementary metal oxide semiconductor (CMOS) components. However, the inferior electrical performance of p-type MO TFTs compared to n-type TFTs remains an ongoing challenge. Herein, for the first time, a low temperature, facile material engineering approach by incorporating n-type nanoparticles (NPs) was proposed for preparing p-type transparent NiOx TFTs. The characteristics of thin films blending NPs and the electrical performances of TFTs were investigated. The field effect mobility of TFTs with doping was nearly 20 times higher than pristine TFTs without doping, which was mainly beneficial from the suitable band alignment between NPs and p-type oxide, the increasing Ni3+ oxidation state in NiOx, as well as the improved dielectric/semiconductor interface quality. Electrons from drain electrode injected into metal oxide turn accepted in NPs rather than being trapped in the dielectric/semiconductor interface due to a strong surface electron depletion effect of NPs. NPs with small particle size and appropriate concentration would promote continuous hole transport by electrons transferring and reducing the interface trap state. The facile material engineering strategy is a promising technique for preparing p-type transparent MO-TFTs at low temperature, which showed great potential to be applicable in CMOS circuits on flexible substrates.

Dispersion of Long and Isolated Single-Wall Carbon Nanotubes by Using a Hydrodynamic Cavitation Method.

Single-wall carbon nanotubes (SWCNTs) are promising materials for electronic applications, such as transparent electrodes and thin-film transistors. However, the dispersion of isolated SWCNTs into solvents remains an important issue for their practical applications. SWCNTs are commonly dispersed in solvents via ultrasonication. However, ultrasonication damages SWCNTs, forming defects and cutting them into short pieces, which significantly degrade their electrical and mechanical properties. Herein, we demonstrate a novel approach toward the large-scale dispersion of long and isolated SWCNTs by using hydrodynamic cavitation. Considering the results of atomic force microscopy and dynamic light-scattering measurements, the average length of the SWCNTs dispersed via the hydrodynamic cavitation method is larger than that of the SWCNTs dispersed by using an ultrasonic homogenizer.

Photoresponse Analysis of All-Inkjet-Printed Single-Walled Carbon Nanotube Thin-Film Transistors for Flexible Light-Insensitive Transparent Circuit Applications

We report daylight-stable, transparent, and flexible single-walled carbon nanotube thin-film transistors (SWCNT TFTs) using an all-inkjet printing process. Although most of the previous reports classified SWCNT TFTs as photodetectors, we demonstrated that SWCNT films actually show two different types of photoresponses depending on the power levels of light sources. The electrical characteristics of SWCNT TFTs show no significant change under daily illumination conditions such as halogen lamps and sunlight, while under high-power laser illumination, they change as reported in the previous results. In addition, the low-temperature solution process of the SWCNT with its one-dimensional nature allows us to realize highly transparent and flexible TFTs and logic circuits on plastic substrates. Our result will provide new insights into utilizing SWCNT TFTs for light-insensitive transparent and flexible electronic applications.

High-mobility flexible/transparent p-type copper iodide thin-film transistors and complementary inverters

High-performance transparent and low-process-temperature p-type devices are essential for portable and ‘invisible’ electronics. In this work, high-performance p-channel copper iodide (CuI) thin-film transistors (TFTs) with a bottom-gate structure are achieved via replacing traditional SiO2 dielectric with Chitosan (CS, a kind of solid polymer electrolytes), with the threshold voltage down to −0.35 V, field-effect mobility (μFE) up to 60 cm2V−1s−1 and on/off current ratio (Ion/Ioff) beyond 103. The CuI films spin-coated on CS-dielectrics in the air with high humidity have smoother surface morphology, tinier grains, higher packing density and hence a higher μFE, in sharp contrast with the SiO2 case. In addition, the CuI films on CS-dielectrics demonstrate a work function ∼ 0.1 eV lower than that on SiO2, which implies a smaller hole concentration and higher Ion/Ioff. And the low process temperature (<50 °C) facilitates the achievement of flexible and transparent CuI TFTs with μFE and Ion/Ioff comparable to those on rigid InSnO (ITO) glass. Furthermore, complementary inverters composed of p-type CuI and n-type ITO TFTs are demonstrated with clear inverting characteristics and voltage gain of over 20.

Real-time High-resolution Measurement of Pancreatic β Cell Electrophysiology Based on Transparent Thin-film Transistor Microelectrode Arrays

Real-time High-resolution Measurement of Pancreatic β Cell Electrophysiology Based on Transparent Thin-film Transistor Microelectrode Arrays

Low‐Temperature Plasma‐Assisted Growth of Large‐Area MoS2 for Transparent Phototransistors

AbstractMoS2‐based transparent electronics can revolutionize the state‐of‐the‐art display technology. The low‐temperature synthesis of MoS2 below the softening temperature of inexpensive glasses is an essential requirement, although it has remained a long persisting challenge. In this study, plasma‐enhanced chemical vapor deposition is utilized to grow large‐area MoS2 on a regular microscopic glass (area ≈27 cm2). To benefit from uniform MoS2, 7 × 7 arrays of top‐gated transparent (≈93% transparent at 550 nm) thin film transistors (TFTs) with Al2O3 dielectric that can operate between −15 and 15 V are fabricated. Additionally, the performance of TFTs is assessed under irradiation of visible light and estimated static performance parameters, such as photoresponsivity is found to be 27 A W−1 (at λ = 405 nm and an incident power density of 0.42 mW cm−2). The stable and uniform photoresponse of transparent MoS2 TFTs can facilitate the fabrication of transparent image sensors in the field of optoelectronics.

UV-Treated ZrO2 Passivation for Transparent and High-Stability In2O3 Thin Film Transistor

Electrical stability is significant in evaluating the application potentials for thin-film transistors (TFTs). In order to enhance the stability of the TFTs, the introduction of passivation layer is considered as an effective strategy. However, the posttreatment in conventional passivation process usually deteriorate the bottom semiconductor layer. In order to minimize the damages to the channel layer, in this work, UV-irradiated ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> was prepared and integrated into the In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> TFT as passivation layer. The device performance dependent on ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thickness is investigated. It is found that the electrical performance of the In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> TFT is improved with the optimal passivation thickness, and the inherent mechanism is explained. In addition to the high performance, the excellent electrical stability of the passivated device is also confirmed by the positive bias stress test. Furthermore, the transparent ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> TFTs on indium tin oxide (ITO) glass substrates with Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> dielectrics were successfully demonstrated, which indicates the great potential of ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> passivation for the fabrication of transparent electronics.

Photonic Cured Metal Oxides for Low-Cost, High-Performance, Low-Voltage, Flexible, and Transparent Thin-Film Transistors

Photonic Cured Metal Oxides for Low-Cost, High-Performance, Low-Voltage, Flexible, and Transparent Thin-Film Transistors