Electrical Performance Of Thin Film Transistors Research Articles

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.

Investigation on Atomic Bonding Structure of Solution-Processed Indium-Zinc-Oxide Semiconductors According to Doped Indium Content and Its Effects on the Transistor Performance.

The atomic composition ratio of solution-processed oxide semiconductors is crucial in controlling the electrical performance of thin-film transistors (TFTs) because the crystallinity and defects of the random network structure of oxide semiconductors change critically with respect to the atomic composition ratio. Herein, the relationship between the film properties of nitrate precursor-based indium-zinc-oxide (IZO) semiconductors and electrical performance of solution-processed IZO TFTs with respect to the In molar ratio was investigated. The thickness, morphological characteristics, crystallinity, and depth profile of the IZO semiconductor film were measured to analyze the correlation between the structural properties of IZO film and electrical performances of the IZO TFT. In addition, the stoichiometric and electrical properties of the IZO semiconductor films were analyzed using film density, atomic composition profile, and Hall effect measurements. Based on the structural and stoichiometric results for the IZO semiconductor, the doping effect of the IZO film with respect to the In molar ratio was theoretically explained. The atomic bonding structure by the In doping in solution-processed IZO semiconductor and resulting increase in free carriers are discussed through a simple bonding model and band gap formation energy.

Solution-processed Li-doped ZnSnO metal-semiconductor-metal UV photodetectors

The electrical performance of thin-film transistors that use an amorphous oxide semiconductor (AOS) is significantly improved by incorporating metal cations as carrier suppressors. However, the effect of these elements on the performance of AOS-based photodetectors (PDs) is still unknown. This study uses a precursor containing lithium (Li) element and a sol-gel process to produce a Li-doped amorphous ZnSnO (a-ZTO) thin-film for UV PD applications. The results of x-ray photoelectron spectroscopy analysis show that the number of oxygen vacancies (V o) in a-ZTO thin-films decreases significantly from ∼32.1% to ∼14.4% after Li-doping (3 at%). The dark current decreases and the photocurrent increases in the ZTO-based PD so an ultra-high photo-to-dark current ratio (PDCR) of 1185 is achieved. The significant increase in PDCR means that solution-processed a-ZTO are eminently suited to use in UV PDs that use In-free AOSs.

Improved High-Performance Solution Processed In₂O₃ Thin Film Transistor Fabricated by Femtosecond Laser Pre-Annealing Process

The low-temperature annealing process has a critical impact on the electrical performance of thin-film transistors (TFTs). This paper reports significant performance enhancements of TFTs using a femtosecond laser pre-annealing (FLA)-based preparation method. The solution-processed 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> films were fabricated by FLA at various laser irradiation times and then annealed on a hot-plate at 230 °C. When the FLA time was set to 30 s, the device exhibited high saturation mobility of 10.03 ± 0.64 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs, I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</sub> of 3.4×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> , low V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> of 0.14 ± 0.64 V, and small SS of 1.44 ± 0.37 V/dec. The FLA process improved the formation of M-O lattices effectively, which led to an improvement in mobility. Furthermore, the gate-bias-stress stability and time-dependent environmental stability were improved considerably by the FLA process. These results show that high-performance 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 can be prepared at low temperatures using FLA-centered annealing technology. This work suggests that the FLA preparation method has tremendous potential for the fabrication of low-cost, high performance, and flexible TFT devices.

Organic/Inorganic Hybrid Buffer in InGaZnO Transistors under Repetitive Bending Stress for High Electrical and Mechanical Stability.

We investigated the influence of the multilayered hybrid buffer consisting of Al2O3/PA (polyacrylic) organic layer/Al2O3 on the electrical and mechanical properties of amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs). The multilayered organic/inorganic hybrid buffer has multiple beneficial effects on the flexible TFTs under repetitive bending stress. First, compared to the PA or Al2O3 single-layered buffer, the multilayered hybrid buffer showed an improved WVTR value of 1.1 × 10-4 g/m2 day. Even after 40,000 bending cycles, the WVTR value of the hybrid buffer increased only by 17%, while the WVTR value of the Al2O3 layer doubled after cyclical bending stress. We also confirmed that the hybrid buffer has advantages in mechanical durability of the TFT layers because of the change in the position of the neutral plane and the strain reduction effect by the PA organic layer. When we fabricate a top-gate a-IGZO TFT with the hybrid buffer layer (HB TFT), the device shows Vth = 0.74 V, μFE = 14.4 cm2/V·s, a subthreshold slope of 0.27 V/dec, and hysteresis of 0.21 V, which are superior to that of TFTs fabricated on an Al2O3 single-layer buffer (IB TFT). From the X-ray photoelectron spectroscopy and elastic recoil detection analysis, the difference in the electrical performance of TFTs could be explained by hydrogen-related molecules. After annealing at 270 °C, the amounts of hydrogen found in the a-IGZO layer for the IB, HB, and OB TFTs were 3.57 × 1021, 5.77 × 1021, and 7.34 × 1021 atoms/cm3, respectively. A top-gate bottom-contact structured a-IGZO TFT fabricated on the PA layer (OB TFT) showed a gate dielectric breakdown because of excessively high hydrogen content and high nonbonding oxygen content. On the other hand, HB TFTs showed better positive bias stability because of the higher hydrogen concentration, as hydrogen (when not excessive) is beneficial in passivating electron traps. Finally, we conducted 60,000 repetitive bending cycles on IB TFTs and HB TFTs with various bending radii down to 1.5 mm. The HB TFT shows improved mechanical durability and exhibits less electrical degradation during and after repetitive bending stress, compared to the IB TFT.

Solution-processable small molecules for bulk heterojunction ambipolar thin-film transistors and complementary-like inverters

Solution-processable thioalkylated bithiophene derivatives with different lengths of side chains (SBT-n; n = 10, 12, 14, 16, 18) have been synthesized and characterized as p-channel organic semiconductors for thin-film transistors (TFTs). Based on a combination of the highest performing SBT derivative (SBT-14) and quinoidals (DTTRQs) as p- and n-channel materials, solution-processed small-molecular bulk heterojunction (BHJ) ambipolar thin-film transistors were fabricated, and the resulting devices showed air-stable and high ambipolar performance with well-balanced electron and hole mobilities as high as 0.70 cm2 V−1 s−1 and 0.21 cm2 V−1 s−1, respectively. Furthermore, complementary-like inverters comprising two ambipolar thin-film transistors were demonstrated, which exhibited a high voltage gain of up to 81. Our study clearly demonstrated that side chain engineering of small molecular organic semiconductors had a significant influence on the electrical performance of TFTs and BHJ transistors, as well as complementary-like inverters.

Rapid Improvement in Thin Film Transistors With Atomic-Layer-Deposited InOxChannels via O2Plasma Treatment

To improve the electrical performance of thin-film transistors with an atomic-layer-deposited Al2O3 dielectric/InOx channel, O2 plasma surface treatments of the InOx back channel are explored in comparison with thermal annealing. It is demonstrated that the O2 plasma treatment can enhance the device performance much more efficiently than thermal annealing, exhibiting an extremely low-thermal budget. Furthermore, it is revealed that the plasma treatment at a higher temperature can improve the device performance much faster than that at a lower temperature. For a 4 min O2plasma treatment at 200 °C, superior electrical characteristics are achieved, such as a field-effect mobility of 11 cm2V−1s−1, a threshold voltage of 0.9 V, a subthreshold swing of 0.38 V/dec, and good gate bias stress stabilities. This is ascribed to faster passivation of oxygen vacancies, removal of more C residues, and weaker surface damage and smaller surface roughness of the InOx back channel in comparison with long plasma treatments at lower temperatures.

Influence of irradiation atmospheres on the performance of ultraviolet-assisted solution-processed NbZnSn oxide thin film transistors

In this study, we study the influence of ultraviolet (UV) light irradiation [the UV source (254 nm) and the UV-ozone source (6% 185 nm and 94% 254 nm)] and irradiation atmospheres on the characteristics of solution-processed NbZnSn oxide thin film transistors (TFTs). The experimental results indicate the ultraviolet-visible absorption spectrum present a strong absorption at wavelengths less than 300 nm, implying that the UV source and UV-ozone source can be effectively absorbed by the NbZnSn oxide precursor. From the infrared (IR) spectra, the UV-ozone source illumination can accelerate the reaction of solution processed NbZnSn oxide channels. An improvement of device performance is achieved by the NbZnSn oxide channel layers with UV-ozone source. In addition, we also investigate the effects of treatment atmosphere (i.e., N2 or O2) on the electrical performance of TFTs. The influence of UV irradiation and irradiation atmospheres on the material properties of NbZnSn oxide channels and electrical characteristics of the NbZnSn oxide devices is also studied. The correlations between the UV treatment and treatment atmospheres on the TFT performance are investigated.

High-performance spin-coated aluminum oxide dielectric fabricated by a simple oxygen plasma-treatment process

A simple oxygen (O2) plasma-treatment process was utilized to achieve high performance aluminum oxide (Al2O3) dielectrics for thin film transistors (TFTs) through modulating the surface wettability of various substrates. Multilayer dielectric films with excellent electrical properties were obtained by spin coating of additive-free Al2O3 precursors. The resulting Al2O3 films were dense, smooth, uniform and kept in an amorphous structure. The TFT with high-performance spin-coated Al2O3 dielectric (three layers) exhibited a saturation mobility of 16.8 cm2 V−1 s−1, a threshold voltage (Vth) of 2.5 V, and a subthreshold swing (SS) of 0.172 V/dec. Particularly, compared with TFTs with thinner dielectric, it displayed a higher on/off current ratio (~107) and better stability of off-state current under the negative bias stress (NBS). Furthermore, the electrical performance of TFTs was independent of the dielectric thickness (four and five layers). High performance Al2O3 dielectric were obtained by the precursor free of additives and with fewer spin-coating times compared with previous works.

Effect on electrical performance of titanium co‐sputtered IZO active‐channel thin‐film transistor

AbstractWe investigated the electrical performance of Ti–IZO active‐channel layer thin‐film transistors (TFTs) using a radio frequency (RF) magnetron co‐sputtering system to co‐sputter IZO and Ti targets. The samples were fabricated by changing the RF gun power of the IZO. The other parameters such as the RF gun power of the Ti target, oxygen partial pressure [O2/(Ar + O2)], and initial and process pressure of the chamber were unchanged. Unlike the sample sputtered only with IZO, the thin films of the Ti–IZO samples could control the oxygen vacancy because Ti reacts with the oxygen in the IZO. Therefore, Ti–IZO thin films can suppress the carrier concentration and thus have an effect on the electrical performance of TFTs.

UV-Cured Reactive Mesogen-YInZnO Hybrid Materials as Semiconducting Channels in Thin-Film Transistors Using a Solution-Process

Electrical performance of thin-film transistors (TFTs) is important for their applications. Solution-processed TFTs have low mobility and high sub-threshold swings (S.Ss) because there are many pores and pin-holes in the films. These characteristics are attributed to electron trapping in the YInZnO (YIZO) channel, the SiO2 gate insulator, or their interface. We fabricated hybrid YIZO TFTs with and without UV radiation, and observed that UV-curing of the film affected TFT performance through promoting a response to reactive mesogen (RM). The UV irradiated TFT showed better performance because of the alignment of the channel materials in the source-drain direction. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0031503ssl] All rights reserved.

Role of Ga 2O 3–In 2O 3–ZnO channel composition on the electrical performance of thin-film transistors

In this work we present a study aiming to determine the role of Ga 2O 3–In 2O 3–ZnO (GIZO) channel layer composition on the electrical performance and stability exhibited by thin-film transistors (TFTs). The GIZO films were obtained by magnetron sputtering using ceramic targets of different compositions (Ga:In:Zn = 2:2:1, 2:2:2, 2:4:1 and 2:4:2 at.). Structural analysis corroborates the fully amorphous character of the GIZO deposited layers. For the target compositional range used we observe a Zn deficiency on the produced films, which affects the In/Ga atomic concentration ratios. Resistivity and mobility are found to show a general trend against the measured In/Ga ratio that reveals the role played by In and Ga cations on the transport mechanisms. Targets with increased In concentrations (2:4:1 and 2:4:2) allow to obtain the best TFT performances with field effect mobilities reaching values of 53.0 and 51.7 cm 2 V −1 s −1, respectively. In addition, the In-richer GIZO compositions result in considerably more stable TFTs, especially under positive gate bias stress conditions. Finally, it is verified that by using a target with a slightly lower In atomic composition (2:4:2 in comparison to 2:4:1), good stability and mobility can be achieved with potentially lower material costs.

Impact of Metal Salt Precursor on Low-Temperature Annealed Solution-Derived Ga-doped In2O3 Semiconductor for Thin-Film Transistors

Sol–gel-derived oxide semiconductors annealed at a low temperature have been of great interest recently in various thin-film transistor (TFT) applications. However, studies on the influence of metal salt precursor on sol–gel-derived oxide semiconductor annealed at a low temperature have not yet been reported. In this study, the impact of metal salt precursor on the chemical structure evolution of Ga-doped In2O3 (IGO) semiconductor and electrical performance of thin-film transistors with a corresponding oxide semiconductor is investigated. X-ray photoelectron spectroscopy (XPS)-based chemical structure analysis is carried out in conjunction with an understanding of the electrical performance of device. It is revealed that in addition to the thermally enhanced evolution of metal oxide chemical structure, the impurities due to the incomplete thermal decomposition of metal salt precursor do not only hinder the formation of metal oxide lattice, resulting in an electrically inactive oxide semiconductor, but also significantly deteriorate the electrical performance, such as field-effect mobility, subthreshold swing, and on/off current ratio, of thin-film transistor.