Performance Of Thin-film Transistors Research Articles

Impact of hydrogen plasma treatment on the electrical performances of ZnO thin-film transistors

In this study, we investigated the effects of hydrogen plasma (H) treatment on the structure, surface morphology, and optical and electronic properties of zinc oxide (ZnO) films, and on the performances of related ZnO thin-film transistors (TFTs). It was found that the performances and stabilities of the ZnO TFTs improved by carrying out the appropriate H plasma treatment. As a result, the ZnO:H (30 s) TFTs were found to exhibit a high field-effect mobility of 18.5 cm2/Vs, small threshold voltage (Vth) of 1.5 V, low sub-threshold swing of 0.32 V/decade, and high on/off current ratio (Ion/Ioff) of 107. These improvements could be attributed to the fact that the H treatment of ZnO was shown to result in the generation of shallow donors and in the defect passivation in ZnO films owing to the formation of HO and VO-H complex bounds. The increase in the carrier concentration and the passivation of the interface trap densities and oxygen vacancies in ZnO TFTs were revealed by X-ray photo-electron spectroscopy (XPS) analysis and density functional theory (DFT) calculations. These high-performance hydrogenated ZnO TFTs obtained as a result may find applications in oxide thin-film electronics.

Role of Fluoride Doping in Low-Temperature Combustion-Synthesized ZrOx Dielectric Films.

Zirconium oxide (ZrOx) is an attractive metal oxide dielectric material for low-voltage, optically transparent, and mechanically flexible electronic applications due to the high dielectric constant (κ ∼ 14-30), negligible visible light absorption, and, as a thin film, good mechanical flexibility. In this contribution, we explore the effect of fluoride doping on structure-property-function relationships in low-temperature solution-processed amorphous ZrOx. Fluoride-doped zirconium oxide (F:ZrOx) films with a fluoride content between 1.7 and 3.2 in atomic (at) % were synthesized by a combustion synthesis procedure. Irrespective of the fluoride content, grazing incidence X-ray diffraction, atomic-force microscopy, and UV-vis spectroscopy data indicate that all F:ZrOx films are amorphous, atomically smooth, and transparent in visible light. Impedance spectroscopy measurements reveal that unlike solution-processed fluoride-doped aluminum oxide (F:AlOx), fluoride doping minimally affects the frequency-dependent capacitance instability of solution-processed F:ZrOx films. This result can be rationalized by the relatively weak Zr-F versus Zr-O bonds and the large ionic radius of Zr+4, as corroborated by EXAFS analysis and MD simulations. Nevertheless, the performance of pentacene thin-film transistors (TFTs) with F:ZrOx gate dielectrics indicates that fluoride incorporation reduces I-V hysteresis in the transfer curves and enhances bias stress stability versus TFTs fabricated with analogous, but undoped ZrOx films as gate dielectrics, due to reduced trap density.

Defect Engineering for High Performance and Extremely Reliable a‐IGZO Thin‐Film Transistor in QD‐OLED

AbstractAn amorphous indium‐gallium‐zinc‐oxide (a‐IGZO) thin‐film transistor (TFT), which exhibits the best electrical stability (PBTS ≤ 0.009 V), is implemented to create quantum‐dot organic light‐emitting diode product. Electrical stability has been explained through various mechanisms involving defects related to oxygen and hydrogen. The defects of a‐IGZO are identified and the parameters of the deposition process are utilized to obtain Vo+ and VZn− values of 1.7 × 1017 and 2.4 × 1018 spins cm−3, respectively, which are quantified using electron spin resonance for the first time. The defects of the gate insulator (GI) in the upper and lower parts of the a‐IGZO TFT and the oxygen and hydrogen inflow/diffusion generated during the process are also controlled. From well‐controlled a‐IGZO and GI, the defect density at the top‐channel interface and near‐interface of the a‐IGZO TFT is reduced by 85% and 70%, respectively. The defects in the bottom‐channel are also reduced by 83% and 75% for the interface and near‐interface, respectively. Electrical stability is secured by controlling Vo+ and VZn− and reducing sub‐gap trap density among interface defects that are not directly observed until now. In this paper, it is reported that the best a‐IGZO TFT performance is achieved through defect engineering.

2+2] Cycloaddition-retroelectrocyclization reactivity and thin film transistor performances of carbazole-based platinum polyyne polymers

Carbazole-based platinum polyyne polymers are a good platform for the postfunctional formation of donor-acceptor type narrow band gap polymers by the [2 + 2] cycloaddition-retroelectrocyclization reaction with tetracyanoethylene (TCNE). The TCNE reactivity depends on the connectivity pattern of the carbazole. The 3,6-cabazole-based polymer shows a higher reactivity than the corresponding 2,7-carbazole-based polymer due to the p-positions with respect to the sp3 nitrogen atom. The connectivity pattern leads to the regioregularity difference in the resulting polymers. When TCNE is added to one of the alkynes of the 3,6-diethynylcarbazole unit, the electron-donating nature of the carbazole is lowered and the second TCNE addition does not occur. Accordingly, the regioregular polymer is formed from the 3,6-carbazole-based polymer, which is revealed from the 1H NMR spectrum. In contrast, the TCNE addition of the 2,7-carbazole-based polymer is mainly governed by the platinum atom, which produces a regiorandom structure. Finally, the charge carrier transporting properties of the precursor polymers are evaluated in thin film transistors. The 3,6-carbazole-based polymer displays a one order higher hole mobility than the corresponding 2,7-carbazole-based polymer. This result suggests that the shallower HOMO level of the former polymer facilitates the hole injection.

Impact of Strategic Approaches for Improving the Device Performance of Mesa-shaped Nanoscale Vertical-Channel Thin-Film Transistors Using Atomic-Layer Deposited In–Ga–Zn–O Channel Layers

Impact of Strategic Approaches for Improving the Device Performance of Mesa-shaped Nanoscale Vertical-Channel Thin-Film Transistors Using Atomic-Layer Deposited In–Ga–Zn–O Channel Layers

The Effect of Bias Stress on the Performance of Amorphous InAlZnO-Based Thin Film Transistors

The Effect of Bias Stress on the Performance of Amorphous InAlZnO-Based Thin Film Transistors

Enhanced current path by circularly and periodically-aligned semiconducting single-walled carbon nanotubes for logic circuit device

Improving the performance of solution-processed single-walled carbon nanotube thin film transistors (SWCNT TFTs) is essential to their wide usage in next generation large-area electronic devices. However, uncontrollable tube-tube junction and random network formation from conventional solution processes of SWCNTs has limited mobility and on-current level of SWCNT TFTs. Herein, we demonstrate a facile method by switching idea of reducing coffee-ring of the conventionally solution-processed or inkjet-printed thin films. Spontaneous coffee-ring formation of the inkjet-printed droplets is found to enhance directional alignment of SWCNTs in the outer rim of the coffee-rings. The evaporation-driven capillary flow toward the rim inside induces migration of SWCNT and thus forms densely aligned SWCNT rings. Periodic connection of such rings can provide high-current path at a given voltage. Therefore, by additionally forming the periodically connected rings on a pre-established random network of SWCNT in channel area of TFTs, we significantly improved the mobility and I on/I off ratio of SWCNT TFTs without degradations in other electrical parameters such as threshold voltage and subthreshold swing. We also demonstrated all-solution-processed inverters with higher voltage-gain in comparison with conventional ones.

Low doping in-situ strategy leading to polysilicon based TFTs exhibiting high stability under stress effects and enhanced electrical performances

In the present work, we investigate the effect of low phosphorus doped polysilicon thin films. These later are deposited on glass substrates by low pressure chemical vapor Deposition (LPCVD) technique and are in situ doped with phosphine adjunction to silane. Doping levels are reported by the phosphine to silane ratio Γ varying from 0 (undoped layer) to heavily doped layer almost 1.2 × 10–3. Films are characterized by different techniques as Photothermal Deflection Spectroscopy (PDS), photoluminescence measurements and x-ray diffraction of polycrystalline layers. The last one reveals that doping concentration giving modification in crystallite size and presence of microstrain, so a clear reduction in the Eg value was observed for the slightest doped layer (Γ = 3.7 × 10–7) by comparaison with the undoped one ((Γ = 0). Results give evidence of an optimum doping level to obtain higher polysilicon films quality. Polysilicon film quality has been correlated to phosphorus doping levels. Thin film transistors (TFTs) are fabricated on glass substrate using a top gate four mask process at low temperature (<600 °C). Electrical characterizations highlight significant improvements in the TFTs performances using slightly doped film instead of undoped one as active layer. Based on Levinson’s model, density of states within the grain boundaries is also found to be the lowest. Stability under stress is enhanced too. For slightly doped films, electrical characterizations indicate that both threshold voltage and density of states NT within the grain boundaries have their lowest values. Although, the field effect mobility μ records its highest values. Additionally, low doping levels enhances the TFT stability under stress. As a result, the in situ low doping strategy opens the way to manufacture polysilicon electronic devices exhibiting high electrical performances and a rather high stability under stress effects.

Solution processed low-voltage metal-oxide transistor by using TiO2/Li–Al2O3 stacked gate dielectric

A solution processed top-contact bottom-gated SnO2 thin-film transistor (TFT) has been fabricated using a TiO2/Li–Al2O3 bilayer stacked gate dielectric that show operating voltage of this TFT within 2.0 V. It is observed that the bilayer dielectric has much higher areal capacitance with lower leakage current density that significantly improve the overall device performance of TFT. The TFT with bilayer gate dielectric shows an effective carrier mobility (μsat) of 9.2 cm2 V−1 s−1 with an on/off ratio of 7.1 × 103 which are significantly higher with respect to the TFT with a single layer Li–Al2O3 gate dielectric. The origin of this improvement is due to the Schottky junction between the highly doped silicon (p++-Si) and TiO2 of bilayer stacked dielectric that induced electrons to the channel which reduces the dielectric/semiconductor interface trap-state. This investigation opens a new path to develop TFT device performance using a suitable bilayer stack of gate dielectric.

Nanospike electrodes and charge nanoribbons: A new design for nanoscale thin-film transistors.

To scale down thin-film transistor (TFT) channel lengths for accessing higher levels of speed and performance, a redesign of the basic device structure is necessary. With nanospike-shaped electrodes, field-emission effects can be used to assist charge injection from the electrodes in sub–200-nm channel length amorphous oxide and organic TFTs. These designs result in the formation of charge nanoribbons at low gate biases that greatly improve subthreshold and turn-off characteristics. A design paradigm in which the gate electric field can be less than the source-drain field is proposed and demonstrated. By combining small channel lengths and thick gate dielectrics, this approach is also shown to be a promising solution for boosting TFT performance through charge focusing and charge nanoribbon formation in flexible/printed electronics applications.

Combustion Synthesis and Polymer Doping of Metal Oxides for High-Performance Electronic Circuitry.

ConspectusTransparent conducting oxides (TCOs) are inorganic electrical conductors with optical band gaps greater than 3.3 eV. TCOs have been extensively explored in functional windows, touch screen applications, transparent displays, solar cells, and even electronic circuits. Amorphous metal oxide (a-MO) semiconductors are a TCO class that has made impressive progress since the first 2004 demonstration of their utility as the semiconducting layer in thin-film transistors (TFTs). Their excellent counterintuitive electron mobilities in the amorphous state fill the performance gap between amorphous silicon and polysilicon, widening TFT applicability to high-value products such as high-resolution flat panel displays and emerging flexible/wearable electronics. The possibility of solution processing MO "inks" from air-stable precursors, via roll-to-roll and high-throughput printing, further expands their appeal. However, most MO TFTs fabricated using solution-processing require postdeposition film annealing at elevated temperatures (>400 °C) to ensure high-quality films and stable charge transport. Thus, MO fabrication on and TFT integration with inexpensive and typically temperature-sensitive flexible polymer substrates remains challenging, as does reducing MO processing times to those acceptable for high-throughput semiconductor circuit manufacture. Consequently, new MO film processing methodologies are being developed to meet these requirements. Among them, science-based combustion synthesis (CS) and polymer doping are promising complementary approaches to optimize materials quality and manufacturing efficiency; they are the topic of this Account.This Account summarizes the progress in CS and MO polymer doping research, made largely at Northwestern University over the past decade, to create high-performance MO TFTs. Regarding CS, we begin with an overview of combustion precursor chemistry that strongly affects the resulting film quality and device performance. Then, single fuel and dual fuel combustion syntheses for diverse MO systems are discussed. Representative examples highlight recent advances, with a focus on the relationship between (co)fuel-oxidizer types/amounts, thermal behavior, film microstructure, and TFT performance. Next, the discussion focuses on polymer doping of several MO matrices as a new approach to achieve semiconducting MO compositions with excellent performance and mechanical flexibility. Thus, the effect of the polymer architecture and content in the MO precursor formulations on the MO film composition, microstructure, electronic structure, and charge transport are discussed. The concluding remarks highlight challenges and emerging opportunities.

Improvement in performance of indium gallium oxide thin film transistor via oxygen mediated crystallization at a low temperature of 200 °C

We report the fabrication of high-performance polycrystalline indium gallium oxide (IGO) thin film transistors (TFTs) at a low temperature of 200 °C. Growth of a highly aligned cubic phase with a bixbyite structure was accelerated at a certain proportion of oxygen plasma density during deposition of the IGO thin film, which leads to outstanding electrical characteristics. The resulting polycrystalline IGO TFT exhibited a high field-effect mobility of 56.0 cm2/V, a threshold voltage (VTH) of 0.10 V, a low subthreshold gate swing of 0.10 V/decade, and a current modulation ratio of >108. Moreover, the crystalline IGO TFTs have highly stable behaviors with a small VTH shift of +0.8 and −1.0 V against a positive bias stress (VGS,ST−VTH = 20 V) and negative bias illumination stress (VGS,ST−VTH = −20 V) for 3,600 s, which is attributed to the high quality of the bixbyite crystalline structure.

The Influence of Climate Conditions and On-Skin Positioning on InGaZnO Thin-Film Transistor Performance

Thin-film transistors (TFTs) based on amorphous indium-gallium-zinc-oxide (a-IGZO) have proved promising features for flexible and lightweight electronics. To achieve technological maturity for commercial and industrial applications, their stability under extreme environmental conditions is highly required. The combined effects of temperature (T) from −30.0°C to 50.0°C and relative humidity (RH) stress from 0 to 95% on a-IGZO TFT is presented. The TFT performances and the parameters variation were analysed in two different experiments. First, the TFT response was extracted while undergoing the most extreme climate conditions on Earth, ranging from the African Desert (50.0°C, 22%) to Antarctic (−30.0°C, 0%). Afterwards, the device functionality was demonstrated in three parts of the human body (forehand, arm and foot) at low (35%), medium (60%) and high (95%) relative humidity for on-skin and wearable applications. The sensitivity to T/RH variations suggests the suitability of these TFTs as sensing element for epidermal electronics and artificial skin.

Cation Composition-Dependent Device Performance and Positive Bias Instability of Self-Aligned Oxide Semiconductor Thin-Film Transistors: Including Oxygen and Hydrogen Effect.

Amorphous oxide semiconductor transistors control the illuminance of pixels in an ecosystem of displays from large-screen TVs to wearable devices. To satisfy application-specific requirements, oxide semiconductor transistors of various cation compositions have been explored. However, a comprehensive study has not been carried out where the influence of cation composition, oxygen, and hydrogen on device characteristics and stability is systematically quantified, using commercial-grade process technology. In this study, we fabricate self-aligned top-gate structure thin-film transistors with three oxide semiconductor materials, InGaZnO (In/Ga/Zn = 1:1:1), In-rich InGaZnO, and InZnO, having mobility values of 10, 27, and 40 cm2/V·s, respectively. Combinations of varied amounts of oxygen and hydrogen are incorporated into each transistor by controlling the fabrication process to study the effect of these gaseous elements on the physical nature of the channel material. Electrons can be captured by peroxy linkage (O22-) or undercoordinated In (In* to become In+), which are manifested in the extracted subgap density-of-states profile and first-principles calculations. Energy difference between electron-trapped In+ and O22- σ* is the smallest for IGZO, and In+-O22- annihilation occurs by electron excitation from the subgap In+ state to the O22- σ*. Furthermore, characteristic time constants during positive bias stress and recovery reveal the various microscopic physical phenomena within the transistor structure between different cation compositions.

Effect of Phase Transformation of Sputtered Hfo2 by Post Annealing Treatment on the Performance of A-Sizo Thin Film Transistor

Effect of Phase Transformation of Sputtered Hfo2 by Post Annealing Treatment on the Performance of A-Sizo Thin Film Transistor

Silicon doping and N2 annealing effects on Zn3N2 thin film transistors

Zn3N2 has high mobility >100 cm2V−1s−1, but its intrinsic carrier concentration (1018-1020 cm−3) has limited its application as thin-film transistor active material. In this work, Si-doped Zn3N2 (ZSN) thin-film transistors (TFTs) were fabricated by magnetron sputtering and annealed in N2 ambient. The influences of Si doping content, annealing temperature and active layer thickness on ZSN TFTs were investigated. It was found that annealing temperature up to 250 °C improved the performances of ZSN TFTs. The threshold voltage (Vth) positively shifts along with improving subthreshold swing (SS) as Si doping content increases. Moreover, further SS improvement was observed by reducing active layer thickness. The ZSN TFT with overall optimal performances exhibited typical Vth of 1.4 V, on-off current ratio of 2.9 × 106, subthreshold swing of 0.86 V·dec−1 and field-effect mobility of 0.69 cm2V−1s−1. Finally, the bias stress stability and the influence of oxide passivation on ZSN TFTs were investigated.

Improved Electrical Performance of In₂O₃ Thin-Film Transistor by UV/Ozone Treatment

In this work, the effect of a UV/ozone source composed of two monochromatic wavelengths of 184 nm and 254 nm irradiated upon the indium oxide film (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> ) at the different irradiation times together with annealing at high temperature is explored. The results showed that the developed 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> thin-film transistors (TFTs) exposed to UV/ozone for the 40 s and annealed at 250 °C for 2 h exhibited a significantly high performance, i.e., saturation mobility of 6.1 ± 0.2 cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{2}/$ </tex-math></inline-formula> Vs, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{I}_{\mathrm{ on}}/\text{I}_{\mathrm{ off}}$ </tex-math></inline-formula> ratio of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.4\times10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> , low threshold voltage (1.5 ± 0.9 V), and a small subthreshold swing (0.25 V/dec). The in-depth analysis of the developed devices through electrical characteristics, surface morphology, and practical aspect of inverter function confirm that UV/ozone irradiation improves the surface trap density, thereby increasing the mobility, and eventually improves the gate-bias stress stability and time-dependent environmental stability. The current work supports the fact that UV/ozone can improve the electrical properties of 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 and can be used for the fabrication of cost-effective, low-temperature, and reliable electronic devices.

Novel benzo[b]thieno[2,3-d]thiophene derivatives with an additional alkyl-thiophene core: synthesis, characterization, and p-type thin film transistor performance

Newly synthesized benzo[b]thieno[2,3-d]thiophene derivatives were employed as active layers of organic field effect transistors, and these transistors showed decent electrical performance.

Effect of N &lt;sub&gt;2&lt;/sub&gt;O treatment on performance of back channel etched metal oxide thin film transistors

In this paper, the rare earth element praseodymium-doped indium tin zinc oxide semiconductor is used as the channel layer of the thin film transistor, and the aluminum oxide-based wet back channel etched thin film transistor is successfully prepared. The effect of N &lt;sub&gt;2&lt;/sub&gt;O plasma treatment on the back-channel interface of thin film transistor is studied, and the effect of treatment power and time on device performance are studied in detail. The results show that the good device performance can be obtained under certain power and time treatment, and the prepared device has good thermal stability of positive bias and negative bias under light conditions. The results from high-resolution transmission electron microscopy show that the amorphous structure of the metal oxide semiconductor material can effectively resist the wet etchant, and that no obvious component segregation phenomenon is found. Further, X-ray photoelectric spectroscopy tests show that N &lt;sub&gt;2&lt;/sub&gt;O plasma treatment can form an oxygen-rich, low-carrier-concentration interface layer at the interface. On the one hand, it can effectively resist the damage of the back channel caused by the plasma of plasma enhanced chemical vapor deposition (PECVD), and on the other hand, it acts as a passivation body of hydrogen from PECVD plasma, suppressing the generation of low-level donor state of hydrogen. This study provides an important reference for low-cost, high-efficiency thin film transistor performance optimization methods.

Improved electrical performance of solution-processed zinc oxide-based thin-film transistors with bilayer structures

A bilayer thin-film transistor (TFT) structure with ZnO and Al-doped ZnO (AZO) was fabricated using a solution process. The film thickness and sintering atmosphere of ZnO and AZO were controlled and then evaluated by measuring their electrical characteristics. By changing the sintering atmosphere, carriers attributed to oxygen vacancies in the thin film increased. Moreover, the ZnO single-layer TFT sintered in N2 exhibited good electrical characteristics. In the ZnO/AZO bilayer TFT laminated with the ZnO sintered in N2 and high-resistance AZO thin films, electrical characteristics, such as the On/Off ratio and subthreshold swing, improved compared to those of the ZnO-TFT. The On/Off ratio of the ZnO/AZO-TFT using the AZO thin film sintered in an O2 atmosphere notably improved to 3.7 × 105 compared to that of the ZnO-TFT (1.7 × 104). In addition, the subthreshold swing in the ZnO/AZO-TFT was 0.36 V/dec, while the field-effect mobility was 2.2 × 10−1 cm2/Vs, thereby exhibiting the best electrical characteristics among the fabricated samples. According to the grazing-incidence X-ray diffraction measurement, the ZnO particle size and crystallinity of the ZnO/AZO bilayer were higher than those of the ZnO single layer. Therefore, improvement of the electrical characteristics was confirmed.