Solution-processed Zinc Tin Oxide Research Articles

Recovery characteristics of solution-processed ZTO thin-film transistors

We investigated the negative-bias illumination stress (NBIS) and the recovery characteristics of solution-processed amorphous zinc-tin-oxide (ZTO)-based thin-film transistors (TFTs). We developed TFTs with a bottom gate structure that used SiO2 films for the gate insulator. The developed TFTs were under NBIS in air at room temperature (RT) with a gate-to-source voltage of −10 V and a white-light power density of 6.2 mW/cm2. For the devices under NBIS, the NBIS-induced instability is attributed to the combined effects of 1) the creation of a low density of subgap states such as ionized oxygen vacancies (V 2+ ) near the Fermi level in ZTO, 2) a fast and large increase in the photo-conductivity at the off-state due to photo-induced band-to-band electron-hole pair generation, and 3) the hole trapping near the ZTO/SiO2 interface. The devices under NBIS also exhibit fast exponential recovery characteristics at RT, which are attributed dominantly to detrapping of holes near the ZTO/SiO2 interface and partially to the weak stabilization of V 2+ near the interface.

Effect of the interlayer for source-drain electrodes on a solution-processed zinc-tin-oxide TFT

An interlayer was introduced between the source and drain (S-D) electrodes and the semiconductor in a solution-processed zinc tin oxide (ZTO) thin-film transistor (TFT). The ZTO TFT with a MoO3 interlayer of 0.5 nm between the ZTO and the S-D electrodes displayed better properties: a mobility of 5.6 cm2/V s, a threshold voltage (Vth) of −1.3 V and a subthreshold slope of 0.9 V/dec with better bias stability and hysteresis. This improvement is attributed to the MoO3’s reduction to a conductor, MoO2, and to the inter-diffusion of the interlayer between the active channel and the S-D layers, as confirmed by the XPS spectra and by a TEM-EDX analysis, respectively.

Effects of O2 plasma treatment on low temperature solution-processed zinc tin oxide thin film transistors

The electrical characteristics such as threshold voltage, saturation mobility, and electrical reliability of low temperature (350 °C) solution-processed zinc tin oxide (ZTO) thin film transistors (TFTs) were improved considerably by employing O2 plasma treatment. O2 plasma treatment was performed by plasma asher and causes preferential dissociation of weak halide-related bonding such as Cl bonding by ion bombardment. After O2 plasma treatment, the threshold voltage decreased from 25.0 to 10.7 V because of an increase in electron concentration due to the reduction of Cl bonding and simultaneous composition of O-related bonding. The saturation mobility was increased from 0.09 to 0.58 cm2 V−1 s−1 because of the increase in electron concentration and reduction of the halide residues such as Cl atoms acting as trap states by employing O2 plasma treatment. Moreover, the electrical reliability such as threshold voltage shift was improved from 5.34 to 3.23 V for positive gate bias-stress because O2 plasma reduced the halide residues such as Cl atoms acting as trap states.

Effects of film thickness and Sn concentration on electrical properties of solution-processed zinc tin oxide thin film transistors

This paper investigates the effect of Sn concentration and film thickness on properties of zinc tin oxide (ZTO) thin film transistors (TFTs) fabricated using a solution process. ZTO solution was synthesized using zinc acetate dehydrate and tin chloride dehydrate dissolved in a solvent composed of 2-methoxyethanol and mono-ethanolamine. A ZTO film was obtained for an active channel on a gate oxide layer by spin-coating the solution at room temperature, drying at 300°C for 10min, and annealing at 550°C for 120min. The thickness and Sn concentration affected the material structure and electrical properties of ZTO film. The best solution processed ZTO TFT was obtained at film thickness of 35nm and Sn concentration of 30at.%. The fabricated ZTO TFT exhibited an on/off ratio of 1.88×107, a field effect mobility of 17.02cm2/Vs, a subthreshold swing of 0.77V/decade, and a threshold voltage of 5.01V.

Impact of Soft Annealing on the Performance of Solution-Processed Amorphous Zinc Tin Oxide Thin-Film Transistors

It is demonstrated that soft annealing duration strongly affects the performance of solution-processed amorphous zinc tin oxide thin-film transistors. Prolonged soft annealing times are found to induce two important changes in the device: (i) a decrease in zinc tin oxide film thickness, and (ii) an increase in oxygen vacancy concentration. The devices prepared without soft annealing exhibited inferior transistor performances, in comparison to devices in which the active channel layer (zinc tin oxide) was subjected to soft annealing. The highest saturation field-effect mobility-5.6 cm(2) V(-1) s(-1) with a drain-to-source on-off current ratio (Ion/Ioff) of 2 × 10(8)-was achieved in the case of devices with 10-min soft-annealed zinc tin oxide thin films as the channel layer. The findings of this work identify soft annealing as a critical parameter for the processing of chemically derived thin-film transistors, and it correlates device performance to the changes in material structure induced by soft annealing.

Combined effect of the large ionic radius and low electronegativity of lanthanum additive on solution-processed zinc–tin–oxide thin-film transistors

Solution-processed lanthanum–zinc–tin–oxide thin films were fabricated with varying La content. A peak shift to small angles was observed in X-ray diffractometer spectra due to the expansion of the zinc–tin–oxide lattice originated from the larger ionic radius of La3+, while oxygen vacancies first increased, and then decreased with increasing La molar ratio. These results indicate that La, which has both low electronegativity and a large ionic radius, plays the role of either a generator or a suppressor of oxygen vacancies. Therefore, when choosing an additive to control the electrical properties of an oxide semiconductor, the ionic radius of the added atom should be carefully considered along with its electronegativity.

Enhancement of solution-processed zinc tin oxide thin film transistors by silicon incorporation

Thin film transistors (TFTs) with Si incorporation in zinc tin oxide (ZTO) channel layer were fabricated using a sol–gel process, and the effect of Si incorporation in ZTO systems was investigated with respect to optical, structural, and electrical properties. The Si effectively controlled the generation of the oxygen vacancies examined by x-ray photoelectron spectroscopy, which affected the electrical properties of the silicon zinc tin oxide (SZTO) TFTs. As the Si concentration increased in the ZTO systems, the threshold voltage shifted in the positive direction, the on–off current ratio increased due to the effective reduction of the off current, and the subthreshold swing decreased. At a Si mole ratio 0.02, the SZTO TFTs exhibit favorable electrical properties of Vth = 3.0 V, μFE = 1.90 cm2 V−1 s−1, S.S = 0.38 V/decade, and Ion/off = 1.66 × 107. Thus, the SZTO is a promising material for backplanes of displays.

退火温度对溶胶-凝胶法制备锌锡氧化物薄膜晶体管的影响

Zinc-tin-oxide( ZTO) thin film transistors( TFTs) were fabricated by sol-gel method.Thermogravimetric and differential thermal analyses( TG-DTAs) were performed to investigate the chemical reactivity in the ZTO solutions. The effects of annealing temperatures on characteristics of ZTO-TFTs were investigated in this paper. With the increasing of annealing temperatures,all samples are amorphous,and surface is uniform. The ZTO thin films annealed at 400 ℃ and 500 ℃ are highly transparent( 85%) in the visible region. When the annealing temperature increased from300 ℃ to 500 ℃,the threshold voltage of solution-processed ZTO TFTs decreased from 15. 85 V to3. 76 V,and the saturation mobility increased from 0. 004 cm2·V- 1·s- 1to 5. 16 cm2·V- 1·s- 1.I on/ I off current ratio of 105was obtained at 500 ℃.

Low Voltage Driven, Stable Solution-Processed Zinc-Tin-Oxide TFT with HfOy and AlOx Stack Gate Dielectric

We report on low voltage driven, solution processed zinc-tin oxide (ZTO) transistors with a spin-coated hafnium oxide (HfOy) and aluminum oxide (AlOx) stack gate insulator (HfOy/AlOx). The ZTO TFT with a HfOy/AlOx dielectric processed at the maximum temperature of 400°C exhibits the field-effect mobility of 3.84 cm2/V s, subthreshold swing of 117 mV/dec., and threshold voltage (Vth) of 0.84 V. The positive gate bias stress degradation of Vth with time follows a stretched exponential behavior with a time constant of 1.13 × 107 s, indicating stable TFT.

Non-hydrolytic ester-elimination reaction and its application in solution-processed zinc tin oxide thin film transistors

Solution-processed oxide thin films have many attractive features for various electronic applications as like a next generation display and flexible electronics. But a high temperature annealing is often required to obtain high quality oxide thin film and the applications of solution-processed thin films are limited. To overcome this limit, we adopted a strategy that utilizes chemical driving force in addition to thermal energy. We chose precursors that can react each other and condensate via non-hydrolytic ester elimination reaction. To prove our concept a zinc tin oxide thin film transistor was fabricated with thermal annealing at low-temperature down to 300 °C. Although the oxide film was processed with low-temperature annealing, fabricated thin film transistors were functional and mobility of those of devices exceeded 1.0 cm2 V−1 s−1.

P‐17: Performance Enhancement of Solution‐Processed Zn‐Sn‐O TFTs Using High‐Pressure Annealing

AbstractIn this paper, we investigated the effects of high‐pressure annealing (HPA) in solution‐processed zinc tin oxide (ZTO) thin‐film transistors (TFTs). The O2‐HPA‐treated ZTO TFTs showed higher electrical performances in aspect of an on‐current (Ion), saturation mobility (μsat) and bias stability. The O2‐HPA treatment could contribute to the elimination of defect states that originated from the oxygen vacancies in solution‐processed metal‐oxide films. The 350°C O2‐HPA‐treated ZTO TFT showed μsat, threshold voltage (Vth), subthreshold slope (S.S) and on/off ratio of 2.35 cm2/V·s, 4.36 V, 0.58 V/dec., and 1.16times107, respectively.

Effects of Annealing Temperature on Electrical Characteristics of Solution-Processed Zinc Tin Oxide Thin-Film Transistors

We investigated the effects of annealing temperature on the electrical characteristics of solution-processed zinc tin oxide (ZTO) thin-film transistors (TFTs). When the annealing temperature increased from 300 to 500 °C, the threshold voltage of solution-processed ZTO TFTs decreased from 16.89 to -0.23 V owing to the increase in electron concentration in the active layer. The increase in electron concentration is caused by the decrease in Cl atomic concentration. When the annealing temperature increased to 500 °C, the saturation mobility increased from 0.18 to 4.75 cm2·V-1·s-1 and the threshold voltage shift for positive gate bias stress as a reliability characteristic decreased from 5.34 to 2.6 V, because of the decomposition of halide residues such as Cl and the nanocrystallization.

Charge transport in solution-processed zinc tin oxide thin film transistors

Abstract

Low-Temperature, Solution-Processed Zinc Tin Oxide Thin-Film Transistors Fabricated by Thermal Annealing and Microwave Irradiation

In this study, we fabricated zinc tin oxide (ZTO) thin-film transistors (TFTs) using a sol–gel solution at a low annealing temperature of 350 °C. We found that the combination of conventional hot plate annealing and microwave irradiation was effective for achieving high performance of ZTO-TFTs. Solution-processed ZTO-TFTs prepared at 350 °C by microwave irradiation showed enhanced device characteristics of 1.84 cm2 V-1 s-1 mobility and a 106 on/off current ratio. X-ray photoelectron spectroscopy analyses confirmed that residual hydroxyls in solution-processed ZTO films can be decomposed at low temperatures by microwave irradiation. Low-temperature microwave-assisted processing makes ZTO TFTs promising for use in flexible, transparent electronics.

Low-Temperature, Solution-Processed Zinc Tin Oxide Thin-Film Transistors Fabricated by Thermal Annealing and Microwave Irradiation

In this study, we fabricated zinc tin oxide (ZTO) thin-film transistors (TFTs) using a sol–gel solution at a low annealing temperature of 350 °C. We found that the combination of conventional hot plate annealing and microwave irradiation was effective for achieving high performance of ZTO-TFTs. Solution-processed ZTO-TFTs prepared at 350 °C by microwave irradiation showed enhanced device characteristics of 1.84 cm2 V-1 s-1 mobility and a 106 on/off current ratio. X-ray photoelectron spectroscopy analyses confirmed that residual hydroxyls in solution-processed ZTO films can be decomposed at low temperatures by microwave irradiation. Low-temperature microwave-assisted processing makes ZTO TFTs promising for use in flexible, transparent electronics.

A light emitting transistor based on a hybrid metal oxide-organic semiconductor lateral heterostructure

A light-emitting field-effect transistor was fabricated, with its architecture based on a distinct heterojunction located midway between the source and drain contacts. Tetracene enabled hole transport on one side of the heterojunction (hole mobility ∼0.071 cm2/Vs), while amorphous solution-processed zinc tin oxide supported electron transport on the other side (electron mobility ∼0.81 cm2/Vs). The drain current vs. gate voltage curves of this device have a bell-shaped profile that is characteristic of lateral heterojunction bipolar field-effect transistors. The green light emission—from tetracene—closely follows the trend in drain current and is naked-eye visible in a darkened room.

Effect of Annealing Temperature on the Electrical Characteristics of Solution Processed Zinc Tin Oxide Thin Film Transistors

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Interfacial study of metal oxide with source-drain electrodes and oxide semiconductor by XPS

As an interlayer for source-drain electrodes in solution processed zinc tin oxide (ZTO) thin-film transistor, MoO3 was introduced between aluminum source-drain electrodes and oxide semiconductor. MoO3 was detected not only in the interlayer, but in the source-drain electrodes and oxide semiconductor layer. The chemical configuration and the structural configuration were confirmed by XPS interfacial study and by TEM analysis, respectively. From these analytical tools, we found that the interlayer exists as a chemically mixed state between the layers, source-drain electrodes and oxide semiconductor.

Effect of Zinc/Tin Composition Ratio on the Operational Stability of Solution-Processed Zinc–Tin–Oxide Thin-Film Transistors

Variation of Zn:Sn atomic composition ratio in zinc-tin-oxide (ZTO) thin films induced a dramatic change in the microstructure and also strongly influenced the device performance and operational stability of ZTO thin-film transistors (TFTs). The large variation of threshold voltage shift under gate bias stress appears to be closely correlated to the excessive or deficient Sn content and the oxidation potentials of the metallic components as well as environmental effects. It is noted that the optimum Zn:Sn atomic composition ratio in ZTO films can improve the device performance and operational stability of the solution-processed ZTO TFTs.

Environmental, Optical, and Electrical Stability Study of Solution-Processed Zinc–Tin–Oxide Thin-Film Transistors

In this paper, we report the environmental, optical, and gate bias stress stability of amorphous zinc-tin-oxide (ZTO) thin-film transistors (TFTs) fabricated by sol-gel spin-coating method. The ZTO TFTs showed excellent environmental and optical stability. The threshold voltage stability of ZTO TFTs was sensitive to both positive and negative gate bias stress. Maximum threshold voltage shifting of +1.9 and -3.2 V was observed under a gate bias stress of +10 and -10 V, respectively, with no significant change to subthreshold swing value.