Solution-processed Zinc Tin Oxide Research Articles

Low-Temperature, Aqueous-Solution-Processed Zinc Tin Oxide Thin Film Transistor

We fabricate solution-processed zinc tin oxide (ZTO) thin-film transistors (TFTs). The solution used is prepared by precipitating metal hydroxide using NaOH and dissolving it using NH4OH. The X-ray diffraction (XRD) data of the spin-coated ZTO film demonstrates an amorphous phase, and the atomic force microscopy (AFM) image shows a smooth surface. The device performance of solution-processed TFTs was analyzed as a function of annealing temperature. The fabricated TFTs were operated in the enhancement mode, and exhibited a carrier mobility of 3.03 cm2 V-1 s-1, a threshold voltage of 10.2 V, an on/off current ratio of 1.23×107, a subthreshold slope of 0.78 V/decade, and high transparency (with ∼90% transmittance) at a low annealing temperature of 300 °C.

Investigation of Indium Diffusion into Solution-Processed Oxide TFTs with ZTO Active Layer and IZO Source/Drain Electrodes

We have investigated the indium diffusion in oxide-based thin film transistors (TFTs) fabricated with zinc tin oxide (ZTO) active layer and indium zinc oxide (IZO) source/drain electrode by employing a solution-process. Oxide TFTs were fabricated with spin-coating process using solution with chloride-, acetate- and nitrate- based precursors. After spin-coating, ZTO active layer and IZO source/drain electrodes were annealed sequentially by rapid thermal annealing (RTA). Rutherford backscattering spectrometry (RBS) result shows that 16.8% of indium atoms in IZO source/drain electrodes are diffused into ZTO active layer after annealing process. The In-diffusion into ZTO active layer cause a considerable negative shift of threshold voltage in solution-processed ZTO TFTs.

Preparation and properties of solution-processed zinc tin oxide films from a new organic precursor

Transparent, smooth and dense zinc tin oxide (ZTO) thin films have been successfully produced by using a new precursor solution, zinc acetate and tin(II) 2-ethylhexanoate mixed with 2-ethanolamine in methoxyethanol. The ZTO films have been prepared by spin-coating, followed by thermal treatment in oxygen atmosphere. The morphology, composition, crystallinity and band gap energy (Eg) of the ZTO thin films have been characterized by Atomic Force Microscopy (AFM), Atomic Emission Spectrometry (AES), X-ray Diffraction (XRD) and UV-vis spectrophotometry. The conductivity of ZTO is about 9.8 × 10−9 S/cm, as estimated from the current-voltage (I-V) curve. The effect of the thermal treatment process on the morphology of ZTO thin films is also discussed.

Fast and Stable Solution-Processed Transparent Oxide Thin-Film Transistor Circuits

Fast and stable zinc-tin-oxide (ZTO) thin-film transistor (TFT) circuits were fabricated by simple and effective solution processing. The solution-processed ZTO TFTs have shown saturation mobility >;2.5 ± 0.29 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V · s (W/L = 100/10 μm) and subthreshold slope <;0.4 ± 0.122 V/dec . The ZTO seven-stage ring oscillators have shown an oscillation frequency of 800 kHz with a supply voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DD</sub> = 60 V, corresponding to a propagation delay of <; 90 ns per stage. In addition, with appropriate passivation onto the semiconductor channel area, the circuits have shown relatively stable operation even at a gate and source/drain bias voltage of >; 50 V for several hours.

Charge carrier velocity distributions in field-effect transistors

The measurement of the distribution of charge carrier velocities in a field-effect transistor can provide considerable insight into charge transport mechanisms and structure-property relationships. We have developed such a method and have applied it to study temperature-dependent velocity distributions in solution-processed zinc-tin oxide thin-film transistors. Two distinct transport pathways, each with a different activation energy, have been observed, in contrast to a single activation energy yielded by steady-state measurements. Our results show that more insight into charge transport behavior and phenomena can be obtained with such time-resolved transport measurements.

Effects of Sol-Gel Organic-Inorganic Hybrid Passivation on Stability of Solution-Processed Zinc Tin Oxide Thin Film Transistors

Effects of Sol-Gel Organic-Inorganic Hybrid Passivation on Stability of Solution-Processed Zinc Tin Oxide Thin Film Transistors

Solution-Processed ZTO TFTs With Recessed Gate and Low Operating Voltage

We demonstrate solution-processed zinc tin oxide thin-film transistors (TFTs) with a patterned-gate configuration. High- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$k$</tex></formula> and solution-processed zirconium oxide <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(\hbox{ZrO}_{2})$</tex></formula> was employed to lower down the operating voltage. Devices with recessed and nonrecessed gate electrodes were compared to study the influence of gate surface relief on the performance of the solution-processed thin films. The TFTs with the recessed gate electrode operate at 5 V and have a threshold voltage of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\sim$</tex></formula> 1 V, subthreshold slope of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\sim$</tex></formula> 0.23 V/dec, saturation mobility of 2.5 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{cm}^{2}/\hbox{V} \cdot \hbox{s}$</tex></formula> , and on/off current ratio of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$&gt; \hbox{10}^{6}$</tex></formula> .

Band transport and mobility edge in amorphous solution-processed zinc tin oxide thin-film transistors

We report on charge transport phenomena in high-mobility solution-deposited amorphous zinc-tin oxide based thin-film transistors. At low carrier concentrations, the dominant transport mechanism is multiple trap and release, with the activation energy steadily decreasing with increasing carrier density. The activation energy decreases to zero and beyond a threshold carrier density, the mobility decreases with increasing temperature. This temperature dependence as well as the value of the mobility clearly indicates that transport is bandlike. Also observed is a clear mobility edge in accordance with the prediction of Mott’s model, which are normally observed in crystalline semiconductors.

Low Temperature Solution-Processed Zinc Tin Oxide Thin Film Transistor with O2 Plasma Treatment

We fabricated solution-processed ZTO TFTs at annealing temperature of 350 °C with employing O2 plasma treatment on active layer in order to improve the electrical characteristics of ZTO TFTs fabricated at low temperature. Threshold voltage of solution-processed ZTO TFTs without plasma treatment was larger than 35 V but reduced to 20.74 V with 15 ml/min and 300 W of O2 plasma treatment since oxygen vacancies in ZnO⋅SnO2 and SnO2 would increase and then electron concentration are also increased by ion bombardment from O2 plasma treatment. Saturation mobility and Subthreshold Swing (S.S) of TFTs without plasma treatment was 0.09 cm2/V⋅sec and 1.65 V/decade respectively, but saturation mobility increased to 0.58 cm2/V⋅sec and S.S decreased to 1.20 V/decade, respectively, with 15 ml/min and 300 W of O2 plasma treatment, since ZnO⋅SnO2 is produced which could work as semiconducting material, rather Zn(OH)Cl is vanished which could work as impurity by O2 plasma treatment.

Solvent-mediated threshold voltage shift in solution-processed transparent oxide thin-film transistors

We investigated solvent-mediated threshold voltage (VTH) shift in solution-processed zinc–tin oxide (ZTO) thin film transistors (TFTs). The ZTO TFTs showed negative VTH shift when exposed to various organic solvents such as hexane, isopropanol, and chlorobenzene. Additionally the magnitude of the shift showed a close relationship with the dielectric constant or electronegativity of the solvent molecules. From the experiments, one of the origins of the VTH shift in the transparent oxide TFTs appears to be closely correlated with the dipole interaction of the solvent molecules and ZTO back channel surface.

Nonvolatile memory transistors using solution-processed zinc–tin oxide and ferroelectric poly(vinylidene fluoride-trifluoroethylene)

The nonvolatile memory thin-film transistor (MTFT) using a solution-processed zinc–tin oxide (ZTO) semiconducting channel and a poly(vinylidene fluoride-trifluoroethylene) ferroelectric gate insulator was proposed. The crystalline phases of spin-coated ZTO films were essentially amorphous even when the films were annealed at 500 °C and the surface morphology was very smooth and uniform. Although the memory behaviors based on the ferroelectric field-effect were confirmed for all the fabricated MTFTs, the field-effect mobility, memory window, and the on/ off ratio were markedly varied with the changes in annealing temperature and film composition of the ZTO channel. The origins for these differences were examined from the changes in electrical conductivities during the thermal process. The best device performances could be obtained for the MTFT using the 50/50 mol% ZTO channel annealed at 500 °C. The memory window at V G sweep of ± 15 V , field-effect mobility, subthreshold swing, and on/ off ratio were obtained to be approximately 8.1 V , 15.8 cm 2 V - 1 s - 1 , 1.1 V / dec , and 6.4 × 10 7 , respectively.

Metal-Semiconductor Contact Behavior of Solution-Processed ZnSnO Thin Film Transistors

We studied the influence of different types of metal electrodes on the performance of solution-processed zinc tin oxide (ZTO) thin-film transistors. The ZTO thin-film was obtained by spin-coating the sol-gel solution made from zinc acetate and tin acetate dissolved in 2-methoxyethanol. Various metals, Al, Au, Ag and Cu, were used to make contacts with the solution-deposited ZTO layers by selective deposition through a metal shadow mask. Contact resistance between the metal electrode and the semiconductor was obtained by a transmission line method (TLM). The device based on an Al electrode exhibited superior performance as compared to those based on other metals. Kelvin probe force microscopy (KPFM) allowed us to measure the work function of the oxide semiconductor to understand the variation of the device performance as a function of the types metal electrode. The solution-processed ZTO contained nanopores that resulted from the burnout of the organic species during the annealing. This different surface structure associated with the solution-processed ZTO gave a rise to a different work function value as compared to the vacuum-deposited counterpart. More oxygen could be adsorbed on the nanoporous solution-processed ZTO with large accessible surface areas, which increased its work function. This observation explained why the solution-processed ZTO makes an ohmic contact with the Al electrode.

Low Temperature Solution-Processed Zinc Tin Oxide Thin Film Transistor with O2 Plasma Treatment

not Available.

Solution-processed zinc–tin oxide thin-film transistors with low interfacial trap density and improved performance

Solution-processed amorphous oxide semiconductors are attractive channel materials in thin-film transistors (TFTs) for low-cost electronics. We demonstrate improved performance and uniformity of solution-processed zinc–tin oxide (ZTO) TFTs by optimizing the prebake process for the ZTO precursor film. ZTO prebake process prearranges the dielectric/semiconductor interface and minimizes the performance variation caused by the uneven thermal distribution during annealing process. Prearranging the interface also reduces interfacial trap density and results in improved performance. A mobility of 27.3 cm2/V s, an on/off ratio of ∼107, and a subthreshold swing of 122 mV/decade have been obtained. Significant improvement in operational stability has also been observed.

Effects on Annealing Temperature for Solution-Processed IZTO TFTs by Nitrogen Incorporation

The effects on electrical properties of solution-processed indium zinc tin oxide (IZTO) thin film transistors (TFTs) by nitrogen incorporation were investigated as a function of annealing temperature. The nitrogen incorporation was controlled by NH 4 0H addition into a precursor solution of zinc, indium, and tin chlorides. At 600°C annealing, the nitrogen-doped IZTO TFTs showed a field-effect mobility of 5.33 cm 2 /V s with an on/off ratio of 2.05 × 10 7 , By the nitrogen incorporation, the annealing temperature could be lowered to 400°C for the fabrication of TFTs having a field-effect mobility of 0.303 cm 2 /V s. Physical and chemical analyses on films at various annealing temperatures were performed and compared, respectively.

Self-Aligned Solution-Processed Zinc-Tin Oxide Thin-Film Transistors with High-K Solution-Processed Gate Dielectric

AbstractWe demonstrate high performance zinc-tin oxide (ZTO) thin-film transistors (TFTs) with low operation voltage, small channel length and low parasitic capacitance. Both the zinc tin oxide and the high-k dielectric, ZrO2, were solution processed by sol-gel methods. A self-aligned process was employed to minimize the parasitic capacitance. The transistors with a channel length of 8 μm operate at 5 V and have a saturation mobility of 2.5 cm2/V·s and an on/off ratio of 5.9×106. Gate-induced surface relief has been found to have strong effect on the performance of the active layer.

High performance solution-processed amorphous zinc tin oxide thin film transistor

Thin film transistors (TFTs) with amorphous zinc tin oxide (ZTO) channel layer were fabricated by a simple and low-cost solution process. The ZTO thin films are highly transparent (>90% transmittance) in the visible region. The ZTO TFTs fabricated at 400 and 500 °C are operated in enhancement mode. The TFT annealed at 500 °C shows a mobility of 14.11 cm2 V−1 s−1, a threshold voltage of 1.71 V, a subthreshold slope of 0.4 V dec−1 and an on–off current ratio greater than 108. In addition, we investigated the gate bias stability of the TFT. Positive gate bias results in a positive shift of the threshold voltage due to the charge trapping in the channel/dielectric interface.